Is there a reason not to use SRB's on launch from Kerbin?

[cephalo]

I see many examples from people, who know more than I do, of launch sequences that use discardable liquid boosters instead of SRB's. Why would you not want SRB's at launch? Aren't they the best way to start the ascent?

[Jovus]

They're potentially less controllable. That's pretty much it. The $$/dV can't be beat.

[Capt. Hunt]

I use solids all the time, but the problem with SRBs is they aren't controllable, you light 'em and they go up. I think a lot of people prefer liquid rocket boosters instead because they can be throttled.

[Red Iron Crown]

Liquid boosters can also feed the core booster with fuel lines so it maintains its full fuel load until staging.

[THX1138]

In my opinion SRBs are the appropriate first stage and most people using liquid-fuelled rockets have failed to adapt to the introduction of cost as an aspect of KSP rocket design.

[cephalo]

Liquid boosters can also feed the core booster with fuel lines so it maintains its full fuel load until staging.

If you jettison those boosters do the fuel lines come loose without causing problems?

[nikolay-spb]

depends on your style, if you play carrier mode then it will be good to use them in first stage because they are cheap.

[Red Iron Crown]

In my opinion SRBs are the appropriate first stage and most people using liquid-fuelled rockets have failed to adapt to the introduction of cost as an aspect of KSP rocket design.

People using stages have not adapted to cost as part of KSP rocket design. An expensive fully recoverable lifter will beat a cheap expendable one just about every time.

If you jettison those boosters do the fuel lines come loose without causing problems?

They do.

[Jarin]

SRBs' primary drawback from what I can tell is weight. Only an issue in early career, obviously.

[ghpstage]

In career they have advantages in being very effective on cost and parts count terms, both of which are particularly attractive early in the game.

The disadvantages are that they are very poor on weight efficiency and dV values now, while also very difficult to control and there still aren't any larger ones.

Since 1.0 I have favoured liquid over solid far more than in 0.9.

The cheap cost doesn't even seem to be an issue now in early career, asince 1.0 funds seem to just fall from the sky. The only reason I use them is parts counts, the small fuel tanks and those fins eat up a lot.

Edited May 8, 2015 by ghpstage

[cephalo]

People using stages have not adapted to cost as part of KSP rocket design. An expensive fully recoverable lifter will beat a cheap expendable one just about every time.

That sounds like you advocate SSTO which obviously does not include boosters. In career mode, do you need a lot of tech to achieve this? I'm almost done with the first level of science center, and I can make a big rocket, but the darn things are very heavy. If I could get it to orbit in one piece, I'd need a hundred parachutes to recover it in one piece too.

[ghpstage]

Nevermind....

Edited May 8, 2015 by ghpstage

[Red Iron Crown]

That sounds like you advocate SSTO which obviously does not include boosters. In career mode, do you need a lot of tech to achieve this? I'm almost done with the first level of science center, and I can make a big rocket, but the darn things are very heavy. If I could get it to orbit in one piece, I'd need a hundred parachutes to recover it in one piece too.

It's true that recoverable SSTO is difficult in the early stages of a career game. I'm not really an SSTO advocate per se; IME career mode gives enough funds to support either strategy, but if you are driving for minimal cost SSTOs are the way to go.

[wossname]

I'd say don't be afraid of using SRBs as an assistive force while launching. It's a good idea to have a vectoring liquid fuel engine in the middle to provide some level of thrust and directional control but it's great to have the brute force of the SRBs to get you off the ground ASAP.

Use some struts to ensure the SRBs don't flap around and tear your ship to pieces. If you have roll issues, then look carefully at the symmetry of your design - are your SRBs twisting? Add more struts if so.

[cephalo]

Aha, usually my SRB's, especially the bigger ones tend to flop around a bit. Do struts come off when the boosters are jettisoned, or do I need decouplers for the struts too?

[THX1138]

The struts automatically disengage whenever decouplers or docking ports necessitate it.

[mic_e]

- SRBs are a lot heavier

- They are usually side-attached, so decoupling them might be risky

- You can't turn them off

- They don't provide control

[aleis]

When you get to the really massive ships the get out classes in terms of thrust. But as stated use them for first staffing a lot

[Motokid600]

I pretty much only use SRB's for sustainer stages for anything but the smallest payloads. Make a very large stage that has most of the DV you need to orbit. Its TWR will be under 1 so you need SRB's to lift the rocket off the ground. By time and SRBs burnout the center engine would have burned enough fuel to sustain itself and go to orbit. Works really well.

[Norcalplanner]

SRBs are peppy and cheap. They make the most sense at launch when used in combination with LF engines. I'll use them in most of my designs, even when it's a big asparagus-staged thing.

[cybersol]

I liked SRBs in 0.9 career mode, but in 1.0 they nerfed them to where I find fuel pumping asparagus LFO stacks better. For instance, in 1.0 the Thumper has 30% less burn time with a 17% reduction in ISP relative to LFO engines and a 50% increase in cost.

[Jouni]

The two largest SRBs are kind of useful for launching small payloads, but otherwise I don't use them that much.

It's true that SRBs are cheap, but it doesn't matter. All rocket parts are cheap compared to contract rewards and buildings. I never care about money when building rockets in the career mode, because the savings from being cost-effective are negligible.

The actual rocket prices in the game are not measured in funds, but in tonnes and parts. Before you can upgrade the launchpad to tier 3, launch mass is the main limit on rocket construction. Because SRBs are so inefficient, you can only use them for launching small payloads. Those payloads are so cheap to launch anyway, that the price advantage of SRBs matters even less than usual.

After the final launchpad upgrade, part count becomes the main limit. Prices still don't matter, unless you're building huge rockets. But if you're building huge rockets, you'll probably try to keep the part count under control, because high part count causes annoying lag during the launch. You can't really use SRBs, because they're so tiny that you'd need a large number of them.

[Guest Darth Gerbil]

SRBs are dangerous for manned launches because if, say, the main engine overheated and took the center tank with it, then the srbs could come loose and smash into the command pod, whilst bipropellant engines can be shut down with the abort button.

[Pax Kerbana]

Thrust, weight, burn time, and part count become considerable constraints when payload to orbit mass starts increasing. For almost all career contracts SRBs can used pretty effectively.

You have a much larger TWR and burn time options available by using liquid fueled boosters. I would say off the top of my head that everything under 100 tons to orbit can make effective use of SRBs so long as part count is reasonable. If your talking 250 tons, forget it... The simplicity of having a 4 boosters is a huge advantage (esp. for part counts) than having SRB bundles strapped to the side of your rocket.

It takes 2 KD25s to get close to a Mainsail's thrust at the pad. But this is with the SRBs at full thrust which means the will need to be discarded quickly while still deep in the atmosphere; the Mainsail can take you much further.

I think an ideal way is to use boosters that consist of SRBs strapped to a core fuel tank without a liquid fueled engine. Trying to get the burn times to line up with fuel consumption is very difficult which makes this an impractical method.

What is really nice is using only SRBs for boosters and dialing back the SRB thrust to 3/4 to 1/2 and riding it out to upper atmosphere. That way you can achieve orbit with a "middle" stage with much lower TWR.... Which if you did it correctly will be the first stage engine.

Plus the rapid acceleration gain at the last part of an SRBs burn is unreal... My Kebals seem to love it, they keep riding these things into orbit!

In 0.90 I would send up Mk1-2 orbiter pods that's could change orbit from LKO to HKO and back to transfer crew between stations and interplanetary ships and then de-orbit. Those pods would be sent up with nothing but SRBs... total of about 15k funds as non recoverable. Not all Kerbals liked this but a select few sure did!

[MacroNova]

SRBs are awesome for boosting your rocket up to an altitude where the liquid fuel engines can be more effective. Use radial symmetry and put between 3 and 8 of 'em around your rocket. Use the control-surface winglets (not the fixed kind) for control authority. Slap a nose cone on 'em, and use sepratrons to make sure they don't smack your rocket when they decouple. These parts are in the game for a reason!

I like my SRBs to provide a TWR of between 1.3 and 2.0 (including atmosphere) during operation. A little excess is OK. If you're getting too much thrust, you can tone it down in the VAB with the tweakables.

The other day I tried building a rocket with them and without them. It was much cheaper with them.