27 rocket engines sounds like some Soviet N1 disaster waiting to happen..

As far as SRB's go, they don't have a big application for anything but putting nuclear weapons into space. They are the worst possible choice for manned rockets and make crew escape basically impossible. NASA uses them to keep ATK in business just in case someone needs to build a bunch of ICBM's again.

So far they have a pretty good success rate. A single Falcon-9 can still fly with two engine failures. They actually had one engine-out on the previous ISS resupply mission in December. Only required the other 8 to burn a tad longer to achieve same orbit.

Well, according to KSP, solid rocket boosters help the efficiency of the flight.

if a rocket is all engine/fuel, then you keep carrying unnecessary weight all the way up, while SRBs are jettisoned after they're spent.



the survival thing is a pointless argument...without a good escape mechanism it doesn't matter what type of rocket it is after it leaves the ground.

But the other thing is payload;


Thrust at sea level;

SpaceX heavy booster - 5580 kN

NASA SLS SRB - 16000 kN

NASA is planning/planned to replace these SRBs with something else. They have a competition going to decide the replacements and there are liquid fuel boosters among the competition.

The exhaust from a solid booster is rather nasty compared to the exhaust from a liquid one, that and not being able to shut them down makes designing a working escape system difficult.

Staging means you aren't carrying all the weight up, once the rocket fuel is used up they are jettisoned, liquid or solid. Fuel/weight gets burned off the same no matter what type of engine it is.

They are very attractive to save cost and improve performance though. Another reason NASA used them was for some military missions they had planned, polar orbits or something that never ended up happening. The o-ring failure between the segments of an SRB on the Challenger changed all of that.

I didn't notice that the Heavy was staged when I posted the first reply.

It's true that by estimates the Heavy will be much more economical at taking smaller payloads into orbit (as long as the stages can consistently land safely), but the SLS will carry about twice the payload into orbit.

But until we unlock orbital assembly and manufacturing, the SLS will be necessary for the large and heavy vehicles we want to use for manned exploration of the moon and mars.

Basically, they're designed for very different purposes.

NASA has sent so many probes out you'd think they would have the science to unlock those by now.