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

[Nutter]

- 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

-Doesn't really matter on the first stage, since it's also where the thrust comes from. And with lighter loads, you can even get away with putting them on the uppers.

-Can be pretty easily fixed or mitigated by offsetting them juuuust right, and if all else, a sepratron is only expensive in part count, but only really needed when you're flying some proper massive abominations anyhow. Though, I will nitpick; an "Ares I" style lifter has carried many a Kerbal past the skies beyond. Even if only counting mine.

-Point, but you generally don't want to do that in their natural habitat of "Just off the pad'" anyhow unless you seriously miscalculated something.

-Which is a bit of a shame, really. There could be at least a couple non-mod gimballed ones for the extra amusement factor. Though, again, thrust vectoring isn't exactly an efficient use of resources when you can use a whole lot of winglets!â„¢ instead.

So, really, they're the best part in of the game!

Edited May 9, 2015 by Nutter

[John FX]

I like SRBs. There is no reason to throttle down during the first part of a launch so lack of throttle or shutdown is no biggie and I treat them like a launchpad that starts at 11km and 600m/s

[Claw]

My 0.90 career game made extensive use of SRB, especially in the early game where they did the majority of my usual lift needs.

I've not made it very far yet in v1.0 career, so I'm not sure how much that's been impacted with the changes they've received...

Cheers,

~Claw

[moogoob]

I sometimes play around with using all-SRB launch stages (The "Fool" line of launchers, I call them), but they mostly serve a need to get the wet thrust-to-weight ratio of traditional liquid stages high enough for a decent launch. This is absolutely essential if you're attempting to do something odd like use the Kerbodyne Advanced engine (which has half thrust at sea level) as a launch stage.

[BluetoothThePirate]

Another wrinkle is the fact that engines have reduced thrust according to air pressure now, so the TWR of a rocket might not be enough on the pad even if it's plenty high 1000 meters up. Solids do a great job adding that bit of front loaded thrust right there at the start. Of course you never use them for anything post-launch unless it's some kind of stunt (cf. Abyssal Lurker or Scott Manley).

[Curveball Anders]

Note that SRB's can be set (pre-launch) with a given thrust value, so when dialled in they can provide a very effective boost during the first part of any launch.

So while uncontrollable post launch, they can be tamed ...

[FancyMouse]

I used much less SRB than my 0.90. Early career still needs that, but the transition seems much earlier. Mainly because (1) actually not that cheap, especially when you need much more mass to keep the same dV, it's not as cheap as it seems; (2) no gimble (3) TWR near end of life of SRB tends to get too large (even when you lower thrust in VAB) and it's easier to screw your rocket up (I found launching much easier after replacing my SRB with LFO engine)

IMO, SRB is mostly for early career when you don't have good LFO take off engine. When you have a usable LFO takeoff engine, then probably you can get rid of SRB

[match]

I always feel that when I need to drop the thrust on the SRBs that I did not engineer something correctly. I want them to burn as fast and strong as they are designed to be... and then stage them off.

-With Sepratrons deeper in the tech tree, I found that I need to be a bit more careful staging. Need to be out of a transition and as close to center of prograde ring to avoid mishaps. I use the extended radial decoupler far more than I used to, especially with the SRBs.

[viktor19]

Cheap SRB's combined with StageRecovery makes me feel so SpaceX...

[wumpus]

... Of course you never use them for anything post-launch unless it's some kind of stunt (cf. Abyssal Lurker or Scott Manley).

Even this isn't always true. As long as the next stage/payload is reasonably big, you won't see the Isp hit of the SRB. My preferred "basic lob a kerbal to orbit" 0.90 was a couple of stages of RT-10s with a high efficiency 48-7s or LV-909 as a third stage. This stayed well under the 18T limit and could even be launched with explosive staging to save the roots on the extra separator. I don't think I've used a third stage of SRBs, though (unless trying to build an all-SRB rocket, or other experiments).In the early game it is hard to beat an extra [explosively staged] stage or RT-10s for cost. Not sure how this works in 1.02's atmosphere (kerbal engineer isn't working for me).

[Yuming]

For a long time I had a problem where the outer layer of asparagus boosters would run out of fuel before the srbs attached to them did. Now that 1.0 has rendered massive asparagus stacks less effective, I'm finding more and more uses for them, as my rocket designs grow more sleek and minimalist.

[Snark]

I always feel that when I need to drop the thrust on the SRBs that I did not engineer something correctly. I want them to burn as fast and strong as they are designed to be... and then stage them off.

I don't see it that way at all-- setting the thrust on the SRBs is PART of engineering things correctly.

A big, big part of designing an efficient launch vehicle is making sure that it balances its speed right as it rises-- too fast too soon, and you end up wasting lots of fuel battling needlessly high drag. That's a big part of why liquid-fuel engines are so attractive, because you can throttle to control that.

The fact that you can't throttle SRBs is a major part of their charm (for me, at least)-- they give a benefit (cheap), at a cost (engineering challenge due to lack of throttling). It means you have to balance them very carefully at design time.

Adjusting their thrust is part of that design. It's highly unlikely that the optimal thrust level of takeoff will just happen to be an integer multiple of the booster you're using, so you fine tune it.

Perhaps the most dramatic example of that is right at the start of career mode, when essentially the only ship you can build is a Mk1 command pod sitting on top of a Flea, with a Mk16 parachute to cap it off. (That ship design should really have a name. I propose "Model T".) Putting a 100%-thrust Flea on that is tremendously overpowered. I did a little experiment: run that with a 100%-thrust Flea, then with a 30%-thrust Flea, and see how high they go. The 100-percenter made it to 4521m altitude; the 30-percenter got to 5704m!

The challenge with SRB is spreading their thrust out to optimize the boost from them. I often find myself using a sort of "poor-man's asparagus" with them. It's like this:

Suppose I work out that to launch my ship, I need 8 radial SRBs (doesn't matter which kind), and upon doing the math, I work out that if I put them all on 80% thrust, I'll have my desired total takeoff thrust.

So instead of putting on a single 8-symmetry group set to 80%, I'll put on two 4-symmetry groups, one of which is at 100%, the other at 60%. It looks exactly the same, and the takeoff thrust is the same. However, the advantage is that the first set of 4 will burn out early, then I can jettison them and I still get another period of thrust out of the remaining 4 (which at that point are probably plenty, given that a lot of mass has burned off by then).

[magnemoe]

Even this isn't always true. As long as the next stage/payload is reasonably big, you won't see the Isp hit of the SRB. My preferred "basic lob a kerbal to orbit" 0.90 was a couple of stages of RT-10s with a high efficiency 48-7s or LV-909 as a third stage. This stayed well under the 18T limit and could even be launched with explosive staging to save the roots on the extra separator. I don't think I've used a third stage of SRBs, though (unless trying to build an all-SRB rocket, or other experiments).In the early game it is hard to beat an extra [explosively staged] stage or RT-10s for cost. Not sure how this works in 1.02's atmosphere (kerbal engineer isn't working for me).

Yes, in 0.90 my standard satellite launcher was an satellite with around 135 liter fuel and a 48-7S. first and second stage was trashcans.

skipper core and four large SRB let me take 15 ton to orbit and return the core stage.

In 1.0 the terrible ISP and the increased cost makes SRB impractical as first stages so I mostly use them for the TWR kick to get me fast past 100 m/s.

[KSK]

Depends on what you're launching, what other parts you have available, ease of flight and simplicity of staging. Cost is a factor for sure but it's not the only one.

To take a recent example from my career game. I wanted to get three kerbals to the Mun and land at least two of them on the surface. Ideally I'd put them there with as much scientific equipment as I have to hand (thermometer, Goo and Science Jr).There are several ways of doing that as you'll know but in the end I opted for a lander based on the Mk1-2 pod, with a crasher stage to handle everything from trans-munar injection to powered descent minus the last 100m/s or so of delta-V needed to land.

To get all that into LKO, I have Skippers and BACCs. Not sure about the larger SRBs and they would probably be oversized for the rest of the rocket in any case. I ended up using an all-liquid design, based on a Skipper core with two shorter Skipper based side boosters. No propellant cross-feed, although that might have helped me trim some weight. I was finding that the problem with SRB based designs was that a single Skipper didn't have an efficient thrust to weight ratio once the initial kick from the SRBs was gone. Also, I was finding it difficult to fit enough fins around the core stage - gimballing from a single Skipper didn't give me enough control.

Total cost - around 54,000 funds if I remember rightly. Not cheap but not a disastrous price per head to the Mun either and easily affordable given the payouts from any sort of Munar or Minmus contract. For comparison, my previous 3-kerbal design (basically the same ship minus the landing legs and crasher stage) was only capable of orbiting the Mun or Minmus (and not doing much in orbit without running perilously close to empty) and set me back about 30,000 funds. That earlier design was based on a Skipper core and four BACCs.

TL: DR. SRBs are great but they're not the answer to everything.

[gom jabbarwocky]

I use SRBs because I am too lazy to faff about with asparagus staging most of the time.

[panzer1b]

Depends on what you're launching, what other parts you have available, ease of flight and simplicity of staging. Cost is a factor for sure but it's not the only one.

To take a recent example from my career game. I wanted to get three kerbals to the Mun and land at least two of them on the surface. Ideally I'd put them there with as much scientific equipment as I have to hand (thermometer, Goo and Science Jr).There are several ways of doing that as you'll know but in the end I opted for a lander based on the Mk1-2 pod, with a crasher stage to handle everything from trans-munar injection to powered descent minus the last 100m/s or so of delta-V needed to land.

To get all that into LKO, I have Skippers and BACCs. Not sure about the larger SRBs and they would probably be oversized for the rest of the rocket in any case. I ended up using an all-liquid design, based on a Skipper core with two shorter Skipper based side boosters. No propellant cross-feed, although that might have helped me trim some weight. I was finding that the problem with SRB based designs was that a single Skipper didn't have an efficient thrust to weight ratio once the initial kick from the SRBs was gone. Also, I was finding it difficult to fit enough fins around the core stage - gimballing from a single Skipper didn't give me enough control.

Total cost - around 54,000 funds if I remember rightly. Not cheap but not a disastrous price per head to the Mun either and easily affordable given the payouts from any sort of Munar or Minmus contract. For comparison, my previous 3-kerbal design (basically the same ship minus the landing legs and crasher stage) was only capable of orbiting the Mun or Minmus (and not doing much in orbit without running perilously close to empty) and set me back about 30,000 funds. That earlier design was based on a Skipper core and four BACCs.

TL: DR. SRBs are great but they're not the answer to everything.

I use them alot with super light satelites that can be launched into almost LKO on a single group of them with no decoupling ect. Aside from that i prefer LFO engines to save on parts.

Since part count is my absolute limitation, and i dont play career, i only use them when it makes sense from a part count perspective. For conventional rockets, i find launching something atop the ks25x4 (the biggest engine availeable) with a 14400 fuel tank or 2 atop is the best option for part count. Basically very lightweight payloads i use just a bundle of the biggest SRBs you can get and tweak thrust to get said payload out of atmo in as close to circularized as possible (and circularize with payload). For anything that is too heavy i tend to use those integrated fual tank+ engine boosters, and anything that one of those+1 orange tank cant lift, i stick atop a nasa part rocket and expand that as needed to get the desired dV.

LFO is also easier to work with, throttleable, can circularize your orbit, and they end up way less pats for any given payload above a certain amount. Since i like to play ksp by making SSTOs, capital ships, vehicles, and ground installations, and then having combat between them, and trying to develop armor thats better and better while keeping low parts, pure rockets never had much love from me. Most often even if its completely overkill i tend to go with a KR2l+14400 tank as upper stage with a adapter to 2.5m and possibly one more to 1.25m, and under that a ks25x4 and 14400 tank with optional radially attached 1440tank+ks25x4. Nnless the craft im launching happens to be extremely small, its what, 6 parts AT MOST (without radian tanks), and itll launch most anything i need it to. I might have to up the part count a tad by adding reaction wheels, but even that is what, 10 parts at most to launch 90% of all my smaller vessels. As for capital ships, the fairings end up weighing over 100t each, so i end up using a much larger rocket just to overcome the massive drag/mass.

Basically i view a rocket as a means to an end, and i dont care about cost, efficiency, ect, i just want the lowest part count that can get deliver whatever craft i want to whatever location i want it at, and even if it happens to have half its fuel remaining so be it, free fuel tank floating around is always nice.

While i might not see much benefits to SRBs (since i never do career), they are indeed way cheaper then actual LFO rockets and in many cases better if you dont care about parts even for very large rockets.

[darqen27]

I tend to build larger rockets, I really like the Saturn V, so I build my rockets tall and lean and I use Procedural SRB's to get off the pad. They are invaluable to me, and with SR I get my money back anyways since the SRB's land on the pad

[wumpus]

[mshnrmoe is quoting my suggestion to use SRBs in a second stage]

Yes, in 0.90 my standard satellite launcher was an satellite with around 135 liter fuel and a 48-7S. first and second stage was trashcans.

skipper core and four large SRB let me take 15 ton to orbit and return the core stage.

In 1.0 the terrible ISP and the increased cost makes SRB impractical as first stages so I mostly use them for the TWR kick to get me fast past 100 m/s.

It looks like I spoke to late, I'm definitely noticing that most of my old SRB tricks have been nerfed to death.

I still use the "kicker" (biggest stock) SRB tied to the sides of a liquid-fueled main stage, but forget about lighting anything after liftoff.

Even using smaller (you would think the new "flea" parts would be ideal for this) cans-o-boom for initial acceleration usually can be replaced with a kicker for better cost-effectiveness (especially if you already have one set there and paid for the separator.

The kicker ISP (atmospheric) is 170 (the other SRBs are worse, although I think the Rokomax BACC is slightly buffed relative to the other SRBs in 1.0.2). Shuttle SRBs have an ISP of 230. Do you think we can have a buff here? The new atmosphere (I don't think the ISPs changed) seems to have knocked the SRBs out of tune a it too much. A (somewhat) rich array of SRB tricks in KSP are no more due to the nerfing, and KSP is losing options (although not having everything outside of a gravity well be either LV-N or 48-7s is a plus).

[Mic_n]

the ISP on them sucks, but the actual cost is dirt cheap, so just slap more on.

Though yes, an awful lot of it is down to the former ubiquitousness (oooh) of asparagus staging, where you could get the benefit of sharing that boosters fuel amongst all your engines before shedding the dead weight of empty tanks as well as drop some engines that weren't so necessary now with that lower weight.

Personally, while we're talking about options, I'd like to see the radial-mount engines suck less. They were already pretty useless, but with the added drag now from radial mounts they're even less so.

[rofltehcat]

SRBs are great for early tech and light payload rockets.

Their only problem is that stock doesn't have 2.5m boosters. Srbs are great because they are simple to use and have low part count but when you get the larger engines this gets switched around completely. Why fuss around with tricouplers, 12 srbs, decouplers and struts (wobble->boom) when 1-2 skippers or larger do the job better with a lot less hassle?

Give us large boosters! And largr radial decouplers that don't require 10 struts to function.

Edited June 10, 2015 by rofltehcat

[Nich]

Funny someone said they use SRBs to get up to 100. I did it the other way using LF to get to 100 then relying on SRB to get me to the upper atmosphere then turning the LF back on. It is true though that once you hit 8 SRBs your better off with LF for additional thrust because of its density and part count.

[viktor19]

Personally, I don't use SRB's because of horrible (ASL) ISP. I know that they are realistically powerful now, but I simply don't like them. Instead of them, my smaller vessels are launched by my Reusable Stageâ„¢ that has 27t lifting capability with full recovery.

[clivman]

The largest solid has errors in the fuel and thruset values

[imaspacestation]

I almost never use them. If I need more thrust, I place a few Thuds.

[cephalo]

Now that I'm on to bigger rockets, I no longer use them either. With the rockets I use now, I would need 24 SRB's to get a couple hundred dv. Not worth the hassle.