Document
ern numerical methods. Among these ments for accuracy, reproducibility, and This work was done by Jonathan K.
methods are efficient Kepler’s-equation efficiency (and, hence, speed). Self-start- Weaver of Johnson Space Center and Daniel time-of-flight solutions and self-starting ing numerical integration also supports R. Adamo of United Space Alliance. For fur- numerical integration with time as the fully analytic regulation of integration ther information, contact the JSC Innovation independent variable. Self-starting nu- step sizes, thereby further increasing Partnerships Office at (281) 483-3809.
merical integration satisfies the require- speed while maintaining accuracy. MSC-23802-1
An Augmentation of G-Guidance Algorithms
This augmented algorithm can be used in small-body proximity operations utilizing model
predictive control with a need for safety from surface-constraint uncertainty.
NASA’s Jet Propulsion Laboratory, Pasadena, California The original G-Guidance algorithm gation of any unexpected trajectory or a control policy (feedback), along with provided an autonomous guidance and state changes that occur during standard sensors to monitor actual spacecraft control policy for small-body proximity mode operations. state. The feedback is designed to en- operations that took into account uncer- In order to have the G-Guidance algo- sure that the spacecraft stays within a tainty and dynamics disturbances. How- rithm detect an unsafe condition, it re- specified proximity to the feedforward.
ever, there was a lack of robustness in re- quired some modification. This modifi- The feedforward is designed to achieve gards to object proximity while in cation provides a policy to safely the goals of each mode: hover for safety autonomous mode. The modified G- maneuver the spacecraft between its cur- mode and maneuver toward target for Guidance algorithm was augmented rent state and a desired target state while standard mode. By giving the spacecraft with a second operational mode that al- ensuring satisfaction of thruster and tra- the ability to re-compute its trajectory lows switching into a safety hover mode. jectory constraints, along with safety con- on-the-fly in response to local condi- This will cause a spacecraft to hover in straints. In standard mode, this modifica- tions, minimization of fuel usage is pro- place until a mission-planning algorithm tion brings the spacecraft from its vided. The original G-Guidance algo- can compute a safe new trajectory. No current position closer to its target state. rithm provides robustness to uncertainty state or control constraints are violated. In safety mode, the algorithm maintains affecting the dynamics. The safety aug- When a new, feasible state trajectory is the spacecraft’s current state at zero ve- mentation provides a form of state-con- calculated, the spacecraft will return to locity. Since the safety mode is designed straint robustness, which further miti- standard mode and maneuver toward to be temporary, the destination location gates risk.
the target. The main goal of this aug- in this mode is also temporary, and once This work was done by John M. Carson mentation is to protect the spacecraft in a new destination location is provided, III and Behcet Acikmese of Caltech for the event that a landing surface or obsta- the spacecraft returns to standard mode. NASA’s Jet Propulsion Laboratory. For more cle is closer or further than anticipated. The G-Guidance algorithm uses both information, contact iaoffice@jpl.nasa.gov.
The algorithm can be used for the miti- a planned trajectory (feedforward) and NPO-46452
Comparison of Aircraft Icing Growth Assessment Software
The goal is to provide software that can predict ice growth under any condition for
any aircraft surface.
John H. Glenn Research Center, Cleveland, Ohio A research project is underway to pro- The Icing Branch at NASA Glenn has The project addresses the validation duce computer software that can accu- produced several computer codes over of the software against a recent set of ice- rately predict ice growth under any me- the last 20 years for performing icing shape data in the SLD regime. This vali- teorological conditions for any aircraft simulation. While some of these tools dation effort mirrors a similar effort un- surface. An extensive comparison of the have been collaborative projects, most dertaken for previous validations of results in a quantifiable manner against have been developed primarily by one LEWICE. Those reports quantified the the database of ice shapes that have person, with some assistance by others. ice accretion prediction capabilities of been generated in the NASA Glenn The state of computing has also the LEWICE software. Several ice geom- Icing Research Tunnel (IRT) has been changed dramatically in that time pe- etry features were proposed for compar- performed, including additional data riod. As these codes have grown in com- ing ice shapes in a quantitative manner.
taken to extend the database in the plexity and have been accepted by users The resulting analysis showed that Super-cooled Large Drop (SLD) regime. as production icing tools, there has LEWICE compared well to the available The project shows the differences in ice arisen a need for the developers to ad- experimental data.
shape between LEWICE 3.2.2, Glen- here to standard software practices used The effects of super-cooled large nICE, and experimental data. to develop commercial software. droplets in icing have been researched 38 NASA Tech Briefs, January 2011 extensively since 1994. Since then, sev- sis was placed on the newer data, which Inquiries concerning rights for the commer- eral experimental efforts have been is predominately SLD. cial use of this invention should be addressed made to document SLD ice shapes and This work was done by William Wright, to NASA Glenn Research Center, Innovative to investigate the underlying physics. Mark G. Potapczuk, and Laurie H. Levinson Partnerships Office, Attn: Steve Fedor, Mail While this project provides comparisons of Glenn Research Center. Further information Stop 4–8, 21000 Brookpark Road, Cleve- to standard icing conditions, the empha- is contained in a TSP (see page 1) . land, Ohio 44135. Refer to LEW-18451-1.
NASA Tech Briefs, January 2011 39