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• View topic - Firefly Space Systems Aerospike

Firefly Space Systems Aerospike

Anything that doesn't belong in one of the other forums goes here.

Firefly Space Systems Aerospike

Postby rick m » Mon Dec 01, 2014 10:18 am

This sounds like a new team for going into orbit using an aerospike.

http://arstechnica.com/science/2014/11/ ... rth-orbit/

I wish them success.

Rick
Hard work is good for you, try it.
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Re: Firefly Space Systems Aerospike

Postby Jay » Sat Dec 06, 2014 10:31 pm

I wish them success too, but they seem to be schooled in the same “minimize weight/maximize performance” mentality of the last fifty years. That’s not surprising since I notice a couple of their technical gurus came from Lockheed Martin and Rocketdyne. Carbon fiber composites are very expensive not only in terms of raw materials, but also in terms of the time, equipment and the fabrication expertise required to produce precise and reliable finished components.

I’m inclined to favor the Minimum Cost Design (MCD) protocols first validated in the 1960’s. Although the MCD argument that costs can be spectacularly reduced by sacrificing performance was specifically directed toward the development of large numbers of heavy-lifters, I’m convinced the same principles can be applied to high-volume spaceflight companies carrying smaller payloads as well. The MCD concept compensates for the higher weight of low-tech aluminum and steel simply by making the rocket bigger. The increased fuel cost is trivial compared to the dramatically reduced fabrication costs. A spaceflight company planning to make hundreds of launches will benefit from the lessons of commercial mass production, which epitomizes minimum cost design.

I like Firefly’s liquid methane/liquid oxygen combination, which is completely consistent with MCD. Across the board the savings are great.

Central to the MCD concept is the use of simple low-cost pressure-fed engines instead of complex and pricey pump-fed designs. Ars Technica clearly describes the Firefly fuel tanks as self-pressurizing and the alpha engine appears to be pressure-fed rather than pump-fed, but the article did not make that quite as clear. A pressure-fed aerospike configuration is certainly compatible with the MCD protocols.

Unfortunately, whenever I look at “plug cluster aerospike” engines, I see bell-nozzles -- lots of them -- which would seem to be counter productive. Everyone knows the arguments favoring aerospike engines in theory, but reducing the theory to practice has proven to be elusive. Don’t get me wrong; Firefly’s engineers are no slouches, but I won’t believe the brochure until I see the data.

MCD was ultimately rejected in favor of the pork barrel space shuttle program based on the conclusions of a couple of clearly biased studies by aerospace industry and government insiders with vested interests in high-priced spaceflight. That bias has continued ever since. Today, the same vested interests feed the media with soundbites describing MCD as old news and no longer relevant with new technology. Even the Ars Technica article parrots the party line, “Metal rockets are for suckers.” The fact that we have abandoned the space shuttle in favor of fifty-year-old concepts such as expendable rockets and crew capsules splashing down in the ocean seems to have escaped their notice. Newer is not always better.

Nevertheless, the economic and physical constraints underlying MCD are inescapable and with the ongoing commercialization of spaceflight services the first company to embrace the protocols will leap ahead of the competition. Other companies will then be forced to adopt MCD as well and spaceflight costs will plummet as a result.

There, that should stir some debate!

Jay
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Re: Firefly Space Systems Aerospike

Postby rick m » Mon Dec 08, 2014 6:45 am

Hard work is good for you, try it.
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Re: Firefly Space Systems Aerospike

Postby Jay » Tue Dec 09, 2014 7:37 pm

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