"Rocket launch in T minus 1 hour".

I have a problem with how this expression is used here. Native speakers have told me that this is natural, however online definitions tell me that "T minus" is used for the point 1 including the timespan from it to point 2.

So using point 1 as a timespan to point 2... makes no sense. Of course the expression includes the timespan and is used as a timespan - But what is meant is point 1, meaning-wise.

In my opinion it is a bit like saying "It is 3am right now. I will eat at 4am, which is in 3am". However 3am is a point of time both in form and meaning of course.

The only way it makes sense is if we said "It is T minus 1 hour until start".

How is this acceptable? There is a conflict between meaning as point of time and timespan.

  • 5
    You're not going to get an answer other than "because that's the way Nasa and other space agencies have done it in the past and still do it". Possibly someone will put together a timeline showing who first used it and when it became popular. Is that the sort of answer you are looking for? Or do you just want someone to agree with you that you're better at English than Nasa is?
    – Stuart F
    Apr 17 at 14:18
  • 4
    To be fair, this is just peculiar NASA jargon. It doesn't have to follow the rules of ordinary English as long as they understand it. Apr 17 at 15:13
  • Which native speakers told you that? Please cite your sources for this.
    – alphabet
    Apr 17 at 16:18
  • 3
    In such contexts, T is the time of the actual launch (in the future), so T minus 5 minutes means the current time is 5 minutes less than launch time. It's nonsense to say It is T minus 1 hour until launch - either say It is T minus 1 hour, then wait a minute and continue with It is T minus 59 minutes, or say It is 1 hour until launch. Apr 17 at 17:28
  • @FumbleFingers, T can be in the future, or in the past. Here's another example I've dug out of the Apollo 7 transcript: "At T plus five, make it read set up pitch rate, et cetera."
    – Juhasz
    Apr 17 at 18:00

4 Answers 4


Indeed it doesn't make more sense once you try to do the math, even more when you could just say "Rocket launch in one hour"... I guess the "T minus" just gives a sense of precision and exactness.

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    Apr 17 at 14:19
  • It is like saying "The development of the Tesla was miles ahead of its competitors" .. Miles is a unit of distance. Sometimes the key words that bring a new feeling to a sentence don't make actual sense. Apr 17 at 14:19
  • The 'distance ≅ time' and 'distance travelled ≅ progress made' metaphors (where ≅ = 'represents') are established and universal. The provenance of this usage, while it might be used merely to sound more expert, needs to be provided, Rafael. Apr 17 at 16:07

You're correct that it doesn't make any sense in the context of it's original use. Originally, it appeared in the context of a countdown to launch, where there was a set of procedures and status reports that were keyed to the countdown clock. So something can happen at T minus ten minutes, but it can't happen in T minus ten minutes (and counting). The countdown is a chronological sequence of events indexed to the countdown clock.

But clearly, this idiom has escaped captivity and has survived as a feral fixed phrase in the wild. Like most ferals, it has adapted to new conditions, and it can't afford to be too choosy about the company it keeps.


The expression t-minus [time measurement] became idiomatic after the public was exposed to NASA mission commentaries. The popular idiom is give a humorous seriousness to a measure of time. Examples found on the internet:

"T-minus 21 days until vacation time!!!!!!"

"Wedding is in t-minus 2 hours!!!"

"Baby due in t-minus 6 days!!!"

As you've noted, these uses do not seem to respect the exact meaning of the terms in the expression. That's OK. We say all kinds of things that are apparently illogical. Here are some borrowed from a Quroa post.

Head over heels - this is the typical standing posture, whereas the expression typically means something like knocked off one's feet

Meteoric rise - a meteor is something from outerspace that has entered the atmosphere and is falling towards the Earth. Meteors don't rise

Back-to-back - means consecutive, though it's not obvious what the "back" of either event is

For what it's worth, the popular (illogical) usage of "t-minus" does not follow the typical NASA usage. In NASA lingo, T stands for "time" and denotes the time that some significant event will take place. They also use other letters, like L (launch) or E (event). You can measure the distance, in time, from the event by using T minus to mean time before the event or T plus to mean time after the event.

Here are some examples from the transcript of the Apollo 7 mission commentary:

"This is Apollo Saturn launch control at T minus 1 hour, 44 minutes in counting."

"The countdown is continuing to go satisfactorily at T minus 1 hour, 43 minutes, 8 seconds and counting."

"The standby crew must depart from the area by the T minus 40 minute mark"

"T minus 6 minutes 20 seconds and counting, however, we just heard a report over the circuit we are asking for a HOLD. We are standing by for further reports. We are now at T minus 6 minutes IS seconds and holding, T minus 6 1S and holding. This is Launch Control 6 mihutes 1S seconds and holding, the test supervisor advises he expects this to be a very brief HOLD."

  • 1
    As is often the case in such matters, what one will think about using the phrase with in depends on where one is on the prescriptivist-descriptivist spectrum. For some people, the fact that such usage is based on a misunderstanding will be a strong reason for avoiding it. Incidentally, seeing t-minus written with a hyphen is itself an indication that the original meaning of the phase has been misunderstood.
    – jsw29
    Apr 17 at 22:31

All languages sometimes break their own rules. This is an example. You are correct that this is technically grammatically wrong. But most people don't notice or care. You asked why it is "acceptable" and the answer is that breaking language rules is acceptable in general. It's a natural and normal part of language evolution.

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