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It's a good article, thanks for reminding me to re-read it. I note that in it, Stephenson makes a prediction, as if it were a known fact, that I think we now h
by jholman 13y ago
It's a good article, thanks for reminding me to re-read it.
I note that in it, Stephenson makes a prediction, as if it were a known fact, that I think we now have significant reason to doubt.
He says "Rockets are as close to perfect as they're ever going to get. For a few more billion dollars we might be able to achieve a microscopic improvement in efficiency or reliability, but to make any game-changing improvements is not merely expensive; it's a physical impossibility."
I think we now have reason to believe that for around a billion dollars ($1b is the estimated total R&D budget as of a year ago), SpaceX has already made better-than-microscopic improvements in efficiency. But more interestingly, there's reason to believe that with little or no additional outside investment (i.e. working on profits), SpaceX is pretty likely to soon make a very large improvement in efficiency, with Grasshopper &c. Rockets are probably not as perfect as they're ever going to get.
- rayiner 13y agoWithout taking away from SpaceX's accomplishments, it's important to keep the performance of the Merlin engines in context. The Merlin 1d is arguably the most efficient rocket engine using a gas-generator cycle and RP-1 (kerosene) fuel. That's a very specific claim. Hydrogen-burning engines like the one on the Space Shuttle are much more efficient (measured by specific impulse), and some Soviet kerosene rockets came very close both in specific impulse and thrust to weight ratio, though they used a somewhat different cycle. Relevant discussion: http://www.flightglobal.com/blogs/hyperbola/2012/06/comment-merlin-1d-is-not-quite.html http://www.flightglobal.com/blogs/hyperbola/2012/06/comment-.... Still a very impressive achievement, but looking at the performance of SpaceX's engines circa 2012 and comparing them to what the Soviets built in 1960 or 1970 helps put the pace of the industry into context.
- jholman 13y agoI had assumed, in my ignorance, that the Merlin engines were not an important advancement. I don't think that specific impulse is necessarily the important sense of "efficiency" (though I do assume that it correlates with the important sense). The relevant efficiency, to me, is "awesomeness achieved per human effort and non-renewable resource", and the useful proxy for this is "awesomeness per price". Arguably SpaceX rockets are cheaper (per given mass to given orbit, obviously) that most or arguably all of the competition. I say "arguably cheaper" because it's a little tough to figure out how to price the shoulders of giants on which they stand. And really I only picked the word "efficiency" in the context of Stephenson's "efficiency or reliability". Anyway, hopefully this explains why I think that true reusable rockets, Musk's often-stated ambition, qualify as a "very large improvement" in efficiency. Specific impulse is not expected to significantly improve, right? Also, I apologize in advance for my legion failings in the area of comprehending aerospace engineering.
- DaniFong 13y agoNot exactly efficiency, (though they have high combustion efficiency) but low cost and very good mass ratio. If they make it reusable, that where the killer improvement is. Elon says they're getting there; I'm crossing my fingers.
- jholman 13y agoI utterly agree in substance, see my cousin-comment. Do you think think it's unreasonable to call "payload per cost" a relevant "efficiency"?