Are there any operating SSTO (single stage to orbit) vehicles? Are there others being tested such as Reaction Engine's Skylon?


Operating? No.

Under development? Maybe. Define under development. Someone is always working on an SSTO, but none have ever delivered (not to say it is impossible, just that the track record to date is null). Is Skylon seriously under development? Hard to say. People WANT to develop it, but the question is, do they have the needed funding. As of now, no. Maybe in the future.

Several rocket stages have been shown to possibly be capable of SSTO performance numbers. (Saturn V second stage, maybe an Atlas without sustainer engines). But generally the payload delivered would be miniscule, or they have some other limitation.

  • $\begingroup$ Sounds bleak so far. The idea of a space plane is really fun, but not practical (yet). $\endgroup$
    – Stu
    Jan 24 '14 at 18:23
  • $\begingroup$ @Stu Wings seem intuitively obvious, but the math does not support intuition. They are heavy, and hard to protect during reentry. The reality is, SSTO is not the goal. Reusability that is cheap, and fast is the goal. TSTO reusable is SERIOUSLY under development at SpaceX. Take heart in that aspect. $\endgroup$
    – geoffc
    Jan 24 '14 at 18:29
  • $\begingroup$ Great point. The cheapest to deliver is going to win this race. It makes a lot of sense to dump any empty or useless weight on the way. Now I understand why there is little-to-no development with SSTO vehicles. $\endgroup$
    – Stu
    Jan 24 '14 at 18:33
  • $\begingroup$ @Stu It may be that Skylon succeeds. Here is hoping. It may be that F9R succeeds. Here is hoping. They may not. It IS rocket science. $\endgroup$
    – geoffc
    Jan 24 '14 at 18:43
  • 1
    $\begingroup$ SSTO is perfectly possible but way below the cost curve of multi-stage with $/kg to orbit cost as it needs to lift all the dead weight of atmospheric launch engine while switching to much more efficient (but lower thrust) orbital ones. The solid state booster of the shuttle would probably be capable of reaching LEO alone, but the payload would be unimpressive. $\endgroup$
    – SF.
    Dec 18 '14 at 13:53

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