For the more than 500 space tourists who have signed up for a trip on Richard Branson’sVirgin Galactic, Monday was a milestone: the spaceship that will be carrying them aloft made its first powered flight and broke the sound barrier for its first time. In a telephone interview after the test flight over Mojave, Calif., Mr. Branson said the craft would go to space at the end of this year or in the first quarter of next year. He and his children are to be the first passengers. Over the past two and a half years, SpaceShipTwo has made a series of unpowered tests, gliding to a landing. On Monday, a carrier aircraft lofted SpaceShipTwo to 47,000 feet before letting it go. The engine fired for 16 seconds, accelerating SpaceShipTwo to Mach 1.2 — 1.2 times the speed of sound — and pushing it to an altitude of 55,000 feet, about 10.5 miles. More test flights will follow before the start of commercial operations.

Richard Branson's Virgin Galactic intends to take passengers into space later this year (Link to video: Virgin's SpaceShipTwo makes first rocket-powered flight)

A spaceship bankrolled by Sir Richard Branson made its first powered flight Monday in a test that moves Virgin Galactic toward its goal of flying into space later this year.

While SpaceShipTwo did not break out of the atmosphere during the test flight, it marked a significant milestone for Virgin Galactic, which intends to take passengers on suborbital joyrides.

During the early morning flight, SpaceShipTwo, strapped beneath a twin-fuselage jet, took off from an airport runway in the Mojave Desert north of Los Angeles. The jet released SpaceShipTwo, which ignited its engine for 16 seconds, then glided to a safe landing.

Until now, SpaceShipTwo has only performed unpowered glide flights. Several powered flights are planned this summer, culminating with a dash into space targeted toward the end of the year.

SpaceShipTwo is the commercial version of SpaceShipOne, which in 2004 became the first private manned rocket to reach space. Since the historic flight, more than 500 aspiring space tourists have paid $200,000 or plunked down deposits, patiently waiting for a chance to float in weightlessness and view the Earth's curvature from 62 miles up.

Branson initially predicted commercial flights would begin in 2007, but a deadly explosion during ground testing and longer-than-expected test flights pushed the deadline back.

No date has been set for the first commercial flight from a custom-designed spaceport in New Mexico, but Virgin Galactic executives have said it will come after testing is complete and it secures approval from the government. Branson previously said the maiden passenger flight will carry his family.