Nasa Scramjet test on Monday
Nasa Scramjet test on Monday
Whoa... Now that is cool.
I wonder how long we'll have to wait before we'll see those things in airports?
("Fasten your seatbelts and straighten your seats. Please do not get up during the next 60 seconds - the cleaning crews have stomachs too, you know...")
It'll be a while. There is no more funding for hypersonic research after this flight is done. The Air Force seems interested, but as far as civilian research at NASA X-43A #3 will be the last hypersonic flight for the forseeable future.Originally Posted by Gullible Jones
Uh, Oh... Bad Yahoo!
From the Yahoo News article:
What about just about every military jet fighter in the world? I thought they had rotating compression blades -- and alot of them can get up to Mach 2+Conventional jet engines use rotating blades to draw in and compress air, and cannot obtain supersonic speeds.
Yeah, not good...but not all bad either. Most of the "jet fighters" you are referring to go supersonic with the help of afterburners. Perhaps a better phrasing would have been cannot sustain supersonic speeds, but even that would not be wholly accurate since the F/A-22 seems to be able to "supercruise" (that is, fly at supersonic speed without the use of an afterburner).Originally Posted by tlbs101
Rereading the Yahoo article I am disturbed by two other little quotes:
This kind of makes it sound as if the scramjet will get the X-43A up to Mach 10. The actual speed at separation will undoubtedly be classified, but since the engine only fires for a few seconds, the Pegasus will likely get it almost all of the way there. The purpose of the test is to make sure that the engine works and that it can attain positive acceleration at Mach 10. Like the above quote it isn't exactly inaccurate, just misleading.The X-43A and its booster will then separate from the B-52B and launch to an altitude of 29,000 meters (95,000 feet), where the scramjet engine will ignite, propelling the X-43A at Mach 10, or 7,000 miles per hour, for about 10 seconds.
I almost don't know what to say about this. I suppose it depends on what they mean "very high speeds". Certainly the ramjet stage on the SR-71 engine did exactly what they are describing. I imagine that they mean that the X-43A is the first scramjet aircraft...that would make more sense. It is a pretty important distinction.The X-43A is the first ramjet aircraft capable of drawing its oxygen fuel directly from the atmosphere as it travels at very high speed, as opposed to rockets, which must transport huge tanks of oxygen to create combustion by mixing it with hydrogen.
How about a privatly funded scramjet.
I believe they mean TurboFan engines, this would be an accurate statement since in a commercial aircraft the fan produces the majority of the thrust, in a military jet the jet turbine produces the majority of the thrust. And technically the military jet doesn't operate above Mach 1 either, the jet's inlet knocks the flow down to subsonic speeds before it goes through the "fan and jet" parts of the engine and the nozzle spools it back up to supersonic.Originally Posted by tlbs101
A long, LONG time. There are huge design problems for scramjet hypersonic aircraft. They would get very hot, there are few materials that can take that kind of temperature for a reasonable period of time, they would require specialized fuel, and would be incredibly fuel inefficient by conventional jet standards. (And if you thought the Concorde was bad ...)Originally Posted by Gullible Jones
There's an argument for a scramjet cruise missile, and maybe a specialized military aircraft, but a suborbital rocket might do as well to get you somewhere on earth fast. For getting something to orbit, it isn't clear all the extra complexity over a rocket would get you much, either. The key cost for rockets is operational, not fuel.
True, but the primary use for scramjets in the forseeable future will be in the launch industry. Whilst the cost of fuel is not the major cost in a launch system, it's mass is a big big cost. If you can build a launch vehicle that does not need to carry an oxidizer, then you can carry more payload ... and that's where the money is in the launch business
I used to think that too, but it isn't accurate. A scramjet/rocket hybrid might carry less oxygen, but it would stay in the atmosphere for a long time during acceleration. There is a HUGE energy loss to atmospheric friction. It might be possible to recover some of that, but that leads to even more system complexity. There is also a great deal more mass for the airframe and extra hardware versus a much simpler pure rocket design. It is questionable whether there would be a payload advantage.Originally Posted by Decromin
But more than that, if you were to create a reusable spacecraft (there is no point in getting fancy with a throwaway) you want something reliable and easy to maintain. Operations is the primary cost component. If you want more payload, you just make the rocket bigger - and it can be cheaper to make it bigger, more reliable, but less mass efficient.
The materials required for a scramjet are right at the edge of available technology. You would have to do a lot of repair and replacement, as is done with the Shuttle on the TPS and SME. That isn't the direction to go if you want economical and reliable spacecraft.
The consensus seems to be that scramjets might be useful for single use cruise missiles and specialized but very expensive military aircraft. News stories might mention earth to orbit and passenger craft for more public consumption, but those are very unlikely, and certainly wouldn't make economic sense.
Ultimately, if it weren't so hard, we'd already have it.
Here's an article on this subject: