Oct 312014

Virgin Galactic’s Spaceship Two exploded over the desert, killing one pilot injuring the other.

Virgin Galactic’s SpaceShipTwo crashes, at least one pilot killed

At this stage, it *seems* that there was an explosion right after the spaceplane ignited its hybrid rocket and that the vehicle tore apart, with one pilot coming down under a chute.

Coming so soon after OSC’s Antares blew itself to bits right off the pad, it’s expected that some eyebrows will be raised about whether something fishy might be going on. While that’s always possible, a simpler explanation is that both suffered from the deficiencies of their propulsion systems. NOTE: I have no special insight here, this is all speculation on my part.


The first stage of the Antares uses two Aerojet AJ26 rocket engines… which are refurbished Russian NK-33’s. More accurately: these are *Soviet* NK-33’s, built about 40 years ago, transferred to Aerojet, stripped and rebuilt. *Any* mechanism that old will need some careful looking-over. And while having them refurbished is good, they were refurbished by a different company that built them, with little to no tribal knowledge. All kinds of problems can be introduced here.


The SS2 uses a hybrid rocket motor that has been troublesome for *years.* Virgin Galactic has recently switched from the original nitrous oxide/rubber (hydroxyl-terminated polybutadiene, commonly used as a binder in large rocket motors, and perhaps better known as tire rubber) propellant combo to one using “plastic” (polyamide, like nylon). This was due to the engine not providing the performance it was supposed to. Rumors I’ve heard held that the original engine fell *way* short, and shook really, really badly, to the point of worries about injuries or structural damage due to the harsh vibrations. This, sadly, is a not-uncommon problem with hybrids. And this new engine has not flown much (if at all) prior to this flight. It would not surprise me if there was a hard start (basically a small detonation on startup) and the plastic-based fuel cracked or shattered. This would eb all kinds of bad, especially if a chunk got caught in the motor throat. This would cause the chamber pressure to spike until it burst. Additionally, nitrous oxide is occasionally rather twitchy. While often considered fairly sedate by liquid oxidizer standards, there’s a problem: the triple point is just under 100 degrees F. This means a tank of compressed liquid N2O is happy forever with a pressure of 800 psi or so, but if the temperature rises to about 100 degrees, the liquid N2O will flash to gaseous N2O and the pressure will climb to 10,000 psi or so. This *probably* wasn’t what happened here, as the vehicle had been dragged to 50,000 feet or so by the White Knight carrier plane. But the air temp at 50,000 is really, *really* cold, so it may be that the plastic fuel was also very cold… and thus, perhaps, very brittle.

If Virgin Galactic pulls through this, they will have to do some serious redesign. Hundreds of rich folk have given them large sums of money for seats; I can see a whole lot of legal hijinks as various celebs or their legal counsels try to back out or start making demands. It seems to me that VG would be well advised to simply bail on the hybrid rocket. The system has been troublesome for a decade… and its not the first time it has killed people.

VG might do well to consider changing to a liquid bipropellant rocket system. Ironically, perhaps their best choice for such a system would be to contract for such a system from XCOR Aerospace. XCORs engines appear to be the most reliable around… perhaps not the most bleeding edge in terms of weight and performance, but if you don’t need the absolute maximum in performance (and a suborbital vehicle is far more tolerant of performance shortfalls than an orbital vehicle… how many passengers would even notice if the craft only attained 98% of predicted apogee?) and you *do* need the absolute maximum in terms of not-blowing-up, then XCOR seems the way to go.

The irony, of course, is that XCOR was just about the only competition VG had in the suborbital tourism market in the form of their Lynx rocketplane, which is under construction now.


Today is a bad day, have no doubt. A pilot was lost (and another seriously injured). A vehicle was lost. A whole program might well be lost. And perhaps worst of all, long term, is that something horrible has been gained: an excuse by regulators and bureaucrats to add yet more layers of laws on top of this, perhaps heading towards simply banning civilian manned rocket flight in the US. And with the wonders of ITAR regulations, it may well be that American rocket companies, banned from flying in the US, will be banned from transferring launches outside the US. And thus space tourism will belong to other nations, less risk averse.

An aside: I’ve got CNN running right now. Like a silly, naive person, I was hoping that they might have some useful information. But… no. Just the usual blather you get from talking heads who have to fill air time but who have minimal data to impart. Sadly – and inevitably –  they’re subtly smack-talking private industry, questioning whether there was insufficient regulation and government oversight

 Posted by at 1:25 pm
  • Anonymous

    Shades of Gilles Villeneuve’s loss in 1982 during a Formula One event. Poor devil met his end still strapped to his seat..

    • Nh_flier

      And thus the Graudinan fails to live up to its own piteous standards. If they weren’t so convinced that they (and their counterpart in the U.S., and France, and every other place I’ve ever been) are the sole arbiters of how the world does and/or should work, they would be merely amusing, rather than frightening.

  • Bob

    Nope, it was a bad week for the Home Team. There is no joy in Mudville tonight.

  • Anonymous

    This pic from AP implies it was a pretty big bang as you can see the “shuttlecock” just falling to bits in the windstream.

    • Anonymous

      I can’t really make heads or tails of what I’m seeing here other than a bunch of debris. It *kinda* looks like it’s flying *backwards* at this point. In which case, the fault need not have been the propulsion system, but perhaps a control issue. Whatever the cause, if the vehicle flipped ass over teakettle, the dynamic pressure it going to convert it into a cloud of junk, explosion or no.

      • Anonymous

        The other pictures in the series show a clean drop, the usual ball of fire when that style of motor is lit, and in the last pre-boom pic clear Mach diamonds, implying stable supersonic flow through the motor. VG’s own page has a witness saying the motor started, stopped, started again, then went boom. I think your fractured-fuel hypothesis bears some serious inquisitiveness.

  • Anonymous

    “Sadly – and inevitably – they’re subtly smack-talking private industry,
    questioning whether there was insufficient regulation and government

    I hate stupid people. Especially whiny, need-a-mommy-state, stupid people.

  • Jon Risque

    I keep hearing “The pilot ejected”…. Do they mean he was ejected?

  • Rick

    I’m thinking, we’ve actually had it pretty good for so long, that we might have been taking success and safety for granted.

    We “knew” there were risks but SpaceX having an absolutely amazing record of not only launch but vertical recovery testing, autonomous orbital spaceplanes, and other successes.

    Now we’re reminded, we KNOW that “rocket science is hard” and dangerous. And totally worth the risk.

    I don’t like to misinterpret “odds” but I think we were “due”.

    • Brianna

      Shhh… don’t remind them. It would burst their little bubbles to think that their magic regulatory agencies can’t make life completely safe by fiat.

  • Jon Risque

    Isn’t this the best scenario for an “anomaly” One pilot has survived so hopefully he’ll recover and tell what he experienced…SS2 was destroyed but not WK2.. The second SS2 isn’t finished so maybe it can be modified or a new engine. More attention will be paid towards the next SpaceX launch. I know one lady who is signed up, put down money and she understands the risks involved and accidents like this will happen. There might be a few who bail out but I think many will stay positive until it either flies or is cancelled. But maybe I’m being naive..

  • Dave Salt

    I thought the greatest danger from N2O was its exothermic decomposition. Like HTP, it’s a mono-propellant at these pressures… something VG found out the hard way in the 2007.

    Having said that, images of the wreckage seem to show the N2O tank reasonably intact and so maybe it was a ‘hard start’ that caused the break-up?