Air-Breathing Rocket Engine Promises Future Space Planes

If you are a certain age, you probably remember the promise of supersonic transports. The Concorde took less than 4 hours to go across the Atlantic, but it stopped flying in 2003 and ended commercial supersonic passenger flights  But back in the 1970s, we thought the Concorde would give way not to older technology, but to newer. After all, man had just walked on the moon and suborbital transports could make the same trip in 30 minutes and — according to Elon Musk — go between any two points on the Earth in an hour or less. A key component to making suborbital flights as common as normal jet travel is a reasonable engine that can carry a plane to the edge of space. That’s where the UK’s Sabre engine comes into play. Part jet and part rocket, the engine uses novel new technology and two different operating modes to power the next generation of spaceplane. The BBC reports that parts of the new engine will undergo a new phase of testing next month.

The company behind the technology, Reaction Engines, Ltd, uses the engine in an air-breathing jet mode until it hits 5.5 times the speed of sound. Then the same engine becomes a rocket and can propel the vehicle at up to 25 times the speed of sound.

The engine has three sections: The front end is a precooler that can take a 1,000C airstream and chill it to -150C almost instantly. The core engine then takes air from the precooler, and forces it back out through relatively conventional rocket nozzles.

Although a company called Boom is trying to revive interest in supersonic jetliners and GE has new engines for the purpose, a commercially viable suborbital transport could obsolete supersonic transport. Reaction Engines is a private venture, backed by BAE, Rolls Royce, and Boeing. It also has research and development help from the British government. The history behind supersonic flight is interesting and perhaps will extend to cover the X-59, soon.

112 thoughts on “Air-Breathing Rocket Engine Promises Future Space Planes

  1. “Novel new engine”.

    Al, I don’t play grammar nazi very often, but this one causes so much disruption in my intake precooler that I just stumble through the rest of the article :)

    1. Novel carries an extra shade of meaning in general, and specifically in this case it can be viewed as necessary. The approach is not only new, but it is novel in that it is different/strange an entirely unprecedented.

      Example: The Beatles Second Album was a new album. Sgt. Peppers’ Lonely Hearts Club band was a NOVEL new album.

      See?

  2. So to drop the compressed 1,000C airstream to -150C, I’m guessing that the fuel used is a liquid that has a boiling point below -150C. So will the fuel be Liquid Hydrogen (with a boiling point of −252.87 °C) or some thing else ?

      1. Another reason is higher surface area for re-entry. The Shuttle came down like a flying brick, the Skylon floats like a feather because it’s mostly empty, and it doesn’t require special fragile insulating tiles.

    1. For me the most interesting part is how they are dealing with the water vapour, and carbon dioxide, in the air. That kind of temperature drop will condense all water and instantly form ice. But maybe there is an easy way to deal with ice/dry ice build up.

  3. The Sabre engine is very clever, but also quite complex which might be it’s Achilles heel. I wonder if it is now too late, because in the meantime processing power has improved to the point we can land rockets backwards. So Sabre is now competing with reusable rockets, not disposable ones, which changes the economics significantly.

    1. There’s a difference between re-using a huge rocket engine a dozen or so times and repeatedly firing up an engine daily to provide hundreds of millions of flight hours for passengers

    2. it doesn’t have to carry oxidizer with it for a big portion of the trip, so it has a significant advantage in terms of the rocket equation, which means a lot less fuel needs to be carried as well.

      1. Yes but the cost of the fuel and oxidiser is not necessarily the limiting factor.
        This enables SSTO but it may end up being uneconomical compared to a reusable conventional 1st stage all the same.

        1. The weight of the oxidizer is the limiting factor, not the cost of it.

          A variation of the Sabre working principle can actually collect more liquid oxygen than it burns, so it can fill its oxidizer tanks along the way, which means it starts off with less mass and lifts a whole bunch more cargo to orbit.

          Re-usable rockets like SpaceX are doing are fighting against the rocket equation, which dictates that the more of the rocket you want to return, the less stuff you can lift. They’re already throwing away 2/3 of the lifting capacity by making the first stage return, which kinda makes the whole thing pointless because if they just made a single-use rocket with the same diminished lifting capacity, it would cost much less than 1/3 the price because it would have a proportionally better payload fraction. Elon Musk is just hoodwinking everyone by playing the powered return gimmick – there’s no real advantage.

          1. There is a key item in deciding if it is an advantage or not, you need to weigh the cost of fuel vs cost of rocket. If cost of extra fuel to lift return fuel is cheaper than building a new rocket, then the reusable rocket is a better option.

            Reusable also could give some reassurance that it is fully tested, most rockets flights are always a “maiden” flight… many aircraft pilots would have issues with first flight on an air frame.

          2. “They’re already throwing away 2/3 of the lifting capacity by making the first stage return, which kinda makes the whole thing pointless because if they just made a single-use rocket with the same diminished lifting capacity, it would cost much less than 1/3 the price because it would have a proportionally better payload fraction.”

            Except for the part where every factual statement there is wrong. Barge landing reduces payload capability by about 1/3 (5.5 t vs. 8.3 t to GTO is officially quoted, and 15.3 t vs 22.8 t to LEO is unofficially estimated). The cost of a rocket launch is nowhere near linearly proportional to liftoff mass. Range costs barely change, and only then if your rocket fits into a smaller launch complex. You still have the same testing process, and while the equipment is cheaper for a smaller rocket, it’s nearly the same amount of labor, and labor is the recurring cost that dominates in the long run. Licensing, insurance, and such still require the same amount of paperwork. The real cost reductions are in manufacturing, tooling, and real estate. And payload fraction gets worse for smaller rockets thanks to aerodynamics and square-cube law sort of things.

            You don’t have to take my word for that, either. Just look at the cost of small launchers. While Electron is the only one flying so far (ignoring Pegasus, which is so overpriced as to be commercially irrelevant), its follow-on competitors are all claiming fairly similar costs, and Electron costs 10% as much as a Falcon 9 for 1% of the payload.

          3. @Ostracus

            the problem is “MORE space launches” will likely just lead to more space junk causing a runaway collision event and the end of all space flight for over a 100 years. that’s the joke here all these “space companies” care about is how much money they can make before it all goes belly up. and just like the fissile fuel, fast food and more don’t care about the damage they cause as long as they get rich.

          4. >”Except for the part where every factual statement there is wrong.”

            Except where it’s right. The first stage of the rocket departs early at mach 6 instead of mach 10 to have enough fuel to brake and do a powered landing. Do the math – the loss of speed results in 2/3 less kinetic energy imparted to the upper stages, which then have to compensate for by carrying more fuel and less cargo.

            And this is recycling just the first stage. If you want to make it comparable to the Skylon, you should also return the second and third stages, which would suffer the same penalty – 2/3 of the lifting capacity to orbit lost.

            >”Not treating everything as disposable is an advantage in itself. ”

            SpaceX’s rockets are “re-usable”, in reality they’re simply recycleable. They have to rebuild them each time. The rocket is actually scrap, because the structure is so flimsy that it would undergo stress failure if they tried to re-fill the tanks a second time and launch. If they were built with any safety and stress margin, they’d be too heavy to launch. This is in complete contrast to a system like Skylon which experiences much less stress at launch and can actually fly the same vehicle thousands of times.

          5. This is a reply to Luke’s later remark: “The rocket is actually scrap, because the structure is so flimsy that it would undergo stress failure if they tried to re-fill the tanks a second time and launch.” Luke, wtf. Have you even looked at a single SpaceX rocket? Do they cover the rebuilt rockets with soot to make them look used? Do they replace the interior tanks and somehow leave the thin outer shell intact? As for 2/3rds… so SpaceX just fakes the launch ratings? 8300 kg to GTO expendable, 5500 kg to GTO reusable. That’s pretty obviously 1/3 of the expendable payload rating wasted to enable reuse. You are talking out of your ass so much I can’t even…

          6. > Luke, wtf. Have you even looked at a single SpaceX rocket?

            No, that’s how rockets are built: the reason why they’re filled with fuel only minutes prior to launch is because the frame will sag under the weight. They are operating on the very edge of structural failure to shave every possible pound off – they are not built with 500% safety margins for failure – they’re built with 5% margins, and if you have a big enough gust of wind while the rocket is standing on the platform, it folds over.

            Think about it this way: steel has a fatigue limit of 50% of its nominal yield strength, assuming symmetric loading (compression and tension). Any weld bead reduces that limit again to about half, so in order to not have a failure from repeated loading (vibrations/shocks etc.), you have to assume the steel is about four times weaker than what it says on the label. Otherwise you have to assume it will only last for some number of cycles that is hard to predict. Then you apply safety margins for unexpected loads, where the standards may require you to design for 1/5th the load. You may have to design with 20 times more material than absolutely necessary for the intended load, and with rockets that just won’t fly – literally. So they don’t.

            And, the rockets aren’t made of steel but aluminum, which hasn’t got a fatigue limit. Microscopic cracks will grow regardless – it’s just a matter of time. In airplanes, you have a certain number of flight hours and then you have to replace frame parts because you can’t engineer them with infinite design life. In rockets, this number is measured in minutes, not hours, because the vibrations and stresses are so much greater.

            That’s why SpaceX can’t actually re-use any of its rockets. They can only take the engine off, refurbish it, and then rebuild the rest from scratch. At best they can use the old rocket as scrap for making the metal. A vehicle like the Skylon however can genuinely fly the same thing hundreds or thousands of times.

          7. > As for 2/3rds… so SpaceX just fakes the launch ratings?

            No. SpaceX just isn’t re-using 2/3rds of the rocket yet. In fact, they’re only re-using the engine of the first stage.

            If they were recovering the entire thing, they could barely launch anything to orbit.

    3. You could land a rocket backwards with an 8086. It’s not about processing power, it’s the 100s to 1000s of little tweaks you have to do to fine tune all the feedback loops so everything is as close to pwrfect as possible and more importantly sinking all that money in the research that needs to be done to get to that point.
      It took SpaceX several years and they had this as one of the main design objectives for the rocket(s).

      Where processing power changed things significantly is simulation and CAD.
      You can do optimalization for for fuel and oxidiser flow for an engine in comfort of your home using FEM on “junk” workstation PC that you buy as surplus for under $200, 30 years ago this would have been impossible on the best new PC money could buy.
      Also we can have stuff machined or 3D printed from Inconel and other exotic materials without ever needing to step outside of your house. Again, would’ve been impossible 30 years ago.

        1. They had power stations way back before microprocessors was invented, so yes it can certainly be done with a ZX80. The question is how far back you want to go.

          https://www.powermag.com/history-of-power-the-evolution-of-the-electric-generation-industry/
          >By 1877—as the streets of many cities across the world were being lit up by arc lighting (but not ordinary rooms because arc lights were still blindingly bright)—Ohio-based Charles F. Brush had developed and begun selling the most reliable dynamo design to that point, and a host of forward thinkers were actively exploring the promise of large-scale electricity distribution.

      1. Sure you could do simulations on a decent PC nowadays, but also consider of the costs to isolate and secure the secrets on said PC and keep the competition in the dark, despite all the various exploits, including human ones to obtain the intellectual property.

        The regulatory environment has changed too… If gasoline was invented today, it would likely never be accepted for public consumption… too dangerous… too polluting… non-renewable… name your flavour to handcuff innovation.

        1. It’d be difficult to imagine a world so comfortably developed to start with the over-regulation we may be seeing now (debatable, really) without at least one kind of cheap energy to power it. If the world has such an energy source, and it doesn’t have gasoline… then it probably doesn’t need it.

    1. The idea has been around for a while. Because at least some of the same people have been working on the concept since the 1980s with HOTOL.I dunno when that show was made, but it very well could have been derived from HOTOL.

      1. It was a TV movie in 1983. The plot was a high altitude near suborbital aircraft had a glitch that kept its engines at full throttle too long so it ended up in low orbit at a height where it couldn’t stay up for too long due to drag but high enough that heating coming back down would destroy it. In the end they used a space shuttle as a flying heat shield ahead of the plane until it could slow down into thicker air.

        I very much doubt that would work to protect another plane coming down close above it.

  4. I’d rather have a transporter a la Star Trek. Much better investment than another noisy gas-guzzling engine. If you want to speed up transport, then please make it (almost) instantaneous and a real usable commodity for all. Anything else is candy for the rich.

    1. You’re not worried that the transporter works by killing the person, then assembling a duplicate somewhere else?

      I think that stepping into a transporter would be a big mistake. I also think that people willing to do so would have such a huge advantage over everyone else that, pretty quickly, everyone would choose to do it.

      Finally, I think the technology is inherently impossible, so we probably don’t need to worry about it (and there’s no point in hoping for it).

        1. It’s not just the book “Spock Must Die”. In an 4th season episode of Star Trek: Enterprise we meet the inventor of the transporter and he brings up the issue (so it’s part of canon). He dismisses the notion that the transported person is killed, but he doesn’t justify his belief.

          1. They get around the issue in the star trek universe by claiming that the person isn’t re-built but merely reconstituted – they’re transformed into some mystical “energy” which flows along another dimension or something, and then turns back to matter — so a continuum is maintained.

            For the transporter to work at all, that would be the only way to do it, because representing the amount of information in a single person would at minimum require the mass-energy of that person. To transmit it as data would take so much power that the beam would destroy the Enterprise, or anything else they were aiming for. The mass-energy of a person would create an explosion equal to 60 Tsar Bombas, with enough energy to make a crater the size of France.

            The usual argument is to use compression, but the compression ratio should have to be billions to one which is not plausible. Instead, you get a loss of precision and inevitable generation loss in the process – the person would turn out like a re-compressed JPEG by going through the transporter multiple times, if they survive even the first.

          2. This just goes to show just how little we actually know about the mind-body relationship. Worse yet, I’m not sure we could effectively test the question of whether the person dematerialized is the same person as the one materialized. Tweedle-Dee Tweedle-Dum, if you can’t tell the difference, there is no difference according to many people but we don’t actually know this.

          3. Forget about the mind-body issue.

            Just simple chemical reactions happening in your body would be disturbed to a disturbing degree by a “replicator” attempting to reconstruct you according to some generic instructions that are averaged out to some spatial resolution.

            If two atoms end up 10 nanometers from where they they originally were, your DNA can do the splits. If this happens billions of times over your body, you get massive organ failure pretty much right as you exit the transporter. Since chemical bonds rely on things like the spin-state of individual electrons (Pauli exclusion principle), if you don’t code for each individual atom and sub-atomic particle, you will end up with proteins that spontaneously decompose right after they’re made by the replicator. This means there is an absolutely mind-boggling amount of information you have to transmit, using some physical carrier like a beam of light or a radio wave, and since each bit of information requires a minimum amount of energy that means your information channel turns into a weapon.

          4. Hence why, the cop-out for the Start Trek replicator is that they don’t encode the information in the person’s body onto a carrier and then decode it in a replicator, but instead they transmogrify your body to some sci-fi woo stuff that is able to cross space and time over another dimension or field. It’s kinda like how a sound wave can enter a piece of metal – a different medium – and come out the other end faster than how it could transmit through air – it’s the same energy going in and out.

            This is then used as a plot device, because this “special energy” has the ability to be mirrored and duplicated as it crosses the barrier to normal space-time, so you end up with evil Spock and evil Kirk materializing somewhere as a result of a “transporter accident” because of a “nebular storm” etc.

          5. Poor Star Trek. All Gene Roddenberry wanted was a way to get off the ship and into the story quickly, and now we’re stuck with metaphysical issues and interdimensional technobabble.

          6. Yea!! Transporters…”What a bunch of hippy dippy phony baloney.” (sorry Lego Movie) It’s an excellent *TV* special effect that helps both the budget and story telling for the Star Trek series. It’s fiction. It’s not real. It’s all a lie. (Thoughts of the film Galaxy Quest come to mind. :-) ) …I could say the same thing about super-luminal travel. We need to get our heads unstuck from the television and embrace reality. Space-X and NASA are infinitely more significant than Star Trek no matter how much we love it. Space-X is to Star Trek as married sex making the next generation is to …(let the reader fill in the blank here) ….when I said “next generation” I mean real children not old blokes like Patrick Stewart or Brent Spiner, bless their souls. :-)

          7. > Sounds like orange juice from concentrate. And we all know how that tastes. ;-)

            Incidentally, Sherry was invented as a result of efforts to transport wine more cheaply. They let the water evaporate and added more ethanol to make a sort of wine concentrate, and the intention was to add the water back in at the port of destination, but then they tasted the result and went “Nah, this is better.”

          8. Nah, that rabbit/rat carcass thing was for Guinness beer, where they supposedly found a dead rat at the bottom of the vat, and decided to throw one in for the next batch because it tasted good.

            Kinda like Worcestershire sauce: it’s fish left to rot in a jar, with spices and salt.

          9. >Poor Star Trek. All Gene Roddenberry wanted was a way to get off the ship and into the story quickly, and now we’re stuck with metaphysical issues

            That’s pretty much the problem of Sci-Fi, or at least the “soft” variety of it. Most of it is just pushing some fantasy (or social agenda) and dressing it up as being “scientific” to throw a lampshade over an obvious contradiction.

            That’s why most Sci-Fi is bad, and what isn’t bad is so over-thought that it’s boring.

      1. I think it would be more likely to work if we could quickly freeze the passenger, slice them up into thousands of thin slices, ship the slices up using a railgun and assemble the slices at the destination with “glue” and then thaw them out. That would be more likely to work than any “teleporter” but I wouldn’t want to try either. Better to stick with rockets, space planes, and maybe some day space elevators, but not teleporters. I agree with McCoy on this one. Teleporters are best avoided when possible.

        1. Yeah, but those are examples of bad sci-fi.

          If you had a perfectly efficient carrier, transmitting the amount of information (mass-energy) of an average 75 kg human being would take about 6742.5 Petajoules of energy. Even if you “blurred” it out a little and took only one billionth of the information into account, you would still have to deal with 67,425 MJ (18,729.2 kWh) which is the energy equivalent of 16.1 metric tons of TNT, or the nearly the year-round energy consumption of the average American household.

          And that’s assuming the energy consumption per bit of information is the smallest possible quantity (Planck energy). In practice, you can’t detect that little, so you need billions of times more energy per bit to be able to make it out over any distance. That means the power of the beam that is carrying the information would best the largest nuclear weapons ever built when it hits the receiver.

          1. >A trope where a tool is a weapon used by those “peaceful” humans.

            If only. In practice it would be like Project Plowshare, but instead of using small kiloton charges, they’d use a dozen Tsar Bombas.

            Completely unmanageable.

      2. Well, another theory of teleportation was a dimensional shift (my words for it) or portal.
        But instead of disassembling a person (or object), you mathematically increased the odds that they are at the destination and less likely to be at their original position.
        But later episodes seemed to go with the matter transport and re-assembly, (more wiggle room for plot development?)

        1. Kirk explained how the transporter works to “Abraham Lincoln”. He said the molecules are converted to energy, beamed into the chamber, and then reassembled. Kirk wouldn’t lie about a thing like that.

  5. …the practical way…
    Convert an A-380 to a carrier-aircraft , using high-strength struts and cables . Install eight GE-90 150k+lbs.thrust engines. Install cryogenic tankage in fuselage , with remote-pilot in cockpit . Lift to altitude , use parabolic trajectory to “throw” spaceplane upwards . Begin “zoom-climb” , once clear of carrier plane . This launch architecture increases the maximum payload by some 200k.lbs . It also greatly decreases the minimum runway length required , thus multiplying the number of potential launch sites . This makes for easier launching , depending upon practical considerations .
    Alright , heavy cargo , done dirt-cheap !
    D.H.

    1. “This launch architecture increases the maximum payload by some 200k.lbs”
      Kilo, and pounds used together.
      I found that a bit confusing.
      So, you are saying it increases payload by 200 tons, which beats Saturn V all to heck!
      Hey, DHL, Fedex, UPS, Amazon are you listening (reading this)?
      B^)
      (Hmmmm. if Fedex, UPS, Amazon, and DHL where all bought up by an oil rich entity in the Middle East, they could call their new conglomerate “FUAD”!)
      B^)

    1. That’s the bit most people fail to recognize about internal combustion engines. They’re more accurately hot nitrogen engines. Most of the work is done by the 70% nitrogen content of the air being heated and expanded by the fuel burning at high temperature with the 20% of air that’s oxygen.

      1. That’s why water injection in engines works. You can spray an amount of liquid water into the intake, and it expands more than the nitrogen, due to the phase change from liquid to gas. There are some esoteric engine designs that squirt every third cycle with water instead of fuel to run a steam cycle instead of combustion.

    2. Not really. The engine doesn’t liquefy the nitrogen, which liquefies at -193 C. The liquid oxygen is passed through the rocket, while the nitrogen passes through the periphery burners where the pressure and temperature isn’t high enough to form significant amounts of NOx – any more than in regular jet engines.

  6. > that can carry a plane to the edge of space.

    And what Elon Mask says about protection from radiation? Are they going to put each passenger in the space suit or cover the plane with a lead shield? I thing the whole thing won’t go that far. Elon will just collect investors money, get some pot and start thinking about the next shit to cuthch the suckers on.

    1. At the edge of the atmosphere (Or LEO for that matter) they are still well within the inner Van Allen belt and thus protected by earths magnetic field. Yes, background radiation levels at that altitude are a little higher because there is no atmosphere to provide additional shielding, but it’s still nowhere near dangerous levels. And outside the Van Allen belt passengers would also be fine for short trips. It’s only if you stay IN the belts for days to weeks or outside them for extended time (months to years) that you start reaching potentially damaging levels of radiation. And then all of that mostly depends on the activity of the sun.

    2. There may be future plans for a manned version but for now Skylon is only designed for cargo. Also as ThisGuy says it has nothing to do with Musk, Reaction Engines Ltd. is a British company.

  7. Looking up in the night sky, oh a meteor! No that’s another Meteor in space. Briton’s doomed novel passenger jet. These super complicated things just seem like so many Popular Science lurid color covers from the 1930’s. Time will tell.

    1. What are you on about? The SABER engine has been in development in some form or another since the 1980’s; the company Rocket Lab was only established in 2006. If anyone is ripping anyone off, it’s the other way round.

  8. The proof of the pudding is in the eating. If this engine and skylon work well for launching satellites into orbit and super-fast transportation between continents they will keep doing it. If not then we will be left with rockets for both satellites and those crazy intercontinental flights with BFRs (absolutely crazy if you ask me) I don’t see how that could compete with a working skylon especially if the skylon could take off and land at a regular international airport rather than some special isolated space port half an hour out from the city.

    1. Yeah that BFR concept for terrestrial passengers flights makes me laugh. I can’t see any nation allowing someone to aim a ballistic rocket full of people at one of their cities.

        1. Oh fo sure, I may laugh at some of his concepts and suggested timescales but on the whole I think he has done a lot of great things that have advanced certain industries that were in danger of stagnating.

        2. Funny how that “wide array of different ideas” is just re-hashing the concepts presented in the 1960’s by The Jetsons. It’s almost like he’s playing on the hopes and dreams and promises presented to the baby boomer generation, who never got their flying cars and space rockets like they imagined it, and are now willing to throw cash at anyone who is promising to make those already debunked ideas a reality.

          1. Some of those “baby boomers” have shatner-loads of money to invest with. Seems to be a good idea to play into their hands. Besides he’s got a vast army of super-loyal minions to drive the tehnology forward. It’s kind of a perfect storm if you ask me and pretty darn interesting to watch….constructive too for the most part. :-)

          2. Debunked ideas? Back in the ’50s sci-fi movies like Destination Moon showed rockets landing on their tails. After Apollo and the shuttle, that idea was “debunked”; people decided that rockets landing on their tails was preposterous, and Hollywood stopped doing it that way. Now, Musk is successfully – and stunningly – landing rockets on their tails.

            He’s not doing the impossible. He’s doing the preposterous! And he’s doing it beautifully.

          3. >Now, Musk is successfully – and stunningly – landing rockets on their tails.

            The question was never whether it was possible – it is – the question is whether it makes any economical or practical sense. The reason why we don’t have flying cars is because it uses too much energy and is far too hazardous to implement. The reason why tail-landing rockets aren’t sensible is because it doesn’t actually save much money and it loses most of the payload capacity of the rocket, requiring unnecessarily large and expensive rockets.

            Elon Musk’s returning rockets are like a 17th century dream of having steam-powered horses drawing carriages – because the person dreaming it up couldn’t imagine a piston engine driving the wheels directly.

          4. Well if that’s the case, then he won’t be able to compete against expendables or other landing strategies and the market will work it out (as long as the government doesn’t distort things with subsidies).

  9. So there will be this plane that can theoretically reach every point on earth in an hour. It will only ever visit 5 places on the globe, because it’s a rocket and most metropolitan areas do not want a travel-spaceport on their turf, most non-metropolitan areas don’t want to fund a travel-spaceport, and most other areas don’t need a travel-spaceport. To board it you’ll have to subject yourself to TSA-with-probes and fork over a month’s pay. After 20 years of service to the rich and/or probe-affine, one of the planes will suffer from [low tech problem in high tech system] and crash spectacularly. Then it will go (and have gone) the way of the Concorde..

    1. prophesy :-) yes, I agree. I could say similar things about Space-X’s plans of intercontinental rocket flight. All this traveling about at wicked speeds seems stupid. It seems to me that realistic tele-existance would make more sense. ….bit of lag >100ms all the way around the Earth but that is livable. Best for leaders and officials to stay home, close to the thing they are managing. I’d even go as far as insisting that US congressmen/senators stay in their office in the district of their constituents rather than gathering in that cest-pool we call Washington D.C. and “meet” at congress virtually. Perhaps they would actually stay loyal to the people who put them in office. Yea, we don’t really need all that wicked fast flying about. Regular 600+ mph airline flights are doing the job reliably and efficiently already.

      1. >.bit of lag >100ms all the way around the Earth but that is livable.

        If only. Tried to have an interview with a guy in Brazil – the Skype call bro…. e… d… pa…. only one sentence… c…. a …. p….

        1. I agree the lag would be initially painful especially for gamers but I bet people could get used to it. Still, doing something and waiting for the results would be a bit tedious with touchy actions. It would be easy to simulate though and learn how people can adapt. I even remember there being a lag inducing diagnostic mode in the linux networking stack. I have used it in the past. Removing computer access from the kids when they refuse to clean up the room can lead to rebellion. Adding 100ms or 500ms or 1000ms of latency to their internet connections can be even more effective. :-) (evil networking Dad mode activated :-) )

          1. I’m sorry, I just had a brain fart. I was thinking along the line of digging holes on the moon and such (different blog). A lot of what you mentioned is still relevant though. :-) I still be they could do it. If Captain Hayes can land an airliner with no hydrolics and Scully can land a plane on the Hudson, I be there’s someone who could control an excavator on the moon. :-)

  10. Is it clean? Combusts air. Air contains nitrogen. Nitrogen and oxygen react and produce nitrogen oxides (NOx). NOx is emitted in the upper atmosphere where delicate chemistry takes place.

    1. Depends on pressure and temperature. Nitrogen combustion is endothermic – it consumes energy rather than releasing it – so it only happens as a side reaction. The point of the SABRE engine is to cool the incoming air low enough to condense oxygen into liquid, which is then passed through the rocket, while the rest of the gasses go around the engine through the bypass burner that combusts the excess liquid hydrogen that is used to cool the intake. The bypass burner operates at a lower pressure, which isn’t sufficient to combust nitrogen, so very little NOx should be generated by the engine.

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