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Some questions about today’s hypersonic test flight

Here are some additional stories describing today’s test flight of the Hypersonic Test Vehicle.

I have several questions, and no answers:

  • What makes this vehicle so different from the shuttle or other lifting body vehicles — all successfully tested and flown from both suborbital and orbital heights — to require these test flights? Granted, the shuttle was manned while the HTV is not. Still, the shuttle was often landed using its computers, with the pilots merely standing by should they be needed.
  • If the HTV isn’t very different from earlier lifting body spacecraft, why the failures? This is proven technology. It shouldn’t be so hard to build an unmanned glider capable of maneuvering at hypersonic speeds. They were even able to do this with the Apollo capsules.
  • If the HTV is different from previous orbital gliders, what are the differences? I noticed that all the above stories are very circumspect about whether the HTV is powered during its flight. DARPA describes the main section of the flight plan as the glide stage, but does not say if the vehicle is actually powered in any way. The text implies it is merely gliding, but that is merely implied and might not be true. And if it is powered, how is it powered? Is this also a test of ramjet technology, as was the case with the earlier test flight of the X-51?

I find myself a bit puzzled by this test program, and am even beginning to wonder if it might be a bit of a boondoggle.


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  • yes it sounds like an expensive program seems like a setback

  • I’m certainly no expert on hypersonic research but I’ll take a shot at your questions:

    1. The goal of DARPA’s hypersonic program is to enable the development of extremely fast response weapons, e.g. hit a target anywhere in the world within an hour. This requires sustained flight at hypersonic speeds. The Shuttle returned hypersonic but it was flying like a brick. It had a great shape for dissipating orbital energy (and of course for carrying a big payload to orbit) but a terrible shape if you want to stay in high energy flight.

    2. The HTV is very different than orbital lifting body designs. It’s a narrow glider shape that is intended to enable long distance hypersonic flight that is fuel efficient. Learning how to fly with that shape at Mach 20 is apparently nontrivial.

    3. The HTV-2 used the Minotaur to get to Mach 20. Even though it was gliding, that’s fine for demonstrating how to fly in controlled manner at Mach 20. The HTV-2 would then enable the HTV-3X or Blackswift hypersonic demo vehicle. (See The Blackswift would fly from a runway to Mach 3 under turbojet power and then switch to ramjet to reach Mach 16. After cruising for some time and perhaps hitting at target, it would return for landing. There’s never been any vehicle like that.

    The Blackswift was canceled by Congress last year but most likely something similar to it will reappear since the AF appears determined to have such a capability. It will probably come back under a new name and with slightly different specs, e.g. slightly lower speed. However, with the failure of the HTV-2, they will first need either to get more money for more HTV-2 flights or start a new program that starts at lower speeds and works up. They need to study this flight regime since they clearly don’t understand it.

  • AstroWill

    I think the idea is that is it actually flying at those speeds through the atmosphere. The shuttle leaves most of the atmosphere pretty quickly and then decelerates pretty quickly once reentering. So it’s not going mach 15 though thick atmosphere.

  • i love this stuff . “Learning how to fly with that shape at Mach 20 is apparently nontrivial.” haha yes

  • Steve Philipp

    Old time engineers like myself are being pushed out of the space business. The new grads replacing us do not have the experience they need to put out reliable designs, but the colleges are pushing aerospace companies to employ them.

    The electrical environment the glider must operate in is very hostile to electronics. Newer electronic circuitry is more sensitive to noise and must be well grounded. I would bet it’s not.

    If carbon fiber materials are being used for the skin the grounding problem becomes even worse.

  • Steve Philipp

    One more comment:

    The vehicle does have a carbon fiber skin. If Lockheed Martin wants it fixed they can find me.

    On re-entry the vehicle will travel through highly charged pockets of plasma. This will induce currents in the electronics by way of capacitance and induction.

  • when clark mentioned this “flight regime” it made me think if we thought like the greeks there would be a different god for subsonic , supersonic, and hypersonic atmospheric flight . we need to learn how to properly appease the god of hypersonic atmospheric flight . wierd analogy sorry hehe

  • Quran (4:104) – “And be not weak hearted in pursuit of the enemy; if you suffer pain, then surely they (too) suffer pain as you suffer pain…”

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