Summarizes my work from my Summer 2010 co-op tour at NASA-Goddard. Includes work for the ARTEMIS mission and GMAT testing.

1. Colin Eaton Graduate Co-op, Code 595 Mentor: Mark Woodard August 25, 2010 ARTEMIS Mission Support 1

2. Overview ARTEMIS Brief mission summary Related projects P2 z-oscillations P2 L1 stationkeeping analysis in STK STK-COM automation P2 L1 ODTK simulator / Tracking schedules Maneuver calibrations GMAT testing Testing methodology MATLAB scripts/functions 2

3. 3 ARTEMIS

4. ARTEMIS mission Extension of the THEMIS mission, and a collaboration with UCB and JPL THEMIS B = ARTEMIS P1 , THEMIS C = ARTEMIS P2 First mission to navigate to and perform stationkeeping operations around the Earth-Moon L1 and L2 libration points Satellites transfer from highly-elliptical lunar orbits Lissajous Libration orbits  Low lunar orbits NMDB is responsible for much of the maneuver planning and calibration, with additional emphasis on Lissajous stationkeeping operations 4

5. The P2 L1 z-component dilemma Targeted P2 Lissajous trajectories yielded uncontrolled RLP z-component oscillations prior to exit Conditions must be controlled in order to capture into lunar orbit 5 km

6. The P2 L1 z-component dilemma Performed Fourier analysis to derive periodicity Long-term Period: ~9 months Attributed to the equations of motion for the CR3BP 6 km amplitude frequency days

7. The P2 L1 z-component dilemma Methods for controlling z-oscillations: DV prior to Lissajous insertion Required too large of a DV to make significant alteration DV at inflection point Requires only ~1m/s down burn to stabilize Maneuver at set frequency Box method 7

8. P2 L1 stationkeeping analysis 8 x

9. P2 L1 stationkeeping analysis Stationkeeping methods DV at each x-axis crossing (a.k.a. half-rev) DV at every other x-axis crossing (a.k.a. full-rev) No significant advantage over half-rev Half-rev for first 2-3 maneuvers, then full-rev Methods for DC convergence Vx=0 Gate method “Give it a push” method Wrote ARTEMIS procedures section outlining the primary methodology in STK 9 x

10. STK-COM Automation Had the desire to make the stationkeeping operations much more convenient Most tasks were very repetitive Became familiarized with STK-COM as per Kevin Berry’s suggestion and learned the basics with Cassie Object-oriented programming using MATLAB to control the STK GUI Wrote various scripts to automate common tasks that did not require “eyeballing” Still exploring ways to add some autonomy to allow less user input 10 { for i=1:3 click.m end

11. STK-COM Automation STOP Add targ. ∆v Targ. param’s Apply∆v Radial-only∆v MATLAB scripts COMbase.m Connects to STK and stores the threads to common objects from the stkp setup (e.g. MCS segments, DV’s, etc.) into MATLAB variables for easier manipulation COMTest_better.m Loops through all (or specific) target sequences to change settings such as: profile action, zeroing out DV’s, applying profiles, DC step/pert sizes, etc. COMTest_fordave2.m Differential Corrector Pass Fail 11

12. ODTK Simulator / Tracking Schedules Wanted to perform trade study on tracking schedules for P2 at L1 using the following tracking systems: DSN (Madrid, Canberra, Goldstone) BGS (UC Berkeley) MILA (GSFC/KSC) 12 Purpose of the study was to determine how much tracking is adequate to yield converged solutions of the orbit state Used ODTK (not to be confused with ODTBX) to simulate tracking data from the stations based on custom tracking intervals

13. ODTK Simulator / Tracking Schedules First studied mathematics behind the software and spent time with Mark to find the “things to look for” Ran results through the sequential filter and fixed-interval smoother to check convergence 13

14. ODTK Simulator / Tracking Schedules The first step was to create the customized tracking schedules for each station Requirements provided: DSN: Alternate between N/S hemisphere, every other day for 3.5 hours/pass BGS: Two 45-min passes every day MILA: One 1-hour pass every day Created random schedules by hand at first Decided to write MATLAB scripts to make my job easier checkSched.m – compares a newly generated schedule to be integrated with an existing schedule (e.g. adding my BGS passes to the DSN schedule I had to check for overlaps) makeSched.m – creates a new tracking schedule of multiple stations with various types of parameters and requirements Currently includes my DSN passes, hope to add BGS and MILA in future 14

15. ODTK Simulator / Tracking Schedules Ran into various software-related and physical problems (even some that Jonathan couldn’t fix!!!) Filter/smoother position/velocity uncertainties and measurement biases sporadically explode from case to case SRP and transponder bias don’t have realistic physical ties when iterations converge 15 ODTK often doesn’t work properly on my computer unless Jonathan touches the keys Unable to make any decisive conclusions thus far in the simulator analysis Also attempted P1 L2 simulation, but ran into same problems

17. Most iterations correlated quite well

18. Also performed pre-maneuver analysis

19. Biased the nominal DV’s to account for maneuver execution error

21. GMAT Testing Asked to help participate in GMAT testing with Steve and Joel for December release of the software Responsible for various aspects of the “Save” command Finding all unique GUI configurations Creating the script and output files necessary for comparison Developing the comparator Running cases through the comparator Had fun learning how to utilize regexp() i.e. translating Joel’s native language 18

22. GMAT Testing 19 GMAT Saved data file Comparator Result (P/F) Report .script / .truth file .tc file .truth file Testing Methodology: Test System

23. GMAT Testing MATLAB scripts/functions: makeSave.m Runs entire comparator process requiring only the object class and setting extension @SaveComparatorompare.m Extracts saved object properties from .script/.truth file Much regexp’ing… Searches for same data in saved/.data file Checks “Create” and property lines Yields pass/fail result Must match property name and property value exactly to pass 20

24. Acknowledgements 21 Mark Woodard Dave Folta Jonathan Lowe Steve Hughes Joel Parker Kevin Berry Conrad Schiff Cassie Alberding (and the LCP)

25. 22 Thanks for your time! Questions?