How many men or women does it take to fly an interstellar space ship?

Question

On a non-scheduled flight, would an interstellar space ship need an active crew consisting of a captain, several officers and a number of technicians, similar to the bridge of the Enterprise, or would one pilot, with maybe a replacement for emergencies, be enough, similar to yachtspeople navigating earth's lakes and oceans alone?

This question only pertains to the flying of the ship, not catering to the passengers, maintenance etc.

Countless unmanned probes have proven that navigation in space is a task which can be adequately handled by autonomous computer systems. — Philipp, Jan 17 '14 at 13:32
But those probes travel within sight of Earth's telescopes. Beyond that, an auto-pilot would have to react to other objects in space that where not visible from Earth (or any other starting point). I'm sure stones smaller than 50 km are dangerous to a space ship, see: http://curious.astro.cornell.edu/question.php?number=588 And while a computer might recognize and react to flying rocks, I have no idea if there might be other things that would make a course correction (or return) necessary. — , Jan 17 '14 at 13:44
a computer system could detect and react to an asteroid on a collision courses much quicker and more efficiently than any human pilot. Besides, the further you are away from a large gravity well (planet or star) the less asteroids you will encounter. — Philipp, Jan 17 '14 at 14:09
How many people does it take to paralleled park? 10 years ago, it took at-least one... now cars can PP solo. 10 years from now, cars will be able to presumably drive themselves - making all the pertinent decisions. Similar, how will cars deal with "unforeseen consequences" like cats, birds, kids, other cars? As the tech expands, properly tuned AI should be able to adjust accordingly. Expand this kind of tech into space ships and it's easy to think that at some point fully autonomous ships will be possible. — WernerCD, Jan 17 '14 at 16:21
Okay. I know I must appear to be pathologically stubborn, but I want to make sure nothing has been overlooked. Since humans built roads and since we have travelled all the roads that we built and encountered all the probable obstacles that a car might encounter about a million times, we know what eventualities we need to program a computer driven car for. But we have never been to outer space, and even after travelling outer space for a hundred years we will not have seen everything that might happen there, so how are we going to program a computer to deal with what we don't know might happen? — , Jan 17 '14 at 16:39
Or do you really think that, as gerrit put it, outer space is "particularly dull" and nothing eventful will happen there (to a ship)? — , Jan 17 '14 at 16:41
@what: Anything invisible from earth is by definition small, and therefore easily avoided by steering left, right, up or down. Space is incredibly boring compared to earth surface. — MSalters, Jan 17 '14 at 17:12
I think stuff near Alpha Centauri is not necessarily small, just because we cannot see it from earth, @MSalters — , Jan 17 '14 at 18:02

score 18 · Accepted Answer · edited Apr 13 '17 at 12:58

18

Zero.

Voyager 1 has left the solar system, and is therefore an interstellar spacecraft. I'm not sure what qualifies a ship, but there is no reason why it would take any humans. Nor do yachts (or cars) need humans for navigation, for that matter.

Interstellar space is particularly dull. You'll be travelling for many years with absolutely nothing happening. To employ a human to fly a ship would quite literally mean letting him or her sit there from birth to death with no events happening for his or her entire life. You can't do that to people. That's what computers are for.

The comment by Mike Adler is a good addition, and I will quote it here in its entirety:

Autonomy is always with respect to a time scale. By necessity, spacecraft have always been autonomous on the minutes time scale. Modern spacecraft are autonomous on the days to weeks time scale. Rosetta took care of itself for more than two years. I would expect an interstellar ship would be designed to be autonomous over much longer periods, but would be designed for Earth to check in once every decade or so to see how things are going, and reprogram around any issues uncovered. The "crew" may very well be frozen embryos, awaiting blastulation upon arrival.

edited Apr 13 '17 at 12:58

Community

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answered Jan 17 '14 at 13:09

gerrit

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So you say there are no unforeseen obstacles on interstellar flight that a computer cannot deal with? – Jan 17 '14 at 13:38
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@what there are none a human could deal with any better. Except for technical issues with the spacecraft itself, of course, but you excluded maintainance from your question. – Philipp Jan 17 '14 at 14:23
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To be fair, there are several people currently flying Voyager 1 and 2. But the gist of the answer is still correct. – Mark Adler Jan 17 '14 at 17:16
@MarkAdler That raises the question, what constitutes flying a spacecraft? – gerrit Jan 17 '14 at 17:42
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It's worth noting that this answer, while entirely correct for our current understanding of physics, doesn't address the potential that some as-yet-undiscovered method of FTL travel (as is standard in science fiction) could require an Enterprise-sized crew. – Bobson Jan 17 '14 at 19:10
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@Bobson That's speculation, but I'd have a hard time imagining that in a speculative future and speculative technology, speculative computers wouldn't be better than humans at performing this task. – gerrit Jan 17 '14 at 22:14
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@Bobson The Enterprise does not have a crew it has a cast. – James Jenkins Jan 18 '14 at 01:48
@gerrit - There's definitely science fiction which postulates FTL methods where a computer either can't function, can't even see the same things as a human, or would otherwise be incapable. They're generally the ones that come down harder on the "fiction" side of the spectrum than the "science" side, though. – Bobson Jan 18 '14 at 23:41
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@MarkAdler That makes me wonder. If we had a manned interstellar ship, who would pilot it? A team on Earth or a team on the ship? Even if a method of suspended animation was used, a rotating crew could still operate the ship (assuming that suspended animation could be exited and reentered multiple times). – called2voyage Feb 04 '14 at 20:56
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That is assuming that autopiloting doesn't advance enough to not need any human maintenance by the time a manned interstellar ship is possible. – called2voyage Feb 04 '14 at 20:57
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Autonomy is always with respect to a time scale. By necessity, spacecraft have always been autonomous on the minutes time scale. Modern spacecraft are autonomous on the days to weeks time scale. Rosetta took care of itself for more than two years. I would expect an interstellar ship would be designed to be autonomous over much longer periods, but would be designed for Earth to check in once every decade or so to see how things are going, and reprogram around any issues uncovered. The "crew" may very well be frozen embryos, awaiting blastulation upon arrival. – Mark Adler Feb 04 '14 at 21:20
@gerrit I think the above information from Mark Adler would be great to have in your answer! – called2voyage Feb 05 '14 at 16:27

score 5 · Answer 2 · edited Jun 17 '20 at 08:54

Defining a ship

If defining a ship as having a minimum of one human crewman...

No FTL

In the absence of FTL drives, a minimum for an active human crew is however many are required to perform the maintenance tasks on the life support, drives, and power systems.

Since this is extremely variable based upon automation and durability, what can be said is merely "you need engineering crew."

Human need to interact

Given human need to interact, this sets a further minimum crew standard. The military has had a number of small outposts for years. Minimum crew size for these correlates directly to maximum duration of assignment. A 4-5 person crew tends to start experiencing issues between 2 and 6 months deployed in isolation, even with routine work contact via radio with outside persons. A 20-30 person crew can go for 4-6 months before similar issues. After this initial period of troubles, many crews are able to work things out, and a stable long term status quo evolves; but when it doesn't, the results are often tragic. NASA long term missions have typically been 3-5 person crews, and the crews have been put in isolation for the requisite several months during training; those who can't handle it have been weeded before flight.

In looking at small communities, the smallest psychologically stable communities appear to be in the range of 20-30 people; smaller communities (such as McGrath, Alaska) tend to be stable until some stress, then violence happens; usually a new stable evolves shortly thereafter. The problem being that a spacecraft can not afford such violence.

So, for an STL ship, you'll want at least 20 active persons, rotating which 20 if practical, in order to maintain the hamlet level of community which seems the minimum for long term psychological stability.

Colonial Genetic Stability

Since any mission to another star system in an STL craft is likely to be one-way, the overall mission crewing needs to be considered as well. And the limit there is the genetic viability of the colony. If completely unrelated individuals and absolute breeding authority can be presumed, as low as 30 individuals may be viable. Long term, the lowest genetically stable populations in isolation seem to be about 100 individuals - a small village level, or several hamlets. At about 200, consanguinity selection for the colonists sent is a low priority.

FTL - Alcubierre-White Warp Drive

Assuming Dr. White's assumption of 10C capability is correct, this puts many nearby stars under a year away. Within a year, the technical needs of the hardware trump the psychology of the crew. Keep them busy, and each with private space, and a crew of 3-5 should be functional long term. Even up to 2 years, to allow for a round trip, a Warp Drive at 10C can reach any of a dozen stars, specifically, any of 9 systems.

We can't yet estimate the requisite engineering/maintenance times.

We can note that, unlike STL ships, not all are one-way trips. Therefore, the colonial need is also able to be ignored.

FTL - other

There is no other FTL drive thought feasible at this time. Therefore, no practical considerations can be made.

Very useful answer. Thank you, @aramis. If I hadn't specifically asked for the flying (i.e. navigation) of the ship only, I'd accept this answer. — , Feb 05 '14 at 07:50
@what - the answer to that portion is ¶ 2 & 3... Navigation isn't needed. Maintenance is. — aramis, Aug 13 '14 at 09:38
The plans for the (scrapped) Apollo Applications manned Venus flyby called for a three-man mission lasting approximately 13 months. That crew would essentially have been isolated; while radio communications certainly would have been a possibility, time delay would make voice communications basically impractical, meaning text-based communications methods (some form of "email over radio") would have been the most that was readily doable. This is similar to what you describe under the Alcubierre-White heading. — user, Jan 23 '15 at 09:47
Note that FTL is not required for human lifetime journeys to other stars, because of relativistic time dilation. "All" that is required is sustained acceleration to get highly relativistic velocities. This would not be possible using any kind of known onboard fuel, as fusion would only be good for a low fraction of c, and antimatter a high fraction. Putting aside that little problem, with a hypothetical free-energy drive and enough acceleration a ship could get anywhere in the universe in an arbitrary short timespan from the perspective of the passengers. — Blake Walsh, Jan 23 '15 at 12:00
Blake, A human lifetime mission generally implies both for the people aboard and for the people back home. Further, any real speed fast enough for dilation to significantly extend lifespan will also be fast enough to irradiate into non-existence the crew, and render the front shielding plate not only non-optional, but positively ablative. That front shield also has to be mirrored on the back end; without Alcubierre-White FTL, Alpha Centauri is over 100 perceived years away given a 0.01% payload fraction and the best delta-V we can muster. (And will take about 110 years back home.) — aramis, Feb 07 '15 at 08:03

score 4 · Answer 3 · edited Apr 13 '17 at 12:58

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Technically, no human presence is required, as elucidated by the previous answer. However, if one considers the subset of manned interstellar missions:

Assuming Sonny White doesn't figure out FTL in the next couple of years, current and near-term technology in propulsion systems dictate an extremely long duration for any interstellar flight. Even the Icarus Interstellar team, the folks redesigning the Daedalus probe, assume a flight time to Alpha Centauri of 100 years. Thus the question of crew size for a manned interstellar mission is either determined by progress in suspended animation (sleeper ship), or minimum population size for genetic viability after a given number of generations (world ship).

Some light on the second option can be found here: What is the smallest number of humans required for colonization?