So far, he added, the program has done no comprehensive ground tests against nuclear assaults.
Ground tests had shown it could be safely fired for 70 seconds, Whitesides said.
In recent ground tests, they failed five of six objectives, the Congressional Budget Office report said.
Months of ground tests are ahead but its creators hope the hybrid craft will fly over the UK this summer.
In late January, the Concorde manufacturer, the EADS consortium in Toulouse, France, began ground tests of a modified Concorde.
The extra thrust was not obvious in ground tests of the engine, he said, because of the atmospheric pressure at sea level.
Before deciding whether to allow passengers to use phones before takeoff, several airlines conducted ground tests to see if cellphones would interfere with systems.
On a visit to London in the first week of October to reassure customers, investors and the media, Whitesides was keen to emphasise that the new fuel had passed its crucial ground tests.
Charles R. McClinton, technology manager for the Hyper-X program at Langley, said researchers have worked on scramjets for more than 40 years, building mountains of data from wind-tunnel and ground tests.
The calculations were based on data from ground tests on the shuttle boosters and some gathered during shuttle flights, as well as best guesses based on the preliminary design of Orion.
As a result, the rocket released its satellite payload into a much lower orbit than it should have done.Since then, engineers have been trying to recreate the launch in ground tests to see what caused the rotation.
