Propellant depot strategy & tactics pow-wow

[TOG]

Uhh... actually ice rink.

Sounds like you would add a Starbuck's there too.  Perhaps a nice strip mall for those tourists (where else to get a "My parents went to outer space and all I got was this lousy T-shirt" shirt?), a service station for refurbishing those reusable tugs, and perhaps a nice zero-g casino?

 

Completely agree with the water/ice concept, but as mentioned earlier, it could take a lot of energy to separate the water (yes the U-V idea looks pretty good).

Oh, and added benefit: water makes a nice shield against radiation.  FWIW.

TOG

[Bill White]

Water, Water, Water. 

Turns to ice, don't need to refrigerate, shade will do.  Stores forever with no boil-off.  Higher density for launching.  Triple use:  Fuel, Breathing, Drinking.  Requires electrolysis capability, either solar or nuclear. Cheaper to launch. Cheaper to purchase.  Less expensive to manufacture (electrolyze?) in space if the equipment is designed with sufficiently amortized life, and un-attended operation.  Does not rule our hypergolics, or other fuel combinations.  Depot should be multi-fuel capable, as well as able to store supplies, consumables, rescue craft, spare parts, ultimately habitat and micro-gravity & radiation experimentation.

Locate at Emily-1. Start small, build-out to 2400m diameter, rotating ring.

What's not to like?

Kerosene . . .

Turns to ice, don't need to refrigerate, shade will do.  Stores forever with no boil-off.  Higher density for launching.

No energy input needed to use as fuel, arrives at the depot with considerable potential chemical energy already contained within the material.

No compressors or giant tanks need for storage (as with the H that comes once the H2O is cracked).

[deltaV]

Kerosene . . .

You forgot to mention the LOX -- kerosene ain't much use without it! Fortunately LOX is apparently relatively easy to store with just a sun shield: http://forum.nasaspaceflight.com/index.php?topic=17962.msg453558#msg453558

[Bill White]

Kerosene . . .

You forgot to mention the LOX -- kerosene ain't much use without it! Fortunately LOX is apparently relatively easy to store with just a sun shield: http://forum.nasaspaceflight.com/index.php?topic=17962.msg453558#msg453558

Yep.

I thought everyone knew that already. 

[Jim Davis]

Depots could cost what, 5x less? 10x less to develop than Ares V? 

How do we know this?

[alexterrell]

As an alternative to pumping around fuels, would it be possible for, say Falcon 9H (EELV too expensive) to launch a standard 25 tons Earth Departure Stage, with a relatively low cost motor.

Rather than transferring propellant, these would be clipped together. Typically three would be clipped side by side (and possibly a fourth on top), and an Altair or Orion unit plugged on top. Two (or three) of these are expended for TLI, and the final one is used to enter Lunar orbit.

Crew missions could use LOR, or EOR, if six Departure Stages are clipped together.

Altair and Orion are only launched after the required number of EDS units are in orbit and report themselves well. It could even make sense to ensure an extra EDS unit is always in place.

If the EDS uses LOX / Kerosene, it can be stored for a long time and launched on a regular schedule, say twice per month (SpaceX might like that).

A Canadian shuttle arm on a truss could be used to assist assembly, or not. This "marshalling yard" could form a base.

So, no propellant transfer needed. Clip on architecture. Standard EDS with large production run and low launch costs.

 

[simon-th]

As an alternative to pumping around fuels, would it be possible for, say Falcon 9H (EELV too expensive) to launch a standard 25 tons Earth Departure Stage, with a relatively low cost motor.

Rather than transferring propellant, these would be clipped together. Typically three would be clipped side by side (and possibly a fourth on top), and an Altair or Orion unit plugged on top. Two (or three) of these are expended for TLI, and the final one is used to enter Lunar orbit.

Crew missions could use LOR, or EOR, if six Departure Stages are clipped together.

Altair and Orion are only launched after the required number of EDS units are in orbit and report themselves well. It could even make sense to ensure an extra EDS unit is always in place.

If the EDS uses LOX / Kerosene, it can be stored for a long time and launched on a regular schedule, say twice per month (SpaceX might like that).

A Canadian shuttle arm on a truss could be used to assist assembly, or not. This "marshalling yard" could form a base.

So, no propellant transfer needed. Clip on architecture. Standard EDS with large production run and low launch costs.

1. EDS hardware isn't cheap - if you require 4-5 stages for just the EDS, you end up paying a lot for all the engines and the structure etc.

2. Every EDS stage is a dry mass. The more you "clip on" the more dry mass you have vs. just one EDS stage.

3. For your "clip on" architecture, you need to have every EDS to have some loiter capability, passive RCS for docking etc. etc. That makes that EDS even heavy (dry).

4. LOX boils off as well. Hypergolics don't have boil-off issues. But the isp of both LOX/RP-1 and hypergolics is much lower than LH2/LOX, so you end up with a huge mass penalty for your "clip on" EDS architecture if you don't use LH2/LOX.

5. Overall, due to multiple dockings etc. your architecture gets rather complicated for one mission.

6. Falcon 9H is just a paper rocket right now. We don't know of its reliability, its costs or whether it will ever get built. On the other hand, fuel-transfer on orbit is real, we do it all the time on ISS.

[rklaehn]

As an alternative to pumping around fuels, would it be possible for, say Falcon 9H (EELV too expensive) to launch a standard 25 tons Earth Departure Stage, with a relatively low cost motor.

Sure, that could be done. I seem to remember some proposals from ULA doing just that: building trains of multiple centaur stages.

But I really don't see why everybody is so afraid of pumping cryogenic liquids around. Every time a centaur stage restarts in orbit, it is pumping cryogenic liquids around.

Insulating tanks in orbit to reduce boiloff to acceptable levels is proven, existing technology. See the planck and herschel telescopes.

ULA (not exactly a paper company or a reckless newspace company) has concrete plans on how to incrementally test and then build propellant depots.

The only reason NASA does not want propellant depots is that they want their own rocket. It does not matter how conservative your proposal is: if it does not require a heavy lifter, NASA will find a way to discredit it.

If they have the audacity to claim that "human rating" an existing launch vehicle will take almost a decade and will cost billions, they will have no problems discrediting even an extremely conservative proposal like a hypergolic depot.

[mmeijeri]

If they have the audacity to claim that "human rating" an existing launch vehicle will take almost a decade and will cost billions, they will have no problems discrediting even an extremely conservative proposal like a hypergolic depot.

They would undoubtedly try, but it would be a hard argument to make. After all, it is 30 year old technology which has seen continuous use ever since Salyut-6 in 1978 as I'm fond of pointing out. It's another gap, the Hypergolic Propellant Transfer Gap and it is high time it was closed. Note that mere in-flight refueling (one-way only) as opposed to a full depot would be even more conservative.

Still, if the Augustine commission doesn't recommend this as an option (and it looks as if they won't ), it's a moot point. If they really do want to put depots on the critical path without risk this would be a way to do it, especially if combined with EELV Phase 1 or J-130/NSC. There's a good chance cryogenic depots could be operational by the time you went beyond LEO, which means you could refuel upper stages in LEO, which means EDS launches would not be restricted to EELVs, which is good for competition.

[William Barton]

Regarding the "clip-on" architecture, I remember a proposal early on in STS development (meaning ca. 1971 or thereabouts). The idea was an EDS that was engine and thrust /support structure that was lofted by Shuttle. It was then fuelled by tanks brought up one at a time and transferred to the EDS entire. More or less the way you "refuel" a gas barbecue grill. That's sort of a half-step between a multi-stage EDS and pumping fluids in zero-gee.

[mmeijeri]

ESA has similar (unfunded) plans for multiple EDSs. You would still need boil-off mitigation, otherwise you would have to do many launches in rapid succession.

[TOG]

My apologies if this has been covered elsewhere-

What would be the desired launch rate/payload size for supplying a Propellant Depot, given, say, 4 flights annually to the moon.

How does this strategy change if the depot is maintained at L1 or L2?

Thanks in advance,
TOG

[adamsmith]

Team-

Any thoughts on this alternative to LH2 - LOX storage: What if the fuel was stored as Stable Water?  Then when the time comes to transfer the fuel the water could be broken into H2 and O2 via energy gathered from solar panels. 

This could reduce the amount of loss due to the "boil off" effect, and would be more stable and less prone to "unfortunate incidents" on orbit.

Thoughts?

Drew Montgomery AKA TOG.

Someone crank the numbers on kw-hours to turn 30mT of water into rocket fuel?  I am too busy right now. 

My guess is a REALLY big number.  I looked a site on using electrolysis at gas stations to make hydrogen and the power requirements were HUGE.  They also stated the process is only 50% efficient and large quantities of waste heat is produced.  This means huge radiators. 

Danny Deger

Make following assumptions:

1) Use slasr array as power source ( see www.slasr.com) 30% efficient conversion of solar light, 3kg/KW (stows at 80KW/m3)

2) In LEO cells 50% efficient due to "night"

3) Assume 8kwh/kg x 50% efficiency
4) Assume 3kg/KW radiators
5) Assume 4kg/KW for everything else

30MT of fuel need 16Kwh * 30,000 = 480MwH

Assume we want to make this in 1000 hours (5 weeks)

Take energy 480MwH divide by 1000 hours 480KW

Take 480KW multiply by 10kg/KW times 2 ( remember "Night") and you have 9.6 tons. A Falcon 9 can lift that.

Please tell me where I am wrong, because if I am not, H2O sounds too good to pass.  If there is water on phobos, it could supply both Mars Landers or even be returned to EML1 for moon landers.

Stanley

[A_M_Swallow]

1) Use slasr array as power source ( see www.slasr.com) 30% efficient conversion of solar light, 3kg/KW (stows at 80KW/m3)

The web site gives a completion date of last year, did it finish?  Or was the project cancelled?

30% efficiency of solar light to electricity conversion can also be achieved using using Stirling engines, which are naturally radiation proof.

A hydrogen based system will need power for cooling.

[adamsmith]

1) Use slasr array as power source ( see www.slasr.com) 30% efficient conversion of solar light, 3kg/KW (stows at 80KW/m3)

The web site gives a completion date of last year, did it finish?  Or was the project cancelled?

30% efficiency of solar light to electricity conversion can also be achieved using using Stirling engines, which are naturally radiation proof.

A hydrogen based system will need power for cooling.

The project did result in a full fledged prototype. And it appears that ATK is looking for customers.  Entech (www.entech.com) has taken the technology and applied to earthly pursuits and is now rolling out a product that provides Power and Heat.

I was looking for good kw/kg in a small package no maintenance package.  This beats a stirling engine in space.

I was examining the practicality of fuel production so I presumed that the Storage part was a separate problem.

I am reviewing the "model" and I think I am on the low side for the other category.  Apparently desktop model Hydrogen generators are about 10 times heavier, but a ratio between industrial and desktop of 10 to 1 is not unusual so I think the ballpark stands about right.

Stanley

[MP99]

Quick question about cryogenic depots - do they have to avoid boiling dry?

Alternate version of the same question - presuming a depot boils dry, it's temperature will then rise. Is there a practical process to restart loading cryogenic fuel and cool the structure back down to the required temperatures? If so, you'd presumably boiloff a lot of fuel from that first load?

cheers, Martin

[Danny Dot]

Team-

Any thoughts on this alternative to LH2 - LOX storage: What if the fuel was stored as Stable Water?  Then when the time comes to transfer the fuel the water could be broken into H2 and O2 via energy gathered from solar panels. 

This could reduce the amount of loss due to the "boil off" effect, and would be more stable and less prone to "unfortunate incidents" on orbit.

Thoughts?

Drew Montgomery AKA TOG.

Someone crank the numbers on kw-hours to turn 30mT of water into rocket fuel?  I am too busy right now. 

My guess is a REALLY big number.  I looked a site on using electrolysis at gas stations to make hydrogen and the power requirements were HUGE.  They also stated the process is only 50% efficient and large quantities of waste heat is produced.  This means huge radiators. 

Danny Deger

Make following assumptions:

1) Use slasr array as power source ( see www.slasr.com) 30% efficient conversion of solar light, 3kg/KW (stows at 80KW/m3)

2) In LEO cells 50% efficient due to "night"

3) Assume 8kwh/kg x 50% efficiency
4) Assume 3kg/KW radiators
5) Assume 4kg/KW for everything else

30MT of fuel need 16Kwh * 30,000 = 480MwH

Assume we want to make this in 1000 hours (5 weeks)

Take energy 480MwH divide by 1000 hours 480KW

Take 480KW multiply by 10kg/KW times 2 ( remember "Night") and you have 9.6 tons. A Falcon 9 can lift that.

Please tell me where I am wrong, because if I am not, H2O sounds too good to pass.  If there is water on phobos, it could supply both Mars Landers or even be returned to EML1 for moon landers.

Stanley

You would make a good conceptual design engineer   

Where did you get the 30,000 from?  Did you take into consideration the need for batteries, the efficiency of conversion, and energy to cool the cryo? 

Even with all this, it doesn't look as bad as I was thinking it might be.

Danny Deger

[adamsmith]

Team-

Any thoughts on this alternative to LH2 - LOX storage: What if the fuel was stored as Stable Water?  Then when the time comes to transfer the fuel the water could be broken into H2 and O2 via energy gathered from solar panels. 

This could reduce the amount of loss due to the "boil off" effect, and would be more stable and less prone to "unfortunate incidents" on orbit.

Thoughts?

Drew Montgomery AKA TOG.

Someone crank the numbers on kw-hours to turn 30mT of water into rocket fuel?  I am too busy right now. 

My guess is a REALLY big number.  I looked a site on using electrolysis at gas stations to make hydrogen and the power requirements were HUGE.  They also stated the process is only 50% efficient and large quantities of waste heat is produced.  This means huge radiators. 

Danny Deger

Make following assumptions:

1) Use slasr array as power source ( see www.slasr.com) 30% efficient conversion of solar light, 3kg/KW (stows at 80KW/m3)

2) In LEO cells 50% efficient due to "night"

3) Assume 8kwh/kg x 50% efficiency
4) Assume 3kg/KW radiators
5) Assume 4kg/KW for everything else

30MT of fuel need 16Kwh * 30,000 = 480MwH

Assume we want to make this in 1000 hours (5 weeks)

Take energy 480MwH divide by 1000 hours 480KW

Take 480KW multiply by 10kg/KW times 2 ( remember "Night") and you have 9.6 tons. A Falcon 9 can lift that.

Please tell me where I am wrong, because if I am not, H2O sounds too good to pass.  If there is water on phobos, it could supply both Mars Landers or even be returned to EML1 for moon landers.

Stanley

You would make a good conceptual design engineer   

Where did you get the 30,000 from?  Did you take into consideration the need for batteries, the efficiency of conversion, and energy to cool the cryo? 

Even with all this, it doesn't look as bad as I was thinking it might be.

Danny Deger

Ah Danny,

First, thanks for the complement.

I was breaking the problem down into two parts: the propellant production part and the depot part.  I "assumed" the existence of the depot part.  This is the incremental part associated with propellant production.  I saw somewhere on the Directlauncher site a reference to a "Large" (>100ton) depot in the 15ton range(?) so I cheated somewhat. But hey the idea was whether adding a good production capability would kill the deal.  I don't think it does.

Stanley

[jongoff]

Quick question about cryogenic depots - do they have to avoid boiling dry?

Alternate version of the same question - presuming a depot boils dry, it's temperature will then rise. Is there a practical process to restart loading cryogenic fuel and cool the structure back down to the required temperatures? If so, you'd presumably boiloff a lot of fuel from that first load?

Yes, there are chilldown techniques that have been developed.  Engines go "dry" on cryo upper stages and need to be conditioned before you can relight them.  If your depot is passively cooled, then you have to waste a bit of the propellant to chill everything down (but not a huge amount).  If your depot is actively cooled, you can rechill the chilldown fluid.

The amount of fuel (especially if it's LH2) doesn't have to be that much.  Remember, boiling anything sucks a lot of heat out, and then the heat capacity of hydrogen is really good.  If you keep the walls of your tank thin, to keep heat leaks down, you can keep the chilldown requirements low.  Plus, if you're using a sunshield, the equilibrium temperature it reaches, even if it is warmer than the normal boiling temperatuer of the fluid is still going to be pretty cold.

~Jon

[MP99]

Jon,

many thanks.

cheers, Martin