Scramjet Test Successful

An Anonymous Coward writes: "The Sacramento Bee is running this story about the first powered device to achieve "hypersonic" speeds in the Earth's atmosphere. In a series of DARPA-sponsored tests, at Arnold Air Force Base in Tennessee, a scramjet engine, encased in a titanium projectile, was fired from a 130-foot cannon, at an initial velocity of Mach 7.1. The scramjet's engines then ignited, and the object moved another 260 feet, in just 30 milliseconds, before it came to rest in a series of steel plates designed to halt the flight. Peak acceleration: about 10,000 G's. Elapsed time, including cigarettes & pillowtalk: less than a second. PS: According to this nifty page at NASA, Mach 7.1 is about 5406 MPH, whereas 260 ft, per 0.03 seconds, is about 5909 MPH."

Comments

passenger problem

[jlemmerer]

if such high velocities are required to ignite the scarmjet, how will they do it in the future. firing it out of a cannon doesn't seem reasonable for me if you want to transport fragile goods such das humans. i heard rumors of bringing the scramjet equpped vehicle to high stratosphere with a carrier aircraft and then drop it to gain speed, but that also seems to be a rough ride.

The cannon is more interesting

[redelm]

I can see how this short test worked, and how they can get some scramjet performace data in the 30 ms of free flight. Ain't microelectronics wonderful?

But frankly, I'm more interested in that super cannon. Mach 7.1 is 7,500 ft/s (2,300 m/s) which is extremely high. It would have a max range (neglecting aerodrag) of 300 miles! Did they use a gas-gun?

Re:The cannon is more interesting

[KFury]

Sorry, there's a big difference between 'sending things into outer space' and 'achieving escape velocity.' The first simply means it could shoot something outside the atmosphere, or around 90 miles up. Having reached outer space, it can fall back down to Earth.

Reaching escape veolcity means that, ignoring aerodynamic drag while departing the atmosphere, the object has enough velocity to fully escape Earth's gravity well, so that it'll never come back. This is a couple orders of magnitude faster.

As for the replies to the post talking about sending things into orbit, that presents a different problem, because you couldn't stabilize an orbit without a burn at the apogee of the flight, to stabilize the flight path from a parabola, which would come back and slam into the earth, to a circular or elliptical orbit. So in addition to having to protect the electronics from the tremendous G-forces (or making it all out of a ferrous metal, so you can pile it through a railgun and not have to worry about it because every piece of the craft is being accellerated identically) you also have to put in enough fuel and an engine to make that stabilizing burn. Of course, ferrous fuel is hard to find...

stupid question?

[Marcus Brody]

From the article:


Scramjets, or supersonic combustion ramjets, burn hydrocarbon fuel but scoop oxygen out of the atmosphere to combust it....


...The Pentagon and National Aeronautics and Space Administration are both studying scramjet technology since it would allow missiles or spacecraft to travel longer distances and carry larger payloads than rockets.

I'm sure i'm missing something fundamental here, but where the hell are spacecrafts supposed to get the oxygen from?
I guess they must just mean using scramjet untill leaving the atmosphere, and then use onboard oxygen, but it is a little misleading

Re:Read the article, plz.

[Anonymous Coward]

Basic maths tells us that covering 260ft in 30milliseconds does yield an AVERAGE speed of about 5909 mph, but it was not moving at constant speed over that 260 ft as it was ACCELERATING.

OK, so basic junior school physics (at least in the UK anyway) tells us that if an object is moving at an initial velocity of u and then accelarates (a) over a time period (t) then the distance covered (s) is calculated by:

s= ut + 1/2at^2

If we rearrange that to get the acceleration (a) as the subject of the formula thne we get:

2(s-ut)/t^2 = a

Using proper SI units of measurement, not the sloppy units that crashed the mars orbiter, then:

s = 79.3 m

u = 2416 m/s

t = 0.03 s

gives us an acceleration of 15028 m/s/s.

Then we use another basic junior school physics formula to calculate acceleration from initial (u) and final (v) velocties and the acceleration period (t):

a = (v-u)/t

rearranged to give:

v = u + at

and given that:

u = 2416 m/s

a = 15028 m/s/s

t = 0.03 s

then the final velocity would be 2867 m/s, or about 6415 mph. Clearly the average speed and final speed are very different.

Of course I have simplified this slightly by not including the decelleration period while the scramjet slammed into the steel plates, as this is of unknown length.

Re:Am I the only dissenting opinion

[jayteedee]

"777 fly-by wire - 80's tech.....shuttle-60's tech"

Yes they are old technology and the use of older-mature technology is going to continue into the future. EVERYTHING on a rocket or commercial plane is certified, validated, and/or qualified. The rocket business industry wide still has a 50/50 chance of succesfully flying a new rocket design. And this is the current state with using tried and true ancient technology. Orbital Science Corp. is still using Ni-Cad batteries in ALL their launch vehicles to this day because the cost of qualifying lighter and more powerful Li-Ion and Ni-Hyd batteries for flight is not something they can sell to a customer. Tried and true is the only way to run these type of companies. Weight is like gold on a rocket, but qualified and tested hardware makes the gold-high-tech-gizmo look like sand.

The airplane business is UNWILLING to go back to the test pilot days of the 50's and 60's. The stigma of losing a test pilot's life is far to big a liability anymore. Even if we had remote pilots, the companies are just not willing to risk half a billion in investment to try something bleeding edge. Even if the problem was a fluke, the political/consumer fallout is far to great a risk to attempt. Nobody is these two business' take risk lightly, and that is NOT going to change anytime soon.

Any oxidizer injection done to a scramjet design can also be done to a ducted ramjet design for a whole lot less money.

Plasma magic is still vaporware (pun intended). It may or may not get fielded, but for certain the volumn production stuff and the workhorses for the industry for the next 10 years will be something else. You and me both might wish for the funding levels from the 50's and 60's, and for another Apollo program, but I'm not holding my breath.