How NASA’s Shuttle Numbering System Worked

Space Shuttle program patch

Space Shuttle program patch

It has been nearly six years since NASA’s final shuttle launch ended an era, but I’m still just not ready to let it go. As I’ve written previously, I’ve dubbed my generation ‘the space shuttle generation’. Today, I want to tell you how the shuttles were numbered and explore whether or not the number scheme changed due to one NASA administrator’s triskaidekaphobia (the fear of the number 13).

Space Transportation System

The official name for the space shuttle program was Space Transportation System (abbreviated STS). The program was envisioned to be America’s routine link to orbit, designed to reuse many major components with the idea of a quick return to service and reduced costs. After a few unmanned test flights of the Enterprise prototype, shuttle Columbia became the first shuttle to complete an orbital mission with astronauts aboard (mission commander John W. Young and pilot Robert L. Crippen). This milestone flight carried the simple designation: STS-1. Subsequent missions were given the numbers STS-2 – STS-9. The mission that would have been numbered STS-10 was cancelled due to payload delays. So, you’d expect the next flight to be designated STS-11, right? Wrong. Try STS-41-B.

Shuttles Columbia, Challenger, Discovery, Atlantis, and Endeavour

Shuttles Columbia, Challenger, Discovery, Atlantis, and Endeavour – Public Domain

A New System

Beginning in 1984, NASA switched to a new flight numbering system. The change is credited to a growing complexity of the program’s launch manifest, as well as an anticipated increase in the number of flights and launch locations. The new system, while more complicated than the original system, isn’t that difficult to understand once you know the formula. The STS prefix was continued, followed by a two-digit number, followed by a letter.

Let’s break down STS-41-B:

The first number, 4, indicated which fiscal year the mission was to launch in (dropping the first three digits of the year). In this case, the year was 1984. The second digit, always a 1 or a 2, indicated the launch location: 1 for Kennedy Space Center and 2 for Vandenberg Air Force Base. Since STS-41-B launched from Kennedy Space Center, it carried that second digit of 1. (Note: Vandenberg was never used to launch shuttle missions, and therefore the ‘2’ digit was never utilized). The final part of the scheme, the letter, indicated which planned launch it was for that fiscal year. In our case, B, indicated it was the second intended launch for that year. Keep in mind, the letter designation was assigned for the planned sequence.

STS-41-B = Space Transport System – Fiscal Year 1984, launching from Kennedy Space Center – the second mission of the fiscal year.

Now let’s decode one to see if we got it:

STS-61-A. Using what we learned above, we know that this was the first mission planned for fiscal year 1986 and launching from Kennedy Space Center. Easy!


The new numbering scheme didn’t last for long. On January 28, 1986, STS-51-L, ended in tragedy, as the Challenger shuttle disintegrated 73 seconds after take-off. There wouldn’t be another shuttle launch for 2 years and 8 months, while NASA rigorously reviewed every aspect of the shuttle program to determine the cause of the catastrophe and to greatly increase safety standards before a return to flight. In the interest of safety, fewer launches would be planned each year. As a result, plans to add Vandenberg as a launch site for the shuttle were abandoned. There was no longer a need for the more complex numbering system. When the shuttle returned to flight on September 29, 1988, that mission was designated STS-26. For the remainder of the program, the simplified numbering system was utilized.

Firing Room 1 configured for space shuttle launches - Source:

Firing Room 1 configured for space shuttle launches – Source: NASA

Rumors of Triskaidekaphobia

At the beginning, I mentioned that the fear of the number 13 might have played a part in the numbering system change. That fear has a name, and it’s a doozy: triskaidekaphobia (pronounce it like this: trice-kai-dek-aphobia). Some, including astronauts (like Paul Weitz) and other NASA employees, believe the numbering system changed, at least in some part, due to then-NASA Administrator James Beggs’s fear of the number 13. Not far from anyone within NASA’s mind was the perilous flight of Apollo 13. Apollo 13 launched at 13:13:00 Houston time, and suffered an oxygen tank explosion on April 13. While it’s possible this played into the numbering system change, NASA officials deny it.

This didn’t stop the crew of STS-41-C from having some fun. Had the numbering scheme not changed, their mission would have been designated STS-13. Coincidentally, it was originally scheduled to launch of Friday the 13th of April, 1984 (the launch date was ultimately changed to April 4, but it returned on that Friday the 13th).

“[The crew] created their own “Black Cat” mission patch. Former crewmember James “Ox” Van Hoften recalls, “We flew around with our STS-13 patch on, and that was a lot of fun. We ended up landing on Friday the 13th, so that was pretty cool.”

The 'alternative' patch designed to make light of the triskaidekaphobia surrounding this mission.

The ‘alternative’ patch designed to make light of the triskaidekaphobia surrounding this mission. Source: Wikipedia / CC

And there you have it. Just like so many things associated with the space program, even the most overlooked items often have fascinating stories behind them.

Bookmark the permalink.

Leave a Reply

Your email address will not be published. Required fields are marked *