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Given how much engineering has advanced since the days of the Mercury program, could a similarly scaled single-person orbital vehicle capable of repeatedly sustaining 48 hours in orbit realistically be constructed as a backyard/garage project by a dedicated and knowledgeable DIY team?

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    $\begingroup$ While cool at the moment this would be a very opinion based question, the intended site format is intended to produce a single 'right' answer which is tricky at the moment. Suggest defining a target capsule mass? If arbitrary mass is allowed this becomes quite feasible just by over-engineering everything. If constrained to the mass of the historical Mercury than answer is a solid no due the small margins. Would also be useful to define number of test launches before it flies manned - given a dozen or so test flights much becomes possible - if it has to work first go not so much. $\endgroup$ Nov 30 '20 at 14:14
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    $\begingroup$ Technology aside, you'd quickly get a visit from some serious men in black suits, regarding the missile you're building. $\endgroup$
    – SF.
    Nov 30 '20 at 14:42
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    $\begingroup$ Are you talking about just the spacecraft, or an orbital booster as well? $\endgroup$ Nov 30 '20 at 15:19
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    $\begingroup$ Capsule only. Not necessarily a capsule form either, a mini X-37 or small-scale Dreamchaser would work. $\endgroup$ Nov 30 '20 at 18:56
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    $\begingroup$ Not sure how 3D printing would help much. I have heard of 3D printing of engine parts, but the launcher is excluded. The toughest part of a capsule may well be the heat shield - and due to the heat that it has to handle, I'm skeptical that 3D printing (which is largely though not entirely based on depositing melted materials in place) would help much with that. $\endgroup$ Nov 30 '20 at 21:16
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(Too much for a comment)

You have excluded the launcher but there are still some very important unknowns in your problem:

At the most basic situation the answer is yes. What's needed to keep someone alive in space for 48 hours is well within the range of DIY work by someone sufficiently qualified. You need a pressure hull, 48 hours of air, temperature control and a toilet of some sort.

Your air system can be pretty much off the shelf--a rebreather for scuba diving provides everything you need, just adapt it to blow into the capsule rather than a mouthpiece.

Temperature control can be some white shutters over black panels, combined with a slow roll like Apollo did.

A toilet can simply vent urine and use the yucky Apollo fecal collection bags.

There are three additional aspects to a space capsule, though, and you haven't defined if they're needed.

  1. Attitude control. Two options here:

1a) Reaction control systems. Now we are getting into some nasty territory. Hypergolic propellants are nasty, nasty things and I would be surprised if your backyard engineers can even get their hands on them, nor are the likely to have the equipment to safely handle them.

1b) Wheels. Slow, but so long as that is acceptable they'll work. Three electric motors simply turning weights will do it.

  1. Deorbit burn. Wheels won't help you here, you have to go with rockets--this could be the same ones used for reaction control, although the shuttle used bigger versions of the same idea.

  2. Reentry heating. Highly specialized materials and I would expect some three-letter guys (look at the various government security agencies--most of them have three word names, normally abbreviated to three letters) to come knocking on your door if you even try to get them. You also have no feasible means to test your design even if you get the material.

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  • $\begingroup$ If you don't care about how heavy the system is, heat shielding isn't a problem. Refractory bricks intended for something like a smelter or kiln should work, and I wouldn't be surprised if you could get away with something as primitive as a good, thick layer of oak. $\endgroup$
    – Mark
    Dec 1 '20 at 4:01
  • $\begingroup$ Agree these are areas more challenging than others and hypergolic fuels are out. In addition to reaction wheels, could a cold gas thrusters meet this need? They're coming along - see spacenews.com/spacety-thrustme-cold-gas-test Deorbit burn - solids? Reentry shield - this seems the most likely part to be overbuilt. Shields with phenolic resin and fiberglass have a solid track record and both ingredients are widely available - phenolic resin is used to make countertops now. Heatshield grade fiberglass might be harder to come by, thus the potential need to overbuild. $\endgroup$ Dec 1 '20 at 4:11
  • $\begingroup$ @Mark Overbuilding makes it easier but doesn't address the problem that the primary job of the shield is to reject the heat in the first place. The capsule is carrying enough energy to vaporize it, that energy must be rejected into the plasma that surrounds the capsule rather than allowed in. $\endgroup$ Dec 1 '20 at 4:34
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    $\begingroup$ Obviously reaction wheels and cold gas thrusters aren't solutions for the deorbit burn, those are intended for attitude control. I suggested solids for the deorbit burn. Shield - one of the main functions is to form a bow wave that prevents most of the heat from reaching the capsule. This work has been done since the mid-50s. Shaped correctly and built carefully, it appears doable. See: thefreelibrary.com/… $\endgroup$ Dec 1 '20 at 4:55
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    $\begingroup$ Mark's comment about a slab of oak - may we someday see an orbital version of "Will it blend?" "Let's try this trilayer of cork, dried cheese and old books on a 12" diameter test capsule, see how it goes," $\endgroup$ Dec 1 '20 at 5:55

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