Bad Testing Doomed NASA's Hypersonic X-43A

RobertB-DC writes "Space.com got hold of NASA's yet-to-be-released report on the June 2001 failure of the air-breathing X-43A hypersonic research vehicle, and it doesn't look good for 'Faster, Better, Cheaper'. The report refuses to single out any one contributing factor, but it cites ground testing 'inaccuracies' and 'misinterpretation' of wind tunnel data -- in particular, failure to retest the vehicle after additional heat protection was added. As noted in the original Slashdot article, the craft went out of control when the fins broke off just seconds into flight."

Comments

A ridiculous concept from the start

[topher_k]

I worked for one of the companies involved in this program, although not directly on the program itself.

Let's see, we've got a scramjet test aircraft, which will be boosted to hypersonic speeds by a modified Pegasus rocket, which will be dropped from a B-52. So, besides developing the scramjet test aircraft, an interface system between the Pegasus and the X-43A needs to be designed and the whole system tested.

That didn't bother me too much. What really got me was what the point of the program was in the first place. The goal was to test the ability of a scramjet engine to propel an aircraft at hypersonic speeds. The Pegasus booster was supposed to accelerate the test aircraft to hypersonic speeds, then detach, at which point the scramjet would be started and the instrumentation would transmit 10 seconds of data. Besides the limited amount of data, if I recall correctly, the scramjet was not supposed to even maintain the aircraft's speed, which calls into question the value of the technology as a means of propulsion, in my opinion.

If I recall, the contract value was $33 million, and was significantly overrun. Your tax dollars at work (if you're American).

Re:A ridiculous concept from the start

[Idarubicin]

To appreciate the test you have to have a basic understanding of what the scramjet does.

I agree completely. So why do you then tell us the following? You have been misled, my friend.

A scramjet seperates the hydrogen and oxygen molecules in the atmosphere and uses the hydrogen molecules as fuel for the engine. In doing this you have an engine that can go significantly faster, an engine that uses up a fraction of the fuel load of traditional aircraft and an aircraft that expels significantly less harmful waste in the atmosphere then a traditional jet engine.

Quick primer on scramjets, from the top:

In a typical jet engine (see here, for example) air enters through an intake at the front, and passes through several fan stages to compress (and heat) the incoming air. Squirt fuel into this hot air, and the rapid combustion generates exhaust at high temperature and pressure. This high pressure exhaust propels the jet (and drives a turbine which turns the fans in the compressor).

The downside of this design is that it is mechanically complex--those compression stages have large, finely-machined, rapidly-moving parts which are subject to wear, tear, and accidental failure; they also add a significant amount of weight to the engine.

Enter the ramjet. (See also cutaway figure.) Instead of using fans to compress incoming air, a ramjet uses a specially shaped inlet. Air enters the jet inlet at high speed, and then is forced through a narrow aperture. The result is compression without fans. Unfortunately, the ramjet will only work when the jet is travelling at significant speed--there isn't going to be any air coming into the engine if the aircraft isn't moving.

A scramjet is a supersonic combustion ramjet. In a plain vanilla ramjet, the incoming air is slowed while it is compressed to the point where it is travelling slower than sound. Combustion takes place in air that is still moving quite quickly, but not supersonically. Although easier to manage from an engineering standpoint, requiring subsonic combustion places an upper limit on the speed of a conventional ramjet.

The scramjet functions in a similar manner--incoming air is compressed and heated through a properly shaped inlet, then fuel is injected, and the combustion products propel the jet. The defining difference is that combustion takes place in a supersonic airflow; in practice, this dictates certain changes to the basic ramjet design. Again, the scramjet requires significant airspeed before it can be started.

Quite correctly, you note that the fuel for these beasts is often hydrogen, though in principle nearly any air-combustible liquid or gas could be used. The fuel must be supplied, however--a scramjet cannot extract hydrogen from ambient water vapour. The hydrogen scramjet is inherently no cleaner burning than any other air-breathing hydrogen engine. Given its high operating temperature, I would be quite surprised if it didn't generate significant nitrogen oxides in operation.

Re:Yeah, but how much are you willing to pay?

[SmilingBoy]

You are way off.

The total cost of the Apollo program was $19.4b.

This is the total program cost starting from 1965 (or was it 1964?) to 1972. Let's assume that the year 1969 was the year with the highest spending, say one quarter of the total sum, ie $4.9b.

The nominal GDP of the USA in the year 1969 was 3928.7b.

Therefore, at its peak, Apollo consumed approximately 0.12% of the GDP of the US.

I think you might be referring to the nuclear program during and after that World War II. That was expensive! (I've got no numbers though)