1. Two-Gyro All-sky Scheduling Study TIPS April 15, 2004 http://www.stsci.edu/org/ess/projects/two_gyro_science

2. 24/15/2004 Personnel at Large v Special Projects Branch (SPB) ä Merle Reinhart ä George Chapman v Operations Planning Branch (OPB) ä Alison Vick ä Ian Jordan v Planning Systems Development Branch (PSDB) ä Mark Giuliano ä Bob Boyer

3. 34/15/2004 Outline v Two Gyro background ä Two Gyro Modes ä Why they impact scheduling v All-sky scheduling study ä Plots galore ä Targets-by-week The Movie

4. 44/15/2004 TGS Modes v Three operational modes ä MSS and two gyros (M2G): Compares MSS output to magnetic field model to control attitude and rates with errors required to be less than 10 degrees; supports vehicle maneuvers ä FHST and two gyros (T2G): Requires one tracker to be visible to use FHST data and gyros to control rates; onboard attitude determination (OAD) using FHST map data from two FHST units will bring attitude error within FGS search radius ä FGS and two gyros (F2G): Requires FGS visibility to use FGS data and gyros to control rates and attitude to allow for science v What does it mean? ä Elaborate process to get on guide stars after a slew ä Less schedulability (big surprise)

5. 54/15/2004 3 gyro vs. 2 gyro Getting to guided science v 3-gyro (current ops) ä Type 2 Slew ä FHST full update ä FGS guide star acquisition v 2-gyro ä Type 2 Slew ä FHST rate control ä First FHST map ä First attitude correction ä Second FHST map ä Second attitude correction ä FHST GOB (overlaps with guide star acq) ä FGS Guide star acquisition

6. 64/15/2004 TGS Scheduling Scenario

7. 74/15/2004 Scheduling Impacts & Constraints v Largest impact is the requirement to have overlapping visibility between the FHSTs and FGSs ä Limits the portion of sky available at any one time v Additionally, several constraints / restrictions are generically affected by the large pointing uncertainty (LAU) in M2G mode ä Thermal off-nominal roll angles ä Avoidance angles (Sun, Moon, Earth) ä Solar array incidence angles ä Solar array shadowing table ä Anti-Sun avoidance / roll angles v 10 degree LAU means ä Targets <60 degrees from sun will not be observable ä An anti-sun avoidance zone of ~8 degrees radius develops

8. 84/15/2004 The TGS All-sky Study v Assess the availability of targets across the entire sky under the FHST driven scheduling restrictions imposed by two gyro mode v Examine how that schedulability is affected by FHST duration requirements and initial error estimates

9. 94/15/2004 All-Sky Study Approach v 5-degree-by-5-degree grid of targets covering 360 degrees in RA and +85 degrees to -85 degrees in DEC v Very schedulable Visit (one 30-minute exposure) v Used updated (reduced) FGS earth avoidance angles v Guide star availability not considered v Used Prototype Long Rang Planning tool (SPIKE) to determine constraint windows v Summed the window durations by target v Vary parameters and rerun

10. 104/15/2004 All-Sky Schedulability: Three-Gyro 50°-180° Usable Sun Angle

11. 114/15/2004 All-Sky Schedulability: Two-Gyro 60°-172° Usable Sun Angle

12. 124/15/2004 All-Sky Schedulability: Two-Gyro 100°-172° Usable Sun Angle

13. 134/15/2004 All-Sky Schedulability: Sky Availability

14. 144/15/2004 All-Sky Schedulability: 3-gyro vs. 2-gyro

15. 154/15/2004 All-Sky Schedulability: S ensitivity to LAU

16. 164/15/2004 All-Sky Schedulability: LAU difference distribution

17. 174/15/2004 All-Sky Schedulability: Visit duration sensitivity

18. 184/15/2004 All-Sky Schedulability: Visit difference distribution

19. 194/15/2004 All-Sky Schedulability: Activity duration sensitivity

20. 204/15/2004 All-Sky Schedulability: Onboard Attitude Determination difference

21. 214/15/2004 Target Availability

22. 224/15/2004 Scheduling under Two Gyro v FHST / FGS overlapping visibility requirement creates the most notable impact v 60 – 172 degrees usable sun angle v Maximum off-nominal roll is 22 degrees v Visit duration will likely be ~30 minutes v On average an individual target is only observable ~120 days per year ä Low-dec targets become observable after the sun passes them ä Hi-dec targets have periodic availability tied to orbital precession v Can absorb small changes to the two gyro activities without drastically affecting schedulability

23. 234/15/2004 All-Sky Schedulability: OAD