You know how sometimes you get a really stupid idea in your head, and it won't just go away until you, somehow, act upon it? Not only is this the story behind 90% of swastika tattoos, but it's also the story behind this post you're reading right now. In this case, the idea is this simple question: if you had to make an actually-produced spaceship into a car, what would be the best choice?
I think this is one of those rare hypothetical questions that actually has a pretty clear, definitive answer, and I think the equally hypothetical result is satisfying as well. There's not all that many actually produced and used spaceships in the first place, and the pool of ones small enough to be effectively converted to automobile use is even smaller.
So let's see what our options are. These are all the types of manned spacecraft so far used by humans for at least Earth-orbital operations: Vostok, Mercury, Vokshod, Gemini, Soyuz, Apollo, the Space Shuttle, and Shenzou... and that's pretty much it, at least for ones that actually were used for multiple manned missions. Of these, I'd say almost any of these craft's return modules except for the Space Shuttle is roughly small enough to be mounted on a reasonably-sized car chassis. Well, maybe not the Apollo CM. That thing was pretty big.
So, leaving out the Shuttle and Apollo, we have a number of options: Mercury is probably too small, both Vostok and Vokshod's return modules were perfect spheres, making them somwehat tricky to adapt to a car. That leaves the Soyuz, Shenzou, and Gemini.
Of these three, both Shenzou and Soyuz' return modules share a common shape: a sort of gumdrop/buggy headlight shape. It's an ideal shape for atmospheric reentry, but it's just not right for use as a car. It's too round in plan, too cramped, and it just doesn't feel car-like enough.
Which leaves us with Gemini, which is fortunate since that is exactly the one I think would be perfect. Gemini was already thought of as the most sports-car like of the early manned capsules, and it's one of the few capsules designed to have as its default orientation horizontal, like a car. It's a two-seater, with gullwing doors, so you'll look plenty stylish as you orbit earth at an altitude of a foot or so.
Plus, the Gemini is the only one that in the horizontal position has forward-facing windows. Forward-facing windows are one of those details in a car that I always seek out. I can't speak for everyone, but for me, the ability to see the road ahead of me just makes the driving experience that much more fulfilling.
The dimensions of the Gemini reentry module — there were service and retrorocket modules on the usual setup as well, both of which would burn up in the atmosphere — are roughly car-like as well. from blunt nose to heat-shield end, the Gemini was about 11.3 feet long. That's pretty car-like. Maximum width is a bit healthier, around 7 feet or so, which would make it right around the width of a Hummer. Still, that's the maximum diameter of the circular cross-section, so it's not a big wide box like the Hummer is. That would be the maximum height as well, being, you know, basically cone-shaped.
The nose is a much more manageable 3 feet in diameter. Based on these dimensions, I'm pretty sure if you were lucky enough to get ahold of an old Gemini capsule and wanted to stick it on a car chassis to, you know, promote your science museum, it'd be possible.
If I was doing it — sorry, when I do it — I think I'd take the easy nostalgic route and use the period-correct method for making weird things into cars: stick it on a VW Beetle pan. This was the go-to starting point for all manner of kit cars from the 60s-80s, and it'd be my solution, because even while daydreaming I'm cheap, a bit lazy, and not 100% on my custom-chassis fabrication skills. Also, historically, the inside of the Gemini was almost always referred to being about the size of the inside of a Volkswagen, so there's some historical synergy there. Of course, there's many other options — I encourage everyone to find something that works best for them.
Size-wise, despite the fact that my drawing is significantly out-of-scale, I think it's do-able. The Beetle pan from transaxle-holding fork to frame head is about nine feet, which would work to support the capsule and let a couple feet of nose extend in front, between the shock towers. My drawing doesn't show the width properly, as there'd be more signifiant side overhangs unless the chassis was widened. Which I, um, did for the drawing.
You'd want to lighten and gut the capsule, of course, and you could mount a fuel tank in the nose, and you'd have to cut holes for the (quite raised) pedal box, steering column, shift linkages and throttle, clutch, etc. cables. You could share holes for many of these, to minimize alteration to the capsule beyond, you know, turning it into a car.
Engine-wise, an outboard rear engine like on a Beetle (or 911, or Corvair) works well because you can just box the engine up and stick it behind the heat shield at the rear, without messing up the look of the capsule too much. Plus, an air-cooled engine means you don't have to find a place for a radiator or any of the associated plumbing. It probably won't be quick, but, come on, we're not racing our historic spaceship-car.
So, I'm pretty sure you're convinced, so how can you build one? Well, getting a VW or Corvair pan/engine (or whatever you decide) is easy enough. For Gemini capsules, you actually have your choice of institutions to pester. In fact, here's a list. My suggestion would be to call the Michigan Space Center, which has an unflown testing vehicle not currently on display, according to that list. I bet they'd love to get that thing out of the basement and onto the road!
Anyone have a better idea? Got a plan for a Soyuz-capsule on a Pacer platform, with an LS1 in it? I'm all eyes here, so let's see what you think!