Thiokol's Star family of space motors provides propulsion for spacecraft and launch vehicle upper stages.  The Star number for each motor indicates its approximate principal diameter in inches, while the letter designations are used to denote configurations tailored to a particular set of needs.  The Star 48 currently comes in two models, the A and the B, with two nozzle lengths to chose from.

The Star 48B rocket motor has two nozzle lengths.  The short nozzle Star 48B is qualified as a Payload Assist Module (PAM) on the Space Transportation System (STS), better known as the Space Shuttle, while the long nozzle Star 48B is qualified as the third stage of the Delta launch vehicle (PAM-Delta).  The PAM-STS has the same 72-inch overall length as the STS version of the Star 48.  The PAM-Delta has the same 80-inch overall length as the Delta version of the Star 48.  The basic version for both missions contains 4430 pounds of propellant and incorporates the same high-energy propellant and high-strength case as the Star 48.  The semi-submerged nozzle uses a carbon-phenolic exit cone. 

The Star 48A rocket motor provides increased payload capability over the Star 48B due to an 8 inch stretch of the motor case.  The Star 48A also comes in two nozzle lengths.  With an overall length of 80 inches the short nozzle Star 48A was designed to fit within the dimensional envelope of the PAM-Delta.  The long nozzle Star 48A has an overall length of 88 inches.