SpaceShipTwo Moves Closer to Powered Flight

1. The variable geometry tail is a work of genius but I do not think the hybrid rocket motor will prove as practical as all-liquid propulsion in a reusable.

   1. It is my understanding that they have abandoned the hybrid.

      1. The builder’s website still says “hybrid”:
         http://www.thespaceshipcomp…

         1. For the short term hybrids, but the long term plan is a switch to a liquid engine.

            Parabolic Arc writeup referencing Aviation Week –

            http://www.parabolicarc.com…

         2. http://www.aviationweek.com…

            “LauncherOne will be powered by a two-stage, liquid-fueled rocket, now in initial development by Virgin Galactic. The same rocket also is intended to ultimately replace the non-reusable RM2 hybrid motor that will power the SS2 to suborbit, Virgin says.”

            1. “Ultimately” … sounds like they are going into service with the hybrid even though they now realize that it is relatively expensive to refuel. Any specifics on the launcher one engine?

         3. Hey, give them another couple of years, and we’ll soon find out!

         4. Thanks guys! Maybe I’ll want to buy a ticket from them after all :_>

2. Folks:

   Don’t get the two programs mixed up here.

   SpaceShipTwo does and always will use the nitric oxide/solid core hybrid. Having safe, storable at room temperature propellent and oxidizer is a good choice for an inaugural service. Also, being able the shut down the motor at any time is a big safety plus. Maybe SpaceShipThree (the next version of a sub-orbital passenger craft) will use a completely liquid fueled rocket motor but it would have a new airframe with the center of gravity in the proper place for that type of motor.

   LauncherOne, on the other hand, will very likely be a liquid fueled rocket. Since the launcher will have to be completely self contained, the fuel would probably be hypergolic (hydrazine). I don’t think solids or LOX/RP1 are an option for a rocket that small. LOX requires topping up until right before launch and I have a hard time imagining Virgin Galactic trying to reproduce something like Orbital’s Pegasus. Not ‘disruptive’ enough! 🙂

   tinker

   1. Who says LOX? You can run a liquid engine using nitrous too. Add the engine, thrust structure and a kero tank. If lighter than the solid grain & chamber they replace, add ballast to move the c/g.

      1. Doc:

         Using nitrous oxide might be an OK oxidizer for suborbital flights but you’d take a serious ISP hit using it to try to make orbit. Either that or do it that way and take a hit on payload mass to orbit. There’s some good reasons to use LOX as an oxidizer the outweigh the hassles of using it.

         Maybe they could compress top-up LOX ‘on the fly’ once they’ve filled the rockets tanks the usual way on the ground. That might work.

         tinker

         1. LOX topping makes sese for an orbital launcher like LauncherOne, but as you said nitrous works for suborbital and SS2 is suborbital. Could an enginerun on either if the losses for nitrous were acceptable in thd suborbital configuration?

            1. Launcher One is orbital, intended for the small LEO market. The challenge for LOX would be limiting boiloff on the hour-long climb to drop altitude. New developments in insulation using aerogels and composites make this entirely feasible. Alternatively the LOX tank can be cooled by an LN2 loop from the carrier aircraft without requiring the umbilical to be sealed at launch. Scaled Composites lost three people killed in a nitrous oxide explosion while working on the SpaceShip One, so I don’t think they still believe it is as innocuous as originally claimed. Hypergols could be used but would be an expensive headache on a manned vehicle because of the morass of exposure controls required. While I agree they may stay with the hybrid for the moment it’s hard to see the CG being a big problem as the hybrid has such a large CG shift already. They could always buy an engine from Xcor.

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