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The X-51 Hypersonic missile will be launched into action later this month.  (Source: Weapons Blog)

Another view of the craft  (Source: U.S. Air Force)
The U.S. Air Force is set to successfully launch a Boeing X-51 for 300 seconds of hypersonic flight

By the end of this month, the U.S. Air Force will begin a series of hypersonic tests that will send a scramjet into the atmosphere for about five minutes, at nearly five times the speed of sound. A scramjet is a supersonic combustion ramjet, while a ramjet is a jet engine using the engine's forward motion to compress air.
If all goes as planned, this will be the first time that an aircraft will have flown at such speeds for more than a few seconds of time.

In previous attempts, the NASA X-43 was powered-up for just 10 seconds of flight.  The X-43 was tested four times in 2004 and was hydrogen-powered.

This time around, the U.S. Air Force will be testing the X-51 Waverunner, which runs on compressed air that ignites fuel by combustion.  The X-51 is designed to be dropped from beneath a B-52 bomber.

A rocket booster will ignite and accelerate the Waverunner.  It will then run its course -- from Mach 1 to Mach 6 -- under its own power,  at which time the nose of the X-51 is expected to reach at least 1,480 degrees F.

The aircraft fuel will then be piped through tubes around the engine surface and will help warm the fuel to the temperature needed to ignite it as well as draw off heat to keep the engine from melting.  

According to 
Popular Mechanics,  the X-51 Waverunner is a global strike missile that is part of the Prompt Global Strike research project being developed by Boeing and the U.S. Air Force Research Laboratory and Defense Advanced Research Projects Agency. 

The Waverunner is said to be a warhead in the making, which will be filled with thousands of rods 12 times as destructive as a .50-caliber bullet, targeted to shower a designated area.

It is being developed for precision, speed, and range and has been designed to strike any place on the planet in an estimated 60 minutes.

The long-term goal is to design airplanes and missiles that would reach Mach 25.  The U.S. Air Force plans to conduct up to four tests of the Waverunner this year.

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RE: Some addl info
By porkpie on 5/9/2010 8:29:30 PM , Rating: 2
Err, like what? A basic chemical explosion by itself isn't very need shrapnel to make it effective. These penetrating rods are just that: shrapnel pre-accelerated to deadly force by the missile itself. Replacing them with a high explosive charge of the same weight would result in a weapon less destructive (as well as less precise).

You could, of course, put a small nuclear warhead on the end...but that essentially defeats the entire purpose.

RE: Some addl info
By AssBall on 5/10/2010 8:26:15 AM , Rating: 2
Like a 50 ton yeild (TNT equivalent) thermobaric device.

RE: Some addl info
By porkpie on 5/10/2010 8:43:12 AM , Rating: 2
Err, the Russian thermobaric "Father of All Bombs" bomb had a little less than 50 tons TNT also weighed over 7 tons. You can't get a warhead that large on even a full-size think you can put it on a much smaller X-51?

Besides, you can't even deliver a fuel-air explosive at a velocity that high and have it successfully'd have to somehow slow down the missile to make it even work.

RE: Some addl info
By AssBall on 5/10/2010 9:53:01 AM , Rating: 2
Yeah, our current thermobaric technology won't allow for a bomb that big on the X-51.
I was just hoping the thing to have a more destructive payload than some mach-5 shrapnel for the cost.

RE: Some addl info
By ekv on 5/10/2010 11:53:02 AM , Rating: 2
using KE = 0.5 * m * v^2 ...
assume 2000lb payload on target, say mach 6 terminal velocity (which is about 2000m/s), we get
KE = 0.5 * 1000kg * (2000m/s)^2 = 2GJ
This link
says 1 Ton of TNT explosion is about 4GJ.

Seems like a helluva lot of trouble to get 1000lb bomb on target, no?

RE: Some addl info
By porkpie on 5/10/2010 12:34:40 PM , Rating: 3
"Seems like a helluva lot of trouble to get 1000lb bomb on target, no?"

It doesn't work like that. A bomb without shrapnel can only kill by overpressure or heat, neither of which are terribly effective (and both of which drop off very quickly...overpressure drops by the cube of distance).

So most bombs meant to kill (rather than simply penetrate) are designed to generate shrapnel....usually by bringing it with them. Often, this is just the bomb casing...designed to fragment into thousand of pieces from the force of the explosion.

The X-51 warhead, however, isn't a 1000 lb bomb that only contains 100 lbs of shrapnel. It's 100% shrapnel ... already accelerated and evenly dispersed over the target area. It's going to be at least an order of magnitude more destructive than a simple energy comparison would suggest.

RE: Some addl info
By ekv on 5/10/2010 2:55:46 PM , Rating: 3
I'm not sure you caught my point. Shrapnel is all well and good, but how much energy are you really bringing to the party?

I think the kinetic energy calc is spot on, so pardon me if I'm not overcome with warm fuzzy feelings 8) I was expecting something a bit more -- I don't know, perhaps on the order of Project Thor (like you and others have mentioned). Of course, with that, the velocity is more like 9000m/s. Something the size of a crowbar is going to do damage but it wouldn't exactly be a bunker buster. At that point, it's more of an assassination tool. If so, then we have more COST effective means of getting there [MQ-9's I've mentioned earlier].

I don't think the X-51 is going to penetrate 300 feet of steel. Likely quite a few feet, but the role of bunker buster is iffy. Methinks. So that limits the roles this tech can play. Hence less cost effective in my book. Damn interesting though.

Another thing, you wrote "evenly dispersed over the target area". I'm curious how these rods would be packed into the payload. I can see how something like 1/2" ball bearings could be packed and dispersed -- just use a small explosive charge, at a precise split instant before impact, to get a desired spread -- but dispersing rods? notta so fast there Kowalski. Sure you could disperse them but then keep them perpendicular to target? don't see it. And if you don't care about perpendicularity then why not use ball bearings, or Ninja stars (Hira-shuriken)?

RE: Some addl info
By porkpie on 5/10/2010 3:24:18 PM , Rating: 3
"I think the kinetic energy calc is spot on"

It was, yes. However, as I said, energy alone is very poor at killing people. A man standing near an artillery simulator (essentially a quarter-stick of dynamite) will generally just be harmlessly blown through the air a few feet. On the contrary, just a couple pounds of pressure on a stiletto knife can kill. In a traditional bomb, most of the energy is wasted simply trying to accelerate shrapnel to lethal velocity.

"I don't think the X-51 is going to penetrate 300 feet of steel"

Nowhere near. I don't know where the previous poster got that figure.

"Sure you could disperse them but then keep them perpendicular to target? "

Air pressure from a Mach 6 wind will do that quite nicely.

RE: Some addl info
By ekv on 5/10/2010 4:05:59 PM , Rating: 4
I still like Ninja stars. [It'd be easier to sell on Capitol Hill too].

"If they're going to pirate somebody, we want it to be us rather than somebody else." -- Microsoft Business Group President Jeff Raikes

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