|Launch vehicle||Falcon 1|
|Launch site||Kwajalein Atoll, Marshall Islands|
|Date/Time||2008-08-03 0334 UTC|
|Payload||Trailblazer, PRESat, NanoSail-D|
The third Falcon 1 flight, officially regarded as the first operational one, ended in failure after a collision of first and second stage following their separation.
SpaceX CEO Elon Musk wrote that "The problem arose due to the longer thrust decay transient of our new Merlin 1C regeneratively cooled engine, as compared to the prior flight that used our old Merlin 1A ablatively cooled engine. Unlike the ablative engine, the regen engine had unburned fuel in the cooling channels and manifold that combined with a small amount of residual oxygen to produce a small thrust that was just enough to overcome the stage separation pusher impulse.
"We were aware of and had allowed for a thrust transient, but did not expect it to last that long. As it turned out, a very small increase in the time between commanding main engine shutdown and stage separation would have been enough to save the mission.
"The question then is why didn't we catch this issue? Unfortunately, the engine chamber pressure is so low for this transient thrust -- only about 10 psi [689 hPa] -- that it barely registered on our ground test stand in Texas where ambient pressure is 14.5 psi [999 hPa]. However, in vacuum that 10 psi chamber pressure produced enough thrust to cause the first stage to recontact the second stage."
Launch Failures Chronology