### Author Topic: L1/2 spacestation with depot  (Read 41325 times)

#### Hop_David

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##### Re: L1/2 spacestation with depot
« Reply #20 on: 08/07/2009 08:21 PM »
David, also consider the effect of an Earth swingby. Look up the Oberth effect and hyperbolic trajectories on Wikipedia. The swingby amplifies the effect of your TMI. There's also a section on this in the documentation (in the "Deep Space Manual") of the freeware Orbiter flight simulator.

In the above I've set apogee at L1 altitude and Martian apoapsis at Deimos altitude. periapsis for both earth and Mars I set at 300 km.

This earth orbit is moving close to escape at perigee. Leaving perigee for TMI only takes about .5 km/sec.

Exiting Hohmann for the Mars orbit is about 1 km/sec.

So leaving earth orbit and entering Mars orbit takes a total of 1.5 km/sec.

However these elliptical orbits aren't your actual departure and destination orbits. You want to drop from a circular orbit at L1 and at your Mars apoapsis you want to do a circularization burn to match velocities with Deimos.

So under normal circumstances I would add apoapsis circulization burns to the 1.5 km/sec. This totals about 3.05 km/sec

But in this case the spreadsheet gives a wrong value for earth's circle V at apoapsis. Without the moon's influence, a circular orbit at that altitude is 1.1 km/sec. But L1 is moving at the same angular velocity as the moon. It's moving about .86 km/sec rather than 1.1 km/sec.

Since dropping from L1 takes a little less than the spreadsheet indicates we can shave off about .25 km/sec from the 3.05 for about 2.8 km/sec.

So I believe my spreadsheet takes the Oberth effect into account and patches conics correctly. But it's off a little bit  because it doesn't include the moon's influence in slowing the L1 circular orbit from the ordinary 1.1 km/sec
« Last Edit: 08/07/2009 08:31 PM by Hop_David »

#### mmeijeri

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##### Re: L1/2 spacestation with depot
« Reply #21 on: 08/07/2009 08:46 PM »
Nice work, I see you are a bit ahead of me on the Mars calculations.
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#### mmeijeri

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##### Re: L1/2 spacestation with depot
« Reply #22 on: 08/08/2009 10:23 AM »
OK, I've dusted off my old Mars calculations and my numbers are similar, though slightly different. I hadn't realised you were talking about both the TMI and the MOI, so your numbers seemed a bit high a first. In my spreadsheet I have a number of 640 m/s for return from L1 to Earth, so dropping your perigee to only 300km should be similar. This is less than what I'd expect from Hohmann combined with the right angular velocity at L1. Should be fun to investigate this with numerical integration.

A perigee lowering burn from SEL-2 should be even cheaper, my Hohmann estimate gives me something like 500m/s, but it might be even less. Farquhar has proposed doing both a lunar swingby and an Earth swingby, though it's not clear to me in what order. He may be thinking about lowering your perigee to moon orbit radius, then doing a further burn at lunar periapsis, lowering the then apogee to LEO altitude (which means it will become the new perigee, with apogee at lunar orbit radius in a much smaller but only slightly less energetic orbit than SEL-2) and doing the TMI there. Or perhaps doing the lunar swingby after the Earth swingby. In any event I believe he expects more efficiency from using SEL-2 instead of L1.
« Last Edit: 08/08/2009 11:45 AM by mmeijeri »
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#### Archibald

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##### Re: L1/2 spacestation with depot
« Reply #23 on: 08/08/2009 10:55 AM »
Quote
In any event I believe he expects more efficiency from using SEL-2 instead of L1.

even without the maths, it is quite obvious when reading Farquhar's papers.
For example in 1985 he proposed an "interplanetary transfer vehicle" (ITV) going back and forth between Earth and Mars. The vehicle was based at a Sun-Earth libration point (SEL-1 I think)

#### mmeijeri

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##### Re: L1/2 spacestation with depot
« Reply #24 on: 08/08/2009 11:12 AM »
At Mars, instead of rendez-vousing with Deimos, you could also brake into a much higher orbit and end up at Sun Mars L1/L2. This should be a lot cheaper. I need to update my spreadsheet for this, but in the mean-time I'd be really interested in what numbers David comes up with. Sun Mars L1/L2 would be a good place to dock with a landing craft or even a transfer craft to Deimos or low Mars orbit. You could also refuel there. Propellant could be prepositioned by SEP and the Interplanetary Transport Network. It could come from Earth or with ISRU it could come from the moon, Phobos/Deimos or Mars itself.

It's fun to see how small the burns are if you stage at high-energy orbits, well within reach of hypergolics. No HLVs needed.
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#### kkattula

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##### Re: L1/2 spacestation with depot
« Reply #25 on: 08/08/2009 03:55 PM »
IMHO, the biggest costs of a depot will be the design, development, facility & tool setup, and testing.  Final manufacture and launch will be but a small part of that.
Therefore, while the cost of one depot may be fairly high, the cost of each subsequent one will be just a small fraction of the first's.

Having multiple depots (in LEO, L1/L2, Mars orbit, etc) will reduce the scale and costs of the other vehicles required for exploration. Thus multiple depots may in fact be cheaper overall than just one.

#### kkattula

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##### Re: L1/2 spacestation with depot
« Reply #26 on: 08/08/2009 04:30 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.

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.

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.

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.

150t+ HLV?  No.  50t to 100t? Yes.

#### mmeijeri

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##### Re: L1/2 spacestation with depot
« Reply #27 on: 08/08/2009 05:01 PM »
The depot doesn't have to be so big it cannot be launched without an HLV, especially if you put it at L1.
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#### Hop_David

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##### Re: L1/2 spacestation with depot
« Reply #28 on: 08/08/2009 05:33 PM »
At Mars, instead of rendez-vousing with Deimos, you could also brake into a much higher orbit and end up at Sun Mars L1/L2. This should be a lot cheaper. I need to update my spreadsheet for this, but in the mean-time I'd be really interested in what numbers David comes up with.

Earth departure remains the same: .7 to drop from EML1 and a .5 burn at perigee for TMI for about 1.2

Putting Mars apogee at 1.08 million kilometers does make the Hohmann exit burn smaller: .6888 Mars perigee burn to park the ship in an orbit with that high apoapsis.

Circle V at apoapsis .1990
Ellipse V at apoapsis .0146
Apoapsis circulize burn .1825

But this is wrong since my spreadsheet is old school 2-body patched conics and doesn't consider the sun's influence on this Mars orbit. The velocity of Sun-Mars L1 wrt  Mars isn't .1990 but 0 km/sec.

So I would guess the "circulize burn" at Mars apoapsis would be .0146.

Totalling all these, my guess would be 1.84 km/sec for EML1 to SunMarsL1

Even though the Sun Mars L1 takes less delta V, I still favor Deimos and Phobos.

These two moons almost certainly have oxygen rich minerals. And possibly volatiles. They could be valuable sources of propellant. If they have hydrogen rich volatiles, they could supply EML1, LEO and the Moon for the non-oxygen part of propellant. The moon's regolith could provide radiation shielding. They are tide locked with Mars which facilitates communication with Mars surface.

These moons should be of great interest to planetary scientists. I often wonder how these two seemingly captured asteroids came to be parked in near circular, equatorial orbits.

Once the Martian moons are developed, they might supply propellant to the Sun Mars L1&2. I believe it'd take 1 km/sec to get something from Deimos to Sun Mars L1.
« Last Edit: 08/08/2009 05:35 PM by Hop_David »

#### kkattula

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##### Re: L1/2 spacestation with depot
« Reply #29 on: 08/08/2009 05:38 PM »
The depot doesn't have to be so big it cannot be launched without an HLV, especially if you put it at L1.

How much propellant does it need?  Of what kind?

#### Hop_David

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##### Re: L1/2 spacestation with depot
« Reply #30 on: 08/08/2009 05:55 PM »
Sun Mars L1/L2 would be a good place to dock with a landing craft or even a transfer craft to Deimos or low Mars orbit. You could also refuel there. Propellant could be prepositioned by SEP and the Interplanetary Transport Network. It could come from Earth or with ISRU it could come from the moon, Phobos/Deimos or Mars itself.

Didn't see this part on my first read.

From the Marsden et al paper we're studying, it doesn't take much to get from the earth-moon Lagrange 1&2 to the sun-earth Lagrange 1&2 regions. So it might be possible to get stuff from EML1&2 to Sun-Mars L1&2 with little delta V. But since the Interplanetary Transport Network is still mysterious to me, I have to admit I'm guessing. If there are low delta V routes to Sun Mars L1&2, I'd expect them to take a long time.

As I mentioned earlier, I think it'd take about 1 km/sec to get cargo from Deimos to SML1.

I don't like the idea of Mars supplying propellant. Mars has an atmosphere comparable to earth's Mesosphere where most meteors burn up. So I believe an ascent burn is needed, like on earth. I've been told Martian gravity/drag penalty is about .8 km/sec. So it would take 6 or 7 km/sec to get stuff from Mars to SML1.

#### mmeijeri

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##### Re: L1/2 spacestation with depot
« Reply #31 on: 08/08/2009 06:26 PM »
Earth departure remains the same: .7 to drop from EML1 and a .5 burn at perigee for TMI for about 1.2

I'm getting 0.88km/s for SEL-2 to TMI, but with a very primitive estimate. Sounds like an excellent exercise for our dynamical systems thread!

Quote
Totalling all these, my guess would be 1.84 km/sec for EML1 to SunMarsL1

Sounds pretty good. I'm getting mass factors of 1.5 for RL-10 and 1.78 for the Orion MPS. This means a penalty for hypergolics of 18% total mass or 54% propellant mass.

Quote
Even though the Sun Mars L1 takes less delta V, I still favor Deimos and Phobos.

I agree they are more plausible as locations for early bases, I was thinking more of a refueling stop and the possibility of not braking the entire Interplanetary Transfer Vehicle into low Mars Orbit, just the much smaller Planetary Transfer Vehicle. You might not even bring that with you from Earth every time, you could have it stationed near Mars, going back and forth from LMO to SML1/2 just like its counterpart near Earth which could go back and forth between L1 and SEL-2.
« Last Edit: 08/08/2009 06:33 PM by mmeijeri »
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#### mmeijeri

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##### Re: L1/2 spacestation with depot
« Reply #32 on: 08/08/2009 06:31 PM »
From the Marsden et al paper we're studying, it doesn't take much to get from the earth-moon Lagrange 1&2 to the sun-earth Lagrange 1&2 regions. So it might be possible to get stuff from EML1&2 to Sun-Mars L1&2 with little delta V. But since the Interplanetary Transport Network is still mysterious to me, I have to admit I'm guessing. If there are low delta V routes to Sun Mars L1&2, I'd expect them to take a long time.

Yeah, I'd love to know more about the flight times. If it's less than five years, it might be interesting. Otherwise we might be better off with SEP.

Quote
As I mentioned earlier, I think it'd take about 1 km/sec to get cargo from Deimos to SML1.

I don't like the idea of Mars supplying propellant. Mars has an atmosphere comparable to earth's Mesosphere where most meteors burn up. So I believe an ascent burn is needed, like on earth. I've been told Martian gravity/drag penalty is about .8 km/sec. So it would take 6 or 7 km/sec to get stuff from Mars to SML1.

You're right, Deimos looks very interesting from a delta-v perspective. Mars ISRU might be easier though, it would mean getting stuff from the atmosphere instead of processing regolith. Deimos ISRU on the other hand would have more commonality with Moon ISRU. Getting fuels might be easier from Mars and oxygen easier from Deimos.
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#### simon-th

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##### Re: L1/2 spacestation with depot
« Reply #33 on: 08/08/2009 07:34 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.

#### Archibald

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##### Re: L1/2 spacestation with depot
« Reply #34 on: 08/08/2009 08:01 PM »
At Mars, instead of rendez-vousing with Deimos, you could also brake into a much higher orbit and end up at Sun Mars L1/L2. This should be a lot cheaper. I need to update my spreadsheet for this, but in the mean-time I'd be really interested in what numbers David comes up with. Sun Mars L1/L2 would be a good place to dock with a landing craft or even a transfer craft to Deimos or low Mars orbit. You could also refuel there. Propellant could be prepositioned by SEP and the Interplanetary Transport Network. It could come from Earth or with ISRU it could come from the moon, Phobos/Deimos or Mars itself.

It's fun to see how small the burns are if you stage at high-energy orbits, well within reach of hypergolics. No HLVs needed.

I like(d) Sun-Mars L1, too.

http://forum.nasaspaceflight.com/index.php?topic=13794.msg299223#msg299223

However then i had an idea. Remeber Farquhar powered lunar swingby ? Well, what about a powered Mars swingby, to Sun-Mars L2 ? If that works for the Moon, it should work for Mars isn't it ?

#### mmeijeri

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##### Re: L1/2 spacestation with depot
« Reply #35 on: 08/08/2009 08:30 PM »
However then i had an idea. Remeber Farquhar powered lunar swingby ? Well, what about a powered Mars swingby, to Sun-Mars L2 ? If that works for the Moon, it should work for Mars isn't it ?

Great idea, but unfortunately that's what David's calculations are already using...
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#### A_M_Swallow

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##### Re: L1/2 spacestation with depot
« Reply #36 on: 08/08/2009 10:59 PM »
Once SEP tugs exist they can be used to push dry depots from LEO to L1 and Mars.

Current EELV can launch depots with a mass of about 25 mT to LEO.

If a SEP tug is used to take hydrogen to L1, Mars and/or LLO
the tank will need a sun-shade and refrigeration.  So the tank would have to be a full depot.

edit: grammar
« Last Edit: 06/30/2010 02:50 PM by A_M_Swallow »

#### Archibald

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##### Re: L1/2 spacestation with depot
« Reply #37 on: 08/09/2009 06:29 AM »
Slightly of topic, I would want to see an update of the 1966 FLEM (Flyby Landing Excursion Mode) integrating Sun-Mars L1 or L2.

Quote

A FLEM mission boosted toward Mars using a nuclear rocket during the favorable 1971 transfer opportunity could have a mass as low as 260,000 pounds at launch from Earth orbit, Titus estimated, perhaps permitting a piloted Mars stopover with only a single Saturn V launch.

Probably way too optimistic, that's sure. But the basic idea is: if you don't stop a large stack in Mars orbit, you save a lot of IMLEO.
FLEM considered a very dangerous rendez-vous of the MEM with a high-speed MArs flyby spacecraft. Maybe we could move this rendez-vous to a halo orbit around Sun-Mars L1...

#### kkattula

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##### Re: L1/2 spacestation with depot
« Reply #38 on: 08/09/2009 12:05 PM »
Current manned Mars mission designs are looking at around 400t of cryo propellant in LEO.  Probably 200+ at EML-1?

Allowing for margin, other propellant & fluids, safe haven crew hab, power systems, docking systems, cooling systems, sun shade, remote maipulator arm, etc, I don't think 35t to 40t is enough. 60t is more like it.  Skylab was 77t.

#### simon-th

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##### Re: L1/2 spacestation with depot
« Reply #39 on: 08/09/2009 12:28 PM »
Current manned Mars mission designs are looking at around 400t of cryo propellant in LEO.  Probably 200+ at EML-1?

You are talking about a human surface Mars mission.

I was talking about the "Flexible Path" scenarios and lunar sorties.

A Flexible Path mission to a NEO or a Mars flyby or even a Mars orbital mission will all be under 50-60t of fuel from EML-1 - and with VASIMR or other advanced technology well below that in the 30t and below range.

If you first only store LOX at your EML-1 depot and you refuel a 40t-ish lunar lander in EML-1 about ~20t+ will be LOX. We can safely assume that a 40t fuel depot module (dry) can hold up to 5 times that dry amount in fuel - looking at upper stages' dry/fueled ratios (which are considerably above that 1:5 ratio - in the 1:10 and more area).

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