Flight Operations for GOCE, ESA’s Gravity Mission

C. Steiger, R. Floberghagen, M. Fehringer, J. Piñeiro, P.P. Emanuelli

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)

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

Commissioning Overview

30/03 to 03/04: checkout of ion propulsion assembly

May/June: checkout of drag-free modes

17/03/2009: launch from Plesetsk/RU on ROCKOT17/03 to 20/03: launch and early orbit phase

13/09: stop of decay at 259.6 km

23/06: Resumption of decay

20/03 to 27/03: AOCS unit calibrations

03/04 to 07/04: gradiometer commissioning

Telecommands Sent in Commissioning

10000

30000

50000

40000

20000

60000

70000

80000

90000

100000

About 600 TCs / day sent in commissioning (30% routine activities, 70% special ops)

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

Routine Operations in Drag-free Mode

05-Apr-2010: strong geomagnetic storm

Oct-2009: drag-free mode interruption, decay 250m/day

Feb-2010: drag-free mode interruption, decay 500m/day

Mean altitude [km] Average IPA thrust level [mN]

• 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)

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

Thank you!

• Contact point: Christoph.Steiger@esa.int• Questions?