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Maybe this question sounds snaive to some educated people, but I'm not clear if the Space Shuttle could and was ever used without a crew.

And what was the smallest and the biggest crew size it ever flown?

Joe Jobs
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    Of course. A ship like that could never possibly fly automatically, least of all with 1980s tech. An automated system could never handle something like a 38 mph crosswind and still land within 10’ of the centerline and within 33’ of the touchdown mark. That would be crazy. – Harper - Reinstate Monica Aug 05 '20 at 02:27
  • @Harper-ReinstateMonica Not sure if sarcasm or serious, because there are automated landing systems for aircraft. – nick012000 Aug 05 '20 at 12:12
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    @Harper I'm pretty sure you're being sarcastic but just in case anyone sees your comment without being familiar with the topic: The Soviet space shuttle flew autonomously without crew. And they stuck the landing too! So the technology in principle existed. (Just not on the Space Shuttle) – user2705196 Aug 05 '20 at 13:20
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    @user2705196 i figured my disturbingly specific figures would give it away, but what I said is exactly what Buran did. – Harper - Reinstate Monica Aug 05 '20 at 14:41
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    Shuttle had an autoland system. They just didn't use it. https://space.stackexchange.com/a/39470/6944 – Organic Marble Aug 06 '20 at 12:22
  • So actually it could be used without a crew – Joe Jobs Aug 06 '20 at 12:23
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    @JoeJobs No, the autoland system didn't support many of the manual actions required to land. That's what the Remote Control Orbiter kit mentioned in my answer was for. The autoland system just flew (steered) the vehicle. And all of this was just for entry. The manual actions required for ascent and post insertion were never automated. – Organic Marble Aug 06 '20 at 12:41

3 Answers3

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It always flew crewed.

After the Columbia failure, provision was made to fly a damaged Orbiter uncrewed back to a west coast landing site, leaving the crew on the ISS. This was called the Remote Control Orbiter and it required an In-flight Maintenance kit to be installed after docking at the ISS. It was never used.

The smallest number was two (STS-1, 2, 3, and 4)

The largest number was eight (twice, on STS-61A and on STS-71’s return from Russian space station Mir)

Source

Organic Marble
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    I've read that former NASA staff say STS-1 was the most dangerous mission in NASA history as there was no way to test the system all-up before manned flight. – GdD Aug 03 '20 at 22:33
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    Wasn't it that the orbiter required humans on board for some trite task like lowering the gear, due to astronauts demanding they aren't made completely redundant by computers? – SF. Aug 04 '20 at 15:53
  • @SF if you read the link about Remote Control Orbiter it explains what normally-under-human-control functions were automated by the IFM. It was more than just dropping the gear, although that was included. – Organic Marble Aug 04 '20 at 16:02
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    Landing STS was such a complex operation. See https://www.youtube.com/watch?v=Jb4prVsXkZU – user1778602 Aug 04 '20 at 20:13
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    @SF., it was opening the gear doors, not lowering the gear, and it wasn't a "trite" task. Rather, opening the gear doors too soon would be a death sentence, either due to excess drag making it impossible to reach a landing site, or if the doors opened much too soon, a Columbia-like breakup. – Mark Aug 04 '20 at 22:11
  • @Mark the gear doors opened and the gear lowered upon the press of the same button. They were mechanically linked. https://www.nasa.gov/centers/johnson/pdf/383449main_mechanical_systems_workbook_21002.pdf "Each door is connected to its associated gear by mechanical linkages, so the doors open automatically as the gear falls. " – Organic Marble Aug 04 '20 at 23:02
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    @Mark there was plenty of telemetry to allow the computer do it autonomously in a safe manner, and a slew of far more dangerous and critical tasks it did. Comparing the complexity of decision of opening the bay door, to complexity of gliding the zig-zag pattern to the runway, it's absolutely trite. – SF. Aug 05 '20 at 08:10
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    @SF "I’ve had three buttons to press in the past five-hundred light-years and that was just to put the coffee machine on to manual." – SusanW Aug 05 '20 at 23:51
  • "After the Columbia failure, provision was made to fly a damaged Orbiter uncrewed back to a west coast landing site" - could you slightly elaborate on the connection here, please? Is the Columbia incident just mentioned for temporal context? Or is there supposed to be a causal link? (In the latter case, I don't see which one - surely, what was left of Columbia after breaking up could not have been remotely controlled to fly back any landing site, so loss of the crew on board would have been a secondary problem.) – O. R. Mapper Aug 06 '20 at 08:04
  • @O.R.Mapper 'supposed to be a causal link'; it was only after the Columbia failure that the heat shield started being inspected in space every flight and the safe haven procedure of waiting in the ISS was started. If the inspection found unsafe damage the crew would hunker down in the ISS till rescued and the damaged Orbiter could be flown back empty. This is a brief summary; fixing the damage was possible in some cases. If this explanation is not clear please ask a new question. – Organic Marble Aug 06 '20 at 10:15
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    @OrganicMarble: Aah, all clear then, thank you. The bit I was missing was that "damaged Orbiter" did not refer to the broken up Columbia, but to the initial damage that caused the accident, which could have been detected in orbit before departure. – O. R. Mapper Aug 06 '20 at 10:41
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The Space Shuttle was America's only crewed spacecraft to fly crewed from the very first flight. Commander John Young and pilot Robert Crippen flew an historic and heroic flight. They were accommodated with ejection seats although over most of even the early flight profile would likely have been at mortal risk ejecting from the vehicle. I had the pleasure in 1981 of Bob Crippen's company over lunch and he confided that once the countdown passed the final possible abort time (at T-31 seconds), his heart rate jumped instantly (in a heartbeat so to say) from 60 BPM to over 120.

called2voyage
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David H.
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  • T-31, but cool story. https://www.space.com/12186-space-shuttle-launch-countdown-minutes-liftoff.html Several things could, and did, stop the count after that. – Organic Marble Aug 04 '20 at 16:10
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    The barrier at T-31 sec (thanks for the correction) was the final check of the three redundant flight computers. If each agreed at this point the countdown proceeded to flight but the failure of individual systems, as now, would have been cause for termination. Of course, once the solids were lit, after the liquid fuelled engines had stabilised, nothing could stop the launch. – David H. Aug 04 '20 at 16:23
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    There were four redundant flight computers plus a fifth backup. – Organic Marble Aug 04 '20 at 16:41
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I think this question sounds strange to many, but I'm not clear if the Space Shuttle could and was ever used without a Crew.

That depends on your definition of "used", I guess. Several Orbiters are currently "used" as museum exhibits without any (flight) crew.

And what was the smallest and the biggest crew size it ever flown?

That depends on your definition of "flown". During ferry flights on the Shuttle Carrier Aircraft, there was no crew on board the Orbiter. It also depends on your definition of "crew", because there was a flight crew on the SCA for those flights.

It was, however, not capable of autonomous operation. For that, it always needed a crew. (In particular, it had to be landed by a human pilot.)

This is in contrast to the Soviet Buran, which was capable of autonomous operation, and in fact had its only flight without any crew, and also the unofficial successor to the Shuttle, the Boeing X-37, which doesn't even have the possibility of carrying a crew.

Jörg W Mittag
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    This is a cute answer, but its fairly clear from the question that "used" means "to be launched, orbit in space, and returned to the ground" The last two paragraphs are where your useful answer is. – Criggie Aug 04 '20 at 12:44
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    pointing out problems in the question should be done in the comments –  Aug 04 '20 at 15:53
  • I agree, this author needs to kill some of their work, hard though that may be. – Harper - Reinstate Monica Aug 05 '20 at 02:29