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Orbit evolution, next steps

Orbit evolution, next steps. Tanja Zegers May 26st 2009. Historical overview. 11 Nov. 2007. 6 May 2004. OCM by increase of semi-major axis. Direct effect of OCMs is Resonance change Orbit period change eclipse duration On the long term this causes a shift in Solar elevation angle

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Orbit evolution, next steps

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  1. Orbit evolution, next steps Tanja Zegers May 26st 2009

  2. Historical overview 11 Nov. 2007 6 May 2004 • OCM by increase of semi-major axis. • Direct effect of OCMs is • Resonance change • Orbit period change • eclipse duration • On the long term this causes a shift in • Solar elevation angle • Latitude drift of pericenter • altitude of pericenter 11:3 25:7 18:5 11 Jan. 2009 2010 2004

  3. What has changed since January 2009 ? • Orbit files for analysis were delivered by FD, products (SPICE, MAPPS, DQC) available on ftp://ssols01.esac.esa.int/pub/data/ • (delayed by HP workload FD) • MEX extension perspective • 1. Science mission: ext. to end 2009, requested to end 2012 • => Maximize science output before 2012 • 2. Support and relay to ExoMars: launch 2016, operations 2017 • => Maximize durability of MEX to reach 2017/18

  4. Study cases, starting from current 25/7 orbit • In all cases Orbit Change 1st Jan. 1010 • Orbit and event files not fully validated by FD (time) • Orbit and general pattern (eclipses etc.) is fully representative, but details are not: • Ground track • Phobos • Ground track propagation was always to the east. • 7/2 has the cheaper ‘west’ version

  5. 25/7 continued to 2019 • 2012 – 2015 no SEA> 5 deg • After 2016 slightly higher SEA

  6. 5 Cases with increasing semi-major axis (max. 7/2E) EXM • SEA change in the period up to 2012: • < 10º • SEA change in period up to 2016: • 15-20º

  7. Pericenter altitude evolution • Apparently correlated to semi-major axis: • Lowest altitude in 25/7, highest altitude in 7/2E

  8. When OCM ? • Earliest Feb 2010 (after long eclipses) • MTP planning mid November 2009 • Orbit file generation 2 months • Decision on OCM mid September ExoMars LS mtp70 mtp71 mtp72 1 Feb. 2010 9 Oct ‘09 6 Dec ‘09 13 Aug. ‘09

  9. Analysis to be done in next months Fuel left Fuel used routinely (now 0.24 kg/yr) Eclipses, battery life ORBIT Change, resonance Solar elevation angle Surface coverage (EXM) Phobos ESOC Pericenter altitude PI-teams Occultations Seasonal/time of day Subsurface

  10. Schedule for next steps • Power analysis – next presentation • Science opportunity analysis • HRSC/OMEGA: effect on (global) imaging of SEA/lat and resonance/swath • MARSIS: effect on subsurface • Teams/MEXSGS: opportunities for atmospheric science, RSI (occultations), RSI gravity • Phobos opportunity analysis • FD – frequency of potential opportunities and cost of optimization • Fuel use in different cases (gravity anomaly effect) – FD • Decisions on MEX use as EXM support – TBD • Early September: Orbit working group meeting if needed to prepare for decision on orbit in mid-September (SOWG TBD)

  11. Fuel • Fuel • Needed for deltaV – 1 m/s = 0.125 kg fuel • Needed for orbit maintenance • 0.25 kg fuel per year for 18/5, higher for lower order resonance • Safe Modes (~ 0.25 per year) Propellant = fuel + oxidizer, oxidizer is over abundant on MEX, Fuel counts May 2009: 9 kg fuel left (worst cumulative case 0.9 kg left) If 4.5 kg fuel left => 9 years of operations (including Safe Mode, without OCM) Orbit change starting from 25/7

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