A B-52 prepares to launch the X-51 "hypersonic" test vehicle.

A B-52 prepares to launch the X-51 “hypersonic” test vehicle.

WASHINGTON: “I believe, today, we could build a Mach 5 cruise missile [with] off-the-shelf materials,” said Charles Brink of the Air Force Research Laboratory. “We could go 500 nautical miles in 10 minutes.”

Brink should know: He ran AFRL’s record-breaking X-51 program. Now AFRL and the Defense Advanced Research Projects Agency (DARPA) are co-funding a pair of follow-on projects: one for a hypersonic jet like the X-51, aspiring for Mach 8, and another for a different high-speed technology called “boost-glide.” Brink told a recent meeting of the Royal Aeronautical Society’s DC chapter that “those will probably both fly in 2018-2020.” The US Army also has a hypersonics program, and China is testing hypersonic missiles of its own.

Why bother? Ballistic missiles have been going at comparable speeds since Werner von Braun invented the V-2 some 70 years ago. The difference is that V-2s, Scuds, Minutemen, and so on follow a ballistic arc up out through space, while hypersonic systems like the X-51 fly at five or more times the speed of sound in the atmosphere.

Skeptics argue that pushing through all that air resistance just makes the engineering problem needlessly difficult. Believers like Brink and Breaking Defense contributor Robbin Laird argue hypersonics makes a major military difference. The value isn’t speed alone, they say, but a combination of speed, flexibility, and surprise.

First of all, a hypersonic cruise missile would be much smaller then a ballistic missile. Hypersonic engines, like other jet engines, are “air-breathing,” meaning they burn their fuel by mixing it with oxygen from the atmosphere. Ballistic missiles and satellites launch on rocket boosters that must carry their own oxidizer with them. On the recently retired Space Shuttle, for example, the largest tank was mostly carrying oxygen. Smaller missiles can launch from a wider variety of smaller platforms — ships, ground vehicles, even aircraft — giving US commanders more options and the enemy more potential threats to track.

Second, a ballistic missile launch is so bright and hot that you can see it from space: The US has an entire network of satellites to do just that. Once that booster cuts off, the warhead and its “reentry vehicle” coast, cold and dark, against the background of space, but they can’t change course: They’re stuck following a ballistic curve (hence “ballistic missile”) which is so predictable that Sir Isaac Newton could calculate where the target has to be. The X-51 also requires a rocket boost, but a much smaller one, enough to reach Mach 4.8 rather than to exit the atmosphere. Then, once the X-51’s scramjet engine kicks in, it burns much less intensely but continuously, providing thrust throughout the flight. So a hypersonic missile would much less detectable and much more maneuverable than a ballistic one.

As a result, said Laird, a hypersonic missile could have “a very complicated launch trajectory which goes very fast into the target, which basically makes it unstoppable.”

“The faster you fly, the more difficulty [enemy systems] have in tracking you, in hitting you,” Brink told me after his public remarks. Even if long-range early warning radars see you coming — which is far from certain, since hypersonics require such a highly streamlined design even the X-51 demonstrator was “inherently somewhat stealthy,” he said — the enemy has much less time to analyze the data, confirm you’re a threat, and transfer the targeting data to short-ranged but higher-precision radars used by interceptor aircraft and anti-aircraft missiles.

“The handoff between those systems and the update of those systems are made much more complex if you’re coming at them at Mach 5 rather than Mach 0.8,” Brinks said. While a Mach 5 hypersonic missile covers 500 nautical miles in 10 minutes, he said, “right now, a conventional cruise missile would take 45 minutes to an hour.”

In the vastness of the Asia-Pacific theater, however, 500 miles is relatively short-ranged: Even a Mach 5 missile would take almost an hour to get from, for example, the US bases on Okinawa to the Chinese space facilities in Xinjiang.

“Mach 5 doesn’t buy you anything,” said Robert Stein, a member of the Pentagon’s Defense Science Board. “If you really want to get up into a regime where its really helping, double that number. Now you’re starting to talk” — and really starting to get into some difficult engineering. “There are niche roles [for hypersonics],” he told me after a recent missile defense conference, “and one can argue whether the niches are really worth the difficulty.”

“There’s nothing magic about Mach 5,” Brink himself told me. “Why not four or seven? We are all looking at all of those,” he said. The Air Force is studying high-speed turbines going Mach 2.5, ramjets going Mach 3 to 4, and boost-glide systems reaching Mach 8 to 10, as well as hypersonic “scramjets” like the X-51.

“There are other capabilities that could get us faster missiles sooner [than hypersonics],” Laird told me. “I think we need to look at missiles across the board.” After committing hundreds of billions to the F-22 and F-35, often called fifth generation jet fighters, he said, “we’re flying fifth generation aircraft with third and fourth generation weapons.” Hypersonics could be one way for the weapons to catch up to the planes that carry them.

“It’s not the Manhattan Project,” Laird said. “I would make a moderate, steady investment” — preferably in partnership with the Australians, who have a hypersonics project of their own — “and see how the technology matures.”


  • Carlton

    “That’s the goal “difficult engineering” that has milked billions of dollars for hypersonics since WWII and produced nothing of value. Current state of the art requires a solid missile to boost it up to Mach 6, then the scramjet kicks in for less than a minute to boost to Mach 10 (with no guidance or payload), then, repeat and repeat until you retire.

  • http://www.usmc.mil @notrizzo

    Again, looking for a “game-changer” and forgetting that weapon systems have evolved in the way they have for a reason, mostly technology and engineering limitations. This is developing a new capability onto existing system types, but there are even more challenges that aren’t mentioned, payload size, system weight, guidance and maneuverability issues, reliability and of course COST.

  • bobbymike34

    Just build and depoly ASALM.
    R&D should continue but we need a prompt strike capability now and it should take the form of medium and long range ballistic missiles with conventional warheads.
    China deploys hundred of missiles in this range class that are pushing the US further and further from shore. We are leaving ourselves at a tremendous disadvantage.
    We need but cannot ‘wait’ for sramjet tech to be ‘weapon’ ready.

  • ycplum

    [..“reentry vehicle” coast, …, but they can’t change course: ]
    Not quite true, but I believe three countries to date have mature MARV (maneuverable reentry vehicle) technology. I don’t know if there are any deployed nuclear MARV warheads.

    • bobbymike34

      I think the Navy’s Mk5 on the D5 is a MARV or has been tested in that configuration

      • http://www.usmc.mil @notrizzo

        I don’t believe that is the case. Also, it’s important to note that none of the system reported to have MaRV capability are true ICBMs, since the speed on reentry is so great that there is no maneuver opportunity(unless you employ a brake system to slow the vehicle in the atmoshphere, which naturally adds even more engineering difficulties).

        • ycplum

          It isn’t like the warheads have to do barrel rolls. I would think minute adjustments are doable without significantly reducing the speed. I would think it is more the case of reducing the acceleration due to gravity than slowing the speed.

          • http://www.usmc.mil @notrizzo

            You have 2 issues, first is the risk of the warhead tumbling and destroying itself, the speed makes even the most minute flightpath alterations highly dangerous.
            The 2nd is guidance, the heat and atmoshperic disturbance makes the use of an internal seeker head impossible, either radar or IR. You can correct the targetting info at mid-course, but once you hit the atmoshere it’s lights out.
            I think so work has been done to try to give terminal off-board guidance via datalink, but even if you make that work it means you need to have sensors in place to give accurate terminal guidance to the warhead. That’s not satellite or EMCON, we’re talking about accurate radar or IR lock, which is not very reliable considering how vulnerable that targetting platform will be to counter-attack.

          • ycplum

            I am somewhat aware of the difficulties of maneuver at those speeds. It is a massive game of finesse. However, I was under the impression that they could do it decades ago, but that there was no urgent need to do so for nuclear warheads.
            As for terminal guidance, I was under the impression that they have inertial guidance (for nukes) since a CEP of 100 meters is usually good enough for counterforce strikes. Hitting a carrier with a conventional warhead is another story.

          • bobbymike34

            Have you read ‘Lightening Bolts’ about the US’s MARV and AMARV programs. The Pershing II for example was deployed with a MARV warhead and the US has tested a few on IBCM’s and SLBM’s.
            As I mentioned up the thread I believe the US has tested a modified Mk5 or Mk4 with fins on the D5 in the PGS CTM configuration.

          • ycplum

            Honestly, I have been out of the loop for a decade or two, picking up an occasional bit of info here and there. I knew the Pershing IIs have MARV warheads, but I wasn’t sure if they were nuclear warheads.
            By the way, what was the impetus for making the warheads on the D5 MARV? For nukes, it was to counter ABM systems. For conventional warheads, it was for accuracy. The D5 is already extremely accurate. Are they planning on putting conventional warheads on the D5s?

          • bobbymike34

            Yes to counter Soviet ABM and prospective ABM systems. There has been an on and off program over the last 10 years or so called “Conventional Trident Missile’ the CTM above for the Prompt Global Strike mission. Google will bring up lots of information. You should check out the Secret Projects website (in your search it is the one with the .uk) and just search around great information on a ton of stuff including the subject of this thread.
            In an article I read years ago an admiral talked about the D5 being so accurate that the ‘target’ was often inside the crater caused by the non-nuclear warhead.

          • ycplum

            I would like that, but I am at work. Shhhhhh! LOL

  • Jeb Hoge

    “Mach 5 doesn’t buy you anything” seems like kind of an odd statement to make. I mean, yes, if you’re only looking as speed as a factor then it could seem an arbitrary pick but if you’re looking at it in terms of what you’d need to engineer into a system to get a functional hypersonic strike platform, then is it more realistic to build to a relatively reachable level of performance at this stage and then evolve from there? Maybe what a Mach 5 operational platform buys you is a functional stepping stone.

  • mycroftxxx

    “On the recently retired Space Shuttle, for example, the largest tank was mostly carrying oxygen.”

    This is highly misleading, as you can see from the referenced link. The liquid oxygen tank held much more liquid by mass than the liquid hydrogen tank; however, the LH2 tank was 2.5 times larger by volume than the LOX tank. More volume, more wetted area, more drag – especially critical if you want to go Mach 5+ in the atmosphere. This is why most liquid fueled rockets are designed with something other than LH2 (RP-1 for example) for the first stage fuel. LOX + LH2 make much more sense for the second stage, where you’re already out of most of the atmosphere and the greater Isp of LOX + LH2 is not counteracted by the drag penalty.

  • Beno

    “Mach 5 doesn’t buy you anything,” said Robert Stein, a member of the Pentagon’s Defense Science Board.
    I find that a wierd statement, Perhaps if your considering land attack ?
    But here in the UK we are up to 4+ for continuous boost long rang A2A and this has significantly lessened the possible escape zone for our Meteor Missle.

    Harpoon for instance would be significantly more useful at Mach 5.
    Reducing the possible reaction time from radar horizon to ship in a sea skimming mode to mere seconds.

  • Lewis Larsen

    There is a new public presentation on SlideShare:

    Revolutionary radiation-free nuclear propulsion for advanced
    hypersonic aircraft – Lattice’s new concept for a LENR dusty plasma scramjet
    L. Larsen, Lattice Energy LLC, June 13, 2014 [98 slides]