Spacecraft
The GRAIL spacecraft design and their components are derived from LM XSS-11 spacecraft heritage. A single-string architecture meets this short mission's reliability requirements. The resulting design meets all the GRAIL mission and science requirements with ample technical margins that provide flexibility to solve problems that may arise during development and which meet or exceed design principles established by the Jet Propulsion Laboratory (JPL; see Table to right).

Each spacecraft bus is a rectangular composite structure. The science payload ranging antennas are in thermal enclosures and are mounted so that they are nominally on the line between the two spacecraft’s center of masses. The other components of the payload instrument are on a single interior bus panel for easy integration and test.

There are 2 non-articulated solar arrays of XSS-11 heritage that are deployed just after separation from the LV. Warm gas systems identical to XSS-11 provide V for maneuvers and unloading of the 3 reaction wheels. Additional attitude sensing components include an IMU, sun sensor and star tracker.

The C&DH, power management, and lithium ion battery are also XSS-11 heritage. The S-band telecommunications system for communication with the DSN uses heritage components (Themis and Genesis).

The spacecraft will be built, the science payload integrated and the systems tested at LM's Denver facility. LM will use two system-level spacecraft test labs (STL) and one software simulator (SoftSim) testbed with unlimited copies that enable integration and verification of all hardware and software throughout the Assembly Test and Launch Operations (ATLO) cycle.

Payload
To measure the inter-spacecraft range-rate, each spacecraft has a Ka-band Lunar Gravity Ranging System (LGRS) derived from the GRACE instrument. The elements of the LGRS are shown to the right.

LGRS performance verification will be done at the JPL Gravity Recovery Instrument for Planets (GRIP) testbed that has X-level per-formance verification capability and sub-X adjustability in an 18-m anechoic chamber.