Author Topic: L1/2 spacestation with depot  (Read 64686 times)

Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #40 on: 08/09/2009 03:16 pm »
The Mars DRM assumes 65mT chunks, and with the delta-v numbers above that means less than 65mT in propellant. A depot that contains such amounts of propellant can fit easily within an EELV fairing.

Note that the DRM also assumes NTR. With L1 staging you don't need the nukes (and you can reuse the ITV). And even if you do want them, L1 will likely give a lot less political problems than LEO. In that case you would not want to use an Earth swingby obviously. And if you are using NTR, why not use ammonia? Much higher density, and it avoids those allegedly difficult cryogenic depots.
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Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #41 on: 08/09/2009 03:27 pm »
A reasonably functional depot (with sun-shade, solar power, active-cooling, safe haven etc) will have reasonably large mass and volume. Think something SkyLab size here. While it would be possible to launch one in several pieces and then launch crew to assemble it, a single 50t+ HLV with a big payload fairing would make the whole process (& depot design) a lot simpler.

I agree we should go for depots that can be launched on one EELV (or EELV Phase 1) launch. Based at L1, that is not a problem, especially with hypergolics, but even for LOX/LH2. Using LH2 NTR from LEO would be problematic volume-wise.

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Next consider the need to launch several depots, plus replacements over time. Possibly 8 HLV launches compared to how many EELV size launches?  Plus expensive crew assembly missions.  I'd rather send the crews exploring.

Agreed, and I believe solved.

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Then consider the in-space tugs to move propellant from one depot to the next.  Yes, an EELV could launch a complete expendable tanker spacecraft each time, but it would be more efficient to just launch full tanks.  Then have a small fleet of high effciency (SEP?) tugs take them to the depots.  Those tugs would tend to be rather large, again benefitting from HLV launch.

Tugs are a good idea. ISS sized solar arrays can be launched on a single EELV launch. EELV Phase 1 could launch two at a time.

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Throw in the requirements of crew trans-habs, Mars EDL vehicles, lunar landers and you begin to see how moderate HLV, (50t+, big payload fairings), complements a propellant depot architecture.

Trans-habs are assumed to be inflatable in the DRM anyway. And imagine the size of a Bigelow hab that will fit inside a 6.5m EELV fairing when not inflated. Horizontal landers do not need bigger fairings. EDL can be done with propulsive braking. Propellant can be prepositioned by SEP, which could give better effective Isp than NTR from LEO on a fast trajectory.

None of the things you mention are inevitable. HLV makes certain things easier, just like any other viable architecture has its strengths and weaknesses.

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150t+ HLV?  No.  50t to 100t? Yes.

I'd say 40mT to 50 mT? Perhaps. Bigger? No.
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Offline meiza

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Re: L1/2 spacestation with depot
« Reply #42 on: 08/09/2009 05:01 pm »
A reasonably functional depot (with sun-shade, solar power, active-cooling, safe haven etc) will have reasonably large mass and volume. Think something SkyLab size here. While it would be possible to launch one in several pieces and then launch crew to assemble it, a single 50t+ HLV with a big payload fairing would make the whole process (& depot design) a lot simpler.

A dry fuel functioning cryogenic fuel depot in the 35-40t range (J-246 capacity to EML-1) will have the capability to store about 5 times its dry mass or up to 200t. That's enough for several lunar sorties or interplanetary missions from your EML-1 space station + fuel depot. That means, your depot can be launched with a single HLV launch to EML-1.

Once you have advanced propulsion technology online like VASIMR (or other electrical propulsion) you can add another depot for a different type of fuel (argon for VASIMR).

That being said, I don't see why you need 8 HLVs or a Skylab-sized depot in any event.

Why would any depot be big?
A Centaur weighs 2 tonnes empty and can house 20 tonnes of LOX-LH2.
In space tankage weighs peanuts.

Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #43 on: 08/09/2009 05:08 pm »
Why would any depot be big?
A Centaur weighs 2 tonnes empty and can house 20 tonnes of LOX-LH2.
In space tankage weighs peanuts.

MMOD protection might be fairly heavy. And even 10% is a sizeable percentage of total fueled mass.
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Offline Archibald

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Re: L1/2 spacestation with depot
« Reply #44 on: 08/09/2009 05:26 pm »
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And if you are using NTR, why not use ammonia?

And if you use ammonia, why not use arcjet thruster and solar electric propulsion ?

Ammonia NTR = 600 s ISP.
Ammonia arcjet / SEP = 1000 s ISP.

The more I look at ammonia, the more I like it. To my knowledge, its the only fuel which is, altogether (!)
- hypergolic (with H2O2)
- "kerosene" (with LOX = ISP is similar)
- Thermal propulsion (either solar or nuclear)
- electric propulsion (if arcjet thrusters are used)

Talk about a versatile propellant !

It is also dense, midly cryogenic (-34°C), easy to ISRU (nitrogen and hydrogen are abundant in solar system bodies).

Last neat thing with NH3: it may replace gasoline in cars. At least it is much easier to handle than LH2. And you benefit from the fertilizer networks and infrastrctures. "Ammonia economy" anybody ?
What a noble mission for human spaceflight: bring ammonia back to Earth, to fuel the World economy...
« Last Edit: 08/09/2009 05:29 pm by Archibald »
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Offline TyMoore

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Re: L1/2 spacestation with depot
« Reply #45 on: 08/09/2009 05:34 pm »
You've got some good points with ammonia.

I wonder, how corrosive is anhydrous NH3 with Al-2195 alloy?
Could ammonia be stored in typical propellant tanks for long periods of time?

Offline meiza

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Re: L1/2 spacestation with depot
« Reply #46 on: 08/09/2009 05:49 pm »
Why would any depot be big?
A Centaur weighs 2 tonnes empty and can house 20 tonnes of LOX-LH2.
In space tankage weighs peanuts.

MMOD protection might be fairly heavy. And even 10% is a sizeable percentage of total fueled mass.

A 200 ton depot might be 25 tons. I don't see that size coming around very quickly.

This is a complete non-issue.

Offline Archibald

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Re: L1/2 spacestation with depot
« Reply #47 on: 08/09/2009 06:14 pm »
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I wonder, how corrosive is anhydrous NH3 with Al-2195 alloy?
Could ammonia be stored in typical propellant tanks for long periods of time?

Oh, probably nothing worse than "storable" propellants. Hydrazine, N2O4, NTO are truly nasty substances...

Forget: the three brave old X-15s flew for ten years with ammonia as propellant.
« Last Edit: 08/09/2009 06:18 pm by Archibald »
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Offline Bill White

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Re: L1/2 spacestation with depot
« Reply #48 on: 08/09/2009 06:29 pm »
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In space tankage weighs peanuts.

How many duty cycles (hot/cold) can a tank handle before needing to be replaced?

= = =

If using hypergolics, why not simply accumulate Fregat modules at yor depot and skip the propellant transfer step altogether?
EML architectures should be seen as ratchet opportunities

Offline kkattula

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Re: L1/2 spacestation with depot
« Reply #49 on: 08/10/2009 05:48 am »
The Mars DRM assumes 65mT chunks, and with the delta-v numbers above that means less than 65mT in propellant. A depot that contains such amounts of propellant can fit easily within an EELV fairing.

Note that the DRM also assumes NTR. With L1 staging you don't need the nukes (and you can reuse the ITV). And even if you do want them, L1 will likely give a lot less political problems than LEO. In that case you would not want to use an Earth swingby obviously. And if you are using NTR, why not use ammonia? Much higher density, and it avoids those allegedly difficult cryogenic depots.

How many 65t chunks?  The every two years launch window is not that large. Are you going to re-fill the depot in a week? What if something goes wrong?  Surely you want enough propellant in the depot for the whole mission, before you launch the high value payloads?  Otherwise it's not a depot, just propellant transfer.

Ammonia has lower Isp than LH2, reducing the advantage of going NTR.


Offline simon-th

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Re: L1/2 spacestation with depot
« Reply #50 on: 08/10/2009 08:08 am »

Ammonia has lower Isp than LH2, reducing the advantage of going NTR.


Yep, if we really want to go for an alternative to chemical propulsion for interplanetary space travel, we need to look into Argon depots. They are entirely possible.

P.S. I assume that a Mars surface mission using an L1/2 depot will look very different from the current DRM. That is, rather than sending payloads to Mars first and separately, I think everything would be lumped together - the NTR stage (which gets fueled at the L1/2 depot), the hab surface module and hardware, the Mars ascent vehicle and the crew Mars in space hab module (which stays in Mars orbit) - in total probably 4 launches to L1/2 with an HLV per mission if you use the depot for fuel purposes. And the lovely thing is, rather than throwing away your NTR stage or your Mars in-space hab module, you can reuse it for your next mission after the first returns from the first Mars mission - reducing the required launches per mission to 2 (without considering launches for fuel to the depot).

Offline Arthur

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Re: L1/2 spacestation with depot
« Reply #51 on: 08/10/2009 12:09 pm »
While I find the concept of small EELVs launching small rockets that can 'fill-er-up' at depots located at multiple Lagrange points fascinating, isn't this the same basic fallacy that caused the Shuttle to fail to meet projected cost and performance goals? Overesimating demand and building an expensive but underused infrastructure?

Would multiple depots really be the most economical investment for a single flag planting mission to the moon and a second flag planting mission to Mars? If NASA only launches one or two missions per year, is a depot arcitecture too expensive to maintain?

If, as I suspect, Depots are most effective when used often (missions in bulk), is there any indication what-so-ever that NASA and Congress would support a program that involves 6-12 missions per year?

Don't get me wrong, I would love to see a permenant manned base on the moon. I would love to see a skylab over Mars scouting locations for Martian outposts. Depots might help make that more affordable.

I just feel like I am very much in the minority when it comes to spending money on space and don't want to spend the limited budget creating depots that will be used 1-2 times in a decade before joining the unused Saturn V Launcher, unused 2nd Skylab, retired early Shuttles and unused Ares I as another waste of potential and valuable resources by a fickled vision for space.

Offline simon-th

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Re: L1/2 spacestation with depot
« Reply #52 on: 08/10/2009 12:23 pm »

Would multiple depots really be the most economical investment for a single flag planting mission to the moon and a second flag planting mission to Mars? If NASA only launches one or two missions per year, is a depot arcitecture too expensive to maintain?

If, as I suspect, Depots are most effective when used often (missions in bulk), is there any indication what-so-ever that NASA and Congress would support a program that involves 6-12 missions per year?


A depot is nothing more than an unmanned module. You build it, you launch it and you send fuel to refill it. It's like a GEO satellite, you "operate" it by just monitoring its life function. That's not costly.

A cryogenic (LOX only or LH2/LOX) depot module would have to include a recooling cycle to not have any boil off as well as a power source (solar panels), RCS for station keeping etc.

Still, the usefulness of a depot structure is not diminished by doing only 1-2 missions per year using propellant from the depot. Your trade is whether the cost refueling the depot with smaller commercial rockets is cheaper than using say 2 HLVs for a lunar mission instead of just one HLV and the fuel from depot option or 4 HLVs for a Flexible Path mission vs. just 1-2 HLVs with use of fuel from the depot. If you go for more missions per year, the trade stays the same. The point where your depot become a bad trade is probably once your commercial refueling missions are so scarce, you don't get a high flight rate for those commercial rockets to your depot (for a L1/2 depot that would mean less than about 50-100mt of fuel to the depot per year).

Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #53 on: 08/10/2009 12:25 pm »
While I find the concept of small EELVs launching small rockets that can 'fill-er-up' at depots located at multiple Lagrange points fascinating, isn't this the same basic fallacy that caused the Shuttle to fail to meet projected cost and performance goals? Overesimating demand and building an expensive but underused infrastructure?

Well, there's the potentially low utilisation of depots on the one hand versus the currently low utilisation of EELVs and projected low usage and high infrastructure costs of an SDLV. I agree with kkatula that design and development costs of depots would likely dominate total costs. In order to reduce costs (or increase benefits or both) you could use in-flight refueling: build one type of universal vehicle that can serve as crew shuttle, lander, depot, mini space station, rescue craft and cargo transfer stage. Constellation plans envisage building two expendable landers a year. Instead of that you could build two reusable universal spacecraft a year, which would allow you to build up reusable infrastructure reasonably quickly.

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Would multiple depots really be the most economical investment for a single flag planting mission to the moon and a second flag planting mission to Mars? If NASA only launches one or two missions per year, is a depot arcitecture too expensive to maintain?

SDLV fixed costs are something like $2B a year, which should buy you two universal spacecraft.

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If, as I suspect, Depots are most effective when used often (missions in bulk), is there any indication what-so-ever that NASA and Congress would support a program that involves 6-12 missions per year?

I think that's out of the question. Two lunar missions perhaps, eventually. Two NEO missions or four Lagrange point missions sound reasonable.

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Don't get me wrong, I would love to see a permenant manned base on the moon. I would love to see a skylab over Mars scouting locations for Martian outposts. Depots might help make that more affordable.

I just feel like I am very much in the minority when it comes to spending money on space and don't want to spend the limited budget creating depots that will be used 1-2 times in a decade before joining the unused Saturn V Launcher, unused 2nd Skylab, retired early Shuttles and unused Ares I as another waste of potential and valuable resources by a fickled vision for space.

Well, I agree about the limited desire to spend money on space, but think it's either depots or HLVs. Either would be little used. Depots would have lower fixed costs, more synergy to the commercial development of space and could have secondary functions if designed in the form of a universal spacecraft.

If there has to be an HLV, let it be EELV Phase 1, since it would have more synergy with commercial launches. Or EELV Phase 2 as a last resort, but only if depots have been shown to be uneconomical.
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Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #54 on: 08/10/2009 01:27 pm »
How many 65t chunks?  The every two years launch window is not that large. Are you going to re-fill the depot in a week? What if something goes wrong?  Surely you want enough propellant in the depot for the whole mission, before you launch the high value payloads?  Otherwise it's not a depot, just propellant transfer.

That's a good point. I don't have a good handle yet on launch windows, mission duration and delta-v. David and I have been doing sums based on Hohmann transfers only.

The hab, lander, depots and propellant could be prepositioned. If those are sent by SEP, I don't think you have to worry about launch windows all that much, but I could be wrong about that.

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Ammonia has lower Isp than LH2, reducing the advantage of going NTR.

Sure, but from L1/SEL-2 you don't need nukes or even cryogenics. Isp of 600s is still very good performance. I'm not in favour of nukes on the critical path, but I am in favour of developing NTR as a later upgrade. Similarly I'm not in favour of putting cryogenic depots on the critical path, but definitely in favour of developing them as later upgrades. In this case even more so because of political considerations. I'm even more strongly opposed to HLV, not just on the critical path, but even as a later upgrade, although it would be good to keep the option as a backup. EELV Phase 2 could be that option.

I would assign the following priorities:

1) depots (initially hypergolic ones)
2) ISRU
3) SEP
4) manned surface bases
5) NTR (using ammonia if payload fairing size is an issue)
« Last Edit: 08/10/2009 01:27 pm by mmeijeri »
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Offline savuporo

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Re: L1/2 spacestation with depot
« Reply #55 on: 08/10/2009 02:19 pm »
Would multiple depots really be the most economical investment for a single flag planting mission to the moon and a second flag planting mission to Mars?

If the goal, the "why" of going, is flag planting, then anything related to it isn't economical investment by definition.
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Offline Archibald

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Re: L1/2 spacestation with depot
« Reply #56 on: 08/10/2009 04:59 pm »
Quote
Ammonia has lower Isp than LH2, reducing the advantage of going NTR.

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Sure, but from L1/SEL-2 you don't need nukes or even cryogenics. Isp of 600s is still very good performance. I'm not in favour of nukes on the critical path, but I am in favour of developing NTR as a later upgrade. Similarly I'm not in favour of putting cryogenic depots on the critical path, but definitely in favour of developing them as later upgrades. In this case even more so because of political considerations. I'm even more strongly opposed to HLV, not just on the critical path, but even as a later upgrade, although it would be good to keep the option as a backup. EELV Phase 2 could be that option.

I would assign the following priorities:

1) depots (initially hypergolic ones)
2) ISRU
3) SEP
4) manned surface bases
5) NTR (using ammonia if payload fairing size is an issue)
NTR and Bimodal NTR are certainly not the panacea. And the fact that NERVA went quite far into testing thirty years ago doesn't change anything to that.

http://forum.nasaspaceflight.com/index.php?topic=1139.0

If you really want to use nuclear reactors for propulsion, go for NEP. Arcjets, hall or Ion thrusters, plus a molten salt reactor - the best fission reactor on hand these days.
« Last Edit: 08/10/2009 05:00 pm by Archibald »
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Offline A_M_Swallow

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Re: L1/2 spacestation with depot
« Reply #57 on: 08/12/2009 02:28 am »
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And if you are using NTR, why not use ammonia?

And if you use ammonia, why not use arcjet thruster and solar electric propulsion ?

Ammonia NTR = 600 s ISP.
Ammonia arcjet / SEP = 1000 s ISP.

The more I look at ammonia, the more I like it. To my knowledge, its the only fuel which is, altogether (!)
- hypergolic (with H2O2)
- "kerosene" (with LOX = ISP is similar)
- Thermal propulsion (either solar or nuclear)
- electric propulsion (if arcjet thrusters are used)

Talk about a versatile propellant !

It is also dense, midly cryogenic (-34°C), easy to ISRU (nitrogen and hydrogen are abundant in solar system bodies).

Last neat thing with NH3: it may replace gasoline in cars. At least it is much easier to handle than LH2. And you benefit from the fertilizer networks and infrastrctures. "Ammonia economy" anybody ?
What a noble mission for human spaceflight: bring ammonia back to Earth, to fuel the World economy...


It is worth testing to see if the VASIMR thrusters can use ammonia as a propellant.  Possibly using an old 50 kW VASIMR.

Offline Archibald

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Re: L1/2 spacestation with depot
« Reply #58 on: 09/21/2009 04:04 pm »
Not sure for VASIMr, but it looks like its competitors may run on ammonia

PIT thruster
http://gltrs.grc.nasa.gov/cgi-bin/GLTRS/browse.pl?1993/E-7941.html

Magnetoplasmadynamic (MPD) / lithium Lorentz force accelerator (LiLFA) thrusters
http://en.wikipedia.org/wiki/Ion_thruster

However I'm not very sure they are mature enough, as of 2009. This paper summarize pros and cons of varied electric thrusters for Mars missions.

http://alfven.princeton.edu/papers/Astrodyn-Final.pdf

The fact PIT/MPd thrusters use ammonia as propellant is nevertheless encouraging.
« Last Edit: 09/21/2009 04:26 pm by Archibald »
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Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #59 on: 09/21/2009 04:08 pm »
Rereading what I wrote above I think I'd now switch the priorities of SEP and ISRU given that SEP from L1 to Mars orbit can be done with existing technology. Only for propellant, but that's good enough.
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