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Personnel at Large

Two-Gyro All-sky Scheduling Study TIPS April 15, 2004 http://www.stsci.edu/org/ess/projects/two_gyro_science. Personnel at Large. Special Projects Branch (SPB) Merle Reinhart George Chapman Operations Planning Branch (OPB) Alison Vick Ian Jordan Planning Systems Development Branch (PSDB)

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Personnel at Large

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  1. Two-Gyro All-skyScheduling StudyTIPSApril 15, 2004http://www.stsci.edu/org/ess/projects/two_gyro_science

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

  3. Outline • Two Gyro background • Two Gyro Modes • Why they impact scheduling • All-sky scheduling study • Plots galore • Targets-by-week The Movie

  4. TGS Modes • Three operational modes • 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 • 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 • FGS and two gyros (F2G): Requires FGS visibility to use FGS data and gyros to control rates and attitude to allow for science • What does it mean? • Elaborate process to get on guide stars after a slew • Less schedulability (big surprise)

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

  6. TGS Scheduling Scenario

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

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

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

  10. All-Sky Schedulability:Three-Gyro 50°-180° Usable Sun Angle

  11. All-Sky Schedulability:Two-Gyro 60°-172° Usable Sun Angle

  12. All-Sky Schedulability:Two-Gyro 100°-172° Usable Sun Angle

  13. All-Sky Schedulability:Sky Availability

  14. All-Sky Schedulability:3-gyro vs. 2-gyro

  15. All-Sky Schedulability:Sensitivity to LAU

  16. All-Sky Schedulability:LAU difference distribution

  17. All-Sky Schedulability:Visit duration sensitivity

  18. All-Sky Schedulability:Visit difference distribution

  19. All-Sky Schedulability:Activity duration sensitivity

  20. All-Sky Schedulability:Onboard Attitude Determination difference

  21. Target Availability

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

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