Author Topic: Why Do we need a Kerolox HLV/Rocket Engine?  (Read 110943 times)

Offline pathfinder_01

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Re: Why Do we need a Kerolox HLV/Rocket Engine?
« Reply #220 on: 04/26/2010 03:29 am »
Actually, why not just purge with gaseous hydrogen on the ground anyway. For first stages, if the gas can't be flared off at the exit bell without damaging the rocket, then the rocket isn't durable enough to be launched in the first place. There must be ways to ensure reasonably even/stable combustion (maybe a flow of oxygen gas or something).

I am no expert, but I think the idea is to remove oxygen and other gasses from the rocket and it's tanks. Putting Hydrogen alone in there might cause an explosion. Putting Nitrogen in there might cause the nitrogen to freeze, so helium looks like the simplest way to do it. The only other way I can think would be vacuuming out the tanks and that could create structural problems.

Offline alexw

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Re: Why Do we need a Kerolox HLV/Rocket Engine?
« Reply #221 on: 04/26/2010 07:12 am »
     Realistically, if we didn't have any helium, we would very likely have to give up on liquid hydrogen as a rocket technology. Helium gas is fundamental to low-temp cryogenic work as an utterly inert gas. Technically, you could construct sequences like the proposed warm-GN2->cold-LN2->LH2, when everything works correctly, but I suspect that as a practical matter, involving humans and industrial liability, helium is just fundamental. But we'd just use something like methane as fuel and GN2 or argon as a purge gas, and life would go on. The lack of helium would be much more serious to science (or medicine) than to rockets.

   Fortunately, we are not going to run out of helium, because we're not going to run out of natural gas fields. It may slowly get pricer, and difficult to source in very large quantities, so it's probably a good idea to design future engines to reduce their helium-specific ground-support purge needs. (It's been said around here that RS-68 is particularly bad in this respect?)

    Sudden thought: a helium-free world is a (bad) fantasy on Earth, but on Mars, it would be (will be!) a genuine design constraint.

-Alex

Offline Jim

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Re: Why Do we need a Kerolox HLV/Rocket Engine?
« Reply #222 on: 04/26/2010 10:47 am »
Actually, why not just purge with gaseous hydrogen on the ground anyway. For first stages, if the gas can't be flared off at the exit bell without damaging the rocket, then the rocket isn't durable enough to be launched in the first place. There must be ways to ensure reasonably even/stable combustion (maybe a flow of oxygen gas or something).

Not realistic.  Flare stacks have another fuel to keep the flame lit. GH2 can enter the fairing or other compartments and cause issues there.  Also the GH2 is not just escaping from the bell, there are many other vents on an engine.

Offline Jim

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Re: Why Do we need a Kerolox HLV/Rocket Engine?
« Reply #223 on: 04/26/2010 10:49 am »
I think Martijn's idea with nitrogen followed by warm hydrogen is pretty workable for an upper stage. All the purges on the ground can be done with nitrogen. Any further purges before chilldown (warm hydrogen then liquid hydrogen) should occur sufficiently high up that the ambient environment is a vacuum.

I'm pretty sure that there's some way to make this work for upper stage without any safety concerns.

The issue is that "warm" GH2 is still colder than solid N2. 

Offline mmeijeri

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Re: Why Do we need a Kerolox HLV/Rocket Engine?
« Reply #224 on: 04/26/2010 10:58 am »
The issue is that "warm" GH2 is still colder than solid N2. 

Can't you just heat it up to above GN2 levels? As long as it is released into an inert gas like GN2 why should that be a problem?

Again, I'm mainly concerned about upper stages, though it would be interesting to know if there are alternatives for first stages as well. Backing up a bit, if LOX/LH2 first stages are out in the long term, then that means no LOX/LH2 (or even tripropellant) SSTO and therefore probably no SSTO at all doesn't it?
« Last Edit: 04/26/2010 11:33 am by mmeijeri »
Pro-tip: you don't have to be a jerk if someone doesn't agree with your theories

Offline MP99

Re: Why Do we need a Kerolox HLV/Rocket Engine?
« Reply #225 on: 04/26/2010 11:47 am »
I think Martijn's idea with nitrogen followed by warm hydrogen is pretty workable for an upper stage. All the purges on the ground can be done with nitrogen. Any further purges before chilldown (warm hydrogen then liquid hydrogen) should occur sufficiently high up that the ambient environment is a vacuum.

I'm pretty sure that there's some way to make this work for upper stage without any safety concerns.

The issue is that "warm" GH2 is still colder than solid N2. 

I can understand that for LH2, but surely GH2 can be any temperature you like above the boiling point?

Or is it an issue of heating the LH2 once it's been boiled?

cheers, Martin

Offline alexw

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Re: Why Do we need a Kerolox HLV/Rocket Engine?
« Reply #226 on: 04/27/2010 08:11 am »
I think Martijn's idea with nitrogen followed by warm hydrogen is pretty workable for an upper stage. All the purges on the ground can be done with nitrogen. Any further purges before chilldown (warm hydrogen then liquid hydrogen) should occur sufficiently high up that the ambient environment is a vacuum.
I'm pretty sure that there's some way to make this work for upper stage without any safety concerns.
The issue is that "warm" GH2 is still colder than solid N2. 
I can understand that for LH2, but surely GH2 can be any temperature you like above the boiling point?
Or is it an issue of heating the LH2 once it's been boiled?
cheers, Martin
    In general there will be trapped N2 purge gas in the lines; once you start flowing LH2 -- even with warm-ish GH2 in front of it (as Jim alludes above) -- the residual nitrogen will freeze, and bad (and perhaps firework-y) events will follow. He is such wonderful stuff not only because it's completely inert, but because it's a gas when every other element, including hydrogen, is liquid. (Well, except 3He :)
   You might be able to construct plumbing where you can get away with it, but it would be awkward: for example, in the window of time between external vacuum and stage separation, heat up a bunch of H2 gas from 14K to > 77K, and reflush all the lines. Inevitably you will have gas lines near the LH2 tanks that would otherwise freeze up (by conduction or radiation) with residual nitrogen (or argon or other trace contaminants), and you'd have to either melt them out or pump them down to hard vacuum beforehand. The complications in flight and added risk on the ground during development would probably negate the benefits of LH2 vs. methane or other classic upper stage fuels.
-Alex

Offline madscientist197

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Re: Why Do we need a Kerolox HLV/Rocket Engine?
« Reply #227 on: 04/27/2010 11:16 am »
Vapourising LH2 is probably not a good way to generate warm H2, probably be better to feed it from a tank of hot compressed hydrogen gas attached to the first stage.

Inevitably you will have gas lines near the LH2 tanks that would otherwise freeze up (by conduction or radiation) with residual nitrogen
It's not that hard to fill a few specific lines with hydrogen gas.

The complications in flight and added risk on the ground during development would probably negate the benefits of LH2 vs. methane or other classic upper stage fuels.
-Alex

Considering how many extra problems hydrogen introduces in general (like embrittlement, leakage etc.), this particular problem really doesn't seem that bad. I don't think there are any fundamental showstoppers despite the opinions of some board members.
« Last Edit: 04/27/2010 11:18 am by madscientist197 »
John

Offline 2552

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Re: Why Do we need a Kerolox HLV/Rocket Engine?
« Reply #228 on: 05/21/2010 12:41 pm »
Hypothetically, how hard would it be to convert the existing ET for an SD-HLV to use kerolox, and use the proposed new kerolox engine on it, and what would this mean for its costs and payload to LEO?

Edit: This would be similar to what Atlas V Phase 3B proposes (http://www.ulalaunch.com/site/docs/product_cards/guides/AtlasVUsersGuide2010.pdf , page 351):

Quote
The 8.4-m diameter core is derived from the Space Shuttle’s external tank and powered by five
RD-180 engines.

Except with Shuttle SRBs and an 8.4 meter, 6 RL-10 EDS.
« Last Edit: 05/21/2010 09:04 pm by 2552 »

Offline JohnFornaro

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Re: Why Do we need a Kerolox HLV/Rocket Engine?
« Reply #229 on: 05/22/2010 02:43 pm »
Are there any links regarding kerolox inspace fuel storage and transfer?
Sometimes I just flat out don't get it.

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