US Air Force to Test Scramjet Aircraft

by Nancy Atkinson on May 13, 2009

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Charlie Brink, manager of the Air Force's X-51 "Waverider" scramjet research project stands with a scale model of the hypersonic aircraft. Credit: Ty Greenlees Dayton Daily News
The US Air Force has been developing an aircraft that employs an air-breathing scramjet engine, and hopes to run test flights in the fall of 2009. Officials hope the X-51 “Waverider” aircraft will provide high speed aircraft for reconnaissance or strike missions, and eventually the engines will be used for rockets to deploy satellites in space.

“The long-range goal of this for the Air Force is access to space,” said Charlie Brink, an Air Force Research Laboratory propulsion directorate official who manages the X-51 program from Wright-Patterson Air Force Base.

The first test flight of the X-51 will be on Oct. 27, 2009, launched from a B-52 aircraft with a missile booster to at least Mach 4.5, the minimum speed at which the air-breathing scramjet engine operates, before the scramjet kicks in and accelerates the vehicle to at least Mach 6 — six times the speed of sound. The Air Force Research Laboratory expects that the aircraft will fly for about five minutes before crashing into the Pacific. The October flight — and three separate test flights planned in early 2010 — are designed to demonstrate the practicality of using the air-breathing scramjet engine to power and control an aircraft at hypersonic speeds (Mach 5 or greater). The $246.5 million development program has been under development since December 2003.

Scramjet is an acronym for Supersonic Combustion Ramjet. A ramjet has no moving parts and achieves compression of intake air by the forward speed of the vehicle. The scramjet differs from the ramjet in that combustion takes place at supersonic air velocities through the engine. It stays aloft, in part, with lift generated by the shock waves of its own flight. It is mechanically simple, but vastly more complex aerodynamically than a jet engine. Hydrogen is normally the fuel used.

In 2004, NASA conducted flight tests of a hydrogen-based scramjet engine which reached speeds of Mach 9.6, or nearly 7,000 mph, powering an aircraft known as the X-43. However, none of the vehicles survived a flight test.

Brink compares the work of developing the scramjet — to complement aircraft turbine engines and rockets — with aviation’s earlier transition from propellers to jet engines. Air Force leadership will decide the scramjet program’s next step, depending on how the project turns out, Brink said.

Lead Photo Caption: Charlie Brink, manager of the Air Force’s X-51 “Waverider” scramjet research project stands with a scale model of the hypersonic aircraft. Credit: Ty Greenlees Dayton Daily News

Source: Dayton (OH) Daily News


Nancy Atkinson is Universe Today's Senior Editor. She also is the host of the NASA Lunar Science Institute podcast and works with Astronomy Cast. Nancy is also a NASA/JPL Solar System Ambassador.

Trippy May 13, 2009 at 1:12 PM


fpb May 13, 2009 at 1:35 PM

For the last 25 years (perhaps more) every third month the cover of Popular Science has been SCRAM JETS – Here they come. Is this for real or just another attempt to get the cover!?!?!

aerandir May 13, 2009 at 1:51 PM

Boy oh boy oh boy..
As excited as I am about these endeavors, I have to say that direct access to space by the military doesn’t sound too appealing.
The next Gulf War might just be at the border of Mare Serenitatis.

wayno@oz May 13, 2009 at 5:25 PM

Can humans survive accelerating to mach 9 or more? I thought the air-force already had this capability with the auroura?

Maxwell May 13, 2009 at 5:44 PM

Astronauts fly at speeds over Mach 24.
Speed isn’t inherently lethal, just the rate of acceleration. You don’t want too much in too short a time frame (which is why a 50G car crash can kill while an 8G rocket ride only shakes the fillings from your teeth).

I suppose I’ve secretly been cheering for the Air Force to put its space objectives in the forefront. Mainly because the way to sustainable and affordable space travel is more likely through a military or commercial program than by way of what NASA does.
Ever since the days of blue Gemini and Dyna Soar tho, they always seem to pull out at the last moment when something promising is just about launch ready.

Heres to hoping my hope aint misplaced again.

Lawrence B. Crowell May 13, 2009 at 7:28 PM

To be honest I see this as NASA/DOD money being pissed into the wind. What is the purpose of this machine? It can’t really have any space science purpose. A launch vehicle needs to get out of the atmosphere quickly and accelerate to 7km/s for orbit or 10km/sec or above for escape. Nobody is going to buy a ticket on this any day soon, and SSTs have been cancelled out as it is. So it all looks like a military program to design meapons against an enemy that does not exist.

Lawrence B. Crowell

aerandir May 14, 2009 at 12:20 AM

Well somebody’s got to start (and finish, evidently) something so we can get on those 2 hour London-Tokyo flights.
I just hope, at the risk of sounding naive, that its not misdirected passion that’s driving this effort.

gilmane May 14, 2009 at 2:58 AM

The X-51 is carried aloft by a B-52 bomber and then launched with the aid of a solid rocket booster. The B-52 is a bomber not a missle.

Maxwell May 14, 2009 at 4:02 AM

For the military, flying at high speed inside the atmosphere has it’s uses in missiles, fighters, and for sueveilance.
For spaceflight, the higher and faster you are at “launch”, the less fuel and oxidizer you need to reach orbit.

If you can make your first stage essentially an air breathing and fly return booster, in theory you can save a chunk of money. It also can be used to make ssto craft.

Its the work of the x-15 that needs to be compleated if we want to get from $10k per pound launches to a point where we can afford large numbers of people in space.

Dark Gnat May 14, 2009 at 5:56 AM

This should be the replacement for the Space Shuttle.

BTW, didn’t the AirForce fix the fuel tank problems on the X-33/Venture Star? I’m not a big fan of the Ares system anyway. I’m no engineer, but the Direct system makes more sense to me.

It would be nice ho have multiple ways to get people and cargo into orbit. That way there can be a backup in case of an emergency.

The X-51 can ride on top a B52, turn on the jets, get to high altitude, then swicth to booster rockets to get into orbit. I would think that this is very feasible, and probably safer than riding on top of a controlled explosion the whole way.

If it’s perfected, then we could see a new age in commercial space flights. If you think about it, most of our flight technology (including rockets) evolved from military applications.

Torbjorn Larsson OM May 14, 2009 at 10:16 AM

powering an aircraft known as the X-43

Heh, perhaps, if you by “powering” means decelerating it while operating. The engine tests were AFAIU done to test operation and survivability (i.e. that it didn’t melted within the ~ 10 s operation.)

The X-51 will IIRC be the first scramjet ever to actually power a vehicle. And then some!

Which is exciting, but not exciting in the sense that it can contribute to space operations. As part of an SSTO it will IIRC waste more mass than a similar powered rocket. Possibly that also applies for being a stage/”launcher”. I have to side with Lawrence B. Crowell in this.

Torbjorn Larsson OM May 14, 2009 at 10:22 AM

As an addendum: I believe the British Skylon has been mentioned as the only SSTO plane that has an air-fuel cycle that has the potential leg up on rockets. (And IIRC marginally, at that, shaving some 10-20 percent off launch weight. But hey, it saves some money!)

If the US military was serious about rocket usage I assume it would cooperate with that effort.

Aqua May 14, 2009 at 1:52 PM

Cryogenic fuel storage is the key word here… or perhaps fast electrolysis?

Maxwell May 14, 2009 at 3:16 PM

@Dark Gnat:

Yes Lockheed did indeed fix the problem it had with making large composite tanks, then went on to build working prototypes (of which we don’t know much because its all skunkworks).
Maybe they are hoping the government will change its mind about SSTO… seems unlikely tho.

Ares is the kind of system you need if you want to work in deep space and you want to do it right now. A big multi purpose booster for unmanned cargo and a reliable “stick” for regular trips. Easy to build, easy to use, but certainly not cheap.
Choosing between it and direct is a moot point. Direct offers no real savings (still have to man rate the booster as if it was a brand new rocket) and its cargo variant shafts us on tonnage to orbit.

NASA has a long running problem of putting all its eggs into only one basket at a time. If your stuck with that mentality then you end up wanting the biggest basket possible.
What they needed to do was keep SSTO research going the whole time. Something the Air Force has gotten closer to achieving than our space agency.

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