Test masses inside LISA Pathfinder payload

The interior layout of LISA Pathfinder's science module.

At the heart of the science module lies the LISA Technology Package. This contains inertial sensors, an optical metrology system, the payload computer and a diagnostic system. The inertial sensors and optical metrology system provide signals to the Drag-Free and Attitude Control System, which in turn commands three clusters of cold-gas micronewton thrusters, as well as feeding back to the inertial sensors.

The solar array (shown here as partly transparent for illustrative purposes) provides the spacecraft with solar power and shields it from the Sun.