Flight Dynamics Analysis Branch

2.2.5 General Space Operations Management Office (SOMO) Sup_port The Space Operations Management Office (SOMO), located at Johnson Space Center, is an important sponsor and funding source for many of the FDAB activities. This includes much of the branch's technology work (covered in Section 4) as well as general mission design and concept development work for future missions (some of the work covered in Section 3 is sponsored by SOMO). The FDAB periodically assists SOMO in its management of mission services and operations activities, including its management of the Consolidated Space Operations Contract (CSOC).

This may be assistance to CSOC in spacecraft anomaly resolution or identification of future mission services. During FY00, the FDAB supported the following SOMO activities: • Technical review of progress by the Flight Dynamics Facility (FDF) to implement the real-time orbit determination (RTOD) system • Formal monthly status reviews to the Goddard Network and Mission Services Project by the FDF • Preparation of material to be included as part of the "'SOMO Architectural Evolution Plan" which identifies roadmaps for future mission service upgrades and technologies • Preparation and review of updates to the SOMO Mission Services Catalog FDAB management meet regularly with CSOC management responsible for the operation of the Flight Dynamics Facility. The purpose of these meetings is not to give direction to routine operations, but to continue to maintain aware- ness of facility upgrade plans and share knowledge of future mission plans, technology development activities relevant to the facility, and software system upgrades.

[Technical Contact: Tom Stengle] 3.0 Study Mission Support One of the primary roles of the Flight Dynamics Analysis Branch (FDAB) within the Guidance, Navigation and Control Center (GNCC) is to serve the science community by providing analysis of advanced mission concepts. This includes development of orbit/attitude designs based on science constraints, evaluation of orbit/attitude errors and attitude dynamics analysis. Members of the branch often represent "first access" by Earth Science and Space Science customers to the services offered by the GNCC and the Space Operations Management Office (SOMO).

In FY2000, the GNC continued its participation in supporting a wide variety of future mission concepts. This section describes some of the analyses pertormed.

3.1 IMDC Integrated Mission Design Center The Integrated Mission Design Center (IMDC) is a human and technology resource dedicated to innovation in the development of advanced space mission design concepts to increase scientific value for NASA and its customers. The IMDC provides specific engineering analysis and services for mission design, and provides end-to-end mission design products. For information about the IMDC, please refer to URL http://imdc.nasa.gov/default.htm Flight dynamics analysis support, in the areas of trajectory design, orbit analysis, mission planning: and ACS design, hardware selection and performance evaluation, was provided in the IMDC for a variety of future mission studies.

Collaboration studies with the Jet Propulsion Laboratory (JPL)'s Team X were performed tot the Ocean Surface Salinity Mission (OSSM) and Nanosat Technologies. Some of the Earth Science Missions supported were Radiation Belt Mapper (RBM), Ionospheric Mapper (IM), Global Precipitation Mission (GPM), Ocean Observing Study (OOS), and Ocean Salinity Mission. The Interplanetary and Space Science Missions supported included Marsat, DS-5, Solar Sail, DS-5 Constellation, and Solar Dynamics Observatory. A total of 8 flight dynamics analysts supported various IMDC sessions this year: Marco Concha, Steven Cooley, David Folta, Lauri Newman, Gregory Marr. Michael Mesarch. Josephine San, and Frank Vaughn.

[Technical contacts: Marco Concha, Josephine San] Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report 13 3.2 Ana Lani The Ana Lani mission concept is from a joint team of scientists from Goddard, University of Washington, University of Michigan and University of Hawaii. The science objective is to generate a map of the mass distribution in the universe to find cosmological constants. The instrument consists of 12 modular foil mirrors, each with a 24-cm diameter and 1.7 m local length. Although the pointing requirement is in arc minutes, the jitter requirement is 2 arc seconds over 20 second.

In addition to the general support provided while the mission was studied in the IMDC, ACS personnel performed analysis to show the feasibility of inertial pointing with a 5 degree Sun pointing constraint, and defined the star tracker optimal location.

lTechnical contact: Josephine San] 3.3 Fluorescence Experiment (FLEX) Flex is an earth observing mission proposed by the University of New Hampshire in response to an Announcement of Opportunity (AO). This mission will use the existing Fabry-Perot spectrophotometer to measure chlorophyll fluores- cence and to monitor globally the stress in vegetation. In support of this low cost mission, FDAB personnel performed a feasibility study of the minimum wheel configuration to pertbrm 180 degree slews; investigated control laws for initial Sun acquisition and safe mode; and carried out attitude sensor trades to develop a minimum hardware ACS design.

[Technical contact: Josephine San] 3.4 Global Precipitation Mission (GPM) The Global Precipitation Mission (GPM) concept study was supported by the FDAB. GPM seeks to deploy a constella- tion of spacecraft that will provide global rainfall measurement coverage with a 3 hour latency. FDAB involvement this year has been to provide feasibility analysis for the design, deployment and maintenance of the constellation. GPM is a TRMM follow on mission. It consists of a core spacecraft similar to TRMM and a constellation with 6 small spacecraft in a 6-pedal orbit configuration. It is a joint venture of Goddard and Japanese scientists. The mission concept was brought to the IMDC three times for different levels of study.

In addition to the routine ACS analysis and design, FDAB personnel provided special analysis in the following two critical system level design issues. First, the constellation satellite instrument Lightweight Rainfall Radiometer (LRR) spinning at 8 rpm is located over a meter from the spacecraft center of gravity. This imposes a critical issue on the spacecraft jitter performance. FDAB personnel performed a detailed analysis on the effect of the LRR imbalance on jitter and defined the LRR offset limit based on a two-body model. Secondly, the core spacecraft in a 70 degree inclination orbit requires large solar arrays, which induce disturbance toque due to plume impingement, as well as other flexibility issues and thermal snapping. FDAB personnel supported the solar array design trade from the ACS perspective.

A next generation GPM (GPM Next) study was carried out together with JPL. FDAB personnel worked with scientists to derived ACS pointing and jitter requirement due to a finer resolution instrument. The IMDC and JPL investigated the newest sensor and actuator technologies to put together a lightweight, low power, and low cost ACS system.

[Technical contact: Marco Concha, Josephine San] 3.5 Joule Joule is an X-ray astronomy mission concept in response to NASA's Small Explorer (SMEX) Program. FDAB engineers worked in the IMDC to provide analysis and design support to complete a mission proposal. Special ACS trades on the maximum slew angle vs. wheel momentum and torque capabilities were performed to reach an optimal design in mass, power, and cost. The proposal was selected as a first round candidate for the SMEX program.

[Technical contact: Josephine Sanl 14 Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report 3.6 Mars Areo-stationary Relay Satellite (MARSAT) MARSAT is a proposed Mars orbiting communication satellite for the Mars Communication and Navigation Infrastruc- ture to be led by JPL. This satellite will use a 2.5-m Ka-band High Gain Antenna (HGA) to communicate with the earth and a l-m x-band HGA to relay other Mars orbiting satellites and Mars's landers to MARSAT. Jitter requirements and recovery from anomalies are major concerns.

FDAB personnel performed rigid body jitter analysis to show the feasibility of 1 dB beam width tor the earth link, performed flexible mode analysis, defined transfer orbit scenarios, evaluated control mode design approaches, and investigated hardware lifetime to ensure a 9 year mission life. Most importantly, FDAB personnel investigated and defined two levels of sate mode, and derived control schemes and operational scenarios to search for the earth.

[Technical contact: Josephine San] 3.7 Living With a Star (LWS) The Flight Dynamics Analysis Branch has been involved in the formulation of missions tor the Living with a Star Program. The FDAB was involved with the generation of orbits and products related to a distributed system of spacecraft used to understand the Earth's environment and the interaction with the Sun. Several missions are supported in this area including Inner Heliopsheric missions that use a Venusian gravity assist to align the space- craft into their respective positions. A sample of these missions is high- lighted below. Each orbit represents a single spacecraft after a Venus encounter. A second concept dealt with the attainment of a Sun Earth L3 orbit. A figure describing this orbit is also provided (Figure 3-1 ). The travel time to the L3 location was of concern and resulted in several options for Figure 3-1.

drift away style trajectories. Figures 3-2 and 3-3 show the transfer trajectories and the final L3 orbit.

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!::!_ "i"" "'_?_ Figure 3-2. Figure 3-3.

This mission concept consists of tour individual missions: Solar Dynamics. Radiation Belt Mapper (RBM), Ionosphere Mapper (IM), and Inner Heliospheric Sentinels (IHS). Each mission has its unique objectives and design challenges.

Solar Dynamic is a solar observer performing continuous and high cadence observations of the full solar disk and coronal imaging in multiple wavelengths to improve understanding and forecasting of the Sun's impact. The pointing requirement is tight, especially the jitter requirement (0.25 arc second/45 second). FDAB personnel investigated jitter perlbrmance using the output from the guide telescope to close the control loop.

RBM is a mission to establish magnetic field properties of the radiation belt. 6 spacecraft will be stacked in one launch vehicle and placed in 6 highly elliptical orbits, 4 in 500 km x 6.5 Re and 2 in 500 km x 2.5 Re. RBM is a spinner with spin axis 15 degrees from the Sun line.

Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report 15 The IM mission objective istomonitor theglobal plasma environment using tomography and tostudy Ionosphere density, gas properties, and magnetic and electrical fields. Eight spacecraft with 6 on one launch vehicle and 2 on another, will be placed in low earth orbit in 3 different inclinations.

IHS is a solar orbiting mission measuring the electric and magnetic field of the Sun. Four spacecraft will be stacked on one launch vehicle. The spacecraft is a spinner with spin axis pointing at the Sun.

The challenging problem for RBM, IM and IHS is the separation and deployment due to the stacking of multiple spacecraft on one launch vehicle and placement in different orbit configurations. FDAB personnel worked along with system, mechanical and power engineers to define feasible operations scenarios, and sub-optimal control design ap- proaches.

For RBM and HIS, having the spin axis not normal to the orbit plane but toward the Sun raises issues of appropriate attitude sensors. FDAB personnel worked with the project scientist to refine the requirements, trading science objective, sensor cost and control complexity.

[Technical contact: David Folta, Josephine San] 3.8 NGST/Nexus The Next Generation Space Telescope (NGST) and its technology demonstration support mission called NEXUS were studied as part of the formulation phase. Several trajectory designs were investigated for possible use. The support provided by the FDAB allowed the NEXUS project to understand fuel, DV, and launch vehicle impacts due to trajectory design. Work performed both at the IMDC and afterward resulted in a clear understanding of the orbit constraints and requirements. A sample trajectory design is shown below for this L2 co-linear Sun-Earth/Moon mission orbit (figures 3-4 and 3-5).

Figure 3-4. Figure 3-5.

The objective of NEXUS is to provide a pathfinder to demonstrate technology required for the Next Generation Space Telescope (NGST). This includes a demonstration of lightweight, actively controlled, cryogenic optics for astronomical observations in the infra red region and a demonstration of disturbance torque isolation and ACS control with a large solar mask. Since this an L2 mission, the momentum unloading will be achieved with thrusters and is required to execute as infrequently as possible due to tight jitter requirements (1 arc second over 1000 second). The pitch axis tilt angle requirement, from 85 to 135 degrees from the Sun line, also imposes a challenge in the ACS design.

FDAB personnel performed detailed solar torque analysis to bound the pitch tilt angle and offset between center of pressure and center of mass. They also developed a relationship between solar torque and the momentum unloading frequency and wheel momentum and torque capability requirements. Detailed rigid body jitter analysis was performed to demonstrate the importance of flexible mode analysis and the necessity of disturbance torque isolation.

[Technical contacts: David Folta, Josephine San] 16 Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report 3.9 NPP The National Polar-orbiting Operational Environmental Satellite System (NPOESS) Preparatory Project (NPP) is a risk- reduction demonstration mission. Another objective of NPP is to provide a continuation of measurements of global change parameters after EOS Terra and Aqua. FDAB personnel evaluated several Rapid Spacecraft Development Office (RSDO) buses to converge on a suitable selection based on quick and simple analysis on the sensor performance, actuator capability for all modes and detailed rigid body jitter analysis. Per the science requirement, two levels of sate mode control were designed and an operational scenario for each level was defined.

[Technical contact: Josephine San] 3.10 Ocean Surface Salinity Mission (OSSM) FDAB personnel provided analysis support for the Ocean Surface Salinity Mission (OSSM) concept which is planned to be submitted in response to the next ESSP AO. The purpose of the proposed mission is to understand processes that control the transport, storage and exchange of fresh water between Earth's atmosphere, land, oceans, and polar regions.

FDAB personnel supported the development of the mission concept by performing analysis for several instrument design concepts to identify suitable candidate orbits that will meet the mission's data collection requirements. The mission concept was studied in the Integrated Mission Design Center (IMDC) to identify the impact of the candidate instrument designs on the spacecraft design. The IMDC study resulted in nan'owing the field of practical candidate instrument designs, and identified key cost and complexity trade issues for the spacecraft design that result from both fixed and rotating instrument designs. The science team is now in the process of evaluating these issues to select the instrument design that provides the best performance without exceeding the cost and schedule constraints for the mission. FDAB personnel will continue to provide analysis support as the proposal moves toward submittal.

Attitude determination and control design and analysis support for the Ocean Surface Salinity Mission concept was also provided. For each instrument design, trades were performed to identify the impact on ACS hardware mass, power and cost. Low-fidelity simulations were performed to prove the control concepts and control mode design options were investigated.

[Technical contacts: Frank Vaughn, Josephine San] 3.11 Solar Sail The Solar Sail mission is a solar sail technology flight demonstration. Its objectives are to validate an integrated solar sail flight system with low volume packages, and to characterize the use of large solar sails for future science observations.

FDAB personnel investigated the pros and cons of gaining 3-axis control by using a sliding mass to offset the center of gravity or by manipulating trim tabs to offset the center of pressure from the center of mass. The trim tab approach is superior from an ACS perspective, but increases integration complexity. FDAB personnel identified limitations and concerns using solar sails as control actuators.

[Technical contact: Josephine San] 3.12 Constellation X Constellation X is a study mission that uses 4 x-ray telescopes in constellation at the Earth's L2 libration point to study black holes and galaxy tbrmation. The instrument consists of a large area X-ray mirror with 100-meter focal length.

Therefore, the detector will be on a 100-meter long boom with 50-kg mass and 1 square meter of Sun shield area, which induces large disturbance torque on the spacecraft. This year the FDAB has provided support to the Constellation X study team in the areas of orbit determination accuracy and trajectory design. The baseline plan is to launch the space- craft in pairs aboard 2 Delta IV or Atlas V launch vehicles. The FDAB is designing the baseline trajectory to accomplish Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report 17 thisscenario. Also, in the event that thelarger launch vehicles arenotavailable inthe2008 mission timeframe, there isa study underway todetermine thefeasibility oflaunching the 4 spacecraft on4 Delta II vehicles, then using acombination ofhydrazine andlow-thrust propulsion toachieve thedesired mission orbit. Various low-thrust options are being considered, and theFDAB isstudying theavailable constant thrust trajectory options.

FDAB personnel also assessed possible spin rates and slew constraints, studied thefeasibility ofspinning optics for thermal control, pinpointed momentum unloading concerns due tosignificant disturbance torque and momentum build up,and investigated dual spin spacecraft stability criteria and performance capability.

[Technical contact: Lauri Newman]

3.13 Magnetospheric Multiscale Mission (MMS) The MMS mission is a four-spacecraft Solar-terrestrial Probe designed to study magnetic reconnection, charged particle acceleration, and turbulence in key boundary regions of the Earth's magnetosphere. The mission is in its study phase.

The Announcement of Opportunity (AO) for the instrument complement and Principle Investigator teams is expected to be released in the summer of 2001.

The analysis tasks are directed toward characterizing the orbit dynamics of the mission, in part because they are needed for the AO, but also because spacecraft design is underway and subsystem engineers need to know them. The orbits are highly elliptical. Near apogee, the size of the tetrahedron formed by the tbur spacecraft varies over the life of the mission, hence the term 'multiscale' in the mission name. The analysis tasks include demonstrating that trajectories can be designed to meet the science and engineering requirements, determining how to control the trajectories and the amount of propellant required to do so. In parallel, a statement of requirements is being developed by the orbit analyst in consultation with the MMS study management and science team. The requirements are evolving as the analysis proceeds and characteristics become known.

Little of the software needed to execute the studies is in the "off the shelf'' category because this is not a routine mission lor which analysis techniques are readily available. Software has been developed to the prototype level that finds and analyzes suitable trajectories. A graphics program was written to illustrate the behavior of the tetrahedron as it changes size and shape throughout each orbit.

For more detailed intormation about the mission, visit http://mms.gsfc.nasa.gov.

[Technical contact: Charles Petruzzo] 3.14 KRONOS The FDAB completed an extensive mission feasibility study for the KRONOS Mission High Earth Orbit (HEO). This unique orbit requires a lunar swingby to increase the orbit perigee radius, lift the orbit out of the ecliptic plane, and rotate the line of apsides such that apogee is in the northern hemisphere. The Final HEO orbit obtained via this lunar swingby has perigee near 10 Earth Radii (R E) and apogee near lunar distance (_-60 RE). A final study report contained a detailed analysis of the HEO orbit characteristics, launch window opportunities, and fuel budget estimates. The results, presented to the KRONOS Project. Deputy PI, were well received and will be used as part of future mission proposals for KRONOS and other missions. The KRONOS trajectory is shown in figures 3-6, 3-7, and 3-8.

18 Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report Lunar Orbit SC Tra ectorv Sun Line (eclipli¢ plmle) E Apogee /' f ,,IF.--- \ /" f / ., ( ,' Enc.xmnt_ Figure 3-6 KRONOS Direct Transfer HEO (5 year Figure 3-7 KRONOS Direct Transfer HEO (Post Lunar Mission), View in Earth - Moon Rotating Coordinates Encounter Apogee), View from North Ecliptic Pole in (June 1) Solar Rotating Coordinates (June !)

......... "....... - _ S CTrajector) ,_""_ Apo_ Lunar I - Enccalnler ................ -I_-__!o._._,,_.r _ ' Lunar Orbil i I SunLinc ".. ............

(ecliptic plane) .......

Figure 3-8 KRONOS Direct Transfer HEO (Post Lunar Encounter Apogee), Vie_v in ecliptic Plane in Solar Rotating Coordinates (June 1) [Technical contact: Steven Cooley] 3.15 Leonardo Leonardo-BRDF is a new NASA mission concept proposed to allow the investigation of radiative transfer and its effect on the Earth's climate and atmospheric phenomenon. Enabled by the recent developments in small-satellite and forma- tion flying technology, the mission is envisioned to be composed of an array of spacecraft in carefully designed orbits.

The different perspectives provided by a distributed array of spacecraft offer a unique advantage to study the Earth's albedo. Over the past year the Flight Dynamics Analysis Branch has been investigating formation flying dynamics concerns in the context of the Leonardo-BRDF science requirements. Together with scientists we have investigated the albedo integral and the effect of viewing geometry on science return. An approach based on Gauss quadrature has been investigated to provide the optimal formation geometry to ensure that the value of the integral is accurately approxi- mated. Secondly, strategies have been developed to achieve the desired orbit geometries within the constraints of orbit dynamics. Both linear and non-linear techniques have been developed for two types of formations such that all orbits composing the formation have the same node rate and mean anomaly rate respectively, in the presence of J2. The relative geometry afforded by each design has been investigated in terms of mission requirements. An optimal Lambert initialization scheme has been implemented to obtain preliminary estimates of the required Delta-V to distribute all spacecraft from a common parking orbit into their appropriate orbits in the formation. Finally, formationkeeping strate- gies have been developed and the associated DV's are calculated to maintain the formation in the presence of perturbations.

[Technical contact: Steven Hughes] Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report 19 4.0 Technology Development Activities .2.

4.1 Advanced Mission Design The Goddard Space Flight Center's (GSFC) Guidance Navigation and Control Center (GNCC) is at the forefront of libration orbit mission design, algorithm and software development, and their application to libration point missions.

This mission design encompasses the detailed analysis of attaining and maintaining Sun-Earth/Moon libration orbits via direct and lunar gravity assist transfers. Upcoming missions such as the Microwave Anisotropy Probe (MAP), Triana, and the Next Generation Space Telescope (NGST) are addressed in light of improved methods for attaining constrained orbits parameters and their control at the collinear libration points. New developments such as invariant manifold theory and optimization based on eigenvector formulation to achieve constrained orbit parameters is currently under investigation.

Sun-Earth libration point orbits serve as excellent locations for scientific investigations. These orbits are often selected to minimize environmental disturbances and maximize observing efficiency. Trajectory design in support of such missions is increasingly challenging as more complex missions are envisioned in the next few decades. Trajectory design software must be further developed to incorporate better understanding of the libration orbit solution space and thus improve the efficiency and expand the capabilities of current approaches. Only recently applied to trajectory design, dynamical systems theory now offers new insights into the natural dynamics associated with the multi-body problem. In a coopera- tive effort, the Goddard Space Flight Center's (GSFC) Guidance Navigation and Control Center (GNCC) and Purdue University are working together to develop this expertise.

Nonlinear dynamical systems theory (DST) offers new insights in multi-body regimes, where qualitative information is necessary concerning sets of solutions and their evolution. DST is, of course, a broad subject area. The DST work has been performed in partnership with Purdue University. At Purdue University, various dynamical systems methodologies are included in a software package called Generator. In Generator, different types of solution arcs, some based on dynamical systems theory, are input to a process that differentially corrects the trajectory segments to produce a complete path in a complex dynamical model. A two level iteration scheme is utilized whenever differential corrections are required; this approach produces position continuity (first level), then a velocity continuity. An understanding of the solution space then forms a basis for computation of a preliminary solution and the end-to-end approximation can then be transferred to GSFC operational software for final adjustments for launch window, launch vehicle error analysis, and maneuver planning. The current goal is to blend dynamical systems theory, which employs the dynamical relationships to construct the solution arcs. and the mission design tool Swingby, with its strength in numerical analysis. A sample of the trajectories calculated using Generator is shown in figure 4-1.

Figure 4-1. Sample of Trajectories Using Generator [Technical Contact: David Foita/572] 4.2 Autonomous Onboard Navigation Systems Increasing interest in maximizing autonomy, operations "beyond LEO," and distributed spacecraft has brought new challenges for navigation systems. Addressing and anticipating new requirements has led to technology initiatives in 20 Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report onboard navigation systems (ONS) using communications links, Global Positioning System (GPS) orbit determination, and autonomous navigation for high-Earth, libration, gravity-assist, and deep-space orbits.

FDAB work develops and infuses autonomous navigation technologies for Earth orbiting, libration point, and deep space missions. In so doing, it enables highly accurate autonomous onboard inertial and relative navigation for multiple satellites, which reduce the cost of autonomous navigation implementation and testing while increasing the efficiency of the navigation process. The work is divided into four areas: • GPS Navigation: Enhances the GPS Enhanced Orbit Determination (GEODE) flight software to support all near- Earth absolute and relative navigation requirements and support its integration with one or more prototype GPS space receivers • Onboard Navigation Systems (ONS) using Communications Systems: Provides onboard navigation system for non- GPS missions by integrating ONS flight software used on the EUVE & Terra spacecraft with a Navigation Processor Board (NPB) within the communications system • Relative Navigation: Determines the performance of relative navigation for various mission concepts via crosslinks and/or GPS, and develops a crosslink receiver • Celestial Navigation: Develops an autonomous onboard system that infuses new ground-based navigation filter processes with onboard attitude and/or Doppler measurements During the past year, several of these tasks have experimented with an increasingly convergent software development process. These two subtasks have been able to leverage common elements in navigation filter design and software architecture to accomplish substantially more development and analysis combined than either could alone. In most upcoming work, it is planned to fold all the tasks into this software process, thereby allowing all to share the overhead of software development and maintenance, where possible. The unified software package, GPS-Enhanced Orbit Navigation System (GEONS), is designed so that although all subtasks' capabilities are resident in the source code, only those elements that are necessary for each specific application are switched on when the package is compiled. This design allows the package to remain lean and last enough to be considered for onboard flight software applications, as well as ground support and analysis functions. The result is a multi-purpose navigation software package that maximizes software reusability and maintainability, and can be easily reconfigured to a user's needs.

The GEONS software uses heritage code to reduce errors and assure reliability and compatibility, which is based on flight-proven ground-based (GTDS) and onboard (TONS) navigation systems. The software has been and will be verified using realistic simulation data and actual satellite data lbr analysis & testing, including actual satellite data from EUVE, Terra, Polar & the Solar and Heliospheric Observatory (SOHO), and hardware-in-the-loop testbeds consisting of GPS signal simulators and closed-loop orbit control capabilities. Measurements will currently include GPS, Federal Aviation Administration (FAA) Wide Area Augmentation System (WAAS), and intersatellite crosslinks, and are planned to include ground station measurements, TDRSS, star, Sun, lunar, and Earth sensor measurements, and forward-link Doppler measurements from command link carrier. During the past year, integrated testing between hardware and software has been initiated for GPS and EONS target platfbrms. These have included an in-house open-architecture GPS receiver (PiVoT), ITT's low power transceiver (LPT). and, the Motorola Navigation Processor Board for their 4th Generation Transponder (the latter, due to heritage interthce structures, does not use GEONS). In its GPS-only incarna- tion, GEODE, the GEONS software was GSFC Software of Year, and was NASA's Software of Year Runner-Up.

Web-based team collaboration, using concurrent version system (CVS) code management, has allowed a diversity of teaming arrangements, involving government, support contractors, universities, and licensees. These have included GSFC, LaRC, Computer Sciences Corporation, the Universityof Colorado at Boulder, Orbital Science Corporation, Ball Aerospace, ITT, Motorola, and the Johns Hopkins Applied Physics Lab. These collaborations and technology transfers have lead to numerous current and planned infusion of our autonomous navigation systems, as listed below: GEODE flight qualified for Lewis mission GEODE Lite to fly on EO-1 GEODE is being transferred to LaRC for evaluation of use by Pathfinder Instruments for Cloud and Aerosol Spaceborne Observations - Climatologie Etendue des Nuages et des Aerosols (Picasso-CENA) iEarth System Science Pathfinder/ESSP) Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report 21 • Potential use ofGEODE onproposed Earth Science missions (Magnetic Multi-scale Mission (MMS), Auroral

Lights) under discussion withscientists and project engineers

• Plan tosolicit missions based onTerra success forEONS

• Current analyses using Aurora Lites, MMSforRelative Navigation mission studies

• CelNav system can beused forground based navigation

• CelNav "Flight Code" maybeincluded inDiscovery mission

• GEODE licensed toOrbital Sciences Corporation foruse onOrbComm

• OSC expressed interest inembedding GEODE filterintoaspace-qualified version oftheir Ashtech G12GPS

receiver

• License agreement in place with MIT/Lincoln Labs via DoD, and with Ball

• License agreements are in negotiation with UCLA & CU/Boulder • Agreement with ITT for infusion into Low Power Transceiver for Shuttle demo • EONS/GEODE potential for commercializatio n by Motorola in their receiver units • Relative Navigation potential for commercialization when integrated with crosslink receiver (APL, Motorola, ITT) • CelNav potential for commercialization when integrated with GEODE, RelNav or EONS Below, more detailed descriptions of the past year's accomplishments are given for FDAB autonomous onboard naviga- tion system technology.

4.2.1 Terra Onboard Navigation - The TDRSS Onboard Navigation System (TONS) Terra is flying an autonomous onboard navigation system to provide accurate orbital parameters to the spacecraft in real time. The system, known as the TDRSS Onboard Navigation System or TONS, is another first for NASA by flying onboard navigation as the operational system for orbit solutions.

TONS measures the Doppler data off the forward communications signal from Tracking Data Relay Satellite System (TDRSS) and processes it in onboard software with a sequential estimation algorithm to produce the real time outputs.

The accuracy requirement for TONS is 150 meters in position and 0.16 meters per second in crosstrack velocity, 3 sigma.

TONS performance has far exceeded the requirement. TONS compares to traditional orbit determination methods to 7 meters, one sigma in position and better than 0.015 meters per second in crosstrack velocity. After on-orbit tuning, TONS is expected to provide Terra with onboard position knowledge to better than 5 meters, one sigma and 20 meters, 3 sigma.

TONS performance was monitored during the Terra ascent maneuvers and indicated excellent recovery within the first few measurement updates after the maneuver. TONS filter reconvergence occurs at the beginning of the second post- maneuver contact. TONS has since been used as the operational solution during the station-keeping maneuvers, staying within the 150 meter position requirement. TONS also estimates the local oscillator frequency, a drag correction factor, and a TDRS measurement bias for Terra. All on-orbit requirements have been exceeded and navigation operations have been performed nominally. TONS data was also used to calibrate the spacecraft clock to aid the operational clock correlation system. Terra scientists obtain the real-time TONS navigation solution in their ancillary data.

[Technical contact: Cheryl Gramling] 4.2.20nboard Navigation Systems Using Communication Links The Enhanced ONS (EONS) flight software package is an integrated navigation system, which can be procured as an option to the existing spacecraft communications equipment. For those requiring autonomous navigation, EONS will be significantly cheaper and more reliable than independent software development and system integration efforts. EONS is derived l¥om TONS, which flew on EUVE and Terra. It is being integrated into a Nay Processor Board (NPB) that will be part of Motorola's 4th Generation Transponder (figure 4-2).

22 Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report

Fourth Generation Transponder

NPB, Top

NPB, bottom

Figure 4-2. Navigation Processor Board Highlights of the past year's accomplishments are • TONS software successfully used to support Terra operations • Developed 1553 Interface Software for executive/driver, embedded processor, and Special Test Equipment • Developed Improved Method for Doppler Extraction (by Motorola & Government) • Generated simulated truth data by modifying existing program to increase validity and realistic qualities of the data • Hosted EONS code on Navigation Processor Board and perfbrmed initial testing [Technical contact: Cheryl Gramling] 4.2.3 Global Positioning System Advanced Concepts Global Positioning System (GPS) satellite navigation is a proven technology that provides potential tor low-cost autono- mous satellite navigation systems. The current GPS algorithms, software, receiver hardware, and simulators, however, need to be enhanced to broaden the mission scope to include all near-Earth missions, such as highly elliptical orbits (HEO) and geosynchronous Earth orbits (GEO), as well as to support relative navigation for formation flying applica- tions. This project is enhancing the GPS Enhanced Orbit Determination Experiment (GEODE) flight software to support such missions, and support its integration with one or more prototype GPS space receivers. Figure 4-3 shows the GPS signal.

GPS Side Lobe GPS Visible Region in PrimaryBeam GPS Side Lobe Figure 4-3. Satellite Orbital Geometry With Respect to GPS Broadcast Signal Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report Highlights of the past year's accomplishments are:

• Won GSFC Software ofthe Year, and Runner-up forNASA Software ofthe Year

• Majornew GEODE release (V5)supporting relative navigation inHEO and GEO missions, and relative navigation • Enhanced data simulation capabilities tosupport weak signal tracking analysis forHEO and GEO missions

• Initialintegration withPiVoT GPS Receiver & ITTLowPower Transceiver

• Papers presented toInternational GPS Workshop & International Flight Dynamics Conference concerning HEO and

GEO capabilities and projected performance

• Supported formal Peer Review forExplorers Technology Development Program

A paper was presented at the International Symposium on Space Flight Dynamics in Biarritz, France. This paper dis- cusses autonomous navigation improvements for high-Earth orbiters and assesses projected navigation performance for these satellites using Global Positioning System (GPS) Standard Positioning Service (SPS) measurements. Navigation performance is evaluated as a function of signal acquisition threshold, measurement errors, and dynamic modeling errors using realistic GPS signal strength and user antenna models. These analyses indicate that an autonomous navigation position accuracy of better than 30 meters root-mean-square (RMS) with selective availability (SA) enabled and 10 meters RMS with SA disabled can be achieved for high-Earth orbiting satellites using a GPS receiver with a very stable oscillator. If the GPS receiver's signal acquisition threshold can be reduced by 5 dB-Hertz to track weaker signals, this accuracy improves to better than 20 meters RMS with SA enabled and 8 meters RMS with SA disabled. Figures 4-4 and 4-5 show the RMS error margins.

RMS Position Error (meters) RMS Clock Error (meters) 1,5 Baseline No SA Iono Delays 5% SRP Baseline No SA Iono Delays 5% SRP Error Error _'_ 35 dB-Herlz Threshold BB 30 dB-Hertz Threshold f_] 28 riB-Hertz Threshold Figure 4-4. Comparison of Steady-State Time-Wise Ensemble RMS True Errors for HEO RMS Position Error (meters) RMS Clock Error (meters) 2§ Baseline No SA Iono Baseline No SA Iono 3% SRP 30-day 3% SRP 30-day Error EOPs Delays Delays Error EOPs 1 30 dB-Hertz Threshold 38 dB-Hertz Threshold 28 dB-Hertz Threshold Figure 4-5. Comparison of Steady-State Time-Wise Ensemble RMS True Errors for GEO [Technical contact." Russell Carpenter] 24 Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report 4.2.4 EO-1 Global Positioning System (GPS) The Earth Observing-I (EO-I) spacecraft launch is currently planned for November 16, 2000, from Vandenburg Air Force base. Since the integration of the Tensor GPS receiver to the EO-1 spacecraft in March of 1999. subsequent tests demonstrated that the integration was successful and that the spacecraft was ready for thermal vacuum testing. The spacecraft was then moved from the construction site at SWALES into the Goddard's building 7 test facility. The first series of thermal vacuum tests were run in November of 1999. During these tests, the GPS receiver was exposed to and operated in no less than two cold soak plateaus each lasting a minimum of 24 hours and two at hot soak plateaus of similar duration. During these tests, the GPS flight system performed flawlessly. However, the same could not be said of the ground support equipment tGSE). Intermittent data dropouts experienced during testing were later found to be a direct result of the poor RF characteristics of the GSE cables used to bring GPS signals from the rooftop antenna to the test chamber. The flight system was deemed ready to fly and the GSE would be upgraded for any subsequent tests.

Figure 4-6 depicts the GPS receiver.

Figure 4-6. EO-I GPS Receiver By April 2000, the EO- 1 ground system was upgraded to allow the GPS flight receiver to be warm started from the MOCC. In a cold start, the receiver is powered on, configured tor orbital operations and allowed to acquire a navigation fix with no further interaction required. This type of self acquisition can be very time consuming (on the order of hours) and may not always be practical in an operational environment. For this reason, it was deemed necessary for the ground system to be capable of executing a warm start of the GPS receiver. In a warm start, the receiver is powered on. config- ured for orbital operations and provided a GPS almanac file (position data of the 32 GPS satellites) and an ephemeris file (position data of the EO-1 spacecraft). Given this information, the GPS receiver can begin acquiring GPS satellites and generating navigation solutions in only a few minutes. Warm staring the receiver from the MOCC would require soft- ware to allow generation and uplink of almanac and ephemeris data. This is a capability even the manufacturer of the GPS hardware does not possess. Since thermal vacuum testing would be employing the MOCC software to communicate with the EO- 1 spacecraft, this newly developed capability would also be tested during the second set of thermal vacuum tests.

From a thermal vacuum testing standpoint, the GPS tests were an unqualified success. Not only did the receiver perform as expected (just as it did during the first set of TV tests), but the new and improved GSE proved reliable as well. This new and improved GSE could now be used at the launch pad for any testing requiring real time GPS data. After a few minor bugs were corrected, the MOCC software was proven to enable a flight operator to download a GPS YUMA almanac file from the Coast Guard navigation web site (where all GPS almanacs are archived) and construct a flight load from the data. In a similar manner, the MOCC was enabled to employ ground orbit data to generate an ephemeris load to the GPS receiver. Given these data, the receiver was able to acquire GPS satellites and begin producing navigation fixes in a relatively short time (several minutes). This capability was tested against the flight GPS using many different YUMA files while receiving GPS inputs from first the actual constellation then from the GPS constellation simulator.

Finally only one difficulty remained. The MOCC ground system was unable to translate atypical (Bus-B) housekeeping telemetry downloads. Routine GPS navigation solutions are fed to the EO-I ACS via the main telemetry bus (Bus-A).

This includes position, velocity and time data. From these data, the EO- 1 ACS is able to create the reference frame against which attitude errors are measured and corrected. Any other (housekeeping) data from the GPS receiver must be telemetered to the ground via Bus-B. Once on the ground, the outputs from the receiver (i.e. signal slrength, configura- tion status and so forth) must be converted from the format they are captured in into engineering units. This was not Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report 25 possible with the software in the MOCC. To correct this shortcoming, an in-house software tool (PKTVIEW - developed by Dr. Charles Campbell of the FDAB) was updated and modified so it could be run in the MOCC. With this tool and the documentation on the receiver itself, operations personnel now have all the capabilities and insight into the GPS receiver necessary to accomplish the EO-I mission. EO-1 GPS is now ready for the expected November 16 launch.

[Technical Contact.' David Quinn] 4.2.5 Relative Navigation The goal of this task is to provide formation flying missions with a real-time capability to determine the relative posi- tions of the individual segments by using tracking data measured from crosslinks and/or GPS.

Highlights of the past year's accomplishments are: • GEODE software modifications to allow multiple simultaneous solutions with multiple data types, to mix GPS and crosslink data: time and frequency models • Paper presented to International Space Flight Dynamics Conference • Implemented upgraded clock model A paper was presented at the International Symposium on Space Flight Dynamics in Biarritz, France. This paper dis- cusses autonomous relative navigation performance for a formation of four eccentric, medium-altitude Earth-orbiting satellites using Global Positioning System (GPS) Standard Positioning Service (SPS) and "GPS-like" intersatellite measurements. The performance of several candidate relative navigation approaches is evaluated. These analyses indicate that an autonomous relative navigation position accuracy of 1 meter root-mean-square can be achieved by differencing high-accuracy filtered solutions if only measurements from common GPS space vehicles are used in the independently-estimated solutions. Figures 4-7 and 4-8 show the position and velocity error margins.

Absolute Position Error Relative Position Error i [[:] RMS (meters) 1 Maximurn (meters) I 2O r With 8A WlUloutS_ 99.8%with 8A 114% w_h Ilia 55%with 8A 99.8% withoutIBA 55%wllbout I;A Percent of GPS SVs in Corn rnon Figure 4-7. Absolute and Relative Steady-State Time-Wise Ensemble True Position Errors Using Filtered Solutions with GPS Measurements 26 Flight Dynamics Analysis Branch End of Fiscal Year 20(0) Report Total RMS Velocity Error (millimeters per second) Total RMS Position Error (meters) 8.

=l, lilJl=lt

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0 0.5 1 1.5 2.5 0.5 1 1.5 2 2.5 Elapsed Days Elapsed Days Figure 4-8. Absolute and Relative Ensemble True RMS Position and Velocity Errors with SA Disabled Using Filtered Solutions with 99.8 percent GPS SV's in Common [Technical contacts: Russell Carpenter, Cheryl Gramling] 4.2.6 Celestial Navigation Celestial navigation of spacecraft opens up high earth, libration point, and deep space missions to autonomous naviga- tion. Celestial navigation is a simulation/navigation system that uses onboard attitude sensor measurements, new algorithms, and high fidelity environmental and filter models to accurately determine the spacecraft state. Autonomous navigation has the potential both to increase spacecraft navigation system performance and success and to reduce total mission cost. Figure 4-9 shows navigation scenarios.

Highlights of the past year's accomplishments are: • Completed Kalman filter design • Completed analysis of ingested simulated and real spacecraft tracking and attitude data and compared to ground based solutions • Paper presented to International Flight Dynamics Conference Autonomous Navigation Scenario Ground-Based Navigation Scenario d_ SIC to Sun measurement ] directional Ground Station ] ' S/C to Earth to SIC Doppler/ :' directional Tracking redicted measuremen_ ,,.' measurement Data Earth Satellite Operations Center Figure 4-9. Navigation Scenarios [Technical contacts: David Folta, Cheryl Gramlingl Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report 4.3 Formation FlyinR Technologies 4.3.1 EO-1 Formation Flying Experiment The formation flying requirement of EO-1 is to maintain a 1-minute separation between EO-1 and Landsat-7 with EO-1 following the Landsat-7 ground track to a tolerance of +/- 3 km tolerance, approximately 6 seconds. This translates into an along-track distance of approximately 450 km with tolerance of 50 km. The mapping of this requirement into a tormation flying requirement is to place a constraint on the initial separation between the two spacecraft, and maintaining that separation. Using the formation flying algorithms developed by GSFC simulations have shown that formation flying requirements can be easily met by a wide margin. By pertbrming this spacecraft separation maintenance, pair scene comparisons between Landsat-7 and E0-1 can be made. Figure 4-10 shows two spacecraft in formation flying configuration.

Figure 4-10. Formation Flying The primary objective of enhanced formation flying is to demonstrate onboard autonomous formation flying control of the EO-1 spacecraft (using the AutoCon system) with respect to the Landsat-7 spacecraft. A secondary goal is to enable the collection of correlated science measurements and to demonstrate significantly improved space science data return through near-simultaneous observations. All algorithms must conform to AutoCon specifications in order to allow uploading during the extended mission. Individual algorithms are invoked through ground commanding of an AutoCon control mode switch.

The EO- 1 maneuvers will be computed onboard under a single system architecture called AutoCon which employs separate maneuver decision/design modules or algorithms. AutoCon will control execution of the modules through an onboard mode switch, and pertorm constraint evaluation via fuzzy logic control.

The enhanced formation flying technology demonstration will be fully validated during the EO-1 mission. In this way, science taken during the first year with autonomous onboard formation flying control operating can be compared to previous ground operations. Likewise, operations costs with and without onboard formation flying control can also be compared. Figure 4-11 shows the observation overlaps.

28 Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report ........................... Fomlabon Flying Space Idlull i_ LocJHtlon J/_" Nadir Direction Figure 4-11. Observation Overlaps The core AutoCon flight control architecture required to support all enhanced formation flying (EFF) algorithms during the extended EO- 1 mission was developed, integrated with the ACS. and placed onboard the spacecraft during the past year. Validation of the core AutoCon architecture will occur during the first year of EO-1 operations. The core AutoCon flight control software must be integrated with the ACS and the spacecraft prior to launch to reduce the risk and the amount of software being uploaded later in the mission. Formation flying control algorithms will be uploaded and executed under the AutoCon flight control software during the extended mission.

The AutoCon flight control system will need data from additional sensors and spacecraft subsystems such as propulsion data, ground track data, and navigation and attitude data. It will then be possible to autonomously generate, analyze, and execute the maneuvers required to initialize and maintain the vehicle fonnation. Because these calculations and decisions can be performed onboard the spacecraft, the lengthy period of ground-based planning, currently required prior to maneuver execution, will be eliminated. The proposed system will also be modular so that it can be easily extended to future missions. Furthermore, the AutoCon flight control system is designed to be compatible with various onboard navigation systems (i.e. GPS, ONS, or an uploaded ground-based ephemeris). The existing automated maneuver plan- ning tool (AutoCon) will be modified for onboard autonomous formation flying control to demonstrate that improved science data return can be achieved by correlating nearly simultaneous data. This will be accomplished by having the flight control system plan a maneuver that places EO- 1 within 1 minute of separation from Landsat-7 and then maintains that separation to a tight tolerance of 6 seconds for an extended period of time.

The EO-1 software test validation certified that all software requirements have been properly implemented and that Phase-1 of the Enhanced Formation Flying (EFF) software meets all operational objectives. The core AutoCon flight control software was qualified by executing a series of test plans, test data, and test scenarios. The results of each stage of validation was checked and documented. These activities were performed by both the developers of AutoCon and the EO-1 ACS software engineers. Quality assurance was integrated into each stage.

Technical Contacts: David Folta, David Quinn] 4.3.2 Integration of a Decentralized Linear-Quadratic-Gaussian Control into GSFC's Universal 3-D Autonomous Formation Flying Algorithm A decentralized control was investigated for applicability to the autonomous formation flying control algorithm devel- oped by GSFC for the New Millenium Program Earth Observer-1 (EO-1 ) mission. This decentralized framework has the lollowing characteristics: The approach is non-hierarchical, and coordination by a central supervisor is not required.

Detected failures degrade the system performance gracefully.

Each node in the decentralized network processes only its own measurement data. in parallel with the other nodes.

Although the total computational burden over the entire network is greater than it would be for a single, centralized controller, fewer computations are required locally at each node.

Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report 29 • Requirements fordata transmission between nodes are limited to only the dimension of the control vector, at the cost of maintaining a local additional data vector. The data vector compresses all past measurement history from all the nodes into a single vector of the dimension of the state.

• The approach is optimal with respect to standard cost functions.

The current approach is valid for near time-invariant systems only. Similar to the GSFC formation flying algorithm, the extension to Linear Quadratic Gaussian (LQG) time-varying systems requires that each node propagate its filter covari- ante forward (navigation) and controller Riccati matrix backward (guidance) at each time step. Extension of the GSFC algorithm to non-linear systems can also be accomplished via linearization about a reference trajectory in the standard fashion, or linearization about the current state estimate as with the extended Kalman filte To investigate the feasibility of the decentralized integration with the GSFC algorithm, an existing centralized LQG design for a single spacecraft orbit control problem was adapted to the decentralized framework while using the GSFC algorithm's state transition matrices and framework.The existing GSFC design uses both reference trajectories of each spacecraft in formation and by appropriate choice of coordinates and simplified measurement modeling is formulated as a linear time-invariant system. Results for improvements to the GSFC algorithm and a multiple satellite formation were addressed. The goal of this investigation was to progressively relax the assumptions that result in linear time-invariance, ultimately to the point of linearization of the non-linear dynamics about the current state estimate as in the extended Kalman filter. Figures 4-12a/b represent a sample of trajectories.

Formal,on fAotio_ Relative to Relere_ce F ¸_, N_ 3_,,,,,_ _ ' I_,_,'_ ]- _ -- L Formation Target Formation Ev_)u0on 0010 ,-,_ -: : ,Y : ---- _, 000_ :- : ,," ! / i ii, z ! o -i z 4 - , FO mahonRen a zalon _,: R adial Vet su$AI °nR TracW Selz'_ra_i°_ I O05 I - " ,, r r oolo + ' ....

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o Figure 4-12a/b. Samples of Trajectories [Technical contacts: David Folta, J. Russell Carpenter, David Quinn] 4.3.3 Tethered Formation Flying Examined for SPECS The Sub-millimeter Probe of the Evolution of Cosmic Structure (SPECS) is a bold new mission concept designed to address fundamental questions about the Universe, including how the first stars formed from primordial material, and the first galaxies from pre-galactic structures, how the galaxies evolve over time, and what the cosmic history of energy release, heavy element synthesis, and dust formation is. Ideally, a very large telescope with an effective aperture ap- proaching one kilometer in diameter would be needed to obtain high quality angular resolution at these long wave- lengths, however this approach proves to be too expensive and therefore impractical. Instead, a spin-stabilized, tethered formation is one possible configuration being considered requiring a more advanced form of formation flying controller.

where dynamics are coupled due to the existence of the tethers between nodes in the tormation network. To this end an investigation into the dynamics and control of multiple tethered spacecraft systems was launched. Figure 4-13 depicts the SPECS spacecraft.

30 Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report Figure 4-13. SPECS Spacecraft The FDAB analysis effort was divided into three separate tasks. Task- 1 involved cooperation with the Naval Research Lab in the development of the equations of motion for a rotating multi-tethered system applicable to the study of fundamental dynamic characteristics of a deep space interferometer concept. The system is assumed to be comprised of a central rigid body from which emanate n-tethered end-masses forming a symmetrical planar arrangement in the nominal configuration. The concept system is intended to execute planar rotation, to deploy and/or retract the tethered end- masses, and be capable of re-orienting the spin axis. Accordingly, the mathematical model must allow full three dimen- sional motion of all the constituent elements. This has been accomplished and the final report and corresponding FORTRAN model are undergoing examination.

Working with the University of Texas at Austin, Task-2 examined key linear and non-linear control methodologies which may prove applicable to the problem of tethered formation flying, specifically gain-scheduled controllers, Lyapunov based non-linear controllers and/or robust adaptive controllers. The object was to build upon the dynamic development from Task-1 in order to create a core dynamics and control model, which permits iteration and expansion while maintain- ing the primary thrust of the tethered formation. The ultimate goal for this task was to develop a set of control laws centered on the core model from Task- 1. This will serve as a first order tool for examining the dynamics and control of a variety of design configurations.

Finally, the main objective of Task-3 was to cooperate with personnel from Payload Systems Inc. to examine possible configurations using the Generalized Information Network Analysis (GINA) framework developed at the Massachusetts Institute of Technology and conduct preliminary configuration trade studies. Here trades such as reel-in-rate versus rotation rate versus aperture diameter were considered as well as angular momentum management and re-targeting and rotation rate versus aperture diameter versus tether tension. Many possibilities were examined in an effort to conduct a "broad-brush" analysis to get a high level understanding of the issues involved with each as well as understand the favorable regions in the trade space. This work has been of immeasurable help by providing insight into the most likely design parameters tbr this complex spacecraft system. As the configuration trades narrow the trade space, the dynamics and control models of Tasks- 1 & 2 will be employed to evaluate the overall feasibility of large multi-tethered spacecraft formation for interferometric and/or large aperture science missions such as SPECS. While detailed design work is expected to take years, this is seen as a crucial first step to making such mission a real possibility.

[Technical contact: David Quinn] 4.4 Attitude Determination and Modeling Techniques 4.4.1 SKYMAP Completion of the SKY2000 Version 3 Master Catalog (MC). The delivery of SKY2000 Version 3 MC in June of 2000 marked the global replacement of the Henry Draper (HD) spectral type data in the SKY2000 catalog, along with the global replacement of the photovisual (ptv) and photographic q_tg) magnitude data. Access to the improved spectral and magnitude data in the MC resulted in a significant improvement in magnitude estimation capability for mission star catalog generation. The SKY2000 Version 3 MC now contains 299,160 entries, an increase of 61 over the 299,099 entries in SKY2000 Version 2. SKY2000 Version 3 contains 273,202 photovisual magnitudes (an increase of 62,280 or 29.5c_ from Version 2) and 255,362 photographic magnitudes (an increase of 73+078 or 40.1% from Version 2). Many other individual corrections to MC data were also made during this period.

Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report 31 Run Catalog Consultation. The FDAB provided star catalog consultation for several current and future missions including: MAP (Run Catalog checklist, 11/99; catalog requirements meeting, 01/00), Terra (CT-601 performance analysis, 12/99), VCL (Run Catalog generation, 02/00), Landsat-7 (Run Catalog content discussion and generation, 03/ 00), and R-XTE (OBC catalog analysis and update).

General SKYMAP Consultation. General information and support was provided to GSFC Projects, Universities, and other external users of the SKY2000 MC data and products. Some examples of partnering during this fiscal year include: Lockheed-Martin (flux to magnitude conversion algorithms, 04/00), U. Texas (Austin; radial velocity data & availability, 05/00), SOHO Run Catalog Generation (11/99), Landsat-7 Run/Supplemental Catalog Generation (06/00).

[Technical contact: David Tracewell] 4.4.2 Attitude Sensor Performance Analysis For this fiscal year horizon radiance modeling was studied as well as gyro modeling from mission experience. Using TOMS data, the following horizon radiance modeling data was obtained (Figure 4-14). Variations in colors/shades correspond to horizon height errors related to latitude and month.

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Summer Autumn Winter Spring Figure 4-14. Horizon Radiance Modeling 32 Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report Long-term gyroperformance foravariety ofmissions was also evaluated overthepast year. Theresults ofthisanalysis indicate along term linear change inbiases. Anexample ofthistrend canbeseen ingyrodata fromthe Rossi X-Ray Tim ingExplorer (RXTE) (figure 4-15 ): RXTE GyTO Bias Correction & Adk4'&' a • L • • d'A • .+? .

.. •

| eeee • I 4_ 215/96 3f26/96 5/15/96 7/4P96 8/23,9{i 10112/96 12/1/96 1/20/97 3/11/97 [_te Figure 4-15. Gyro Performance [Technical contact: Rick Harman] 4.4.3 Advanced Attitude Determination and Sensor Calibration Techniques A new gyro calibration utility was developed which has proven to be faster and more accurate. The old algorithm involved estimating attitudes betbre and after each maneuver followed by combining that data with the spacecraft gyro data in another algorithm to estimate the gyro parameters. This proved to be a cumbersome process with very little flexibility. A new process was developed this year to estimate the attitude and gyro parameters in one utility. Besides the timesavings involved in only running one utility, the ability to include non-sequential batches of data has been included.

Thus, more batches of data from a variety of different times can be included in the estimation process allowing fbr greater observability of the estimation parameters. This utility has been flight tested on both the TERRA and WIRE data.

The WIRE gyro in particular demonstrates what gyro calibration can do for a mission. Figure 4-16 demonstrates the typical attitude propagation errors though maneuvers before and after gyro calibration: Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report 33 Allllu_.e EslirralFon Error_(de_l vsTime 10 .3 Att_lude Esttmal_er_ E,Tors (de£1 w Time I 0.2 1.5 ....

r F i, ii, Ul i Ci 42I > -0.2 -0._ -03 -1 ..0,1 -1_ l I I I .') I I I i -0_ 1_4_ 018 "601 _.t-_- 161821-'5 1635 _.1 1".'45 O1 160141 6 1618216 tG 35_ !553 21 E 161C O: 6 16 2E 4 _6 1853216 1610CI 6 1626416 Tin= _h mmss m' Tir_eI_h mrr s._ml Figure 4-16. Attitude Propagation Errors Before (left plot) and After Gyro Calibration (right plot) The overall RSS error at the end of the maneuvers was 0.5 degrees before calibration and 0.0024 degrees (9 arc-seconds) after calibration with the new utility.

In addition, GNCC was directed to assist in reconstructing the HST rate profile during its gyro failure, which occurred 5 weeks before a shuttle-servicing mission. The gyro failure mode known as "Zero Gyro Mode" consisted of pointing the HST z-axis at the Sun using Sun sensors and inducing a small rotation rate about the z-axis. During orbit night all actuator commands are disabled, and the spacecraft drifts with the Sun line rotation providing some dynamics rigidity.

The goal is to keep the spacecraft z-axis close to the Sun line when HST enters orbit day. The results shown in Figure 4- 17 were obtained using HST magnetometer, reaction wheel, torquer bar, and remaining gyro data.

The y-axis of the plot contains the estimated rate in degrees/second, and the x-axis is in seconds. The orbit night periods can be picked out in the above plots by looking at the negative peaks in the rates. During orbit night the spacecraft is rotating about the z-axis with an approximate constant rate with actuators being turned off. When the computed rate was compared to the rate from the remaining gyros, an excellent fit was obtained.

[Technical contact: Rick Harman] 34 Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report 0.15 0.1 0.05 -005 -0.1 -0.15 -02 -025 I I I I I I2 0 2 4 6 8 10 1 14 X 10 4 Figure 4-17. HST Estimated Rates Using Only Magnetometer and Sun Sensor Data 5.0 Branch Infrastructure 5.1 Flight Dynamics Tool Program Flight dynamics analysis services can only be provided with a suite of specialized analytical tools. The branch currently uses a large complement of commercial and in-house developed software tools. Missions such as LISA, Marsat, MAXIM, Constellation X, GEC, MMS and Leonardo continue to drive the need for improved modeling and computa- tional techniques. Thus, the tools program provides a means of enabling new missions.

The majority of the effort in the Flight Dynamics tools program supports the development and enhancement of software tools for advanced mission planning activities. Flight Dynamics Tools activities are conducted in direct response to customer (Earth Sciences Enterprise, Space Sciences Enterprise, Human Exploration and Development of Space Enter- prise) requirements. These tools are required in support of all aspects and phases of mission tbrmulation, design, implementation, and operations. These tools are also required in support of the flight dynamics technology development activities associated with the Flight Dynamics Analysis Branch. Newly developed tools are also used in the Goddard Integrated Mission Design Center (IMDC). Thus, the tools program performs the following: • Implementation of new computational techniques in existing mission planning and analysis tools • Development of new mission planning and analysis tools (based on needs identified for future missions) • Error correction • Configuration control of FDAB tools The institutional software tools used by the Flight Dynamics Analysis Branch are upgraded to use results of various technology initiatives in order to improve capabilities and responsiveness to the Earth Science and Space Science customers. An example is the research into dynamic system theory for improved trajectory targeting capability. This and other basic research is supported through the SOMO technology program and cross enterprise progranls.

The FDAB tools program requires contractor services to assist with software configuration control. Support is also provided to commercialization efforts. This includes packaging of software approved for extemal licensing. Currently, software available for licensing includes: • Goddard Trajectory Determination System (GTDS) • Attitude Determination Error Analysis Systems (ADEAS) Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report 35

• OrbitDetermination Error Analysis System (ODEAS)

• Swingby Trajectory Design Program (SWINGBY)

• General Maneuver Program (GMAN)

• Multimission Three-Axis Stabilized System (MTASS)

• Multimission Spin-Axis Stabilized System (MSASS)

• GPS Enhanced OrbitDetermination (GEODE)

• Elements Conversion Program(ELCONV)

• Guide Star Occultation Utility(GSOC)

[Technical Contact: Thomas Stengle]

5.2 GNCC Flight Dynamics Data Lab The Flight Dynamics Lab completed its initial configuration during FY2000. This lab is used for the development, test, integration, and operation of software systems as well as analysis for the performance of flight dynamics functions for operational and new missions. Installation of servers and migration of branch personnel was completed. Several new computers were installed. In addition to the servers, the lab now houses two Sun Ultra 60 workstations, two HP worksta- tions, 6 Dell dual processor workstations, an online storage device with approximately 700GB of usable storage as well as printers, scanner, overhead projector, voice and video equipment. Branch commercial software licenses are now managed by the servers and the online storage device provides the users with regular tape backup capability. Addition of this equipment enabled FDAB personnel to do advanced mission analysis, mission system prototyping and test. The CGRO Re-entry was supported using two of the Dell machines and the TRIANA mission maneuver planning is sched- uled to be supported from the lab. The TRMM dynamics simulator was transferred to the FD Lab. The FD Lab also houses the on-line documentation server and the GNCC and Branch WEB page servers.

The FD Lab provided consultation to the GNCC Information Technology Security Officer (ITSO) for security configura- tion and monitoring. The lab security plan will be used as a model for the other area within GNCC.

Plans for the coming year call for the FD Lab to implement a wireless network capability, upgrading the internal lab network and testing of upgraded operating systems and networking configurations. The FD Lab will also provide voice lines for the Expedition One support.

[Technical contact: Sue Hoge] 5.3 Branch Library During FYO0, the FDAB implemented a new online technical library. This library uses the commercial tool Docushare, which is a web based tool that can catalog, store, search and access a wide variety of files. Initially, the library was populated with various document files created over the last several years, which contain technical reports from various branch technology research activities, presentation slides from many spacecraft project technical reviews, and software documentation. The library continues to be expanded and will contain all future analysis reports, future mission studies, software specifications and control system documentation created by the branch. General spacecraft reference documen- tation will also be placed in the library to enable branch engineers to quickly access spacecraft information during anomaly investigations. Access to the library is controlled to protect proprietary and International Traffic In Arms Regulation (ITAR) restricted data. In the future, the library will also contain selected flight data.

[Technical Contact: Catherine Waltersdorff] 5.4 Employee Handbook The initial draft of the FDAB Employee Handbook was completed. Authored by more than a dozen members of the FDAB staff, the purpose of the handbook is to document for all branch employees a standard set of procedures for supporting flight projects, future mission analysis activities and technology projects. The handbook also clearly docu- ments various administrative procedures important to the branch (for example, procedures for technical paper approval).

36 Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report While notyetcomplete, future updates tothe document in FY01 will include detailed technical guidelines forcontrol system design and trajectory design. The handbook will also capture flightdynamics "best practices."

lTechnical Contact: Thomas Stengle]

6.0 Interagency Activities 6.1 GSFC Standards Program The FDAB supports the GSFC standards program and the Consultative Committee for Space Data Systems (CCSDS).

The GSFC standard program aims to expand the scope of best practices, and to develop an agency-endorsed database of preferred technical standards for NASA The Consultative Committee for Space Data Systems (CCSDS) is an international organization of space agencies interested in mutually developing standard data handling techniques, to support space research conducted exclusively for peaceful purposes.

The CCSDS Sub-Panel P1J is specifically chartered to investigate and recommend Navigation Data standards. PIJ has a membership representing several international agencies. The work of PIJ is accomplished primarily at workshops, conducted at least twice a year, at iacilities coordinated by the hosting member agency. The main task of PIJ is to generate documents defining the preferred standards tor the exchange of navigation data. The latest workshops were conducted at Annapolis, Maryland, in May, and at the European Space Agency (ESA) Vilspa facility, Spain, in October.

Currently P1J is working on a green book, for navigation definitions and conventions, with projected completion on December 2000. Response to the CCSDS Proximity- 1 Space Link Protocol, Red Book, will be provided through a red book, generated by P1J, providing recommendations for navigation data exchange in support of proximity operations.

New CCSDS red books on recommendations for orbit, tracking, attitude, proximity ops, environmental models and astrodynamic constants will be developed in the future.

For information about CCSDS and the GSFC standards program please refer to http:/[www.ccsds.org/ and http://iov.gsfc.nasa.gov/GTSP/ [Technical contact: Felipe Flores-Amaya] 6.2 Mars Climate Orbiter Mishap Investigation A service provided by the Flight Dynamics Analysis Branch is to support the peer reviews and investigation reviews of missions. Last year the Mars Climate Observer (MCO) unfortunately failed in its Mars mission due to an underlining unit conversion error. As part of the MCO mishap board, the FDAB supported the investigation by providing leadership in the trajectory design, navigation, and control areas. The FDAB participated in the MCO Mishap board with the MSFC Center Director, NASA HQ, and independent individuals. The findings for this mishap were released under a document that not only provided information regarding the mishap, but also established new guidelines for t'uture NASA mission. It detailed the expectations of all future missions with respect to mission success. The findings addressed the use of faster, better, cheaper in the context of mission success and mission safety. Copies of this document can be obtained through NASA HQ.

[Technical contact: David Folta Flight Dynamics Analysis Branch End of Fiscal Year 2(X)O Report 37 7.0 Outreach Activities 7.1 Educational Outreach: International Space University A part of the FDAB eft'on for educational outreach, a student of the Intemational Space University (ISU) was selected to participate in analysis with the FDAB in order to fulfill his requirements for a Masters degree. A part of his 10-week effort, a Matlab demonstration tool was developed to study formation-flying concepts at the L1 LaGrange point. The student, Mr., Christoph Wagner of Germany, completed an initial investigation that included libration orbit generation, linear Quadratic Regulator controls, and formations. A sample of his Matlab work appears in Figure 7-1a/b.

e Figure 7-1a/b Libration Orbit Control, About an Orbit and Relative Motion [Technical contact: David Folta] 7.2 SAMPEX University Operations The University of Maryland Aerospace Engineering Department completed its first full year of sole responsibility for flight dynamics support of the Solar Anomalous and Magnetospheric Particle Explorer (SAMPEX) spacecraft. In this role, a team of University of Maryland undergraduate and graduate students provides routine spacecraft orbit determina- tion, attitude determination, attitude sensor analysis, and flight dynamics product generation. This effort is sponsored and supported by the FDAB, which provides consultation support as needed and periodically reviews the overall program status. This has been a very successful outreach initiative and gives the student team practical experience and training in spacecraft flight dynamics computations, the use of several commercial ground support tools and analysis of flight data.

The operation also serves as a test bed for researching ground system automation techniques. During the past year, new team members were successfully trained following some losses due to graduation. Some members of the team that have graduated have taken jobs in private industry supporting spacecraft operations. This is another measure of success for the program.

[Technical Contact: Tom Stengle] 7.3 Educational Outreach: NASA Academy As part of the GSFC outreach eftort to support universities, the FDAB took part in the NASA Academy, a summer internship for undergraduate and graduate students who are considered tops in their field• This year the FDAB hosted two students, Ms. Corissa Young from Colorado and Mr. Adam Ross from Harvard. Their subject was to complete mission design concepts for Unique Non-Keplerian orbits. This cooperative work was enabled under a director's discretionary fund for advanced research topics. The work covered 10 weeks during the summer with final results presented to a GSFC peer review panel. An example of their efforts is shown in figure 7-2, the orbits of a vertical libration orbit and Earth polar sitters that enable continuous viewing of the Earth's polar regions.

38 Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report Looking at the Ecliptic Figure 7-2. Vertical Libration Orbit and Earth Polar Sitters [Technical contact: David Folta] 7.4 PREST Program During FYO0. the FDAB supported two students under a grant with the George Washington Universit3, Program of Research and Education in Space Technology (PREST). One of these students is currently in residence at the GSFC and is working with branch members on research of formation flying control techniques. The other student completed analysis of new algorithms for attitude determination and rate estimation using GPS measurements.

[Technical Contact: Tom Stengle] 7.5 Graduate Student Research Program (GSRP) The FDAB continued its long standing support of the GSRP program. In FY00, one GSRP sponsorship came to a close.

while two new GSRP eftbrts were initiated: "'Decentralized Control of Distributed Satellite Networks" to be performed by Mr. Belanger of UCLA "'Feasibility of Atmospheric Penetration for Satellite Formation Flying Experiment" to be perlormed by Mr. Joseph Schultz of the University of Maryland [Technical Contact: Tom Stengle] Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report 39 7.6 Public Education/Community Outreach The following outreach activities were supported in FY00: Science Fair & Engineering Judging • District of Columbia Citywide Science Fair, Howard University, WDC, 3/19/00 Rocket Building/Engineering Design Projects • Take Our Daughters to Work Program, Egg Drop Contest, NASA GSFC, Greenbelt, MD, 4/14/00 Career Presentations • University of Maryland Department of Aerospace Engineering Sigma Gamm Tau Chapter • National Academy of Science, Women in Science and Engineering (WISE) Committee, WDC 10/30/99 • Joint Education Facilities, 2574 Naylor Road, SE, WDC, 1/8/00 • Tarrant County College, "'Careers in Science & Tech. - A-A Contributions to Tech.", Ft. Worth, TX, 2/7/00 • PG Community College, Science Engineering Education Day, 301 Largo Rd, Largo, MD, 2/1/00 • QEM/MSE National Conference, "You meet the Scientist", JW Marriott Hotel, WDC, 2/12/00 • Jeremiah E. Burke High School, 60 Washington St., Dorchester, MA, 3/10/00 • The Stone Ridge School, School of the Sacred Heart, 9101 Rockville Pike, Bethesda, MD, 3/13/00 • Ferrebee Hope Community School, 3999 8'h St., SE, WDC, 3/20/00 • GW Univ., Women & Power Leadership Program, Mt. Vernon Campus, WDC, 4/20/00 • DC Metropolitan Organization of Scientists, Boiling AFB, WDC, 9/12/00 • Trenton & Plainville HS, Rutgers Campus, Piscattaway, N J, 7/20/00 Career Day Presentation • NTA Scientist and Engineer School Visitation Day, Kingsford, ES, Mitchellville, MD 11/4/99 Speech (Open, Award, Closing & Graduation Ceremonies, Luncheon) • National School Boards Association, The Education Technology Program, Dallas TX, 11/12/99 • Zonta International Club of Charles County, "Flying into the new millenium", Charles County, MD. 1/11/00 • NCA&T, Ronald McNair Memorial Program, Greensboro, NC, 1/28/00 • Tarrant County College. Luncheon, Ft. Worth, TX, 2/7/00 • National Academies' 2000 African American History Day Program, WDC, 2/14/00 • Defense Intormation Systems Agency, Women's History Month-Kickoff, Arlington, VA, 3/8/00 • US Department of Veteran's Affairs, Women's History Month, 810 Vermont Ave., NW, WDC, 3/14/00 • Grant County All Academic Team Dinner, Grant IN, 5/20/00 • Richard Montgomery H. S. Graduation-Rockville, MD, Constitution Hall, WDC, 6/8/00 • Tech 2000 Symposium, Breakfast Keynote Speaker, Eden Roc Resort, Miami FL, 7/21/00 • Tuskegee Airmen's National Convention, Youth Luncheon, San Antonio, TX, 8/10/00 • Rutgers University, Off.Min.Under.Prog. Freshman Orientation, Piscataway, NJ, 8/20/00 • Minority Access National Role Models Conference, Washington Marriott, WDC, 9/17/00 Program Visits NASA GSFC/Mentor Student/Fellow • MIE, Faculty visit, setup by NASA HQS, 10/21/99 • Sunbeams Program, St. Frances Xavier MS, Greenbelt, MD, 1/13/00 • Delta Academy Baltimore. A-A Girls mentoring program, Greenbelt. MD, 2/17/00 Education/Career Conference or Panel • National Academy of Science WISE Committee, WDC 10/30/99 • Department of Defense (DoD) Leaders of Educ. Programs w/SME Dimensions Conference, Doubletree Hotel Arlington, VA 11/5/99 • QEM/MSE Natl Conf., "Career Pathways for Ph.D.'s ...", JW Marriott Hotel, WDC, 2/12/00 • NAFEO's Annual Black College Student's High Tech Expo, Hilton Hotel and Towers, WDC, 2/15/00 • Penn State, Math Options Day, Erie, PA, 5/9/00 • Women's Information Network, National Democratic Club, WDC, 6/1/00 40 Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report

• MITMites 25 th Anniversary Conference, MITSloan Bdg, Cambridge, MA,7/15/00

• Tech 2000 Symposium, Women's History & Issues inScience & Technology, MiamiFL,7/22/00

• Congressional Black Caucus, "Chic Geek on Cyberstreet", WDC, 9/15/00

Online/Video Conference Interactive Session • Women of NASA (WON) Chatline, NASA GSFC, MD, 2/2/99, 2/25/00 • Network Resources and Training Sites (NRTS) Program, South Carolina State Univ., Video conference, 6/12/00 • "Digital Diversity: Power to the People'?", Videoconference WHUT TV 32, Howard University, 1(I/27/99 • Minority University - Space Interdisciplinary (MU-SPIN) Space Mission Involvement Workshop • Videoconference, Morgan State University, 12/10/99 (Ref. http://nasa.utep.edu/miwc/) External Advisor/Mentor • Howard University. Graduating Senior Architectural Student: Rodney Lapson, Thesis: Moon Base.

Television/Radio/Magazine/Website Interviews • NBC Nightly News, "'Women to Watch", Andrea Mitchell, 1/13/00 • iVillage.com, "'Women Who Rule", 2/(X1 • NSBE Engineer, Malik Russell, 2/3/00 • Spacekids.com, Denise Jewell, 2/3/00 • ScienceMaster.com, "Meet Dr. Aprille Ericsson-Jackson", Gene Mascoli, 3/00 • The George Lucas Foundation, Edutopia: "Bridging the Digital Divide", Spring 2000, Sara Amlstrong Essence Magazine, "Ya Done Good Girl", 5/00 • Yahoo Intemet Life, "'How America Uses the Net", Jeremy Kaplan, 212-503-5167, 9/00 • Howard University Magazine, Martha Frase-Blunt, 703-683-5658, 9/00 • Woman Engineer. "'To Give is to Receive", Anne Baye Eriksen, 10/(X) Committees • NASA GSFC: Black History Club, NTA GSFC Chapter-President, Diversity and Recruitment Team; National Technical Association: National Conference Planning Committee, National School Visitation Committee Chair, Publications and Editorial Committee; Building STEPS Board Member.

Proposal/Application Reviewer • Graduate Student Researchers Program, NASA GSFC. Code 160, Greenbelt, MD 20771, 3/00 • National Science Foundation (NSF) Undergraduate Engineering Education, Arlington, VA, MOO [Technical contact: Aprille Ericsson- Jackson] Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report 41

Appendix A-Awards List of awards earned in FY2000: Earth Observing System-AM Project Team 2000 GEODE was a runner-up in NASA's Software of the Year competition.

Group Achievement Award. Customer Service Excellence Award Microwave Anisotmpy Probe (MAP) Flight Software Team, February 9, 2000 Group Achievement Award, Quality and Process Improvement Annual Award Microwave Anisotropy Probe (MAP) Simulation Team, October 15, 1999 Group Achievement Award. Quick Scatterometer (QuikSCAT) Observatory and Mission Operations Team, August 14, 20(X) GSFC Annual Moe I. Schneebaum Memorial Award for Engineering was given to David Folta GSFC Award of Merit was given to Robert L. DeFazio for support to numerous Earth and space science flight projects GSFC Certificate of Appreciation to the CGRO Re-entry Team GSFC Outstanding Mentor Award was given to David Mangus GSFC Performance Awards to the FDAB CGRO Re-entry Team GSFC Quarterly Customer Service Excellence Award to the MAP Maneuver Team GSFC Quarterly Outstanding Teamwork Award to the EOS AM Project Team GSFC Quarterly Outstanding Teamwork Award to the Terra Flight Dynamics Team GSFC Special Act Awards to the FDAB CGRO Re-entry Team NASA Academy Certificate of Recognition was given to David Folta NASA Group Achievement Award / Center of Excellence for Lunar Prospector Support NASA Group Achievement Award/Mars Climate Orbiter Mishap Investigation Board, Achievement Award via MSFC Director Outstanding Teamwork Group Award to the IMDC team Terra Flight Dynamics Team 20(YO Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report 43

Appendix B-University Grants The following university grants being administered by FDAB engineers were in place in FY00: 1.

GRANT NAG5-9961 with the University of Maryland Department of Aerospace Engineering titled "Precise Virtual Rigid Body Control of a Satellite Constellation." This grant is developing a possible control strategy for formation flying.

[Technical Contact: Thomas Stenglel 2.

GRANT NAG5-9890 with the University of Maryland Department of Aerospace Engineering titled "Rarefied Flow Aerodynamics for Stability and Control of Formation-Flying Satellites." This grant is researching problems and control strategies for spacecraft flying in formation with low perigee passes. This research may benefit the develop- ment of control approaches for the Geospace Electrodynamics Connections (GEC) mission.

[Technical Contact: Marco Concha] .

GRANT NAG5-8697 with the University of Colorado at Boulder titled "Algorithms for Autonomous Orbit Determi- nation and Formation Flying." The focus of this grant is on algorithms for use of GPS for formation flying missions in highly elliptical orbits, including signal acquisition and tracking and relative navigation.

[Technical Contact: Steve Hughes] 4.

GRANTS NAG5-8694 and NAG5-8879 with the University of California at Los Angeles titled "'Decentralized Estimation and Control of Distributed Spacecraft," and "Precise Relative State Estimation and Control of Distrib- uted Satellite Networks." These grants are developing and applying new decentralized control architectures for satellite formations.

[Technical Contract: Russell Carpenter] .

GRANT NAG5-9829 with the University of Texas at Austin titled "Spacecraft Rendezvous Navigation with Inte- grated INS-GPS.'" This grant is focusing on GPS/INS software architecture development for relative navigation and attitude determination.

[Technical Contract: Russell Carpenter] .

GRANT NAG5-9612 with Comell University Sibly School of Mechanical and Aerospace Engineering titled "New Algorithms for Magnetometer Orbit and Attitude Estimation." This grant is studying the feasibility of a moderate precision navigation (<10 km orbit, <0.5 degrees attitude) using Magnetometer data.

[Technical Contract: Richard Harman] 7, GRANT NAG5-9748 with Princeton University Department of Mechanical and Aerospace Engineering titled" Satellite Attitude Estimation with the Two Step Optimal Estimator." This grant is studying the ability of the two- step algorithm to out perform the standard Extended Kalman Filter currently used for spacecraft and ground attitude estimation.

[Technical Contract: Richard Harman] ° GRANT NAG5-8770 with Technion-Israel Institute of Technology Department of Aerospace Engineering titled "Improvement of the REQUEST Attitude Determination Algorithm for Aiding MAGNAV.'" This grant is studying the possible advantages of using the Recursive QUEST algorithm in place of the pseudo-linear and extended Kalman Filters in the real-time Magnetometer Algorithms.

[Technical Contract: Richard Harman/572] 44 Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report

Appendix C-Conferences and Papers List of conferences and professional papers in FY2000: Lauri K Newman, Paul J. Noonan, and Cheryl. J. Gramling, "Ground System Support Of An Onboard Navigation System: Implementation And Operations Experiences", AAS 00-121. AAS/AIAA Space Flight Mechanics Meeting, Clearwater, FL, January 23-26, 2000.

G. Lightsey, C. Campbell, R. Carpenter, J. Simpson, G. Davis, "Design and Performance of Space Algorithms for the GPS Receiver used on International Space Station and Crew Return Vehicle," Proceedings of the International Workshop on Aerospace Applications of the Global Positioning System, Jan 31-Feb 2, 2000, Breckenridge, CO.

E Bauer, J. Bristow, R. Carpenter, J. Garrison, K. Hartman, A. Long, T. Lee. D. Kelbel, V. Lu, J. How, F. Busse, P.

Axelrad, M. Moreau, +'Enabling Spacecraft Formation Flying in Any Earth Orbit Through Spacebome GPS and Enhanced Autonomy Techniques+" Proceedings of the International Workshop on Aerospace Applications of the Global Positioning System, Jan 3 l-Feb 2, 2000, Breckenridge, CO.

R. Carpenter, "A Preliminary Investigation of Decentralized Control for Satellite Formations," Proceedings of the 2000 IEEE Aerospace Conference, Mar 18-25, 2000.

A. Long, D. Kelbel, T. Lee, R. Carpenter, C. Gramling, ++Autonomous Relative Navigation for Formation-Flying Satel- lites Using GPS,'" CNES 15th International Symposium on Space Flight Dynamics, June 26-30, 2(X)O. Biarritz, France.

A. Long, D. Kelbel, T. Lee, R. Carpenter, J. Garrison, '+Autonomous Navigation Improvements for High Earth Orbiters Using GPS," CNES 15th International Symposium on Space Flight Dynamics, June 26-30, 2000, Biarritz. France.

R. Carpenter, D. Folta, C. Wagner, "'Formation Flying with Decentralized Control in Libration Point Orbits," CNES 15th International Symposium on Space Flight Dynamics, June 26-30, 2000, Biarritz, France.

Cheryl Gramling, "Preliminary Operational Results of the TDRSS Onboard Navigation System (TONS) for the Terra Mission", June 2000, ISSD conference, Biarritz, France.

Lauri K. Newman, Richard J. Mclntosh, and Paul J. Noonan, +'Terra Ascent Planning to Meet Landsat-7 Phasing Requirements,"AIAA 2000 -4342, AIAA Astrodynamics Specialist Conference, Denver, CO, August 14-17, 2000.

Julie Deutschmann, Itzhack Bar-Itzhack, and Rick I-Iarman, "'A LEO Satellite Navigation Algorithm Based on GPS and Magnetometer Data", International GPS Workshop & International Flight Dynamics Conference. Biarritz, France.

Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report 45

Appendix D-Acronyms and Abbreviations This appendix gives the definitions of acronyms used in this document.

AAS American Astronautical Society ACS Attitude Control System ACT Attitude Control Thrusters AETD Applied Engineering and Technology Directorate AI Artificial Intelligence ALl Advanced Land Imager AO Announcement of Opportunity APL Applied Physics Laboratory AST Autonomous Star Tracker ATMS Advanced Technology Microwave Sounder CCSDS Consultative Committee for Space Data Systems CETDP Cross Enterprise Technology Development Program CGRO Compton Gamma Ray Observatory COTS Commercial Off-the-Shelf CPT Comprehensive Performance Test CSOC Consolidated Space Operations Contract CVS Concurrent Version System DACC Distributed Active Archive Center DoD Department of Defense DSN Deep Space Network DSS Digital Sun Sensor DST Dynamical Systems Theory EFF Enhanced Formation Flying EMOS LOS Mission Operations System EO Earth Observing LOS Earth Observing System ESA European Space Agency ESSP Earth System Science Pathfinder EUVE Extreme Ultraviolet Explorer FAA Federal Aviation Administration FDAB Flight Dynamics Analysis Branch FDS Flight Dynamics System FDSS Flight Dynamics Support System FDF Flight Dynamics Facility Flex Fluorescence Experiment FOT Flight Operations Team FSW Flight Software FY Fiscal Year GEO Geosynchronous Earth Orbit GEODE GPS Enhanced Orbit Determination Experiment GEONS GPS-Enhanced Orbit Navigation System GINA Generalized Information Network Analysis GNCC Guidance, Navigation, and Control Center GOES Geostationary Operational Environmental Satellite GPM Global Precipitation Mission GPS Global Positioning Satellite 46 Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report

GRO

Gamma Ray Observatory

GSE

Ground Support Equipment

GSFC

Goddard Space FlightCenter

GSRD

Ground System Requirements Document

GSRP

Graduate Student Research Program

GTDS

Goddard Trajectory Determination System

GUS

Gyroscopic Upper Stage

HD

Henry Draper

HDS

Hybrid Dynamic Simulator

HEO

High Earth Orbit/Highly Elliptical Orbit

HGA

High Gain Antenna

HTML

HyperText Markup Language

ISEE-3

International Sun-Earth Explorer 3

I&T

Integration and Test

ICD Interface Control Document

IHS

Inner Heliospheric Sentinels

IM

Ionosphere Mapper

IMDC

Integrated Mission Design Center

IMU Inertial Measurement Unit

ISU

International Space University

ITAR

International Traffic In Arms Regulation

ITSO

Information Technology Security Officer

JPL

Jet Propulsion Laboratory

LEO Low Earth Orbit

LOR

Launch and Orbit Raising

LPT Low Power Transceiver

LQG Linear Quadratic Gaussian

LRR

Lightweight Rainfall Radiometer

MAP

Microwave Anisotropy Probe

MARSAT

Mars Areo-stationary Relay Satellite

MC

Master Catalog

MCC Mid Course Correction

MCO Mars Climate Observer

MIT

Massachusetts Institute of Technology

MLS Microwave Limb Sounder

MMS

Magnetic Multi-scale Mission

MOC

Mission Operations Center

MOCC

Mission Operations Command and Control

MODIS

Moderate Resolution Imaging Spectroradiometer

MOPSS

Mission Operations Planning and Scheduling System

MOST

Mission Operations Support Team

MOWG

Mission Operations Working Group

MSRD

Mission Specific Requirements Document

MU-SPIN

Minority University - Space Interdisciplinary

NASA

National Aeronautical and Space Administration

NGST

Next Generation Space Telescope

NMM Normal Maneuver Mode

NOAA

National Oceanic and Atmospherics Administration

NPB

Navigation Processor Board

NPM

Normal Pointing Mode Flight Dynamics Analysis Branch End of Fiscal Year 2(XX) Report 47

NRTS

Network Resources and Training Sites

NSF National Science Foundation

NT

New Technology

OAT

Orbit Adjust Thrusters

ONS

Onboard Navigation Systems

OSSM

Ocean Surface Salinity Mission

PC

Personal Computer

Pl

Principal Investigator

PICASSO-CENA

Pathfinder Instruments for Cloud and Aerosol Spaceborne Observations - Climatologie Etendue des Nuages et des Aerosols

PLT

Post Launch Testing

PREST

Program of Research and Education in Space Technology

QuikSCAT Quick Scatterometer

R&D

Research and Development

RBM

Radiation Belt Mapper

RMS

Root-Mean-Square

RPO Radiation Protection Office

RSDO

Rapid Spacecraft Development Office Real-time Orbit Determination

RTOD

RWA

Reaction Wheel Assembly

RXTE

Rossi X-Ray Timing Explorer

SA

Selective Availability

SAMPEX

Solar Anomalous and Magnetospheric Particle Explorer

SMEX

Small Explorer

SOHO

Solar and Heliospheric Observatory

SOMO

Space Operations Management Office

SPECS Evolution of Cosmic Structure

SPS

Standard Positioning Service

ST

Space Technology

TDRSS

Tracking Data Relay Satellite System

TMM Thruster Maneuver Mode

TONS

TDRSS Onboard Navigation System TRACE Transition Region and Coronal Explorer TRMM Tropical Rainfall Measuring Mission URL Uniform Resource Locator USN Universal Space Network VCM Velocity Control Mode VIIRS Visible Infrared Imaging Radiometer Suite WAAS Wide Area Augmentation System WIRE Wide-Field Infrared Explorer WISE Women in Science and Engineering WON Women of NASA WRS World Reference System WWW World Wide Web 48 Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report

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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED December 2000 Technical Memorandum 4. TITLE AND SUBTITLE 5. FUNDING NUMBERS Flight Dynamics Analysis Branch End of Fiscal Year 2000 Report 572 6. AUTHOR(S) Tom Stengle and Felipe Flores-Amaya 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS (ES) 8. PEFORMING ORGANIZATION REPORT NUMBER Goddard Space Flight Center 2001-00785-0 Greenbelt, Maryland 20771 10. SPONSORING I MONITORING 9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS (ES) AGENCY REPORT NUMBER TM_2000-209971 National Aeronautics and Space Administration Washington, DC 20546-0001 11. SUPPLEMENTARY NOTES 12a. DISTRIBUTION I AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE Unclassified-Unlimited Subject Category: 18 Report available from the NASA Center for AeroSpace Information, 7121 Standard Drive, Hanover, MD 21076-1320. (301) 621-0390.

13. ABSTRACT (Maximum 200 words) This report summarizes the major activities and accomplishments carried out by the Flight Dynamics Analysis Branch (FDAB), Code 572, in support of flight projects and technology development initia- tives in Fiscal Year (FY) 2000. The report is intended to serve as a summary of the type of support carried out by the FDAB, as well as a concise reference of key accomplishments and mission experi- ence derived from the various mission support roles. The primary focus of the FDAB is to provide expertise in the disciplines of flight dynamics, spacecraft trajectory, attitude analysis, and attitude determination and control. The FDAB currently provides support for missions and technology devel- opment projects involving NASA, government, university, and private industry.

14. SUBJECT TERMS 15. NUMBER OF PAGES Flight dynamics, spacecraft trajectory, attitude analysis, attitude determination 16. PRICE CODE and control.

17. SECURITY CLASSIRCATION 18. SECURITY CLASSIRCATION 19. SECURITY CLASSIRCATION 20. LIMITATION OF ABSTRACT OF REPORT OF THIS PAGE OF ABSTRACT Unclassified Unclassified Unclassified NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89) Pr¢===_rih_d hv ANRI .¢;Ird 7R_ 1R