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Everything posted by AckSed

  1. Were the electron beams a way to model the plasma generated during reentry?
  2. How would water-cooled heat shields (which I've seen mentioned here and there) stack up against H2-cooled? I imagine they have a denser coolant and pretty damn good cooling, but the system is dead weight that doesn't contribute to propulsion.
  3. So what kind of heat load would the heatshield experience upon re-entry from LEO? Are we talking 'rocket combustion chamber' temperatures and pressures? Higher?
  4. At Venus temperatures, how much softer is volcanic rock after it cools? On the one hand, there's no water to hydrate minerals. On the other hand, being immersed in a sea of supercritical CO2 has to do something.
  5. It is not wholly silly, just mostly silly, as I think spirits have a lower viscosity. Besides, if I was designing a walking stick as a tot flask, I'd have a stopper with a smaller hole for pouring, which, by the size of the stream, this might have.
  6. Fascinating experiment launched in Crew Dragon: https://www.nrl.navy.mil/Media/News/Article/3328656/nrl-to-launch-first-in-space-laser-power-beaming-experiment/ It'll be beaming it down to the ground, but this is the first step towards making "an extension cable long enough".
  7. And not because it looks cooler. All right let's see what we can work out here. Rotation on the hands, shoulders, hip joints... boots? Unless it's just detatchable, which I approve: a quick way to swap out a part that sees the most wear, at the cost of another seal.
  8. Thanks. Maybe I'm making it too complicated. I now realise what I want is the surface area of a dome 1 metre tall and 3.4 metres wide (I'm cutting out the outer circle with the ring of combustion chambers), the heat radiated by the plasma of the shockwave and the mass flow rate required to keep the surface of that area at around 200-500 deg. C. ...I am definitely not a rocket scientist. None, just assumed that the hydrogen would burn due to the heat once vented. I didn't mean that something would light it.
  9. That is a lot of hats, many of them military. I know before NASA came along, America's Air Force developed a parallel space program to serve their needs, with development also done by the Navy and a bit by the Army. The inter-departmental rivalries were at times destructive. Indeed, it's safe to say that in the early days, space was highly militarised until the civilians came along. CNSA seems to be much more tightly wedded to the military. Could they ever grow to the point they would be allowed to be mostly civilian? Are there any similar rivalries or tensions between CNSA and branches of the PLA?
  10. We know that the wider a hypersonic blunt body becomes as it descends through the atmosphere, the lesser the heat load on the shield, as the compressive shock is pushed back. LOFTID reached this diameter, though it simply resisted the heat with silicon carbide fabric and was not carrying much load. An ablative heatshield helps resist heat by charring (creating a hard-to-burn outer layer) and vapourising (creating gas that carries away some of the heat and pushes back the shockwave). Stoke's heatshield is not only actively cooled on the inside, it feeds out the exhaust gas through the centre, which, though it ignites, is still cooler than the re-entry plasma. The exhaust, still mostly hydrogen and a bit of water, then carries away some of the heat of the outside. The bulk of the heating in re-entry is radiative, so a shiny, cool, stainless steel surface will reflect some of that. Every little bit helps. It's also set up so that the hotter it becomes, the more H2 will flow. So I'm mostly certain it will scale. In fact, I'm pretty sure that on a graph, the line of second stage wet mass versus hydrogen used for heatshield cooling would cease to be linear and begin to flatten out. This is only intuition though. As we know, the limitation of an aerospike is its cooling. The fact that there are 15 small combustion chambers to one expander bleed cycle turbopump would also help wring useful work out of the heat. All I can give you is the strength of LH2 for cooling is not in its specific heat capacity (10 kilojoules per kilogram), but its heat of vapourisation (around 440 kJ per kg). I don't know the surface area of the heatshield. If we assume that it forms a spherical cap of a sphere... but it'd have to be a larger sphere to create the curve we saw. I throw my hands up and ask someone who numbers gooder to calculate the area of a spherical cap based on where it intersects with the outer slightly-conical cylinder of the sidewalls and that of the upper stage, based on the depth of around 1 metre and an overall diameter of 4 metres. Mmm... not sure. There will be 30 combustion chambers, but one, maybe two turbopumps feeding them, so it's technically one or two engines. The fact that they are already aiming for thrust-vectoring by differential throttling would make shutting one combustion chamber down a minor inconvenience: they could close off the opposing chamber or just modulate the burn on the other chambers. If a turbopump failed, then that's bad. I don't know if they'll have two turbopumps feeding 15 chambers each, but I'd want redundancy. If they do, I'd say it's an asset.
  11. My disappointment is unexpected, but I am not too surprised. Should have done a holddown test. Edit: Oops.
  12. I think the lower skirt on the booster is new. Looks good.
  13. Ach, another hold at less than a minute. Edit: we're back on! Edit edit: aaany minute now... ...least there's no music so I can background the stream.
  14. Hold has un-frozen, we're looking at about 40 minutes.
  15. Very glad something like this is actually being built. Looking at the actual specifications, this thing is wider than Skylab. It also anticipates StarShip if "Capacity for 50+ tons of interior outfitting" is any indication. I can't help but imagine this coupled to the Spacecoach concept: simple spacecraft with water walls for radiation protection, clustered electrical water-propelled thrusters for travelling between Luna, Mars and Earth, and partially-open-loop life-support. Hydrogen peroxide can be generated onboard to fuel the attitude control thrusters. You'd need a powerful solar array, but that's not too onerous.
  16. I briefly thought this was about the proliferation of iron nitride magnets and became excited.
  17. Question: if this works, how long would it take to print and certify another one?
  18. I see how it is, you have to advance the tech tree to "Armoured Launch Platform" before "Reusable Heavy Lift".
  19. When strapped in a chair in zero-G, humans naturally rest their arms such that their arms are bent but parallel with their chest, and their fingers are level with their chin. This fact brought to you from the livestream of the Crew-6 mission. ...This means that the astronauts in Crew Dragon perpetually look like they are seconds away from making the Gendo pose (or the Mr. Burns "Excellent!" pose, if you prefer).
  20. Huh. Given the dire warnings of cooling phenomena I've heard floating about - polymerisation, coking and sulphur - how common is using kerosene to cool? I wonder if they have to be careful about where they source their RP-1?
  21. Insert, "You have failed me for the last time..." joke here.
  22. The designer of the Sea Dragon performed some underwater tests with small rockets and found the water reduced the shock and noise significantly. These likely lads may be trying to hang on to those coattails.
  23. It is a throwaway tweet, but according to Casey Handmer, the phased arrays and software-defined radios on Starlink satellites already compensate for atmospheric distortion, and are a software upgrade away from using that to predict weather and perform synthetic aperture radar. I don't know how deeply it could penetrate other atmospheres but measuring the weather and imaging the surface of, say, Venus in resolution comparable to other Earth-imaging sats would be valuable science points. I'm sure we could stick a GoPro on each of them as well. The constellation might need a specially-built base station to store and transmit the findings back to Earth, and I'm not sure what radiation-hardening might be needed outside of Earth's magnetosphere, but there it is.
  24. That is very interesting. The argon is the key takeaway: the thrust's rubbish in comparison to xenon or krypton, but it's really cheap and (say it with me) present in Mars' atmosphere. The thrust to electrical power ratio is also not world-leading either, but the mass of the thruster itself is about a sixth of the BHT-6000 HET on the Artemis Lunar Gateway for half the thrust. That's more mass that can be given over to propellant or solar panels. The lighter atoms help raise the specific impulse to something on par with other thrusters. Surprisingly, the total efficiency of your average high-power HET I saw quoted was around 55%. 50% is pretty good going.
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