1. Flight Operations for GOCE, ESA’s Gravity Mission
C. Steiger, R. Floberghagen, M. Fehringer, J. Piñeiro, P.P. Emanuelli

2. Complexity and Specifics of GOCE
Complexity of GOCE:
2487 telecommands
42000 telemetry parameters
991 procedures written by ESOC to operate the S/C
What sets GOCE flight operations apart:
Low orbit => short ground station contact times
Atmospheric drag => orbit prediction intricate, S/C heavily affected by (changes in) the environment
Complex S/C with no clear distinction between ‘platform’ and ‘payload’ => high level of expertise required in case of anomalies
Routine science operations consist of letting the S/C fly in drag-free mode (no complex payload operations campaigns)

3. GOCE Flight Operations at ESOC
7 to 8 contacts per day
Low altitude => short contacts
Pass operations automated
Orbit prediction based on SSTI data
Strict requirements on complete-ness of science data

4. Commissioning Overview
17/03/2009: launch from Plesetsk/RU on ROCKOT
17/03 to 20/03: launch and early orbit phase
20/03 to 27/03: AOCS unit calibrations
30/03 to 03/04: checkout of ion propulsion assembly
03/04 to 07/04: gradiometer commissioning
May/June: checkout of drag-free modes
23/06: Resumption of decay
13/09: stop of decay at km

5. Telecommands Sent in Commissioning
100000
90000
80000
70000
60000
50000
40000
30000
About 600 TCs / day sent in commissioning (30% routine activities, 70% special ops)
20000
10000

6. Orbit Prediction during Orbit Decay
S/C attitude error around Yaw [deg]
Orbit decay rate [m/day]
Performance of attitude control impacts orbit when not drag-free
±100 m/day => variation of ±2 sec per day in contact predictions

7. Routine Operations in Drag-free Mode
Mean altitude [km]
Average IPA thrust level [mN]
Feb-2010: drag-free mode interruption, decay 500m/day
Oct-2009: drag-free mode interruption, decay 250m/day
05-Apr-2010: strong geomagnetic storm
Drag-free mode is working well
DFM interruption requires rapid intervention from ground (e.g. update of orbit prediction to ensure correct pointing of antennas)

8. Conclusions
Main challenges for flight operations were due to the unique features of GOCE:
Low orbit
Operations in a drag environment
High S/C complexity (no distinction between platform and payload)
Intense commissioning phase successfully completed, GOCE is in routine since October 2009
ESOC’s flight operations approach for GOCE is working well
ESOC is looking forward to supporting a possible mission extension

9. Thank you!
Contact point:
Questions?