Due to technical difficulties I have been unable to blog live but a video recording of the key part of the press conference will be available later today
However I can report that;
Burt Rutan, looking frail after a recent illness, said that they still did not know what caused the accident at Scaled's facility last July but they were working with Californian authorities and aerospace consultants to find out. Once a cause was found that would be published.
Talking about the twin-fuselage White Knight II (WKII) the aircraft, when not carrying SpaceShipTwo, can make a 6g descending wind up turn and that can be used to give passengers g training prior to their flights. Using parabolic flight the WKII will also simulate weightlessness for a few seconds
Burt Rutan said that on reentry passengers will experience 4g and above for 20s and that the build up from microgravity to 1g will be 20-25s.
More soon, including that video
"Burt Rutan, looking frail after a recent illness, said that they still did not know what caused the accident at Scaled's facility last July but they were working with Californian authorities and aerospace consultants to find out. Once a cause was found that would be published."
What caused the explosion is the fact they're using liquid nitrous oxide instead of liquid oxygen or hydrogen peroxide. Saying you don't know the cause of the explosion yet still proceeding with construction of SpaceShipTwo as designed is incomprehensible to me.
In Burt's defence he did say, in response to questions, that the propulsion system could be redesigned following the investigation's outcome.
But if they are saying that it was just a cold flow gas test, what is there to redesign?
Scaled and Virgin also said that the components in the test "were not specific to SS2". So I guess they are trying to reuse SS1 parts.
I think for the greater thrust needs of SS2 the N2O has to be injected at higher pressures and this higher pressure containment combined with the heat of the Sun on 26 July led to decomposiiton and the explosion.
Rob.
Below is a link to a 1935 paper that documents the explosion potential of nitrous oxide. Extrapolating from the data in the paper, eliminating the explosion potential of nitrous oxide requires storing it at pressures too low (under 13 atmospheres, 188.5 psi) to make it practical as an oxidizer for large scale rocket systems.
http://www.iop.org/EJ/article/0959-5309/48/1/326/prv48i1p189.pdf?request-id=0PAS-PnJ3BG0c7MJ3Ai7Kg
Under the right conditions a detonation wave can be initiated in liquid nitrous oxide that will propagate all the way back to the storage tank unless a check valve or some other form of trap stops it. It appears in the case of the July 2007 explosion at Mojave there was nothing to stop the propagation of the detonation wave all the way back to the tank.
An alternative is using concentrated hydrogen peroxide as the oxidizer for the hybrid motor (or perhaps eliminating the hybrid portion altogether and running the motor just as a monopropellant). A thin wall tank for the peroxide could be used with a turbopump system feeding the peroxide to the motor (just like the Germans did back in WWII with the Me163A and Me163B Komet).
Using concentrated hydrogen peroxide, thirty years ago lone individuals working on shoestring budgets instead of multi-million dollar funding designed and built fully throttleable fully reuseable rocket motors for dozens of manned rocket vehicles yet managed to never blow up anybody.
http://www.draglist.com/stories/SOD%20Mar%202002/SOD-031402.htm
http://www.arvilporterprojects.com/index.htm
http://www.dragracingonline.com/features/miller_1.html
The first manned hybrid rocket vehicle of any kind – air or ground – was the Budweiser hydrogen peroxide rocket car.
http://www.artemisimages.com/gallery.aspx?photomode=3&categoryid=4255
In terms of propulsion system, The Blue Flame land speed record car with its throttleable reuseable hydrogen peroxide and liquid natural gas motor remains the most sophisticated private manned rocket vehicle.
http://members.aol.com/KingstonChas/TheBlueFlame.html
My partner Ken Mason and I have been working with liquid rocketry for many years and N2O2 in all it's forms has a history of unkonwn detonations. It is a molecular thing that would take time and money to isolate by a team of very competant chemists. This is a fuel with a demon in it because it is really a monopropellant. All demons can be be beat with time and money. NASA turned away from N2O2 in the 1950s and 60s because they didn't have time to play with it because of the time constraints of the space race with the Soviets.Glen May a close friend of mine was killed in the explosion at Mojave and knowing Glen he would be quite disapointed if SS2 became a hanger queen. Pioneering efforts by man have always been expensive. Somtimes they cost lives but over all they are worth it. People die everyday for lesser things.I know Glen May would agree with me. It is not Rutan's fault things like this happen but it is his fault if he lets his dream fall away because bad things happened. Rutan can make it work but his company is going to have to spend some money and Branson is going to have to wait a little longer. They have nothing to fear as all the other so called space tourism companies aren't any closer to launching clients no matter what they claim. A year or 18 months of focused work won't make any difference. A propulsion redesign will deal a death blow to the entire project. Franklin Ratliff is right about alternatives but if you are going to spend money and time fixing things, fix what you have. If this project fails it may put off personal space travel for decades and isn't progression into space what we all want? Scaled Composites and Burt Rutan have given this nation great things. I hope Rutan can buck up, pull it together and not beat himself up over this. Knowing Glen for years I know he wouldn't have wanted that.