13 thoughts on “Virgin Galactic Motor Progress”

  1. Nonsense. VG and SNC simply have a non-disclosure agreement. They’ve told Doug this a dozen times. I was sitting next to him one of the times they told him.

    It’s no surprise that they can talk about their own rocket development but not SNC’s.

  2. I’m assuming Trent’s comment is a joke because if RM2 engine development was going well, both SNC and Virgin would be publicizing the hell out of it.

    SNC says everything is proprietary, go ask Virgin. Virgin claims everything is proprietary to SNC and they can’t comment. It’s like a hilarious Catch-22?

    1. It’s a ridiculously common catch-22. I can’t believe it’s the first time you’ve ever dealt with two companies working together. Go ask ULA about XCOR’s progress on their LH2 engine, or vice-versa. Neither will be able to tell you anything that isn’t already in a press release. Now ask ULA about their next Atlas launch or XCOR about their Lynx progress, you’ll might have a hope of getting new information.

      1. If something is going well, there will be a press release, no matter the organizational challenge.
        It’s when something isn’t working out so good, that the PR starts getting fuzzy or
        non-existent.

      2. The problem, Trent, is that RM2 development is all over the map.

        There’s the rubber-nitrous RM2 engine that Sierra Nevada developed for Virgin. They’ve flown three times using it. But, they can’t go any further with it because of oscillations and vibrations.

        Sierra Nevada has been trying to fix that all along. There may be a way to do it, but it carries drawbacks.

        Scaled tested an alternative RM2 engine in Mojave two weeks ago that burns nitrous and nylon. That’s a potential solution, but more tests are needed.

        There have been other RM2 engines tested along the way of different designs. I’ve seen several of the tests conducted live. Branson is also touting a liquid-fuel replacement that is supposedly under development right now and providing what is probably a very optimistic schedule.

        The tests of different engines are all jumbled together on Scaled’s RM2 Hot Fire Summaries page as if they were testing a single design. There is so little detail in these summaries that it’s impossible to know what’s actually happening.

        The bottom line is if SS2 engine development was going well, both companies would be publicizing the hell out of how it. They’d agree on what videos and details could be released and then go about releasing them.

    2. Also there’s the fact that they aren’t offering service and haven’t been going suborbital in tests either. Those are facts that a nondislosure agreement doesn’t effect, which indicate that something is wrong with the rocket.

  3. I hope they solve their problems and that information about them percolates into the education system in the form of some case studies.

  4. I’m trying to think of a general solution to the hybrid burn rate problem, in which at large scales the grain regression might have the wrong feedback with burn rate (which I assume is basically what’s happening) so that pitted areas burn faster. If you treat the oxidizer flow as a fluid traveling through a pipe, the pressure is going to drop where the pipe narrows, due to the Bernoulli effect, and lower pressure is going to mean the burn rate slows down (due to the pressure exponent on the burn rate), causing the narrowed sections of the core to burn even slower, worsening the problem.

    One thing that immediately comes to mind is to mechanically ensure that the core remains relatively linear regardless of the local burn rates, perhaps by making the the core a rectangle instead of a circle and dividing the fuel grain into individual plastic bricks whose hot sides are pushed up against a mechanical stop, perhaps some kind of ceramic screen, as if each is being fed into a meat slicer. You couldn’t do that with a solid because you’d get a new burning surface in between the bricks and the motor would explode, but it might work in a hybrid where there just wouldn’t be enough oxidizer flow between the bricks to support much combustion.

    It wouldn’t be nearly as efficient at using space and mass, and mechanically it’s rather a horrible way to do things, but it might sidestep some of the issues in scaling up a hybrid.

    2. Well, that’s why I’ve never devoted much thought to the problems of hybrids. ^_^

      All the large ones seem to propel is horror stories about how they don’t scale up.

      My prior thought was that perhaps you could make the grain out of a nested bunch of layered plastic and rubber cylinders, graded by burn rate, so that the inside layer is rubber, and then you burn through to nylon, and then to a carbonate, etc., to try and create a stepped regression that roughly re-establishes a cylinder as the grain has to start on a new boundary. You could possibly combine it with a series of different oxidizers that favor the combustion of particular grain materials. But it’s still adding complexity with no guarantee that it would accomplish anything.

      My thought before that was to conduct the burn in stages and have a hydraulic ram and a drill head periodically re-bore the cylinder, which is equivalent to conducting a short burn of a section and then ejecting the rest of it to establish a new smooth surface, which is of course just dumping unused fuel on the way up like a liquid with a pipe leak.

      It would almost make more sense to feed plastic cords off a spool and into a modified liquid engine combustion chamber, or feed it in as a slurry, or better yet, break the plastic into shorter alkanes that are liquid at room temperature, pump them as a liquid, and call it RP-1 (short for Rocket Propellant). There wouldn’t be any waste, the combustion would be more stable, the tank wouldn’t have to take full combustion pressures, and refueling the rocket would be a snap.

  5. Another thought is that flow induced erosion doesn’t like to form straight lines, it likes to form sinuous shapes that meander like a river, equalizing the energy per unit length. Perhaps if a series of test burns were run with each partially burned grain used as the starting point for the next test (using the previous core as a mold and then adding some thickness back), they could determine what the low-energy shape of the core wants to be, and work from there.

    1. A lot of the instability in hybrid combustion seems to derive from the fact that the grains burn along the entirety of their I.D. lengths. If you mounted the oxidizer injector on a circular bulkhead the same diameter as the I.D. of the grain, but mounted well down toward the nozzle, you could make the burn area independent of the total length of the grain and keep it short enough to prevent the worst of the usual instabilities. This would also give the motor a more “liquid-like” as opposed to “solid-like” thrust/acceleration profile on ascent. To burn the entire grain you would, of course, need to put a ram behind the grain to push it, at a controlled rate, past the injector bulkhead and into the burn area. If you also had a ram of some kind behind the injector bulkhead, you could increase or decrease the length of the active burn area dynamically. Along with controlling the rate of grain feed into the burn area and the rate of flow of oxidizer into same, you would have the ability to throttle the engine rather deeply.

      All of this would add weight and complexity to the engine and would also reduce its maximum thrust; perhaps by enough, in combination, to render the notion counterproductive. Given the necessity for the fuel grain to slide along between the outer motor casing and the injector bulkhead, the ideal grain composition would probably not be something springy with a high coefficient of friction like rubber, but something comparatively stiff, yet slippery, like paraffin wax or the nylon-based formulation being tested by Virgin.

      As a final note, grains designed to slide within the engine during operation would seem to offer advantages with respect to ground operations and turnaround time. The nozzle hardware could be hinged to swing away and then back as a unit, allowing a fresh fuel grain to be slid into the engine casing and quickly closed up again.

Comments are closed.