TA Activation Flight #2 (took place on Jan 15, 2010) “Quick Look” Data Review

1. TA Activation Flight #2(took place on Jan 15, 2010) “Quick Look” Data Review Thomas Keilig, 661-276-2011, keilig@dsi.uni-stuttgart.de Holger Jakob, 661-276-2594, jakob@dsi.uni-stuttgart.de

2. Card 9: VIS Uncaging and Caging in 15kft a) Dp 6psi • adjustment of axial position worked very well (although some overshooting) • axial uncaging 7min:40sec (pressure working point not optimized for 6 psid) • identified points for further performance improvements

3. Card 9: VIS Uncaging and Caging in 35kft b) Dp 8psi • at 8 psid time for axial uncaging improved to 4min:30sec • working pressure was better adjusted, no overshooting • the VIS stayed at this axial position until the end of TA Activation

4. Card 9: VIS Uncaging and Caging in 15 and 35kft • Successful in flight demonstration of improved VIS performance since 1st TA Activation Flight in December 2007: • VIS caging, uncaging and centering at different altitudes • a) Uncaging and Adjust (x-centering): • time needed improved from 9m:10s (2007) to 4m:30s • air consumption improved from 100 psi (2007) to 50 psi (caused by x-centering, not by uncaging) • b) Caging: • time needed improved from 3m:20s (2007) to 2m:20s • air consumption improved from 200 psi (2007) to 140 psi • VIS Auto Center Mode handles cabin pressure changes and TA movements during turns, gusts etc. (see next slide) • VIS was operated in auto center mode for nearly 4 hours • TA will be re-centered with the axial air springs in x-direction when out of range (cabin pressure change) • TA will be re-centered with the tangential air springs in y-z-direction when out of range (turns or gusts) • average air consumption determined ~70 psi per hour • air consumption for science missions ~30 psi per hour

5. Card 9: Air Bottle Use • VIS Auto Center Mode handled cabin pressure changes very well • VIS was operated in auto mode for 3:57 hours (also during turns) • air consumption from the bottles determined ~70 psi per hour • air consumption for science missions ~30 psi per hour

6. Card 9: VIS Uncaging and Caging in 15k and 35k Telescope x-position (translational fwd/bwd movement) ±3 mm Hardstop contact with VIS brackets would occure at ± 18 mm • TA stayed in its centered x-position (within ±3mm) until the end of the TA activation (for 3:57 hours) • If x-position >±3mm TA starts to re-center (never happened during that flight) no risk of x-hardstop contact during star observations • y-z-centering performance improved and tested on ground before flight

7. Card 9 VIS: ATAC Accelerometers PSD Plots VIS Modes Filtering of aircraft loads >6Hz by VIS

8. Card 15, 16, 17: Control Raps for Airframe/TA dynamics characterization The purpose of these 3 Test Cards was the Airframe / TA dynamics characterization with TA uncaged / unbraked / inertial. The fall back from INERTIAL to LOCAL during these excitations was expected and is a safety feature of the TA controls (velocity limit error). No further analysis of this maneuvers were performed by the TA Team. • Gyro-Performance: • no performance degradation in Gyros observed during these Control Raps • degradation bit send caused the “image jump” issue during HIPO Line Ops • valid for all the flight, but mentioned here

9. Card 10: Filter Fan Unit (FFU) activation • Successful activation of FFU (located in the cavity): • was running for 5 minutes, no EMI effects observed • no notable temperature change inside WFI and FFI housings observed • FFU is able to exchange the air volume inside WFI and FFI housing every ~10 minutes • FFU is intended as a Ground System active after Cavity Drying and before Cavity Pre-Cooling

10. Card 11: Gate Valve activation Cross section through Flange Assembly (FLA): Bypass valve Nasmyth Tube(cavity pressure) INF tub SI Flange with SI Mass Dummy installed

11. Card 11: Gate Valve activation Closures of Bypass Valve to measure the remaining differential pressure < 30 mbar • Operated via TA pass-through command • Bypass Valve was auto-cycled 7 times before pressure between INF tub and TA Cavity was < 30 mbar (precondition for Gate Valve opening)

12. Card 12: Nasmyth Tube Fans activation +16˚C end of Nasmyth Tube (Gate Valve) +2˚C half way inside Nasmyth Tube -2˚C -7˚C cavity air temperature • worked as expected: fans were running for 5 minutes • fans are sucking the air out of the Nasmyth Tube  cold air flows in • fans cooled the air inside the Nasmyth Tube down to cavity air temperature • short increase of cavity temperature due to air exchange • fans should remain ON during science flights to keep thermal background low

13. Card 14: Fine Balancing Drives activation Drive Speed 2 mm/sec • functional check and EMI check out only • re-balancing of the TA must be performed with closed door

14. Card 18, 19: Autopilot Characterization (Heading Changes) Autopilot in Manual Mode: heading error (degrees) roll angle (degrees) roll rate (degrees/sec) • manual mode requires a minimum of 7 degrees of roll angle to initiate a heading change • new heading is not established until the roll angle is less than 3 degrees • max deviation in heading is 0.70 deg, standard deviation is 0.26

15. Card 18, 19: Autopilot Characterization (Heading Changes) Autopilot in Command Mode: heading error (degrees) roll angle (degrees) roll rate (degrees/sec) • before the AIU (Autopilot Interface Unit) is completed, science missions will be flown in command mode • headings are close to the magnitudes expected for AIU requirements • max deviation in heading is 0.28 deg, standard deviation is 0.11

16. Card 20: EMI / Radio Interference • Performed as expected • Imagers did not pick up any interference from the Radios • Cavity Imagers (FFI and WFI):colder CCD sensors show the lower darkframe noise FFI dark field image

17. Card 20: EMI / Radio Interference Fine Field Imager (FFI): EMI check • a single FFI frame (1000 ms) • mean darkframe noise of 1070 counts • looks just like a ground-based darkframe • faint vertical streaks are usual thermal noise (added during the slow readout)  • RMS is typically only 16 counts • shot noise would be about 11 counts •  that is very good • difference of two consecutive FFI frames • mean value of 0.0 (as it should) • RMS = 8 counts •  didn't see any EMI effects (bright spots or streaks) in these difference images

18. Card 20: EMI / Radio Interference Focal Plane Imager (FPI): EMI check • difference of two FPI images • mean = 0 counts • RMS = 11 counts • single FPI frame • mean darkframe noise 1230 counts • RMS = 47 counts • evidently warmer as expected  first impression is the images are very clean and quiet

19. Card 21: Simulated Science Observations Legs SOFIA left the R-2508 complex to the south, crossed LAX airspace in >41 kft and turned around at Santa Catalina Island: - Flight Path up to Card 20 - Simulated Science Legs - Turn in between - Descent/Approach KPMD

20. Card 21: Simulated Science Observations Legs Coarse and Fine Drive movement LOS Rewinds Heading Change 1st leg 2nd leg

21. Card 21: Simulated Science Observations Legs Aircraft roll and Fine Drive movement (6 minutes of 2nd leg): FD takes care of the remaining differences. Only a small fraction is "leaking-through" into the pointing budget(fiber optical gyros) Low frequency A/C roll is compensated by Coarse Drive (spherical sensors) 0.2 – 0.25 Hz (5 – 6 sec) • This was with TA in Coupled_Continuous • Needs repeat in Coupled_Step and Coupled_Off for further analysis

22. Card 21: Simulated Science Observations Legs Aircraft/Autopilot stability LOS Rewinds Heading Change 1st leg 2nd leg

23. Card 21: Simulated Science Observations Legs Aircraft behavior during heading changes on science observation legs: for a 1 degree heading change as much as 2 degrees over shoot bank angles were 5-7 degrees for these small heading changes the autopilot takes out the heading overshoot in about 3 min Variation in aircraft pitch of +/- 0.9 deg not quite understood yet, but obviously correlated with air speed

24. Card 21: Simulated Science Observations Legs • Flown two long 25+ min N-S legs in 43 kft • Operated the TA in INERTIAL Stabilization during these legs • Commanded LOS Rewinds (as needed) • Coordinated small heading changes with the cockpit (as needed) • Activated Flexible Body Compensation (FBC) on the 2nd leg no negative impact seen so far with closed door need view to the stars to verify FBC performance with the imagers

25. Card 13: Inertial Stabilization via TAOC in 35kft ≈ “pointing stability“ Aircraft Roll Motion visible (ca. 0.2 Hz), see Ed Erickson Sep.06 EL(residual of CD coupled mode) XEL (compensation of heading oscillations) LOS

27. Card 13: Inertial Stabilization via TAOC in 35kft Slightly increased control deviation between 0.2 Hz and 4 Hz. Above 4Hz no difference visible. Could be due to differences in inertial disturbance or coupled mode. Max. difference ca. 0.015 arcsec, pointing budget allows for up to 0.04 arcsec • same behavior seen during HIPO Line Ops • Coupled_Continuous is only useable in very very smooth air • Coupled_Step recommended for Short Science in 35 kft

28. Card 13: Inertial Stabilization via TAOC in 35 kft • *)Aircraft inertial loads only!! • Cumulative RMS of Control Deviation is very close to the value estimated in the pointing budget, but: • Almost exclusively concentrated between 0 and 10 Hz • Pointing budget is specified for image motion, which includes flexible TA deformation. This not captured by the Gyros and hence not included in the control deviation. • Dropouts in data recording on DCC due to overload may have disturbed the measured control deviation (dropouts every 5 sec  additional control deviation around 0.2 Hz) • Telescope imbalance was large during this TA Functional Checkout  additional pointing error in the 0-12 Hz range

29. Card 21: Simulated Science Observations Legs increased cumulative error which can be attributed to data dropouts • increased altitude of Card 21 (43 kft) compared to Card 13 (35 kft) • hence a more stable environment leads to smaller control deviations • the additional control deviation around 0.2 Hz can be attributed to data errors • close to ES requirement, but also a few points for improvements identified • ES requirement for overall Image Quality is 5.3 arcsec (D80%) in the optical

30. Card 22: Secondary Mirror activation via TAOC Focus Center Mechanism (FCM) Cold Test: • Coldest temperatures reached so far • Cavity Air Temp: -28˚C FCM Actuator Temp: -6.5˚C • Reached all end positions without any problems • Weakened new threat TRT_102 • Needs repeat with open door and lower temperatures

31. Card 22: Secondary Mirror activation via TAOC Tilt Chop Mechanism (TCM) Test: • waveform identical as on ground • higher noise identified as the 300 Hz oscillation New SMM controller (without low pass filter) optimized on ground is not robust enough to handle in flight closed door vibration levels. Low pass filter can be implemented easily as successfully demonstrated during HIPO Line Ops Lessons Learned:  Not everything that performs like expected on ground does so in flight

32. Temperatures in Cavity FFI WFI

33. Temperatures in Cavity • coldest cavity air temperature (green) seen was -28˚C • PM temperature (yellow) after nearly 6 hours was only +3˚C • air probes on WFI and FFI (green) correlate very well with spider legs (purple) • FFI is located higher in the cavity and therefore warmer than WFI • first bypass valve opening correlates with INF temperature drop (red dotted curve at the top) • Nasmyth tube fan activation drops temperatures inside Nasmyth tube down to nearly cavity temperature (blue and red) • at the end of the flight a few things took place in parallel: • URD Seal inflation • Descent started • CECS Dryer switched to Dry-Mode • Bonus question: What causes the drop of the Pressure Window temperatures during descent (red dotted curves at the right)?

34. Summary of TA Activation Flight #2 • Successful in flight demonstration: • performance of repaired gyro unit (inertial stabilization) • VIS caging, uncaging and x-centering at different altitudes • x-centering: 9:10 min to 4:30 min (100 psi to 50 psi) • caging: 3:20 min to 2:20 min (200 psi to 140 psi) • VIS auto center mode handles cabin pressure changes • air consumption ~70 psi per hour • coupled mode: coarse and fine drive together in inertial_stab • First time in flight activation: • Filter Fan Unit • Nasmyth Tube Fans • Gate Valve opend and closed • Fine Balancing Drives • Characterized TA stability in inertial stabilization mode • Characterized Secondary Mirror chopping operation cold soak • Characterized WFI and FFI: cold, and in flight noise level