AckSed

Most of the time it's simpler to just pick one fuel, but... I have an idle thought about chilled propane/oxygen/hydrogen. It's never been tried as far as I know, but what with propane being both dense as kerosene at LOX temps and able to cool cryogenically, mixing in hydrogen for extra specific impulse, then using the expanded H2 in an expander bleed cycle... there's something there.

This is only if you assume that multiple injectors are needed. The Merlin 1D uses a single large pintle injector and has gone on to be a successful kerelox engine. Tuning that for two different fuels would indeed be a pain, but it depends upon the state of what's being fed into it. A gas-liquid or gas-gas staged-combustion would increase the stability. Anyway, going by the RD-701 and its single-chamber brother, the 704, they found injectors that would work, with 50 firings and a "smooth transition" between modes. So it has been done. Had to reach chamber pressures of 300 bar for the boost mode, but it was done. Side note, I was wrong earlier: it wasn't switching between fuels, it was a true tri-propellant engine, burning hydrogen AND kerosene. In fact it used more H2 in the boost stage until the kerosene ran out than in the H2-only sustain mode. Perhaps for cooling? Edit: on further thought, nozzle and combustion chamber cooling is a good argument for keeping the LH2 flowing all the way through the climb.

Trampolines and Broomsticks II: The Return.

Oh dear. That whine after the cutout did not sound healthy.

What does it take to bring that down? It's the aerial equivalent of Opportunity by this point. Side speculation: I wonder if it or another like it could blow dust off solar panels by hovering over a probe?

This is the kind of thing that would be ideal for a Dyson swarm. I can imagine an automated fleet of solar super-battery charging stations near the orbit of Mercury, with pickup drones gathering a continuous stream of charged packs. Propellantless thrusters solve a lot of problems. I don't think such a ridiculous power density would be worse than fusion, it would be different than fusion. For an idea of how ridiculous, this What If? about an electron moon and proton earth has the moon's mass in electrons collapsing into a black hole the size of the known universe. Storywise, this would lead to a different focus - harvesting energy instead of burning fuel. No-one says you can't have a whole mess of fusion, fission, solar power satellites all trying to charge up these batteries to approach the near-antimatter levels of power density.

Got it. Now I know that, the designers of the TAN definitely had this on their mind. It's a neat way of combining the booster engine and sustainer into one rocket engine. Interestingly, they used the same injector and combustion chamber used for the LANTR testing. They may even have been thinking of the 300-bar RD-701, as they cite a lack of need for high combustion chamber pressures when you inject the propellant downstream of it.

Ahh, this one. "Chemistry horror story" is an underrated genre. 1.5 stage refers to a rocket that gets you most of the way there and a lightweight kick stage to finish, correct?

Coming back to this, I realised I had not covered tri-propellant mixtures, and those are interesting, not least because some combos pushed the envelope of materials science and even sanity in trying to make the damn things work. In no particular order: Fluorine/oxygen/any, AKA FLOX has been talked about from time to time (and upthread), despite the difficulties of working with fluorine. Apart from the modest increase in specific impulse, when used with RP-1 or another hydrocarbon, it is hypergolic, simplifying engine starts, yet has enough oxygen to react sufficiently with the carbon. Oxygen/hydrogen/kerosene is actually a compelling combination, except they are not always used together together. Rather, in the two engines I know of, kerolox is used in the ascent for the high thrust, then it switches over to hydrolox for greater specific impulse once the rocket has ascended high enough that that matters. The interesting part is where this switchover is applied. The MAKS spaceplane would have been powered by the RD-701, using separate turbopumps in each combustion chamber for H2/O2/kero and shutting down the kero once it was depleted. The other example was Aerojet's invention of thrust-augmented nozzles, injecting the kerosene downstream of the combustion chamber (and producing an interesting shock pattern). The cool thing about this was it let the engine use an over-expanded nozzle but without the instabilities of flow separation because of the higher pressure in the nozzle. Not so cool was the tradeoff in specific impulse, but it didn't matter because of the extra thrust at the beginning of the ascent. Hilariously, a TAN might also be used in a pseudo-tripropellant hydrogen/oxygen/oxygen setup: injecting extra oxygen into the nozzle of a hydrolox engine to burn stochiometric, and thus increase thrust by throwing out more water. Fluorine/lithium/hydrogen is infamous. Take one of the strongest oxidisers known, combined with hot, liquid lithium that is hypergolic with air and corrodes any gasket material known, and then throw in cryogenic hydrogen. But oh, the shiny, shiny specific impulse. It had a measured vacuum impulse of 542s with a long nozzle, with the ferocious heat of the Li-F reaction leaving the hydrogen acting like the propellant in a nuclear-thermal engine. But oh, the exhaust products. This would only ever be considered as a vacuum engine, but the handling difficulties (and the difficulty of packing a liquid metal at the same temp. as a deep fat fryer into the same rocket as two cryogenic liquids) would be immensely annoying. Aluminium/oxygen/helium is a new one on me, but the more I read, the more attractive it becomes, at least as a lunar-ISRU fuel. (At the time, water on the Moon was not a sure thing. The other alternatives, sulphur/O2, magnesium/O2 and phosphorous/O2 give me a bit of pause.) As we know, a rocket throws out reaction mass in the form of molecules. It's simplified, but the more heat these molecules have, the more energy they have. The heavier molecules in the exhaust, like CO, H2O and CO2, give more thrust, while the lighter molecules like H, H2 or helium have more velocity for the same amount of energy. That's what this does: take the heat of combustion of Al/O2 and flow 5-10% of the lightest inert gas through the combustion chamber to reduce the molecular weight and increase specific impulse. Theoretical calculations predicted an impulse of 373s from Al powder carried in 10% LHe, but acknowledged that a) actual experiments would be needed b) helium would need to be brought from Earth. Hydrogen/beryllium/oxygen was only mentioned in passing, but they give the impression that it's theoretically good, but a horror practically. Beryllium is one of those metals that's fine as a block, but really quite toxic in powder form, which is what it would need given its high melting point. It burns extremely hot, which is great for a rocket. However, it creates beryllium oxide, which has an extremely high melting point. As soon as the engine cuts out it then condenses out into a powder coating the inside of the nozzle, injectors, combustion chamber and throat... and it's toxic and carcinogenic as well.

Sea launch makes me think of Sea Dragon, and while I don't think they'd go for underwater launch, I'm thinking of them ditching the 1st stage in the sea. Would the booster be strong enough to be refurbished after soft-landing in the sea? To do it on the regular, or in an emergency, you'd certainly have to do waterproofing of any electronics or access holes, maybe find some way of keeping the rocket end out of the water. Or just drop a test Raptor in the sea, fire it up and see what explodes. If the smaller electric-pump-fed Electron can survive, I wonder how the more corrosion-resistant alloys in the Raptor turbines and injector would fare. Perhaps it's as simple as sending a 'pintle injector close' command before it hits the water?

If BO is setting itself up for supplying the equipment to live on the moon, and in space, I'm all for it. It's kind of needed.

Kilowatts-to-megawatts-worth. It'll probably need to be bootstrapped with commercial panels brought from earth. Further, it doesn't give the output. However, if we take them at their word that they're making 99.999% pure silicon, and assume from that the processes are producing monocrystalline silicon, then at a guess this cell's efficiency could range anywhere from 13% to 22-23%.[1] I'm deducting a percentage point for the use of aluminium wiring, even if I think that's one of the cooler things about this. A lot of commercial modules use conductive silver paste to join the individual cells to the panel, which makes it trickier to recycle.[2] Using aluminium means you can just crush these up and toss them back into the electrolyser. Edit: I was going to make the calcs but it's too early. Just pull the solar irradiance of the moon, the area of a typical commercial 3kW solar panel array (18-20 m2), the number of cells in a panel (60-72) and have fun. [1] Monocrystalline solar efficiencies taken from NREL. [2] PV Magazine, "Novel tech to recycle silver, aluminum from end-of-life solar panels"

I would be more interested in beaming power to spacecraft, powering mass drivers and even beaming lightsails to interstellar speeds. As Xykon says, "Power equals power."

Awww. Though I get it. Even if it would have provided a sort of emergency landing site, it would have been a money pit (oil rig workers need to be paid well, and so do rocket engineers) and not used much otherwise.

Next stop, the Luna Ring.

I am highly interested in this, and not only because ye olde Artemis program and SpaceX are going back to the moon. This has been a dream of a fair few lunar scientists for a while, and it's now a reality. I do wonder what efficiency the cells produced operate at? Still exciting.

*reads* Much as I actually want to talk about it in the correct thread... I will not be sticking my face in to that crossfire of dogma. Then they moved on to just comparing SS/SH with other approaches. I'll be good.

I suppose SH as a reusable Neutron-style smallsat launcher (RTLS first stage, very light second stage) would be too out-there. Even if it would be funny. When's SH supposed to stage-separate? How far could it push this in terms of altitude and velocity before it was required to land at a downrange site (maybe that floating oil rig that we haven't heard of for a while)?

I've heard mention that with a fairing, the Superheavy could be a single-stage-to-orbit. Probably expendable in this mode, but how much could it lift?

Don't believe it is. Looking at the NSF livestream and it's mounted slightly higher. The lack of fins and tiles also makes it look longer.

I wonder how much mass removing the TPS and Elonerons and cargo capacity saves.

The resistojet is essentially a giant toaster element. The liquid H2 keeps it cool enough that the kiloamps of current passing through the resistor heating elements do not melt it down, but I don't know how prone to arcing it is. You could control it well enough by limiting the electricity flowing and the amount of gas coming through for a great range of throttleability. Designing one might be comparable to creating a solid-core nuclear engine, but without the radioactivity. Though if you are charging up the nozzles, I might go ahead and assume you already have the power system to handle all that electricity. Arcjets actually use electric arcs to heat the propellant, and their electrodes do wear down over time. But designing for reliability in that is not impossible... it might be like changing your spark plugs.

The horrible thing is that people tend to believe what they read. ChatGPT in bing would be autocorrupt for search engines.

There is a lot to be said for not pushing the envelope and optimising for reliability. A real-life rocket manufacturer, Rocket Lab, has set out to make a 'boring' rocket engine for the Neutron rocket, that was based on liquid methane and liquid oxygen. The aim was and is to be able to loft a payload and return to the launch site, ready to be fuelled again. They switched from the proven gas-generator cycle to the incredibly complex full-flow staged combustion cycle, but are deliberately under-driving it, because it is actually less stressful on the pre-burners that power the turbines that power the turbopumps. However, if you have energy densities that high in your accelerating nozzles, that store that much electrical energy, you already have so much energy to spare it would make a nuclear reactor seem like a petrol generator. All you have to do is create a lower grade and optimise whatever this material is for safety, install it in the engine bay as your battery/powerplant, then charge it on the ground. Resistojets are some of the simplest rockets going, as all they do is electrically heat propellant. Tungsten has one of the highest melting points so a tungsten resistojet can get pretty hot, and flowing H2 through one gives respectable impulse and some thrust. Hell, since you have power to spare, it can be augmented with an electric arc to be even hotter. Add in your accelerating nozzle to augment the thrust and you have your SSTO.

Well, yes, but also no. Comparing aerospace to the car industry is not a matter of the propellant, it's like... Imagine if every single car manufacturer had begun business trying to build a dragster as their main passenger car. There would be a whole load of blown engines along the way, a lot of impractical fuels like nitromethane or methanol and only the richest customers would commute in one. Instead the vast majority of cars are all about getting from A to B along a road at about 30-60 mph. It's about meeting much less extreme requirements than riding the recoil of a continuous flamethrower to reach supersonic speeds and leaving the atmosphere. Besides, if you want to get technical, a car engine is a bi-propellant, as it uses atmospheric oxygen. Now hold on. Again, this is "it depends". High-concentration 85% hydrogen peroxide has been used in Britain's Black Arrow, a bi-propellant rocket, and was used to cool the nozzle. Since science fiction's on the table, Diatomic Metastable Helium is a godlike solid monopropellant activated with a bit of heat, but it's also hard to make. If you'll allow a bit of handwaving to actually produce the stuff, this is your substance.