28 thoughts on “SpaceShipTwo”

  1. It would be pretty embarrassing if SpaceX got a reusable sub-orbital rocket into commercial service before them.

  2. Rand,
    Do you think they went down a blind alley with the hybrid solids and will this have an effect on the SNC Dreamchaser ultimately too?

    1. Absolutely. It was a silly choice from the beginning. They aren’t safer. They aren’t more reliable. They’re not easier to manufacture. They don’t facilitate faster turnaround times. They’re certainly not higher performance than liquids.

    2. In my observation, the blind alley was their choice of an oxidizer with a very bad temper. Other liquid oxidizers could have been used that required some other means of pressurization, but wouldn’t be inclined to go high order if a feed line had a speck of dirt or shockwaves. Solid-hybrid prevents failure modes involving mixed fuel burning uncontrolled, but can do nothing if an isolated propellant misbehaves.

      Re: turn around times: opening up a chamber, inserting a rubber composite slug, and closing everything up again need not take that long with a good design and crew.

      1. But you must remember, they just had to win the X-Prize so they didn’t have time to do it right, but needed to cut corners to do it quick.

  3. SNC says there’s nothing wrong with their rockets, and plan to use them on the Dreamchaser.

    It’s it at least possible that Scaled’s problem is just excess caution?

    They are kinda banking on being “the safest”.

        1. Careful Trent, don’t attribute to malice what is likely pure stupidity. DN might need a citation to what “excess” means. He seems to have problems with what others of us learned in primary school.

        2. The day you bury 3 co-workers because something you were told was “Safe” wasn’t,
          perhaps you will then be able to judge VG in their caution.

          I think nobody at VG understood how hazardous Nitrous could be, and,
          once they learned, they discovered the hazard mitigation was not
          easy to put in

          1. Um DN, the workers were from Scaled Composite plus what Chris L says below.

            Further, for a guy that doesn’t know the first thing about Air Worthiness certification or the Carnot Cycle; I think you might want to stay clear of telling others about hazard mitigation in aerospace, especially on this blog.

  4. Well, I think one way to tell if going to launch in 2014 is how many SpaceShipTwo have they made:
    “In October 2010, TSC announced plans to build three WhiteKnightTwo aircraft and five SpaceShipTwo spaceplanes”
    http://en.wikipedia.org/wiki/SpaceShipTwo
    Did they make three motherships and 5 SpaceShipTwo which were planned?

    If they have 2 motherships and 2 SpaceShipTwo that seems pretty much like a minimal and any number up three motherships and 5 SpaceShipTwo would allow more confidence they are actually planning commercial flights in 2014. Because if they don’t duplicates, and resolve all issues, they would then be delayed by having build more planes and flight test them before they can really do commercial flights.

  5. The choice of a hybrid concerned me from the start because hybrid engines have a poor track record of scaling up without encountering problems with uneven burning.

  6. SNC has been walking back their position on hybrids for a while. I almost ruined a laptop by spitting out my drink when I saw their original Dreamchaser concept. Definitely not enough Isp to put something into orbit that’s a reasonable size, and once the “it’s safe” veneer fell away, the arguments for staying with it became few. Of course, it has the advantage of being able to fly with salami as a fuel, like the Mythbusters proved, though I don’t know what Isp that yielded. It will be very interesting to watch any conversion, considering how the center of mass point will change in SS2.

    1. Not sure what you’re on about. Dreamchaser was originally a SpaceDev project, and it never involved a booster. So far as I’m aware, their propulsion plans have always been hybrids and still is.

      1. I guess I’m ‘on about’ the original design for the Dreamchaser that was based on the X-34, only scaled up to carry people. The first version would be VTHL hybrid suborbital, but with the later addition of (hybrid) boosters, would lift people to orbit. I assume someone eventually did the math and realized a hybrid booster would be too large, switched designs to the HL-20 and boosters to the Atlas V. A short search understandably didn’t lead to any of the old concept drawings of the orbital version, but here’s a Space.com article showing the suborbital concept and talking about longer-term plans: http://www.space.com/347-spacedev-build-piloted-spaceship.html

  7. Parabolicarc.com is reporting that WhiteKnightTwo and SpaceShipTwo are currently airborne for another test flight, the first since September. It appears this will be another glide test, perhaps for crew proficiency. They’re going to need to really step up the flight test rate if they ever want to become operational.

  8. If you want a bit more in depth history of the hybrids, get hold of a copy of my article in the Summer 2012 Ad Astra.

  9. Scaling up may be a genuine problem for hybrids, but even with SpaceShipOne-size grains burning what amounts to a steel-belted radial with laughing gas literally blew chunks. The chunks are just bigger and more obvious in the case of SpaceShipTwo. There was an obvious combustion instability hiccup just after ignition on the first powered test flight that was flagrantly obvious on the video footage released. I hope VG is vigorously investigating some more reasonable – and stable – combination such as paraffin wax-LOX or paraffin wax-hydrogen peroxide. If scale problems still intrude, going to a two, three or four-chamber design would still allow for minimum disruption due to altered weight distribution. I don’t think small ball fiddling around the edges of the current design is going to work.

  10. I have worked with all 3 types in either design, operations, or manufacturing. Solids are great for amateur rocketry because they require minimal tooling and expertise and you don’t care about Isp or flat thrust profiles. Liquids are best for everything else. In my experience you do a hybrid project if you have limited resources, some solids experience, and you want to learn how to deal with liquids. Then you throw it away and go full liquid post haste. Hybrids have all the same valve, plumbing, backflow, injector optimization, pressurization, and lighting-a-candle-in-a-hurricane problems that liquids have qualitatively; just quantitatively half as many. And they have all the same casting consistency, regression control, burn-through, plugging, and extinguishing-something-that-really-wants-to-burn-once-lit problems that solids have. Just a dumb choice for SS2 and even dumber-er for DreamChaser.

      1. Hybrids are appealingly simple to the simple minded.

        If you think simple is the only metric, why don’t you just go to a solid?

      2. I did not see a schematic for Sapphire on the page, but here is something similar that calls itself valveless. As you can see, it’s not. Pressurant, purge, and check valves are still valves – ask SpaceX about that. Other things about this design that are not simple:
        * The chamber assembly is actually significantly more complicated than a liquid rocket of the same class, due to the 3-wall design with large pressure drops and cryo seals between each. This thing is going to squeeze the chamber like a corset prior to ignition. And how on earth will you instrument the regen layer?
        * “Before supplying the liquid oxygen, the [3-way] valve prevents pressure rising in the liquid oxygen tank by releasing gasified oxygen into the combustion chamber.” Um…
        * Since you’re regen cooling with oxidizer any burn-through, leak, or hard start blowback will feed itself, unlike fuel cooling where a chamber leak tends to cool itself due to the rich mix ratio.
        * And that chamber that can’t burn through and needs to fit and seal inside 2 pressure vessels? Oh yeah, that needs to be replaceable.
        * Also, this particular “valveless” system relies on a downward gravity (or force) vector to work. So you can rule out horizontal, parabolic, or free fall flight.
        * And even if it did, this sacrifices the supposed safety benefit of hybrids that they are easy to shutoff. You have to blow down the entire LOX tank once’s it’s pressed up.
        * Where does the igniter go?

  11. Keep in mind going commercial doesn’t necessary mean daily, weekly or even monthly flights. VG could do a single flight from Spaceport America and declare its commercial 🙂

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