sevenperforce

Yeah, nothing's going to stop the initial progression, but a catalyst that would render the reaction more complete while also making it controllable is what I was thinking of. The Al + water = alumina reaction is of course very exothermic so perhaps that waste heat can be used to induce thermal decomposition of the hydroxide.

Slight quibble...it is indefinitely large; it might be infinitely large. To the OP: observations of the observable portion of the universe suggest very strongly that the actual universe is much, much larger -- indefinitely so -- than what we observe.

I wonder if any catalytic salts could arrest the production of Al(OH)3.

I can't see how they would have managed to get enough LOX to get as high as they did.

https://en.wikipedia.org/wiki/Liquid-propellant_rocket#Engine_cycles Full flow combustion is a form of staged combustion. All pump-fed rocket engines have to get energy to turn the turbopump that pumps them. If they don't have a pump, they're pressure-fed from tanks that hold higher pressure than the combustion chamber. Pressure-bearing tanks are heavy AF so high-performing architectures use pumps to force low-pressure propellant into a high-pressure combustion chamber. Most pump-fed engines historically have been "gas generator" engines, where a small amount of propellant is burned in what is essentially a small internal combustion engine, turning the pump. This wastes propellant but in the end it's a pretty good equation. Common GG engines include RS-68, Merlin, and F-1. You can use an electric pump, which wastes no fuel but requires you to carry heavy batteries all the way up. The Electron by Rocketlab makes an end-run around this by jettisoning batteries as they are spent. Another option, pioneered by Blue Origin in the BE-3, is the "combustion tap-off" engine, where a small amount of chamber gases are rerouted out of the chamber to spin the turbine. This is hard to do with kerolox because it doesn't burn very cleanly so you get a lot of soot and coking in the turbopump. And then you have staged combustion. Staged combustion is like a gas generator cycle, except that you burn the propellant in an off-ratio, ending up with either fuel-rich or oxygen-rich exhaust. Then, rather than dumping the exhaust, you route it into the chamber. This means all the propellant ends up getting pushed through the engine. It's called "staged combustion" because the combustion occurs in stages. The SSME used fuel-rich staged combustion (FRSC); they burned a lot of hydrogen with a tiny amount of LOX, then routed that fuel-rich exhaust into the main chamber along with the rest of the LOX to burn. The Russians pioneered oxygen-rich staged combustion (ORSC) with engines like the RD-180, burning a lot of oxygen with a tiny amount of kerosene, and then routing that hot oxygen-rich exhaust into the chamber along with the rest of the kerosene to burn. Oxygen-rich staged combustion is challenging because superheated oxygen gas basically eats anything it touches, but the Russians figured it out, and that's the design for the BE-4 (although it's using methane not kerosene) and this new startup engine as well. Full flow staged combustion (FFSC) is the big guy. That's where you have two different miniature engines running two different turbopumps. One preburner burns a bunch of fuel with a tiny amount of oxidizer, and one preburner burns a bunch of oxidizer with a tiny amount of fuel. Each preburner spins a different turbopump. You end up with two exhaust flows: one of oxygen-rich gas, one of fuel-rich gas. Those two gas flows are routed together into the main chamber using turbine force. The advantage here is that both turbopumps are smaller and lighter (since each one is pumping only one type of propellant) than using a single turbopump, and ALL of the propellant is "staged". Having all that propellant flow means that the turbopumps have way more power and can create much higher chamber pressure. Also, gas-gas reactions are far more complete, which means more efficiency. So there you have it. Idk if that was ELI5 but maybe ELI9?

That link says it is staged combustion. Presumably that means ORSC which is huge for any American rocket engine, let alone a tiny smallsat engine like this.

Yeah that's an odd choice. What are they using for their fuel? The flame looks like kerolox but that's just a guess. LOX is so corrosive that it's almost never used for regenerative cooling.

As probable a solution as any. Kerosene is ridiculously hard to ignite.

It has separated even without a decoupler. It wouldn't get worse. The orbiter breakup in the Challenger disaster did separate the crew cabin more or less cleanly from the rest of the vehicle structure, as far as can be determined. But there was no guarantee that this would happen. If Challenger had been equipped with ejection seats that fired as soon as the orbiter started to break up, they all would have been dead. The only way it would have worked would have been if the cabin fell clear of the explosion and then the eject was manually triggered.

Tap-off? Interesting! Following BO's lead in cycle even if it's SpaceX/RocketLab in prop choice. Coking will be a problem for that, though, so reuse is unlikely.

It is a good learning experience, yes, but at the cost of too many lives. The crossrange requirement was pathetic.

Only if actual astronauts died, which no one wants.

Successful chute deployment would have been the challenging part. I think they decided against the "cabin capsule" approach primarily because there was no way to build in large enough abort motors for a 0-0 abort, but it still would have been better than nothing in a Challenger situation. They would have needed to bake in detcord all around the crew cabin (which then becomes a hazard on its own) and pack chutes in a way that they would be protected during vehicle disintegration but still be able to pop during descent. Ridiculously difficult problem.

The real utility for the ejection seats was in the gliding approach if something major had gone wrong during the Enterprise tests. Putting people on a rocket with solids is just a bad idea all around. SLS and Atlas V N22 included. I'd wager decent money that if the SRBs could have had thrust termination between 90 and 120 seconds, they could have been separated a few seconds early without LOV.

Yeah no part of this makes sense.

The first four Columbia missions flew with operational ejection seats for use in a LOV contingency abort. However, since they were only good for the first 100 seconds of ascent (due to altitude issues) and the boosters don't burn out until after that, any ejection would have launched the crew into the booster fire trail, which would have been unacceptably toasty. The only thing that would have made a contingency abort survivable would have been ejection seats combined with thrust termination on the SRBs. STS-5 and after had no ejection seats, of course, so booster thrust termination would have been LOCV. The one exception would have been a booster thrust shortfall somewhere between 90 and 120 seconds, the brief period during which the orbiter had just enough thrust to maintain acceleration but the SRBs had not yet separated. If one of the boosters experienced a thrust shortfall without actively breaking apart during this period, then conceivably they could have terminated thrust on both boosters and separated early, then completed a RTLS abort. Still rather limited utility. The Shuttle was never more than an experimental launch system. Technically there are black zones within which even an ejection is not survivable because the crew would hit the atmosphere moving too fast to open chutes. That's one reason why the Dreamliner will launch on a never-before-used Atlas N22 with two RL-10s on the Centaur; the extra thrust on the Centaur means the first stage trajectory is less lofted. With a single Centaur, the first stage has to kick straight up to keep the apogee high enough to permit circularization, but an abort during first-stage boost ends up with an unacceptably high entry angle, even for a full capsule. But yeah, I think @CatastrophicFailure misunderstood that I was talking about ejection seats.

The original hopper fairing had a pretty long straight section so I don't think the dimensions will be any different. But definitely less wrinkly. Each Merlin has an independent processing unit and each processing unit contains three redundant computers. All are enclosed inside the Octaweb's frag shield. Unless those three computers are continually telling the turbopump to pump fuel, the engine will shut down nominally. Commanded shutdown is a solved problem for Falcon 9. I wonder why they didn't install thrust termination on the Shuttle SRBs. The first flights had ejection seats which would have saved the crew (or at least the crew with the ejection seats) in the event of a failure early in launch, but the SRB plumes would have cooked them, so it wasn't actually a survivable option. Unzipping the SRBs also would have cooked the ejecting crew. Thrust termination vents would have been the only survivable abort. I doubt it would have been a mass budget problem.

They will trigger the abort by shutting down the first-stage engines. If these were SRBs then that would be one thing, but they are not, and they will shut down very obediently when commanded. Shutting off engine thrust on the first stage is part of the abort sequence.

It may be that the cost of low-grade scrap aluminum is low enough that the process is an affordable means of generating hydrogen without using fossil fuels; the alumina would just be scrapped. Heat could probably be used to separate out the gallium.

I don't see anyone suggesting this is a free lunch. But it could be a way of generating energy from scrap aluminum (if you recycle only the gallium) or a fast way to turn electricity into hydrogen (if you recycle both) or a fantastic way of powering hydrogen fuel cells (if you put it in a car).

It's a carbon-neutral way to produce hydrogen. That's all. Also, if the reaction can be catalyzed properly, it's a VERY dense hydrogen storage mechanism. You could fill your tank with water and change out an aluminum powerpack as needed.

Yes, it's real. https://phys.org/news/2007-05-hydrogen-aluminum-alloy-fuel-cells.html It's not currently economical because the aluminum and gallium you need cost too much. If we can figure out a way to cheaply recycle aluminum oxide and gallium (saltwater electrolysis might work) then it would end up working much better.

Correction: it's all vodka. Fregat engineers are opening celebratory vodka; Soyuz-2 engineers are opening conciliatory vodka. But damn, that's as "everyday Kerbal" as anything I've ever seen. "Whoops, accidentally selected retrograde during the insertion and now my insertion stage doesn't have enough dV. But heyyyyyyyyyyy look at all this monopropellant!"

Just occurred to me that the Draco develops 300 s in vacuum. Clustering Dracos wouldn't be enough for a lander, but would they be enough to perform an LOI burn at the gateway? Because that would both save mass and make everything ridiculously simple.

Boiloff wouldn't be an issue for a solar-electrolysis prop depot; you'd already need a massive array of radiators to liquefy everything in the first place.