After surviving 100 successful test runs, a crucial 2012 components test, and a 2014 feasibility study by the European Space Agency, Reaction Engines' new SABRE (for "Synergistic Air-Breathing Rocket Engine") space plane is getting ready for prime time. Encouraged by the results, the British government recently designated SABRE a "high priority" technology project, and allocated $90 million to support it.

And now the U.S. Air Force is climbing on board as well.

Earlier this month, UK-based Reaction Engines confirmed that the United States' Air Force Research Laboratory has echoed Europe's confirmation of SABRE's feasibility. What's more, the Air Force plans to cooperate with Reaction Engines on developing the engine.

Now, the holy grail for the Air Force, as it is for Reaction Engines, for Boeing (NYSE: BA  ) and Lockheed Martin (NYSE: LMT  ) at the United Launch Alliance -- for everyone, really -- is development of what's called a "single-stage-to-orbit," or SSTO, technology. One engine that can take a spacecraft from ground to space, and then come back again.

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