WASHINGTON — Virgin Orbit, the spinoff of Virgin Galactic that is developing the LauncherOne small launch vehicle, is now planning a first flight of that rocket in the first half of 2018, the company said Aug. 1.

Virgin Orbit updated the timetable for LauncherOne in a statement announcing the arrival of the rocket’s carrier aircraft, a converted Boeing 747, at Long Beach Airport in California, where Virgin Orbit has its manufacturing facility. The plane recently completed an extensive modification program to serve as the air-launch platform for LauncherOne.

When Virgin Galactic announced LauncherOne in July 2012 at the Farnborough International Airshow in England, it planned to use the same WhiteKnightTwo aircraft built for the company’s SpaceShipTwo suborbital spaceplane. The original intent was to minimize development by focusing on only the launch vehicle.

The company changed direction in December 2015 when it announced it was acquiring a 747 to serve as a dedicated aircraft for LauncherOne missions. The 747, previously in service as a Virgin Atlantic jetliner and known as “Cosmic Girl,” underwent extensive inspections and modifications in Texas to serve as the launch platform for LauncherOne. Those modifications include the installation of a pylon between the left inboard jet engine and aircraft fuselage where LauncherOne will be mounted.

Those modifications are now complete, and Virgin Orbit, spun off from Virgin Galactic in March, said that the aircraft has now received an experimental airworthiness certificate from the Federal Aviation Administration, allowing test flights to begin.

“Cosmic Girl, our first stage to orbit, is finally home,” Virgin Orbit Chief Executive Dan Hart said in an Aug. 1 statement, a day after the aircraft flew to Long Beach. “Virgin Orbit is in the home stretch of integrating our LauncherOne rocket and ground systems for launch and to support our customers’ missions.”

“It has been amazing to watch Cosmic Girl transform from a commercial airliner to a flying launchpad,” Tim Buzza, vice president of launch for Virgin Orbit, said in the same statement. “We are excited to begin our flight test program and continue towards our vision of launching anyone, anywhere, any time.”

The flight test program, and initial launches, will take place from the Mojave Air and Space Port in California. Those launches, the company said in the statement, are now expected to begin in the first half of 2018.

Earlier this year, when Virgin Orbit spun out from Virgin Galactic, company officials still believed that an initial launch could take place by the end of 2017. In a presentation at the Small Payload Rideshare Symposium at the Applied Physics Laboratory in June, a NASA presentation listed a December 2017 launch for the LauncherOne mission under contract through the agency’s Venture Class Launch Services program.

LauncherOne, in its current configuration, can place about 300 kilograms into a 500-kilometer sun-synchronous orbit. In a June 21 panel discussion on small satellites held by the Center for Strategic and International Studies, Richard Dalbello, vice president of business development and government affairs for Virgin Galactic, said the estimated price for a LauncherOne mission was “about $12 million.”