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 motors. 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:
The PAM-D module, used as the third stage of the Delta II rocket, was the last version in use. As of 2018, no PAM is in active use on any rockets.
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 the GPS satellite 2A-11 in 1993, crashed in the sparsely populated Saudi Arabian desert, where it was positively identified.