Hmm, IMO the shuttle was a very unfortunate diversion.
The first casulty was the Skylab space station, launched in 1973!! Remember= ? It was lost because of huge Shuttle schedule overruns. http://en.wikipe= dia.org/wiki/Skylab Skylab launch:
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Look how big it was:
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Shuttle was never man-rated because during early launch stages there is no = possibility of crew escape and survival (Soyuz-TMA is man-rated).
The wings are a huge liability. They prevent launch if there is anything a= bove a light breeze (Soyuz has no trouble launching in high wind and blizza= rd conditions). Wings are a problem during the early re-entry too because = they force a thermally very sub-optimal attitude and required brittle, high= temperatute tiles. For landing a 70+ ton vehicle the wings are rather sma= ll, forcing high landing speeds.
Lack of redundancy. Single engine out can only be tolerated very late in t= he launch phase. By contrast, Saturn-5 could successfully continue the mis= sion with one engine out (happened more than once). Space-X Falcon also ha= s engine redundancy (on the first stage).
Segmented, solid strap-ons. They can't be turned off -- once ignited the s= huttle WILL leave the launchpad, even if the explosive hold-down nuts are n= ot fired! With the solids, there is no way to test correct engine operatio= n during hold-down. Segmentation required seals which could (and did) fail.
Huge external tank. Forced by a bad case of the "liquid hydrogen religion"= at NASA. First stages are better suited to LOX and kerosine - the Isp is = a little lower but the tank can be much smaller, thus making up for it.
The Shuttle Launch system can actually launch about 90t to LEO. Unfortunat= ely 70t of that is the orbiter and 20t is the max payload. So, of the 2000= t launch mass, only 1% is delivered to orbit. Cargo-only rockets typically= deliver 5%.
There is a lot to be said for separating cargo and personnel delivery. Cre= w safety is expensive, so keep it to the smallest practical vehicle. Cargo= replacement costs are lower than the extra cost of using a man-rated launc= h system would be - so an occasional loss of cargo can be tolerated.
Watch Space-X. AFAICS, they are on the right track for launch systems. Bigelow Aerospace seem to be on the right track too with their inflatable s= pace station modules.
Without NASA developing their own launch vehicles, what Space-X, Bigelow an= d other enterprises are doing now could have happened 30 years ago.