shynung

The point of having many engines is redundancy. That is, the failure of one engine should not cause mission failure. In 8 October 2012, during the SpaceX CRS-1 mission, the Falcon 9 rocket experienced a single engine failure. The rocket compensates by firing the remaining 8 engines longer than usual, and the spacecraft reaches orbit.

N1 didn't fail because of its many engines. It did because a stray bolt got into the turbopump. I'd say it failed because of shoddy engineering. Having many engines aren't a problem by itself if those engines can be properly managed.

In other words, when SpaceX recover their boosters, they do it by suicide-burning.

Wasn't FH-Reusable's payload closer to 20 tons rather than 53? It would need 3 FH-Rs clustered together, if that's even possible.

It must be noted that SEP is barely useful past Mars orbit, due to the inverse-square law. When we go to Jupiter's moons, we would be well-advised to have a more potent propulsion system.

Hmm. A single SLS first stage with propulsive-landing-flyback boosters, that returns to Earth by a massive inflatable heat shield, and glides to the runway via parafoils. That sounds like it would carry well past 60 tons. Also, the Russian Baikal flyback booster has a jet engine in the nosecone for returning the booster to a runway. Were we talking about LH2 tanks? If so, yes, I should've noted them being costly

Yes, it does. I'm wondering out loud what kind of design would suit that purpose well. Also, even though I'm using the word 'Shuttle', I'm not implying a winged return vehicle. The thing doesn't have to come back in one giant vehicle. Stuff like fairings and fuel tanks can be thrown away - the returning parts are engines, crew cabins, the expensive stuff. Costs are down to maintaining the engines and manufacturing new tanks and fairings.

The mission is a simple cargo run. Here is the OP:

Except the SD-HLLV is a non-reusable design. All the components - SRBs, external tank, and the SSMEs - are disposed of like a regular rocket. Since we're looking for something that's mostly reusable, that really IS cheating. If we approach by redesigning the HLLV, there's plenty of extra mass available. The goal was a 60-ton-to-LEO rocket, and this can lift 90. I'd say sparing 10 tons on reusability-related equipment could go a long way. So I think it could go like this: Space Shuttle External Tank with a detachable engine mount on the bottom, with SSMEs bolted on them, aided by Baikal-style flyback boosters that glide back to the runway after it's spent (so all propellant is available to lift the payload, instead of being used for propulsive landing), topped by either a cheap hypergolic upper stage, or a reusable nuclear thermal rocket. At first stage MECO, the engine mounts detach from the tank, deploy an inflatable heat shield, and reenter, and lands on parachutes.

So a fusion rocket still needs some power source to ignite and sustain the fusion reaction. That brings another can of worms - where do we get that power?

Speaceplanes are hard. Even without an external tank, the Space Shuttle Orbiter was a maintenance nightmare. Also, you mentioned hybrid boosters. Did you mean solid+liquid fuel booster (e.g. Al/LOX), or was it something else? SERV was somewhat interesting. 57 tons to LEO with a disposable fairing and an 'Extended Nosecone' (basically a long spike projected ahead of the vehicle), and capable of SSTO. Though, I doubt the feasibility of this vehicle - like Skylon, there's a lot of new technology (for that era, at least) that has to work perfectly all at once. Also, it doesn't look very aerodynamic.

It's still a really long time before we have space-grade fusion reactors or rockets. We don't even have build-ready space-grade fission reactors by now.

From our experience with the old Space Shuttles, spaceplanes are costly to use. The maintenance costs alone are comparable to building a new dumb booster from scratch with a similar delta-V capacity, mostly because of the heatshield tiles. That said, this concept could work. The question changes to how big we'd have to make it. Seemed similar to the Russian Baikal flyback boosters planned for the Angara rockets. So yeah, that could work. Probably. This is probably one of the cheaper approaches: reuse old tech. We still have the designs, we just have to recreate the tooling to make them. Still a lot of work there, but it's got a decent headstart compared to all-new designs. -Dry mass, of course. No point in bringing back fuel. -This was a thought-experiment hypothetical booster. Nobody needs 60 tons now, but I imagine there is a time in the future where space exploration is advanced enough that a 60-ton booster would be necessary. It is by no means a short-term objective. -I think CH4 is okay. LH2/LOX was primarily because of performance of the propellant mix; CH4 was close to, albeit better than, RP-1 fuel Not exactly a problem. Mishmash rockets are fine.

Interesting. So, you're saying an Orion pulse drive with matter-antimatter bombs are better off without a propellant slab than with? If so, how would that affect the drive design?

Propellant. A detonating nuclear bomb emits its energy mostly in the X-ray spectrum, which is useless for thrust. Pictured above is a typical bomb/pulse unit design for a nuclear pulse drive, AKA Orion. At detonation, the nuclear device releases most of its energy in the X-ray spectrum. The radiation case, opaque to X-ray, channel the emissions to one direction. The channel filler absorbs this mad flurry of X-rays, and transforms it into a mad flurry of heat. This intense heat turns the slab of propellant, which can be made out of any solid material, instantly into ionized plasma, while simultaneously accelerating it to 150,000 meters per second. This jet of plasma smacks right into the ship's pusher plate, transferring its momentum to the ship.

Don't forget bladder tanks!

Guess this is what happens when English isn't your first tongue. I agree with your choice.

I fail to see how the former and the latter can coexist. Care to enlighten me?

I've got a better idea: liquid methane (CH4). It's cryogenic, but only as much as liquid oxygen is cryogenic (CH4 boiling point is 112 K, LOX is 90 K), as opposed to liquid hydrogen (boiling point 20 K). Specific impulse is slightly better than RP-1/kerosene (377 vs 357 seconds). It can be acquired from Martian atmospheric CO2 and water via Sabatier reaction. And best of all, unlike LH2, liquid methane stays put in the tank; it won't boil off and disappear when you need it most.

They still do oxygen acclimation, but the modern procedure only takes an hour, because they integrated some kind of low-load exercise regime to be done while prebreathing.

Argon or Xenon is barely harmful if it leaks into the cabin. Liquid hydrogen is a fire hazard, but not poisonous by itself. These gases, at most, excluding flammability, present little to no danger of intoxication, and a minor danger of suffocation, unlike NTO/50-50. Minor loss of deltaV is survivable in some situations. And yes, ASTP Incident was due to RCS prop. No, I am merely suggesting that we do not use hypergolics as a main propellant. Other propulsion technologies use less-harmful propellants.

Just let it fall into the ocean. Any large pieces that doesn't burn up on the way down will fall onto a vast expanse of water.

Nice to meet you, Orc. The problem with a solar thermal rocket is similar to solar electric rocket: one would need a large surface area to catch enough energy from the sun. Thankfully, while solar panels are heavy, solar concentrators can be built lighter, by using an inflatable with half of the inner surface coated with a reflective metal, and the other half transparent. However, a solar thermal rocket has a lower effective Isp than a solar electric rocket(comparable to a solid-core nuclear thermal rocket), due to material thermal strength limitations. According to the Atomic Rockets site, a typical STR has a specific impulse close to 1000 seconds, while a VX-200 VASIMR electric rocket can handle 2900 seconds at the highest thrust/lowest Isp setting.

Right. Radiator mass need to be considered, too. Forgot to account that. Except for nuclear thermal rockets. These don't need radiators, because the heat is used directly on the propellant. It runs like an open cooling system, with the propellant doing double duty as the coolant.

That's actually not a bad idea. The US Ohio-class nuclear ballistic submarines have a single S8G nuclear reactor, which produces 220 MWth and weighs 2750 tons. Assuming the same power ratio applies to a 10 ton reactor, we get an 800 kWth reactor. Assuming a 50% thermo-electric conversion efficiency, that's 400 kWe, just enough to run 2 of Ad Astra's VX-200 VASIMR thrusters. Now, the question is whether we get such a reactor ready within a few decades. While I'm optimistic from the tech side, I doubt that the general public can simply agree to the idea. At least, I hope they're indifferent.