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Orbit evolution, next step

Orbit evolution, next step. Tanja Zegers January 14 th 2009. Historic overview. 6 May 2004. 11 Nov. 2007. 11 Jan. 2009. 11/3. 25/7. 18/5. Historic overview. Direct effect of OCMs is Resonance change Orbit period change eclipse duration On the long term this causes a shift in

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Orbit evolution, next step

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  1. Orbit evolution, next step Tanja Zegers January 14th 2009

  2. Historic overview 6 May 2004 11 Nov. 2007 11 Jan. 2009 11/3 25/7 18/5

  3. Historic overview • Direct effect of OCMs is • Resonance change • Orbit period change • eclipse duration • On the long term this causes a shift in • SEA • Latitude drift of pericenter 11:3 25:7 18:5

  4. Current orbit and future Change • 25/7 – decided June SWT 2008, OCM 12/19 January 2009 • At June 08 SWT: A further orbit change will be needed to keep conditions acceptable for HRSC to continue the global coverage • A limited number (3) of cases will be studied in early 2009 • - ESOC: power, Phobos, general FD effects • PI-teams: science opportunities • MEXSGS: long term science operations/opportunities • A decision on the orbit strategy will be taken at the mid 2009 SWT, to be implemented at a TBD time.

  5. Today: define orbit cases to be studied • Resonant • Very high resonance • Non-resonant 2.8 m/s = 0.3 kg fuel Increase of semi-major axis ~7 m/s = 0.76 kg fuel • Effectively two decision to make: • 1. Semi-major axis, i.e how much fuel can we use, and what resonance is required ? • 2. When should the OCM be done ? Early 2010, or later ?

  6. Effect of period increase • From discussion in 2006, different cases with all OCM early 2007, starting from 11:3

  7. Effect of timing of OCM • From 25/7 to 7/2 • With different OCM timing • 2010 • 2011 • 2012

  8. Orbit change, to take into account I • Day/night balance • At particular latitude • N. Pole at night (MARSIS) • Mid southern latitudes in day time (HRSC,OMEGA) • Coverage pattern • Resonance => construction sites (mainly for HRSC) • 25/7 on high side: 7 days before next swath • 7/2 on low side: too few construction sites • Very high or non-resonant orbits 46/13 and higher

  9. Orbit change, to take into account II • Seasonal/Latitude coverage • PFS seasonal/time of day gaps • SPICAM seasonal/time of day gaps • RSI occultation gap southern latitudes • Landing sites • ExoMars – 5º South to 45º North, MEX August-October 2009 • MSL ? • Phobos Grunt ?

  10. Orbit change, to take into account III • Phobos • The orbit choice (resonance) affects the possibilities for Phobos optimization • Repeated close fly-by’s are achieved by tuning the orbit such that a MEX/Phobos resonance results • Very difficult to predict before orbit generation, can be checked once orbit file exists • Not driver for orbit choice

  11. Orbit change, to take into account IV • Fuel • Needed for deltaV – 1 m/s = 0.125 kg fuel • Needed for orbit maintenance: higher for lower order resonance – currently (18/5) 0.24 kg fuel per year Propellant = fuel + oxidizer, oxidizer is over abundant on MEX, Fuel counts June 2008: 9.3 kg fuel left, worst case 1.16 kg left (In discussion at SWT: realistic error 4 kg, worst case 8 kg) If 4 kg fuel left => 16 years of operations (without OCM) Orbit change starting from 18/5

  12. Proposal for study cases • Case 1 (done) • 7/2 (OCM 2010, 2011, 2012) • ~ 0.76 kg fuel (-3 years of operations) • Case 2 • High order resonance, ratio ~3.51 • ~ 0.65 kg fuel (-2.5 years of operations) • Case 3 • 45/13 • ~ 1.2 kg fuel (- 5 years of operations) • When do the OCMs ?

  13. OCM timing • Not during long (>30’) eclipses • Not before MTP 71– planning starts 27 July (7432) • Preferably not during night-side (MARSIS affected) • At MTP boundary • => • OCMs in MTP71 (start 18/19 October 2009) • Or • Late February 2010 ExoMars LS mtp70 mtp71 mtp72 1 Feb. 2010 9 Oct ‘09 6 Dec ‘09 13 Aug. ‘09

  14. Proposal for study cases • Case 1 (done) • 7/2 (OCM 2010, 2011, 2012) • ~ 0.76 kg fuel (-3 years of operations) • Case 2 • High order resonance, ratio ~3.51 • ~ 0.65 kg fuel (-2.5 years of operations) • Case 3 • 45/13 • ~ 1.2 kg fuel (- 5 years of operations) • When do the OCMs ?

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