CAPE CANAVERAL, Fla. — Hoping to give customers a higher ride aboard its suborbital, six-passenger spaceship, Virgin Galactic will switch to an alternative plastic fuel rather than the original rubber propellant used by the prototype SpaceShipOne a decade ago and in SpaceShipTwo’s powered test flights.
The company, an offshoot of Sir Richard Branson’s London-based Virgin Group, expects to make the change from hydroxyl-terminated polybutadiene rubber-based fuel grains to a type of thermoplastic called polyamide that was developed by Mojave, California-based Scaled Composites, designer and manufacturer of SpaceShipOne and SpaceShipTwo.
“We’ve tested both of these fuel grains a lot,” Virgin Galactic Chief Executive George Whitesides said.
“Both of them have been good, but we’ve gotten better indications of performance with the polyamide. We think it will get higher performance for our customers, and so will result in a higher apogee, which we think is an important thing for the different users who will be using the system,” Whitesides said in an interview.
Both fuels burn with nitrous oxide. Virgin Galactic is developing an all-liquid engine for its orbital LauncherOne small-satellite launcher.
Whitesides said the decision to switch SpaceShipTwo’s fuel was not in response to recent questions about whether the vehicle would be able to reach at least 100 kilometers, the so-called Karman Line that the International Aeronautical Federation considers the boundary to space.
Although Virgin Galactic has repeatedly said its customers could expect to reach at least 100 kilometers in altitude aboard SpaceShipTwo, the company’s service agreements stipulate a minimum height of at least 50 miles, or 80 kilometers. Whitesides said that has been the case since Virgin Galactic first began selling rides on SpaceShipTwo about nine years ago. So far, more than 700 people have paid or put down deposits to fly on SpaceShipTwo, with ticket prices now selling for $250,000.
The vehicle’s hybrid engine, manufactured by Sierra Nevada Corp., will need to undergo what Whitesides called “minor tweaking” to accommodate the plastic propellant.
“We think we can maintain schedule,” Whitesides said, with the next powered flight of SpaceShipTwo expected this summer.
“We just need to tweak the plumbing line in the motor to go with the plastic, which is sort of a minor mod,” he said.
No repeats of the spaceship’s three previous powered test flights are planned.
“We’ve been planning for this,” Whitesides said, adding that Scaled’s permit application to the Federal Aviation Administration includes use of both types of fuel grains. “We’ll be able to go able to go straight up to our PF (Powered Flight) 4 goals … and we’ll just keep expanding the envelope out to about 60 seconds” of engine burn time.
As to whether additional motor modifications or changes may be coming for the rest of the SpaceShipTwo fleet — Virgin Galactic has announced plans for five — Whitesides said the company’s goal now is to get the first one flying.
“We’ve always said that we’re going to keep on improving our engine over time. Our main focus now is getting this ship into service,” he said.