Afternoon InquisitionScience

AI: The Falcon HTV-2 and All That That Implies

Today the US military lost contact after 36 minutes with rocket-launched carbon fibre spaceplane designed to fly at 13,000mph.

The Falcon HTV-2, launched aboard a rocket, is the fastest plane ever built, and it disappeared during a hypersonic test flight over the Pacific. After separating from the rocket at the edge of space and beginning its return to Earth, the aircraft “went silent during the gliding stage of the test flight, when it was due to perform a serious of manoeuvres as it hurtled through the atmosphere”.

Even though the project experienced some trouble today, I had to use this AI to talk about it, because it’s just so effing cool. The aircraft had been expected to reach a top speed of Mach 20, or 13,000 mph. That would get you from New York to Los Angeles in 12 minutes!!

Oh, and in case you’re wondering, the aircract can withstand temperatures of 2000C caused by the ultrafast flow of air around it.

Only two Falcon prototypes were built, and today’s test was the last chance to prove success before the project is considered for closure.

But what are your thoughts on projects of this type? Speak up engineers? What of costs versus potential benefits? What of costs of development versus potential profit of success? What of peripheral technologies? And what of adventure and human achievement? Are these endeavors worth undertaking, or are there other pressing issues in the world toward which we should apply our brain power and resources?

Sam Ogden

Sam Ogden is a writer, beach bum, and songwriter living in Houston, Texas, but he may be found scratching himself at many points across the globe. Follow him on Twitter @SamOgden

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  1. I may be wrong but I thought the high temperatures were caused by the compression of air in front of the object rather than friction on the surface of the object.
    It’s a small point but I remember believing that it was friction once too before being disabused of the belief.
    As far as the project; I think, at least at this stage, it is basically a carbon-fiber paper airplane.

    1. It’s a small point but I remember believing that it was friction once too before being disabused of the belief.

      1) Heating the air up to 2000C requires energy, and that energy had to come from somewhere. Any process that coverts work or kinetic energy into heat is doing an excellent job of imitating friction. So, if it leaves a trail of hot air behind it, the glider is going to slow down rather quickly, and I don’t see how the “supersonic drag” or whatever could not be considered friction.

      1. There is both kinetic heating (molecules bumping into the aircraft, sometimes called skin friction) and adiabatic compression heating. They are very different processes, so a lot of detail and comprehension is lost if drag, kinetic heating, and adiabatic compression heating are all conflated together as just “friction.”

        More particularly, the kinetic heating / skin friction acts as you described, robbing kinetic energy from the aircraft and turning it permanently into heat energy. But that’s not so good a description of adiabatic compression heating – Following the gas laws you grew to love in high-school chemistry, the temperature of the air flow soars as it is compressed ahead of the aircraft, but then it _cools back down_ as it decompresses behind the aircraft.

        So, if the airflow is perfectly adiabatic there is no “trail of hot air behind [the aircraft]” because the decompression cooling exactly reverses the compression heating. Clearly this process – particularly in its reversibility – is very different from friction. It’s a gas-law effect, not a rubbing-and-bumping contact effect.

        Of course in the real world the compression heating is “mostly adiabatic” rather than “perfectly adiabatic.” Just a bit of heat radiates or conducts out of a parcel of hot suddenly-compressed air in the brief moment before it rapidly decompresses and cools back down, and that will steadily bring up the temperature of the aircraft until a steady state is reached. For a hypersonic airflow, “mostly adiabatic” is maybe “kinda adiabatic” and the steady state is really friggin’ hot.

        Same story for meteors – You always read that they’re heated by friction with the atmosphere, but at meteor speeds, the compression effect is way-the-hell dominant over skin friction.

        So that’s why I’ll lobby for keeping a distinction between skin-friction kinetic heating vs. compression heating, even though the non-ideal part of compression heating is indeed *sorta* like friction in that, ultimately, it irreversibly steals some kinetic energy and converts it to heat. “Friction” should imply direct rubbing-and-bumping.

    2. It might be that the front of an object traveling very fast in the atmosphere gets faster and earlier hotter than the rest because the air molecules have a tangential trajectory on a lot of area compared with the rest of the frame. So if an ‘air molecule’ hits something very fast, the amount of energy released as heat is increased by the angle from 0° to 90°.
      Applying the simple fact that a lot of energy in the form of heat is released by the ‘air molecules’ hitting the frame, you get a cumulative effect that increases the temperature on a superficial layer following the contour of the frame, a lot of the heat is absorbed by the frame, even more if it is highly heat conductive.
      Think the real process is complex and a lot of variable play a part in this phenomena, including the roughness of the frame.
      Problem with phenomena increasing the temperature of the frame at supersonic speed was worked around early on by building the airframe of planes, that could reach speeds posing a danger, with loose tolerances which allows for the expansion of the frame without damage.

      But regarding the story. (mechanical engineer here)
      Scientifically this might yield some useful results, as pointed out, in communications technology. And those might, i say, might prove to be of use; we most likely never know as these things go.

      I see no extensive civil applications due to couple of practical concerns:
      – energy cost for such decadent objects is through the roof, the more speed the more energy needs.
      – the sources of that energy might be environmentally detrimental, and atmospheric catastrophic if mass transit is pursued that way.
      – controlling an object at those speeds it is still at best unreliable
      – it can be another Concorde, high cost, benefits society little beside being a noisy pest, which only the rich can afford
      – other, more efficient means can be pursued, with technology we already have (MagLev) if we are thinking about transport
      – in general technology that is used only to benefit few is a wasteful thing to spend money on. For this project i would say that cost vs. foreseeable benefits are not worth it, but ofc the unforeseeable benefits are those that really make up for it.

      I am not against these kind of activities, just think that those money could be spend much wiser on actually implementing some of the technologies we have developed in the past activities of that sort, while cutting down in general on military focus research, which this definitely is.

  2. Re: “…are there other pressing issues in the world toward which we should apply our brain power and resources?”

    Yes, there are, but we have enough brain power and resources to address any issue we can dream up, if we choose to. Too bad we don’t choose to.

  3. If you want to keep the design as light, simple, and cheap as possible, make it a ballistic missile without wings or any way of gliding. The whole gliding business bloats the design, like the space shuttle. The weight is increased greatly by the extra heat shielding for the extra surface area and the extra structure necessary to support the wings. That extra weight makes the launches more expensive.

    1. I suppose the gliding bit is not so useful when re-entering the atmosphere, but rather an important part of the vehicle’s mode of movement once it gets into the atmosphere and needs to travel some distance to reach a destination. Wings allow you to do that, missiles just keep falling (or require fuel to counter the falling part).

  4. I’m interested in Skepchick’s take on the many reports of secret planes which supposedly can reach speeds of up to Mach 20. Is this nonsense or does secret technology undoubtedly exist? If true, why would so much money be spent on this program – and why is this plane proving so difficult to successfully fly if already much more advanced technology does secretly exist?

  5. I think materials and technologies developed to overcome the problems this particular plane faces, will eventually find other applications.

    Assume for example, that they figure out what caused the communication problem (assuming it’s not just an ordinary component malfunction) and several years down the line, that technology might potentially be used to make your iPhone’s network connection more reliable. Etc…

    There are plenty of pressing problems that need to be addressed (primarily global warming and carbon emmisions), but it’s the often crazy projects like these that allow scientists and engineers to push the boundaries of what’s technically possible, to the point where a wacky idea in another area of research suddenly becomes feasible.

  6. If they make a verticle take off model, I want one. I can keep it in my back garden here in the united queendom and use it to visit my freinds in Melbourne for lunch.

  7. If you want to deliver a package at high speed (Is this research funded by FedEx? I doubt it.) punching through the upper atmosphere at 15,000 mph is doing it the hard way. With a slightly bigger launch rocket you can put your package into a low orbit at 18,000 mph and de-orbit it wherever you like. Wings are optional but handy if you want pin-point targeting accuracy.
    There’s only one snag. Developing such a “Fractional Orbit Bombardment System” (FOBS, see Wikipedia.) would infringe on the SALT II treaty, hence the sub-orbital glider.
    Curiously enough, towards the end of WWII the Germans tried to develop a high-altitude glider with which to bomb the United States. Wikipedia has the details of that project under “Silbervogel.”

    1. It’s all about blowing people (and things) up before they can run away and hide.

      The purpose behind the Falcon project is to develop a method to put a large quantity of conventional explosives anywhere in the world in less than an hour, according to DARPA sources quoted in the linked articles.

      We can already do this with nukes, but that poses political problems, and chemical explosives require much better targeting. We can also do it with bombers, drones or cruise missiles, but they are much slower. It’s the combined problem of high-speed and accuracy that they are trying to solve.

      Putting the bomb in orbit would solve the aerodynamic problems, but unless it has some ability to steer after reentry, the accuracy won’t be good enough. Parachutes definitely won’t cut it. Also good point about SALT II, but the government is pretty good about weaseling around such things. (“It’s not a WMD, so the treaty doesn’t apply” or some such reasoning.)

      I think the most likely civilian application would be transporting (very expensively) people in sort of a super SST. You would still need to arrive at the airport 3 hours early for your 40 minute flight to Tokyo, though, and go through Customs at the other end. Unlike bombs, FedEx parcels usually have to go through Customs, which introduces an unpredictable delay of up to several days. Cargo would have to be small, expensive repair parts or similar items. It would make much more sense to set up a pipeline over a conventional transportation system for production parts, unless the quantity involved was extremely small and the parts were incredibly expensive and the cost of waiting was huge. Almost all documents and all information these days can be transmitted electronically. Gone are the days of shipping boxes of 7-track magtapes full of Skylab UV telescope data by Emery Airfreight from Houston once a week.

      1. We still get in California magnetic data tapes from Germany weekly in the mail to process. It is hard to get the Air Force to change sometimes.

  8. Nebula, I think there’s some good evidence that there is/was a “Aurora” type aircraft out there, possibly based on Shuttle technology and fueled with hydrogen. Whether it is/was useful or practical is another story. Some think “Aurora” was why the SR-71 was retired, even though very useful and still essentially invulnerable to air defense systems.

    I’m not aware of any definitive proof of “Aurora’s” existence, though. It might even be more than one type of vehicle. There are some very interesting sightings from very competent observers that leave me wondering, though. Before the advent of reasonably reliable UAV’s, that might have been the way the Pentagon thought they needed to go. Maybe someday it will be declassified and we’ll know for certain.

    As to the Falcon, we can never be certain of what we will find until we acutally experiment and see. I’m not an aerospace engineer, so I can’t say much about possible applications.

  9. Some of the stuff that DARPA does is amazing. I am a little surprised they didn’t bring this to Australia (specifically, Woomera) to launch though

  10. I like the research. Thing itself, like many have said, would be commercially impractical and I hope we don’t need another weapon delivery system like this. But the lessons learned in the details could be useful for many unanticipated uses from thermal insulation for your toaster to Titan atmospheric re-entry vehicles.

  11. I don’t know about transporting people with this plane – the G forces of the acceleration must be hellish.

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