The Spacecraft Bus
Spitzer's Spacecraft Bus is an octagonal structure at the base of the Observatory that houses the avionics and the warm electronic parts of the science instruments. The Spacecraft Bus supplies the science instruments with the electrical power generated by the Solar Panel Assembly, orients and stabilizes the telescope, collects, compresses and stores the science data for transmission to Earth, executes the stored commands to carry out the planned observing schedule, and communicates with the ground systems.
The bus structure has nine bays in which the equipment is housed, made up of four side modules, four corner modules, two heat pipe equipment panels, and six equipment panels. The equipment panels are sandwiched between the modules and are bolted and bonded together for maximum stiffness and structural integrity. On the outside of the bays, panels are bolted to the modules. These panels are removable, and provided access to the outer bays during the assembly and testing of the Observatory. The center bay of the nine was assessed through the top of the bus.
The Spacecraft Bus is also the mounting point for the star tracker and gyroscopes that allow Spitzer to orient itself in space. The main antenna for communication with Earth, called the High Gain Antenna is mounted on the back of the bus, and the secondary antennae (the Low Gain Antennae) are mounted on the side. The maneuvering thrusters are mounted on outriggers attached to the bus.