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Mission Design Dr. Sabine Frey University of California - Berkeley

Mission Design Dr. Sabine Frey University of California - Berkeley. Mission Design. Overview Orbit Requirements Orbit Design Mission Orbits Orbit Placement Maneuver Planning Eclipse Duration Conjunction Analysis Delta V Budget, P1 Status and Next Steps. Orbit requirement.

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Mission Design Dr. Sabine Frey University of California - Berkeley

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  1. Mission Design • Dr. Sabine Frey • University of California - Berkeley

  2. Mission Design Overview • Orbit Requirements • Orbit Design • Mission Orbits • Orbit Placement • Maneuver Planning • Eclipse Duration • Conjunction Analysis • Delta V Budget, P1 • Status and Next Steps

  3. Orbit requirement Orbit Requirements to Accomplish Science Objectives • Five probes in 1-, 2-, and 4-day orbits at strategically-selected apogee distances to act as timing monitors and in situ platforms for diagnostic plasma and fields measurements. • Space segment coordinated in space and time with Ground Based Observatories (GBO’s) to form a constellation capable of determining the order of events within a substorm. • Probes are placed in science orbits prior to first tail observation season, and orbital phases are adjusted periodically (period tweaks) to optimize amount and quality of conjunction time. • Inclination of outer probes (P1-2) is restored prior to second-year tail observation season to counteract drift due to orbital perturbations. • Maindrivers for orbitdesign to meet scienceobjectives and mission requirements • Eclipse durations < 180min [pick appropriate RAP and inclination] • Conjunctions with GBO’s [Pick sidereal day period multiples] • Conjunctions with plasma sheet [pick appropriate tail center geotail epoch, RAP and inclination] • Ensure re-entry within 25 years [perform end-of-mission maneuvers] • Maneuvers shall meet delta-V of 566m/s+15% contingency (TBC) • (RAP-Right Ascension of Perigee, fixed for target epoch )

  4. Orbit Design 1 A Compromise Between Shadows and Conjunctions Maximum conjunctions: March 21 Minimum shadows: December 21

  5. Orbit Design 2Selection of Tail Epoch: Shadows Parametric study on shadows for INC=5…15deg relative to center tail elements(here shown for inc=15deg):

  6. Orbit Design 3Selection of Tail Epoch: Conjunctions • Parametric study on conjunctions relative to center tail elements:

  7. Orbit Design 4 Selection of Tail Epoch • From CSR: Targeted center geotail (wedding season) to be Feb-21 +/- 1 week

  8. Orbit Design 5 • Software Tools for Orbit Generation: Since 1998 the THEMIS team has been using the following tools for maneuver planning, science optimization, DV analysis and RCS sizing: • Excel spreadsheet (UCB/Swales) • Perigee/apogee/inclination changes • RAAN, APR, INC drifts due to J2 terms • RAP drift for season selection • Raise, maintenance and replacement strategy • DV margin, mass margin • GTDS (UCB/GSFC) • Workhorse of spreadsheet result validation • Includes all appropriate perturbation terms (lunar, solar, drag, etc) • Shadow and conjunction parametric studies & forward analyses • Geometric and gravity effect assessment, and realistic RCS performance assessment • GMAN (UCB/GSFC) • Realistic RCS, ACS validation at the thruster pulse level (includes reors) • Final validation of mass and deltaV estimates • Leads to Mission Operations command generation

  9. Mission Orbits 1 • Results from orbit design study • Center geotail epoch, RAP, Inclination : • February 21 (WD), 330 deg, 7 deg • Geotail observation season: December to April • (RAP-Right Ascension of Perigee, fixed for target epoch )

  10. Mission Orbits 2 Ground Based Observatory in North America CCA

  11. Orbit Placement 1 • Orbit Placement Entire Mission: • Launch, Early Orbit, and Initial Science Orbit • First Year Tail In-Season Maneuvers • Flank and Dayside • Second Year Tail Alignment, In-Season Maneuvers • Flank and Dayside • Third Year- Extended Mission conjunction w/ MMS • End of Mission • Orbit Placement Through First Tail Season: • P3 Reference placement first year tail season • Select parking orbit to catch up with CCA • Crude lock over CCA • Fine tune lock over CCA before deployment • P4 Same as P3 • delta mean anomaly at apogee:approximate 10 deg • Maneuvers at least one orbit apart Catch Up With CCA By Various Parking Orbits Perigee up Apogee chg 02:00

  12. Orbit Placement 2 • Orbit Placement Through First tail season • P 1,2 • Start with stable, low inclination orbit. • Late apogee raise to reduce • differential precession • Final alignment with P3, P4 before • EFI deploymentbefore first in-season maneuver • P 5 • Early raise to final perigee • Lower to final period to recur • once per 4 days

  13. Maneuver Planning Maneuver Plan: P1,2 Early orbits and P 3,4 Initial Science Orbits LD+5 Orbits Target perigee, lower Inclination P1,P2 M0b LD+10 Orbits Target Apogee P3 M01 LD+10+n Orbits Target Apogee P4 M01 LD+15 Orbits Raise Perigee, Lower Inclination P3 M02 LD+ 15+n Orbits Raise Perigee, Lower Inclination P4 M02 (LD-Launch day, n-days) ( WD-’Wedding Day’ center geotail epoch) Selected Orbits P1,P3 WD+60d P1, P2 Relative to WD First Year Tail Season WD+24d WD-120-4 d 1st Apogee Raise M1a WD-120 d 1st Perigee Raise M2a WD- 90-4 d 2nd Perigee Raise, Incl. Raise M2b WD- 90 d 2nd Apogee Raise M1b WD- 60 d 1st Period Tweak M3 WD- 24 d 2nd Period Tweak M4 WD +24 d 3rd Period Tweak M5 WD+ 60 Drift into Dayside WD-24d WD-60d WD-90d

  14. Eclipse Duration 1 • Shadow Analysis • Earth and Lunar shadows • Two Methods compared • Shadow entry/exit Condition = %50 of Full Sunlight, extended object, cone shape, Geoid,atmosphere • Determining partial and total eclipses, extended objects, cone shape • Time Frame: 2007-Jun-02 P1, P2 • 2007-Apr-24 P3, P4, P5

  15. Eclipse Duration 2

  16. Conjunction Analysis 1 • Satisfaction of the conjunction requirement is established via orbit simulation using GTDS and a neutral sheet model. A Conjunction satisfies the following criteria: - Four probes within 2 Re in Ygsm. - Inner probes within 2 Re of model neutral sheet. - Outer probes within 5 Re of model neutral sheet. • Conjunction Example: GSM Criteria dY<2Re Orbits in GEI Coordinates:x,y Wd +24 days P1 P2 P3

  17. Conjunction Analysis 2 Conjunction Estimation Example: GSM x,y plane Wd-60 to Wd -24 Wd+24 to Wd -24 dawnside duskside Wd-24 to Wd +24 midnight

  18. Re-Entry • P1,2 have periods adjusted to bring them into Lunar resonance. • P3,4,5 have perigees lowered to initial injection perigee to increase drag and decrease lifetime. • PCA orbit (injection orbit) has lifetime less than 10 years. • Delta-V budget (P-5 example)

  19. Delta V Budget: Example of P1 • Assumptions for Maneuver Calculator (MC): • Latest (September 2003) bus and instrument predicted mass • Arde tank size (procurement commenced) • 5N thrusters (RCS procurement commenced) P1 total first geotail delta V= 0.456 km/s MC estimate of delta V= 0.411 km/s Projected mission total delta V= 0.611 km/s MC mission total delta V= 0.566 km/s

  20. Mission Design Flow

  21. Status and Future Work • Status • Simulation of Orbit Placements for P1, P2, P3, P4, P5 through first tail season in high precision mode to accomplish • Shadows < 180min • Conjunctions with Canada • Feasible maneuver schedule • Verify delta V Budget for perturbations included • Future Work • Improve conjunctions with plasma sheet - in progress • Finish Dayside and second year mission • Verify and implement maneuver scenarios with GMAN - in progress • Maneuver performance verification and if necessary correction • Study effects by change of launch day - in progress • Replacement scenarios • delta V Budget with attitude maneuver • Re-iterate according to Mission Design Flow Chart to improve flexibility in • parameter selection, to optimize ground contact and maneuver schedule • –in progress

  22. Back Up

  23. Orbit Placement back up • Geographic Longitude of P3 at Apogee Parking - Intermediate - Science Orbits

  24. Maneuver Planning back up • Schedule P2 Through 1st Tail Season • ID UT dV [km/s] n1 n2 • ; M1a_P2 2006-Oct-22 06:41:34.31 0.08235 006 006 • ; M2a_P2 2006-Oct-24 07:04:34.31 0.00426 060 054 • ; M0b_P2 2006-Aug-27 17:09:34.31 0.07773 061 001 • ; M2b_P2 2006-Nov-18 20:52:04.31 0.08959 080 019 • ; M1b_P2 2006-Nov-23 13:57:34.31 0.08639 083 003 • ; M03_P2 2006-Dec-20 23:29:34.31 0.00156 097 014 • ; M04_P2 2007-Jan-29 09:55:34.31 0.00009 116 020 • ; M05_P2 2007-Mar-15 18:08:04.31 0.00191 138 023 • ; P2 total dV= 0.34388931 • ; MC estimate of dV= 0.34300000 • ; Projected mission total dV= 0.43588932 • ; MC mission total dV= 0.435000 (n2- orbits after last maneuver) • (n1-orbits after LD)

  25. Maneuver Summary back up P1,2 Early orbits and P 3,4 Initial Science Orbits MID UT dV dD Purpose ; M00_PP 2006-Aug-21 14:14:34.31 0.00000 0.500 Release ; M0b_P1 2006-Aug-26 16:40:34.31 0.03009 5.101 INCLINATION dn, PERIGEE chg ; M0b_P2 2006-Aug-27 17:09:34.31 0.07773 1.020 INCLINATION dn, PERIGEE chg ; M01_P3 2006-Sep-01 07:20:04.31 0.01079 4.591 APOGEE chg ; M01_P4 2006-Sep-02 07:49:04.31 0.01078 1.020 APOGEE chg ; M01_P5 2006-Sep-03 08:18:04.31 0.00473 1.020 APOGEE chg ; M02_P5 2006-Sep-05 22:27:04.31 0.08590 2.590 PERIGEE up, INCLINATION dn ; M02_P3 2006-Sep-06 16:54:04.31 0.03600 0.769 PERIGEE up, INCLINATION dn ; M02_P4 2006-Sep-07 18:02:04.31 0.03633 1.047 PERIGEE up, INCLINATION dn ; M1a_P1 2006-Oct-21 06:24:34.31 0.08156 43.516 APOGEE up ; M1a_P2 2006-Oct-22 06:41:34.31 0.08235 1.012 APOGEE up ; M2a_P2 2006-Oct-24 07:04:34.31 0.00426 2.016 PERIGEE up ; M2a_P1 2006-Oct-24 15:02:34.31 0.00386 0.332 PERIGEE up

  26. Maneuver Planning backup • Schedule P3,P4 Through 1st Tail Season • ID dV [km/s] n1 n2 • ; M01_P3 2006-Sep-01 07:20:04.31 0.01079 011 011 • ; M02_P3 2006-Sep-06 16:54:04.31 0.03600 016 005 • ; P3 total dV= 0.046791709 • ; MC estimate of dV= 0.051000000 • ; Projected mission total dV= 0.51979171 • ; MC mission total dV= 0.52400000 • ; M01_P4 2006-Sep-02 07:49:04.31 0.01078 012 012 • ; M02_P4 2006-Sep-07 18:02:04.31 0.03633 017 005 • ; P4 total dV= 0.047109795 • ; MC estimate of dV= 0.051000000 • ; Projected mission total dV= 0.52010980 • ; MC mission total dV= 0.52400000

  27. Maneuver Planning • Schedule P5 Through 1st Tail Season • ID UT dV [km/s] n1 n2 • ; M01_P5 2006-Sep-03 08:18:04.31 0.00473 013 013 • ; M02_P5 2006-Sep-05 22:27:04.31 0.08590 015 015 • ; M03_P5 2006-Dec-22 21:43:04.31 0.10730 118 118 • ; P5 total dV= 0.19793251 • ; MC estimate of dV= 0.19500000 • ; Projected mission total dV= 0.55993251 • ; MC mission total dV= 0.55700000 • (n2- orbits after last maneuver) • (n1-orbits after LD)

  28. Maneuver Planning back up P1, P2 Maneuver Schedule in intervals relative to WD First Year Tail Season MID UT dV dD Purpose ; M2b_P2 2006-Nov-18 20:52:04.31 0.08959 25.243 PERIGEE up, INCLINATION up ; M2b_P1 2006-Nov-19 04:42:04.31 0.13107 0.326 PERIGEE up, INCLINATION up ; M1b_P2 2006-Nov-23 13:57:34.31 0.08639 4.386 APOGEE up ; M1b_P1 2006-Nov-24 01:16:34.31 0.20310 0.472 APOGEE up ; M03_P2 2006-Dec-20 23:29:34.31 0.00156 26.926 APOGEE chg ; M03_P1 2006-Dec-22 20:17:34.31 0.00363 1.867 APOGEE chg ; M03_P5 2006-Dec-22 21:43:04.31 0.10730 0.059 Apogee chg ; M04_P2 2007-Jan-29 09:55:34.31 0.00009 37.509 APOGEE chg ; M04_P1 2007-Jan-30 13:07:34.31 0.00154 1.133 APOGEE chg ; M05_P2 2007-Mar-15 18:08:04.31 0.00191 44.209 APOGEE chg ; M05_P1 2007-Mar-17 18:47:04.31 0.00104 2.027 APOGEE chg

  29. P2 Eclipse Duration back up

  30. P3 Eclipse Duration back up

  31. P4 Eclipse Duration back up

  32. P5 Eclipse Duration backup

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