The GRACE Project is divided into five systems. Each of the five systems is described in the following paragraphs.
Launch Vehicle System (LVS)
The LVS includes the ROCKOT launch vehicle, multi-satellite dispenser, and the personnel, test equipment and facilities for preparation, integration and launch of the satellites. The LVS is managed by the DLR Launch Vehicle System Manager and supported by the JPL Project and its contractors.
Satellite System (SAT)
JPL leads the development of the Satellite System in partnership with Space Systems/Loral (SS/L) and Astrium GmbH (GmbH). GmbH provides major elements of two flight satellites based on an existing small satellite designed for the CHAMP mission. SS/L provides the attitude control system, microwave instrument electronics and system and environmental testing.
Science Instrument System (SIS)
The SIS includes all elements of the inter-satellite ranging system, the GPS receivers required for precision orbit determination and occultation experiments, and associated sensors such as the Star Cameras. This System also coordinates the integration activities of all sensors, assuring their compatibility with each other and the satellite.
Mission Operations System (MOS)
The MOS consists of facilities and resources of the German Space Operations Center, tracking antennas at Weilheim and Neustrelitz, and other stations and facilities needed for supporting LEOP and contingency operations. These facilities are used to monitor and control the satellite, perform initial processing of the telemetry data, and deliver all data to the SDS for further processing and generating science products. In addition to real-time operations, the MOS function provides the Central Checkout System for ground testing using command and data interfaces. The operations team also monitors satellite performance and health throughout the duration of the mission. Mission operations are conducted at the GSOC control center in Oberpaffenhofen, Germany.
Science Data System (SDS)
The SDS functions include science data processing, distribution, archiving and product verification. The SDS is a distributed entity and managed in a cooperative approach by JPL and UTCSR in the US and GFZ in Germany. The cooperative approach includes sharing of processing tasks, harmonization of product archives and validation/comparison of products. Data and products to be processed and archived by the SDS include corrected inter-satellite range and accelerometer measurements, GPS orbit and occultation data, orbit, gravity field and GPS occultation products. The SDS also receives, processes and archives ancillary data (e.g. meteorological fields) necessary for data processing and verification.