Officials decided this spring to modify the space plane’s rocket motor to use a different type of fuel. Instead of burning a rubber-based fuel mix known as HTPB used on SpaceShipOne and SpaceShipTwo’s initial test flights, Virgin Galactic selected a new propellant grain known as polyamide which officials said offered improved performance.
“This was a new fuel formulation that had been proven and tested on the ground many times,” Mickey said in a press conference.
Let us hope for Virgin's sake that "many times" doesn't mean six times for ten seconds each.
I have heard of one long duration test on the plastic fuel reported by the "Virgin watchers" in Mojave, so unless they are doing long duration tests somewhere else it doesn't seem like much. Rocket engine testing is extremely noisy so long duration tests are quite noticeable.
“This was a new fuel formulation that had been proven and tested on the ground many times,” Mickey said in a press conference.
http://spaceflightnow.com/2014/10/31/virgin-galactics-spaces...