We're fortunate to live in an era where there are so many advances being made in aerospace engineering. There are a lot of new companies creating new machines to get to space. However, a lot of them are of the SSTO/spaceplane variety: Dream Chaser, Skylon, SpaceShipOne and variants, the Lynx, . . . You get the idea. Yet there aren't a lot of rockets being privately developed, with Elon Musk and SpaceX leading the charge with the Falcon family. Does this pattern indicate a trend towards spaceplanes and away from rockets?
1$\begingroup$ I suggest you should rewrite the question to make it more focussed on a specific problem: like what are the advances that may make SSTO possible. Otherwise the question is likely to be considered starting an opinionated debate. $\endgroup$– Deer HunterOct 7, 2014 at 2:51
$\begingroup$ If you mean suborbital flights, it might turn out to be correct. It has thus far been taken care of by conventional rockets for military use (ICBM). Both technology and application would be revolutionizing. However, both still remain a challenge. SpaceX uses conventional style rockets for existing orbital markets. $\endgroup$– LocalFluffOct 7, 2014 at 10:09
$\begingroup$ Related: space.stackexchange.com/questions/5531/… $\endgroup$– David HammenOct 7, 2014 at 22:36
I don't think there's any sort of trend here; of the spaceplanes you mention, one exists only on paper, and none of the others are SSTO: they're all suborbital and mostly multistage. They're spaceships, not launchers.
None of them can do anything near what Atlas 5 or Falcon 9 are routinely doing today.
There's not a lot of need for development of new conventional launchers, because we have a fair selection of proven reliable designs, and no obvious way to make dramatic performance improvements to them.
Consider bullets. Gunpowder has changed a little since it was invented, but the bullet being propelled has changed significantly, in shape and material and advances like explosive tips. So it is with spaceplanes and suborbital vehicles - the rockets are largely the huge explosive that gives you lots of kinetic energy. Making a rocket that doesn't explode in construction, on the launchpad, in the launch sequence, on takeoff or in motion is difficult, and then there's not really much improvement to make after that. Messing about with the payload has much more capacity for variation; spaceplanes, satellites, space stations, weapons.
Rockets are brutally constrained by the combination of chemistry and the Tyranny Of The Rocket Equation. The rest is just minor tweaks and optimisations. Multi-stage launch vehicles were perhaps the greatest advance in rocket science, and people are always trying to put that genie back in the bottle, asking for fully reusable vehicles, smaller vehicles, greener fuels, cheaper launches. But without new chemistry or an entirely new engine based on nuclear power, it's all doomed to repeat the lessons of the 20th century.
Alternatively, give up on carrying the energy source on the launch vehicle, which is the source of tyranny for chemical rockets. Perhaps the best candidate is beam-powered propulsion, which quotes a rough number of 1 MW per kg payload.
TLDR: Rockets are big, expensive and there's not much to do to improve on what exists after decades of military research. The only option for significant improvement is to replace the entire technology with nuclear or beam-powered propulsion.
3$\begingroup$ I would never rate beam-powered propulsion as the best candidate to replace rockets. Fairy dust is more likely. $\endgroup$ Oct 7, 2014 at 22:33