The Payload Assist Module (PAM) is a modular upper stage designed and built by McDonnell Douglas (now Boeing), using Thiokol Star-series solid propellant rocket engines. The PAM was used with the Space Shuttle, Delta, and Titan launchers and carried satellites from low Earth orbit to a geostationary transfer orbit or an interplanetary course. The payload was spin stabilized by being mounted on a rotating plate. Originally developed for the Space Shuttle, different versions of the PAM were developed:
PAM-A (Atlas class), development terminated; originally to be used on both the Atlas and Space Shuttle
Saudi officials inspect a PAM-D module that re-entered the atmosphere in 2001.
On January 12, 2001, a PAM-D module re-entered the atmosphere after a "catastrophic orbital decay". The PAM-D stage, which had been used to launch a GPS satellite in 1993, crashed in the sparsely populated Saudi Arabian desert, where it was positively identified.