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Second Hypersonic X43 Scramjet Ready for Testing
Dan writes "I am sure most of you remember how NASA was forced destroy their first hypersonic X43 seconds in it's maiden flight, which was a big setback for the american hypersonic scramjet program. Well NASA just finished one of the final tests and is preparing to launch it as early as February 21! I wish them the best."
Supersonic is Mach 1.0 to 4.9, Hypersonic is Mach 5.0+. I'm not an aerospace engineer, but I vaguely remember an article in Popular Science that talked about how over Mach 4, the airflow through the engine would disrupt combustion.
Have you been touched by his noodly appendage?
Been there done that.
Basically, yes.
The thing about getting to orbit isn't so much the vertical velocity required, its your horizontal velocity. Rockets going to orbit don't go straight up; if they did they would end up coming straight back down... The trick is getting enough horizontal velocity so that as gravity pulls you down towards the earth you are moving fowards fast enough that you are continually "falling over the edge" of the horizon.
With a scramjet you only need half the fuel of a traditional rocket, as you burn oxygen from the atmosphere instead of carrying it all with you. Yes, a traditional rocket IS needed to get you out of the atmosphere, but using a scramjet for the initial acceleration would end up saving a lot of fuel, and hence weight.
So, why carry the oxygen, why not get oxygen from the air? For LH2-LO2, that eliminates most of the mass and solves the mass fraction problem right away. The 1960's Aerospaceplane project originally considered liquifying the O2 from the air -- careful tweaking can be enriched on LO2 over LN2 on account of boiling point differences. You used (boiled off) some of your LH2 to get the coolant.
The trouble with LACE (liquid air cycle engine) is that you have to slow down the air rushing into the inlet (or speed it up to your rushing vehicle). If you are going fast enough relative to orbital velocity, slowing the O2 down in the inlet will heat it so much that you cannot burn it with H2 and get any energy -- the stagnation temperature of the shock front gets higher than your flame temperature. Hey, if this were not the case, orbital velocity would be low compared to rocket exhaust velocity and mass fraction would not be a problem.
Ah, the scramjet, and scramjet was also considered for Aerospaceplane. It is literally the taking a drink from a fire hose. You only slow down the inlet air stream a little bit so you get some compression, and burn H2 in that hypersonic air blast and 1) hope that the flame doesn't blow out and 2) hope that you get any positive net thrust out of the works.
If you could get any single-stage-to-orbit vehicle built that had reasonable engineering margins, you could fly it like an airplane, and even if it had a very small payload, you could fly it often enough to make a profit. NASA blew a wad in the late 80's, early 90's with National Aero Space Plane (NASP) and pulled the plug. But forget the scramjet -- if you could build a rocket out of composite materials, you could get the mass fraction. NASA blew a wad in the late 90's on the X-33 and then pulled the plug.
Jerry Pournelle states that the Strategic Defense Office (which needed a way to loft Star Wars into orbit) could have done the job -- the DC-X demonstrated the control of vertical-takeoff vertical-landing (lands tail first on rocket flames just like in Buck Rogers -- maybe not so wasteful of fuel because reentry is mainly aerobraking and landing is to last applying the brakes on a mainly empty vehicle), and he talks about a program called Have Region (don't know the source of Air Force code names, although NASA these days seems to have projects code named Have Boner) that proved that the mass fraction target was achievable and one didn't need scramjets.
Humans will not be free until they have stopped being afraid of death and the scare tactics used to control the weak religious minded, such as belief in heaven, hell, judgement day, etc. nothing good will happen. All are used as tools by the Leaders and Pontiffs to keep the masses in line.
Until the substitution of reason and thought for blind faith happens nothing will ever change.
But honor the 2 biggest killers of mankind - the military class and religion as advancers of society? Fuck, no. They are the biggest millstones around the human condition.
This is only relevant for scramjets that use hydrogen as a fuel. If there were a scramjet which used jet fuel B, then that type of savings would be much smaller.
However, the X-43A vehicle does indeed use hydrogen for its fuel. (Perhaps for that very reason?)
Whoever modded this as interesting knows even less about physics and aerospace technology than did the writer. The heat generated by friction at high speed is an issue that must be addressed, but while there will be drag it's not going to rip anything apart unless it's not designed properly in the first place. That's one of the things wind tunnels and computer modeling help deal with long before a model is test-flown.
The SR-71's fusalage expanded from heat, true. The material is going to have to deal with heat, true. The NASA shuttle deals with the heat of mach 25 on re-entry, and it is not torn apart by drag unless something goes wrong, but the same happens when a commecial airliner gets seriously out of shape in-flight. Like the one that lost its rudder over Long Island Sound a couple years ago.
The stealth bomber (B-2) is subsonic. Carbon fiber is used due to its strength-to-weight and radio-frequency transparency, not heat resistance. I would be looking at exotic metal alloys, metal composites, ceramics (which is what the space shuttle tiles are) and use of circulating fuel for cooling of critical areas. The flight profile for a long duration hypersonic craft would probably involve extended flight at altitudes where drag is less of an issue, further reducing friction heating.
To hear the gods laugh tell them your plans.
That's not entirely correct. The O2 is a third of the mass. Keep in mind that in addition to eliminating the weight of the 02, scramjets push such an amazing amount of air out the back that they are far more efficient than rocket engines.
The main problem with space launches is the initial climb and acceleration, when you are pushing forward all of the craft's stages and fuel. By eliminating the 02, it translates into vastly, vastly smaller requirements.
Better to simply make the fuel and oxidizer tanks bigger (because fuel and oxidizer is -so- much a -tiny- part of a launch cost) and stick bigger engines on it.
Scramjets are far simpler than rocket engines. It would be much cheaper to build boosters that use a scramjet as a first stage as opposed to a rocket engine. The fuel savings, the increased payload, and the cheaper cost all make the scramjet a superior option.
If you don't understand any of my sayings, come to me in private and I shall take you in my German mouth.
Scramjet technology began around the 1950's. It has been since the 1970's research in to plasma torches in supersonic flows. The plasma torch servers as an igniter and combustion enhancer. Plasma torches offer a couple of advanrages. The plasma torch servers as an ignition source for the fuel and combustion enhancing radicals produced by the plasma torch.
Scramjets also use the hypersonic shock wave for compression. A high compression "point" is where the forebody and engine fence shock waves cross. One of the problems faced it is how to design the inlets to maximise the compression. To keep things simple many scramjet engines are designed as 2D engines.
Designs my attempt to use air stream swirl to enhance fuel and oxidizing air mixing.
For more details please see http://citeseer.nj.nec.com/cache/papers/cs/3623/ft p:zSzzSztechreports.larc.nasa.govzSzpubzSztechrepo rtszSzlarczSz1998zSzaiaazSzNASA-aiaa-98-2506.pdf/r ogers98experimental.pdf
That's not entirely correct. The O2 is a third of the mass.
...twice as many hydrogens as oxygen but
I'm not sure what relavence the % of Oxygen's mass is. The main point is that the mass doesn't matter if it is fuel/oxidizer mass. Typically you want -more- of it because it makes life so simple if you can have more powerful engines that consume it in large quantities.
--You are both wrong. In a Liquid Hydrogen/Liquid Oxygen rocket, 8 times as much oxygen mass is needed compared to hydrogen mass.
4H + O2 => 2H2O
Oxygen is 16 times more massive.
Rocket engines are -very- efficient, but of course they have to push their own oxidizer along.
--I dont know how you define efficiency but in my aproximation having to lift 20x the payload mass because of extra fuel is an inefficency.
Vastly smaller requirements for what? O2 which is amazingly cheap? Why bother?
--Going back to the previous point. Its not a matter of the price of oxygen, but the bulk that it causes to carry it. This results in hugely more complex lift vehical, which is... um... huge, and expensive.
You don't get very far up before you run out of oxygen to power a scramjet
--In fact it cant operate at low altituteds because there is too much oxygen.
scramjet... weighs quite a bit itself.
--Compared to fuel weight ???? Are you nutts ?
Sir, I dont think you understand this at all.
Im not here now... Im out KILLING pepperoni
The current thinking is so:
Use turbojet stage for takeoff.
Bring in Ramjet stage at transsonic speeds, transitioning to full ramjet about Mach 1.5 to Mach 2.
Bring in Scramjet stage from Mach 3-4, transitioning to full scramjet at Mach 5-7.
Bring in Rocket stage at mach 10-12, transitioning to full rocket at Mach 14-16.
You see, that it's rare that any single stage is purely one thing or the other. Scramjets are not the solution to space travel. They're one piece of the puzzle. Reducing the cost of flight to space by 5% is something which would still be worthwhile, and airbreathing flight certainly has great promise to do far more than that.
The problem is that at the moment it's only that: promise. These tests are to see if we can turn promise into reality.