Other than being cost-efficient (?), how useful are Solid Rocket Boosters in KSP?

[DasWarEinBefehl]

I've only played this great game for one week, but so far I found that I've always gotten better deltaV when using liquid fuel rockets instead of SRBs where I had them. This is mostly intuitive though, I've only recently discovered the addon which shows technical stats even before lauching. Haven't been able to double-check this gut feeling, so I was hoping if you guys could share your experience with SRBs?

[Guest]

Stock SRBs aren't really good for anything. Mods have some useful ones, though. You'd usually use them for an increase in launch TWR, but in stock KSP, it's rarely too low.

[thescientist]

they're a little more weight efficient than a rocket engine, that's probably why they're still interesting

[The Jedi Master]

The whole point of SRBs is that sometimes liquid isn't enough and the ship needs a little extra "push" to get off the pad. They were never meant for other uses. It's like it is in, ya know, real life.

[Tex]

As in real life, Solid Fuel rockets are a cheap way to provide extra thrust to heavier rockets. For example, everyone knows that the US Space Shuttle utilized two solid rocket boosters mounted to either side of the external fuel tank. Without these, the main engines on the shuttle would only provide a third as much thrust.

You can also see in Kerbal that the solids available do provide more thrust than a liquid engine with the same mass of engine itself and fuel. The main downside to solids is that once ignited, they can't be shut off until the fuel is depleted. As the great Eugene Kranz once said, "There was no way to shut 'em down, no way to throttle 'em, so if you had a problem with those, you rode it out until you could separate from the solids."

[Epthelyn]

As above, they do provide slightly better TWR than liquid rockets + fuel tanks, but in the current state of the game it really doesn't make much difference and it's nice to have full control over throttle. If a rocket starts spiraling out of control with SRBs ignited there isn't much you can do about it aside from hoping the they don't hit anything when you fire the decouplers.

When career mode requires currency, they'll be the cheapest way to lift pretty much anything.

[numerobis]

they're a little more weight efficient than a rocket engine, that's probably why they're still interesting

They used to be in some applications; now they aren't, because the 48-7S is lower total mass (taking into account fuel) in all practical circumstances.

[Murph]

They used to be in some applications; now they aren't, because the 48-7S is lower total mass (taking into account fuel) in all practical circumstances.

That's simply not true, that they are no longer useful because of the 48-7S. You need 10.5 48-7Ss to give the same thrust as a single BACC. For launching from the pad, I'd much rather slap a pair (or 4,6,8, etc) of BACCs on the side of my main tank, than deal with attaching LOTS of 48-7Ss for the same thrust. It's just easier and simpler to use the BACCs or RT-10s, especially if you want to play around by varying the number to find the sweet spot. Give me the SRBs every time, even if they are not quite as efficient, the simplicity and ease of construction more than makes up for hat.

[numerobis]

That's simply not true ... Give me the SRBs every time, even if they are not quite as efficient

If you agree that the 48-7S is more weight-efficient than the SRBs, what did I say that was false?

For sure, mass efficiency is not the only consideration -- I still use mainsails, for example, even though you can replace a mainsail with 50 48-7S engines to get the same thrust with less mass and higher Isp. And I use trusses even though cube struts are massless. Part count matters a lot, and complexity, and aesthetics also, and career-mode limitations, etc.

[Murph]

If you agree that the 48-7S is more weight-efficient than the SRBs, what did I say that was false?

Oh, my mistake, I apologise. I interpreted what you said as saying that they effectively made SRBs obsolete. Re-reading it, I now see a much narrower interpretation, that it's just the mass efficiency. Sorry.

[Dispatcher]

Good posts above. I find myself using SRBs as supplemental to other booster techniques; but whether or not to use them is often constrained by the craft design. Try experimenting with the large SRB vs. the LVT30 or some Radial 55s and see how they all compare.

[Motokid600]

Install Mission Controller Extended. Boom.. currency. With a budget my rockets are always 3-4 stages of solid fuel with a small liquid stage for the final boost into orbit. SO cheap. I can put a 10ton payload in orbit and keep the budget under 60k. Even cheaper if I put parachutes on the spent stages. MCE reimburses you once they unload for a certain %. A truly great mod. Highly recommended.

[SSSPutnik]

You can use them to lift fuel tanks which don't have engines on them. Using asparagus cleverly you can get the fuel tank to empty at the same time the SRB expires.

It may be more efficient just to stick an engine on the tank though.

[Anton P. Nym]

Solids definitely have their place. I use the larger solids to boost aerospike-driven stages (with high-efficiency but low-ish thrust) until they've burned off enough propellant to exceed an unassisted 1:1 TWR, for instance; makes for a much lighter craft overall. And I find Sepratrons invaluable; separating from radial heavy boosters, de-orbiting spent insertion stages, propelling ejector capsules, and even cheap de-orbit engines on my tiny Popcorn probes to save the liquid propellant for landings.

When currency gets involved, I think a lot more people will pay attention to the use cases for solids.

-- Steve

PS: They also really help with parts counts; engine and fuel tankage for each is 1 part, instead of three or more for asparagus designs. Folks with slower CPUs might be interested in trying solids.

Edited December 8, 2013 by Anton P. Nym

[allmhuran]

Their good thrust to weight makes them useful for exactly what you would expect: Lifting heavy ships off the launchpad.