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

Status GRACE Mission Operations

1GSTM – Potsdam - 15 October 2007


Joseph G. Beerer, JPLOperations Mission Manager

Franz-Heinrich Massmann, GFZDeputy 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

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



Orbit Status 15-Oct-2007

- 2038 days in orbit - 31170 revolutions completed

- 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

GR1 leader GR2 leader



Mission Lifetime Predictions

- End of Life (pred.): GR-1 2019-2012-2012 (gas-thrust-decay) GR-2 2023-2016-2012

Remaining Resources:

• Battery Cycles: > 12 years (?)• Thruster actuations: > 5 years

• Cold gas: > 10 years• Orbit decay: > 6 years



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



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



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)



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



German Space Operations

Control Center Oberpfaffenhofen Weilheim

Ground Station

Neustrelitz GS &Raw Data Center

GSOC



Ny-Aalesund Station

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.

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.



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.



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)



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



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

Documents

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