Author Topic: Exploration Enterprise Workshop Day 1 and Day 2 Presentations released  (Read 18715 times)

Offline pathfinder_01

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They also seem to be leaning towards a LOX/methane upper stage/depot (page 16).

I'm not sure how much I agree with it, but here's the current rationale (presumably subject to change as the RFI proceeds) on preferring LOX/LCH4 over LOX/LH2:

http://www.nasa.gov/pdf/458814main_FTD_CRYOGENICPropellantSTorageAndTransferMission.pdf
Quote
Cryogen Options Review: Why Methane (vs. Hydrogen)
• A early LOX/Methane demo offers advantages:
– Enables methane-based systems and mitigates risks for LH2 systems.
– Allows direct comparison of active vs. passive cooling.
– Leverages recent investments in LO2/LCH4 cryo fluid management
– Leverages recent investments in pressure-fed engines
– Breaks the barrier for long-duration cryo systems.
• A LOX/Hydrogen demo in foreseeable future is possible.
– Low cryo cooler TRL implies shorter mission duration.
– No accurate gauging method for unsettled propellants.
• Due to similarity of LOX and LCH4 properties (e.g. temp, density, etc.), the same components may be qualified and used for ground test and flight hardware.

I still don't follow the desires for methane.  Every EDS supporting EM-L1, LLO, NEO, LMO, Lunar surface, Mars Surface (you get the picture) is base lined to use LH2 thanks to the much higher ISP.  We also have 50 years experience with handling LH2 on orbit, with existing flight hardware but relatively little experience with methane.  So what about cryo-cooler TRL, just use passive thermal protection and deal with the modest boil-off, performance wise you are still way ahead.



It isn’t so much for EDS stages, it is more for in space propulsion in general. We know how to build LH2 rockets. However we don’t know how to build Methane ones and a methane engine could be useful for mar s landers or just a better in space propulsion system in general.

Right now we can use hypergolic for long term propulsion (i.e. propellant for missions that last months or years). However hypergolic do not deliver the same performance as cryogenics (LH2 or Methane). LH2 is the hardest propellant to store in space. They haven’t totally ruled it out, but they think that it is going to be much too hard for a quick cheap mission to advance our confidence in propellant transfer technology.

In theory a lox\methane rocket would offer better ISP than a hypergolic one. It would also give confidence to plans like Zurbin’s that require generating methane on mars. However the reality is a little murky due to the additional mass a lox methane rocket might need (insulation…although at mars distance the problem will be keeping the lox and methane from freezing in space).

« Last Edit: 06/03/2010 01:31 AM by pathfinder_01 »

Offline neilh

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It isn’t so much for EDS stages, it is more for in space propulsion in general. We know how to build LH2 rockets. However we don’t know how to build Methane ones and a methane engine could be useful for mar s landers or just a better in space propulsion system in general.

Right now we can use hypergolic for long term propulsion (i.e. propellant for missions that last months or years). However hypergolic do not deliver the same performance as cryogenics (LH2 or Methane). LH2 is the hardest propellant to store in space. They haven’t totally ruled it out, but they think that it is going to be much too hard for a quick cheap mission to advance our confidence in propellant transfer technology.

In theory a lox\methane rocket would offer better ISP than a hypergolic one. It would also give confidence to plans like Zurbin’s that require generating methane on mars. However the reality is a little murky due to the additional mass a lox methane rocket might need (insulation…although at mars distance the problem will be keeping the lox and methane from freezing in space).

If methane depots are indeed pushed, I wonder how much commonality there would be between a methane-based upper stage or EDS and their SpaceX's current kerosene-based stages. It'd be different of course, but from my outsider's perspective it seems like it'd have more in common than their Raptor LH2-based stage.
« Last Edit: 06/03/2010 03:30 AM by neilh »
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Offline Nancyloo

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We have 50 years of working with LH2 in space near zip with methane.  I believe that a LH2 depot by 2015 is far easier to develop than a methane depot as long as we don't demand zero boil-off.  The vent gas is useful for station keeping anyways.

We aren't going to Mars for a couple decades minimum.  To go to EM-L1 we need LH2 plus Orion's storable propellant  service module.  For LLO we need LH2 plus Orion's storable propellant service module.  For NEO's we need LH2 plus likely an updated Orion SM.  So that takes care of the next 15 years.  Once we start talking lunar surface, and Mars orbit the debate over the correct return propellant get's interesting, but that is further in the future and should drive the debate over the post 2015 depot demo.

As for ISRU the H2 for cracking the CO2 needs to come from somewhere. Is it from Mars water ice?  Then you have H2 and O2.  Hard to store in large quantities on the Martian surface.  It isn't clear what the Mars ascent propellants should be H2, methane, pentane, or other higher order more storable hydrocarbon.  Jumping to methane today seems a stretch.

Offline MP99

As for ISRU the H2 for cracking the CO2 needs to come from somewhere. Is it from Mars water ice?  Then you have H2 and O2.  Hard to store in large quantities on the Martian surface.  It isn't clear what the Mars ascent propellants should be H2, methane, pentane, or other higher order more storable hydrocarbon.  Jumping to methane today seems a stretch.

Carry the H2 from Earth (it's very light), then convert the H2 + atmospheric CO2 to hydrocarbon + O2.

Of course, this relies on carrying the H2 through Mars transit, but that shouldn't be a big issue in 30 years time.

The alternative is just to convert CO2 to CO + O2.

cheers, Martin
« Last Edit: 06/03/2010 01:24 PM by MP99 »

Offline isa_guy

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NASA want to develop multi-mw electric thrusters but not the power source ( nuclear or solar ) to power them quite odd dont you think so ?
« Last Edit: 06/03/2010 04:14 PM by isa_guy »

Offline Robotbeat

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NASA want to develop multi-mw electric thrusters but not the power source ( nuclear or solar ) to power them quite odd dont you think so ?
Not odd. We already have solar panels which could do the job (150-200+W/kg) and larger solar arrays using thin-film cells could be much lighter (potentially 1000W/kg or even more) but would require more money.
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Offline robertross

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NASA want to develop multi-mw electric thrusters but not the power source ( nuclear or solar ) to power them quite odd dont you think so ?
Not odd. We already have solar panels which could do the job (150-200+W/kg) and larger solar arrays using thin-film cells could be much lighter (potentially 1000W/kg or even more) but would require more money.

IIRC it was in the presentations online...Nuclear AND Advanced Solar. They even used the ISS arrays as a comparison.
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Offline robertross

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We have 50 years of working with LH2 in space near zip with methane.  I believe that a LH2 depot by 2015 is far easier to develop than a methane depot as long as we don't demand zero boil-off.  The vent gas is useful for station keeping anyways.

Nothing wrong with having something else in your back pocket anyway. We have seen, too many times, systems that could benefit from R&D started years ago.

Not dissing LH2, it's just not something I would have all the 'eggs in one basket' approach. If we solve LH2 storage as a multi-purpose propellant, that's great, but that may not help you everywhere you go.

Anyway, all this is notional at this point.
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Offline Robotbeat

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It will pretty much always be about 10 times harder to cool liquid hydrogen than liquid oxygen or methane. This is just because it simply gets less and less efficient to remove heat the colder you get.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline A_M_Swallow

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NASA want to develop multi-mw electric thrusters but not the power source ( nuclear or solar ) to power them quite odd dont you think so ?

Not odd, NASA is simply letting the military pay for development of the solar arrays.

Offline Nancyloo

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It will pretty much always be about 10 times harder to cool liquid hydrogen than liquid oxygen or methane. This is just because it simply gets less and less efficient to remove heat the colder you get.

You make the assumption that one needs to actively cool the LH2.  I don't know anyone working with hydrogen that proposes that.  Hydrogen has 10 times the sensible heat capacity of oxygen and 4 times that of methane.  With an efficient thermal design the heat of vaporization and vapor cooling is sufficient for propellant depots where one uses the vented hydrogen to provide cold gas station keeping.  An actively cooled broad area system can be added to the MLI to intercept acreage heating at a moderate temperature as an added augmentation.

Offline Nancyloo

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We have 50 years of working with LH2 in space near zip with methane.  I believe that a LH2 depot by 2015 is far easier to develop than a methane depot as long as we don't demand zero boil-off.  The vent gas is useful for station keeping anyways.

Nothing wrong with having something else in your back pocket anyway. We have seen, too many times, systems that could benefit from R&D started years ago.

Not dissing LH2, it's just not something I would have all the 'eggs in one basket' approach. If we solve LH2 storage as a multi-purpose propellant, that's great, but that may not help you everywhere you go.

Anyway, all this is notional at this point.

No disagreement.  It is just an order of priorities.  We need hydrogen to go anywhere, we have the expertise, lets demonstrate it and enable a crewed lagrange mission this decade.  Methane can follow.

Online Ronsmytheiii

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NASA want to develop multi-mw electric thrusters but not the power source ( nuclear or solar ) to power them quite odd dont you think so ?
Not odd. We already have solar panels which could do the job (150-200+W/kg) and larger solar arrays using thin-film cells could be much lighter (potentially 1000W/kg or even more) but would require more money.

Solar energy decreases massively as one moves away from the inner solar system, Nuclear does not suffer such an issue.
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Offline A_M_Swallow

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It will pretty much always be about 10 times harder to cool liquid hydrogen than liquid oxygen or methane. This is just because it simply gets less and less efficient to remove heat the colder you get.

You make the assumption that one needs to actively cool the LH2.  I don't know anyone working with hydrogen that proposes that.  Hydrogen has 10 times the sensible heat capacity of oxygen and 4 times that of methane.  With an efficient thermal design the heat of vaporization and vapor cooling is sufficient for propellant depots where one uses the vented hydrogen to provide cold gas station keeping.  An actively cooled broad area system can be added to the MLI to intercept acreage heating at a moderate temperature as an added augmentation.


Robotbeat is making a safe assumption.  The process is starting with hydrogen gas produced by the electrolysis of liquid water.  That will require the hydrogen to be cooled by at least 250 degrees kelvin.

Heat the super cooled ice up, melt it, perform electrolysis and liquefy the oxygen and hydrogen by refrigeration - that is going to be a high energy process.  Even using heat exchangers.

Offline Nancyloo

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It will pretty much always be about 10 times harder to cool liquid hydrogen than liquid oxygen or methane. This is just because it simply gets less and less efficient to remove heat the colder you get.

You make the assumption that one needs to actively cool the LH2.  I don't know anyone working with hydrogen that proposes that.  Hydrogen has 10 times the sensible heat capacity of oxygen and 4 times that of methane.  With an efficient thermal design the heat of vaporization and vapor cooling is sufficient for propellant depots where one uses the vented hydrogen to provide cold gas station keeping.  An actively cooled broad area system can be added to the MLI to intercept acreage heating at a moderate temperature as an added augmentation.


Robotbeat is making a safe assumption.  The process is starting with hydrogen gas produced by the electrolysis of liquid water.  That will require the hydrogen to be cooled by at least 250 degrees kelvin.

Heat the super cooled ice up, melt it, perform electrolysis and liquefy the oxygen and hydrogen by refrigeration - that is going to be a high energy process.  Even using heat exchangers.

That is accomplished here on Earth.  To get people to the first Flexible path destination EM lagrange poitn you need LH2/LO2 in LEO.  The LH2 can be launched already liquified, potentially even subcooled.  No need for high power space rated cryocoolers, which don't currently exist.  What you describe is an issue years (decades) down the road with ISRU.

Offline pathfinder_01

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That is accomplished here on Earth.  To get people to the first Flexible path destination EM lagrange poitn you need LH2/LO2 in LEO.  The LH2 can be launched already liquified, potentially even subcooled.  No need for high power space rated cryocoolers, which don't currently exist.  What you describe is an issue years (decades) down the road with ISRU.

As  it stands now LH2 is difficult to store for long periods. Meaning current upperstages can only contain enough LH2 to last for a few days not months or years. We need a cryogenic fuel that can be stored for months. Right now we lack the technology to do so. In theory LH2 storage is achievable, in reality it is harder to store than methane. NASA might change it’s mind and go for LH2 storage, but doubtful.  Methane storage helps because you can use methane for propellant instead of LH2. Lox methane should give better ISP than hypergolics. The reality is more complicated.  Hypergolic storage is known.


Offline Nancyloo

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That is accomplished here on Earth.  To get people to the first Flexible path destination EM lagrange poitn you need LH2/LO2 in LEO.  The LH2 can be launched already liquified, potentially even subcooled.  No need for high power space rated cryocoolers, which don't currently exist.  What you describe is an issue years (decades) down the road with ISRU.

As  it stands now LH2 is difficult to store for long periods. Meaning current upperstages can only contain enough LH2 to last for a few days not months or years. We need a cryogenic fuel that can be stored for months. Right now we lack the technology to do so. In theory LH2 storage is achievable, in reality it is harder to store than methane. NASA might change it’s mind and go for LH2 storage, but doubtful.  Methane storage helps because you can use methane for propellant instead of LH2. Lox methane should give better ISP than hypergolics. The reality is more complicated.  Hypergolic storage is known.



You are correct that cryo coolers are much easier at LCH4 temperatures than at LH2 temperatures.  You are also correct that it is easier to store methane with zero boil-off than LH2.

However there is no need for either of the above.  Storing LH2 with modest boil-off is not particularly hard.  This boil-off/vent GH2  is useful for station keeping anyways, so is not lost from a systems perspective.  A depot could actually vent half of the hydrogen over the course of a year and still demonstrate substantial performance benefit  over a zero boil-off methane system for even the smallest dV beyond LEO mission.

Offline Robotbeat

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Another benefit in a gravity well: methane's greater density means greater thrust for a given flowrate.

Personally, though, I think a carbon monoxide/LOX rocket for Mars makes the most sense. Use hydrolox everywhere else.
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Offline A_M_Swallow

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You are correct that cryo coolers are much easier at LCH4 temperatures than at LH2 temperatures.  You are also correct that it is easier to store methane with zero boil-off than LH2.

However there is no need for either of the above.  Storing LH2 with modest boil-off is not particularly hard.  This boil-off/vent GH2  is useful for station keeping anyways, so is not lost from a systems perspective.  A depot could actually vent half of the hydrogen over the course of a year and still demonstrate substantial performance benefit  over a zero boil-off methane system for even the smallest dV beyond LEO mission.


It is not just the depots that need zero boil off technology, the spacecraft need it as well.  In a 2 year return trip to Mars you can boil off a lot of hydrogen.  The easiest way to account for the boil off could be to treat it as an extra stage with a tiny Isp.

Offline Nancyloo

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You are correct that cryo coolers are much easier at LCH4 temperatures than at LH2 temperatures.  You are also correct that it is easier to store methane with zero boil-off than LH2.

However there is no need for either of the above.  Storing LH2 with modest boil-off is not particularly hard.  This boil-off/vent GH2  is useful for station keeping anyways, so is not lost from a systems perspective.  A depot could actually vent half of the hydrogen over the course of a year and still demonstrate substantial performance benefit  over a zero boil-off methane system for even the smallest dV beyond LEO mission.


It is not just the depots that need zero boil off technology, the spacecraft need it as well.  In a 2 year return trip to Mars you can boil off a lot of hydrogen.  The easiest way to account for the boil off could be to treat it as an extra stage with a tiny Isp.

I'm a huge fan of the evolutionary development concept.  Don't let notions of "it could be better if only" get in the way of what is possible today.  The crewed missions that are potentially going to be undertaken this decade include EM LaGrange points, low lunar orbit and maybe NEO's.  Mars and the lunar surface are out of the question in the next decade.  A cryogenic EDS coupled with a storable service module can readily support these near term mission opportunities.  Zero-boil-off may eventually have its applications but it is not necessary to get started.  Let's get operational experience with a depot and then continue to improve it.  All of the enhanced thermal protection work on a vented depots as well as the market it offers to enhance our launch capability and the prox-ops is required for zero-boil-off depots. 

Demanding zero-boil off and brand new large methane engines and in-space stages will result in Constellation like investment requirements while deferring any mission capability another decade down the road.

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