Advanced solid rockets.

[Galane]

The Kerbals' solid rockets are behind the technology curve of what humans had circa 1960. The Polaris submarine launched missile was a two stage solid rocket with thrust vectoring and an abort system that could extinguish the burning fuel, at least in the first stage.

I haven't found a direct online reference for the Polaris shutdown capability but I remember it from an old book on submarines my grade school library had in the late 1970's. IIRC it covered submarine technology from the Turtle through the Nautilus and the first SSBN ships to carry the Polaris, the George Washington class. Could be that ability was only used during early tests. It would be heavier and more complex than a simple explosive charge to break up the missile.

What would it take to put out a large SRB, or even a small one? Certainly wouldn't be able to be ignited again. Adding thrust vectoring would increase cost and weight.

And then there's this...

http://www.dtic.mil/docs/citations/ADA020461 (Have not found how to get the complete file.)

Accession Number : ADA020461

Title : Shutting Down the Solid Fuel Rocket Engine,

Corporate Author : FOREIGN TECHNOLOGY DIV WRIGHT-PATTERSON AFB OHIO

Personal Author(s) : Andreev,Todor

Report Date : 07 JAN 1976

Pagination or Media Count : 11

Abstract : Up to now there are two ways known for shutting down a solid rocket engine, or stopping the thrust; extinguishing the burning fuel, and neutralization of the thrust (reversing the thrust). These two methods can be applied separately or combined.

Descriptors : *SHUTDOWNS, *THRUST CONTROL, *SOLID PROPELLANT ROCKET ENGINES, TRANSLATIONS, THRUST, BULGARIA, EXTINGUISHING, THRUST REVERSAL.

Subject Categories : Solid Propellant Rocket Engines

Distribution Statement : APPROVED FOR PUBLIC RELEASE

[Skorpion]

I'd be amazed if this hadn't been suggested before, but it would be real nice if SRB nozzles were separate parts from the propellant, like we have with liquid engines. That way we could build taller SRBs without requiring purpose-built parts. It would also allow for high-tech nozzles with vectoring or emergency shutdown, as you suggest.

[TwoHedWlf]

What would it take to put out a large SRB, or even a small one?

Realistically, it would be impossible. Even if you were somehow able to flood the entire combustion chamber(Which is essentially the entire interior of the booster) with water it probably wouldn't do it. If I remember right the boosters that could be "Shut down" used doors at the top or or could blow the entire top off the booster. Essentially letting out all the pressure/exhaust.

I'd be amazed if this hadn't been suggested before

Has been, surprised it's not on the What not to suggest list.

but it would be real nice if SRB nozzles were separate parts from the propellant, like we have with liquid engines. That way we could build taller SRBs without requiring purpose-built parts. It would also allow for high-tech nozzles with vectoring or emergency shutdown, as you suggest.

It would be nice, but if done in a realistic fashion it would be a bit complicated. Say you have the nozzle and one segment of fuel produces X thrust for Y time. Adding a second identical segment on top will result in roughly 2X thrust for Y time. Possibly more like 3X thrust for .5Y given the higher temperatures. This can be changed by modifying the interior structure of the fuel to give it more or less surface area to burn. But without doing that if you want a longer burn time you'll need a wider booster, not taller.

Edited August 8, 2013 by TwoHedWlf

[Galane]

The space shuttle's SRBs were built of stacked metal rings with the fuel cast inside. That's the design feature that destroyed Challenger because soon after launch the hot gasses were right against the outer casing, trying to burn through the joints. A review of all prior launches showed several puffs of escaping gasses and IIRC at least one other instance of escaping flame. Fortunately all prior incidents of joint failure were aimed away from the big fuel tank.

Until the destruction of Challenger I thought the SRB fuel was cast all at once inside a tube made of rings bolted together. My thoughts when I learned how the fuel was done were something along the lines of "What a <censored> stupid, idiotic design. It's a wonder one didn't blow up sooner!". Seems like a perfect design for the Kerbals...

In theory those SRBs could be built with differing numbers of segments. I bet they'd be safer if the fuel was offset some so it would be recessed at one end and sticking out at the other so the seams in the fuel wouldn't align with or be so close to the joints. The unburned fuel would shield the joints until close to burnout.

Edited August 8, 2013 by Galane

[Fifi]

Up: True, that's why the whole propulsion method makes me react like this:

Solid boosters + safety?

But more specifically: of course one can put out a missile solid booster, but when it comes to bigger - and more complex - boosters it becomes harder. I don't say it's impossible, cause I'm not a rocket scientist (despite my flights in KSP and Orbiter), but it's probably seriously complicated, cause nobody at NASA ever tried to do this (or I'm missing something).

[allmappedout]

It would be nice, but if done in a realistic fashion it would be a bit complicated. Say you have the nozzle and one segment of fuel produces X thrust for Y time. Adding a second identical segment on top will result in roughly 2X thrust for Y time. Possibly more like 3X thrust for .5Y given the higher temperatures. This can be changed by modifying the interior structure of the fuel to give it more or less surface area to burn. But without doing that if you want a longer burn time you'll need a wider booster, not taller.

I think you're overcomplicating it here - yes you can vary the thrust profile of an SRB by changing the interior shaping, but the SRBs in KSP burn at a constant thrust, so sticking another one on top would simply double the time, at the same thrust rate. Certainly, that's how I would want it to work, and how a new person would expect it to work. I guess the only risk is the complication of explaining the newbies the difference between Solid fuel and liquid fuel nozzles and whether there was compatability between them (expecting there not to be).

[Anton P. Nym]

I don't see how you could extinguish an SRB once lit; it carries its own oxidiser, so you can't smother it, and if it is to generate the thrust needed it needs to burn much hotter than the ignition point of any feasible fuel. Maybe if it's a "cigarette" profile engine burning from one end you could cut it partway up, though the cut part would still be burning which means it'd still be thrusting and thus likely to hit your craft.

I seem to recall discussions that the devs would include "custom cores" for SRBs somewhere as part of the pending "tweakables" option list, but I don't know if that's actually the case or not.

-- Steve

[shand]

I think you're overcomplicating it here - yes you can vary the thrust profile of an SRB by changing the interior shaping, but the SRBs in KSP burn at a constant thrust, so sticking another one on top would simply double the time, at the same thrust rate. Certainly, that's how I would want it to work, and how a new person would expect it to work. I guess the only risk is the complication of explaining the newbies the difference between Solid fuel and liquid fuel nozzles and whether there was compatability between them (expecting there not to be).

they burn at a constant rate because that is an acceptable profile (being a bit generous). but increasing the length of the booster - or any method of enlargement that increases the SA and volume at the same ratio would simply increase thrust. burn time is changed by adjusting the SA:Volume ratio. I'd expect a slider in the tweakables will allow you to fine tune that ratio. I wonder if procedural parts will one day appear - so you could adjust the length of your SRB and watch the thrust increase, and then tweak the SA:volume ratio (or switch between different internal layouts if thats how they choose to do it) to balance thrust and time. THAT would work. but just doubling the "fuel" and getting double the time seems a bit TOO simplified - and completely ruins the seperation between liquid and SRB at this time (IMO)

[Themohawkninja]

I have heard that you CAN put out an SRB by plugging it in-flight, however you still cannot re-ignite it. What I would like to know, is why they didn't implement SRB's to be modular. It would allow us to make much more accurate re-creations of real rockets.

[Galane]

If someone can find the 11 page paper from the late 70's that I referenced, then I expect we can discover how an SRB can be shut off after being lit.

One method I can think of is a separate section at the top that when lit produces an exhaust gas which 'poisons' the burning surface of the fuel below, perhaps in combination with the fuels exhaust gas, to create a coating that won't burn. There are some burn resistant plastics which will only char a bit and won't sustain a flame.

Aside from being able to be stopped before burnout, the more useful aspect of an SRB would be a thrust vectoring nozzle, which has been implemented on a production scale with submarine launched missiles.

I'd settle for ASRBs with just thrust vectoring capability as an added feature. More sizes would also be nice. The two available tend to often be too large or too small.

[marach]

There's a mod for this It's still very much in development though.

As for how you shut down an SRB you blow out the choke and the top killing the pressure, it still burns but there's no real thrust.

[Burninate]

Another note: The other big downside of using solid rockets is vibration. That is totally unaccounted for in KSP.

[rdfox]

I don't know about Polaris, but the Minuteman ICBM added third-stage thrust-kill ability in the mid-60s; it used blowout panels at the top of the stage that would dump the internal pressure and essentially "blow out" the fire to stop the thrust for precision targeting.

There were proposals to include the same technology on the Shuttle SRBs, but NASA rejected them in the mid-70s as too expensive and heavy--about the same time they rejected the orbiter abort rockets, too--in favor of their thinking that the Shuttle would be so inherently safe that they didn't NEED launch abort options...

[Yourself]

they burn at a constant rate because that is an acceptable profile (being a bit generous). but increasing the length of the booster - or any method of enlargement that increases the SA and volume at the same ratio would simply increase thrust.

Unless the SRB was an end-burner type. An end burning rocket has roughly a constant thrust and the burn time is proportional to length.

[Frederf]

End burning is bad as the walls of the lower casing have to survive the punishment from upper fuel traveling past it. It's best for there to be a constant layer of fuel as a guard as long as possible.