The last week of October is marked by costly spaceship disasters. Orbital Sciences' Antares rocket exploded on Oct. 28 in its second attempt to carry the Cygnus cargo spacecraft, which was bound for the International Space Station (ISS). Fortunately, no one died in the incident.

Another disaster on Oct. 31 involved Virgin Galactic's SpaceshipTwo (SS2) and this time the accident killed one of two pilots. The incident occurred over the Mojave Desert in California at 10:10 a.m. PST during a test flight of the ship designed to carry tourists into space.

The SS2 dropped from its carrier vehicle WhiteKnightTwo from a height of 45,000 feet and then fired its engine. Two minutes later, however, the spacecraft encountered a problem causing it to plummet into the desert, killing one pilot and seriously injuring another. The pilot who survived managed to parachute to the group but the other pilot died on impact.

"Local authorities have confirmed that one of the two Scaled Composites pilots onboard SpaceShipTwo died during the accident. The other pilot parachuted to the ground, and is now being treated at a local hospital," Virgin Galactic said officially. "All of us are deeply saddened by today's events, and our thoughts and prayers are with the families of all those affected by this tragic accident."

It is not yet clear what exactly caused the accident, but Virgin Galactic pointed to a serious anomaly.

The ill-fated aircraft notably used a new kind of fuel never before used by Virgin Galactic: a plastic-based fuel. The SS2 previously used rubber-based fuel.

The new fuel was thought to provide longer burn and allow the SS2 to fly higher and give passengers a smoother ride. Kevin Mickey, president of Scaled Composites, which built the aircraft, however, downplayed the new fuel's role in the crash.

"We were flying a rocket motor today that had been thoroughly tested on the ground and had been through a qualification series, and of course we expected no anomalies with the motor today," Mickey said.

Prior to the incident, a tweet from Virgin Galactic revealed that there were some concerns about the weather, particularly the winds on the ground:

We’re still closely tracking the weather—mainly winds on the ground and aloft. Stay tuned for updates.

— Virgin Galactic (@virgingalactic) October 31, 2014

The Federal Aviation Administration (FAA) and the National Transportation Safety Board (NTSB) are investigating the crash.