# How do shuttle flights get assigned their number, i.e. STS-121 or STS-115?

Update:

When Discovery was launched on July 4th, it was STS-121. Atlantis will be launched later this month, and it is STS-115. So, the numbers are not sequential. How do they determine the STS numbers?

Relevance

The shuttle flights are given their designations in the early design period by NASA flight directors, several years in advance. Over time, events occur which force the administrators to change the schedule; the Columbia accident being an obvious example.

If the flight numbers were changed as these events occur to keep them consecutive (i.e., STS-114, STS-115, etc.), then it might be confusing to keep track of the changes for the workers to keep track of the paperwork. STS-115 could then become STS-121 next week, and a worker may confuse the two flight numbers when reading a technical report. Therefore, the schedulers at NASA don't fiddle around with the flight numbers.

Slightly off topic, but the current system is, believe it or not, much less confusing than the pre-Challenger system. The flight numbers were a three-digit code, like STS-61A or -41D. The first digit signified the year (i.e., 1985 = 5, 1984 = 4) that it was first planned to be launched. The letter signified the order in which the flight was to be launched in that year; the first flight was A, second was B, and so on.

The middle digit is the interesting one; it signified the launch site. A value of "1" meant that it was launched from Kennedy Space Center, but they planned on launching military missions from Vandenberg AFB in California, which would have had a number "2". There was going to be a launch from there in mid-1986, but the Challenger accident scrubbed those plans. That's why you only see "1"s for the middle digits of those early shuttle flights.

Orbiter Vehicle Designation

Each NASA space shuttle designation is composed of a prefix and suffix separated by a dash. The prefix for operational shuttles is OV, for Orbiter Vehicle.

The suffix is composed of two parts: the series and the vehicle number.

Series:

The vehicle number is the sequentially assigned within the series, beginning with 1. Therefore, there can never be a OV-100 as it would read "Orbiter Vehicle Series 1 Vehicle 0".

Many proposals to build a second generation of orbiters, externally compatible with the current system but internally new, refer to them as "OV-200" or "OV-2xx" in order to differentiate them from the "current generation", the OV-100s. This terminology is informal, and it is unlikely that any Shuttle-derived vehicle built will be given such designation.

Orbiter Designations

OV-098 - Space Shuttle Pathfinder, a structural mockup

OV-099 - Space Shuttle Challenger, originally STA-099

OV-101 - Space Shuttle Enterprise

OV-102 - Space Shuttle Columbia

OV-103 - Space Shuttle Discovery

OV-104 - Space Shuttle Atlantis

OV-105 - Space Shuttle Endeavour

Notes: Challenger was originally intended to be used as a Structural Test Article, rather than a flight-capable orbiter; as such, the numbering was changed when she was rebuilt. Enterprise, on the other hand, was intended to be rebuilt into a flight-capable orbiter; it was found to be cheaper to rebuild STA-099 than OV-101, so she remained unflown. The designations were not altered, despite this change in fortune.

Note that whilst Pathfinder is referred to as OV-098, she should not be confused with MPTA-098 - the Main Propulsion Test Article, a steel frame (looking nothing like an Orbiter) used to test the Space Shuttle Main Engines on. Pathfinder was originally a "fit check" unit, a simple mockup resembling the production Orbiters in size, shape and weight, intended to be used to ensure that ground handling facilities would be sized to handle Orbiters. She was later rebuilt to resemble them cosmetically, and is currently on display with the external tank used during the propulsion tests (designated MPTA-ET). To further add to the confusion, it appears that Pathfinder was never formally numbered, and the OV-098 designation is both unofficial and retroactive. MPTA-098 was later rebuilt into the Shuttle-C mockup during the 1990s; it has not surfaced since.

In keeping with this theme, other pieces of ground hardware used by the Space Shuttle program have been given OV-xxx designations; these include:

OV-095 - a mockup in the Shuttle Avionics Integration Laboratory (SAIL) at Johnson Space Center.

MPTA-098 - the Main Propulsion Test Article, as above

OV-106 - an administrative name given to the set of structural components manufactured to replace those used in the construction of Endeavour; however, the contract for these was cancelled shortly afterwards, and they were never completed.

Category: Space Shuttle program

Source(s): Wikipedia - give them money

STS refers to Space Transporting System. I'm not aware of how the number is being alloted

• 4 years ago

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