THEMIS MIWG #7 BBQ Roll Rate Study 29 November 2006 Dave Peterson

1. THEMIS MIWG #7BBQ Roll Rate Study29 November 2006Dave Peterson

2. THEMIS BBQ Roll StudyPreliminary DTO (November 2006) • Preliminary (November 2006) DTO shows 6°/sec BBQ roll rate for flight times from 830 to 3300 sec (2470 sec duration) • Analysis results show there is insufficient ACS gas available to maintain 6°/sec BBQ roll rate over this time interval • RIFCA alignment error is the primary error source causing the large gas usage • Current analysis results assume normal distribution for RIFCA alignment error • Standard Delta II gas budget analyses used uniform distribution (more conservative) • Maximum RIFCA alignment error 0.5° (per Error Source DRA) • Based on preliminary DTO (November 2006) • For BBQ roll with pitch/yaw coast guidance • Maximum BBQ roll rate (for zero 3s gas reserve) is approximately 3.3°/sec • July 2006 analysis (for 2760 sec BBQ roll duration) showed maximum BBQ roll rate of about 3.1°/sec for BBQ with coast guidance (for zero 3s gas reserve). • Maximum mean + 3 sigma X-axis drift is approximately 1° during BBQ roll • For BBQ roll without coast guidance • Maximum BBQ roll rate (for zero 3s gas reserve) is approximately 4.7°/sec • July 2006 analysis (for 2760 sec BBQ roll duration) showed maximum BBQ roll rate of about 4.2°/sec for BBQ without coast guidance (for zero 3s gas reserve) • Maximum mean + 3 sigma X-axis drift is approximately 3.8° at this spin rate

3. Preliminary Sequence of Events Used For Analysis

4. THEMIS BBQ Roll StudyPreliminary Gas Budget Summary • Total impulse available: 1490 lb-sec • Mean Impulse used for settling: 529 lb-sec • Mean Impulse available for controls: 961 lb-sec • Mean Impulse used for maneuvers (other than BBQ roll): 476 lb-sec • Mean impulse available during BBQ roll: 485 lb-sec • Mean impulse used for 6°/sec BBQ roll (duration 2470 sec) with coast guidance: 1030 lb-sec • Mean impulse used for 6°/sec BBQ roll (duration 2470 sec) w/o coast guidance: 566 lb-sec

5. THEMIS BBQ Roll StudyAnalysis Tool • Gas budget analysis performed using program SIMRAC • 6DOF Delta II coast control system simulation • Monte Carlo analysis tool (typically run with 1000 cases) • Simulation features • Coast control system RACS and switchline logic and sequencing • Coast guidance logic • Aerodynamic torques • Mass properties – typically mass properties with propellants settled aft are used (conservative for gas budget analysis) • Propellant slosh torque (for BBQ roll analysis) • Monte Carlo variables • RIFCA sensor misalignment • 3s value 0.5°; normal distribution • Standard Delta II analyses assume uniform distribution • Thruster misalignment • 2.0° maximum (3s); normal distribution • Guidance error • Roll (0.39° ± 0.46°), Pitch (1.49° ± 1.49°), Yaw (-1.02° ± 0.94°); normal distribution • Timing for initial RACS interval counter • 5 sec maximum; uniform distribution • Initial body rates and attitude errors • 3s values determined based on switchlines

6. Three-Sigma Reserve at End of Mission vs. BBQ Roll RateThree-Sigma RIFCA Alignment Error = 0.5°(Preliminary THEMIS DTO Sequence)

7. Mean + 3 Sigma Maximum X-Axis Drift vs. BBQ Roll RateThree-Sigma RIFCA Alignment Error = 0.5°(Preliminary THEMIS DTO Sequence)

8. Sample Case Results: Body Rates Unguided BBQ: Guided BBQ:

9. Sample Case Results: Body Attitude Errors Unguided BBQ: Guided BBQ:

10. Sample Case Results: Impulse Usage Unguided BBQ: Guided BBQ:

11. Sample Case Results: X-Axis Drift Unguided BBQ: Guided BBQ:

12. Three-Sigma Reserve at End of Mission vs. BBQ Roll RateThree-Sigma RIFCA Alignment Error = 0.5°(Preliminary THEMIS DTO Sequence)

13. Mean + 3 Sigma Maximum X-Axis Drift vs. BBQ Roll RateThree-Sigma RIFCA Alignment Error = 0.5°(Preliminary THEMIS DTO Sequence)

14. Deep Impact Flight DataBBQ Roll (6.1°/sec, 415 sec Duration) • Deep Impact Flight Data • Deep Impact flew with 6.1°/sec BBQ roll rate (approximately 415 sec duration) • Coverage not complete throughout this portion of flight • Impulse Usage Between SECO-1 and Restart Ignition: 333 lb-sec • Estimated Usage for orientation maneuvers: 80 lb-sec • Estimated Usage to Remove BBQ Roll Rate: 30 lb-sec • Obtained from ITOT data for roll rate change from 6.1°/sec to 0°/sec • Multiply by 4 to get usage to start/stop/start/stop BBQ roll rate • Estimated Usage During BBQ (roll rate changes not included): 133 lb-sec • Usage scaled to 2470 sec duration (roll rate changes not included): 789 lb-sec • Usage scaled to 2470 sec duration with roll rate changes added: 909 lb-sec • Deep Impact gas usage (6.1°/sec BBQ rate) consistent with usage predicted for THEMIS (6.0°/sec BBQ rate) • See plot on following page

15. Impulse Usage vs. BBQ Roll Duration6°/sec BBQ Roll With Coast Guidance, 0.5° Max RIFCA Alignment Error

16. Impulse Usage vs. BBQ Roll Duration3°/sec BBQ Roll, 0.5° Max RIFCA Alignment Error

17. Effect of Moment of Inertia Variations on X-Axis Drift

18. Concluding Remarks • Gas budget analysis shows that there is insufficient ACS gas available to sustain 6°/sec BBQ roll rate for 2470 sec (preliminary November DTO BBQ roll duration). • BBQ roll rate duration expected to increase by 150 to 200 sec for final DTO • Duration will be closer to 2760 sec BBQ roll duration from July 2006 DTO • Recommendation for BBQ roll rate: • 3°/sec BBQ roll rate without pitch/yaw coast guidance