Print 13 comment(s) - last by maugrimtr.. on May 8 at 10:50 AM

It also achieved Mach 5.1 at 60,000 feet

The X-51A Waverider completed the final flight of its test program last week, which proved to be the longest air-breathing hypersonic flight ever. 

The X-51A Waverider is an unmanned scramjet demonstration aircraft for hypersonic flight testing. Boeing developed the X-51 Waverider, and its first flight took place May 26, 2010. The idea of the program was to prove the viability of air-breathing, high-speed scramjet propulsion. 

May 1 marked the fourth and final test flight of the X-51A Waverider. It took off from the Air Force Test Center at Edwards AFB, California a little after 10 a.m. It was coupled with the B-52H Stratofortress, and released at 50,000 feet.

The X-51A Waverider reached Mach 4.8 in 26 seconds while powered by a rocket booster, but after separation from the booster, it achieved Mach 5.1 at 60,000 feet. 

Once the fuel supply was gone, the X-51A Waverider splashed into the Pacific Ocean. During its test flight, it traveled over 230 nautical miles in just over six minutes and collected 370 seconds of data.

"It was a full mission success," said Charlie Brink, X-51A program manager for the Air Force Research Laboratory Aerospace Systems Directorate. "I believe all we have learned from the X-51A Waverider will serve as the bedrock for future hypersonics research and ultimately the practical application of hypersonic flight."

Source: Wright-Patterson Air Force Base

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By DanNeely on 5/6/2013 1:39:20 PM , Rating: 2
The SABRE appears to be a hybrid jet/ramjet/rocket; because of the ~mach5 switch over to pure rocket operation (the SR71 used a jet/ramjet combo). Ramjets have a peak efficiency around mach 3; and become unworkable around mach 6 due to the increased difficulty in slowing the air intake to subsonic speeds prior to the combustion chamber.

Scramjets avoid the problem by keeping the air flowing through the combustion chamber moving at supersonic velocities this requires relatively high mach numbers to ignite (the X51 was boosted to mach4.5 before activating its scramjet); but can remain airbreathing to much higher mach numbers. Current estimates are between mach 12 and 24. The latter would allow for a surface to orbit vehicle roughly an order of magnitude smaller (for a given payload) than possible with a conventional rocket.

By Amiga500 on 5/6/2013 3:05:12 PM , Rating: 3
Skylon takes off from a runway, flies from ground to space, using aerodynamic lift where it is most efficient to do so and with not requiring air for the ultra-high altitude portion of flight - it is a single vehicle to orbit. By removing the need for carrying oxidiser till ~25km altitude, a serious amount of vehicle weight is saved.

In contrast, the SCRAMjet needs:
- a dedicated lift vehicle to altitude.
- a dedicated booster to get to high supersonic speed (or the dual-mode ram/scram noted below).
- a dedicated rocket motor to elevate payload to full orbit [21km is far short of 300km!].

Furthermore, a SCRAMjet by its nature needs air - therefore it is operating in an environment where drag is still an issue. It is always at a disadvantage to SABRE at very high speeds, as SABRE can elevate above air and hence into very low drag.

While there are dual mode ram/scramjets on test benches (such as facet), I have yet to see anything with a turbo/ram/scram motor beyond concept papers.

By geckor7 on 5/6/2013 11:47:44 PM , Rating: 2
@ Amiga500, what you contrast as necessary prerequisites for SCRAMJET use aligns quite nicely for a hypersonic cruise missile application to satisfy DoD's directive of prompt global strike ability with conventional weapons in as little as 1 hour. Maybe some learnings trickle into research for civilian applications years down the road, but x-51 has validated research and provided a viable path for a HSCM program.

By Amiga500 on 5/7/2013 6:22:46 AM , Rating: 2
True. I was thinking more useful things than missiles :-)

But then, using something akin to Skylon to place a load of tungsten bolts in orbit means they will re-enter with extremely high Vmax, and with less time spent in hostile
"air-space"... and won't be delicate enough to be destroyed
at the first hint of SAM shrapnel.

DARPA/DoD have looked at orbiting tungsten rods for quickStrike before. Nothing ever came of it... possibly out of fear of "weaponising space", which would be pushing on a few treaties.

By maugrimtr on 5/8/2013 10:50:58 AM , Rating: 2
I can understand why. At low Earth orbit, any weapon would be zipping along above Europe, Russia, and Asia. You can imagine their reaction - it would be the same as ours!

"When an individual makes a copy of a song for himself, I suppose we can say he stole a song." -- Sony BMG attorney Jennifer Pariser
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