Payload Assist Module

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:

• PAM-A (Atlas class), development terminated; originally to be used on both the Atlas and Space Shuttle, designed for satellites up to 4,400 lb (2,000 kg)
• PAM-D (Delta class), uses a Star-48B rocket motor, designed for satellites up to 2,750 lb (1,250 kg)
• PAM-DII (Delta class), uses a Star-63 rocket motor, designed for satellites up to 4,150 lb (1,880 kg)
• PAM-S (Special) as a kick motor for the space probe Ulysses

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.