I think I have an idea about the propulsion system that SpaceShipTwo (SS2) will use and with so many things in life the information that took me down this particular route came my way sort of out of the blue
Oddly, in a bizarre twist of fate, Clark Lindsey mentioned in his blog a rumour he had heard that Virgin Galactic would use a wax based solid fuel for the hybrid rocket motor many people believe is planned. Investigating the propulsion options for SS2 back in 2006 I asked Will Whitehorn about the possible use of a wax, well paraffin really, based solid fuel and he took demonstrable enjoyment in telling me, “no”
I had come across various reports of solid fuel research including material about Stanford University and NASA’s involvement but it wasn’t until a few days before Clark’s blog post that I came across some key information in southern France, of all places
Now I am focusing on the solid fuel because I think the oxidiser is likely to remain nitrous oxide despite the accident that occured in July 2007. The most obvious alternative to nitrous oxide is liquid oxygen (LOX) but while it does provide better motor performance it presents difficult handling issues
As USAF chief scientist Mark Lewis explained after our interview earlier this year, LOX can spontaneously combust, even small drops of it
That is not to say there are not other alternatives. There is nitrogen tetroxide (N2O4) and there is hydrogen peroxide (H2O2) but both are highly reactive and present handling issues just as LOX does
So coming back to the solid fuel, we know SpaceShipOne used Hydroxyl Terminated Polybutadiene (HTPB) but what are the alternatives to that?
Now maybe Burt Rutan and his team of engineers will surprise us and go for a wax based Paraffin, HTPB fuel, which would mean Clark’s rumours are sort of correct?
But I think HTPB with a hydride additive is the option Scaled Composites could take. In the work that I have seen with solid fuels in Europe HTPB with Aluminum hydride (AlH3), or Alane as it is also known, shows extremely good performance improvements over a pure HTPB motor. Metal particles, including nano aluminium, as an additive to HTPB are not as good
So you heard it here first, SS2′s propulsion system may well be N2O and HTPB/AlH3
Alane also has a public relations advantage for Virgin Galactic as this hydride is viewed as a hydrogen storage technology and the mass media is alays ready to grab on to the hydrogen economy as a panacea for all of humanities ills
As to why I have been talking to European solid fuel experts, I will leave to your imagination