X-43A Hits Mach 7 405
quiggy writes "As previously reported, NASA tested the X-43A yesterday. The results are in, and the scramjet hit Mach 7, setting a new speed record. CNN is also reporting the story, with a note that a similar jet could be tested by the end of the year, hopefully reaching Mach 10."
But at that speed... (Score:4, Funny)
Uhh guys...this has been done before (Score:5, Informative)
Not exactly the same... (Score:5, Insightful)
As the spent motor and its attached payload falls back to Earth, they gather speed, and the trajectory is designed so that between 35km and 23km, they are travelling at Mach 7.6
http://www.uq.edu.au/news/index.phtml?article=346
The recent HyShot(TM) launch was designed to take the scramjet engine to a speed of Mach 7.6 (or more than seven times the speed of sound) for the experiment, using a Terrier Orion rocket. The rocket and payload reached an altitude of 314km before the rocket was configured to fly in a new trajectory pointing the payload back down to earth.
HyShot was simply free-falling to earth in order to reach Mach 7.6 so the engine could be ignited. It achieved that speed regardless of whether or not the scramjet fired. The X-43 was flying horizontally, and was actually powered by the scramjet engine during a controlled flight.
So there is a difference between what was accomplished. The distinction is that HyShot achieved combustion, while the X-43 was the first scramjet powered craft to be flown.
Dan East
Re:Uhh guys...this has been done before (Score:3, Informative)
Re:But at that speed... (Score:3, Interesting)
"Paul said although signs so far are positive, it still is too early to say the scramjet experiment succeeded. The scramjet experiment took place during the final few seconds of the flight, which lasted almost 10 minutes."
A quick search with google also did not turn up any reports of confirmed success. Do you have any?
Re:But at that speed... (Score:3, Insightful)
sublight speed ;) (Score:5, Interesting)
10 mach = 3340 m/s = 3.3 km/s
speed of light c = 300 000 km/s
(3 km/s)/(300 000 km/s) = 1/100 000 of c
this engine travelled at aprox 0.00001c !
good work scientists
Re:sublight speed ;) (Score:2)
Re:sublight speed ;) (Score:4, Insightful)
Of course, rockets launched into space have to travel at least 11.18 km/s to reach escape velocity, which is a lot faster than mach 7. This isnt a speed record, really more of a design change in that the engine doesn't need to carry its own oxygen.
Congrats to NASA though.
Re:sublight speed ;) (Score:5, Insightful)
Re:sublight speed ;) (Score:5, Informative)
Re:sublight speed ;) (Score:2, Informative)
Orbital mechanics tells us that the velocity of an orbiting object is dependent on the mass of the object you're orbiting, and the distance you are from the surface. Thus, when Shuttle is orbiting at 300km altitude, it is traveling at 7.73 km/sec. In order to achieve that orbit, it has to achieve that speed, tangential to the direction of gravity. It can do this (neglecting frictio
Re:sublight speed ;) (Score:3, Informative)
I don't have a physics book handy, but I'm pretty sure mass has nothing to do with the velocity.
Re:sublight speed ;) (Score:5, Interesting)
Seriously, there's a need for a "wrong" modifier, so people can mod such posts down without fear of recourse from meta-moderators who think the post is correct.
Re:sublight speed ;) (Score:5, Informative)
Not exactly true. When solving the two-body system, a number of coordinate transformations change the equations of motion into a simple one-body equation that can be solved exactly. The mass in the transformed one-body system is called the reduced mass, which is defined as mu=(A*B)/(A+B), where A and B are the masses of the two bodies in question.
Assuming A>>B (ie, Earth is much greater than the mass of a satellite), this can be rewritten exactly as mu=B/(1+B/A), or w/ a first-order taylor expansion as mu=B-B^2/A. For a standard communications satellite, the second term is approximately 10^-18 times smaller, and can realistically be dropped, and the mass of the satellite is to within measurable uncertainties B.
But you're wrong in general when you say it's independent of the mass of the object it's orbiting. In the system of the moon orbitting Earth, there's about 1% error by replacing the reduced mass by moon's mass. For a more dramatic example look at a binary star system where one star has 3x the mass of another.
Re:sublight speed ;) (Score:3, Informative)
The whole point of the Taylor expansion was to give an estimate of the difference between B and mu, and in this case it's -B^2/A (to 1st order). If you don't like the expansion then keep the e
Re:sublight speed ;) (Score:4, Insightful)
If space rockets are perpendicular (well, they're not really) to the tangent of the atmosphere on exit, their speed still has to be enough to let them escape, but this speed can be really low - I take it implicitly you mean the firing of the rocket is necessary to overcome gravity rather than to reach a certain speed. Conversly, planes in the outer atmosphere can go really fast (speed) but as their velocity does not have a vector pointing upwards they won't exit.
Acceleration has little to do with it other than making the escape more efficient (of course the rocket changing vector is also acceleration).
Re:sublight speed ;) (Score:5, Informative)
Re:sublight speed ;) (Score:3, Funny)
Re:sublight speed ;) (Score:2, Insightful)
Re:sublight speed ;) (Score:5, Informative)
Rockets have gone faster, but they carry their own oxygen.
Re:sublight speed ;) (Score:3, Interesting)
Re:sublight speed ;) (Score:3, Funny)
Scientists my eye.... (Score:5, Insightful)
ENGINEERS had more to do with getting this ship up to Mach 7 that did the scientists!
Re:sublight speed ;) (Score:3, Funny)
Mach 7? (Score:5, Funny)
Mach 10? Mach 10? (Score:5, Funny)
4 posts... (Score:5, Funny)
Comment removed (Score:5, Interesting)
Re:Mach10?! (Score:2, Interesting)
Re:Mach10?! (Score:3, Insightful)
Re:Mach10?! (Score:2)
"Escape velocity [physlink.com] is defined to be the minimum velocity an object must have in order to escape the gravitational field of the earth, that is, escape the earth without ever falling back. [...] So, an object which has this velocity at the surface of the earth, will totally escape the earth's gravitational field (ignoring the losses due to the atmosphere.)"
For the small of brain, the 11 km/s value applies only to unpowered shots (e.g. a cannon) launched from the surface of the earth. Ro
You go higher... less air resistance, less heat (Score:2)
Kjella
Re:Mach10?! (Score:2)
Re:Mach10?! (Score:2, Informative)
Re:Mach10?! (Score:5, Informative)
The real problem here is that a scramjet engine is very sensitive to its input (the air coming in) as it only spends literally milliseconds in the combustion chamber. So you have to wonder what aerodynamic tricks the X-43A designers are pulling to smooth that flow before it goes into the intake. Notice the side-view of the aircraft; the belly is smooth and curvy in order to produce many small shocks ahead of the intake and slow down the air as much as possible. A terrific aerodynamic feat, I just have to wonder if it will be reproducible (i.e. stable enought and robust to any aerodynamic event) for a manned aircraft. [Yes, I am an aerodynamicist].
Re:Mach10?! (Score:2)
Seriously though, someone else said that Mach isn't 757 mph higher in the atmosphere. Considering that, and the known fact that air is thinner at higher altitudes, I don't think you would have as many problems as you think you might... I would be more worried about what happens when the thing hits a pair of migrating European swallows carrying a coconut.
Stupid, Slightly OT Question (Score:2, Informative)
And, to keep a little more on topic:
18 tiems the speed of light!
Re:Stupid, Slightly OT Question (Score:5, Informative)
Re:Stupid, Slightly OT Question (Score:5, Insightful)
Damn gravity.
Re:Stupid, Slightly OT Question (Score:3, Interesting)
The problem is that a scramjet trades a dense propellant (LOX) for more of a low density propellant (LH2). As a result, the propellant tanks on a scramjet vehicle would end up being larger (and heavier) than those on an SSTO rocket with similar payload. LH2 is also much more expensive than LOX, so your propellant costs go up (not that propellant cost is currently import
Re:Stupid, Slightly OT Question (Score:5, Informative)
IIRC, Mach5 is the speed at which the scramjet is released, and ignited... up until then it's just being boosted by a conventional rocket.
During the first test, the scramjet failed.
During this test, it worked, pushing the rocket up another mach or two.
This was not meant to be any kind of speed record.. that's just how fast you need to go to get a scramjet working.
Re:Stupid, Slightly OT Question (Score:5, Informative)
It's the engine... (Score:5, Insightful)
Kjella
Re:Stupid, Slightly OT Question (Score:4, Informative)
As some have noted, it's because of the engine type - air-breathing - that makes this so significant.
The economics of space travel are dominated by the cost to put something in orbit. Sitting on the launch pad, the payload to weight ratio of the Shuttle system is something like 1:50. Picking up the oxygen just lying around gives you a big increment in payload to weight ratio.
Re:Stupid, Slightly OT Question (Score:2, Informative)
X 15 (Score:5, Informative)
Re:Stupid, Slightly OT Question (Score:2)
Another question: Doesn't the space shuttle enter the atmosphere at some crazy mach value like 20? At what point are you defined as being in space, I wonder?
Mach 10 (Score:5, Informative)
or 12247 kilometers per hour
or 7610 miles per hour
Re:Mach 10 (Score:5, Funny)
Re:Mach 10 (Score:3, Informative)
Re:Mach 10 (Score:3, Insightful)
How soon before... (Score:4, Funny)
Speed of sound (Score:5, Informative)
basically the higher you go, the less air there is, and the slower sound travels. So, the mach number, which is the ratio of your speed to the speed of sound, will be higher at high altitudes if the speed is constant.
Re:Speed of sound (Score:5, Informative)
The speed of sound in a gas is affected mainly by temperature... not density or pressure.
From the page you just linked to:
"The speed of sound depends on the state of the gas; more specifically, the square root of the temperature of the gas."
Mach at 35,000 ft is 663mph
Mach at 150,000 ft is 732mph
The reason higher aircraft hit higher mach numbers is due to decreased air resistance... concorde can hit mach at 50,000 ft, but not at 20,000.. not because mach is perceptibly slower, but because there is less drag.
Re:Speed of sound (Score:5, Informative)
The reduction of sound speed at altitude is due to the reduction of temperature. The temperature rises again in the upper stratosphere (ozone heating) and then drops down to its coldest temperature at the mesopause (around 120 K, at 85 km). However, the temperature increases rapidly above that, getting back to room temperature by 110 km, and heading for 1000k and beyond by the time you get to LEO.
At high altitudes the mass density is decreasing as you get more and more atomic species (e.g. O rather than O2) as well as larger fractions of light constituents (e.g. H2, H), so the speed of sound is quite high at LEO. At altitudes above the "turbopause" (somewhere around 105 km) the components of the atmosphere are no longer well-mixed, thus the different component gases stand at their own scale heights.
see scale height [wolfram.com] and speed of sound [wolfram.com]
CNN gets it wrong (Score:5, Informative)
Considering Concorde did that in three hours, thit wouldn't be much achievement. I make it that it could do NY-LON in just over one hour.
What I think they should have said is that it could go from any point on the earth to any other, including the antipodes, in less than five hours.
Mind you, it would take three hours to get through security on departure and an hour on arrival to collect your baggage, if it had arrived with you.
Re:CNN gets it wrong (Score:5, Funny)
Total time 6 hours. Your bags though would arrive 2 days later assuming that they hadn't been blown up in an anti-terrorist "controlled explosion" at LAX.
Re:CNN gets it wrong (Score:2, Interesting)
The Mach 10 is not enouth... (Score:2, Informative)
Great Things to Come (Score:2, Informative)
Hopefully it will be designed with a space station or dock in mind. It's my understanding that the shuttle was retrofitted for in-space docking such that the International Space Station almost had to be built around it.
"And how much more black could it be? None more black." - Spinal Tap
CNN slipping,... (Score:4, Interesting)
Kudos to Fox, to CNN: do a better job, or you will fall further behind FoxNews.
later,
epic
Re:CNN slipping,... (Score:5, Interesting)
--
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Re:CNN slipping,... (Score:3, Interesting)
News is supposed to be "PC" (Score:4, Insightful)
The term "Politically Correct" (PC) is a satirical epithet applied to liberal doctrine by conservatives. It mocks the presumption that liberal opinions are the "correct" opinions, in an absolute sense, not one perspective among many.
The term "PC" is made more amusing to conservatives by the liberals' conviction of their own political correctness preventing liberals from recognizing the joke that liberals' are unawaredly convinced of their own political correctness. "Of course our beliefs are the correct beliefs, why is that funny ?" ask the liberals.
Which brings us to your assertion that "News is supposed to be PC" What you are telling us ?
1. That news should be reported from a liberal perspective because...
2. Liberals are right and conservatives are wrong.
3. You are blind to the fact that you are promoting your own perspective in absolutist terms.
Note, "PC" denotes both the status of a particular belief as liberal and the associated presumption of correctness. For example, consider the statement "Johnny failed first grade, but he is African-American, therefore holding him back at that grade level would not be PC". In this sentence, "PC" serves to associate with liberals the principle that unqualified indviduals should be promoted if they are members of a particular ethnic group. But "PC" is also meant to characerize the attitude of those who would defend that principle as an absolutist faith that they are "right" and others are "wrong".
Fox News is unpopular with liberals not becuase it sets forth alnternative and consertavie "correct" notions, but because it undermines the very notion of correctnees in political discourse. Fox betrays the news broadcast tradition of delivering news in somber, ministerial tones which close off question and doubt; "Though shalt not question the word of Jennings". "The shalt now question the word of Brokaw." The informal on-air attitude of Fox news is like "Here are our correspondents and here is what they seem to to think is going on." It's more upbeat and friendly. We are allowed to ask questions. Fox news conveys to television viewers the dangerous attitude that what you see on TV is people telling you what they think is going on, not sacred and unquestionable truths. It undermines the notion of TV news as a conduit for absolute and correct truths, subverting the entire system of liberal propagandizing through control of unexamined "correct" news content.
News should not be PC.
Re:CNN slipping,... (Score:2, Funny)
heh.
How fast .. (Score:5, Funny)
African or European?
10 seconds (Score:4, Interesting)
Re:10 seconds (Score:3, Insightful)
It worked for 10 seconds. That was all this design is supposed to do, and all it is likely capable of doing, but it proved their combustion chamber design works.
Now they can strap big fuel tanks on and go for a longer sustained burn, if they want to.
Doubt it Re:10 seconds (Score:3, Interesting)
Besides, where would they put the bigger tanks? The thing is tiny; and hydrogen is seriously not dense; meaning very little fits into the vehicle.
Re:Doubt it Re:10 seconds (Score:3, Informative)
Compare this to liquid oxygen which is (IRC) more like 1100 kg/m^3; or water 1000kg/m^3. Gasoline or kerosene is slightly lighter than water, but not a lot. Liquid Hydrogen is seriously not dense- that's actually the biggest problem with it.
Re:10 seconds (Score:5, Informative)
If you want a good paper on the subject, I suggest this one [anu.edu.au] from the Australian National University.
Why its important (Score:5, Informative)
Conventional Ram jets are limited in top speed by the necessity to slow the incoming air down to sub sonic velocities.
Not only does the SCRAM jet have potential military applications, it can also serve as a 'midrange' stage for a lower cost to orbit booster.
SCRamjet = Supersonic Combustion Ramjet (Score:5, Informative)
There's one fundamental difference between an ordinary jet engine and a scram jet engine: The Ramjet has no moving parts.
The all jet engines,operate according to Newton's Third Law of Motion:
For every action, there's an equal opposite reaction
The standard jet engine, invented by Sir Frank Whittle, sucks in air at the front. Then this air is mixed with fuel, and made to combust. The combustion causes the air to exit the engine at a velocity greater than when it came in, thus creating thrust. The escaping air causes the turbine to spin, and this intern activates the compressor, sucking more air in.
The Ramjet has no turbine and compressor unit. Ramjets fly supersonically and have an inlet which injests subsonic air after it goes through a shock wave in front of the inlet. The intake is slowed down aerodynamically, and then mixed with fuel and made to combust. But after about Mach 5, ramjets don't work so well.
The scramjet is almost but not quite entirely like a ramjet. The only difference being in a scramjet the combustion takes place as the air is travelling through the chamber at supersonic velocities.
More [uq.edu.au] about the scram jet. Or another [aviation-history.com] more concise explanation.
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First Mach 10... (Score:5, Funny)
Adtional information on scramjets (Score:3, Informative)
THE PROGRAM IS BEING HALTED! (Score:5, Interesting)
A new plane doesn't make a new engine possible: A new engine makes a new plane possible.
That's why when NASA went for the moon a critical development was the F-1 first stage rocket engine. Capable of 1.5M lbs. of thrust it allowed the Saturn V first stage to be built with only 5 engines. Compare this with the Russian failed manned lunar rocket the N-1 which had 20 engines. They never were able to work all together (vibrational problems) and abandoned it after several launch disasters.
So why is NASA stopping development? (The successor the X-43C will not be flown). Why are we freezing this enabling technology? Are we (under Bush's program) sacrificing everything to plant a flag on Mars and not making space flight practical? It might be worth it if we ever got to Mars but it looks highly doubtful that his proposal is a serious attempt at anything but votes!
Sorry for the (mostly) repost but I really wish we would move "faster" towards developing the technologies towards practical* spaceflight.
*As noted in previous posts, by not carrying the oxygen on board you save a LOT of weight. Remember the reaction is H2 + O = H2O (and energy) and since the atomic weight of oxygen is 16 compared to hydrogen for every kilo of hydrogen you carry you carry EIGHT of oxygen. The weight savings (could be in the millions of pounds) makes up for the turbo-fans/rocket engines you must carry for the takeoff/orbital transition parts of the flight.
Re:THE PROGRAM IS BEING HALTED! (Score:4, Interesting)
I'd rather doubt they are. If it can be made to work and there is a need, either the NASA program will be funded or it will disappear in to an Air Force black program and will just appear to have been killed.
It does appear it can be made to work and it would presumably add a new top end to Aurora or whatever the Air Force's current black program is.
Its use for civilian transportation is dubious. Its pretty dangerous and would take a LONG time to be made safe, cheap and comfortable. I'm also doubtful it will prove to be a great launch vehicle though you never know.
Its military applications are obvious. The DOD has a pretty desperate need to drop bombs on targets of interest that arise quickly and move around like Bin Laden. When they get intelligence he is at a place they need to drop ordinance there as quickly as possible before he moves and with some targeting flexibility. A manned or remotely controlled Mach 11 bomber would seem ideal. An RPV version of this could come to fruition a lot faster than a manned version, Cruise missiles, the stealth bomber etc are to slow to get to the target in time. Using ballistic missiles tends to set of alarm bells in Russia, China and everyplace else where governments have satellites watching for launch signatures. Targeting for ballistic missiles also can't be redirected at or stopped at the last minute.
It would also be priceless for strategic and tactical reconnisance. Spy satellites are to predictable and inflexible since they are locked in to orbits with limited manueverability. Most countries know the schedule and hide stuff when they are overhead. A Scramjet would be flying fast and high enough it would be hard to shoot down, or even detect until after its done the job.
NASA Dryden deserves a huge pat on the back for finally bending metal and flying something. They've been wasting money on computer generated fantasies for this concept for more than a decade and haven't done much to realize it. It would be fantastic if it lead to a better launch vehicle and civilian transport, I just doubt that it will.
Re:THE PROGRAM IS BEING HALTED! (Score:3, Interesting)
Actually, the weight savings is non-existent. Sure, you save about 25% of the LOX in your first stage, but that's more than made up by the increased structural weight and thermal protection. Fact is, when the numbers are added up, you frequently come out worse in both weight and cost.
Using a re-useable airbreathing first 'stage' is a pow
Yeah!! (Score:4, Funny)
NASA overclockers RULE!!
Armchair physicists are idiots (Score:5, Informative)
2) As has been already posted. The speed record isn't for ANY vehicle. The record is for a vehicle with an air breathing engine (ramjet, scramjet, etc). It doesn't apply to vehicles such as the X-15, Apollo capsules, the space shuttles, etc as their speeds were/are either rocket powered or unpowered reentry.
3) During the first test the scramjet engine did NOT fail. It was never even fired. The booster engine that was supposed to get the scramjet to mach 5 is what failed. If I remember right the fins or something fell off and it went out of control so the remote detonated the booster and consequently the scramjet testbed attached to it.
4) The toyota corolla attachment won't be out until 2006.
Re:Armchair physicists are idiots (Score:5, Funny)
Bullshit. Toyota announced that they will not be selling *any* vehicles with the scramjet until it completes product safety retesting, which will be finished in 2008 at the earliest. Apparently, the flux capacitor doesn't perform as expected above about 88 mph.
From the CNN article (Score:3, Funny)
Throwing away information (Score:3, Insightful)
CNN Errors and the quarter mile (Score:3, Insightful)
Now this intrigues me: It was taken to mach 5 by the Pegasus, then it accelerated under the scramjet to mach 7, BUT the engine was only lit for 10 seconds. Does that mean this succer gained nearly 1400mph in 10 seconds???? Wonder what it would do in the quarter? How many Gs is that?
Re:CNN Errors and the quarter mile (Score:4, Informative)
Re:CNN Errors and the quarter mile (Score:4, Informative)
It was taken to mach 5 by the Pegasus, then it accelerated under the scramjet to mach 7
This is not true. The pegasus booster took it all the way to mach 7. The scramjet proved it could make positive thrust, but it did not accelerate, it actually decelerated during those 10 seconds. Maximum speed was at booster burn out. This is according to their press conference yesterday.
Also, see this video: (remove the space in the URL)
http://www-pao.ksc.nasa.gov/kscpao/videos/metafi les/ksc_032504_x-43.ram
This thing is (*TINY*) (Score:5, Informative)
All the pics were of the Pegasus booster rocket which was dropped from a B-52. You can't even resolve the X-43 in those photos.
That X-43 is smaller than most of the bombs that B-52 has dropped in its lifetime.
12-feet-long. Small in proportion (Score:3, Informative)
"The unpiloted 12-foot-long vehicle, part aircraft and part spacecraft, will be dropped from a B-52,aircraft. It will be boosted to nearly 100,000 feet by a rocket..."
from this [nasa.gov] NASA page is one source.
I think you are underestimating the size of the Pegasus rocket and B-52 bomber. I know I did. A quick google search found a page on the Pegasus rocket: it is 55.4 feet long and about 4 feet in diameter.
Re:At the present rate (Score:5, Insightful)
Re:At the present rate (Score:5, Funny)
Re:At the present rate (Score:4, Informative)
The current problem is that of relitivty, at which there is a certian point where energy stops creating speed, and goes into increasing the mass of the moving object, thus making light speed impossible.
Alcubierre's idea was that the ship doesn't move. Instead, it modifies the space around it much like an esclator. Since the ship doesn't move in relitive terms, it doesn't gain mass or suffer time dialation.
However, at this time, there was a problem with obtaining the required energy, which was quite alot [think total solar output of the sun in its current life, per second].
In 1999, however, Thomas Valone spotted an answer. Zero Point Energy. In a nutshell, one can theoretically harness the binding energy of a particle. This energy, if harnessed, would be enough energy to power an Alcubierre warp drive.
However, both ideas are still in the working stage, and I think we will see Duke Nukem Forever before we see warp drive from either of these two concepts.
NeoThermic
Re:At the present rate (Score:5, Insightful)
I'm with you so far.
However, at this time, there was a problem with obtaining the required energy, which was quite alot [think total solar output of the sun in its current life, per second].
The main stumbling block to Alcubierre's drive is that it requires negative energy. My understanding is that the human race can't produce that right now, at least in appreciable quantities.
All of the FTL drive concepts that I've seen involve something currently unobtainable (or outright impossible) like this - infinitely long neutronium rods, creation of a pocket universe to put the ship in, etc.
In 1999, however, Thomas Valone spotted an answer. Zero Point Energy.
No. Pseudo-science can solve lots of problems theoretically, but it is not the answer to real-world problems.
no, (Score:2, Insightful)
Re:Mach 10 enough to sail into orbit? (Score:4, Interesting)
Re:Feasibiliy of High Speed Travel (Score:2)
Re:Feasibiliy of High Speed Travel (Score:2, Informative)
Shall we calculate?
Let's say for rough estimation purposes mach is about 1000km/h, or 277.8 m/s
So mach 7 is 1944m/s
Let's say that G is 9.8m/s^2 (It is)
1944/9.8= 198.4 seconds
In other words, at 1G, after 3 minutes and a bit
IN that time, you would have gone approximately 193km.
Factor in the same for deceleration... and we could say.
You could comfortably go 400km in about six minutes. Less than that and this speed is not practical.
For that matt
Re:Feasibiliy of High Speed Travel (Score:3, Insightful)
However they get up to minimum scramjet ignition speed, there is likely to be a pretty good kick in the pants when the scramjet ignites.
And the question of how they get up to that speed is a very important one to work out. If a rocket is used, then acceleration will be very brisk. Also, if you are going to use a rocket anyway, why bother with the sc
Re:CNN should take a look at the history books... (Score:2, Funny)
Re:the scramjet did not accelerate to mach 7 (Score:3, Informative)