Stuart Witt guns the motor of the white SUV known as Mojave One and drives it up a dun-colored mound of earth. From atop his wind-swept perch, the CEO of the Mojave Air and Space Port surveys a fleet of graders and other heavy equipment churning up 19 acres of dirt beneath a blue desert sky.

At the moment, it's just a sprawling construction site, but within two years, work will be completed on a pair of hulking buildings. One will be a fabrication facility for the world's biggest airplane. The other will be the hangar that houses it. "You're looking at something that's going to be fundamentally breathtaking," Witt says.

The official name of the mammoth aircraft is Model 351, but it already has a nickname: the Roc, after the mythological bird big enough to carry away elephants for dinner.

The record-breaking plane, which will have six engines and twin fuselages, is being built to carry a rocket to 30,000 feet. From there, the rocket will drop from the plane and blast into space. The first payloads will consist of satellites and other cargo, but the program's backers say the rocket will eventually carry passengers. The Roc will be a flying launchpad—government and private-sector customers welcome.

"For the first time since John Glenn, America cannot fly its own astronauts into space."

Incredibly, the project has been in development for more than eight years under total secrecy. Then, this past December, billionaire Paul Allen announced his Stratolaunch project to the world at a press conference in Seattle. When the space shuttle fleet was retired in 2011, the United States lost its only way to get astronauts off the planet. Stratolaunch is the latest private-sector initiative to try to fill that void. "For the first time since John Glenn, America cannot fly its own astronauts into space," Allen said in Seattle. "Stratolaunch will build an air-launch system to give us orbital access to space with greater safety, flexibility, and cost effectiveness, both for cargo and manned missions."

In the process, the Stratolaunch team hopes to build a new American spaceflight industry. But there are more than government contracts at stake: When the cost of launches decreases, more industry satellites, tourists, and science projects will reach orbit. Space will truly be open to the public.

To reach that lofty goal, Allen has assembled a team of mavericks from the private space industry to make Model 351 into flight-ready hardware. Scaled Composites, a Mojave-based firm founded by designer (and Popular Mechanics Breakthrough Award winner) Burt Rutan, will make the airplane. "To allow public access to orbit, we need to increase safety by a factor of 100," Rutan, who sits on the Stratolaunch board of directors, says. "I think airborne launch will be a significant part of the safety solution."

The rocket will also be made to order. For that, Allen approached PayPal co-creator Elon Musk, who founded Space Exploration Technologies (SpaceX). Building a two-stage rocket that will be dropped from an airplane is the kind of bold challenge that SpaceX was created to tackle, but hitting the specifications for mass, center of gravity, and other technical details will be tricky. "We're in what I call the rocket-design box," Gwynne Shotwell, SpaceX's president, says, "where we can be only so long and weigh only so much but still need to get a specific amount of payload to orbit. Piece of cake."

Flight of the Roc

In 2015, hangar doors wider than the length of a football field will slide open. The 600-ton Stratolaunch mother ship will lumber directly onto Mojave's Runway 30, which extends 12,500 feet through the desert scrub toward the windmills churning the air in the foothills of the Tehachapi Mountains. The Roc's gleaming white, 385-foot wings will cast long, slender shadows as the plane moves into the bright California sun.

When air traffic controllers clear the Roc for takeoff, its crew will throttle up six Pratt & Whitney 4056 turbofan jet engines, each of which generates about 60,000 pounds of thrust. The high-pitched turbine whine of a four-engine 747 reaches 140 decibels during takeoff. That's 20 decibels above the pain threshold—and the Stratolaunch vehicle will have two additional engines. The shriek of the Roc on takeoff will echo for miles—one good reason to base its development in the empty desert at Mojave. Accelerating down the runway will put some flexion into the wings, likely giving them a bit of a flapping quality as the plane takes off.

Mojave will host test flights. Paid space launches, scheduled to begin in 2020, will depart from Cape Canaveral, Fla. There the aircraft will carry a 120-foot rocket mounted to the bottom of the spar connecting the fuselages. The sight will be dramatic—an airplane with a wingspan greater than the length of a football field, carrying a rocket with wisps of vapor escaping from its cryogenic liquid oxygen tanks.

Allen envisions the system one day delivering as many as six people per flight into space. The passengers will buckle into seats inside a capsule at the rocket's tip. Assuming the capsule has windows, these paying customers will be treated to views of the receding Florida coastline and, after a steady climb, the curvature of Earth.

And then it gets exciting. Once at 30,000 feet, the Roc's crew will start a brief countdown and flip the sequence of switches that releases the rocket. The Roc's pilots will then veer away sharply to stay clear of the rocket's flight path.

Imagine tipping over your chair, and that brief but gut-wrenching free-fall

During the drop, the rocket's fins will pitch the rocket at a steep angle for its impending climb to space. The capsule passengers' orientation will shift: Imagine tipping over your chair, and that brief but gut-wrenching free-fall. And then imagine being slammed back into your seat by g-forces as the rocket's engines ignite, expelling a half-million pounds of thrust.

Once in space, 298,000 feet above the release point, the rocket will drop the first stage, and the second will fire, flinging the capsule (or 13,500 pounds of payload) the rest of the way into orbit. By then, the passengers will be floating in their harnesses.

Blastoffs From Altitude

A Pratt & Whitney PW4056 on a United Boeing 747 CC BY-SA 3.0/Piotrus

Launching spacecraft from airplanes is an idea that is as old as spaceflight. In the early 1960s, pilots—including future Apollo 11 astronaut Neil Armstrong—began shooting for the edge of space in X-15 rocket planes dropped from B-52 bombers. In the late 1990s, the Pentagon began investing in air-launch ventures to develop the capability of deploying a spy satellite over an unexpected hotspot or replacing a disabled sat. Private space companies have launched small rockets from converted civilian airliners and the cargo bays of military transport aircraft (see Why Air Launch?). But the concept has never before been tried on the scale of the Roc.

Rutan and Allen's earlier space collaboration now seems like a test run for Stratolaunch, both in terms of strategy and design. In 2004, a mother ship called the WhiteKnight carried a manned spacecraft, SpaceShipOne, to launch altitude. From there SpaceShipOne reached 328,000 feet and then landed under its own power. When Scaled was able to repeat the feat within 14 days, the company won the $10 million Ansari X Prize. Like the Roc, the WhiteKnight carried its payload between twin spars, but the Stratolaunch aircraft's cockpit is nested at the tip of one spar.

Allen won't confirm Stratolaunch's price tag, but he says it "is going to end up costing at least an order of magnitude more than what I put into SpaceShipOne [$28 million]." Allen and company believe that the hundreds of millions of dollars and the design challenges of the project will be offset by an "any orbit, any time" capability.

When launching a spacecraft to a target in orbit—say, a space hotel—a launch provider can either wait until the facility is overhead or launch, enter orbit, and spend days chasing the destination. But the Roc will be able to take off from any runway long enough to accommodate it, fly 1500 miles, and launch a rocket when the orbital facility is overhead.

The Stratolaunch team isn't speculating as to who or what will eventually hire the system to fly to space. "Paul has tasked us with getting the design moving forward," Stratolaunch president and former NASA chief engineer Gary Wentz says. "Right now we're not pursuing customers."

Scavenged History

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In early February a pair of United Airlines 747s from Victorville, Calif., landed at Mojave. They won't leave intact. The two aircraft will be cut to pieces and their parts repurposed for the Stratolaunch prototype, including the six engines that will be mounted on the Roc's wings. Engineers will also cannibalize the airliners' landing gear.

The Roc's airframe will be new, built of carbon fiber. Aerospace engineers are finalizing that design in Scaled's engineering offices in Hangar 78 at Mojave. "We've grown up with airplanes that are of a scale where you call 10 of your buddies over and say, 'I'm going to put this wing on today,'" Kevin Mickey, Scaled's executive VP, says. "Building an airplane of this size is more of a shipyard-type logistic challenge." So cranes and big jigs will be the order of the day.

"We're all aircraft guys; we love swoopy shapes."

The Roc is not regarded as pretty, even by its creators. "We're all aircraft guys; we love swoopy shapes," Scaled program manager Joseph Ruddy says. "But that's not this thing's job. This thing's job is to carry this rocket and drop it."

Engineer and test pilot Doug Shane, Rutan's successor as head of Scaled, says the team will fabricate as many identical carbon-fiber-skin sections as possible. "If you look at our products, it's very unusual to have any common geometry to any adjacent part of the vehicle," Shane says. With flat sides on the fuselage, Scaled can make panels and clone the part for use almost anywhere on the airplane.

Given Rutan's penchant for aviation firsts—aircraft based on his designs have set multiple round-the-world records—one might suspect he joined the Stratolaunch project partly because it gives him a shot at one last career-capping superlative. But Rutan strongly disagrees with that view. "It would be nice to not have to build the world's largest airplane to do the Stratolaunch mission."

For-Hire Rocketeers

No one at Mojave is currently building rockets at the Stratolaunch scale, so Allen turned to Elon Musk. His SpaceX skunkworks is brazenly rewriting the rules of spaceflight by creating and launching rockets quickly and cheaply.The company has already flown the Falcon 9 rocket, named for its nine main engines, and the Dragon space capsule into orbit. The company is now preparing for cargo flights to the International Space Station. Musk says manned flights could commence as early as 2014.

The Stratolaunch rocket will have the same diameter as the Falcon 9 (12 feet), but engineers will trim its length by about 60 feet. "We call it the Falcon 9 Shorty," SpaceX president Shotwell says. Engineers will stunt the rocket by taking out some of the barrel sections that they weld together to make up a typical Falcon 9.

Many elements of the design are not yet finalized. Even the number of rocket engines has not been settled: Shotwell wants to stick with nine engines; Wentz wants fewer. "Nine engines are not required for the performance or control of this rocket," he says. "Including them would add cost and mass."

They have to come to an agreement quickly, as the project is on a tight schedule. Wentz's timetable calls for Roc flight tests to start in 2015; flights with an actual rocket won't begin until 2020 in Florida.

No one will easily mistake the 1.2-million-pound Roc for the 605-pound 1903 Wright Flyer

Scaled must lure engineering and design talent to Mojave to staff up Stratolaunch. "The biggest challenge is finding the people who have the right mindset to do this kind of work, who want to take responsibility for the parts they do [create]," Ruddy says. "We have to adjust them to our culture. A lot of aerospace is geared to production-type mentality. The prototype world is a little different."

Stratolaunch suits Witt's vision of Mojave as the center of this prototype world, where cutting-edge aerospace companies have the room to innovate. "What brought the Wright brothers to Kitty Hawk was freedom from encroachment of the press, freedom from industrial espionage, and a steady breeze," Witt says. "The fact that we were able to keep this under wraps for nearly nine years says that we still enjoy the elements that took Orville and Wilbur to Kitty Hawk."

No one will easily mistake the 1.2-million-pound Roc for the 605-pound 1903 Wright Flyer. But if this astounding piece of engineering takes to the sky, engines screaming and rocket blazing, the aerospace pantheon will welcome a new aircraft—a very big one.

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