Using the MultiMission Flight Dynamics Center CLEO for deorbiting SPOT1

1
Using the Multi-Mission Flight Dynamics Center
CLEO for de-orbiting SPOT-1

• Corinne SALCEDO
• Space flight dynamics department
• CNES, French Space Agency

2
I - Limitation of the SPOT-1 ground segmentII -
SCAO modes and TC generationIII - The flight
dynamics tools CLEO IV - Chronology of the
operations and main results
3
Limitation of the SPOT-1 ground segmentSchedule
of the operations
4
Main problems encountered
The SPOT-1 ground segment was not designed for
such operations analytic orbit determination
model limited to the SPOTs circular
orbit incapacity of calculating the de-orbiting
maneuvers incapacity of calculating a
post-maneuver ephemeris then impossibility to
predict the conflicts with the others
satellites impossibility to predict the collision
risk. impossibility to calculate the pointing for
the ground station impossibility to calculate the
orbital event, visibilities incapacity of
generating the telecommand of the de-orbiting
maneuver for the satellite.
5
Relative positioning of the SPOTs satellites
During the de-orbitation, SPOT-1 will pass under
the other SPOTs satellites generating CONFLICTS I
NTERFERENCES

6
Scenario

• Hydrazine mass remaining for the de-orbiting
  maneuvers 53 to 60 kg.
• Hydrazine used to lower the perigee at the
  minimal altitude possible
• Single burns of 1000s (5 kg of hydrazine) at the
  apogee
• To secure the operations one burn per day, on
  the ascending orbit on the night side (in
  visibility of AUS / KRN)
• Two maneuvers (Hohmann transfer) will be achieved
  at the beginning to put the satellite in a
  circular orbit lower than the nominal orbit in
  order to avoid any collision risk with the other
  satellites of the SPOT family.
• ?a -15 km and ?ey -0.001144 km
• Lowering the orbit will accelerate SPOT1. The
  SPOT2 satellite is located 111 ahead SPOT1. So
  SPOT1 will pass under SPOT2 seven days after the
  first manuvre and generate some interference
  with SPOT 2.

7
Apogee evolution rotation of 3/days
Eccentricity
Rotation of -3/j of the apogee First
maneuver around Latitude 24 and final maneuvers
around 0 Duration of the maneuver 1000s
spread of 60 in orbital position
Argument of Perigee
8
SCAO modes and TC generation
9
The SPOT-1 AOCS Pointing modes of the satellite

• Nominal Pointing modes
• De-orbiting Pointing modes (simplified to avoid
  survival mode)

MPF Fine pointing stabilization with momentum
wheels
MAF2 stable mode stabilization with thrusters
MAF1 acquisition of the yaw pointing
MAG rough pointing mode
MCO mode used for orbit control
MAF1 acquisition of the yaw pointing
MAF2 stable mode stabilization with thrusters
MAG rough pointing mode
MCO mode used for orbit control
?Adaptation of the Telecommand generator to
create the TC of the de-orbiting transition modes
10
Generation of the TC maneuver sequence
MCO
MAF2
MPF
MAG-MAF1-MAF2 (auto)
poussée
apogée
10 s
Order for transition MPF/MCO
60 s
Order for transition MAF2/MPF
Order for withdrawal in MAG
Orders for the beginning and the end of thrust
Order for Gyros Preheating
Order for Thrusters preheating
200 s
10 s
1000s
5 s
Modifications Delay for preheating thrusters
and Gyros has been reduced.
11
Constraint Terrestrial sensor mask/ Transitions
MPF/MCO
12
Development of a specific tool for generating the
TC

• The principle was to patch the values on a TC s
   skeleton  generated by the SPOT-1 ground
  segment.
• TC for changing the pointing mode, for
  programming the maneuver, thrusters preheating,
  propulsion, gyros preheating and TC for sensors
  mask.
• A specific tool has been developed to patch
  automatically the TC profile. The tool has been
  integrated into the ground segment.
• The tool takes the output of the flight dynamics
  software and generate automatically the TC
  profile while verifying the sun constraints
  limitation of human operations and limitation of
  risks.

13
The flight dynamics tools CLEO
14
What is CLEO ?
 To answer to the increasing number of new LEO
missions, CNES Flight Dynamics division (MS) has
decided to develop a multi-mission workshop for
building LEO FDC 
Software Components for
Low
Earth
Orbit satellites
15
CNESs LEO satellite missions
16
CLEO -Therapy
MS Division components
Operational SPOT-HELIOS2nd generation space
flight dynamics software OMGS
CNESs Flight dynamics libraries MSLIB
Development features
CNESs Framework components PIMS(GENESIS)(MADONA
)(XTRACE)(DIAMS)
17
Activation modes vs operational activities
BATCH mode
MMImode
18
SFDCS Main Functions
Main orbital and attitude functions from a LEO
Flight Dynamics Center are IFEX Orbit
Determination Maneuver Determination Time
Determination Guidance law Determination Chronolo
gy of Events Antenna Pointing Data
19
Other Functions
20
MMI mode
21
Visualizations of the results
22
Chronology of the operations and main results
23
Chronology
24
End of maneuver 21h03mn32 TU
Beginning of maneuver 20h23mn32 TU
25
Orbit targeted the 28/11/03 21h30 TU Last
maneuver
Orbit achieved Perigee targeted 570.4
km reached 580 km Apogee targeted 804.6
km reached 801 km Inclination -0.0006
26
Graphical output Historic of pressure, Temp.,
Hydrazine Mass (Pmoy)
27
Reentry duration
Perigee Apogee
Reentry of the satellite ensured in less than 25
years Reentry estimated in 18.5 years
28
CONCLUSIONS

• The main problem was the difficulties to estimate
  the hydrazin left in the satellite, the
  de-orbiting operation had a total consumption of
  54 kg against the 67 kg expected.
• Apogee has been lowered to 801 km and the perigee
  to 580 km to ensure the reentry of the satellite
  within 25 years.
• The quick reactivity of all the de-orbiting team
  allowed the success of that operation. Satellite
  and ground segment adaptations that have been
  made for the de-orbiting operations gave precious
  insights for the design of the future missions