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Status GRACE Mission Operations Joseph G. Beerer, JPL Operations Mission Manager

Status GRACE Mission Operations Joseph G. Beerer, JPL Operations Mission Manager Franz-Heinrich Massmann, GFZ Deputy Operations Mission Manager. Project Status. The design lifetime (5 years) has been reached in March 2007 We are now in the bonus part of the mission

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Status GRACE Mission Operations Joseph G. Beerer, JPL Operations Mission Manager

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  1. Status GRACE Mission Operations Joseph G. Beerer, JPL Operations Mission Manager Franz-Heinrich Massmann, GFZ Deputy Operations Mission Manager

  2. Project Status • The design lifetime (5 years) has been reached in March 2007 • We are now in the bonus part of the mission • NASA & DLR/GFZ have approved funding through 2009 • Provisional approval through FY11 in NASA Senior Review 2007 • Satellites and ground segment are performing well • Payload performance continues meeting mission expectations • Nearly 100% of dump data has been collected and analyzed • Data dumps almost every orbit at Ny-Aalesund station (since May 2006) • Batteries beginning to show signs of age - has caused some data loss

  3. - Semi-major axis: 6840 km, 470 km above 6370 km - Altitude decrease: ~ 5 m/day - Inter-satellite Distance: ~ 195 km (170 - 270 km) - Orbit Manoeuvres: 04-Jan-07, 26-Sep-07 - 2038 days in orbit - 31170 revolutions completed Orbit Status 15-Oct-2007 GR1 leader GR2 leader

  4. Mission Lifetime Predictions Remaining Resources: • Battery Cycles: > 12 years (?) • Thruster actuations: > 5 years • Cold gas: > 10 years • Orbit decay: > 6 years - End of Life (pred.): GR-1 2019-2012-2012 (gas-thrust-decay) GR-2 2023-2016-2012

  5. Satellite Status No noticeable degradation due to radiation in 5.5 years on orbit. Fault tolerance status: • GR-1 unchanged since 2002 • Relies on 3 backup units: Microwave, Ultra-stable Oscillator, Instrument Control Unit of the Accelerometer • GR-2 apparent failure of IPU in May 2007 • Relies on backup unit Battery status: • GR-1: cell short (momentary) observed Nov 2006, Jun 2007 • GR-2: cell failure Aug 2007 Expected life of the system exceeds 10 years in every category: battery life, altitude, propellant, cumulative thruster actuations, solar panel power, and component life

  6. Satellite Events since Last GSTM Battery-related: Low voltage events (DSHL*) • GR-1 17-Jan and 12/13-Jun • GR-2 23-Jul and 15-Aug Upload of new heater table with lower temperature settings to reduce power load in response to battery cell failure on GR-2 • GR-2 4-Aug • GR-1 26-Sep 90 deg. yaw turn to prevent cell short (in full-sun orbits) • GR-1 10-Apr and 26-Sep • GR-2 not required * Disable Supplementary Heater Lines

  7. Satellite Events since Last GSTM (II) Software Uploads: February/March, upload of new OBDH software to both satellites • removes the safe mode risk in case of a failure of the last thermistor on the –Z CESS (Coarse Earth & Sun Sensor) head. • provides an alternate means of steering satellite in safe mode using magnetometer measurements. June, upload of new IPU software module (automatic restart of KBR in case of an anomaly). September, upload of new IPU software module (resolve spontaneous occultation stop)

  8. Satellite Events since Last GSTM (III) Miscellaneous: Orbit manoeuvres to reverse the inter-satellite drift rate • GR-2 4-Jan and 26-Sep Collection of ionospheric occultation data begins • GR-1 28-Feb * * Atmospheric occultations added in May 2006 Center-of-Mass management • GR-1 & 2 CoM trim 12-Apr • GR-1 & 2 CoM cals 17-Apr and 4-Jun IPU side switch due to apparent failure of IPU-redundant • GR-2 3-May

  9. German Space Operations GSOC Neustrelitz GS & Raw Data Center Control Center Oberpfaffenhofen Weilheim Ground Station

  10. Ny-Aalesund Station The Ny-Aalesund station on Spitzbergen Island is used for frequent data dumps (almost 1/rev) and consists of two independently operating devices. They enable the timely delivery of atmospheric occultation data from CHAMP, GRACE-1 and later TerraSAR-X. Device one also tracks GRACE-2 with low priority for battery monitoring reasons and in order to improve the redundancy. The dump data is transmitted to GFZ within 5-8 min. for processing with minimum delay and major parameters are displayed in a browser.

  11. Dump Data Monitoring Two different data browsers (GFZ, JPL) allow a detailed look at the dump data quantity (data gaps, missing dumps, periods dumped twice,..) and quality (high gas consumption, ..) with only a few minutes delay.

  12. GSOC Activity since Last GSTM • “Recommendations”: 144 (directives to the operators) • Software uploads: 2 OBDH (v6 to each satellite) 6 IPU libraries • Anomaly Reports: 24 opened • 15 satellite-related* • 9 ground-related 13 still open * Satellite-related anomalies are distributed as follows: • 8 Instrument Processing Unit (IPU) • 4 Battery • 2 On-Board Data Handler (OBDH) • 1 Accelerometer Instrument Control Unit (ICU)

  13. Plans • Splinter meeting at GFZ on 18-October to address: • Contingency plans if further battery degradation • Orbit raise maneuver for extending mission life • Proposal to add rising GPS occultations measurements

  14. Summary The design mission lifetime has been exceeded and there is a good chance of getting another 5 years of lifetime Excellent performance of flight and ground segment, however the batteries are a concern

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