The Payload Assist Module (PAM) is a modular upper stage designed and built by McDonnell Douglas (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.^[1] 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)^[2]
• PAM-DII (Delta class), uses a Star-63 rocket motor, designed for satellites up to 4,150 lb (1,880 kg)^[2]
• PAM-S (Special), uses a Star-48B as a kick motor for the space probe Ulysses^[2]

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".^[3] 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.^[3]

• 
  PAM-D stage in assembly
• 
  SBS-3 satellite with PAM-D stage being launched from Space Shuttle Columbia
• 
  Saudi officials inspect a PAM-D module that re-entered the atmosphere in 2001
• 
  SATCOM KU-2 attached to a PAM-DII is being released from the cargo bay of the Space Shuttle Orbiter Atlantis during STS-61B
• 
  Ulysses is mated with the PAM-S

• Payload Assist Module Archived 2016-12-21 at the Wayback Machine at the NASA Shuttle Reference Manual
• Payload Assist Module at GlobalSecurity.org