In a statement on its website, Scaled, a wholly owned subsidiary of Northrop Grumman, called Thursday's incident "minor" and noted that SpaceShipTwo was not attached to the carrier aircraft, known as WhiteKnightTwo, at the time.
Aviation Week & Space Technology, an industry trade publication, is reporting that WhiteKnightTwo's left main landing gear collapsed on the runway. It was not known if the plane was taking off or landing at the time.
Scaled said no one was injured in the accident at a Mojave, California, airport. The Federal Aviation Administration is investigating.
WhiteKnightTwo began flying in 2008 and was making its 37th test flight on Thursday. The aircraft is designed to carry SpaceShipTwo to an altitude of about 45,000 feet.
The six-passenger, two-pilot spaceship would then be released so it can fire its rocket engine to punch through Earth's atmosphere, experience a few minutes of weightlessness in suborbital space and then land on a runway.
Virgin Galactic, which is selling tickets to ride SpaceShipTwo for $200,000 a seat, has signed up about 340 customers so far. The company is an offshoot of Richard Branson's London-based Virgin Group and hopes to begin commercial space operations in late 2011 or 2012.
SpaceShipTwo is based on a prototype known as SpaceShipOne, which made a trio of suborbital piloted spaceflights in 2004 to clinch a $10 million contest for private human spaceflight.
Scaled did not say how the damage to WhiteKnightTwo will affect the testing program for SpaceShipTwo and pilot training.