Usage of Solid Rocket Boosters versus Liquid Rocket Boosters

[leops1984]

Can someone more familiar with the history and technology of rocket design - what are the factors that go into the deciding whether to use SRBs as opposed to LRBs? I ask because it seems to be that there seems to be a distinct pattern of booster usage depending on when the rocket family in question was developed:

1. early Cold War - liquid boosters, if any (Soyuz, early Atlas, Saturn)
   
2. mid to late Cold War - massive solid boosters (Titan, Space Shuttle, Ariane 5)
   
3. end of Cold War/present - smaller add-on strap-on solids, modular liquid cores (Delta II/IV, Falcon Heavy, Angara)
   

Is it a matter of available technology (i.e., one particular tech was more feasible at different points in time), or differing rocket design philosophies at different times, etcetera?

[Streetwind]

Humans like seeing patterns in things (that tendency even has a name, which I forget), but correlation does not imply causation. Especially in such a small sample pool, with just a handful of launch vehicles in each era. It might be that this is simply a coincidence.

For example, the fact that Ariane 6 will no longer be using giant solid strap-on boosters but instead shift to small solid strap-on boosters is partly due to being expressively designed for modular payload capability, and partly because those small solid strap-on boosters are borrowed from the Vega project so they can save money by not having to develop new ones. And Ariane 6 would never go all liquid or all solid either, because France is producing solid fuel tech and Germany is producing liquid fuel tech, and these two countries alone account for more than 50% of ESA's budget between themselves and are thus required to find a compromise before ESA can do anything at all. As you can see, none of these reasons actually involve the discussion of liquid vs. solid in any way.

If there is a pattern, though, then perhaps it is driven by payload needs and technological advances. Solid motors have always had a price advantage and a performance disadvantage. During the space race, price was irrelevant, performance was all that mattered. Your rockets had to lift more and fly farther than the other country's rockets. The payloads were huge, and losing was not an option. Then after Apollo, the space race evaporated, and space budgets evaporated with them. Solid boosters suddenly looked a whole lot more attractive. And finally in the modern era, payload sizes plummeted as the ISS was finished and hardly anything larger than a commsat remains to launch (and even those are getting lighter). Now you want to downsize, have rockets as modular as possible so they can handle different payload sizes at minimum price. Very large solid boosters don't deliver that, better use larger numbers of smaller ones. Or try to save money by copypasta'ing your liquid mainstage instead of having to develop a new solid solution for a profile where no existing ones are readily available.

(And by the way: Ariane 5 is a post cold-war vehicle, launching first in 1996 - seven years after the collapse of the Soviet Union.)

[Kryten]

Because there are only a few nations with launch capability in the first place, individual policy changes and technological advancements have a large effect.

Some countries have consistently used solids since the start of their programmes-Israel, India, Japan, Brazil-with only India using large segmented similar to US efforts.

Some simply don't use solid boosters-Iran, both Koreas

Some only use solids in missiles, and relatively small launch vehicle derived from missiles-China and Russia

US dropped large solids for HLVs for cost reasons, but they're being retained for SLS

[magnemoe]

The first space rockets was ICBM with an extra stage, liquid fueled with storable propellant and oxidizer.

They was expanded as you wanted larger payloads.

later you got specialized space rockets with LOX, an satelite launcher has very diferent demand from an ICBM. An ICBM need to be stored for decades and be ready in minutes.

An space rocket need to be reliable, this is not so important for an ICBM, you can always launch an new one, cost is important but you don't need to store it and you have weeks making it ready for launch.

ICBM moves to solid fuel as its easier and safer to store, size and accuracy of nuclear weapons goes down so you manage with an smaller launcher, solid has lots of benefits on an submarine where an leak from the rocket would be very dangerous.

However large solid rockets are pretty hard, Russia still have lot of problem with their solid fuel ICBM, yes it might be mission creep as it will replace all existing ICBM including the ones on submarines.

For space rockets SRB are cheap and it make it easy to expand performance.

[Bill Phil]

The main factor is usually cost. LFBs are generally more expensive for a given size. Especially for a shuttle like vehicle.

[kerbiloid]

SRB has less ISP and is sensitive to a frost (is important if you don't have KSC in a tropical country).

[Nibb31]

SRBs are used for ICBMs because you light the fuse and they go. LRBs need propellant storage and fueling before you can launch them, which is maintenance intensive.

In civilian rocketry, SRBs are often used because they are derived from military rockets, which is a way of assuring solid fuel fabrication and ICBM capability. This also makes them cheaper, because resources are shared between military and civilian contracts. Everyone gets a good deal.

[magnemoe]

SRB has less ISP and is sensitive to a frost (is important if you don't have KSC in a tropical country).

Artilery rockets uses solid fuel and works at any temperature. More likely that the US and French use some who don't like cold as its not important for them.

[rodion]

SRB has less ISP and is sensitive to a frost (is important if you don't have KSC in a tropical country).

if you're thinking of challenger, the problem was in the sealing of the segments that the boosters were constructed from rather than an intrinsic temperature-dependent design deficiency with solid rocket motors.

[Sandworm]

Solid rockets are more storable, ie they don't contain chemicals that eat through metal rocket bodies. This means they can it "fueled" indefinitely and launch on short notice. That makes them better for weapons. Shuttle use of SRBs was mostly a political decision. It supported the solid fuel industry which would otherwise have languished, harming the readiness of the ICBM/SLBM fleet.

Solid fuel also has a higher energy density. There is talk of how this improved low-atmosphere performance, but the it is far more important for weapons. Some treaties limited the size of ICBM launch silos. Solid fuel means you can stick a more powerful missile into a smaller silo, particularly important for SLBMs. Also good if you want don't want to bother building new silos to fit bigger/better missiles.

Thirdly, solid fuels are more easily ignited at 0g where liquid fuels would be sloshing around. Again, for weapons. SLBMs do not ignite inside the sub. They are pushed upwards using steam and ignite only once above the surface. Specifically, they ignite as soon as the missile starts to fall back towards the sub, at 0g.

See this vid:

The launch is at 1:00. Watch the missile stop in mid air before ignition. Note there isn't any flame as it breaches the surface. That's all steam.

Oh, and solid fuels work better on spin-stabilized rockets where liquid fuels might stick to the sides of the tank. This harmed a recent SpaceX experiment when they lost fuel flow prematurely because the rocket was spinning to quickly.

Edited December 6, 2014 by Sandworm

[kerbiloid]

Artilery rockets uses solid fuel and works at any temperature. More likely that the US and French use some who don't like cold as its not important for them.

Artillery rockets have 10-20 cm diameter and less than 100 kg of solid fuel. Launch vehicle are a bit bigger.

[kerbiloid]

if you're thinking of challenger, the problem was in the sealing of the segments that the boosters were constructed from rather than an intrinsic temperature-dependent design deficiency with solid rocket motors.

No, I'm thinking of North of USA has the same latitude as South of Russia.

Also it's not my opinion, I have no my own rockets except of KSP ones.

[Kryten]

The US has repeatedly launched all-solid launch vehicles from a site in Alaska, and the US and Russia have both launched solid sounding rockets from bases in Antarctica.

[Sandworm]

if you're thinking of challenger, the problem was in the sealing of the segments that the boosters were constructed from rather than an intrinsic temperature-dependent design deficiency with solid rocket motors.

Challenger's problem wasn't bad sealing. It was that they were doing sealing in the first place. They wanted to spread Shuttle's manufacturing budget to other states. (Insert rant about congressional budget politics.) They needed the boosters in segments so they could be manufactured in and shipped by rail from Utah. The better and safer design would have been to build them in one piece close to the launch site. SRB design was also influenced by the idea that Shuttle would launch military/polar flights from Vandenberg and so would need delivery of parts to multiple locations.

http://www.tsgc.utexas.edu/archive/general/ethics/boosters.html

Edited December 8, 2014 by Sandworm