Virgin Galactic has sold 100 more space tickets

The current price of the fare is $450,000 per seat, well above the $200,000-$250,000 paid by some 600 customers from 2005 to 2014.

In total, the company has now sold 700 tickets, a spokesperson said.

"We are entering our fleet enhancement period with a clear roadmap for increasing the durability, reliability and predictability of our vehicles in preparation for commercial service next year," said CEO Michael Colglazier in a statement.

"Demand for space travel is strong, and we've been selling seats ahead of the pace we had planned."

Established in 2004, Virgin Galactic is seeking to cash in on the success of a high profile test mission in July, which saw Branson beat by a matter of days Blue Origin owner Jeff Bezos in their billionaire space race.

But since then, the company, which flies out of Spaceport America in the New Mexico desert, has faced setbacks.

In September, it was briefly grounded by the Federal Aviation Administration (FAA), which found the July flight deviated from its assigned airspace and Virgin Galactic did not communicate the "mishap" as required.

In October, Virgin said it was postponing by several months a mission with members of the Italian Air Force, after lab testing revealed certain materials used in its vehicles might have fallen below required strength margins, necessitating further analysis.

The company is currently in the process of enhancing its vehicles.

Unlike Blue Origin and SpaceX, its main competitors in the nascent space tourism sector, Virgin Galactic deploys a massive carrier aircraft that takes off horizontally, gains high altitude, and drops a rocket-powered spaceplane that then soars into space.

As a publicly traded company, Virgin Galactic is also required to be more transparent about its finances.

The cost of tickets on Blue Origin's suborbital New Shepard rocket, capable of roughly ten-minute hops into space and back, is unknown, but likely to be substantially higher.