Thoughts from Trent Waddington. I’m on pretty long record of thinking that hybrids were a mistake, as was Scaled attempting to develop in house. The Mojave accident could have provided an opportunity to rethink the approach, but I guess they didn’t want to bite off the vehicle redesign issues of going to a liquid, and as Trent says, much of the sales hype has revolved around the supposed safety of hybrids. But as Dave Salt notes in comments there, continuing down that path will put them at a competitive disadvantage in terms of ops tempo and cost.
17 thoughts on “Is Scaled Having Engine Development Problems?”
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From what I hear, they are. Trent’s article asks good questions, and the answers aren’t apparent. But the problem is bigger than he poses, and his suggestion that better engines are now “available” is a little short of the mark.
From what I know, SpaceShip 2 weighs about 30,000 pounds. The X-15 weighed 33,000 pounds, and had a 57,000 pound thrust engine. Now, the flight profiles of the two vehicles are completely different, but that doesn’t change the problem significantly. There are only two “existing” alternatives to their engine which can deliver the performance they need: the NK-39, and the RD58-M. The first has over 90,000 pounds thrust (but can be throttled), the second a little over 19,000 pounds thrust (but can, of course, be clustered, and is in production).
You need a big engine (or a small cluster of relatively big engines) to do the job, but they are available…but not in this country.
Also, hybrids are MOSTLY safer than either liquids or solids. The single exception of which I’m aware is the nitrous hybrid. I’ve built some nitrous rockets, and seen others. They explode more often than any other kind of rocket, and no one knows why. I’ve had some nitrous explosions myself, and wouldn’t use the stuff for a large propulsion system.
An origional SpaceX Merlin (before the thrust upgrades) would be about the perfect size for the SS2. The problem is that LOX won’t work in the composite SS2 tank.
Is Scaled going directly to their big engine from the get go? Even the X-15 used the same motor going back to the Bell X-1 during it’s early testing. It seems like Scaled would also want to just break mach a few times to shake the airframe down. Seems like you could put some solids together and shift the weight to simulate the hybrid system it has replaced. Then, give yourself some time to get the full up hybrid engine in order.
Wow didn’t know that. I was an avid drag racer for a while. Lots of wicked stories I can tell about nitrous explosions. Many a fiberglass hood popped straight up into the air from a backfire out the manifold.
It seemed to me that Scaled should have switched to LOX/HC, like many other new space companies concluded around that time (after serious experience and consideration). There were many options, XCOR being the obvious one. Now they have kind of set themselves up to fail.
If they did not have the adaptability/developmental freedom to make such changes as demanded by the real world, then their odds of success were not going to be that great anyway. Even with good marketing, they still needed a good design to work from.
Gee, it looks like Virgin Galactic is becoming the new NASA, at least in terms of the Monday morning quarterbacks 🙂
What’s the sport without the cutting edge commentary? =-P
Engineering design is not noted for being forgiving nor sensitive to the the thoughts and feelings of engineers.
As engineers know only too well – reality does not give a s**t what you think, nor is reality into group hugs.
What Pete said. Anybody anxious enough to need a hug box can move up to San Jose and join the Aspergers Club there.
They should have totally rethought their propulsion philosophy when they had the accident, and I agree about XCOR, they are right next door and would be an excellent solution.
They should have totally rethought their propulsion philosophy when they had the accident, and I agree about XCOR, they are right next door and would be an excellent solution.
Just out of curiosity…
Is it possible that Scaled and/or Virgin Galactic did rethink their propulsion philosophy and contacted XCOR but was unable to come to satisfactory terms for some reason?
Perhaps we’re not giving Scaled/Virgin Galactic enough credit.
Is it possible that Scaled and/or Virgin Galactic did rethink their propulsion philosophy and contacted XCOR but was unable to come to satisfactory terms for some reason?
Anything is possible, but based on my own knowledge of the principals involved, I think it unlikely.
I think that the problem was that they were unwilling to do a major redesign of the airframe to accommodate an entirely new propulsion concept (and didn’t want to accept the PR consequences of refudiating (to use Governor Palin’s wonderful neologism) their hybrid hype). They may be regretting that now, but I think that’s how they got to where they are.
Ohhh, it seems I’ve created a sewing circle. *I* heard there’s some bad blood between Jeff and Burt. 🙂
Success requires a lot of failure. Failure has to be an option.
What’s needed is Wendy’s. The was no scarcity of burger joints when they came on to the scene. Rutan is an innovative genius, but he needs lots of competition… or is the tourist market too small?
“They should have totally rethought their propulsion philosophy when they had the accident…”
They did at least reconsider the choice of oxidizer, contemplating a switch to LOX. I don’t know whether George Whittinghill is still on this program, but he knows how to do very large LOX/rubber hybrids.
XCOR is an excellent engine (and propulsion system) developer. But the requirement here is for an order of magnitude larger engine than their largest (at least the largest one I know of). It’s a risk.
Josh Reiter Said:
“Is Scaled going directly to their big engine from the get go? Even the X-15 used the same motor going back to the Bell X-1 during it’s early testing.”
The use of the old X-1 engine on early X-15 flights was not planned from the start of the program. It was the result of bad development delays with the LOX/Ammonia main engine selected for the X-15. LOX/Ammonia has trouble burning well enough to avoid explosions, it seems. They needed to start getting value from their investment, and Kelly Johnson already needed data for the A-12. So they used the old engine.
Mysteries indeed abound. Why not an XCOR liquid engine is a good question. Why not a LOX-rubber hybrid is a good question. Why not an XCOR cryogenic-capable composite tank for a LOX-rubber hybrid might be an even better question. Or why not a SpaceX-subcontracted LOX-HC engine? If there is a personal feud stopping potential XCOR-Scaled collaboration, why not at least a no-XCOR-required peroxide-rubber or peroxide-paraffin hybrid alternative by now? The world wonders.
Not a lot of people around with experience building hybrid rockets. Scaled should have gone for the more well known liquid fuel approaches on this one. One have a backup engine design, or whatever. It was a major risk in the program.
Why not an XCOR liquid engine is a good question.
Aren’t they competitors?
Why not an XCOR cryogenic-capable composite tank
Or a Microcosm tank?