Diapositive 1

1
Content

• Geostationary end-of-life disposal

• CNES experience with TDF2 satellite
• Reorbitation
• Passivation orbit impact
• Possible causes

• Passivation scenarii for Astrium Eurostar 2000
• Basic simulations
• Complete scenarii

• Conclusion

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Geostationary end-of-life disposal
Inter Agency Space Debris Coordination Committee
recommends

• Spacecrafts must be removed from geo region
• Protected region geo ring relocation area
  200 km
• Minimum recommended perigee altitude increase
  300 km

• Spacecrafts must be passivated
• Pressure must be lowered as much as possible in
  spacecraft elements
• Propellant tanks are mainly concerned

3


CNES experience with TDF 2 satellite

• TDF2 satellite

• Telecom geostationary satellite
• Launched in 1990

• Station-keeping performed by CNES
• End-of-life operations in 1999, (from May 19th
  to June 1st)

• Helium pressurized bi-propellant (MON-1 MMH), 4
  tanks
• 14 thrusters (10 N) for attitude control and
  station-keeping

4
TDF2 reorbitation

• First reorbitation step
• Target circular orbit with Da 300 km
• 4 East manoeuvres every 12 hours
• With maximum uncertainty, tanks might be empty
• Apogee geo 291 km Perigee geo 256 km

• Second reorbitation step
• Aim continue East manoeuvre until gas is
  detected raise perigee
• 6 near-apogee East manoeuvres (tanks swapped each
  time)
• Last manoeuvre manually stopped on attitude
  criteria
• Helium bubbles have appeared in propulsion system
• Apogee geo 648 km Perigee geo 298 km

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TDF2 passivation orbit impact

• Passivation operations
• Transition to Sun Acquisition Mode (better
  attitude robustness)
• Manual firing phases with opposite thrusters 5A
  and 5B
• 1) Propellant run-out step cold thrusts for 1
  hour
• ? More and more bubbles, good attitude control
• 2) Tanks depressurization step steady-state
  thrusts (9 h over 2 days)
• ? Final pressure lt 2 bar
• Apogee geo 671 km Perigee geo 271 km

• Orbit slightly affected
• No impact on North-South parameters (i, W)
• No impact on semi-major axis
• Significant eccentricity increase 4. 10-3 ? 4.7
  10-3
• ? greater difference between apogee and perigee
  altitude
• ? 27 km perigee altitude decrease

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TDF2 possible causes
A simulation tool was used to study several
possible causes

• Other thrusters activity
• Transition to Sun Acquisition Mode lt 50 s
  on-time ? low impact
• Attitude control (mainly during firing phases)
  low impact

• Thrust dissymetry
• During propellant run-out 1 ? low impact ( 2
  km)
• During depressurization 0.02 N ?significant
  impact (12 km)
• Partial thruster freezing ? significant impact
• ? Very low thrust levels could explain the orbit
  modification

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Astrium Eurostar 2000 platform

• Eurostar 2000 propulsion subsystem
• Same bi-propellant
• as TDF 2 (4 tanks)
• 12 thrusters (10 N)
• for station-keeping

• Passivation hypotheses
• X-spinned sun-pointed
• -X wall towards sun
• thruster 4 impulses
• significant force expected
• along spin axis

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E2000 basic simulations hypothesis

• Expected radial orbit disturbance in some simple
  cases ?

perigee altitude 300 km (graveyard area), 1
hour cold thrusts

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E2000 impact on perigee altitude
Orbit shape depends on reorbitation manuvres !


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E2000 complete passivation scenarii

• Reorbitation hypotheses
• Target near-circular orbit, altitude geo
  300 km
• Several manoeuvres. Gas bubbles appear during the
  last one
• Apogee geo 300 km Perigee geo 250 km

• Passivation hypotheses
• Spinned sun-pointed attitude acquisition with
  other tanks
• ½ h combustion cold thrusts around 18h (best time
  chosen)
• depressurization steps the next day around 18h

• Following simulations show different possible
  final orbits
• after the same complete sequence of passivation,
• for an identical fuel consumption,
• according to initial orbit after reorbitation

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E2000 complete passivation scenarii
Best case initial apogee at 18h
Final perigee geo 300 km
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E2000 complete passivation scenarii
Middle case initial apogee at 0h
Final perigee geo 265 km
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E2000 complete passivation scenarii
Worst case initial apogee at 6h
Final perigee geo 250 km (unchanged)
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E2000 complete passivation scenarii
Catastrophic case initial apogee at 6h and
passivation thrusts at 6h
Final perigee geo 185 km
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Conclusion

• In 1999, TDF2 was reorbited, and a complete
  passivation was successfully performed without
  losing the satellite control.

• Unfortunately, propellant and gas expelling
  degraded the final orbit.

• Even though main thrusts components cancelled
  each other, very small residual forces proved to
  be able to have significant impact.

• The case of Eurostar 2000 passivation was studied.

• It was shown that initial orbit shape (to be
  managed during reorbitation) and thrust hour
  choice had a significant effect on the orbit.

• Situations to favor or to avoid were identified.

• These results remain valid for any platform with
  sun-pointed attitude and spin axis passivation
  thrusts.