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Ignorant question: are solid-fueled rockets at all interesting, anymore? Do they have any advantages (e.g. simplicity of design) over the fancy throttle-able li

by jpm_sd 5y ago

Ignorant question: are solid-fueled rockets at all interesting, anymore? Do they have any advantages (e.g. simplicity of design) over the fancy throttle-able liquid-fueled engines?

anarazel 5y ago
Depends on the purpose. E.g. for military uses like ICBMs they're quite important...
j8asic 5y ago
Not really. Gel propellants are a new direction.
evo 5y ago
I suspect their primary advantage remains shelf-stability at room temperatures, which will make them stay relevant for military applications, e.g. you don't want a cryogenics facility in your submarine or cruise missile launch platform. Historically, I think they're cheaper than an equivalent disposable liquid fueled engine but don't hold up to the fully reusable designs of today, and from a reliability perspective there's not a lot of room between working-as-intended and "activate the flight termination system" at a total loss.
- Terr_ 5y ago
  > I suspect their primary advantage remains shelf-stability at room temperatures, which will make them stay relevant for military applications I while ago I read--but barely understood--a book that went into a lot of this: "Ignition! An Informal History of Liquid Rocket Propellants" by John D. Clark. _____________________ IIRC there were some cases where a fuel was not militarily-acceptable because you would need to warm/thaw the mobile missile prior to firing in a Russian winter, or other cases where a permanent missile-silo meant it was cost-effective to run heating/refrigeration all the time, etc. > [I]n applications which do not require a low freezing point, hydrazine itself is fused, either straight or mixed with one of its derivatives. The fuel of the Titan II ICBM doesn't have to have a low freezing point, since Titan II lives in a steam-heated hole in the ground, but it does need the highest possible performance, and hydrazine was the first candidate for the job. _____________________ Another fuel-choice issue involves how badly it might self-destruct if anything unusual happened: > [I]n the summer of 1960, we tried to fire a 10,000-pound thrust Cavea B motor. [...] Well, through a combination of this and that, the motor blew on startup. We never discovered whether or not the [detonation] traps worked—we couldn't find enough fragments to find out. > The fragments from the injector just short-circuited the traps, smashed into the tank, and set off the 200 pounds of propellant in that. (Each pound of propellant had more available energy than two pounds of TNT.) I never saw such a mess. The walls of the test cell—two feet of concrete—went out, and the roof came in. The motor itself—a heavy, workhorse job of solid copper— went about 600 feet down range. And a six-foot square of armor plate sailed into the woods, cutting off a few trees at the root, smashing a granite boulder, bouncing into the air and slicing off a few treetops, and finally coming to rest some 1400 feet from where it started. The woods looked as though a stampeding herd of wild elephants had been through. > As may be imagined, this incident tended to give monopropellants something of a bad name. Even if you could fire them safely—and we soon saw what had gone wrong with the ignition process—how could you use them in the field? > Here you have a rocket set up on the launching stand, under battlefield conditions; and what happens if it gets hit by a piece of shrapnel? LRPL came up with the answer to that. You keep your monoprop in the missile in two compartments: one full of fuel-rich propellant made up to A. = 2.2 or 2.4, and the other containing enough acid to dilute it to X = 1.2. Just before you fire, a can-opener arrangement inside the missile slits open the barrier separating the two liquids, you allow a few seconds for them to mix, and then push the button.
jandrese 5y ago
They are useful when you need a rocket that can take off at a moments notice but sit idle for decades at a time. For typical rocket launches they don't make much sense. I suspect the Space Shuttle SRBs were chosen because they were a handout to ICBM manufacturers.
dylan604 5y ago
Depends on your definition of "interesting". If you mean do people still use them for practical purposes, then yes they are. If you mean are people still researching them for use in exploring space, then probably not.
Robotbeat 5y ago
Extremely simple (basically just one big rocket combustion chamber with the propellant already inside, no pumps or plumbing) and shelf storable and potentially extremely high thrust to weight ratio. Useful for munitions and for one-time-use. I’d like to think we’re going to reusable rockets and not as much war, so I’d LIKE to think they have fewer uses, but…
- numpad0 5y ago
  Biggest drawback is Americans don’t like them built in volume and ITAR-free. They didn’t like it in free hands so much that they once did a civilian “military aid” to let an ally build a clone of then top of the line Delta II. Looking back at history, maybe what goes on top actually do keep the peace in the world, so maybe we could safely go back to building solids at scale for peaceful space transportation. But not likely without an American nod, I would imagine.
  - Robotbeat 5y ago
    Solids are not ideal for space exploration as they are difficult to control and reusing them is expensive (& thus usually isn’t worth it). I am fully on board to reusable liquid rockets, which can use extremely cheap propellants liquid liquid methane or liquid hydrogen fuel and (70-90% of the mass of propellant) liquid oxygen. These propellants are extremely cheap, about 25¢/kg of propellant on average, enabling very cheap launch costs, compared to around $5/kg in solid rocket motor propellant costs (and greater difficulty in reusing them and much higher dry mass and lower Isp). And the exhaust is really bad for the environment. The high acceleration and sometimes high vibration and inability to turn off in an emergency make them non-ideal for human spaceflight. And they’re basically use-once (with possibly of remanufacture) so you can’t acceptance-test the same motor like you can for liquids, and refueling them is a complicated process that can’t easily be done off-planet (unlike liquid rockets which can be and are refueled such as the ISS’s propulsion systems). So while there are some niche uses of them for space exploration (interplanetary kick stages for probes), from an energy, performance, safety, reusable cost, and ride comfort standpoint, I’m rooting for liquids.
magicalhippo 5y ago
Interesting enough to still be of use. Japan has a three-stage solid-fuel rocket[1] for example, with several launches planned. [1]: https://en.wikipedia.org/wiki/Epsilon_(rocket) https://en.wikipedia.org/wiki/Epsilon_(rocket)
- jcims 5y ago
  Two of them just helped get JWST into space.

by jpm_sd 5y ago

Ignorant question: are solid-fueled rockets at all interesting, anymore? Do they have any advantages (e.g. simplicity of design) over the fancy throttle-able liquid-fueled engines?

anarazel 5y ago

Depends on the purpose. E.g. for military uses like ICBMs they're quite important...

j8asic 5y ago

Not really. Gel propellants are a new direction.

evo 5y ago

I suspect their primary advantage remains shelf-stability at room temperatures, which will make them stay relevant for military applications, e.g. you don't want a cryogenics facility in your submarine or cruise missile launch platform. Historically, I think they're cheaper than an equivalent disposable liquid fueled engine but don't hold up to the fully reusable designs of today, and from a reliability perspective there's not a lot of room between working-as-intended and "activate the flight termination system" at a total loss.

Terr_ 5y ago
> I suspect their primary advantage remains shelf-stability at room temperatures, which will make them stay relevant for military applications I while ago I read--but barely understood--a book that went into a lot of this: "Ignition! An Informal History of Liquid Rocket Propellants" by John D. Clark. _____________________ IIRC there were some cases where a fuel was not militarily-acceptable because you would need to warm/thaw the mobile missile prior to firing in a Russian winter, or other cases where a permanent missile-silo meant it was cost-effective to run heating/refrigeration all the time, etc. > [I]n applications which do not require a low freezing point, hydrazine itself is fused, either straight or mixed with one of its derivatives. The fuel of the Titan II ICBM doesn't have to have a low freezing point, since Titan II lives in a steam-heated hole in the ground, but it does need the highest possible performance, and hydrazine was the first candidate for the job. _____________________ Another fuel-choice issue involves how badly it might self-destruct if anything unusual happened: > [I]n the summer of 1960, we tried to fire a 10,000-pound thrust Cavea B motor. [...] Well, through a combination of this and that, the motor blew on startup. We never discovered whether or not the [detonation] traps worked—we couldn't find enough fragments to find out. > The fragments from the injector just short-circuited the traps, smashed into the tank, and set off the 200 pounds of propellant in that. (Each pound of propellant had more available energy than two pounds of TNT.) I never saw such a mess. The walls of the test cell—two feet of concrete—went out, and the roof came in. The motor itself—a heavy, workhorse job of solid copper— went about 600 feet down range. And a six-foot square of armor plate sailed into the woods, cutting off a few trees at the root, smashing a granite boulder, bouncing into the air and slicing off a few treetops, and finally coming to rest some 1400 feet from where it started. The woods looked as though a stampeding herd of wild elephants had been through. > As may be imagined, this incident tended to give monopropellants something of a bad name. Even if you could fire them safely—and we soon saw what had gone wrong with the ignition process—how could you use them in the field? > Here you have a rocket set up on the launching stand, under battlefield conditions; and what happens if it gets hit by a piece of shrapnel? LRPL came up with the answer to that. You keep your monoprop in the missile in two compartments: one full of fuel-rich propellant made up to A. = 2.2 or 2.4, and the other containing enough acid to dilute it to X = 1.2. Just before you fire, a can-opener arrangement inside the missile slits open the barrier separating the two liquids, you allow a few seconds for them to mix, and then push the button.

jandrese 5y ago

They are useful when you need a rocket that can take off at a moments notice but sit idle for decades at a time. For typical rocket launches they don't make much sense. I suspect the Space Shuttle SRBs were chosen because they were a handout to ICBM manufacturers.

dylan604 5y ago

Depends on your definition of "interesting". If you mean do people still use them for practical purposes, then yes they are. If you mean are people still researching them for use in exploring space, then probably not.

Robotbeat 5y ago

Extremely simple (basically just one big rocket combustion chamber with the propellant already inside, no pumps or plumbing) and shelf storable and potentially extremely high thrust to weight ratio. Useful for munitions and for one-time-use. I’d like to think we’re going to reusable rockets and not as much war, so I’d LIKE to think they have fewer uses, but…

numpad0 5y ago
Biggest drawback is Americans don’t like them built in volume and ITAR-free. They didn’t like it in free hands so much that they once did a civilian “military aid” to let an ally build a clone of then top of the line Delta II. Looking back at history, maybe what goes on top actually do keep the peace in the world, so maybe we could safely go back to building solids at scale for peaceful space transportation. But not likely without an American nod, I would imagine.
- Robotbeat 5y ago
  Solids are not ideal for space exploration as they are difficult to control and reusing them is expensive (& thus usually isn’t worth it). I am fully on board to reusable liquid rockets, which can use extremely cheap propellants liquid liquid methane or liquid hydrogen fuel and (70-90% of the mass of propellant) liquid oxygen. These propellants are extremely cheap, about 25¢/kg of propellant on average, enabling very cheap launch costs, compared to around $5/kg in solid rocket motor propellant costs (and greater difficulty in reusing them and much higher dry mass and lower Isp). And the exhaust is really bad for the environment. The high acceleration and sometimes high vibration and inability to turn off in an emergency make them non-ideal for human spaceflight. And they’re basically use-once (with possibly of remanufacture) so you can’t acceptance-test the same motor like you can for liquids, and refueling them is a complicated process that can’t easily be done off-planet (unlike liquid rockets which can be and are refueled such as the ISS’s propulsion systems). So while there are some niche uses of them for space exploration (interplanetary kick stages for probes), from an energy, performance, safety, reusable cost, and ride comfort standpoint, I’m rooting for liquids.

magicalhippo 5y ago

Interesting enough to still be of use. Japan has a three-stage solid-fuel rocket[1] for example, with several launches planned. [1]: https://en.wikipedia.org/wiki/Epsilon_(rocket) https://en.wikipedia.org/wiki/Epsilon_(rocket)

jcims 5y ago
Two of them just helped get JWST into space.