Space Shuttle Jr.

After 2010, the only spaceplane in the U.S. inventory will be the Air Force's mysterious X-37.

  • By Michael Klesius
  • Air & Space magazine, January 2010
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The Air Force hopes its unmanned X-37 The Air Force hopes its unmanned X-37 (in taxi tests in 2007) will take on some of the functions of the shuttle

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A Boeing technician adjusts panels on the X-37A drop-test vehicle

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The X-37 will also demonstrate a new-generation Conformal Reusable Insulation blanket technology, which provides better protection for top surfaces, along with a hard, smooth finish that produces less drag than the shuttle's 1970s-era thermal blankets.

The X-37's most notable thermal advance is on the wing leading edge. On the shuttle, that vulnerable area was covered with reinforced carbon-carbon; the X-37 uses a different material, called TUFROC, for Toughened Uni-piece Fibrous Reinforced Oxidation-Resistant Composite. TUFROC (pronounced "tough rock") was developed at NASA's Ames Research Center in California by a group led by David Stewart, who has worked on thermal protection systems since the shuttle program.

Stewart explains that during reentry, heat is generated not just by friction of the vehicle against the atmosphere, but also by atoms on the surface recombining. In the shuttle's case, the carbon-carbon oxidizes. As the name implies, the new material resists oxidative damage. The surface of the shuttle's tiles heats up very fast because the insulator's high-density coating is very thin. TUFROC's surface material is thicker, and therefore takes longer to heat up. And the new material will reduce weight, which will enable the spaceplane to carry more payload.

The X-37 embodies other modifications of shuttle technology. All shuttle-era hydraulics have been eliminated; the new spaceplane's flight controls will be operated electromechanically, making the X-37 fly-by-wire. Unlike the shuttle, with its one vertical stabilizer, the X-37 has two short diagonal ones, called ruddervators—surfaces that combine the functions of rudders and elevators. These reduce the amount of propellant needed to handle trim and control during the high-speed, high-angle-of-attack reentry, and provide room for a centerline speed brake that manages the vehicle's glide energy just before landing.

Upon reaching orbit, the craft will deploy a solar array that will power batteries. Those batteries have replaced hydrogen fuel cells, the shuttle's power source in orbit. The vehicle will maneuver in space powered by a combination of nitrogen tetroxide and hydrazine. Theoretically, the X-37 could rendezvous with other satellites of interest to the Air Force, friendly or otherwise.

If the X-37 is to carry out such national security missions, its roots will extend back beyond the space shuttle, to earlier spaceplanes. Says Mark Lewis: "I would draw a heritage not only to the shuttle, but to my very favorite program that never was: the X-20."

A follow-on to the X-15 rocketplane, which didn't have the power to get to orbit, the X-20 Dyna-Soar spaceplane, initiated in 1957, would have ridden a massive Titan III booster all the way to orbit if needed, and carried a pilot. (Neil Armstrong was one NASA test pilot selected to fly it, but in 1962 he transferred to the Apollo program.) Dyna-Soar would have given the Air Force a manned system that could have filled a variety of needs: research, reconnaissance, or even attack. It was designed to reach any target in the world in 45 minutes, deliver a weapon, and glide to a friendly base. Its altitude and hypersonic speed would have made it very difficult to intercept.

While this type of capability sounded like something the Air Force needed, the service had difficulty justifying it. NASA was making progress with blunt-body capsules that reentered the atmosphere without the need for pilot control, and intercontinental ballistic missiles were dominating the nuclear delivery mission. A controlled-reentry spaceplane puzzled Secretary of Defense Robert McNamara; he directed the Air Force to study whether concepts such as NASA's Gemini could handle some of the roles better. In December 1963, shortly after prime contractor Boeing started building the vehicle and after about $660 million had been spent, McNamara killed the X-20.

It's been a long wait—in some ways, more than 50 years—but in April 2010, the U.S. Air Force is scheduled to launch an Atlas V booster from Cape Canaveral, Florida, carrying the newest U.S. spacecraft, the unmanned X-37, to orbit. The X-37 embodies the Air Force's desire for an operational spaceplane, a wish that dates to the 1950s, the era of the rocket-powered X-15 and X-20. In other ways, though, the X-37 will be picking up where another U.S. spaceplane, NASA's space shuttle, leaves off.

With a wingspan of 15 feet and a length of 27.5 feet, the X-37 looks like a tiny space shuttle. It has a blunt (though windowless) nose, and one rocket engine bell instead of the shuttle's three. Two cargo doors open just as the shuttle's do, revealing a four- by seven-foot bay. Like the shuttle, the X-37 was designed for low Earth orbits—in the latter's case, altitudes of 125 to 575 miles. And the craft will fly like a shuttle, reentering the atmosphere with the orbiter's 40-degree nose-high attitude. After reentry, it will change to a 20-degree nose-down glide and, flying at up to 220 mph, land at Vandenberg Air Force Base in California, with Edwards Air Force Base as an alternate.

But as for the period between launch and landing, no one, save for a select few in the Department of Defense, knows exactly what the little Boeing-built spaceplane will do, or for how long. The Air Force Rapid Capabilities Office, which is running the program, says only that the orbital test version, the X-37B, will take a suite of next-generation technologies to orbit and will break new ground in the realm of launch, recovery, and reuse, all with an unmanned twist that the shuttle never offered.

At a 2008 Space Foundation breakfast in Washington, D.C., Gary Payton, deputy under secretary of the Air Force for space programs, recalled the X-37's origins. Payton started the program while at NASA. "Then, the X-37 was intended to be a testbed for new technologies that could retrofit into the shuttle: predominantly guidance, navigation, and control, and [thermal protection system] technologies," he said. In that era, planners imagined the shuttle carrying the X-37 to space in its cargo bay and releasing it.

Now, with the shuttle's retirement looming, it appears the X-37 will have an independent, post-shuttle life. Payton envisioned such a role for the X-37, saying: "It would be really advantageous in my mind if we had a system you could launch, recover, change out the payload bay quickly, and put into a different orbit, and do all that measured in weeks instead of decades." David Hamilton, director of the Rapid Capabilities Office, says in an e-mail: "Eventually, I see the unique possibility to operate X-37B more like an aircraft and explore the needs of responsive, reusable spacecraft." Unlike a satellite, he points out, the spaceplane returns, enabling "detailed inspection and significantly better learning than can be achieved with [a satellite's] remote telemetry alone. Experiments can be modified and reflown, with the objective of shortening the technology maturation timeline."

"The space shuttle was designed to be a very heavy payload lifter, and it has performed that job extremely well," says Mark Lewis, a University of Maryland hypersonics expert who recently completed a four-year appointment as chief scientist for the Air Force. "But you don't need to send a Mack truck into space when a Toyota Celica will do."

The question is: Will do what? Lewis, whose enthusiastic speech barely keeps pace with his mind, is happy to talk about the skin-deep similarities between the shuttle and the X-37. ("A lot of the basic reentry physics is treated the same way," he says. "Blunt configurations. The shuttle has very blunt leading edges.") But when he's asked about anything more than the X-37's aerodynamics, he clams up.

So does everyone else. "While some aspects of the…program have been designated as unclassified and been released to the public; information regarding specific technical and performance capabilities will not be released at this time," writes David Hamilton. "Hide it in plain view," says one observer of the Air Force's practice of letting out just a little about the X-37, enough to make it seem like it will never be more than a research tool.

Hamilton does say that "once declared operational, the X-37B could have applications to support missions such as space situational awareness; intelligence, surveillance, and reconnaissance; on-orbit servicing and repair; and satellite deployment and/or retrieval."

It's possible the spaceplane could have a role in national security, particularly since China, India, Japan, and even Iran have begun to exploit space. In December 2007, photographs of an unmanned, classified Chinese spaceplane, the Shenlong, or "Divine Dragon," began to appear on Chinese Web sites. Though hitched to the underside of a bomber, rather than perched atop an expendable booster, the mysterious Shenlong has a blunt nose and single rocket engine bell, making its appearance strikingly similar to the X-37's.

The U.S. program started out relatively open to view, a research effort jointly shaped by the Air Force, NASA, the Defense Advanced Research Projects Agency, and Boeing. The Air Force ordered the first prototype, the X-40A, from Boeing in 1996. When it came time to produce the next iteration, the X-37A drop-test vehicle, NASA had the company increase the size by about 20 percent.

But since then, the X-37 has taken a winding and perplexing path among NASA, DARPA, and the Air Force. From 2004 to 2006, DARPA oversaw it. Along the way, both the X-40A and the X-37A have been drop-tested (first over New Mexico in 1998 and California in 2006, respectively), which proved their automated approach and landing abilities. Finally the program was taken over by the Air Force. Today, call up any of these organizations and say "X-37" and it's like spraying a garden hose at housecats.

"I tried to get to the bottom of this program three or four years ago and could not," says John Pike, the director of www.globalsecurity.org. "All this ‘orbital spaceplane' stuff, ‘space maneuver vehicle,' ‘orbital test vehicle,' ‘X-37,' ‘X-40,' et cetera—six different names for one and a half real programs."

The press-shy Rapid Capabilities Office, established in 2003, is charged with getting special combat support and weapon systems developed and fielded as fast as possible. The office answers directly to the Air Force Chief of Staff, the Secretary of the Air Force, and two high-level procurement officials. Given that short chain of command, it's not unreasonable to imagine that the X-37 could carry classified military payloads like those deployed in 11 shuttle flights made between 1982 and 1992.

We know more about the X-37 itself than about its possible payloads. "Its resemblance to the shuttle is pretty straightforward," says Mark Lewis. Like its shuttle forebear, it has a "cold structure" design: It is made of metals that would melt at reentry and thus need to be shrouded. But while the shuttle's structure is made of conventional aluminum, the X-37's uses lighter composite materials, explained Secretary of the Air Force public affairs officer David Small last March, and "advanced, higher-temperature, more durable thermal protection materials are used to protect the structure during re­entry."

Those materials include silica tiles impregnated with the latest version of Toughened Uni-Piece Fibrous Insulation (TUFI), some of which have flown on the shuttle since the 1994 mission STS-59. The tiles will provide most of the thermal protection for the X-37's underside, and are more durable than earlier shuttle tiles, which have been pocked by debris as light as paint chips. In a TUFI tile, the surface material permeates the underlying insulation, which supports and reinforces the outer surface and renders it more resistant to impacts. In contrast to the shuttle's older, more rigid glass-fiber composite tiles, TUFI tiles have a porous nature that stops cracks from spreading.

The X-37 will also demonstrate a new-generation Conformal Reusable Insulation blanket technology, which provides better protection for top surfaces, along with a hard, smooth finish that produces less drag than the shuttle's 1970s-era thermal blankets.

The X-37's most notable thermal advance is on the wing leading edge. On the shuttle, that vulnerable area was covered with reinforced carbon-carbon; the X-37 uses a different material, called TUFROC, for Toughened Uni-piece Fibrous Reinforced Oxidation-Resistant Composite. TUFROC (pronounced "tough rock") was developed at NASA's Ames Research Center in California by a group led by David Stewart, who has worked on thermal protection systems since the shuttle program.

Stewart explains that during reentry, heat is generated not just by friction of the vehicle against the atmosphere, but also by atoms on the surface recombining. In the shuttle's case, the carbon-carbon oxidizes. As the name implies, the new material resists oxidative damage. The surface of the shuttle's tiles heats up very fast because the insulator's high-density coating is very thin. TUFROC's surface material is thicker, and therefore takes longer to heat up. And the new material will reduce weight, which will enable the spaceplane to carry more payload.

The X-37 embodies other modifications of shuttle technology. All shuttle-era hydraulics have been eliminated; the new spaceplane's flight controls will be operated electromechanically, making the X-37 fly-by-wire. Unlike the shuttle, with its one vertical stabilizer, the X-37 has two short diagonal ones, called ruddervators—surfaces that combine the functions of rudders and elevators. These reduce the amount of propellant needed to handle trim and control during the high-speed, high-angle-of-attack reentry, and provide room for a centerline speed brake that manages the vehicle's glide energy just before landing.

Upon reaching orbit, the craft will deploy a solar array that will power batteries. Those batteries have replaced hydrogen fuel cells, the shuttle's power source in orbit. The vehicle will maneuver in space powered by a combination of nitrogen tetroxide and hydrazine. Theoretically, the X-37 could rendezvous with other satellites of interest to the Air Force, friendly or otherwise.

If the X-37 is to carry out such national security missions, its roots will extend back beyond the space shuttle, to earlier spaceplanes. Says Mark Lewis: "I would draw a heritage not only to the shuttle, but to my very favorite program that never was: the X-20."

A follow-on to the X-15 rocketplane, which didn't have the power to get to orbit, the X-20 Dyna-Soar spaceplane, initiated in 1957, would have ridden a massive Titan III booster all the way to orbit if needed, and carried a pilot. (Neil Armstrong was one NASA test pilot selected to fly it, but in 1962 he transferred to the Apollo program.) Dyna-Soar would have given the Air Force a manned system that could have filled a variety of needs: research, reconnaissance, or even attack. It was designed to reach any target in the world in 45 minutes, deliver a weapon, and glide to a friendly base. Its altitude and hypersonic speed would have made it very difficult to intercept.

While this type of capability sounded like something the Air Force needed, the service had difficulty justifying it. NASA was making progress with blunt-body capsules that reentered the atmosphere without the need for pilot control, and intercontinental ballistic missiles were dominating the nuclear delivery mission. A controlled-reentry spaceplane puzzled Secretary of Defense Robert McNamara; he directed the Air Force to study whether concepts such as NASA's Gemini could handle some of the roles better. In December 1963, shortly after prime contractor Boeing started building the vehicle and after about $660 million had been spent, McNamara killed the X-20.

Still, Lewis admires the X-20 from an engineering standpoint: "When we look at Dyna-Soar, we say: Gosh, that's the program we should have had. Imagine if we had a cheaper way to get to the International Space Station."

Unlike Dyna-Soar, the X-37 will always be unmanned. Without humans who would limit the amount of time it could orbit, the little spaceplane might be able to stay aloft for as long as nine months. Operationally, the X-37 could become a space version of a long-endurance unmanned aerial vehicle—the world's first space UAV.

Even with no astronauts, however, safety will be a big issue—in this case, for the payload. After the 2003 disintegration of the shuttle Columbia, mission planners developed concepts that would protect the X-37 from a similar fate: damage from insulation coming loose during launch. One idea had the spaceplane perched vertically atop a booster, an odd configuration that resembled an aerospace awards trophy. Still, the spaceplane would ride safely above any insulation that broke off.

But the aerodynamics posed a problem. "People learned thousands of years ago that you don't fly arrows with the feathers first," says John Muratore, NASA's former chief engineer for the canceled X-38, an emergency return vehicle for ISS crews. "Feathers in the tail are stabilizing and feathers in the front are destabilizing," he says, referring to the wings of an exposed spaceplane perched vertically atop a tall, cylindrical booster.

So the Air Force covered the new little spaceplane with a launch shroud. For now, two big problems have been solved: The rocket should fly right, and when they roll it out to the launch pad, no one will see that the X-37 is inside. Hidden. In plain view.

Michael Klesius is an Air & Space associate editor.


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Comments (17)

One possible role of the X-37, or whatever it eventually becomes, could be to rescue personnel from the ISS. It could carry a life-support capsule in its cargo bay and return under remote control or pre-programmed control to a suitable airfield. The cargo bay capacity sounds like it would be large enough to accommodate at least four astronauts in spacesuits.

If equipped with a remote manipulator such as the Space Shuttle's Canadarm, it could retrieve items from orbiting spy satellites, or play havoc with them.

Posted by J. A. Poth on November 18,2009 | 04:41 PM

The author considers the X-37 on top of its booster an odd configuration, but the X-20 Dyna-Soar was configured on top of the Titan III in *exactly* that configuration. Since the X-37 inherits from the X-20, that configuration should actually be *expected* (at least conceptually).

Posted by Luke Vaxhacker on November 18,2009 | 04:48 PM

At the speed its booster is accelerating, there wont by any air for the mini shuttles wings to grip after the first minute of flight. This is more about avoiding months of expensive aerodynamics testing to see if the concept itself is worth the trouble.

Personally, I think it is.
There are many rockets that put payloads in space, but only shuttles can bring them back. With this You get a ship that is better than the space shuttle in every way except payload and passengers.

If it works, I don't see why they shouldn't scale it up to carry 3 men and the mail to the ISS.
It would certainly be better than that dinky Orion capsule for the task. Better to save those for the moon shots.

Posted by Maxwell on November 24,2009 | 10:22 PM

The X-37 can properly be called the SPACE SHUTTLE, Jr. and it is certainly a rescue type vehicle which explains why the USAF has been so quiet about it. If you would like to see the SPACE SHUTTLE,Sr., you can view it at: http://www.cyrus-space-system.com or go to: www.NASA.gov > U.S. Spaceflight Review Committee (the Augustine)> Emails to the Committee > look for 6 entries by Daniel Sterling Sample. The SPACE SHUTTLE, Sr. will be capable of being launched from the ground at a velocity equal to one third the required velocity for low earth orbit (LEO) insertion.

Posted by Daniel Sterling Sample on November 25,2009 | 10:44 AM

Looks like an Orca.

Posted by nikolai on November 25,2009 | 04:30 PM

The heat generated during reentry isn't caused by friction but by compression. At those speeds (>Mach 25) air just does not go out of the shuttle's way, it will be compressed and hence heated.

Posted by J Willems on December 2,2009 | 06:13 AM

Speaking of feathered arrows, I have wondered why the Constellation concepts don't have "tail fins."

Posted by Freehawk on January 8,2010 | 01:24 PM

We (the U.S.) need this. If it's going to ride an Atlas V into orbit, then it's achieved a very special status--it looks like a concept about to join the realm of the real. I hope it isn't canceled like so many other X-whatevers.
Good luck to it, and congrats to those who designed and built it.

Posted by PX on January 25,2010 | 12:09 AM

There is a new simulator of the space shuttle available for the iphone!

Posted by Michael on February 4,2010 | 10:46 AM

USAF is putting an X-37 into orbit atop an Atlas rocket in March or April of 2010. This must be a prototype testing for a future "spaceplane". Meanwhile, NASA is floundering, directionless. To see THE SPACE SHUTTLE SENIOR (aka THE SUPER SHUTTLE), go to: http://www.cyrus-space-system.com GOOD RIDDANCE TO THE TROUBLED CONSTELLATION MOONDOGGLE!

Posted by Daniel Sterling Sample on February 4,2010 | 05:25 PM

The plot thickens! Now we learn that during the same week that X-37B is in orbit, the AF plans to launch an HTV-2 hypersonic vehicle from Vandenberg to Kwaj. I wonder if X-37B will happen to be overhead during the Mach-5 test vehicle's plunge back into the atmosphere?

Posted by Jim Oberg on February 23,2010 | 02:31 PM

The China's astronauts lunar landing could happen within 8 years and seen on standard and 3-D TV by over 6,000,000,000 people worldwide. However, the Constellation program is wrong, flawed and TOO expensive and the new "commercial space" is up to FIVE TIMES more expensive than the Space Shuttle. As a consequence, NASA and USA will face a deep DECLINE and, soon, will be no longer a space leader.

Posted by gaetano marano on February 23,2010 | 04:03 PM

The x-37 was designed to be launched in the Space Shuttle payload pay when it was a NASA project, so it was not tested for launch aerodynamics. The shroud also avoided weather and bird damage. The most important characteristic of the vehicle is the fact that it is reusable. It is intended to test technologies for a new generation of reusable spacecraft and launch vehicles intended to lower the cost of launching and retrieving satelites.

I can find little data on why it was abandoned by NASA and why it was picked up by DOD. One would think NASA would be interested in new technology for access to space.

Posted by Dan Woodard on May 16,2010 | 11:13 PM

This is not the Sixties. China is as capitalist as the US. China is an economic competitor, not an ideological adversary. China has no intention of engaging the US in a race to the moon, or anywhere else in space. If they lost, they would look incompetent. If they won, they would irritate their biggest customer.

China flies manned missions only about once a year, just a fraction of what would be needed for an aggressive "space race". The goals of their human spacefight program are 1) to market their civil aerospace technology, 2) to provide a source of national pride to overcome the still painful memories of two centuries of invasion. Their goal in space is not to race the US to the moon, it is to be invited to join the ISS program. They see the latter as a way of demonstrating that they are "in the club" of the world's industrial leaders, and at the same time to build trust and thus stability, which they see as the key to their own economic growth.

Posted by Dan Woodard on May 18,2010 | 11:55 PM

@Dan Woodard

I believe you are referring to the X-38 CRV (Crew Return Vehicle) that was designed to ride up in the Shuttle. That project was canceled back in '02/'03 due to budget shortfalls with the Space Station primarily. It was on-budget and on-time at the time they canceled the project. The main difference is that the X-38 was designed for 7 passengers, used a module for the descent burn (which then detached) and it used a parachute for the final descent phase.

Posted by Flame on October 20,2010 | 04:52 PM

I think this is one of the few times imo when privatization is a really good idea. Whether we think it’s necessary or not, we need to continue to develop new forms of space travel and technology to facilitate it. What the ppl whose only argument is “we have too many problems down here to be worrying about this,” they fail to understand the two most important implications of aeronautical research. The first is for national defense… it’s bad enough that nasa has to rely on Russia to ferry them to the ISS. If we keep going at this rate, our disadvantage will only grow as they continue to develop new technologies in their space program while we pump the brakes on ours. Is air and space superiority something you really want the Russians to have? It doesn’t seem like a good idea for any one country to have, let alone one whom we have a sketchy history with. The second is that with aeronautical research comes a flood of new technologies, most of which are very applicable to us down on earth. For example, if it wasn’t for nasa, we wouldn’t have the chips that we use for non-invasive biopsies, solar energy, and a whole litany of other things. And if you’re one of those ppl that are so skeptical (or cynical imo) that you still don’t think that any of the things on this list warrant a larger investment in a privatized space industry, just remember that while you sleep at night, you most likely have nasa to thank for that, too. If you use any type of home security system, chances are they use infrared and laser technology that came out of nasa’s research.

Posted by mason storm on November 29,2010 | 08:30 PM

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