<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>All nice, valid points...up to a point! But when you are riding that rocket, it's nice to be able to shut it down in an emergency and not have to get such a kick in the pants to get away from it. Keep in mind, the last thing Challenger telemetered to the ground was that the SSME's were trying to shut down, having "run out of fuel" (due to disintegration of the ET)! An all-liquid bird got us to the Moon quite nicely, thank you! And on several of those flights, and IIRC two Shuttle Flights, a shutdown of a liquid engine resulted in a successful Abort-to-Orbit! Rockets are inherently dangerous beasts! And I have worked more solid systems than big liquids (though I cut my teeth on my own nitric acid/analine jobs as early as 15 years old), and I trust perfected liquids for high-value (manned or expensive satellite) payloads more than those firecrackers! Make no mistake: liquids make lousy quick reaction missiles (ICBM's, etc.), and it is a proven fact you do NOT want one aboard your submarine! But for big boosters, give me a high DENSITY-SPECIFIC IMPULSE combination like LOX/RP-1 or even hypergols.Ad Luna! Ad Ares! Ad Astra! <br /> Posted by trailrider</DIV></p><p>Either way you have known conditions that can lead to failure, whether mechanical, human or PFM failures happen in everything, that's what statistics proves, there is a number for everything. Liquids have more avenues for failure then solids, but most of them can be dealt with by having multiple engines and the expectations one or more will fail. Solids fit in a different category, with more then one you could have either or some, fail to ignite, or you could have a Challenger type event. I would even go as far as to say if such a failure as happened to Challenger had been planned for, and as pointed out the computers saw the problem, it may have been possible to save the vehicle and crew, if the failure had been anticipated. Challenger probably wouldn't have made a normal landing, but an ocean ditching might have saved the crew.</p><p>20/20 hindsight is great, but being able to anticipate, and plan for problems is more important. The real downfall of the Shuttle is that was not an option. The crew module is an independant structure mated to the airframe,get rid of all the stuff to support a two week mission and the crew module could be separated and safely recovered.</p><p>Too bad Shuttle 2.0 was never developed. </p><p> </p> <div class="Discussion_UserSignature"> </div>