Wikipedia's STS-61 says that it is not to be confused with STS-61A, STS-61B or STS-61C.

Why were there so many STS missions where the name included the number "61"?

STS-61 is not to be confused with STS-61A, STS-61B or STS-61C

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    $\begingroup$ Does this answer your question? How were the Space Shuttle missions named? $\endgroup$ Feb 13, 2020 at 5:37
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    $\begingroup$ @RussellBorogove no, at least not as well as the answer below does! I don't think this should be closed as duplicate. $\endgroup$
    – uhoh
    Feb 13, 2020 at 6:55
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    $\begingroup$ Because NASA was jealous of NCC-1701-A, NCC-1701-B, NCC-1701-C, NCC-1701-D,.... $\endgroup$ Feb 13, 2020 at 12:48
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    $\begingroup$ @JCRM To my understanding, yes in fact it does! "Duplicate" is a misnomer. In Stack Exchange, deciding if a question is a duplicate is based on how well the answers there answer the question here. It is not based on the similarity of the question. It's a bad choice of terms, but the decision should be strictly answer-based. $\endgroup$
    – uhoh
    Feb 13, 2020 at 15:46
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    $\begingroup$ @JCRM if you've been voting to close questions as duplicate based on the similarity of the questions, then you've been doing it wrong. $\endgroup$
    – uhoh
    Feb 13, 2020 at 15:48

2 Answers 2


STS-61 was the 61st scheduled mission.

The other three happened from 7 to 10 years earlier and are relics of the goofy "let's hide our launch scheduling issues by obfuscation" scheme where the first digit is the last digit of the fiscal year, the "1" is the launch site, and the letter is the sequence within the fiscal year.

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From here

The goofy scheme was in effect from the 10th mission (41-B) through the Challenger failure (51-L) when sanity was restored, at least to mission numbering.

The steely-eyed rocket builders at KSC refused to fully sign up for this goofy scheme and continued to use consecutive numbers internally. Hence when flights resumed after the Challenger failure with mission STS-26, you will sometimes see this written as STS-26R, because the KSC documentation already had an STS-26.

Here's the list of the affected missions, written KSC # / JSC #
Missing numbers are flights that got cancelled, e.g. STS-10

Note that there were even more "51"s than "61"s!

  • STS-11/41B
  • STS-13/41C
  • STS-14/41D
  • STS-17/41G
  • STS-19/51A
  • STS-20/51C
  • STS-23/51D
  • STS-24/51B
  • STS-25/51G
  • STS-26/51F
  • STS-27/51I
  • STS-28/51J
  • STS-30/61A
  • STS-31/61B
  • STS-32/61C
  • STS-33/51L
  • STS-26R
  • STS-27R
  • STS-29R
  • STS-30R
  • STS-28R
  • STS-034 (not affected but in the list because some "R mission" slipped to after it)
  • STS-33R
  • STS-32R
  • STS-036 (not affected but in the list because some "R mission" slipped to after it)
  • STS-31R
  • $\begingroup$ Should I interpret this as: 51L was the 12th mission of year 5 (which year?). I didn’t know they did so many missions in a year. Or am I misunderstanding “fiscal year”? $\endgroup$
    – Ludo
    Feb 13, 2020 at 5:02
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    $\begingroup$ Yes, it was the 12th one planned for fiscal year 1985. US government fiscal years run from October - September. You can tell from the list in my answer that many of the fiscal year 1985 missions got canceled - E, H, K. NASA was trying to ramp up the flight rate and things were a bit crazy in the scheduling department. A contributor to the Challenger failure IMHO. Remember that even though the Challenger accident was in January, it was the 2nd shuttle mission of that calendar year. $\endgroup$ Feb 13, 2020 at 5:06
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    $\begingroup$ If you look at the document I linked in the answer, you can see that they were planning 14 missions in calendar year 1986. The date on the document is stamped Received January 2 1986. $\endgroup$ Feb 13, 2020 at 5:12
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    $\begingroup$ So, based on the mission number starting with "5", 51-L had been delayed for at least 4 months (from late September of 1985 to late January of 1986). Kind of explains NASA management's frustration of not wanting to delay the launch again despite the known safety issue. $\endgroup$
    – dan04
    Feb 15, 2022 at 18:15
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    $\begingroup$ @dan04 and even once it made it to the pad, it had a troubled launch campaign: It was postponed twice (before the countdown started) and then scrubbed twice (after the countdown started). $\endgroup$ Feb 15, 2022 at 19:29

After the Challenger disaster, NASA returned to using a sequential numbering system, with the number counting from the beginning of the STS program. Unlike the initial system, however, the numbers were assigned based on the initial mission schedule, and did not always reflect actual launch order. There were seven STS-51 launches

  • $\begingroup$ -1 because this is not an answer to the question. $\endgroup$
    – uhoh
    May 28, 2020 at 1:44

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