1 TIPS Feb 21, 2008 One-Gyro Science On-Orbit Test & Kalman Filter Sunpoint Safemode Test Merle Reinhart

2 TIPS Feb 21, 2008 What is 1-Gyro Science Mode? In this mode, only 1 gyro is available for rate sensing Now have a gyro-less plane rather than just a gyro-less axis as 2- gyro mode Has three main sub-modes like 2-gyro mode –M1G - Attitude errors can be as large as 9 degrees »Sensors are: The Gyro Magnetic Sensing System Coarse Sun Sensor »A Kalman Filter which is an attitude predictor-corrector is used to combine all the sensors along with aerodynamic and gravity gradient torque compensations to provide for a 3-axis stabilized control. –T1G - Attitude errors can be as large as a few tens of arcseconds »Sensors are: The Gyro Fixed Head Star Trackers »Perform OnBoard Attitude Determinations to reduce the attitude errors –F1G - Attitude errors typical at the catalog error of about 0.3 arcseconds »Sensors are: The Gyro The Dominant FGS

3 TIPS Feb 21, 2008 Why 1-Gyro Science Mode? SM4 is only 27 weeks away. Why are we still talking about 1- Gyro mode? Gyro run times (21-Feb-2008) –G hours (5.69 yrs)- operational, powered –G hours (6.55 yrs)- failed 31-Aug-2007, flex lead –G hours (3.79 yrs)- failed 29-Apr-2003, rotor restriction –G hours (6.10 yrs)- operational, turned off 28-Aug-2005 –G hours (1.84 yrs)- failed 28-Apr-2001, rotor restriction –G hours (1.91 yrs)- operational, powered –Mean time to flex lead failures is (4.77 yrs) hours All 6 gyros (3 rate sensing units - RSUs) are slated to be replaced during SM4 in EVA2

4 TIPS Feb 21, 2008 Gyro Lifetime Estimates Chart below shows approximate gyro failure probabilities assuming a gyro failure in July 2007 (close to time of Gyro #2 failure) Jul-2007 May-2008 Jan-2009 Feb-2011 SM4 Predictions from Helen Wong (Aerospace Corp) as communicated to Art Whipple (HSTP)

5 TIPS Feb 21, 2008 The OGS On-Orbit Test Visits from 4 proposals – WFPC2 – Astrometry – Mars – PCS Tests OGS Test was a full 2 days KFSP Test was 18 hours Total time 2 d 21 h

6 TIPS Feb 21, 2008 OGS High Level Results Completed OGS on orbit testing –Assessment indicates performance as expected 60/60 OBADs with nominal performance –Max correction for 1st OBAD was 2.44 degrees and 2nd OBAD was 38 arcsec 18/18 guide star acquisitions/reacquisitions were successful –Astrometry, 2-GS with re-acq, 1-GS with re-acq, K13 variations, Mars

7 TIPS Feb 21, 2008 F1G OOT Performance Jitter computed over entire guiding interval with merged data Values shown are the 60 second root sum squared of the V2 and V3 standard deviations of position path Data Start Time FGSs In Use Dominant mV, catalog Max Jitter, DVTHEP, mas Mean Jitter, DVTHEP, mas Min Jitter, DVTHEP, mas Comments 29/17:032,3, Astrometry 29/18:392,3, Astrometry 29/20:152,3, Astrometry 29/21:511,2, WFPC2 29/23:342,3, WFPC2 30/01:112,3, WFPC2 30/02:462,3, Reacq 30/04:222,3, WFPC2 30/05:582,3, WFPC2 30/07:341,3, WFPC2 30/09:091,3, WFPC2 30/10:452,1, Mars 30/15:242,0, Ast/1FGS 30/16:542,0, Reacq/1FGS 31/02:382,3, Acq test 31/04:132,3, Acq test 31/05:492,3, Acq test 31:08:522,3, Astrometry Note that the DVTHEP jitter during persistent disturbances from simulations is ~2-3 mas larger than science instrument jitter for faint stars

8 TIPS Feb 21, 2008 New Kalman Filter Sun-Point Safemode The Safe Mode Flow Down Science Mode Inertial Hold Kalman Filter Sunpoint Zero Gyro Sunpoint PSEA Hardware Sunpoint

9 TIPS Feb 21, 2008 KFSP Performance Design Goals were for better performance than ZGSP KFSP performance met ALL expectations –Entries into orbit day following captures during orbit night had no discernable attitude errors –Captures had minimal overshoots –Slews to the sun-line appeared to be pure eigenvector maneuvers –No noticeable rates about the sun-line after capture One of the major advantages of KFSP over ZGSP is that the attitude is held even at night such that the aperture door is not required to be closed