What will real space vehicles look like in the future?

Question

Most sci-fi today is imho unimaginative and unrealistic when it comes to future orbital and interplanetary vessel design.

What will spaceships and habitats look like when we build them in zero-g using vacuum deposition techniques and materials mined from asteroids? Gone are the familiar cylinders, wings, aerodynamics which are all legacy to an atmosphere. Gone too are spindly thin constructions, since construction material mass will be plentiful (when mined from asteroids).

I don't think vehicles will be long with engines on the end. This means the crew would be constantly climbing ladders and using elevators when under thrust.

This leaves squat, fat blobs. Who has explored this area the most, where can I find the best collection of well thought out plausible designs?

Answer 1

This is a bit of a frame-shift answer. I am answering as a space enthusiast, but also as a person at an aerospace company.

Let's not dismiss the simple shapes, such as cylinders, as hangovers from aerodynamics too quickly! There are some important considerations, even with plentiful material and practically no gravity, which may lead to simple shapes (cylinders, spheres, rectangular prisms) dominating spacecraft development.

Center Of Mass and Center Of Thrust

There are still virtues in aligning center-of-thrust and center-of-mass, like not spinning out of control! For those unfamiliar with these terms, the center of mass is the 'middle point' of all your mass, and center-of-thrust is where your 'push' from your engines points to. Not lining these up results in your spacecraft spinning, so something needs to be done to counteract this. A design which avoids spending more fuel to counter any moment/torque produced by oddly-placed engines on oddly-placed shapes will be preferred over others.

It turns out if you build a known shape, (such as a sphere, a cylinder, a brick) you have a decent idea of where the center of mass and center of thrust could be. This even accounts for odd loading! If you build an irregular shape, you need to do a lot more math to account for mass distribution and thrust. Depending on loading, even rockets with gimbals (ones whose nozzles can point) may not cut it on these eccentric shapes.

This issue gets compounded if the engines used cannot be throttled or more than one engine needs to fire for 'forward' motion. Odd shapes could easily rely on multiple engines for simple 'forward' motion to account for loading or structure. This introduces more failure points, which is a less robust design, which mean it will be less favored by practical design. Further, if the engines' output must always be full blast or nothing (no throttle), good luck getting 'backup' engines in the correct place. Simple shapes usually mean you need less engines for 'forward' motion and rely on modest gimbaling to account for a lost engine or irregular loading.

You Still Need to Build It

Hey, there may be a galaxies' worth of material out there, but you still need to put in the time and effort to build the ship. That still costs something; time, possibly money, and certainly resources.

It turns out simple shapes allow you to minimize the amount of material while still getting the volume you want. Okay, maybe ships will not always a brick or spheroid, but these shapes do have nice volume-to-surface area ratio compared to others!

Mechanical Stability Considerations

It is cool that your spaceship looks like an anemone, but it bends like one, too. That is not fun when your mess hall is on one tentacle, sleeping quarters on another, and your pilot is on another. Poor Bill had to wait until the acceleration maneuver was finished (which was a full year!) before the hall to his quarters bent back into shape. That is better than Steve- his tentacle just snapped off during the last emergency correction.

Maybe if the ship was a simple shape to bear the loads of thrusting and maneuvering, issues like this would never happen. Something like a spheroid or rectangular prism... These shapes are capable of supporting themselves with less material and clear load paths when compared to something more spindly.

A more robust shape may allow for more aggressive maneuvers for less material (or 'primary structure'). Less primary structure means more room for payload or yet higher acceleration maneuvers. Overall, these things are desirable for most spacecraft.

Thermal Considerations

You need to be careful about your thermal control surfaces. If a radiator (to get rid of excess heat, one of the only ways in space to do so) is next to your thermal camera, all you will see is your radiator. How do you avoid this?

You choose a shape which have surfaces pointing away from each other. Spheroids, cylinders, and cubes do not have this issue. The other solution is to have 'cleverly placed' sensors, which does open up some possibilities for odd shapes. (See ISS- not all of those panels are solar panels!)

Answer 2

One reason (well a couple of related reasons actually) why ships designed to operate beyond Mars WILL be long and spindly is they will probably have a nuclear powered engines. In that case you will want the Red Hot Glowing Nuclear Death as far from the crew compartment as possible. This is because you don't want to shield the whole reactor (shielding is heavy and every gram counts) so you will use a Shadow Shield just big enough to ensure the crew compartment is in the shadow. The further away the reactor and shield are, the smaller the shield can be, but equally you want the structure to be as light as possible too, or it will end up weighing more than the shield would.

Therefore you end up with the engine (or at least its power supply) on the end of the longest, lightest possible boom that is strong enough to do the job, and a long spindly ship...

Habitats of course are not as restricted on their mass budget and may well have more freedom of form, although as pointed out by PipperChip in their excellent and comprehensive answer, spheres, cylinders and the like are well understood engineering forms with good surface to volume ratios and other desirable characteristics, so are likely to be preferred for those reasons. Plus, if the habitat is large enough, a cylinder can most easily be spun to produce artificial gravity.

As for "...the crew would be constantly climbing ladders..." Near future space craft are likely to use very efficient engines that consume little propellant, but also have very low thrust. Accelerations are likely to be well below one tenth of a G, so crew should be able to pull themselves along quite easily.