The GRACE Project was divided into five systems. Each of the five systems is shortly described in the following paragraphs.
Launch Vehicle System (LVS)
The LVS included the ROCKOT launch vehicle, a multi-satellite dispenser, and the personnel, test equipment and facilities for preparation, integration and launch of the satellites. The LVS was managed by the DLR LVS Manager and supported by JPL and its contractors. GRACE was launched on March 17, 2002. Read more about “GRACE Launch”.
Satellite System (SAT)
JPL led the development of the satellite system in partnership with Space Systems/Loral (SS/L) and Astrium GmbH (Astrium). Astrium provided major elements of two flight satellites based on an existing small satellite designed for the CHAMP mission. SS/L provided the attitude control system, microwave instrument electronics and system and environmental testing. Read more about "GRACE Satellites”.
Science Instrument System (SIS)
The SIS included all elements of the inter-satellite ranging system, the GPS receivers required for precise orbit determination and radio occultation experiments, and associated sensors such as the two star cameras. Within the SIS also necessary integration activities of all sensors were coordinated, assuring their compatibility with each other and the satellites. Read more about "GRACE Payload".
Mission Operations System (MOS)
The MOS consisted of facilities and resources of the German Space Operations Center (GSOC) in Oberpfaffenhofen, tracking antennas at Weilheim and Neustrelitz, and other stations and facilities needed for supporting LEOP (Launch and Early Mission Operation) and contingency operations. These facilities were used to monitor and control the satellites and instruments, perform initial processing of the telemetry data, and delivered all these data to the Science Data System for further processing and generation of science products. In addition to real-time operations, the MOS function provided the Central Checkout System for ground testing using command and data interfaces. Read more about “GRACE Operations”.
Science Data System (SDS)
The SDS functions included science data processing, distribution, archiving and product verification. The SDS was a distributed entity managed in a cooperative approach by JPL (Jet Propulsion Laboratory) and UTCSR (University of Texas, Center of Space Research) in the US and GFZ in Germany. The cooperative approach included sharing of processing tasks, harmonization of product archives and validation/comparison of products. Data and products to be processed and archived by the SDS included, e.g., corrected inter-satellite range and accelerometer measurements, GPS orbit and occultation data, or gravity field products. The SDS also received, processed and archived ancillary data (e.g. meteorological fields) necessary for data processing and verification. Further information is provided on other pages such as "Products" or "Gravity Field Results".