I think that was a complete failure
U,S hypersonic test flight"However after 16 seconds, a fault was identified with one of the cruiser control fins.
"Once the X-51 separated from the rocket booster, approximately 15 seconds later, the cruiser was not able to maintain control due to the faulty control fin and was lost," the Air Force statement said.
One of four X-51A vehicles remains after a series of tests with mixed results.
U.S hypersonic flight test
The other hypersonic programs such as Falcon HTV-2 are related to "pure" ballistic missiles hence they are not pursued eagerly.
The ballistic missile launch can be detected as a nuke attack.
The information given is misleading because mach numbers are inconsistent.