Behind the Air Force's Secret Robotic Space Plane

Move over NASA. The U.S. Air Force has spent decades on the concept: an unmanned space plane that can be used to spy, reposition satellites, possibly even bomb targets, then return to base. A successful launch next week could turn that vision into a reality.

 

When the engines of a 19-story Atlas V ignite in April at Cape Canaveral Air Force Station in Florida, the liftoff will look like any other for the workhorse launch vehicle. After about 4 minutes, the engines will cut off and the rocket's first stage will fall away, freeing the second stage to boost the upper section of the rocket into low Earth orbit.

Away from prying eyes, the mission will cease to be ordinary. A few seconds after the second stage fires, the fairing, a protective shroud that surrounds the cargo at the rocket's tip, will split in half, revealing the classified payload: a 29-foot-long delta-wing spacecraft called the X-37B Orbital Test Vehicle. It might look like a miniature version of the space shuttle, but this spacecraft is unmanned, and instead of NASA, the U.S. Air Force is operating it. The moment the X-37B emerges from the shroud will mark the fulfillment of a dream the Department of Defense has been pursuing for nearly 50 years: the orbital flight of a military vehicle that combines an airplane's agility with a spacecraft's capacity to travel in orbit at 5 miles per second.

At the end of its maiden trip, which could last days or even weeks, the X-37B will glide to Earth under robotic control without the benefit of engines. Instead, it will rely on flight-control surfaces in the tail to steer it through a fiery re-entry, during which the nose and leading edges of the wings must resist 3000-degree-Fahrenheit temperatures. The flight will end in secrecy with a 230-mph touchdown on an isolated runway at an Air Force base in California, most likely Vandenberg.

Though based in many ways on the shuttle-the only operational orbital space plane in the world-the X-37B showcases plenty of innovation. The shuttle uses hydraulic lines to power the control surfaces on its wings and tail, but the X-37B takes advantage of small, powerful electromechanical actuators instead, eliminating the weight of fluid and hoses. In lieu of the ceramic tiles used on the shuttle, the X-37B's leading edges and nose cap are made of an easily shaped composite material that NASA developed when the space agency ran the experimental craft's development, before the military took charge of it in 2004.

The stubby 15-foot wingspan also echoes the shuttle's design, but unlike the larger craft, which has one tall vertical stabilizer, the X-37B has a V-tail with two ruddervators, a combination of a rudder and an elevator. David Hamilton, the director of the Air Force Rapid Capabilities Office, explains that the shorter V-tails are easier to package in a fairing, something that's not a concern for the shuttle. Those V-tails also help guide the X-37B through its 40-degree, nose-high re-entry, while a speed brake along the upper centerline helps it slow down as it prepares to land. Since the X-37B is unmanned, it does not need hardware to maintain a pressurized compartment for a crew and does not have to carry supplies for an extended manned mission.

 The X-37B's simplicity and small size are part of what makes it appealing to the military. "There was always this issue with the space shuttle that you were sending up this enormous truck no matter what you were launching into space," says Mark Lewis, the former chief scientist for the Air Force. "There are times you want the Mack truck and times you want the Volkswagen Beetle. Unfortunately, with the shuttle, you were forced to fly the Mack truck."

The Air Force won't say what the X-37B will do during its first trip to orbit because the program has sunk into the "black" world of classified programs. Until a couple of years ago, the spacecraft was regarded as just another experimental prototype. Today, Air Force officials are skittish to mention even the smallest details. Asked in a recent PM interview what he could say about the X-37B, Werner J.A. Dahm, the Air Force's chief scientist, replied, "Nothing very useful," before quickly changing the subject.

Most of what the Air Force will now publicly acknowledge about the vehicle is contained in an opaquely worded two-page fact sheet: Built by Boeing's secretive Phantom Works division and managed by the Air Force's Rapid Capabilities Office, the X-37B Orbital Test Vehicle "will demonstrate a reliable, reusable, unmanned space test platform for the United States Air Force." Because the program did not start as classified, many of its design details can be gleaned from documents drafted before the program went dark.

The Pentagon's X-37B program stands out at a time when there is a dearth of radical, groundbreaking government-sponsored aircraft and air transportation concepts. "We retired the SR-71," says Vincent Sabathier, a senior associate and space policy specialist at the Center for Strategic and International Studies, based in Washington, D.C., referring to the legendary Blackbird supersonic spyplane. "We will retire the space shuttle. This is something that is still exciting."

Despite decades of work and billions of dollars, the X-37B is the Pentagon's only surviving space plane program after post-Cold War budget cuts. "I think what we had in the last decade was an interruption, or intermission, in space plane development," says Rebecca Grant, a former Air Force official and now the president of the Washington, D.C.-based IRIS Independent Research. "Hopefully now [with the X-37B launch] we're looking at the next act." 

Reusable launch vehicles (RLVs) and space planes have suffered from the promises of scientists and politicians who overestimated their utility and underestimated their complexity. The X-20 Dyna-Soar, a flat-bottom glider that used rockets to take off but made powerless landings, was touted as an unstoppable hypersonic space bomber but was canceled in 1963. Designers billed the quixotic single-stage-to-orbit X-30 as a new Orient Express, leading President Ronald Reagan to say in a 1986 speech that it would be able to "take off from Dulles Airport and accelerate [to] up to 25 times the speed of sound, attaining low Earth orbit or flying to Tokyo within 2 hours." But as the complexities of reusable spacecraft became clearer, the government started cutting space planes from the budget.

NASA took over the development of RLVs from the Pentagon in the 1990s, but critics soon assailed the agency for pursuing endless testbeds rather than operational spacecraft. One of the most ambitious space planes of the era was the X-33, a 69-foot-high craft that did not need a heavy rocket to reach orbit. A test craft was nearly complete in 1999 when engineers discovered cracks in the overweight vehicle's fuel tank. NASA officials canceled the program in 2001, and like nearly all previous space planes, it never flew. "The X-33 required at least one miracle," Lewis says.

In a 2001 congressional hearing, Henry Cooper, the former head of the Strategic Defense Initiative Organization, blamed both NASA and the Air Force for killing space planes: "The Air Force has not been a serious advocate for military space programs-otherwise it would not have supported transferring the reusable launch mission to NASA, an organization that has shown little responsiveness to supporting innovative military space programs."

But civilian space planes did not perform as expected, either. The space shuttle failed to reach its primary goals of making transportation to space cheaper and more efficient. The prospects for a new generation of reusable space planes went from bad to catastrophic when, on Feb. 1, 2003, the space shuttle Columbia broke up during re-entry. NASA's shuttle program, which was originally supposed to carry the X-37 orbital test vehicle, faced an early retirement, and the agency lost interest in RLVs and space planes.

The X-37B, though more modest than its predecessors, seemed to be on a familiar path to extinction. NASA started work on the X-37 in 1999, and soon after, agency officials developed a plan to build an approach and landing test vehicle and an orbital test vehicle. But in 2004 NASA dropped them both. The Defense Department then adopted the X-37 and placed it under the auspices of its research arm, the Defense Advanced Research Projects Agency.

DARPA contracted Burt Rutan's Scaled Composites to conduct drop tests of the X-37 off its White Knight carrier aircraft over California. (The jet-powered White Knight gained fame as the mother ship that launched SpaceShipOne, the suborbital craft that won the Ansari X Prize in 2004.)

In 2006, the X-37 again changed hands, this time going from DARPA to the Air Force, and a cloak of secrecy fell over the program. The new plan focused on building a single orbital test vehicle, rebranded as the X-37B. "I can't say a lot about it," says Lewis, the former Air Force chief scientist. "I had to actually start asking questions about what this thing is, because it was being kept so secret."

The presumption that the space plane's mission is important because it's classified might be a smokescreen, says John Pike, the director of GlobalSecurity.org. "Maybe it's a bad idea," he says. There are reasons for a military program to go "black" that don't have to do with national security.

Secrecy also protects the X-37B and its funding. With tight budgets and skeptics alert for failure, "you put it in the black and you operate it without telling people," Sabathier says. The Air Force declines to disclose how much it's spending on the X-37B, and, because of the classified status, the figure is not otherwise available. 

One very public event may have secured the future of military space planes. On Jan. 11, 2007, China destroyed one of its obsolete weather satellites with a missile ("Battlefield Space," July 2007). Though China's test was hardly a complete surprise to the military or intelligence communities, the incident became a dramatic reminder of the vulnerability of critical satellites.

In an emergency-like a rapidly unfolding crisis or an attack on a vital U.S. satellite-a space plane could become a reconnaissance platform by scanning the Earth below or by observing other objects in orbit. The ability to launch orbital surveillance platforms quickly-what the Pentagon calls "operationally responsive space"-has been a longtime goal of the Defense Department.

"The weird thing to me is that they are being so coy about the types of missions they want space planes to do," says Theresa Hitchens, a space policy expert and director of the United Nations Institute for Disarmament Research. "The first thing that comes to mind is a pop-up reconnaissance vehicle for a place where you don't have satellite reconnaissance or can't move a satellite fast enough."

It can take the Air Force months to prepare a military satellite and days to move one into a new position, compared to about an hour or two to position a space plane kept on alert. Also, any nation with intelligence about U.S. satellite paths can predict when the satellites are overhead, so a space plane offers an element of surprise.

In current conflicts, military commanders have a hard time sharing orbital images because satellites controlled by the National Reconnaissance Office are often tasked to stare at another target. "All the strategic applications are still very appealing if the technology can come together," Grant says.

But if getting satellites into space cheaply is the main goal, then a reusable spacecraft like the X-37B is by no means the best option. Peter Wegner, the director of the Pentagon's Operationally Responsive Space Office, says he's watching advances in RLVs, but his focus instead remains fixed on finding ways to slash the price of expendable rockets. "I think we can hit the [launch] timelines with the expendable vehicles and still cut the cost dramatically," Wegner says.

The most daring job of a space plane, and the one least discussed, is the role of a bomber. The craft could fly over targets within an hour of launch to release cone-shaped re-entry vehicles that would both protect and guide weapons through the atmosphere. A craft the size of the X-37B could carry 1000- or 2000-pound re-entry vehicles armed with precision munitions like bunker-busting penetrators or small-diameter bombs, or simply use the explosive impact of kinetic rods cratering at hypersonic speeds to destroy targets.

However, widespread concerns about stationing weapons in space, possibly starting an orbital arms race with China, could make this option unappealing. In 2001 Boeing pitched a space bomber system to the Pentagon, but there is no evidence that the X-37B is being used to create such a weapon system.

Others in the U.S. government are also expressing interest in the space plane concept. The Pentagon recently completed a document outlining the requirements and development path for a space plane that could insert small teams of Marines anywhere in the world in 2 hours. In February NASA awarded $20 million in research funds to a private space company called Sierra Nevada Corp. to build a passenger space plane called Dream Chaser. The craft would launch on a rocket, ferry up to seven people to the International Space Station (or private space hotels) and then land like the space shuttle. The Air Force's X-37B has the clear lead on these conceptual contenders-Hamilton says the X-37B team is currently preparing for a second launch sometime in 2011.

What may differentiate the X-37B from its predecessors-and what confounds the critics trying to make sense of it-is precisely that its goals don't sound overly futuristic. "I'm more concerned about the programs that are touting themselves about all they will achieve," says Richard Hallion, a former Air Force chief historian and one-time special adviser to the Pentagon on space programs. "The ones that are quiet, the ones that maintain a more modest public posture, we often find have the potential for true greatness."

The X-37B might lack a flashy name, a made-for-the-movies mission and public hoopla, but this space plane's low profile might be just the thing that helps it beat the long odds and become a success.

Hypersonic Cruise Missile: America's New Global Strike Weapon

The mission: Attack anywhere in the world in less than an hour. But is the Pentagon's bold program a critical new weapon for hitting elusive targets, or a good way to set off a nuclear war?

Launched from a B-52, the proposed X-51 hypersonic cruise missile could travel 600 miles in 10 minutes to strike elusive, fleeting targets

A tip sets the plan in motion--a whispered warning of a North Korean nuclear launch, or of a shipment of biotoxins bound for a Hezbollah stronghold in Lebanon. Word races through the American intelligence network until it reaches U.S. Strategic Command headquarters, the Pentagon and, eventually, the White House. In the Pacific, a nuclear-powered Ohio class submarine surfaces, ready for the president's command to launch.

When the order comes, the sub shoots a 65-ton Trident II ballistic missile into the sky. Within 2 minutes, the missile is traveling at more than 20,000 ft. per second. Up and over the oceans and out of the atmosphere it soars for thousands of miles. At the top of its parabola, hanging in space, the Trident's four warheads separate and begin their screaming descent down toward the planet. Traveling as fast as 13,000 mph, the warheads are filled with scored tungsten rods with twice the strength of steel. Just above the target, the warheads detonate, showering the area with thousands of rods-each one up to 12 times as destructive as a .50-caliber bullet. Anything within 3000 sq. ft. of this whirling, metallic storm is obliterated.

If Pentagon strategists get their way, there will be no place on the planet to hide from such an assault. The plan is part of a program—in slow development since the 1990s, and now quickly coalescing in military circles—called Prompt Global Strike. It will begin with modified Tridents. But eventually, Prompt Global Strike could encompass new generations of aircraft and armaments five times faster than anything in the current American arsenal. One candidate: the X-51 hypersonic cruise missile, which is designed to hit Mach 5—roughly 3600 mph. The goal, according to the U.S. Strategic Command's deputy commander Lt. Gen. C. Robert Kehler, is "to strike virtually anywhere on the face of the Earth within 60 minutes."

The question is whether such an attack can be deployed without triggering World War III: Those tungsten-armed Tridents look, and fly, exactly like the deadliest weapons in the American nuclear arsenal.

QUICK HIT

The military is convinced that in the coming years it will need to act with this kind of speed against threats—terrorist leaders, smuggled nuclear or chemical arms—that emerge and disappear in a flash. There may be only hours, or minutes, to respond. "We know how to strike precisely. We know how to strike at long distances," says Kehler, whose office is in charge of the Defense Department's Global Strike mission. "What's different now is this sense of time."

The leading candidates to deliver Prompt Global
Strike's swift knockout punch are the sub-launched
Trident II missile and the X-51, a cruise missile
launched froma B-52 and boosted to
supersonic speed by a rocket.
A scramjet takes it hypersonic.

Every strategist remembers Aug. 20, 1998, when the USS Abraham Lincoln Battle Group, stationed in the Arabian Sea, launched Tomahawk cruise missiles at an Al Qaeda training camp in eastern Afghanistan, hoping to take out Osama Bin Laden. With a top speed of 550 mph, the Tomahawks made the 1100-mile trip in 2 hours. By then, Bin Laden was gone—missed by less than an hour, according to Richard A. Clarke, former head of U.S. counterterrorism.

The American military already has weapons that can destroy just about anything in a matter of minutes: nuclear missiles. That terrifying capability was designed to contain Soviet adversaries. But as the Cold War recedes into memory, U.S. strategists worry that our nuclear threat is no longer credible—that we are too muscle-bound for our own good. Are we really prepared to wipe out Tehran in retribution for a single terrorist attack? Kill millions of Chinese for invading Taiwan? The answer is no.

Paradoxically, the weaker our enemies have grown, the less ominous our arsenal has become. Military theorists call it self-deterrence. "In today's environment, we've got zeros and ones. You can decide to engage with nuclear weapons—or not," says Capt. Terry J. Benedict, who runs the Navy's conventional Trident program from a nondescript office a few miles from the Pentagon. "The nation's leadership needs an intermediate step-to take the action required, without crossing to the one."

In 2001, Defense Department planners began searching for something that could hit a foe almost instantly without risking a nuclear holocaust. Most of the solutions—unmanned bombers, faster cruise missiles, hypersonic "glide vehicles" coasting in from space—required a decade or more of development. The Navy, however, had been testing conventionally armed Trident II missiles since 1993. With a few hundred million dollars, strategists said, the first Prompt Global Strike submarines could be ready to go in just two years.

The $60 million conventional missile needs to be far more accurate than the nuclear version. But the multiple warheads can lock onto GPS coordinates while streaking through space. Upon entering the atmosphere, the warheads use flaps to steer to a target. With the Trident II's range of 6000 nautical miles, subs armed with the missiles could threaten a whole continent's worth of enemy positions. "Now," says Benedict, who leads the Trident conversion effort, "we've got the capability to hold all of these targets in all these hot spots at risk at one time."

In 1988, Lockheed Martin's Trident II D5 nuclear ballistic missile entered service on Ohio class submarines. In the Prompt Global Strike program, each sub would be armed with 22 nuclear Tridents, along with two retrofitted Tridents, each with four independently target able warheads. here's how a conventional Trident II would work.

1 Gas pressure ejects the Trident II from a patrolling submarine. Once the missile clears the water, the first-stage engine ignites and the aerospike at the nose extends to improve aerodynamics. Stage 1 burns for approximately 65 seconds. When the Trident is locked onto targets at its maximum range (roughly 6000 nautical miles), this burn carries the missile a few hundred miles downrange at a 45-degree angle. Because all propellant must be used, the missile corkscrews to burn off excess fuel for closer targets.

2 As stage 1 falls away from the missile, the second-stage engine ignites for another 65-second burn that carries the Trident an additional 500 to 800 miles downrange. The nose cone fairing (blue) is ejected to shed weight.

3 After separation from stage 2, the third stage engine burns for approximately 40 seconds, concluding the boost phase and lofting the Trident II up to 600 miles above the Earth—the altitude of some weather satellites.

4 At the apogee of the Trident's trajectory, the third stage falls away, leaving the post-boost vehicle, or bus (red). It receives navigational updates and deploys the four individually targeted warheads (green). Traveling at 13,000 mph and accurate to 30 ft., the warheads are GPS-guided on descent by means of tiny flaps. Two types of warheads are under consideration: the fragmentation version, which shatters tungsten rods just above a target, and a bunker-busting metal "shock impactor" that relies on kinetic energy for its destructive power.

NUCLEAR AMBIGUITY

Almost immediately, congressional critics and outside analysts attacked the missile plan. Everyone seemed satisfied that, technically, modified Tridents could meet Global Strike's requirements. But the Pentagon can't explain how the weapon will be deployed and who will be its intended target. "I just don't think they've got a plan for using these things," says a frustrated senior congressional aide.

First, there's the matter of intelligence. If a president is going to launch the first intercontinental ballistic missile attack in history, he'll need overwhelming evidence. Our ability to nail down that kind of quality information is patchy, at best. On March 19, 2003, the United States launched 40 cruise missiles at three locations outside Baghdad in hopes of killing Saddam Hussein and other senior military officials. It turned out the former Iraqi leader wasn't in any of the locations; the strikes killed at least a dozen people, although it's not clear if they were civilians or leadership targets.

The mission failed even though friendly forces controlled the area. At the heart of Prompt Global Strike is a much darker scenario: American troops are far from their intended target—or the enemy's air defenses are too tough to penetrate. "So let me get this straight," says Jeffrey Lewis, a Harvard University nuclear energy and weapons analyst. "We've got exquisite, fleeting intelligence in an area of immediate concern, but no forces nearby and, miraculously, a sub in just the right spot to attack. I suppose there's some chance of that. But it's pretty small."
 

More difficult to explain is how a conventional Trident could be launched without provoking a crisis even bigger than the one that it was meant to solve. The Navy's plan calls for arming Ohio class subs with two conventional and 22 nuclear Trident II missiles. (The Navy intends to cut its Ohio class fleet from 18 to 14 subs, with 12 in the water at any one time.) To outside observers, the subs' conventional and nuclear weapons would appear identical—the same size, the same speed, shooting from the same location.

Traditionally, the U.S. strategy is to shoot missiles over the North Pole. But the current, most likely Prompt Global Strike targets, North Korea and Iran, lie south of China and Russia—which would put those countries right under a pole-launched flight path. "For many minutes during their flight patterns, these missiles might appear to be headed towards targets in these nations," a congressional study notes. That could have world-changing consequences. "The launch of such a missile," Russian president Vladimir Putin said in his 2006 state of the nation address, "could provoke an inappropriate response from one of the nuclear powers, could provoke a full-scale counterattack using strategic nuclear forces.

The Navy and Strategic Command have proposed all kinds of fixes to address what a Senate Armed Services committee described as Prompt Global Strike's "nuclear ambiguity issues." The subs could be positioned in different locations for a conventional attack than for a nuclear one, military leaders argue. (But that could put the boats out of position for an instant strike.) Hotlines to Moscow and Beijing could warn leaders in those capitals of conventional missile attacks. That is, if those leaders take us at our word—and don't warn their allies in Pyongyang or Tehran to get out of the missile's way.

Former Secretary of Defense Donald Rumsfeld, in a press conference, didn't seem that concerned. "Everyone in the world would know that [the missile] was conventional," he said, "after it hit within 30 minutes."

Congress is decidedly less blasé. The House and Senate have ordered the Pentagon to come up with something more certain before they'll provide the $127 million requested in this year's budget for conventional Trident modification.

While Trident II missiles with conventional warheads could be deployed in a few years, it may take a decade or more to develop the X-51 WaveRider. The WaveRider destroys targets by simply crashing into them at hypersonic speeds. But the technology in this remarkable missile may have wider applications, including ultrafast planes and new space vehicles. Designed by Boeing and Pratt & Whitney for the Air Force Research Laboratory, the X-51 uses just one moving part—the fuel pump—to hit Mach 5, or 3600 mph.

 

Rocket booster The X-51 is carried to 45,000 ft. by a B-52 bomber or a fighter jet, then released. A rear-mounted Army Tactical Missile Systems rocket kicks in to propel the 1600-pound missile to Mach 4.5 and 100,000 ft. The rocket then drops away and the X-51's engine takes over.

Internal inlet The missile's sharp nose funnels shock waves produced at hypersonic speeds into a rectangular opening on the craft's belly. The shock waves compress the air, eliminating mechanical parts that normally do this.

Isolator This component adjusts airflow—which can reach 2500 pounds per square foot—to a stable pressure for the combustor. Slowing airflow increases drag on the vehicle, but allows for more complete combustion.

Combustor Thrust is created when the compressed air mixes with a mist of JP-7 jet fuel and is ignited. Because hypersonic speeds generate sustained temperatures of up to 4500 degrees, the propellant also acts as a coolant—and prevents the X-51's engine walls from melting.

Airflow PM consulted NASA to estimate the fluid dynamics for external airflow around the nose, engine, stabilizers and tail of an X-51 traveling at Mach 5. The rear contour illustrates the engine exhaust plume shape.

The USS Tennessee and other Ohio class subs carry 24 Trident II ballistic missiles in midship tubes. The 65-ton weapons are about 44 ft. long and 7 ft. wide. (Photograph by Yogi Inc / Corbis)

 WAVE-RIDING WEAPON

 
Some officials in the Defense Department want to answer concerns about the Tridents with more radical solutions: exotic, high-tech devices capable of outracing any machine in their class to catch fleeting foes. If these weapons work as planned—and that's a big if—they could let the Pentagon launch lightning-quick attacks without risking a worldwide nuclear storm.

On the coffee table in his cavernous office in the Pentagon's E Ring, Air Force chief scientist Mark J. Lewis has a model of such a machine, a 14-ft.-long missile called the X-51 WaveRider. With an angled nose, flaps in the middle and an inlet on the underbelly, the device looks like a cross between a spaceship and a futuristic cruise missile. It's designed to go nearly seven times faster than a Tomahawk—a flight from the Arabian Sea to eastern Afghanistan would take 20 minutes—and destroy targets with its own kinetic energy. Test flights are scheduled for 2008.

The pressure, drag and high temperatures associated with hypersonic speeds (typically, greater than Mach 5, or 3600 mph) used to be considered too extreme for an aircraft to handle in a controlled way. Only ballistic missiles and spacecraft burning rocket fuel, shooting into space and roaring back to Earth, could go that fast.

What the X-51 does is to turn some of the most brutal effects of hypersonic flight to its advantage. Take shock waves, for example. Bursting through the air at a hypersonic rate produces a train of waves, one after the other, which can drag down an aircraft. But the X-51 is a "wave rider," with a sharp nose shaped to make the waves break at precisely the right angle. All of the pressure is directed beneath the missile, lifting it up. The shock waves also compress the air to help fuel the X-51's combustion process.

The craft is the same size and shape as a Joint Air-to-Surface Standoff Missile, so it can be attached to a B-52 or fighter jet. It runs on standard JP-7 jet fuel, not on rocket fuel, so it fits in neatly with the military's existing logistical chain. The X-51 is made from a fairly standard nickel alloy, not from exotic materials. And the advanced engine technology is very real. In 2004, NASA broke speed records while testing its X-43A, a precursor to the X-51 (see "Breakthrough Awards 2005," Nov. 2005). In a final test flight, the 12-ft.-long aircraft hit 7000 mph—nearly Mach 10. In other words, the X-51 is not just some lab experiment; it's being designed from the start to deploy. "I've got tremendous confidence in it working," the Air Force's Mark J. Lewis says.

That doesn't mean the X-51 will be in competition with a conventional Trident. It will have a range of only 600 nautical miles. And it first needs to be lifted into the air by a plane, then accelerated by a rocket-fueled booster before its hypersonic engine kicks in. But if the 2008 test flight is a success, the X-51 will be the first weapon other than a ballistic missile to fly at hypersonic speeds.

NO CONFUSION

The Trident II iteration of Prompt Global Strike foresaw a pushbutton war, fought from the White House. It assumed that the United States would have few allies or bases abroad from which to attack. Local commanders would be largely circumvented.

But alternate scenarios being drawn up let U.S. forces act much as they do today, only faster. Hypersonic weapons could make that happen. Put an X-51-equipped plane in the air, and it could enable commanders to hit targets for hundreds of miles around in minutes. Tips could be acted on instantly; subs wouldn't have to be in a perfect position in order to strike. Intelligence wouldn't have to race all the way to the Oval Office. Wrong information would produce local damage. And because the X-51 wouldn't be confused with a nuke—or have to fly threateningly over nuclear-armed countries—"you don't worry about starting World War III" when you score a direct hit, Lewis notes.

Hypersonic technology will take longer to develop than a conventional Trident. But the X-51, and weapons like it, might make the most sense for the Global Strike arsenal. After all, they reduce potential fallout from the riskiest part of the program: the human element.