X43-A on to Mach 10

Cat_Byte writes "On March 28 we read about the X43-A hitting Mach 7 with a successful scramjet test. Prior to that on June 2, 2001 the craft tore itself to pieces during a trial run. Well now they are preparing to hit Mach 10. The upcoming Mach 10 run of the X-43A appears to mark an end of the program. The seven-year, approximately $250 million Hyper-X program was created to provide unique "first time" data on hypersonic air-breathing engine technologies. "At Mach 7, the front leading edge of the vehicle would see about 2,400 degrees Fahrenheit. At Mach 10, its probably twice that -- twice the heat load essentially," Sitz explained FYI, Mach 10 is about 2 miles per second."

Comments

I'm impressed

[TheAdventurer]

I'm some one who is impressed by interesting numbers, and I just get a thrill out of the idea of travelling 2 miles per second. That is incredibly cool.

I could do my daily commute in 15 seconds. That would be fun.

Anyone...

[AKAImBatman]

...have data on its trajectory? It seems to me that if you want to reduce heat, you need to fly it in a steep climb. Of course, the air then gets thinner, thus providing less boost. Your lifting body is also less effective with that sort of trajectory.

Re:Anyone...

[AKAImBatman]

I think it's interesting that they are wondering how the engine will perform. I am much more interested how the human body reacts to this.

That's actually pretty well known. Rockets have been capable of giving a hellva lot more Gs, and experiments with Jet Pilots have pretty well established human's capacity for acceleration tolerance.

The thrust to weight ratios are interesting, however. A 15-20 to 1 ratio would provide one serious kick in the pants. :-)

Re:4,800 degrees farenheit..

[mattjb0010]

4,800 deg. F is not twice as hot as 2,400F. Use SI units: 2,400 ~=1589K, so twice as hot is 3178K

A Third of the Way There...

[apikoros]

"At Mach 10 -- or 10 times the speed of sound -- the X-43A is traveling at about two miles per second. Thats in the range of 7,500 miles per hour."

Which sounds really impressive until you realize that escape velocity is 25,000 miles per hour and we are less than a third of the way to an air-breathing launch vehicle.

186,000 mi/sec... it's not just a good idea, it's the law!

Re:A Third of the Way There...

[Moofie]

Saves a lot of mass, costs you a lot of drag. Say I need to have a rocket applying a 1000 lb force to do my mission. (Yes, I am radically simplifying numbers). In order to get that 1000 lb force out of a scramjet, the frontal area of the vehicle needs to be about four times as big as the rocket. Since wave drag (the primary component of the drag force on a body travelling supersonically) goes as the square of frontal area, you can see that this is not a winning strategy.

I don't believe air-breathing engines will ever make productive parts of the high-speed boost phase of a satellite launch. Now, something like Pegasus or SpaceShip 1 that uses a low speed air-breathing craft to get above lots of atmosphere, that's a pretty good idea.

Re:A Third of the Way There...

[grozzie2]

You then attempt to start a fire in that supersonic airflow (imagine trying to light your zippo while holding it out a car window and multiply that difficulty by about a million).

This is a HUGE problem in some speed ranges, and it's _trivial_ in others. The neat thing about shock waves is, you get a rapid temperature rise during shock compression. One of the 'tricks' to the design of a scramjet, is to plan out the shock wave pattern in such a manner, the ambient temperature in the vicinity of your fuel injectors, is higher than the ignition point of your fuel. Then the only trick is, getting the system up to the velocities required for ignition to be spontaneous. Standard igniters just wont work in those velocity regimes.

As you suggested in the initial post, the problem of escaping atmosphere is huge for the orbital equation. Aerodynamic drag is 'inconsequential' whilst subsonic, but grows exponentially once you start playing with shock waves. 50% of the atmosphere (by mass) lives below 6,000 meters (18,000 feet) altitude. In the range of 80% lives below 13,000 meters (40,000 feet). The most efficient path out of the atmosphere is to utilize atmospheric lift at subsonic speed until well above these altitudes, to get past most of that sticky stuff called air. The messy problem of all that sticky air living below 40,000 feet really makes a single stage runway to orbit vehicle impractical. Efficient lift and reduced hypersonic drag are diametrically opposed concepts when designing the airframe. For the former, you want large smooth rounded surfaces, for the latter you want sharp edges and zero curves, as curves promote 'lotsa little shocks' and a 'shock fan', whereas an abrupt square corner still produces but a single shock wave.

If you look at modern heavy lift, long range airframes, they tend to all operate most efficiently between 32,000 and 40,000 feet. A 747 loaded to the max cannot climb above 32,000 till it's burned off a chunk of fuel (lower for older models), and then it MUST climb higer to be able to achieve it's maximum range, to take advantage of reduced fuel burns at 36 and 38 thousand. it's not really an accident that the transoceanic airways are 'busy' in the 32 to 38 thousand range, with virtually no traffic below or above those altitudes, except a few big ones in the early stages of step climbs as they burn off fuel. The combination of modern jet engines, and aerodymanic lifting bodies, this is the altitude range that is the 'sweet spot' for fuel efficiency. Aerodymanics prevent them from going higher (atmosphere gets to thin to generate the lift required), and engine efficiencies prevent them from operating lower. It's also not completely co-incidental that these are the tropopause altitudes, where you run into things like jet streams, which can give you a significant 'free ride' enroute. 80's and earlier vintage equipment operates 'at jet stream altitudes' eastbound, and 'just below them' westbound typically. Late 90's vintage equipment is slightly more efficient, so you operate above jet streams rather than below, when going westbound.

There have been many trillions of dollars spent on the engineering required for subsonic heavy lift above the majority of the atmosphere. We've got the point where it's efficient enough to be widely deployed. for a wide deployment of orbital transport, it doesn't make sense to NOT leverage this knowledge/technology base for the lower portion of the flight.

Scramjets are cool, but, they want to operate in the atmosphere, and at velocities that produce problems with the rest of the materials. In theory it's more efficient to not carry your oxidizer like a rocket does, but there's this little 'reality' problem with scramjets. We dont know how to build the tankage to carry the fuel for it, in a manner it wont melt from continued exposure to the hypersonic airstream that's presenting stagnation temperatures in the thousands of degrees (and at those high numbers, doesn't really matter if you are using C, K, or

why is this public knowledge?

[spacerodent]

why do we even know about this? Shouldn't this be some classified secret or do they already have craft that handily surpass mach 10 and thus don't care if we know about it? The stealth project was a secret for over 40 years and they're just parading this around (arguable if equal importance) for the cameras...what gives? What secret shit are they NOT telling us about I wonder.

Re:why is this public knowledge?

[Cecil]

That was during the cold war, when the US had an enemy who actually had the capability to destroy them. Now they're at war with terrorism instead, and the the combat strategy seems to run more along the lines of "shock and awe".

Re:why is this public knowledge?

[Anonymous Coward]

The times are different. Back in the cold war, if the USSR had gotten wind of us making a stealth jet, they'd have done the same thing to level the playing field. The US had a lot to gain by keeping it secret.

Now, we're allied with pretty much any country with the money and technology to develop competing weapons, so there isn't much reason to keep it secret. If an enemy knows we can kill them faster and/or cheaper and there's not much they can do about it, they're just that much less likely to attack us.

Re:Big deal...

[Elwood P Dowd]

This is unrelated to passenger travel. We are conducting this research so that we can drop a bomb on any location on Earth in under an hour. From Wired Magazine:

Ron Sega
Director, Office of Defense Research and Engineering, DOD

ADVISES: Defense secretary Donald Rumsfeld

WHY HE MATTERS: Responsible for bringing the missile shield to life.

TECH CRED: IEEE fellow and NASA astronaut who used to teach electrical and computer engineering at the University of Colorado.

ON HIS RADAR: Dominating outer space through hypersonics. He foresees superfast missiles and spaceships that can zap any target. His goal is to increase US flight capabilities by one Mach a year until 2012.

Why is that his goal? You tell me. (Nice way of avoiding ICBM treaties, BTW.)

Commercial human use? Probably not.

[Bones3D_mac]

Every time I hear about these scram jet things, I keep picturing the Ghost fighter/Guld Bowman fight from Macross Plus, where Guld's body ends up crushed like a tin can just before his suicide collision with the Ghost fighter.

While it may be possible to control the rate of acceleration to human-tolerable limits, I can't see this being open to anyone who isn't trained and endurance tested prior to flight. How would you explain a flight where half the passengers end up having strokes or heart attacks from the stresses such a beast would generate during an instance of turbulence?

Re:Not for commercial flight

[Rei]

It may not be an official goal, but that's beside the point. Scramjets may well be a technology that finally enables suborbital commercial travel. Unlike getting to orbit, getting on a long-range suborbital trajectory isn't nearly as hard, and reentry requirements aren't nearly so severe. The benefits are really incredible, though - you can visit anywhere in the world within a little more than an hour, and you use no propellant mid-flight. It'd be perfectly silent, and you'd be near weightless, enabling the average person to not only get where they want to go, but to experience "space". The benefits would justify significantly lower payload-per-dollar-of-investment (to an extent, of course).

What I find interesting is that the leading edge heating only doubles between mach 7 and mach 10. For macroscopic objects, drag is proportional to v^2, so the drag coefficient must decrease a lot faster than I thought.... I should modify my rocket simulator. :) Unless, of course, they're travelling at a different altitude (?).

Mach Question....

[imsabbel]

Are those mach speeds representing the actuall factor at flying altitude or is there a standart altitude?

Because if its at traveling altitude, your mach 6 35km altitude vehicle would be faster then your mach 7 15km vehicle (speed of sound is presure dependent).
But if it were otherwise, you could travel at mach 1.1 and still be subsonic if you are high enough, which doesnt make sense either.

So why dont they just give the speed in km/h (or mph)? Mach may be usefull if you are dodging around the speed of sound, but at mach 2,3 (or 10), who cares?

Re:AWESOME!

[DigiShaman]

Trouble with the concord wasn't a technical issue though. It was more of a social/political issue involving the "sonic boom" that it generated over cities and towns. But super sonic flight over water wasn't an issue. As for the scramjet, being that it would be partially in space this may not be an issue. But I wouldn't be the one to give you an answer on that. Anyone else claim to know the answer on this?