RCgothic

The only way to hold a balloon in position is to tether it in multiple directions with the tethers at a reasonable angle to resist the wind and excess buoyancy such that the balloon can resist the tendency of the wind to cause it to dip. But as has been mentioned the weight of the the cables themselves cause the tethers to hang almost vertical at the balloon, so the restraint is much reduced. Plus now your tethers are more like 6km long, the excess buoyancy is additional load (e.g. Weight) they have to bear, your balloon needs to support at least 3 of them, and your tether base stations are on a circle 12km in diameter. Distinctly non trivial. It would probably be easier to design a drone that actively resists the weather with propulsion, even if you have to land to refuel. If you need constant coverage have more.

Testing to failure? Of the tank pathfinder? I thought they were assembling SN1...

My team had a little bit of experience with rocket exhausts interacting with warship coatings. It's very hard to get away from "just go out and repaint whatever the exhaust just burned off". Not saying it's impossible at a spaceflight budget level, but we certainly struggled with a frigate. Metal plates are sturdier than tarps/coatings. But hard to ship to the moon though.

You can get around atmosphere pushing the medium down by having the inside be lower than the outside. The pressure head of the liquid on the exterior side will resist the push of the atmosphere on the inside. If ethanol is almost as suitable as mercury it would be a far better choice from a hull pressure point of view. A 5m tall vehicle would have approx 10atm of pressure at the base of the hull in a pool of mercury, but only about 1.5atm in a pool of ethanol. Add 1atm internal pressure and that becomes 9barG Vs 0.5barG.

A vacuum airship *might* be possible on Mars. The atmosphere there has a higher density to pressure ratio than here. This is important because density is what gives buoyancy but pressure is what crushes. This is because of the higher average molecular weight of the atmosphere there - CO2 is denser than N2. Also the gravity that needs to be overcome is less. All other things being equal simply being in a thinner atmosphere doesn't work. As pressure reduces so does buoyancy.

The accident investigation determined the aircraft was lost due to an explosion caused by electrical arcing in a fuel tank. I think it's in pretty poor taste to perpetuate alternate conspiracy theories such as the aircraft being hit by a missile.

The only thing SLS is any good for is enormous C3 for unmanned probes, which kind of obviates the expense of man-rating the thing. SLS cannot by itself land a manned mission on the moon. It can't comanifest enough payload. Orion by itself is never going beyond earth's sphere of influence. It's too small. Orbital construction is required. I would rather scrap the pair of them and delay the manned space flight programme in exchange for a design that can either put man back on the moon in a single launch, or preferably a big dumb cheap booster that can put massive payloads into leo frequently and inexpensively and rendezvousing with a capsule put into orbit on a far smaller man-rated booster, usable for many purposes. Ares really did have the right idea.

Building space stations isn't that hard really. The major problem is mass and volume. What makes gateway hard is a limited throw to NRHO and then any mission needs to get down to the lunar surface as well.

Antimatter is insanely dangerous stuff in the quantities required for a bomb. The slightest imperfection in containment and you get a premature detonation.

I suppose if you entered the atmosphere with greater than escape velocity it's possible the atmosphere wouldn't scrub off enough speed to capture you, and then you wouldn't come back to earth again. That's still not really skipping off.

And maybe there exists a dangerous edge case between "captured safely" and "not captured this pass". On a steep entry peak thermal loading is higher (and may overload the heat shield) but as it takes less time the capsule absorbs less energy through thermal transfer from the plasma sheath overall. And as the outer skin is hotter it actually re-radiates that heat quite efficiently. As a result inside temperatures remain bearable. A shallow re-entry may cause the capsule to be exposed to the plasma sheath for longer, causing it to absorb more energy over time. And it's cooler, so it doesn't re-radiate as efficiently. The inside of the capsule heats up and the contents get fatally cooked. Not sure if this mode exists for Apollo, but a certain combination of entry angle, capsule mass and lift to drag ratio could experience it.

Although the Apollo Capsule did in fact use a lifting re-entry profile, coming in too shallow would only look like it was skipping off on a graph of altitude vs time. The actual path followed would still be elliptical. It's just that the apogee wouldn't lower enough to ensure a capture on the first pass. You would get a second pass, and a pass after that and so on, but the consumables might not last. An orbit touching lunar altitude would take another week or more to complete (less depending on how much apogee gets lowered), and you'd probably run out of consumables. Also, you would have very little control over your profile on subsequent passes and may come in too steep as a result. Or land somewhere not conducive to safe recovery, such as over land or a long way from friendly rescue teams.

It means cumulatively. 95000lbs is approx 43tonnes, over 19 flights that's about 2.3 tonnes per flight. Well within dragon's capabilities.

The main difference between a cone and a bell with the same area ratio and exit angle is that the bell diverges quickly to begin with, allowing it to equal the cone within a shorter overall length. This is lighter. And it allows other structures such as interstages to be lighter as well.

Primary energy sources. Whether that's coal, oil, uranium, or hydrogen in the sun, it gives you energy you didn't have before. Whether it's inexhaustible or not (in the long term none are) is irrelevant. You find it, dig it up, whatever, and it gives you energy. Hydrogen fuel cells, pumped hydro, batteries, compressed gas, whatever, these are secondary energy sources. You don't find them lying around and they don't give you anything for free. You have to expend an existing power source to get them and this *costs* energy. Whenever you use a secondary energy source instead of a primary one it is because of a specific advantage that makes it more useful than a primary one - usually portability. I don't think compressed/liquid/solid CO2 as a storage medium is a good idea. It's heavier than air and an asphyxiant. Small volumes become very large volumes that are easy to suffocate in. Pressurised storage is also a specific deadly hazard, highly regulated for a reason. Vehicles that are subject to accidents are a particularly bad place for a pressurised CO2 system. Plus it doesn't take CO2 out of the atmosphere to address climate change, it just recirculates it.

Ground Support Equipment

Actually, NASA doesn't know why *some people* experience taste differently in space. Some don't notice a difference at all, and afaik there's no supposed biological mechanism that would make food taste different in the long term (stuffy "space head" doesn't tend to last that long). It could just be that foods have been prepackaged for a long time before consumption. Or it could be that food scents just have to compete in an extremely odorous environment, and a larger living area with better air conditioning would solve the problem. We haven't ruled out all the non-biological factors, basically.

Equal compensation for equal service

I suppose this means that SpaceX will simply bid more in future.

If the goal is to send Orion *and* a capable lander to the surface of the moon, then as tater said the baseline is 76t to TLI in a single launch. Can any version of SLS do that? No. Block 1b can comanifest 10t to the moon with Orion. If you use that as additional propellant, that gets you only to LLO. It's not enough to accomplish a mission. Block 2 can comanifest 19t with Orion. *Maybe* that gets Orion into LLO with a minimal lander. Except that's not planned. The only architecture which makes any sense using SLS and Orion is to put Orion in LEO using a different booster (falcon heavy can lift the mass, 2/3 reusable, possible form issues), and mate it to a large cargo on an EUS for TLI. The bigger the cargo the better. SLS block 2.

And not only because of the better architectures a larger rocket enables, but because constantly having to prove all new stages, as well as retooling VAB bays, MLPs and Pad 39B for different rockets, is completely stupid. Block 2, all up, go! Maybe the rocket explodes. Maybe bits fall off à la Apollo 6. But then you fix it.

They should always have gone straight to block 2.

Yellow is frequently lifting or handling equipment, I think that's pretty common across industries.

Well I feel sheepish. I must have been overcomplicating my search terms.

What are Soyuz's exact numbers? I've struggled to find them in my own searches.