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How tricky would it be for a stationary platform to focus sunlight into a beam with such optics? If it can be directly used, rather than requiring conversion to electricity then to e.g. a maser to transmit power, the system should be less complex (efficiency is a far less pressing issue in this case, given how much sunlight is available). Stationary platforms will not be so mass constrained, so they can be scaled up to ensure the same beam intensity whether around Terra or out at the Trojans or by Saturn. Illuminating a ship with 10kW/m^2 of sunlight should give pretty good power to mass ratio for its collection system...
Abiotic food might not be appetising for humans, but there may be a viable market for animal feed. We do eat a lot of eggs and fish after all, and meat (and other protein) production is the most resource intensive part of agriculture. Switching to synfeed for this would dramatically lower the land take.
The bigger issue is that compression requires heavy tanks. Maybe carbon nanotubes have changed that.
The other option is to use something like ammonia that can be liquified. Or ethane, even, though that doesn't provide any lift its about the same density as air.
Mark Carney? Not the same Mark Carney who was governor of the Bank of England? Oh so he is the same Mark Carney who was governor of the Bank of England. Huh.
Carnivores are pretty resistant to prion disease, as you'd expect from animals that subsist on eating other animals. Some humans are resistsnt to BSE (mad cow disease), which is a good thing because the British government almost killed the country off in the 90s, something we ought to have had executions for. A single amino acid substitution seems to do the trick , though you have to be homozygous for the resistance allele in order to be fully protected; in heterozygotes, there seems to be a delaying effect, we've had people dying from BSE a decade or so afterwards.
Prions are nasty things. Good candidate though for the poison in a retelling of Sleeping Beauty IN SPACE! Suspended animation should slow the spread, and 100 years of medical advancement might be able to treat it...
James Cameron, who loves submarines so much he makes films to fund his expensive hobby, insisted on the ballast release for his submersible being on its own circuit. His engineers wanted to all the electrics on the same circuit IIRC. A circuit which then failed whilst he was down there, proving that he was right to refuse them.
Re. the Titan submersible, I figured it had imploded when I heard what they were using for the pressure vessel, thanks to reading discussions on here about how composites respond to repeated pressure cycling.
A hovercraft might be able to do it. An Addis Single Rail Tramway, too. I expect ground conditions preclude traditional dual rail, but perhaps an Addis Tramway could do it, since there's no need to align rails. Just one rail to bear the weight and something vaguely road like for the balancing wheels. Might need quite narrow and long trains to keep the ground pressure low idk.
Going back to the older way of having walls radiating heat into the house.
You'd want to do this work at the same time as the other walls are being stripped for insulation I expect. I wonder if you could repurpose the underfloor heating kits to do it?
I recall talking about ceiling mounted radiators? Easier to retrofit and don't get covered up by furniture.
Hmm. If a habitat was built underwater, in a diving bell type arrangement, the sign of air leakage would be the water level rising rather than the pressure dropping. Possibly better for survival, since you have until you're up to your neck to find and fix the problem rather than asphyxiating when you've lost half your air. At any rate it should be easier to spot and straightforward to rig up an alarm for. But then, I guess that's true for air pressure sensing too.
Once you reach maybe 20-30mb, you can have water covering your habitat to provide the counterpressure. Hellas Basin is 7km down and has double surface pressure, so maybe 14km would do the trick to get stable ish surface water?
Obsessing somewhat over self launching gliders in recent days, though should I have the money to pursue flying I will probably go the microlight route rather than sailplanes -- as much as I wish to soar, I wish more to have consistent and reliable flight. But ultimately I want to be able to take advantage of both to have a small affordable aircraft that can use soaring flight to extend flight time and a motor to get between areas and avoid land outs.
Launch requires far more power than sustaining flight, which makes the low power density of lithium ion batteries a problem. AFAICT this is typically dealt with by having enough cells that you can get the power needed. But of course, there are other means to store energy. Could a flywheel provide the power needed to get off the ground?
It's certainly possible to launch a model airplane using a flywheel. It would be spun up just before launch, so losses to friction should not be too severe. In the air, a battery would power the sustainer motor. Perhaps it could be recharged in flight if a source of lift is available, enabling a generator to run during descent? True wilderness aircraft.
The viability of launch assist for SSTO would seem to depend a lot on whether its for humans or for dumb cargo. Containers of plastic or water or metal can take the high accelerations needed. Squishy humans cannot.
Fortunately, most of the stuff we need to get up there is stuff that can take the high accelerations, especially if we can turn it into what we need once its on orbit.
It makes sense; humans typically spend a third of their day in bed rest conditions, and a substantial amount sat down, our full exposure is already intermittent. There may be other health issues to consider from microgravity such as fluid distribution, but bone and muscle loss should be straightforward to mitigate. The other issues I *suspect* will not require anywhere close to 1g to deal with, just enough that the body knows which way is down.
I had that idea also, but thats not what I'm suggesting here. This is about using an electromagnet to pick up an object and swing it around. It's a centrifugal accelerator using a magnetic transmission.
A rotating drum could be used for coilgun switching. Put magnets along its length in a spiral pattern, as it turns the magnets pass and activate the switches. Or even a single flywheel, the spacing is what matters e.g. at a constant RPM, if magnets are placed at 0, 180, 270, 315 deg. the time between each switching will be half the previous one. For a coilgun you could also energise all coils at the start and use the switches to turn them off?
Tough SF -- Hypervelocity Tether Rockets.
The problem is transferring the energy from the flywheel to the object. Thats a lot of fiction involved in Matterbeams proposal.
I'm wondering if electromagnetic coupling could be used. So we have a 3km/s flywheel with an electromagnetic rim and a track around half of its circumference. When the magnet is switched on, a ferrous vehicle on the track would experience a force dragging it around with the flywheel, accelerating it. Once it is halfway around the magnet would be switched off, sending it in straight line and launching whatever payload was on it. The flywheel would enable energy to be accumulated and released in one quick burst.
A Terran application might be winch launch for aircraft. The same magnetic coupling would work I think for that, and thats something that also needs a short burst of high power.
Coming back to Earth, I'm wondering what sort of performance compressed air/propane rockets could get. Not for sustaining flight, but for providing the high thrust needed for launch, particularly for a microlight/glider. It would only be used for a few seconds, so the tank can be refilled on the ground using solar power or other sources. The compressor would only operate one way, since the air is leaving via the combustion chamber; idk if that makes it easier and lighter to build. The weight of the tanks may make it tricky to use for for VTOL, though carbon fibre might be light enough. Could allow STOL though if retrorockets are included.
For Martian transport, Lithium Hydride Thermal Rocket. Robert Zubrin proposed an NTR that would use CO2 propellant, the Nuclear Indigenous Martian Fuel (NIMF). That would have been designed to reach orbit. This would not, but it should be capable of at least short range ballistic hopping. Molten LiH has a heat of fusion of 2.9 MJ/kg at 690c; if the Isp was 145, that would mean 4 kN-s of thrust per kg, so a craft that has 10% of its mass dedicated to a thermal battery would have enough energy for a delta V of 400m/s. Enough for a few km of high speed hopping. 20% battery would be able to hop 10km with some napkin math. Or more likely, enough to get a fixed wing aircraft airborne and up to cruising speed?
2) is unreasonable. That mandates massive centrifuges, since your head is always going to be 1.5-2m closer to the axis of rotation if you're standing up. Rules out short axis gyms. Or means you can only do lying down excercises, which is not what we need.
TH,
Its not an issue of understanding. I understand GW perfectly well, I just reject his vibes based design in favour of solid evidence that it's massively overkill.
Why is it so difficult for you to understand that making the entire thing 1g is massively overengineering it beyond what is needed for astronaut health? Why are you so wedded to full 1g designs at an RPM of 2 or less?
The baton design locks you into providing full 1g for the entire ship and stops you providing a dedicated gym centrifuge at higher g than the rest of the ship. It is a bad design.
Key highlights
PBR-20 (Water-based Resistojet Thruster) is a low-pressure (<60 kPa) propulsion system with a scalable water tank and a redundant flow control system with a fail-safe valve. The thruster unit is modular and it is possible to expand the overall system by clustering multiple units and scaling the propellant tank as needed. The limits of such clustering or scaling are determined by the mass, volume or power of a spacecraft.
The individual units provide a total impulse of >220 Ns and a specific impulse of >70 s, with a thrust of 1 mN. The first model was demonstrated aboard a 3U ISS-deployed CubeSat in 2019 and two flight model thrusters are to be delivered in 2021 and launched by SLS and Falcon-9, respectively. The thruster operated in low earth orbit in March 2023 on board the Sony "EYE" satellite.
TECHNICAL SPECIFICATIONS
Wet Mass: < 1.5 kg
Power: 20 W
Thrust: 1 mN
Envelope: 1 U
Total Impulse: 220 Ns
ApplicationsOrbit insertion
Orbit maintenance
De-orbit
Collision avoidance
Formation flying
https://satsearch.co/products/pale-blue … t-thruster
Assuming the energy cost per N-s for a lithium hydride thermal rocket is 2kJ, we would need 440kJ to match this for total impulse. That would be about 150g of LiH, with double the Isp. But of course, we wouldn't be using anywhere near that much, since the point is to regenerate with solar power. Such a storage system would be useful for raising orbits through perigee kicks, not something feasible with solar electric systems.
Lithium Hydride melts at 690 celcius with a heat of fusion of 2.9 MJ/kg.. This is a similar temperature to the exhaust of a hydrogen peroxide monopropellent rocket. A steam rocket using molten lithium hydride might get an isp of 140 based on the performance of peroxide, though the lighter exhaust (pure H2O instead of H2O/O2 mix) should improve on this. As a replacement for cold gas thrusters I think it has potential, given the simplicity of the design. Each kg of LiH might be enough for 1500 N-s of thrust.
On earth applications could be in rocket assist to achieve short takeoff and landing -- or, in the case of paratroopers, very rapid entry without a parachute. In the latter case the ability to recharge and refill the system would be less important than having something that can be easily throttled and has very high reliability. In the former though, a system that runs on electricity and water would be logistically trivial to provide compared to any other form of rocket.
I have thought for a while about stratospheric light gas gun launch. Reading the spin launch thread, it appears that 10,000g is doable. To get to 8km/s at that acceleration, the barrel needs to be just over 300m long. For a stratospheric airship that is not a great length. The advantage over a ground based system is the far reduced air density to get through, as well as the ability to move where the accelerator is pointing to access different orbits.
It may also be possible that an airship could reach 2km/s under its own propulsion. Maybe solar thermal, even. If it could do this repeatedly without much issue, that would be a very good first stage.
Hmm. A cross shaped spaceship is an interesting design. Spinning on its long axis but with the living quarters extended outwards. Reminiscent of designs with wheels but a lot smaller. Doesn't have to be all that large.
The gym would go in the centre, where it can spin in it's own centrifuge. A downside of the baton design is that a gym centrifuge would be tricky to install, there's not much space at the axis of rotation for it. A major downside, really. I don't think we should use it.
I already linked the study in the original thread. They had people use them for 25 minutes at a time, each day for 50 days. I'm going off data here, not vibes.
https://pmc.ncbi.nlm.nih.gov/articles/PMC7450067/
The reason fairground rides don't last longer than a couple of minutes is that they need a high throughput of people to make money, not because they're hitting some fundamental limit of biology.