Spate of Hypersonic Vehicle Tests Fuels Global Strike Debate

The military’s reusable space plane, the X-37B, and its classified payload lifted off in April only one day after the maiden flight of the Defense Advanced Research Projects Agency’s Hypersonic Technology Vehicle-2 suborbital glider. It flew nine minutes before operators lost its signal and were forced to abort the mission.

These two vehicles, along with a hypersonic missile that made its first test flight one month later, the X-51 WaveRider, have all been mentioned as means to carry out the “prompt global strike” concept, which calls for the U.S military to deliver a conventional warhead anywhere on the planet in significantly shorter time spans than are currently possible.

Intelligence can be fleeting. The location of a high-value target such as a terrorist leader can be confirmed, but he may move before an air strike is arranged. Or he could be located in a nation that doesn’t allow the Air Force to fly over its territory. U.S. Strategic Command has been looking into ways to deliver bombs on such targets for several years.  

The X-37B’s top-secret payload has nonproliferation experts wondering if it is meant to deliver weapons. Air Force leaders won’t say how high up the experimental spacecraft is, how much it costs, or exactly how long it will loiter before returning to Earth. And it definitely won’t reveal what it is carrying in its bay.

“I think the secrecy is the key problem — not necessarily the technology, itself — it does allow people’s imaginations to run wild,” said Theresa Hitchens, director of the United Nations Institute for Disarmament Research in Geneva, Switzerland.    

“The concept of 24/7 global strike capabilities makes almost everyone nervous, including U.S. allies,” Hitchens said.

“Such capabilities could be highly destabilizing in a crisis; and also raise the risk of mistaken strikes because of the pressure to respond rapidly to intelligence without taking the time to closely verify that intelligence,” she told National Defense in an email.

Diplomats based in Europe have asked Hitchens her opinion about the space plane, formally known as the orbital test vehicle. “The X-37B has caused quite a stir in China, at least in the Chinese press and there have been some pointed inquiries here,” she said.

“The problem is primarily the heavy secrecy surrounding the experiment, which always causes the international community to become suspicious when it involves U.S. military space activities,” she added. She believes the X-37B is carrying National Reconnaissance Office payloads, which automatically makes the mission classified. NRO operates the nation’s spy satellites.   

The aircraft resembles the space shuttle, and like NASA’s soon to retire spacecraft, is designed to land on a runway after its mission is completed. Unlike the shuttle, it is not manned, so it can remain in orbit for long periods. This mission is expected to last around nine months, although Gary Payton, Air Force deputy undersecretary for space programs, told reporters before the launch that the mission could last longer.

It is about 29 feet long, about four times smaller than the shuttle. Like its reusable predecessor, it has a cargo bay, it can maneuver in space, and glides to its landing spot. The Air Force can refurbish the spacecraft and possibly launch it again. It also has ordered a second space plane from the contractor Boeing.

Payton denied that the X-37B would be used to deliver weapons.

Hitchens said the Soviets once claimed that the space shuttle would be used to weaponize space. It was not, but it could have been, she added. In its current size, it’s unlikely that the X-37B would carry weapons. However, it could be scaled up to do so, she added.

“It’s not really big enough. Nor does the concept of operations make much sense — pretty much anything you could do with the thing you could do more easily and cheaply with other platforms,” she said.

Other analysts agreed.

Brian Weeden, in a report released by the Secure World Foundation, rated the possible uses for the space plane. The feasibility for it being employed as a sensor test bed was “high,” he said. As for it being used as a conventional strike weapon, with either kinetic weapons being deployed from its bay, or it re-entering the atmosphere and becoming a bomb, itself, he rated the possibility of that as “zero.”

The small bay, which is about the size of a pick-up truck bed, would not hold such bombs, he said. And since it is a glider, it could not fly toward a target at a tremendous speed.

The “X-37B after re-entry would be a slow moving, not very maneuverable glide bomb, easy prey for any air defense system along its path to the target,” Weeden wrote.
David Wright and Laura Grego, writing for the Union of Concerned Scientists, found little utility for the space plane at all, especially when comparing it to other less expensive means of launching and recovering space assets when needed.

“It is difficult to find a mission for which the space plane makes sense, the authors wrote in their “All Things Nuclear” blog. The only unique capability it offers is landing on a runway, they asserted. The heat shielding, wings, and other features needed for re-entry adds extra mass, which makes launching the vehicle prohibitively expensive. They acknowledged that there might be some benefit in capturing failed satellites, or returning experimental payloads to Earth where they can be examined. Yet, the extraordinarily high cost of launching objects into space, which they estimate at $20,000 per pound, calls into question the cost versus benefit reasoning behind this. Loaded, the X-37B weighs up to six metric tons. The program’s budget is also classified.

For that reason, the space plane “is a poor choice for placing weapons into orbit, including hypersonic strike vehicles intended for a conventional global strike mission,” they wrote.

More overt in its intended purpose is the HTV-2, a DARPA program that is experimenting with an expendable vehicle designed to hit speeds of Mach 20 and above, then slam into a target.

The first experimental flight, where the vehicle was launched from a Minotaur IV Lite rocket, was intended to leave the atmosphere at “several hundred thousand feet,” perform a series of maneuvers for 20 minutes, then perform a controlled crash into the Pacific. However, the first test ended after only nine minutes, according to DARPA fact sheets.

Lt. Gen. John Sheridan, Air Force program executive officer for space, said the second scheduled test will have a warhead mounted on it to test its utility as conventional strike platform. The glider will be directed to hit a specific target, he told reporters at the Space Symposium in Colorado Springs, Colo., shortly before the first test.

“The question is what do you do with that information. Is that the kind of information you want to take forward with a program? Do you need to do more? Do you need to look at different methodologies besides the HTV-2 as a delivery platform? I don’t know the answers to that yet,” Sheridan said.

DARPA spokesman Eric Mazzacone said he had no further information on the future of the program other than an April press release that said an investigation into the first test was ongoing.

One issue with prompt global strike concepts that propose using conventional warheads on ballistic missiles, whether launched from a silo in North Dakota or from a Trident submarine, is that friends or foes following their trajectory can’t know whether they are carrying nuclear weapons. Their flight paths would be identical.

The HTV-2 provides a possible solution to that problem because it would have a completely different trajectory, said Mark Lewis, former chief scientist of the Air Force, and now a professor of aerospace engineering at the University of Maryland.

It would fly high enough to avoid over-flight issues and it couldn’t be mistaken for an intercontinental ballistic missile, he said.

“I think it gives you a more politically tenable solution,” he said at an Air Force Association talk on hypersonic technology.

Also promising was the X-51 flight in May, he said.

The WaveRider was launched from the wing of a B-52 and broke a longevity record by sustaining a Mach 5 speed for 200 seconds using a scramjet engine, and did so while climbing, he said. The test flight was supposed to last 300 seconds and reach Mach 6. Nevertheless, the length of the flight was a significant milestone in hypersonic flight, Lewis said.

Hypersonic speed is generally defined as beginning at Mach 5, which is the point where aerodynamic heating caused by the speed of the vehicle cutting through the atmosphere becomes a factor. The space shuttle and the space plane enter the atmosphere at hypersonic speeds, and therefore require heat shielding.

“The X-51 removed any future doubt that a scramjet engine can power a vehicle at hypersonic speeds and accelerate it through the atmosphere,” Lewis said.

Air-breathing scramjets take the heat created by the engine, and recirculate it into the combustion system. The X-51 reached a thermally balanced state, and could have continued as long as it had fuel to burn, Lewis said.

As far as prompt strike, hypersonic missiles such as the X-51 are a possible solution, Richard Hallion, former chief historian of the Air Force, said at the talk. Although they would have to be launched regionally and aren’t global in reach, he added.

They can significantly shorten the so-called sensor-to-shooter loop, he said. For example, the 80 minutes it took cruise missiles to reach the Osama Bin Laden training camps in Afghanistan in 1998 could have been shortened to 12 minutes if a Mach 6 hypersonic missile had been employed, Hallion said in a paper, “Hypersonic Power Projection,” which was published by the Mitchell Institute.

“The advantage of striking at hypersonic, as opposed to subsonic, velocities is self-evident,” he wrote.                              

Topics: Science and Engineering Technology, DARPA, Space