Creating a model of a rotating space habitat in CoaDE
Dec 22, 2017 11:28:28 GMT
qswitched, apophys, and 6 more like this
Post by lucubratory on Dec 22, 2017 11:28:28 GMT
So I've been thinking for a while about what the design of a rotating space habitat on the small city scale would look like (~250,000-~450,000), with some small amount of delta-v and general stationkeeping aids, like a laser battery. Because I've recently discovered CoaDE I decided to try modelling an approximation in it. I made this, the "Rotating Space Habitat" (original name I know), with a human carrying capacity of 240,000 according to CoaDE, and just under half a km/s of delta-v and 40x 100MW lasers. I used components from the [AE] standard library that was posted on here. Here are some pictures (I'm sorry I don't know how to hide them behind a spoiler tag, please let me know how and I'll edit them. Edit: thank you cosmogator!):
And this one:
There are a bunch of things that aren't accurate for this model. The actual concept is two equally weighted, 250m diameter cylinders ~400m long, rotating at 2RPM in the vacuum between the cylinders and the outer shielding (tentatively, the cylinders would have magnetic rail bearings like the ones in maglev trains connecting them to the outer shield, running on high-temperature superconductors, both around the cylinder and in circles at the endcaps). They're connected to each other through their magnetic bearing connection to the outer shield, and so in counter-rotating they cancel out the negative gyroscopic destabilisation caused by their aspect ratio. The rotating cylinders are structural steel, and this is the major area of inaccuracy I think is in the model. I'm not very familiar with CoaDE, so to get that 250m diameter I had to give the 20*1000*3 crew modules 10m steel plating. I'm not envisioning empty cylinders of grassland, more like an urban end that probably would have an internal steel latticework and a high bio-diversity end, in each cylinder. Even for very conservative estimates of atmosphere, water, landscape, flora & fauna, and habitat mass, a 10m outer shell of steel would be an extreme level of overkill in terms of structural safety factor, and this design using CoaDE has two or three orders of magnitude more mass than that because each 1000 crew module has 10m of steel plating. I think ~two metres would still be an order of magnitude more than necessary with a decent safety factor for the rotating cylinders themselves. For the outer armour shell which isn't rotating, it would need considerable structural strength to maintain the load of moving the cylinder's inertia and preservation of angular momentum, and de-spinning the cylinders via their magnetic bearings would have to be done extremely slowly so that the exterior armour shell doesn't get ripped in half. Thankfully, despinning the cylinders should not need to be done particularly often as the temporary loss of gravity in the habitats (for hundreds of thousands of people) would be a severe enough consequence that a structure like this would need to be designed to almost never stop spinning, which should be easy in frictionless conditions.
The outer shell in this model is actually not that different from the concept. It would be hydrogen tanks, because volume is not a concern, hydrogen provides excellent shielding properties per unit of mass from both radiation and micrometeoroids, and because the engine can use it as propellant. The lasers and radiators are all pretty similar to what the concept would be, except the lasers would be spaced around the vehicle partially to provide better protection, as would the NTRs as vernier thrusters - I ran into issues doing this because CoaDE thought the components were intersecting when they were on the same circular plane, not sure why. I thought about liquid droplet radiators instead of stiff radiatiors, but honestly they're quite small and unlikely to be an issue for the station in any feasible situation that wouldn't also be catastrophic for the inhabitants. I think LDRs would have at least one use in the concept, though: transferring heat from the rotating cylinders to the outer shell. The centrifugal force should be more than enough, and they can be collected in a circular trough and then run through a heat exchanger with the outer radiator system.
The design as-is in CoaDE uses 4x 1GW powerplants, which are capable of running the components in-game, but I strongly suspect more power generation (and storage) would be necessary in the actual concept for maintenance of the magnetic bearings, and provision of light and electricity for both industrial and ecological processes, in the cylinders and in the plate between the cylinders which would house true zero-g industry (there would be zero-g in the exact centres of the habitats, but it wouldn't be stable due to drag with the rotating atmosphere - high quality zero-g work would need to be done in a compartment decoupled from both rotating habitats). That central section is where I chose to place power generation, to minimise transmission losses (the entire structure is ~1.6km long). Ideally, this would be a fusion plant or two, supplying power for the whole vessel and able to run off the hydrogen-deuterium fuel for, back of the envelope calculations, billions of years (I imagine other concerns would probably cause issues before that, like maintenance and whether or not the sun is getting too hot).
The design in CoaDE also uses NTRs for thrusters, pictured primarily for stationkeeping of such a massive structure in orbit around the sun (solar power is totally viable in addition to the fission or fusion reactors, too - I would probably have a very high surface area, low weight deployable mirror and photovoltaic setup for industrial processes that require very high heat or power). They produce (if I'm reading the interface right), 3.62mg of thrust. That seems really high for the mass of this thing, and I suspect it might be an overflow or potentially me not knowing what that little subscript 0 means. In reality, the thrust for stationkeeping would probably best be provided by those electric thrusters. If the magnetic bearings could handle it, some degree of (small) acceleration to actually travel may be possible, and the limiting factor would then be what lateral g-forces would be acceptable in a 1G rotating habitat. I suspect anything over a mg would produce noticeable effects, probably on bodies of water, and may be dangerous for people in the urbanised areas and deleterious to the local wildlife on the ecological end of each cylinder. A good real-world example could be the effects and magnitude of the moon and sun tides that we experience now - I don't know what their magnitude is, but we can probably take them, add them together, and say that value, at least, is a safe lateral acceleration for a rotating habitat. Provided the magnetic bearings can take the load - I don't know what the maximum theoretical loads maglev trains can take is, and how much power it would draw. I suspect that even if nuclear fusion thrusters that are direct (not electric) are feasible, the amount of thrust they would provide would fall outside what the magnetic bearings can support, so some sort of electric thruster could potentially do the job.
I'm still investigating and putting all of this together; I very much welcome input, feedback, criticism, knowledge etc. In particular, I'm wondering if a more realistic mass estimate could be achieved by somehow making crew modules (or maybe propellant tanks) actually to size (250m diameter). I've got the equations for figuring out hoop strain, breaking in tension, etc somewhere around here, and could pull them out to figure out exactly how thick the cylinders's walls would need to be.
Finally, because this is a military game for many of you: one of these cylinders (or a few from the same federation, or one using the same principles but much larger, and so on) could hang in orbit around a planet using their considerable industrial and population base to both begin deconstructing nearby planetary bodies to produce materiel and train actual military personnel in numbers that could be sufficient to occupy a planet properly. Destroy all major rocketry, air bases, military manufacturing etc with orbital bombardment, send in mass manufactured and real-time controlled UAVs to destroy military opposition in detail and begin the process of negotiating local surrender, and simultaneously train a human invasion and occupation force (even born and raised and trained in their gravity) for the beginning of actual administration of the occupation. I would say the majority of crushing military victories in history have been caused by a confluence of strategic opportunity, economic ability, and logistical competence. Having control of orbit gives an obvious strategic advantage, but if your whole economy and thus your very short logistics chain is with you there in orbit the rest of the ingredients are there as well. I'm primarily interested in structures like these because they're wonderful and I think living in space is the future of humans, but they would also be a strategically terrifying opponent for those planetside.
The outer shell in this model is actually not that different from the concept. It would be hydrogen tanks, because volume is not a concern, hydrogen provides excellent shielding properties per unit of mass from both radiation and micrometeoroids, and because the engine can use it as propellant. The lasers and radiators are all pretty similar to what the concept would be, except the lasers would be spaced around the vehicle partially to provide better protection, as would the NTRs as vernier thrusters - I ran into issues doing this because CoaDE thought the components were intersecting when they were on the same circular plane, not sure why. I thought about liquid droplet radiators instead of stiff radiatiors, but honestly they're quite small and unlikely to be an issue for the station in any feasible situation that wouldn't also be catastrophic for the inhabitants. I think LDRs would have at least one use in the concept, though: transferring heat from the rotating cylinders to the outer shell. The centrifugal force should be more than enough, and they can be collected in a circular trough and then run through a heat exchanger with the outer radiator system.
The design as-is in CoaDE uses 4x 1GW powerplants, which are capable of running the components in-game, but I strongly suspect more power generation (and storage) would be necessary in the actual concept for maintenance of the magnetic bearings, and provision of light and electricity for both industrial and ecological processes, in the cylinders and in the plate between the cylinders which would house true zero-g industry (there would be zero-g in the exact centres of the habitats, but it wouldn't be stable due to drag with the rotating atmosphere - high quality zero-g work would need to be done in a compartment decoupled from both rotating habitats). That central section is where I chose to place power generation, to minimise transmission losses (the entire structure is ~1.6km long). Ideally, this would be a fusion plant or two, supplying power for the whole vessel and able to run off the hydrogen-deuterium fuel for, back of the envelope calculations, billions of years (I imagine other concerns would probably cause issues before that, like maintenance and whether or not the sun is getting too hot).
The design in CoaDE also uses NTRs for thrusters, pictured primarily for stationkeeping of such a massive structure in orbit around the sun (solar power is totally viable in addition to the fission or fusion reactors, too - I would probably have a very high surface area, low weight deployable mirror and photovoltaic setup for industrial processes that require very high heat or power). They produce (if I'm reading the interface right), 3.62mg of thrust. That seems really high for the mass of this thing, and I suspect it might be an overflow or potentially me not knowing what that little subscript 0 means. In reality, the thrust for stationkeeping would probably best be provided by those electric thrusters. If the magnetic bearings could handle it, some degree of (small) acceleration to actually travel may be possible, and the limiting factor would then be what lateral g-forces would be acceptable in a 1G rotating habitat. I suspect anything over a mg would produce noticeable effects, probably on bodies of water, and may be dangerous for people in the urbanised areas and deleterious to the local wildlife on the ecological end of each cylinder. A good real-world example could be the effects and magnitude of the moon and sun tides that we experience now - I don't know what their magnitude is, but we can probably take them, add them together, and say that value, at least, is a safe lateral acceleration for a rotating habitat. Provided the magnetic bearings can take the load - I don't know what the maximum theoretical loads maglev trains can take is, and how much power it would draw. I suspect that even if nuclear fusion thrusters that are direct (not electric) are feasible, the amount of thrust they would provide would fall outside what the magnetic bearings can support, so some sort of electric thruster could potentially do the job.
I'm still investigating and putting all of this together; I very much welcome input, feedback, criticism, knowledge etc. In particular, I'm wondering if a more realistic mass estimate could be achieved by somehow making crew modules (or maybe propellant tanks) actually to size (250m diameter). I've got the equations for figuring out hoop strain, breaking in tension, etc somewhere around here, and could pull them out to figure out exactly how thick the cylinders's walls would need to be.
Finally, because this is a military game for many of you: one of these cylinders (or a few from the same federation, or one using the same principles but much larger, and so on) could hang in orbit around a planet using their considerable industrial and population base to both begin deconstructing nearby planetary bodies to produce materiel and train actual military personnel in numbers that could be sufficient to occupy a planet properly. Destroy all major rocketry, air bases, military manufacturing etc with orbital bombardment, send in mass manufactured and real-time controlled UAVs to destroy military opposition in detail and begin the process of negotiating local surrender, and simultaneously train a human invasion and occupation force (even born and raised and trained in their gravity) for the beginning of actual administration of the occupation. I would say the majority of crushing military victories in history have been caused by a confluence of strategic opportunity, economic ability, and logistical competence. Having control of orbit gives an obvious strategic advantage, but if your whole economy and thus your very short logistics chain is with you there in orbit the rest of the ingredients are there as well. I'm primarily interested in structures like these because they're wonderful and I think living in space is the future of humans, but they would also be a strategically terrifying opponent for those planetside.
