There are two main parts to each TDRS satellite, its unique telecommunications payload, and its bus (elements common to most spacecraft). The Bus of the TDRS K/L Spacecraft is a derivative of the Boeing 601 (BSS-601). The Boeing 601 was first introduced in 1987 and was designed with communications applications in mind. It was first designed to meet potential requirements for multiple-payload satellite applications from direct television broadcasting to small receiving antennas, such as very small aperture terminals for private business networks, and mobile communications. When the TDRS HIJ contract was awarded in February 1995, Boeing began adapting their 601 bus to a much larger scale communications payload.

The Boeing 601 body is composed of two modules, one, the primary structure that carries all launch vehicle loads and contains the propulsion subsystem, bus electronics, and battery packs; and, two, a structure of honeycomb shelves that hold communications equipment, electronics, and isothermal heat pipes.

Reflectors, antenna feeds, and solar arrays mount directly to the payload module, and antenna configurations can be placed on three faces of the bus. This modular approach allows development and test integration work to proceed in parallel, thereby shortening the manufacturing schedule and test time.

For more information about the BSS-601, check out the Boeing Website here.