Virgin Galactic's experimental commercial spaceflight vehicle crashed after experiencing an "in-flight anomaly" during a test flight on Friday. One person was killed and another was suffered serious injuries.

SpaceShipTwo took off with two pilots on board at 12:20 p.m. ET from Mojave, California in a powered test flight that the company called a "Halloween treat."

But less than an hour later, the company tweeted that something had gone wrong.

Virgin Galactic confirmed the loss of the spaceship but has given no other details about the cause of the accident, which occurred in the desert northeast of Los Angeles. SpaceShipTwo was running on a new fuel formulation, and officials said it had been "proven and tested on the ground" four times.

The incident occurred shortly after SpaceShipTwo separated from WhiteKnightTwo, which is the vehicle that carries the spaceship aloft. The WhiteKnightTwo landed safely.

SpaceShipTwo separated from its carrier aircraft, WhiteKnightTwo (left), then exploded in the air (right). Image: Kenneth Brown/Associated Press

Kevin Mickey of Scale Composites, the aerospace company that employed the test pilots, said the aircraft was "in several pieces" and strewn across the crash site when emergency responders arrived on scene.

"Space is hard, and today was a tough day," Virgin Galactic CEO George Whitesides said at a press conference on Friday afternoon.

The space tourism company, which has promised to shuttle hundreds of paying customers to orbit when it begins commercial flights next year, said it is working with authorities to determine the cause of the crash. The Federal Aviation Administration is investigating. Officials did not release the names of the pilots. Mickey said their families have been notified.

Richard Branson, founder of the Virgin Group, is en route to the crash site. Whitesides said Brandon would arrive to Mojave on Saturday morning. The National Transportation Safety Board is expected to arrive around that time as well to begin an investigation.

Thoughts with all @virgingalactic & Scaled, thanks for all your messages of support. I'm flying to Mojave immediately to be with the team. — Richard Branson (@richardbranson) October 31, 2014

A tough week for private spaceflight missions

The crash comes just days after an unmanned private cargo ship operating under a NASA contract exploded on launch. The Orbital Sciences Antares rocket was headed to the International Space Station to deliver supplies, but it blew up just six seconds after takeoff from NASA's Wallops facility in Virginia.

"It hasn't been an easy week," said Stuart Witt of Mojave Air and Space Port. "But this is where you find your character."

However, the Virgin Galactic crash on Friday is a setback of a different kind for the private space industry. Antares was designed to to carry cargo. SpaceShipTwo was designed to carry humans. Both instances are stark reminders of the complexities behind spaceflight.

"The future rests in many ways on hard days like this," Whitesides said.

Tragedy struck the Virgin Galactic team about an hour ago. Terrible news. Prayers for crew and families. — Mike Fossum (@astro_aggie) October 31, 2014

SpaceShipTwo was first unveiled on Dec. 7, 2009. Branson promised a few hundred people who had booked tickets to space that flights would begin within two years. The company has sold more than 700 tickets so far.

"I am not reconsidering, yet," ticket-holder Jim Clash told Mashable after the crash on Friday afternoon. "Rockets are a tough business — and they are risky."

Virgin Galactic has completed more than 35 test flights of SpaceShipTwo. Friday's test flight was the company's first rocket-powered one since January, when SpaceShipTwo reached its highest altitude yet with 71,000 feet.

Although Virgin Galactic has been the front-runner in the fledgling space-tourism industry, the program's suffered a number of setbacks. The timeframe for launch was pushed back to February or March in 2015. Branson is due to be on board on that flight. However, Friday's crash could bog down the program even more.

"Stay the course. This business is a worthy business," said Witt on Friday afternoon. "It's a cause far greater than one of us singularly. I equate it to the Magellan mission."

These vehicles are expensive to test and build but cheap to fly when compared to a typical space shuttle. SpaceShipTwo was the company's primary vehicle. As of April, Virgin Galactic was "pretty far along" in building a second vehicle. The company has said that it wants to build a spaceship fleet.

Inside the aircraft

Earlier this year, we got a close-up look at a full-scale SpaceShipTwo replica. The vehicle is relatively large in person (though tiny compared to, say, one of NASA's space shuttles) and will have enough room for six passengers and two pilots.

There's ample room inside for the seats and, when the time is right, moving about the cabin. There are also a lot of windows.

Inside the spacious SpaceShipTwo cabin. Image: Flickr, Virgin Galactic, Mark Greenerg

Details about the commercial flight

Unlike a classic spaceflight, where the rocket sits on a launch pad and blasts off into space, Virgin Galactic's SpaceshipTwo is attached to the belly of an airplane. The plane flies to an altitude of approximately 50,000 feet and then releases SpaceshipTwo.

The spaceship free falls for a few seconds, then the pilots light up the vehicle's hybrid rocket motor, which burns for about a minute. It "accelerates you from not very fast to the speed of sound in about seven seconds or so," said Vice President of Special Projects at Virgin Galactic Will Pomerantz.

When the engine stops firing, you’ll be traveling at Mach 3.5 (more than three times the speed of sound). During this time you are traveling completely vertical. When you reach the peak altitude of your flight, you'll be higher than 76 miles above Earth's surface, the boundary that NASA defines as the edge of our atmosphere and the beginning of space.

For the next four-to-five minutes, you can unbuckle your seatbelt and float about the cabin. Virgin Galactic said will train its astronaut passengers on how to orient themselves in zero gravity and float without bumping into each other.

An hour-and-a-half later, you're back on the ground, in the same New Mexico facility from where you first launched.

Virgin Galactic has touted the safety of its launch procedure. "If there were any problems during the boost phase, the rocket motor could simply be shut down and the spaceship would return as a glider to the runway," the company's website says.

Amanda Wills, Lance Ulanoff, Brian Ries and Jonathan Ellis contributed to this report.