Home » Air Force » Second X-51A Hypersonic Test Flight Ends Early

Second X-51A Hypersonic Test Flight Ends Early

As we referenced earlier today, the Air Force’s X-51A Waverider hypersonic test vehicle is now two-for-two when it comes to test flights being cut short.

On June 13, the Waverider was dropped from a B-52 at 50,000 feet and it was successfully boosted by a rocket to Mach 5 where its scramjet engine ignited on ethylene. Things went wrong when it tried to transition to the deliberately tough to ignite JP-7 jet fuel (originally developed for the SR-71 Blackbird). Apparently, the JP-7 wouldn’t light despite several attempts to do so and the craft glided itself into the Pacific Ocean in the waters of the Navy’s Point Mugu test range off the California coast.

From an Air Force announcment on the “less than successful flight test”:

According to Charlie Brink, the Air Force Research Laboratory’s X-51A program manager, AFRL, Boeing and Pratt-Whitney Rocketdyne engineers are reviewing the large amount of telemetry data collected during the test flight to identify the cause of the anomaly.

“Obviously we’re disappointed and expected better results,” said Brink, “but we are very pleased with the data collected on this flight.”

“I am extremely pleased with the AFFTC and Point Mugu’s support and execution of this complex flight test mission as they provided us every opportunity for success in this endeavor,” said Brink. “We have attempted two scramjet experiments now where one successfully lit, and one did not.”

“We will continue to examine the data to learn even more about this new technology,” he said. “Every time we test this new and exciting technology we get that much closer to success.”

Boeing and Pratt & Whitney Rocketdyne built four X-51A flight test vehicles with the program goal of reaching Mach 6 in hypersonic flight. The next flight is tentatively schedule for fall 2011.

Last year’s test flight saw the scramjet ignite but a manufacturing flaw led to hot engine gas seeping into the airframe after it had flown for143 seconds at a max speed of Mach 5. The gasses fried the aircraft’s control and telemetry circuits; cutting off communication with test controllers whereby range safety officials hit the kill button causing the craft to self destruct. That flight was supposed to last 300 seconds and engineers hoped the vehicle would reach Mach 6.

This week’s flight was originally slated for late March but was scrapped at the very last minute due to unknown issues with the test range.

{ 25 comments… read them below or add one }

Achilles June 15, 2011 at 5:47 pm

Glad I wasn't surfing up by Point Mugu today.


Thomas L. Nielsen June 16, 2011 at 1:52 am

"I don't think the Waverider can punch through Fordo mountain…" - Not in its current incarnation, certainly. That's why it's called "X".

"Or should they be placed into suborbital position, can come down on their own when called and targeted…" - you mean "orbital", right? "Sub-orbital" means "goes-up-then-comes-back-down". Think early Mercury-Redstone missions. Sure, suborbitals will come down on their own, but when Sir Isaac tells them to, not "when called". An orbital system was investigated under the "Rods from God" moniker back in the day, but you'd be talking weaponization of orbital space, and that releases a whole pack of potentially nasty questions.

Regards & all,

Thomas L. Nielsen


ben June 16, 2011 at 7:36 am

The DoD is never going to test the "straightforward approach" for several reasons.
Chief among these is that the vehicle is NOT a precursor to a missile, but rather for a mach 6 UAV platform.

Also you seem to have some misconceptions which I would correct.
1. if you did not notice, the test vehicle is the final stage on a theater ballistic missile enlarged with an extra stage, and even the 12ft x-43 was launched using a 50ft+ 2 stage rocket normally used for satellites. No one is ever going to be launching hypersonic missiles from internal bays.

2. this is not some cheap throwaway device. At the speeds involved, it has more in common with an ICBM than a cruise missile. Sure it gets more thrust per pound of fuel, but it also has to contend with hypersonic drag. All things considered, the ICBM is probably more cost effective. Particularly in these early versions where the vehicle IS just a ballistic missile with the scramjet third stage instead of a rocket.

3. The vehicle is air-breathing, and is not actually fast enough to achieve orbital velocity on its own, making one of your ideas moot. Also important is that the orbital deployment system you described is of questionable legality due to the provisions of the SALT II treaty which prohibited fractional orbit bombardment systems (potential loophole for non-nuclear systems).

4. there are only 2 reasons to use a scramjet vehicle.
I.E. When you need performance that approaches that of a ballistic missile, but you
a. don't want to panic the russians when it launches. or
b. want the vehicle to be able to turn around and fly home.
And you are willing to pay ballistic missile prices, for cruise missile capabilities.


ben June 16, 2011 at 7:58 am

Now there has been some talk of weaponizing vehicles like the x-51, to replace the proposed conventional warhead ICBMs which got poo-poo'd by a veiled threat from Putin.
Of course this is nonsense, and I can give you 2 reasons why.

1. the damn things will cost just as much if not more than the 30mil tridents they were planning on using. And no-one is going to be able to justify flushing that much money down the drain just to shave 20 minutes off the flight time of a 100k subsonic cruise missile.

2. A mach-6 missile as the final stage of what used to be a ballistic missile, is actually just as big a threat than the same missile with traditional sub-orbital warhead. Both vehicles put nuke at hypersonic speeds into your airspace, and while the scramjet gives more intercept time, it maneuvers better than a re-entry capsule.
The russians are just going to say the same thing about detecting the launch of hypersonic missiles that they said about conventional ICBMs.


Maxtrue June 16, 2011 at 9:42 am

First of all, I meant sub-orbital in the sense that the orbit lies under what commonly would be called low-orbit. This would be achieved by on board propulsion that would compensate for the sub-orbital decay. SpaceOne would require 60 times the energy it carries to achieve full orbit, but with modification could circle the planet several times over at the edge of spce. From this sub-orbital height however, one could deliver MASS with the velocity to achieve a greater energy yield on impact that the largest non-nuclear ground penetration bombs provided the MASS is large enough. This may be splittting hairs, but the effort here would be to avoid "weapons in space". Only these weapons could cut through Fordo mountain…..

Second, if you noticed, the X-51above is not too large to fit into a bomber's payload and the new bomber is going to provide space for hypersonic missiles as well as future drones scaling up. If I remember correctly, back in the seventies, we built fairly small MD missiles capable of extremely high acceleration. I don't doubt we can build more efficient and smaller booster that can ramp up scram missiles to their required speed.

Third, add a spear to the X-51 and I don't know what hull can withstand a strike over 6 Mach. A link below provides some DOD thoughts on hypersonic applications including the X-51 concept. The Waverider might be a potential UAV platform, but who would overlook its role as a missile avoiding the consideration you mentioned involving ballistic missiles? In fact once the ablative aspect is worked out, it has less mechanical parts than a cruise missile. http://www.dtic.mil/ndia/2007disrupt/Borger.pdf And this is from 2007.

Last, my original point stands. From either a space plane (violates some understandings), a sub-orbital platform or even a large ultra high altitude drone, the most powerful ground strike weapon we can build short of a nuke would be a modification of the Rod of God concept. Mass time velocity. Imagine a mach 10 booster on a mass fired DOWN rather than UP. This doesn't involve scram. A weapon mentioned in the Bible in the form of David's slingshot…

In the future, I suspect rail technology will fire up scrams from the ground. As my link above shows, there are real reusable concepts for scram, but in the size range of the X-51 presently, it makes a potent non-reusable hypersonic weapon. It moves well beyond BraMos and most defensive systems when perfected and that's what is worrying the Chinese and Russians.


Thomas L. Nielsen June 16, 2011 at 1:12 pm

"SpaceOne would require 60 times the energy it carries to achieve full orbit, but with modification could circle the planet several times over at the edge of spce."

Circle the planet several times over? And your basis for that statement is what?

"From this sub-orbital height however, one could deliver MASS with the velocity to achieve a greater energy yield on impact that the largest non-nuclear ground penetration bombs provided the MASS is large enough"

Mass is all well and good, but the larger the mass, the more energy you need to expend getting it up there in the first place. The payload of SpaceShipTwo (calculated from 2 crew and 6 passengers) is only something like 2000 lbs.

Regards & all,

Thomas L. Nielsen


Maxtrue June 16, 2011 at 3:13 pm

Well, 2000 lbs x mach ten + is what compared to the latest MOAB? Are we into substantial fraction of a kiloton with tremendous downward thrust?

seven times around the globe would require refueling obviously, or more efficient engines. Its actually not the revolutions but the ability to stay high up over a targeted area over extended time. An advanced Proteus could edge up the ceiling height with augmented power supply. And lift about 6000lbs. The height factor is most important when releasing missile, but the missile itself could boost into a sub-orbital when fired.

Last, in terms of the energy or even the effort expended in hoisting a mass driver to high altitude without a ballistic missile is off-set by the novel capacity of penetrating a facility that is presently invulnerable to non-nuclear strikes. I would say that is a whole new ball game…..

Its funny but what did in the Rockoon was that it had to fire up into what was lifting it to a high altitude. In the case of penetrators, they are firing down. How big a balloon could hoist 2-3000 lbs to 100,000 ft or what could stabilize its position is beyond my arm chairing at the moment……Earthwinds was designed to lift 1200lb capsule more than 70,000 ft.


anon June 16, 2011 at 5:08 pm

Look up Project Gusto:

"The Navy introduced a submarine-launched inflatable rubber vehicle that would be lifted to altitude by a balloon, boosted to speed by rockets, and then cruise using ramjets.
Johnson reported on the Navy concept and demonstrated that it would require a balloon a mile wide for launching; the submission was then dropped. "

Every pound of buoyancy is a function of the difference in gas density between what is in the envelope and what is outside.

And for earthwinds:

"In a successful liftoff, the craft would soar about 35,000 feet to link up with the jet stream for an eastward trip around the world that is projected to take 12 to 21 days."


"Earthwinds consists of a 190-foot helium gas bag, a small compartment for the three-member crew below that and a 110-foot, air-filled anchor balloon on the bottom as a stabilizer. It cannot fly without the bottom ballast."

Where did you get 70,000 feet for a 1,200 pound capsule?

Excelsior III needed a 3 million cubic feet balloon to get the test pilot to 102,000 feet for his jump. Still looking for gondola weight at the moment.


anon June 16, 2011 at 5:33 pm

Addition to my previous post:

From: http://stratocat.com.ar/fichas-e/1960/HMN-1960081…

Excelsior III ascended at ~ 1200 feet/min and reached its desired height of 100,000 feet in a bit under two hours, and that was a 2,320 pound payload. The balloon is described elsewhere as 60 meters high with a three million cubic foot capacity.

However, these hypersonic missiles are not 2,000 pounds, by any stretch. A meaningful long range payload would require massive lift; unless you propose to inflate this thing, ascend for two hours and wait for the winds to carry it over your target before dropping a kinetic payload.


Thomas L. Nielsen June 17, 2011 at 9:37 am

"Well, 2000 lbs x mach ten + is what compared to the latest MOAB? Are we into substantial fraction of a kiloton with tremendous downward thrust?"

No, we're not. 2000 lbs at mach 10 carries a kinetic energy of approx. 6 GJ. One metric ton of TNT releases approx. 4.2 GJ of energy, so 2000 lbs at mach 10 is approx equal to 1.5 tons of TNT. Not shabby, but not even within shouting distance of the yield of the MOAB, "tremendous downward thrust " or not.

And whether 1.5 tons constitutes a "substantial fraction of a kiloton" depends entirely on your definition of "substantial fraction".

Thomas L. Nielsen


anon June 17, 2011 at 4:04 pm

And at which point, government saves money by throwing sticks of bombs out of the B-52.

DefTech had a snippet on a bomb that could drill into the ground before detonating…a very interesting testbed scheme. Probably dating from Schachtman's tenure here.

Fordo Mountain lives. It might even be a great deftech meme.

anon June 16, 2011 at 5:44 pm

While I am digging through my Project Excelsior references, Kittinger free-fell from ~102 kfeet to ~14 kfeet and reached speeds of ~600 mph, less than mach one. For ballistic missiles, the number wikipedia gives is ~ 4 km/s( 14,000 kilometers/hr vs Mach 1's 1225 km/h. Then again, ballistic missiles boost to 3,000-6,000 km (also from dreaded wikipedia), and 100,000 feet is 23 km.

To get the massive speeds (and thus KE's) you desire, you will be much higher than a mere balloon.


Maxtrue June 16, 2011 at 11:14 pm

Perhaps I was not clear enough. I stated that 2000lbs accelerated to mach ten. That obviously doesn't happen by gravity alone. The acceleration is increased beyond gravity by an attached rocket, not unlike the X-51 or perhaps more like those old Hercules X series boosters (see 35 year old Sprint technology).

The high altitude serves several purposed the most important perhaps being the energy released by "enhanced kinetics", the non-ballistic trajectory, and stealth.

Proteus lift air craft is owned by NG and is 12 years old. A bomber version has already dropped 500lb bombs. Perhaps an advanced military redesign would be as surprising to DT as the stealth chopper. The reference to Rockoons was simply to suggest ways to loft dead weight to high altitude.

I thought for some reason the new stealth bomber would serve as a platform for hypersonics and DEW, being able to deliver them past the enemy's first lines of defense. Seems the wings should be variable as extremes in ceiling are required. The comment above is correct. Hypersonics and scrams must undergo considerable shrinkage to fit inside stealth air craft. Unfortunately they have to work first…..

The B-1 loads 125,000 lbs. I'm not sure how much is internal. The B-2 is 100.000 lbs internal. If height via non ballistic means is important, the perhaps a Proteus on steroids makes sense…

And while the X-51 appears to be a great platform concept, rail technology might be able to reach scram speed for missiles on a surface ship which offer a self guidance hypersonic warheads alone don't..

excuse the bandwidth use…..


anon June 17, 2011 at 3:59 pm

If you're going to use a rocket to provide most of the KE, why go with a balloon, asides from the fact they have higher max altitudes than aircraft?

The Soviets always mused on the possibility of the Space Shuttle being used for weapons (or using the space shuttle's booster/fuel combo to deliver large payloads), and we have an ambiguous "space plane" in military hands. The /Prompt/ part will come from close land basing (though I remain in favor of submarines if the military is committed to ground-launch).


ben June 17, 2011 at 1:36 am

spaceship one is a rocket not a scramjet, and has very limited endurance. It goes straight up, then falls straight back down, and still barely makes it out of the atmosphere. The engine cuts out halfway up, and the aircraft coasts over the limit of space and then falls at terminal velocity which is why it does not need a heat shield.
If you pointed it sideways, it would accelerate up to mach 3 over about a minute, and then run out of fuel.
Remember that Kinetic energy is Mass x Velocity x Velocity. Something going half as fast requires 4 times the mass to deal the same damage.

The X-51 and X-43 are mounted on external pylons on a B-52, not the bomb bay. No bomber aircraft on the planet has the ~50ft long bomb bays which would be required. It would theoretically be possible with the b-52 by removing the bulkhead between its two bomb bays, but the whole airframe would have to be redesigned to compensate for the loss of structure.
The only missile of equivalent size that was every carried internally was the single air launch test of the minuteman. Which was slid out the back end of a c-5 galaxy.

In terms of a hull which could withstand getting hit with a x-51. I would be willing to bet you money that one of the Iowa or South Dakota class battleships could have survive at least one hit. Potentially any of the supercarriers as well.
It wouldn't be pretty, and whatever is immediately in the path of the vehicle would be gone. But at mach 6, first layer of hull would act as a whipple shield causing the x-51 to disintegrate/vaporize and reducing further penetration drastically. A large enough ship can just seal off the damage, counterflood, and then hightail it back to the naval yard for repairs.
Kinetic energy wise, it would be 4x more per pound than the existing mach 3 missiles, but would be less mass on target than on a slower vehicle with better specific impulse. So it would be like getting hit with 2-3 normal missiles in the same spot. Bad, but not inherently fatal.

Your original idea with a scramjet sub-orbital platform dropping warheads was non-feasible. A sub-orbital platform is inherently on a ballistic trajectory. Hence the term ballistic missile for existing sub-orbital missiles.
What you described is EITHER
a. already a job performed cheaper by a normal ballistic missile. or
b. an illegal fractional orbit platform, which requires a full blown LEO launch vehicle, and cannot be performed by a scramjet.
(SABRE excepted, since that vehicle is planned to carry 4 engines, a turbojet inside of a ramjet like the SR-71, with an a scramjet 3rd engine and a rocket for final orbital burn. but that is a space shuttle replacement concept, not a missile.)

I can imagine a mach10 booster fired down instead of up, but you have to think about logistics and cost here.
You are describing an ICBM or vehicle of equivalent price tag and size, which fires smaller theater ballistic missiles at the ground.
It is certainly possible, but it would cost a vast sum of money and be tremendously vulnerable to anti-satellite weaponry.
If you want a reusable vehicle, then you are effectively describing weaponizing the space shuttle, and the 100 million per launch price tag.

A railgun cannot be used to launch a scramjet with our current materials science. the rails and projectile have to be conductive metal, and conductive metals have unfortunately low melting points. When you put amperage through the projectile, it heats up like an electric stove element, and if you overdo it it vaporizes. The only way we have found around the problem is to keep the bore size low. Far to low to put a missile on top.
There are other types of magnetic mass drivers which can launch whatever you want, but they operate on the coilgun principle which limited to a maximum velocity too slow for scramjet operation by the laws of physics. You could totally use them to launch a slower mach 3 ramjet though.


Maxtrue June 17, 2011 at 8:26 am

I had a few comments that would clarify several comments (to wrong interpretations of what I said). Proteus already has dropped 500lb bombs. With more work I am sure it can carry up a larger load as it has been 12 tears since creation. It loiters at high altitude and does not have ballistic trajectory.

Add a Hercules X type booster to a tungsten spear and there is the impact I referred to when dropped above 70,000 ft or higher perhaps from a Proteus like platform. You do the math. I never suggested a scram jet as a suborbital platform, that is JUST scram. If however you attached a tungsten spear to the underside of the X-51 in its present size you would have something that would go through a hull. Who said drive the X-51 alone into anything? If one is making a scram platform, it is easy enough to make a scram cruise missile armed with mass v explosives…

The missile fired down would not be equivalent to hoisting up an ICBM into the sky. First you don't need the booster to obtain height and then gravity assists on the way down. Where do you come up with your comments? As far as rail technology launching a scram jet, Nasa and others have been working on the concept. as well as a ram/scram hybrid which would solve you laws of physics problem.

The other comments were either answered in posts not posted by DT, or items characterized from my comments that are false. It is also possible for a SpaceOne Proteus carries a missile that can lift itself into sub-orbital and then descend at the appropriate spot .

Let's see if this will post..


Thomas L. Nielsen June 17, 2011 at 9:19 am

At the risk of coming across as a nit-picker:
Kinetic energy is 0.5 x Mass x Velocity x Velocity

Regards & all,

Thomas L. Nielsen


Maxtrue June 17, 2011 at 1:57 pm

http://www.rand.org/content/dam/rand/pubs/monogra… I add a booster to compensate for less than orbital heights. The math is presented in the Rand report….


Stormcharger June 16, 2011 at 11:52 am

"the JP-7 wouldn’t light despite several attempts to do so"

Rocket scientist does not apparently mean the same thing it used to… how long has the formulation for JP7 been in our inventory and these geniuses have yet to figure out how to light it off? Really? How much are we as taxpayers paying them? They need to call up AARP and track down a couple of senior citizens who were able to land on the moon with an Atari computer and a slide rule.


ben June 16, 2011 at 1:57 pm

They were trying to light the proverbial match in a hurricane. Since their problem last time was that the the engine lit the avionics on fire, it looks to me like they broke one thing trying to fix the other.


anon June 16, 2011 at 5:16 pm

The historical ignition fuel was triethylborane, which was used in SR-71, Saturn V and the Falcon 9 rocket from SpaceX. I wonder if there was a change in their ignition protocol, or they tried to eliminate that particular component.

This is all stuff they could have tested on the ground in a chamber at low air pressure to simulate high altitude conditions. They would not have test launched if they weren't confident in proper function.


Blight June 17, 2011 at 9:29 am

I'm not sure if you can from an object accelerating at 1g from only 70k to 100kfeet.


Maxtrue June 17, 2011 at 1:43 pm

Sprint accelerated an enhanced nuclear warhead at 100 gs from 0 ft. in 1975. It is likely considerably easier to do with gravity, you think?


anon June 17, 2011 at 3:52 pm

Accelerated at 100G's to what velocity? The ascent rate of a high-altitude balloon is something on the order of one to two hours, which makes "prompt" global strike questionable.


anon June 17, 2011 at 3:55 pm

It's likely just a crowd of people using "Anon" and variants thereof. Or I am a script and not a meat popsicle.


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