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Space Science Technology

First Ever Scramjet Reaches Mach 10 235

Posted by Zonk
from the really-super-very-short-take-off-and-landing-or-rsvstol dept.
stjobe writes with the news that a group of US and Australian scientists successfully tested a supersonic scramjet engine in the Australian Outback on Friday. The Sydney Morning Herald reports that a rocket carrying the engine reached mach 10, and climbed to an altitude of 330 miles before the apparatus re-entered the Earth's atmosphere. "Australia's Defense Science and Technology Organization (DSTO) said it was believed to be the first time a scramjet had been ignited within the Earth's atmosphere ... Scramjets are supersonic combustion engines that use oxygen from the atmosphere for fuel, making them lighter and faster than fuel carrying rockets. Scientists hope that one day a scramjet aircraft fired into space could cut traveling time from Sydney to London to as little as two hours."
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First Ever Scramjet Reaches Mach 10

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  • X-43A? (Score:5, Informative)

    by Chairboy (88841) on Saturday June 16, 2007 @01:32AM (#19529393) Homepage
    What about the X-43A? It also ignited successfully and flew under power.

    http://en.wikipedia.org/wiki/Boeing_X-43 [wikipedia.org]

    This is cool, yes, but the emphasis on "first" seems a bit off.
    • Re:X-43A? (Score:5, Funny)

      by evil_neanderthal (1024405) on Saturday June 16, 2007 @02:10AM (#19529635)
      mach 10? not fast enough! i want one for my microwave! faster pizza bagles! faster ezmac! faster! can i mount one to my pelvis! can't wait to see what the missus thinks. miss. mistress! huh? i need a gun that shoots scramjets with knives on the end! can we start calling it warp 10 instead of mach 10? they should have taped a dvd to it to set a data transfer record! we need a new unit for that! dvd-mph! gigafoot-hertz! i want the 13 gfhz model for my toaster! butter the whole toaster so it doesn't get incinerated from air friction! does it come with internet? i want one with internet! it needs bluetooth! eeeeeeee
    • Re:X-43A? (Score:4, Insightful)

      by tbischel (862773) on Saturday June 16, 2007 @03:02AM (#19529837)
      ...it was believed to be the first time a scramjet had been ignited within the Earth's atmosphere
      Ah I see... as opposed to the many airbreathing scramjets ignited outside earths atmosphere.
    • Re:X-43A? (Score:4, Insightful)

      by Gorshkov (932507) <(moc.oohay) (ta) (vokhsrogmda)> on Saturday June 16, 2007 @03:22AM (#19529947)
      From my quick reading of the wiki on the X-43A you linked to, I get the impression that it only it it's scramjet at about 100,000 feet .... but TFA states that this was the first to ignite and operate it's scramjet *within the atmosphere*. I'd guess that's the difference.
      • by Anonymous Coward on Saturday June 16, 2007 @04:44AM (#19530313)
        According to wikipedia, (I know), the atmosphere is usually considered to end at 328,000ft. (Karman line)

        The Stratosphere goes to 160,000ft. You have to go above 50 miles (264,000ft) to be considered an astronaut, and atmospheric effects are noticeable at 400,000ft during reentry.
        • by Gorshkov (932507)
          gotcha .... I stand corrected. I gotta learn to NOT post at 4am ..... it's causing a lot of pissyness in the global warming article just down the hall :-)
      • by Moraelin (679338) on Saturday June 16, 2007 @06:41AM (#19530763) Journal
        Scramjets need an atmosphere anyway, just like ramjets and turbojets. That's the whole idea. The air flows through it, fuel is injected into that air and ignited. Trying to operate a scramjet in a vacuum would make as much sense as trying to operate a turbojet there. Pretty much all 3 are the same jet engine, more or less. A turbojet uses a compressor in the front to push the air into the engine. A ramjet relies on the fact that if you fly fast enough to start with, you get air pushed into the engine anyway. (Plus some clever design of the intake so the flame doesn't go in both directions.) But the air is slowed down to a subsonic speed at the point where the fuel is injected and lit. A scramjet is a ramjet where the air does flow at supersonic speed through the engine, so basically it's choked. You can add the fuel past the choke point and, since waves can't move backwards in a supersonic flow, whatever pressure you generate there by burning fuel can only go towards the back engine. The front of the engine can't "notice" the higher pressure in the back half because a pressure wave would have to travel through that air faster than sound speed, which isn't possible. Another rough description would be that a scramjet is like a turbojet with an afterburner, only without the turbojet. (Sorta like the sound of one hand clapping, I guess;) Instead of having the turbojet push air through a nozzle and add extra fuel to it, the engine _is_ the nozzle and the airplane's existing speed is what pushes air to it. So you just add the fuel and light it. It's an afterburner without a turbojet. But in the end all 3 work by the same basic principle: air comes through the front, fuel is added, hot air comes out the back. No air, no flame, the engine stops. The plans to use a scramjet to get to a highe enough orbit or even leave the planet, involve getting enough speed while still having enough air for the scramjet, or as boosters in addition to the normal rocket engines, or both.
        • Re: (Score:3, Informative)

          by Gorshkov (932507)
          now, THAT was an explanation. Right now I regret that I'd already posted to this discussion - I can't use my mod points on you. Thanks.
        • by dyslexicbunny (940925) on Saturday June 16, 2007 @12:34PM (#19532825)

          A ramjet relies on the fact that if you fly fast enough to start with, you get air pushed into the engine anyway. (Plus some clever design of the intake so the flame doesn't go in both directions.)
          Not necessarily. The ramjet inlet's design is such that the air is compressed through ram compression, essentially the air is compressed as it is slowed down. There really isn't any clever design on the inlet. The pressure in the inlet area is greater than the that of the combustor and so long as that is true, no flame will come out. You're essentially correct but I just wanted to nitpick.

          Explaining the turbojet is easier after explaining the ramjet. Ramjet performance suffers below Mach 1 because you can't get enough compression for efficient combustion. The turbojet adds a compressor to add work to the flow so you can get the desired pressure ratio coming into the burner. Then you have to go through the turbine such that you can power the compressor.

          Engines with compressors are far more interesting as they can be pushed to the point (whether by power setting or flight condition) such that the compressor can stall and flame will shoot out the front of the engine. It's something pretty important in compressor design since they operate with an adverse pressure gradient (pressure out > pressure in). This is why you see compressors with 10+ stages powered by only 1-2 turbine stages. It's really quite interesting.

          You basic principle explanation isn't great for non-engineers. Try using "Suck, squeeze, bang, blow." I explained that to some friends of mine and they were way more interested. They not only laughed but they then wanted to hear more detail. But solid explanations on your part, I just wanted to nitpick a couple things since I'm a propulsion guy.
      • by Moraelin (679338) on Saturday June 16, 2007 @06:45AM (#19530775) Journal
        Scramjets need an atmosphere anyway, just like ramjets and turbojets. That's the whole idea. The air flows through it, fuel is injected into that air and ignited. Trying to operate a scramjet in a vacuum would make as much sense as trying to operate a turbojet there.

        Pretty much all 3 are the same jet engine, more or less. A turbojet uses a compressor in the front to push the air into the engine. A ramjet relies on the fact that if you fly fast enough to start with, you get air pushed into the engine anyway. (Plus some clever design of the intake so the flame doesn't go in both directions.) But the air is slowed down to a subsonic speed at the point where the fuel is injected and lit. A scramjet is a ramjet where the air does flow at supersonic speed through the engine, so basically it's choked. You can add the fuel past the choke point and, since waves can't move backwards in a supersonic flow, whatever pressure you generate there by burning fuel can only go towards the back engine. The front of the engine can't "notice" the higher pressure in the back half because a pressure wave would have to travel through that air faster than sound speed, which isn't possible.

        Another rough description would be that a scramjet is like a turbojet with an afterburner, only without the turbojet. (Sorta like the sound of one hand clapping, I guess;) Instead of having the turbojet push air through a nozzle and add extra fuel to it, the engine _is_ the nozzle and the airplane's existing speed is what pushes air to it. So you just add the fuel and light it. It's an afterburner without a turbojet.

        Downside: a turbojet can start at zero speed, ramjets and scramjets need enough airspeed to start. Hence all these experiments involve booster rockets.

        But in the end all 3 engines work by the same basic principle: air comes through the front, fuel is added, hot air comes out the back. No air, no flame, the engine stops.

        The plans to use a scramjet to get to a highe enough orbit or even leave the planet, involve getting enough speed while still having enough air for the scramjet, or as boosters in addition to the normal rocket engines, or both.
    • by pipingguy (566974) *
      Eff that, I'm more worried about what kind of impact this new technology might possibly have on global climate change.
  • From TFA: "Australia's Defence Science and Technology Organisation (DSTO) said it was believed to be the first time a scramjet had been ignited within the Earth's atmosphere."

    http://en.wikipedia.org/wiki/Hyper-X [wikipedia.org]

    Is there something I'm just not getting here?
  • Holy cow, this thing can achieve Earth orbit! So why focus just on the Sydney-London thing (or to use that ol' "New Orient Express" analogy, New York-Honk Kong) instead of cheap space travel?
    • by Rei (128717) on Saturday June 16, 2007 @01:51AM (#19529503) Homepage
      Holy cow, no it can't! Not only isn't it going nearly fast enough, but the vast majority of that delta-V came from a conventional rocket. The scramjet experiment only operated for 14 seconds [theage.com.au].

      This is an experiment. Scramjets are still in the "data-gathering" phase, not the "let's make a realistic engine" phase, nor the "let's make a scramjet-powered craft" phase.
      • Re: (Score:3, Informative)

        by Lisandro (799651)
        Holy cow, no it can't! Not only isn't it going nearly fast enough, but the vast majority of that delta-V came from a conventional rocket.

        Not only that, scramjets need an additional propulsion system in order to reach working speeds. Usually, yes, conventional rockets [wikipedia.org] are used. This is one of the major drawbacks in these type of designs.
      • I am sure the skunk works at CIA/Boeing have all the data/results/secrets already.

        Hell, they made the SR71 back in the old days, imagine what they have NOW!!!

        They wont say ever!!! Stupid top secret morons, showing it off will not hamper anything. I bet Boeing just wants to make another $500billion to $1500 billion selling conventional aircraft for
        the next 25 years, then they will bring online the new models later.

        Good article at http://www.americanantigravity.com/documents/NASA- TM-2006-214547.pdf [americanantigravity.com]

        "NASA Memo
        • Re: (Score:2, Informative)

          by deopmix (965178)
          I really do hate to nitpick, but the skunk-works are Lockheed Martin, not Boeing.
        • Re: (Score:2, Insightful)

          by Keys1337 (1002612)
          I'm sure they could develope some insane passenger aircraft, but they need to make money not bleed it. If I came up with a proposal to build basically the concord on steroids I don't think people would buy it. I'd try to sell them more cost effective and reliable planes since that's what they are buying.
        • by dbIII (701233)

          I am sure the skunk works at CIA/Boeing have all the data/results/secrets already.

          That relies on the yet unproven assumption that they would be competant enough to find their arse if allowed the use of both elbows. Conspiracy theories that rely on unseen internal perfection of groups that make obvious public mistakes are fatally flawed.

          • by dosquatch (924618)

            That relies on the yet unproven assumption that they would be competant enough to find their arse if allowed the use of both elbows.

            There's something to the conspiracy theories here. The engineers and scientists in other countries are just as capable and clever as our own, yet no other country has managed to do stealth? It's those alien spacecraft from Roswell, I'm tellin' ya...

            • by Nyeerrmm (940927)
              I'd imagine that has more to do with military budget more than anything else. Most countries probably know basically how it works (RAM, proper geometry), but they don't have the money available for the military to develop it fully, since the basic concepts are only a small part of the picture, and I'm sure all that RAM, and the design time to match aerodynamic needs with low visibility geometry probably takes a lot of time, money, and experience (we've been doing it for a long time, relatively.)
      • When you say 'most' your saying that the conventional rocket got it to 51% or higher of its speed?
        A Mach 5 conventional rocket? Cool!
      • Re: (Score:3, Interesting)

        by MikShapi (681808)
        You seem to be sharing the common misconception that LEO altitudes and above cannot be reached at low speeds.

        Dude, you can reach an altitude of 330 miles just fine with a perfectly low speed. There's nothing unphysical about it that requires the invocation of holy cows. It is also true that with the lack of a *horizontal* velocity of about mach 30 (at ~100km, you'd need less if you get as far as 330 miles high), you fall back down (well, not back to the same place, you may have traveled halfway around the w
        • Re: (Score:3, Insightful)

          by dbIII (701233)

          Not that it wouldn't be nice if it actually got done after 20 years of R&D.

          Oddly enough I was looking at a scramjet model at around this time in 1987. Subsequent revisions used less fuel and had other advantages - but while it's relatively cheap to do computer modelling and to build a shock tunnel to test these things at mach 8 on the ground it costs a lot to launch a rocket to get the higher speeds. It's not that surprising that it has taken over 20 years on a shoesting budget in a relatively small

        • Actually, at least theoretically a scramjet would continue to accelerate as long as you have air and fuel. You have enough air you have of that ascent (after that you have the speed anyway), and fuel you'd carry anyway. A rocket carries its fuel too.

          That's actually one thing that makes scramjets tempting: the fact that it doesn't cap lower than that orbital velocity, and it can work with rather thin atmosphere too. So if you can go upwards at all with it, and modify the trajectory to have enough air for mor
    • "uses oxygen" oxygen in space O.o?
  • Bzzzt. Wrong! (Score:5, Informative)

    by tritone (189506) on Saturday June 16, 2007 @01:44AM (#19529475) Homepage
    "scramjets are supersonic combustion engines that use oxygen from the atmosphere for fuel"

    Scamjets use oxygen from the atmosphere as an oxydizer unlike traditional rocket engines which need to carry their oxydizer. Scramjets still need to carry fuel.

    No. I am not a rocket scintist.
    • by Teun (17872)
      You are very right.
      And just as curious is the statement that it was the first time a scramjet had been ignited within the Earth's atmosphere, because by design a scramjet doesn't carry it's own Oxygen the atmosphere is the only place it can ignite.
      All together a rather sad summary of a nice engineering feat.
  • I don't know about traveling that fast. If you do it enough the time dilation might make it that my friends and family would die a few seconds sooner (relative to me of course).

    </sarcasm>
  • by thesolo (131008) * <slap@fighttheriaa.org> on Saturday June 16, 2007 @01:54AM (#19529527) Homepage
    This event took place in Australia, and was reported by an Australian paper; therefore, it was correctly reported in the metric altitude of 530 kilometres.

    So why was the summary changed by slashdot editors to the imperial unit?

    Firstly, not everyone who reads this site is American, and secondly, this is an audience of nerds. I think we can handle kilometres! Even the USA's NASA is all metric now.

    The scientists who developed this scramjet used metric, the country it was tested in used metric, the newspaper that reported it used metric, so how about we keep it that way?
    • Re: (Score:2, Insightful)

      by Anonymous Coward
      Don't forget, this was the country that elected George Bush. They're only comfortable with simple things, thinking confuses them.
    • by cheekyboy (598084) on Saturday June 16, 2007 @03:00AM (#19529825) Homepage Journal
      Yeah nerds, learn KM, not Miles.

      No self respecting scientist or nerd would ever use the word MILES in their own documents.

      Slashdot is NOT mainstream, get back to being NERDY!!!
    • Its a American website.

      From my experiences they are very bad at converting anything.
      Timezones, Metric -> Imperial, etc...
    • Re: (Score:3, Funny)

      by Chibi Merrow (226057)

      So why was the summary changed by slashdot editors to the imperial unit?


      Mostly just to piss people like you off.
    • by Heir Of The Mess (939658) on Saturday June 16, 2007 @04:33AM (#19530279) Homepage
      You missed another Americanisation. It's Defence Science and Technology Organisation. Check their website http://www.dsto.defence.gov.au/ [defence.gov.au]. Not everyone uses Americanised spelling.
    • by haraldm (643017)
      Maybe this is the New World Order [ministrymusic.org].

      The SRP (*) trying to dominate everything, and the thoughtlessness of some of their inhabitants, makes me sicker every day. No this is not a troll post or a flamebait, I'm just worried.

      (*) Single Remaining Superpower

  • by caseih (160668) on Saturday June 16, 2007 @01:57AM (#19529545)
    This is very interesting to read as I just finished reading Ben Rich's book "Skunk Works" where he talks about the SR71. When president Reagan announced the administration's intention to build a hypersonic airplane, he just shook his head. It's simply not practical, with or without the scramjet engine. The SR71 flew at 85,000 feet at about Mach 3.2, and reaches skin temperatures of 2000-3000 degrees (F I presume) just from moving through the atmosphere. Accelerating to Mach 10 would burn up or otherwise compromise any current building material, except for the carbon-carbon and ceramic materials used on the space shuttle's heat shield, but aren't practical for airplanes. So what good is this scramjet, at least as far as a hypersonic airplane goes? Seems to me all this talk of Sydney to London in 12 hours is a bit fanciful. So the question is, how exactly will this engine be used to accomplish this? The only way to reach hypersonic speeds without burning up is to make the trajectory sub-orbital so that the aircraft is in the thinnest atmosphere possible when it's firing it's engines to go Mach 10. But of course there's not a lot of oxygen at that altitude. And to really achieve sub-orbital trajectory you need a rocket engine, not any kind of air-breathing engine. So my questions are: Is Ben Rich right that hypersonic travel is essentially impossible? Will the scramjet help with a suborbital trajectory? I understand that igniting the scramjet is a breakthrough. Jet turbines at supersonic velocity have always been problematic.

    Off-topic, Ben Rich says in his book that the codename Aurora that everyone likes to think refers to some hypersonic aircraft, was actually the codename placed on the B-2 project as Lockheed and Northrop were competing for the contract. It's funny to think that to this day, folks still hang onto this and imagine some mythical hypersonic airplane. Which never existed. Or does it?
    • by caseih (160668)
      Ahem. Sydney to London in 2 hours.
      • Re: (Score:3, Informative)

        by richdun (672214)
        Technically speaking, yes, hypersonic travel will always be impossible, barring some super-material able to take the heat. The trick is that once you get out of the atmosphere, a term like "hypersonic" is nonsensical. The speed of sound in a vacuum approaches a theoretical infinity, so to reach it, let alone top it by a factor of 7 or more, would be nonsense (unless, of course, your name is Brannon Braga! *rimshot*)

        Often, though, for simplicity sake, we use terms like "mach 10" to mean mach 10 at sea level
        • Re: (Score:3, Interesting)

          by richdun (672214)
          Er, it's the night for corrections - the speed of sound in a vacuum approaches a theoretical asymptote, not infinity. The speed of sound generally gets lower as the material loses density, higher as the material gains density (think about a wave traveling through a solid block, as opposed to one traveling through water, then one traveling through the air)
        • by mpe (36238)
          Technically speaking, yes, hypersonic travel will always be impossible, barring some super-material able to take the heat. The trick is that once you get out of the atmosphere, a term like "hypersonic" is nonsensical.

          Once you get out of the atmosphere you need a rocket engine to provide any thrust you might need to alter your course. If you want to make quick climb through the atmosphere you need a thrust to weight ratio considerably greater than unity as well as a way to package passengers and cargo whic
    • by Rei (128717) on Saturday June 16, 2007 @02:09AM (#19529623) Homepage
      All of his points are basically correct in the present day. However, the most critical one -- the expense of heat-resistant materials -- may only be temporary. It's hard to say. Carbon fiber was once the "we'd love to use it, but it'd be too expensive except for pricey custom luxury jobs" material for airplanes. Now look at the Dreamliner -- a mass-produced majority-carbon-fiber giant by Boeing, which despite delays, companies have been snapping up.

      I wouldn't rule out the concept of hypersonic travel just because heat resistant materials are expensive today. If the rest of the tech is there and is affordable, and there is sufficient demand... who knows? The airline industry is bloody huge and there is lots of money to be made by faster travel, so it could draw a lot of R&D money if the other tech looks good.

      • Re: (Score:3, Informative)

        by mduell (72367)
        Now look at the Dreamliner -- a mass-produced majority-carbon-fiber giant by Boeing, which despite delays, companies have been snapping up.

        I think you're confusing the Dreamliner with the WhaleJet.... Dreamliner hasn't had any delays.
    • by khallow (566160)

      I think you ignore several things. First, I think regenerative cooling (using the fuel to absorb the excess heat) has progressed since the days of the SR71. So my take is leading edge surfaces will take a higher thermal load. Second, why not fly higher? I understand that thermal heating is still a problem at higher elevations merely because there's less atmosphere to transfer the heat to, but the less atmosphere there is, the less heat that your fuel needs to absorb. Finally, I figure the Shuttle is a demon

      • by mpe (36238)
        Finally, I figure the Shuttle is a demonstration that ceramics and similar materials can be used on an airplane.

        You'd undoubtely want a mechanism to detect a bird strike (or similar) to the leading edge of the wing.
    • by moikka (1085403) on Saturday June 16, 2007 @04:13AM (#19530185)
      This is prime example of technology that has almost purely military applications.
      However since that does not excite public positively, they are instead fooling the public talking about civilian use.
      What might be possible some day is to deliver a bomb from Sydney to London in very short time. Not human passangers.
      The inherent heat problems are about 100 times easier to solve, if you imagine
      the payload is 50kg of plutonium instead of 5000 kg of humans.
      • Re: (Score:3, Interesting)

        by moikka (1085403)
        Also think about their primary selling-point,
        capable of using oxygen from air and not having to carry it,
        is only an advantage over rocket-engines.
        Jet engines already use oxygen from the air.


        In civilian travel there is great need for fuel-efficiency.
        If their biggest problem is excess heat,
        it automatically means they are wasting huge amounts of fuel to create that heat.
        Only military can afford this wasted fuel.


        Also there is a huge problem in take-off and landing from ground.
        Ramjet is not going t
    • by dbIII (701233)
      It is useful because multi-stage rockets that don't need as much propellant to lift the same amount of stuff to the same height and the same speed can carry more stuff. Forget the Buck Rodgers spaceplane the journalist threw in to flesh out the article, it's no more relevant than the little submarines in people's blood that get brought up in nanotech articles.
    • by mpe (36238)
      The only way to reach hypersonic speeds without burning up is to make the trajectory sub-orbital so that the aircraft is in the thinnest atmosphere possible when it's firing it's engines to go Mach 10.

      It still needs to get to that altitude first, flying at a speed which will generate a suitable amount of aerodynamic lift.
  • Sooo...it only goes to 10.

    This one goes to 11!

    Okay, now my funny bone has been buried....

    Kudos to these people. It may have only been for some seconds, but at least they are forging onward, and I salute their work!

    Proving theory is usually no easy task, a working prototype seems to be 3/4 of the battle.

    Seriously, hat's off!!!
  • by eyebits (649032) on Saturday June 16, 2007 @02:52AM (#19529789)
    330 miles is approximately 5 times the minimum altitude for entry into "space." The Kármán line is at an altitude of 62 miles (100 km) which is the boundary that defines where space begins. 75 miles is where atmospheric drag starts to have an effect. This means the craft traveled well into the Thermosphere. People who travel above 50 miles are called astronauts by NASA.
    • Significant atmostpheric drag occurs AT much hiGHer elevaTIonS. To say that it starts to have an effect at 75 miles is nuts.

      tHE International space station constantly looSEs eleVATion dUe to atmostpheric drag, it's usual elevation is around 500 miles. When the space shuttle visits, it usually burns its rockets to push the ISS back to an elevation close to that.

      Just last year the ISS was in a very low orbit becuase solar storms had caused the upper atmosphere to bulge, placing more drag on the station.

      (my k
  • engine reached mach 10, and climbed to an altitude of 330 miles before the apparatus re-entered the Earth's atmosphere.
    Does it bother anyone else that they're using the speed of sound IN THE ATMOSPHERE to measure a speed of a vehicle NOT IN THE ATMOSPHERE? Or is the summary just misleading?
  • by WindBourne (631190) on Saturday June 16, 2007 @04:05AM (#19530155) Journal
    getting these to fly without using a rocket to start it. If we can get it to start from say a mach 2 or better sub sonic mach .9, then this will be feasable for more than just bombs. As it is, the only place that this will be of use is in intercontental bombs (small and cheaper).
  • 2 hours (Score:5, Funny)

    by Anonymous Coward on Saturday June 16, 2007 @04:33AM (#19530277)
    Including airport queues that's only about 5 or 6 hours.
  • 330 miles ? (Score:3, Insightful)

    by Yvanhoe (564877) on Saturday June 16, 2007 @05:00AM (#19530399) Journal
    How is an altitude of 330 miles within earth's atmosphere ?
    • by jkerman (74317)
      Its not. it reached that altitude /before/ returning to the atmosphere. its right in the summary!!
  • by Richard Kirk (535523) on Saturday June 16, 2007 @06:46AM (#19530777)

    Scramjets look good on paper. The thin air coming in is compressed by a series of standing shock waves. Unfortunately, the geometry of these shock waves can easily be upset by small distortions in the engine, which in turn can lead to changes in the stresses with in the engine, which - to cut a long story short - can mean the engine spectacularly demolishes itself when faced with real bits of atmosphere with unpredictable air currents. I found the flight time in...

    http://www.abc.net.au/science/slab/hyshot/default. htm [abc.net.au]

    It may not sound like much, but six seconds is very respectable for a scramjet. Yay!

    There is a lot of touting about how this would get you from London to Sydney in 40 minutes and stuff. I am not sure how true or economical this is, even if scramjets can be made safe. When you are flying fast, you can either take your oxidant with you (as rockets do) or you can scoop it up as you go along. Scooping it up as you go along means taking in air that was initially at rest and getting to move at the speed the engine is currently going. As only 20% of the air is actually the oxygen you want, this is not necessarily an effective thing to do. It becomes most effective when the oxidant (oxygen) is a lot heavier than the reductant (fuel - and hydrogen is particularly light), so scooping it up as you go takes a lot off the take-off weight.

    The other London to Sydney option is to get just beyond the atmosphere using a conventional rocket, then going ballistic and weightless for the main distance, and re-entering and gliding, a lot like the space shuttle. While being weightless is fun, being weightless for 20 minutes makes most people puke, so a large passenger jet might skip the atmosphere and retain a little gravity. A scramjet might be used for this.

    Nevertheless, yay!

    • cooping it up as you go along means taking in air that was initially at rest and getting to move at the speed the engine is currently going.

      One quibble:

      Actually, the whole idea of the scramjet is that you don't boost the air up to the speed the engine is currently going. You burn the fuel in the air as it passes through the engine at supersonic speed. That's the "SC" in Supersonic Combustion Ramjet.

      There are, of course, lots of practical difficulties; you listed some of them.

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