Author Topic: Hypergolic depots versus Cryogenic depots  (Read 65017 times)

Offline mmeijeri

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Re: Hypergolic depots versus Cryogenic depots
« Reply #160 on: 08/01/2013 11:04 pm »
If your propellant depot is at the edge of Earth's gravity well, you have the option of refueling but you'll need more propellant for the same trip using chemical because you can't use the Oberth effect.

Another point: it's not a matter of either/or: in time we will likely want depots both in LEO and at L1/L2.
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Offline Robotbeat

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Re: Hypergolic depots versus Cryogenic depots
« Reply #161 on: 08/05/2013 03:21 pm »
You can DEFINITELY use the Oberth effect if you're at the edge of Earth's gravity well.
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Offline jg

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Re: Hypergolic depots versus Cryogenic depots
« Reply #162 on: 08/05/2013 03:41 pm »
I remember a few weeks back looking around at the temperatures for a fuel depot in Earth orbit.

IIRC, anything in the temperature range of LO2 can be kept liquid with radiative cooling in earth orbit (which means an insulated tank won't have any significant loss, and the insulation's importance will come in depending on the altitude of the depot (it gets easier the higher you are, as deep space is a larger and larger fraction of the heat equation, and the universe's background temperature is 4 degrees K...).

What this means is that storing LH2 will involve some sort of loss with time, but many other compounds (including LCH4, e.g. Methane) can be stored pretty indefinitely without problems (also very important on a long transit time orbit such as Earth/Mars transfers).

So it's pretty obvious why SpaceX is planning their next engine to be LCH4 rather than use LH2.  As far as I can tell, Elon Musk is really, really serious about getting to Mars; it's not just talk...

LH2 is just a PITA; we'd never use it if the ISP wasn't so high...

Offline mmeijeri

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Re: Hypergolic depots versus Cryogenic depots
« Reply #163 on: 08/05/2013 04:26 pm »
IIRC, anything in the temperature range of LO2 can be kept liquid with radiative cooling in earth orbit (which means an insulated tank won't have any significant loss, and the insulation's importance will come in depending on the altitude of the depot (it gets easier the higher you are, as deep space is a larger and larger fraction of the heat equation, and the universe's background temperature is 4 degrees K...).

Are you sure? I think this is true for high altitude orbits (say L1/L2), but not LEO.

Quote
LH2 is just a PITA; we'd never use it if the ISP wasn't so high...

It's also an excellent coolant.  ;D
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Offline A_M_Swallow

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Re: Hypergolic depots versus Cryogenic depots
« Reply #164 on: 08/05/2013 07:40 pm »
The other substance to watch out for is helium.  It is used to flush pipes and pressurise propellant.  With a boiling point of 4.22 K, −268.93 °C, −452.07 °F it matters whether helium is kept as a gas or a liquid and at what pressure.

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