Just as Virgin Galactic to launch small satellites from a plane, another plan to use atmospheric airplanes to get small payloads to space is riding off into the sunset. DARPA gave Boeing funding to investigate ways to get small payloads to space riding on a F-15 fighter jet. Now, it's pulling back on that because both tests resulted in explosions.
The root of the problem in the tests was nitrous oxide-acetylene, the kind of propellant used in the rockets. It behaved unpredictably, enough that the defense department considered it a liability on board aircraft. Some variation of the technology will still be developed, albeit without the schedule 12 flights meant to take place in 2016.
If Boeing and subcontractor Orbital ATK can pull off making nitrous oxide-acetylene more stable, then DARPA may fund more flights, as it still wants to pursue low cost, launch-any-time satellite launches that are fired like missiles that go into space. But for now, 2016 is not that year.