Mission Designations

When a payload is first proposed for flight, NASA gives it a name such as Astro-2, TDRS-G, or USMP. Later, when the payload has been selected for flight, it is assigned a place in the flight manifest and given an "STS" designation.

STS is an acronym for Space Transporation System. This is followed by a "-" and a number incremented every time NASA assigns a new flight. Therefore, STS-78 will be about the 78th Shuttle flight. But, since the designation is made so early, five or six years before launch, the exact order of flights isn't certain. That is why we don't always launch in strict numerical order and STS-66 flew before STS-63.

Shuttle flights are most properly referred to by their STS designation, but we sometimes use their primary payload name for convenience (or out of affection...). That's why you might see different references to the same mission. For example, STS-35 was always "Astro-1" to those of us who were planning the mission long before it was given an STS number.

There are usually enough resources available onboard to manifest several secondary payloads along with the primary. For example, STS-65 not only flew the primary payload IML-2 (2nd International Microgravity Lab), but also APCF, CPCG, AMOS, OARE, MAST, and SAREX-II.

The composition of all the Shuttle flights is described in detail on the Shuttle's Pages