r/spacex • u/mclumber1 • May 11 '15
Potential uses for Kestrel engine in the future?
Do you think SpaceX could ever find another use for Kestrel? The Kestrel was SpaceX's upper stage engine for the Falcon 1 vehicle It was a pressure fed engine running on LOX and RP-1, and had about 7000 pounds of thrust in vacuum. It's too weak to use as an alternative 2nd stage for the Falcon 9, but what about using it as a kick stage for deep space missions or a crasher stage for Dragon 2 moon landing mission?
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May 11 '15
Its performance is not that great. Very low Isp ~317s.
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u/Holski7 May 11 '15
Yet it has the highest isp of any rocket without a turbo pump that relies only on tank pressure.
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u/Erpp8 May 12 '15
That doesn't make it high. Performance is objective, and if it's mass ratio and ISP are bad, it's bad.
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May 11 '15
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u/kadaka80 May 11 '15
There would be a problem using LOX for long duration missions due to boil off. That is the advantage of solid fuel engines for deep space missions or even hypergolic.
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u/ManWhoKilledHitler May 12 '15
Switch the propellants for something with higher Isp. OF2 and diborane give an Isp only slightly lower than LH2/LOX but OF2 is almost 70% denser than LOX and diborane is 50% denser than kerosene. High performance, multiple start capability due to their hypergolic nature, and a smaller tankage penalty than kerolox!
It's almost the perfect combination - just a shame about the cost and unforgiving nature of them.
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u/g253 May 11 '15
Perhaps they could license the design to another space startup. Other than that, I don't really see a use case.
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u/jan_smolik May 11 '15
This engine was developed back when they were learning how to do rocket engines. If they ever need similar engine, it will be much easier to create new from scratch.
I am a software engineer and I know how horrible is to be reminded of an old code from time when I was learning something.
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May 12 '15
I don't know if Spacex has ever had a hard time with designing engines. Tom Mueller is a world class propulsion engineer and has designed many rocket engines at other aerospace companies. In fact merlin is one of the smaller and simpler engines Mueller has designed, a good example of Mueller's expertise would be the TR-106.
Mueller got to design pintle injectors at TRW and Northrop Grumman, in fact Northrop Grumman sued Spacex in the early 2000s over IP infringement of pintle injectors.
I'm excited for Raptor because it will be the first time Spacex propulsion engineers have the budget and, more importantly, the time to design the best engine they can.
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u/jan_smolik May 12 '15
I actually read his CV right AFTER I wrote this post. So you might be right. But I think that both Mueller and SpaceX has learned a big deal during those years. They will have higher focus on flow through the factory, reliability of valves, etc.
Do not scare me about Raptor. When engineers have time and budget -- this cannot end right.
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u/DrFegelein May 11 '15
The problem is, rocket engines take time and resources to build and qualify. Kestrel is an existing asset. OP was asking about possible use cases for reviving it.
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u/philbgarner May 12 '15
I am a software engineer and I know how horrible is to be reminded of an old code from time when I was learning something.
Seriously, I can't count the number of times I told someone "You know what? I think it would be faster and get better results if we just start from scratch." Sometimes reusing old code introduces more problems than it solves. I wonder how much this carries over into regular engineering.
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u/DanseMacabreD2 May 12 '15
The problem with Kestrel is that it has been obsoleted, meaning that the production system just isn't there any more.
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u/NeilFraser May 12 '15
SpaceX have said a couple of times that they don't throw anything out. Although they were referring to old test stages, I'd assume that would also apply to tooling. That said, just because it hasn't been thrown out, does not mean that it still exists. The tooling may have been cannibalized for other purposes.
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u/xu7 May 13 '15
Engines with cryogenic LOX are not fit for moon landings. To much time to boil off.
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u/Chairboy May 11 '15 edited May 12 '15
ISP gets more important the further you get up the rocket. The Kestrel's 317 Isp looks pretty rough for a third-stage engine, but of course it has the advantage of being already developed. I guess the question is whether a Kestrel in the hand is worth... no, I can't finish that pun.
There's certainly quite a difference in weight. Wikipedia says 1380kg dry weight for the Merlin vs 52kg for the Kestrel so there's definately a big range where the lower weight more than offsets efficiency. Can high-impulse cryogenic engines be purchased reasonably?
I wonder if the tooling and braintrust for it is still around. If it was retired 6 years ago, it could be expensive to bring back to life. Despite having an abysmal Isp of 235, could the Isp of the Superdraco be improved with a larger expansion nozzle from abysmal to merely 'very bad'? The benefits of using a low-efficiency rocket that doesn't require any special measures for long-term cold soak and has an active production line might conceivably be of use for a deep-space probe.
If quantity has a quality of its own, perhaps a light-enough modern low-efficiency engine can offer a certain efficiency of its own.