Originally posted by nuub
From what I understand the X-43 is not ment to be a shuttle replacement but rather to test their new scramjet propulsion system (I am just doing a project on this and I would appreciate it if you told me if this is correct or not).
Yes, this is correct. The X-43A is just a testbed for the scramjet principle. But one of the reasons we are interested in proving that scramjets can work is because they would make an excellent launch vehicle. As you may already know, the big problem of getting into orbit is not the power required to get up to the right altitude, but to achieve sufficient speed. A hypersoar vehicle could carry payloads to an altitude where atmospheric resistence is no longer a factor, and accelerate to near-orbital volocities, all under the thrust of an air-breathing engine. From there, a small booster rocket released form the cargo bay could put payloads into orbit at a fraction of current cost. Or, a version of the vehicle that has some oxydiser carried on board could continue to run the engines outside the atmosohere and propell the entire vehicle into orbit. This version would be the "shuttle replacement", and would be much cheaper than any current method of launching people into space.
Also from what I understand the scramjet doesn't opperate below supersonic speeds because it required the speed to compress the air, so that it can do away with the moving parts of a regular jet engine, rather like the ramjet but wothout slowing the air down first.
Right. Just as the ramjet doesn't work below supersonic speeds, the scramjet won't work below hypersonic speeds. AFAIK, all current vehicles with ramjets use hybrid engines that function like regular jet engines to get up to supesonic speeds, then switch to ramjet operation. The scramjet would do the same type of transition, I should think.
Also could someone please tell me why so much money is being spent on it, we already have the ramjet which is not used very much, except in a few rockets, and the scramjet has the same basic problems i.e. accelerating the plane up to supersonic speeds, so what will be its use?
It's applications to the space program I've already mentioned, but it would have advantages as a passenger liner as well. New York to LA in 45 minutes, for example. London to Tokyo in 90. Not many comforts; the ride will be mostly, "Sit down, strap in, shut up and hang on!" and "No, there won't be a movie; no, we won't serve you drinks; do not unfasten your safety belt, you should have gone before we took off".
Some of the engineers trying to market the idea have even proposed that it will be cheaper to operate in the long term, since the engines have no moving parts for most of their operational time. And there might even be fuel savings, since the hypersaor concept involves leaving the atmosphere at speeds only slightly less than those required to stay in orbit. The vehicle will then coast until it comes back into the upper atmosphere, where the engine can be lit to climb out again. The reduced drag of traveling through a vacuum means better fuel economy. The vehicle's engines will actually be off for most of each flight (up to 2/3, according to some).
For delivery companies like Fed Ex and UPS, speed = money. With this vehicle, they could offer a special service in which a currier could pick up a package from an office in Hong Kong at 9:00 AM on Wednesday, and it would arrive on Bill Gates' desk before 5:00 PM
Tuesday! You know, for those bosses who keep telling you "this has to get there YESTERDAY!", it actually would.
