ГЛА X-51 с разгонным блоком
Boeing has been contracted to produce four X-51As, with lessons learnt during each proceeding flight resulting in modifications to the subsequent vehicles.

Экспериментальный БПЛА Boeing / NASA X-51 под крылом NB-52 - возможно, на его основе проектируется гиперзвуковая крылатая ракета HABWC

The X-51A WaveRider hypersonic flight test vehicle loaded on a B-52H assigned to the 412th Test Wing at Edwards Air Force Base prior to the first of three flights, one captive, one dress rehearsal and the final live release, in 2009. Developed by the Air Force Research Laboratory, the Defense Advanced Research Projects Agency, Pratt & Whitney Rocketdyne, and Boeing, the objective of the X-51A programme was to demonstrate the ability to use air-breathing, hydro-carbon propulsion in the hypersonic flight regime, which is flight more than five times the speed of sound.

Prior to the first test flight of the X-51A the vehicle was flown under the wing of the B-52H mothership on several captive flights.

ГЛА X-51 с разгонным ускорителем на пилоне самолета-носителя B-52

The X-51A with its ATacMS booster, under the port wing of B-52H 60-0050 Dragons Inferno of the 412th Test Wing.

The X-51 is a technology demonstrator for a jet-fuelled scramjet, which has applications for long-range quick strike missions and single-stage to orbit space launches.

In addition to the flightworthy SJX61-2, Pratt & Whitney Rocketdyne also produced SJX61-1 s for ground testing.

The high speeds and conditions encountered by scramjets are difficult to replicate on the ground. The SJX61-2 was tested in a NASA wind tunnel at Langley, Virginia.