Author Topic: L1/2 spacestation with depot  (Read 41248 times)

Offline simon-th

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L1/2 spacestation with depot
« on: 08/07/2009 08:13 AM »
Let's have a dedicated thread about a small spacestation (doesn't have to be occupied permanently at the beginning) at L1/2 with a depot considering all the discussion about depots and Flexible Path recently.

Benefits include:

 - Depots at L1/2 make more sense than depots in LEO - you don't have to store all the EDS propellant
 - You can go from L1/2 to a variety of destinations and come back to L1/2:
 e.g. Moon's surface: 2.5km/s delta-v to nearly everywhere and the same delta-v back to L1/2
       to a Mars transfer orbit, you require about 0.8km/s delta-v from that station and another 0.9km/s into a Mars capture orbit - the same thing back
 - Rather than having to take a 20mt Orion along on deep-space travel, you just leave Orion at the station (probably even gets used for station crew rotation and you take the next Orion back to Earth after you return) and only take a dedicated hab on your journey
 - you could have a dedicated depot for LH2/LOX or only LOX or at the beginning only hypergolics for lunar missions and a dedicated depot for argon for interplanetary missions using VASIMR (or derivatives)
 - rather than throwing away your perfectly good VASIMR stage, 1MW solar power generation unit and interplanetary hab module (aka your spaceship which you could give an inspiring name...) after one mission, you use it for several missions
 - at some point, if technology improves, even lunar landers could be made reusable (As suggested by many people already)
 - a sustainable Mars mission architecture could be construed this way after you have done several Flexible Path missions - rather than putting all your structure on Mars in different launches, you use 2 launches for your Mars surface mission modules (40t each with heatshield) to get them to your L1/2 station, dock with your spaceship which you have already been using for a previous Mars orbital mission, fuel up your VASIMR stage with quite some argon and off you go for a Mars mission with just one spacecraft in the say 300t range (fully fueled) - and rather than throwing all your infrastructure away after each mission you just reuse it on the next mission.

EDIT: VASIMR
« Last Edit: 08/07/2009 12:36 PM by simon-th »

Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #1 on: 08/07/2009 08:24 AM »
Quote
- Depots at L1/2 make more sense than depots in LEO - you don't have to store all the EDS propellant

I don't think this is true. For one you couldn't refuel your upper stage in LEO, so you would need a bigger launcher to launch a fully fueled EDS. Now I'm actually in favour of doing it this way in the short run (since it gets cryogenic depots off the critical path), but in the slightly longer run it is a disadvantage. Another disadvantage is that L1 rules out participation in propellant launches by small launch vehicles, which negates most of the benefit of depots. There is a very good case for doing both LEO and L1 depots and gateway stations however.
« Last Edit: 08/07/2009 08:28 AM by mmeijeri »
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Offline Archibald

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Re: L1/2 spacestation with depot
« Reply #2 on: 08/07/2009 11:21 AM »
Quote

Another disadvantage is that L1 rules out participation in propellant launches by small launch vehicles


Unless you use Belbruno trajectories.

Another alternative would be SEP/ STP tugs build by private entrepreneurship ( when talking about private SEP tug I think about Dennis Wingo Orbital Recovery /Hubble rescue  proposals > a SEP tug build from existing satellite electric thrusters plus ISS solar arrays) 

Why couldn't these tugs  refuel a NASA L1 / L2 station through COTS-like contracts ?

To summarize, a private entity would first launch a fuel tank to LEO. Then, a second private entity would pick the tank and send it to the L1 station via a STP or SEP tug.

Now that would boost the number of launches to LEO. Lots of fuel tanks, lots of tugs to launch !
« Last Edit: 08/07/2009 11:22 AM by Archibald »

Offline simon-th

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Re: L1/2 spacestation with depot
« Reply #3 on: 08/07/2009 12:24 PM »
Quote
- Depots at L1/2 make more sense than depots in LEO - you don't have to store all the EDS propellant

I don't think this is true. For one you couldn't refuel your upper stage in LEO, so you would need a bigger launcher to launch a fully fueled EDS.

I am not entirely sure I understand what you are getting at. A L1/2 depot (with a small manned space station - permanently manned or just temporarily manned) would be supplied by commercial launch providers. Of course only rockets with a launch capacity of several tons to EML-1 or EML-2 make sense to use for this task. This would rule out small rockets such as Taurus II. I'd say you are in the 10-35mt to LEO launcher field with about 4 to 15mt payload capacity to EML-1/2 for depot supplying duties. Entirely ok, if you ask me.

And the big benefit is, your depot doesn't have to store 1000mt fuel or more, it just has to hold in the range of 250-350mt of fuel for the same purpose than a LEO depot (+ you get all the added advantages above from a mission architecture perspective that a LEO depot doesn't provide you with - reusing in-deep space flight hardware - VASIMIR stages, Orion only to EML-1 or EML-2 and not all the way to Mars etc.).

Quote
Now I'm actually in favour of doing it this way in the short run (since it gets cryogenic depots off the critical path), but in the slightly longer run it is a disadvantage.

How so? I'd say it's the other way around. For NEO and circumlunar precursor missions, you really don't need any fuel depots. But once you go for lunar surface missions and interplanetary missions all those nice advantages that I listed pop up for a EML-1/2 depot.

Quote
Another disadvantage is that L1 rules out participation in propellant launches by small launch vehicles, which negates most of the benefit of depots.

I addressed that above. I very much disagree. Small rockets (in the 5-10mt to LEO range) are inefficient in kg to cost anyway. Launching 20 rockets with a 25mt to LEO and 12mt to EML-1/2  capacity gets you a much better price per kg to LEO/EML-1/2 than 50 rockets with a 10mt to LEO launcher. That's because your variable cost start to lead your total expense line when you get into the 15-20 launches per year range.


Offline simon-th

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Re: L1/2 spacestation with depot
« Reply #4 on: 08/07/2009 12:26 PM »
I attach a flowchart of how I would envision a development and ops timeline from 2010-2030 with a L1/2 spacestation with depot capability, Flexible Path, directly shuttle derived HLV and lunar sorties added to Flexible Path with a long term goal of a human Mars surface mission in the late 2030s.

Of course, this would be an "above budget" option, in the 90-100 billion range to 2020 (in line with FY2009 budget guidance however...).
« Last Edit: 08/07/2009 08:54 PM by simon-th »

Offline iontyre

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Re: L1/2 spacestation with depot
« Reply #5 on: 08/07/2009 12:32 PM »
Before we go much further, let's get one thing straight:

It is VASIMR, not VASIMIR.

Variable Specific Impulse Magnetoplasma Rocket
« Last Edit: 08/07/2009 12:41 PM by iontyre »

Offline Arthur

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Re: L1/2 spacestation with depot
« Reply #6 on: 08/07/2009 12:38 PM »
- you could have a dedicated depot for LH2/LOX or only LOX or at the beginning only hypergolics for lunar missions and a dedicated depot for argon for interplanetary missions using VASIMIR (or derivatives)

If you will permit a question born out of ignorance:
I know that the vacuum of space is a terrific insulator.
I also know that cryogenic fuels (like LOX and LH2) like to boil off.

So how fast would a L1/2 depot loose LH2 to boil off?
Could I fill the depot and use the fuel a year later, or would it be empty in a couple months?

I am just attempting to get a feel for what the practical usefulness and limitations are for fuel depots.



With respect for Hypergolics vs Cryogenic fuels, I was under the impression that LH2 was overwhelmingly superior than Hypergolics for long range missions (like Mars).

What would the typical mission mass penalty be for using Hypergolics over LH2?

Any idea how long of a storage/mission length is required to make Hypergolics better than Cryogenics?
Earth to Mars?
Earth to Jupiter?
Earth to OORT cloud? (unmanned of course)
« Last Edit: 08/07/2009 12:40 PM by Arthur »

Offline DGH

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Re: L1/2 spacestation with depot
« Reply #7 on: 08/07/2009 12:45 PM »
The station has many other benefits as well.

A safe haven.
Solar sells to help power the Orion.
A check out point before lunar landing.

Also a depot does not have to be only fuel.
Food, water, spare parts and other equipment could be stored there.
A Delta IV heavy could deliver about 3-4 mt of supplies more if fuel to an EML station.
Most equipment and fuel could take the slow route.

The trick would be to keep the station simple.
Say a single Bigelow Sundancer with additional docking ports not an ISS.

Mixing flexible and Lunar base in this way seems to me most in line with the original VSE proposals.

Offline simon-th

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Re: L1/2 spacestation with depot
« Reply #8 on: 08/07/2009 12:47 PM »

So how fast would a L1/2 depot loose LH2 to boil off?
Could I fill the depot and use the fuel a year later, or would it be empty in a couple months?

I am just attempting to get a feel for what the practical usefulness and limitations are for fuel depots.

You need to develop the technology which deals with boil off, that is you have a cycle where you constantly use the "biol off propellant" after you bring it to the required low temperature again and add it back to the depot. Of course that means you need such a cooling cycle system and a power system which runs that system as well as shielding which mitigates the amount of propellant you need to get through your cycle constantly.

Quote
With respect for Hypergolics vs Cryogenic fuels, I was under the impression that LH2 was overwhelmingly superior than Hypergolics for long range missions (like Mars).
For interplanetary travel you should (not necessarily must) go for alternative propulsion system - e.g. VASIMR or similar high-isp, medium thrust engines.

Quote
What would the typical mission mass penalty be for using Hypergolics over LH2?

isp hypergolics 320
isp LH2/LOX 450
for a delta-v of 1000m/s a 20mt spacecraft (Orion) requires 5.5mt of fuel if you go for hypergolics, for the same delta-v with LH2/LOX you only need 4mt of fuel.

Quote

Any idea how long of a storage/mission length is required to make Hypergolics better than Cryogenics?

See above. For a depot to work you need to get rid of the boil off entirely through a regenerative cooling cycle.

Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #9 on: 08/07/2009 12:48 PM »
I am not entirely sure I understand what you are getting at. A L1/2 depot (with a small manned space station - permanently manned or just temporarily manned) would be supplied by commercial launch providers. Of course only rockets with a launch capacity of several tons to EML-1 or EML-2 make sense to use for this task. This would rule out small rockets such as Taurus II. I'd say you are in the 10-35mt to LEO launcher field with about 4 to 15mt payload capacity to EML-1/2 for depot supplying duties.

Agreement so far.

Quote
Entirely ok, if you ask me.

Here's my worry: one of the main benefits I see for depots is that they provide a way for new launchers to prove their worth. I'm assuming new entrants will likely intially field very small launchers. See Falcon and Taurus, see the Scorpius and Aquarius concepts, see what Masten is doing. One of the nice things about propellant is that it is essentially infinitely divisible, allowing even small vehicles to compete. Another aspect is RLVs. They need high flight rates, which is easier to achieve with small payloads.

Therefore I would prefer both a LEO depot and an L1 depot. Bigger launchers could launch directly to L1, smaller ones could launch to LEO. This also requires transport from LEO to L1, which could be done by larger launchers launching fully fueled upper stages as transport vehicles, or topping up existing ones.

Quote
And the big benefit is, your depot doesn't have to store 1000mt fuel or more, it just has to hold in the range of 250-350mt of fuel for the same purpose than a LEO depot (+ you get all the added advantages above from a mission architecture perspective that a LEO depot doesn't provide you with - reusing in-deep space flight hardware - VASIMIR stages, Orion only to EML-1 or EML-2 and not all the way to Mars etc.).

Yes, high energy orbits offer many advantages. The thing is, you still need to get your crew capsule to such a higher energy orbit. If you can top up an existing upper stage in LEO, you need a much smaller launcher to get there.

Quote
How so? I'd say it's the other way around. For NEO and circumlunar precursor missions, you really don't need any fuel depots. But once you go for lunar surface missions and interplanetary missions all those nice advantages that I listed pop up for a EML-1/2 depot.

I'm totally in favour of an L1 depot, not instead of a LEO depot but in addition to it. Remember, my plan was for a hypergolic depot which essentially requires it to be at L1, or it would be far too inefficient to make sense. An L1 depot would still be useful for NEO missions, since it would allow you to launch bigger payloads for a fixed volume available to your EDS. And if you want to use the very heavy Orion and avoid the need for bigger upper stages, you will still need propellant transfer even for cis-lunar or NEO missions.

Quote
I addressed that above. I very much disagree. Small rockets (in the 5-10mt to LEO range) are inefficient in kg to cost anyway. Launching 20 rockets with a 25mt to LEO and 12mt to EML-1/2  capacity gets you a much better price per kg to LEO/EML-1/2 than 50 rockets with a 10mt to LEO launcher. That's because your variable cost start to lead your total expense line when you get into the 15-20 launches per year range.

I was thinking of RLVs (reuse to reduce cost) or maybe things like Scorpius (reduced cost through mass production) or Aquarius (mass production + lowered reliability).
« Last Edit: 08/07/2009 12:49 PM by mmeijeri »
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Offline simon-th

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Re: L1/2 spacestation with depot
« Reply #10 on: 08/07/2009 12:56 PM »
I understand where you getting at in your posts. I just think we can't have both LEO depots and L1/2 depots from a budget perspective and rather opt for one that is geared towards lunar flights and interplenatary flights


Yes, high energy orbits offer many advantages. The thing is, you still need to get your crew capsule to such a higher energy orbit. If you can top up an existing upper stage in LEO, you need a much smaller launcher to get there.

Just a note on that point. Orion is a given. So we are stuck with a 20mt spacecraft that - once we have killed off the Ares I - can go back to a 6-crew capacity. The committee will opt for an HLV in any event which at least a 75mt to LEO and about 30mt to TLI capacity (or more if you develop J-246). That being said, any down-the line (of course not simple precursor missions) beyond-LEO mission would use Orion with some kind of MPLM/Hab or Lunar Lander (dry) (all depending on the mission) to the L1/2 space station architecture. Maxing out your HLV with Orion and that additional payload is enough for any conceivable beyond-LEO mission WITHOUT refueling your EDS in LEO.

Offline Bill White

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Re: L1/2 spacestation with depot
« Reply #11 on: 08/07/2009 01:02 PM »
Bridges are usually built in both directions simultaneously. A LEO depot extends one side of a bridge from Earth, but to where?

An EML-1 / EML-2 depot augmented with RLLs gives purpose to a LEO depot. Without a destination out there, a LEO only depot is merely a government funded "make work" project which some people hope will stimulate RLV development.

But without a pre-existing destination "out there" a government depot cannot possibly buy enough fuel (IMHO) to generate enough demand to change the economic realities of Earth-to-LEO launch.

Therefore, try something different. If someone deploys an EML Gateway to the Moon and supports it with existing launchers (Proton Block D can be clipped to any payload for delivery to EML-1 / EML-2 easily enough) that creates a MARKET for private developers of depots to sell to.

Seek to create markets, Martijn, not mandates from government.

Am I truly less "statist" than you? That would be ironic.  ;)
« Last Edit: 08/07/2009 01:03 PM by Bill White »
EML architectures should be seen as ratchet opportunities

Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #12 on: 08/07/2009 01:06 PM »
I understand where you getting at in your posts. I just think we can't have both LEO depots and L1/2 depots from a budget perspective and rather opt for one that is geared towards lunar flights and interplenatary flights

Ah, I see, that makes sense. If I had to choose, I too would choose the L1 depot if it were hypergolic. Otherwise it would be a very difficult choice, but I'd lean towards L1.

If cost is the obstacle, one thing to consider is using in-flight refueling instead of a dedicated depot. This is one reason I'm fond of a universal fully reusable lander: it can be used as a lander, a cislunar and translunar crew shuttle, a rescue vehicle, a depot and a mini-space station. It would have reduced capability in each of these functions compared to a specialised vehicle, but development cost would be much lower. In that sense I think it would be ideal for the initial phase of an exploration program, much like the shuttle was very early on.

Quote
Just a note on that point. Orion is a given. So we are stuck with a 20mt spacecraft that - once we have killed off the Ares I - can go back to a 6-crew capacity. The committee will opt for an HLV in any event which at least a 75mt to LEO and about 30mt to TLI capacity (or more if you develop J-246). That being said, any down-the line (of course not simple precursor missions) beyond-LEO mission would use Orion with some kind of MPLM/Hab or Lunar Lander (dry) (all depending on the mission) to the L1/2 space station architecture. Maxing out your HLV with Orion and that additional payload is enough for any conceivable beyond-LEO mission WITHOUT refueling your EDS in LEO.

If you accept HLV as a given this is true and I agree it is likely. My thinking was centered around demonstrating an HLV was not in fact necessary. Initially it was even intended to show J-120 + Delta upper stage would be enough so at least you would not need a new upper stage even if you were stuck with an ET-derived core.
« Last Edit: 08/07/2009 01:35 PM by mmeijeri »
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Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #13 on: 08/07/2009 01:10 PM »
Seek to create markets, Martijn, not mandates from government.

Absolutely, but that does not absolve government from the responsibility to procure services commercially where it can. I would say it has a fiduciary duty to its taxpayers to do that.

Quote
Am I truly less "statist" than you? That would be ironic.  ;)

Well, since you are a proponent of government-owned launchers that would seem to be impossible. If there were no exploration program, I would not be lobbying the government to create one or to create depots. If there's going to be an exploration program anyway, I say it ought to be geared towards commercial synergy. I think that makes me less statist than you. Not that I think there are any prizes for being the least statist or anything. ;)
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Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #14 on: 08/07/2009 01:25 PM »
With respect for Hypergolics vs Cryogenic fuels, I was under the impression that LH2 was overwhelmingly superior than Hypergolics for long range missions (like Mars).

There are some additional advantages to hypergolics, but those are not crucial. The main argument is a political one: hypergolic fluid transfer is:

1) good enough for full-blown exploration to the moon, Mars and beyond without HLV, provided you put your depot at L1 and use LOX/LH2 and efficient trajectories to get there, perhaps augmented with high Isp propulsion
2) proven technology. NASA is using the alleged difficulty of cryogenic depots as a pretext, but this cannot apply to a technology that has seen continuous operational use ever since Salyut-6 in 1978 and is used on the ISS today.

Minor advantages to hypergolics include higher density (more oomph by volume, which might be an issue if restricted by EELV fairings especially since the reduced oomph by mass can be fixed with depots), higher reliability, no need to develop boil-off mitigation systems and no new engine development. Higher delta-v missions would suffer more from lower Isp, but longer duration missions might benefit more from having no need to consider boiloff.

But I'd say it's a wash technically, with politics being the crucial reason why I'd support hypergolics first. You may be surprised to hear this. How can I say it's a wash with the lower Isp? The thing is, Isp doesn't matter so much if

1) you start from a high energy orbit like L1 and get there with LOX/LH2,
2) use an Earth swingby,
3) preposition propellant using high Isp propulsion and/or
4) use ISRU.
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Offline randomly

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Re: L1/2 spacestation with depot
« Reply #15 on: 08/07/2009 05:22 PM »
What about having a LEO Propellant depot so that it can be filled by a variety of smaller launch vehicles, then move that depot to EML1, either with SEP or just a standard engine using some of the available propellant.

Assuming a hypergolic depot how much fuel would you need to boost it to EML1 and deliver 100mt of propellant? Or if you had something like a 200 Kw Solar powered VASIMR, how long would it take to move it from LEO to EML1?

Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #16 on: 08/07/2009 05:25 PM »
Do you mean moving the depot itself back and forth? That sounds a bit impractical. It's not an option for hypergolics, since that would be very inefficient.
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Offline randomly

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Re: L1/2 spacestation with depot
« Reply #17 on: 08/07/2009 05:35 PM »
yes, I'm proposing moving the depot back and forth. If SEP is a feasible option it could be efficient. Even with chemical rockets it might be feasible.

If the mass fraction of the depot is pretty good it may be relatively easy to move it back down to LEO again once it's empty.

As to using hypergolics instead of Cryo to boost it from LEO to EML1 how bad would the mass to LEO penalty be?

The other option is to use a cryo EDS to move the depot to EML1. You could probably use hypergolics to move it back.

It might be more efficient to move the depot to EML1 than to send a bunch of small rockets with upper stages out to EML1 to dock with the depot there and fill it up. You avoid all those upper stages, and you avoid the communications delay if you are controlling docking real time from the ground (I don't know if that's preferred or not).

If you had several depots cycling between LEO and EML1 you might be able to tolerate the long transit times from using SEP. You would also have backup depots in case of failures.
« Last Edit: 08/07/2009 05:44 PM by randomly »

Offline Hop_David

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Re: L1/2 spacestation with depot
« Reply #18 on: 08/07/2009 05:46 PM »
With respect for Hypergolics vs Cryogenic fuels, I was under the impression that LH2 was overwhelmingly superior than Hypergolics for long range missions (like Mars). cloud? (unmanned of course)

When you have a big delta V budget, a high exhaust velocity is desirable. That's because both delta V and exhaust velocity are in the exponent of the rocket equation for the ratio of fuel mass to payload mass:

Mf/Mp = e(dV/Ve) - 1

e is Euler's number, about 2.72.

Delta V from earth surface to Mars is about 15 km/sec. With a number like 15 in the the above exponent you can see the Mf/Mp is big. Unless Ve is big.

LOX/LH2 has a higher exhaust velocity than LOX and kerosene, methane, propane etc.

However fuel depots could change the picture. Delta V between LEO and L1 is about 4 km/sec. Delta V between L1 and Deimos is about 3 km/sec.

Fuel depots at LEO, L1, and Deimos would break the delta V budget into smaller hops. You'd still need about 10 km/sec to get from earth to LEO. But moving between fuel depots could be done in 4 km/sec and 3 km/sec hops.

When your delta V budget is 4 to 3 km/sec, there's not the pressing need for a fuel with a high exhaust velocity.

Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #19 on: 08/07/2009 06:09 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.
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Offline 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 »

Offline 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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Offline 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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Offline 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)




Offline 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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Offline 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.


Offline 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.

Offline 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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Offline 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.

My spread sheet gives
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 »

Offline 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?

Offline 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.

Offline 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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Offline 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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Offline 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.

Offline 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 ?


Offline 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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Offline 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 »

Offline 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.

http://www.google.fr/search?hl=fr&q=%22Flyby-Landing+Excursion+Mode%22&meta=

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...

Offline 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.


Offline 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).

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.

Quote
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.

Quote
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.

Quote
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.

Quote
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 »
Quote
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 »

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 »
Quote
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 »

Offline Bill White

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Re: L1/2 spacestation with depot
« Reply #48 on: 08/09/2009 06:29 PM »
Quote
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.

Quote
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.

Quote
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.

Quote
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.

Quote
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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Online 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.

Quote
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 »

Offline A_M_Swallow

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Re: L1/2 spacestation with depot
« Reply #57 on: 08/12/2009 02:28 AM »
Quote
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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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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Offline Archibald

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Re: L1/2 spacestation with depot
« Reply #60 on: 09/21/2009 04:32 PM »
My own objective is to try marrying SEP and ISRU, both being IMLEO-killers.
Why do I want diminishing IMLEO ?
Because of recent events showing that the maximum booster NASA can afford at current budget levels is around 40-70 Mt to LEO.
The current problem is that chemical and electric thrusters tends to works with very, very different propellants. Xenon has nothing common with hydrogen...
Fortunetaly, arcjets works with "chemical" propellants.
A second way may be Hall thrusters with oxygen
http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/20239/1/98-1133.pdf

Or, third way, the PIT/MPD mentionned above...





Offline alexterrell

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Re: L1/2 spacestation with depot
« Reply #61 on: 09/21/2009 04:49 PM »
Depots high up make sense if your propellant is coming from high up. There are a few threads about Phobos, and this could be an easy, all be it slow, source of water.

From Phobos, water cargos would be placed into an Earth intercept orbit, then brake just above Earth, probably using aerocapture. The resulting target orbit would have a Apogee of 300,00-500,000km. So would it make more sense for a propellant dump to be in a HEEO, say 1,000km (above surface) x 400,000km. Such an orbit could also be made with a 1/3 lunar cycle, thereby coming close to L1, L4 and L5 every month. It's also fast to reach from Earth, so an Orion capsule could transport a larger crew.

It's also energetically much better for access to deep space.

Offline Robotbeat

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Re: L1/2 spacestation with depot
« Reply #62 on: 09/21/2009 04:50 PM »
I don't know as much about the other electric propulsion systems (because they don't have as effective marketing), but VASIMR can certainly run on hydrogen.
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Offline Patchouli

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Re: L1/2 spacestation with depot
« Reply #63 on: 09/21/2009 04:53 PM »
My own objective is to try marrying SEP and ISRU, both being IMLEO-killers.
Why do I want diminishing IMLEO ?
Because of recent events showing that the maximum booster NASA can afford at current budget levels is around 40-70 Mt to LEO.
The current problem is that chemical and electric thrusters tends to works with very, very different propellants. Xenon has nothing common with hydrogen...
Fortunetaly, arcjets works with "chemical" propellants.
A second way may be Hall thrusters with oxygen
http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/20239/1/98-1133.pdf

Or, third way, the PIT/MPD mentionned above...



VASIMR thrusters also can work with a wide variety of propellants and may be able to cope with using O2 as a propellant better then a Hall thruster.
They also can use hydrogen.

As for arcjets I don't think they have good enough ISP for any low thrust propulsion you really want an ISP of around 2,000 to 3,000.
Arcjets only have an ISP of around 1000sec you might as well run an NTR rocket 860 to 1000sec ISP and get high thrust as well.
« Last Edit: 09/21/2009 04:58 PM by Patchouli »

Offline Robotbeat

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Re: L1/2 spacestation with depot
« Reply #64 on: 09/21/2009 05:03 PM »
What is the thrust/weight ratio for Arcjets vs. VASIMR?
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Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #65 on: 09/21/2009 06:05 PM »
So would it make more sense for a propellant dump to be in a HEEO, say 1,000km (above surface) x 400,000km.

Or L1/L2. A HEEO has the advantage of not needing a perigee lowering burn for an Earth swingby and not needing an L1/L2 insertion burn for the propellant flights. On the other hand there exist ballistic trajectories to L1/L2 and L1/L2 orbit doesn't take you through the van Allens repeatedly.
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Re: L1/2 spacestation with depot
« Reply #66 on: 09/21/2009 06:29 PM »
So would it make more sense for a propellant dump to be in a HEEO, say 1,000km (above surface) x 400,000km.

Or L1/L2. A HEEO has the advantage of not needing a perigee lowering burn for an Earth swingby and not needing an L1/L2 insertion burn for the propellant flights. On the other hand there exist ballistic trajectories to L1/L2 and L1/L2 orbit doesn't take you through the van Allens repeatedly.
Good point about the Van Allen belts. How about 500,000km x 20,000km. Then only a small change is needed to exploit the Oberth effect.

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Re: L1/2 spacestation with depot
« Reply #67 on: 09/21/2009 06:44 PM »
That might work, although an Earth swingby down to LEO altitude from circular orbits between MEO and GEO does not appear to be worthwhile. I haven't done the sums for elliptical orbits. Is there a specific reason you don't like L1/L2?
« Last Edit: 09/21/2009 06:47 PM by mmeijeri »
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Re: L1/2 spacestation with depot
« Reply #68 on: 09/21/2009 08:14 PM »
That might work, although an Earth swingby down to LEO altitude from circular orbits between MEO and GEO does not appear to be worthwhile. I haven't done the sums for elliptical orbits. Is there a specific reason you don't like L1/L2?
At L1/L2, you have a velocity around the Earth of close to 1km/s. If you want to swing by the Earth for an Oberth effect transfer to Mars, you have to kill most of that 1km/s. That's a waste. The more elliptical your orbit, the less waste you have.

Equally, if you bring in mass from NEOs or Mars/Phobos, you're going to come in on a HEEO, especially if you use Oberth effect and aerobraking. Once your cargo reaches Apogee, you need a 1 km/s boost.

Have a look at the picture here: http://en.wikipedia.org/wiki/Delta_v_budget

If your main destination is the moon, and propellants come from Earth or Moon, then L1/L2 are fine. They're on the way to the moon.

If your destination is beyond Earth Orbit, then L1 is a detour. You want to be as close to C3=0 as possible. But to be at C3=0, you have a transfer time of several days, so a HEEO is the next best thing.





Offline kfsorensen

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Re: L1/2 spacestation with depot
« Reply #69 on: 09/21/2009 10:10 PM »
Lots of things are being glossed over here.   The orientation of a highly-elliptical Earth orbit makes all the difference.  You can't look at some table on Wikipedia and think that explains it.

From L2, you have the opportunity over the course of a month to select an optimally-oriented HEEO via a departure from L2 and a powered lunar swingby.  These consume about 300 m/s of DV but put you in the right HEEO, with the right ascending node and the right argument of perigee, to enable you to do a very effective transfer into heliocentric space.

And no, being close to C3=0 is NOT necessarily what you want.  For ballistic transfer, you want to be able to take advantage of a DV deep in the Earth's gravity well to minimize overall DV.

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Re: L1/2 spacestation with depot
« Reply #70 on: 09/21/2009 11:09 PM »
That might work, although an Earth swingby down to LEO altitude from circular orbits between MEO and GEO does not appear to be worthwhile. I haven't done the sums for elliptical orbits. Is there a specific reason you don't like L1/L2?
At L1/L2, you have a velocity around the Earth of close to 1km/s. If you want to swing by the Earth for an Oberth effect transfer to Mars, you have to kill most of that 1km/s. That's a waste. The more elliptical your orbit, the less waste you have.

Equally, if you bring in mass from NEOs or Mars/Phobos, you're going to come in on a HEEO, especially if you use Oberth effect and aerobraking. Once your cargo reaches Apogee, you need a 1 km/s boost.

Have a look at the picture here: http://en.wikipedia.org/wiki/Delta_v_budget

If your main destination is the moon, and propellants come from Earth or Moon, then L1/L2 are fine. They're on the way to the moon.

If we can get propellants from the moon, L1 and 2 become very attractive.

I may have been using two high of a gravity drag penalty for Mars so 6.6 from Mars to Deimos may be too high. Red lines indicate aerobraking routes. Since making this illustration I've learned L2 is even closer to the earth than L1 delta V wise. To drop something at EML1 to a 300 km perigee takes about .6 or .7 km/sec.

Offline Hop_David

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Re: L1/2 spacestation with depot
« Reply #71 on: 09/21/2009 11:26 PM »
Such an orbit could also be made with a 1/3 lunar cycle, thereby coming close to L1, L4 and L5 every month. It's also fast to reach from Earth, so an Orion capsule could transport a larger crew.

Believe that's a typo, should be L3, L4 and L5 each month as those are 120 degrees from each other.

An ellipse having one third lunar period (what I call a Terrell orbit) would have a semimajor axis of (1/3)^(2/3) * (1 Lunar Distance) or .4807 * 384400 km.

This is 184800.245 km. If you had a 300 km perigee, the apogee would be 356544.19 km altitude.

Here is a pic of a Terrell orbit from two frames: top is moon centered, bottom is the more conventional earth centered.

If you would like to input the numbers indicated you can use the sim at http://clowder.net/hop/railroad/FromEarth.php

True, you're going nearly escape velocity at perigee. A nice place to exploit the Oberth effect. IF you're in the right place at the right time. Unfortunately the likelihood of this perigee being well positioned during, say, a Mars launch window, is slim.

The apogee of an orbit dropped from L2 or L1 rotates 360 degrees each month. Thus by judicious timing of when you drop from L2, you can do your perigee burn at the right place at the right time.
« Last Edit: 09/21/2009 11:28 PM by Hop_David »

Offline Archibald

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Re: L1/2 spacestation with depot
« Reply #72 on: 09/22/2009 06:27 AM »
Quote
As for arcjets I don't think they have good enough ISP for any low thrust propulsion you really want an ISP of around 2,000 to 3,000.
Arcjets only have an ISP of around 1000sec you might as well run an NTR rocket 860 to 1000sec ISP and get high thrust as well.

I have to agree with this statement. I was interested by arcjets only because they used ammonia. 1000 seconds ISP is not enough to balance the large delta-V penalty for SEP mars missions ( = no Oberth effect = 4* more delta-V, see the Phobos thread)

Well, PIT thruster may be better ;)  but (contrary to arcjet) has not flown yet. I'll try gather more information on this concept.

Quote
I don't know as much about the other electric propulsion systems (because they don't have as effective marketing)

http://en.wikipedia.org/wiki/Ion_thruster
VASIMR competitors :)

« Last Edit: 09/22/2009 06:33 AM by Archibald »

Offline kkattula

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Re: L1/2 spacestation with depot
« Reply #73 on: 09/22/2009 08:37 AM »
Well ULA seem to think LOX/LH2 depots would not be too difficult:

1)  No active cooling needed. Boil-off rates are <= station keeping requirements.

2)  No zero-g cryo transfer. Micro-g settling is sufficient and has been demonstrated.

3)  Using the same two propellants for all in-space propulsion (orbital injections, RCS, descent & ascent, surface power etc), has a lot of synergies. Simplicity, commonality, residual reclamation, etc.

According to their recent arcitecture proposal, development of the one ACES stage, with relatively straight forward modifications, gives:

Common Upper Stage
Orion Service Module
Propellant Depot
Propellant Tanker
Descent stage
Surface Depot

I'm rapidly coming to the conclusion that a depot consisting of multiple ACES based depots modules might be optimal, for big missions.  If one has a problem, you wouldn't lose any propellant from the other modules, and could quickly send a replacement.

Later on, you could link them via a spoked hub truss, with a very slow rotation. Attaching other modules as required.

Offline meiza

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Re: L1/2 spacestation with depot
« Reply #74 on: 09/22/2009 12:26 PM »
Without the internet and probably this forum, most people would never have gotten to know propellant depots or the L points really... Everybody would just assume heavy lifters and LOR or EOR-LOR.

Btw you can use hydrogen or ammonia in the Helicon Double Layer thruster too. In a sense it's a bit like a glorified arcjet where you heat with microwaves. Also you have less wearing parts.
« Last Edit: 09/22/2009 12:27 PM by meiza »

Offline Archibald

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Re: L1/2 spacestation with depot
« Reply #75 on: 09/22/2009 04:19 PM »
Quote
Without the internet and probably this forum, most people would never have gotten to know propellant depots or the L points really... Everybody would just assume heavy lifters and LOR or EOR-LOR.


Absolutely. "An alternative lunar architecture" is an excellent thread.

Quote

Btw you can use hydrogen or ammonia in the Helicon Double Layer thruster too. In a sense it's a bit like a glorified arcjet where you heat with microwaves. Also you have less wearing parts.



Good! So far MPD, PIT and Helicon may work with NH3.

The more I look at it, the more I think that, in some way are three generations of electric thrusters.

Arcjets & resistojets represent the first generation. Rugged, low performance.

Ion & Hall thrusters came second.
Much better specific impuse, but "bizarre", exotic propellants - Xenon, Krypton, Bismuth (!).
These one have flown as of 2009.

MPD, VASIMR, PIT, helicon thrusters would be the 3rd generation.
Back to "common" propellants (one you can ISRU...). 
High ISP.
 And, icing on the cake, MAYBE, high thrust.

But they have not flown yet, although things may change rapidly (helicon and VASIMR tests are planned in the next future ?)

Offline Hop_David

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Re: L1/2 spacestation with depot
« Reply #76 on: 09/22/2009 06:31 PM »
Well ULA seem to think LOX/LH2 depots would not be too difficult:

1)  No active cooling needed. Boil-off rates are <= station keeping requirements.

2)  No zero-g cryo transfer. Micro-g settling is sufficient and has been demonstrated.

Haven't been following ULA. They think LH2 is doable?

How do they do Micro-g instead of zero-g? Will the depots be rotating?

Offline randomly

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Re: L1/2 spacestation with depot
« Reply #77 on: 09/22/2009 07:29 PM »
How do they do Micro-g instead of zero-g? Will the depots be rotating?
They just thrust with boiloff gasses or some such. Apparently LM has proven the system to work at 0.0001g, and they've flight demonstrated settling at 0.00001g.

Offline jongoff

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Re: L1/2 spacestation with depot
« Reply #78 on: 09/22/2009 08:12 PM »
Well ULA seem to think LOX/LH2 depots would not be too difficult:

1)  No active cooling needed. Boil-off rates are <= station keeping requirements.

2)  No zero-g cryo transfer. Micro-g settling is sufficient and has been demonstrated.

Haven't been following ULA. They think LH2 is doable?

How do they do Micro-g instead of zero-g? Will the depots be rotating?

Here's a paper I just presented that I coauthored with several of the ULA and Boeing depot guys (as well as a professor from the U of Memphis).  It has some details:

http://selenianboondocks.com/wp-content/uploads/2009/09/NearTermPropellantDepots.pdf

There are some more on the ULA publications page:

http://www.ulalaunch.com/index_published.html

~Jon

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Re: L1/2 spacestation with depot
« Reply #79 on: 09/22/2009 10:28 PM »
Well ULA seem to think LOX/LH2 depots would not be too difficult:

1)  No active cooling needed. Boil-off rates are <= station keeping requirements.

2)  No zero-g cryo transfer. Micro-g settling is sufficient and has been demonstrated.

Haven't been following ULA. They think LH2 is doable?

How do they do Micro-g instead of zero-g? Will the depots be rotating?

Here's a paper I just presented that I coauthored with several of the ULA and Boeing depot guys (as well as a professor from the U of Memphis).  It has some details:

http://selenianboondocks.com/wp-content/uploads/2009/09/NearTermPropellantDepots.pdf

There are some more on the ULA publications page:

http://www.ulalaunch.com/index_published.html

~Jon

Jon, you et al. rock!  "Flight demonstration tools ... provide methods for affordably retiring the remaining technical risks."

This is the message that the space enthusiast community (and Congress) need to hear right now!
-- sdsds --

Offline jongoff

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Re: L1/2 spacestation with depot
« Reply #80 on: 09/22/2009 11:33 PM »
Well ULA seem to think LOX/LH2 depots would not be too difficult:

1)  No active cooling needed. Boil-off rates are <= station keeping requirements.

2)  No zero-g cryo transfer. Micro-g settling is sufficient and has been demonstrated.

Haven't been following ULA. They think LH2 is doable?

How do they do Micro-g instead of zero-g? Will the depots be rotating?

Here's a paper I just presented that I coauthored with several of the ULA and Boeing depot guys (as well as a professor from the U of Memphis).  It has some details:

http://selenianboondocks.com/wp-content/uploads/2009/09/NearTermPropellantDepots.pdf

There are some more on the ULA publications page:

http://www.ulalaunch.com/index_published.html

~Jon

Jon, you et al. rock!  "Flight demonstration tools ... provide methods for affordably retiring the remaining technical risks."

This is the message that the space enthusiast community (and Congress) need to hear right now!

Thanks!  It's an important one.  Once I'm out from under the gun for getting our LLC vehicle together, I'm going to be putting out a white paper with more details.

~Jon

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Re: L1/2 spacestation with depot
« Reply #81 on: 09/23/2009 08:19 AM »
Lots of things are being glossed over here.   The orientation of a highly-elliptical Earth orbit makes all the difference.  You can't look at some table on Wikipedia and think that explains it.

From L2, you have the opportunity over the course of a month to select an optimally-oriented HEEO via a departure from L2 and a powered lunar swingby.  These consume about 300 m/s of DV but put you in the right HEEO, with the right ascending node and the right argument of perigee, to enable you to do a very effective transfer into heliocentric space.

And no, being close to C3=0 is NOT necessarily what you want.  For ballistic transfer, you want to be able to take advantage of a DV deep in the Earth's gravity well to minimize overall DV.
Looking at the table in Wikipedia again  ;D I see that the energy from L1/L2 to C3 is only 0.14km/s. This does seem low, but if correct, then it makes sense.

Being close to C3=0 is what you want, because from there, you can enter an Earth grazing orbit with zero energy. (Strictly speaking, only zero if you have infinite time).

I agree the point about timing, so I'm now persuaded that L1 or L2 is a good base, even for Mars trips.

Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #82 on: 09/23/2009 10:46 AM »
I agree the point about timing, so I'm now persuaded that L1 or L2 is a good base, even for Mars trips.

The swingby concept is very powerful. Huntress et al propose an incremental architecture based around that in The next steps in exploring Deep Space. The idea probably comes from Farquhar who was one of the co-authors. They propose stationing a reusable Interplanetary Transfer Vehicle at SEL-2. A perigee lowering burn from SEL-2 is even cheaper than from EML1/2. The trick includes swingby's of both the Earth and the moon.

Combined with SEP this eliminates the need for nuclear propulsion, which was one of the goals for the architecture. Conveniently, it even eliminates the need for HLV or cryogenic depots, although the latter remain desirable for both exploration and the economic development of space.
« Last Edit: 09/23/2009 10:49 AM by mmeijeri »
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Offline kfsorensen

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Re: L1/2 spacestation with depot
« Reply #83 on: 09/23/2009 12:15 PM »
But from SEL2 you only sweep through all values of right ascension once per year, whereas from EML2 you sweep through all values of right ascension once per month.  That's an important consideration when trying to get your pre-departure HEEO oriented properly.

Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #84 on: 09/23/2009 12:40 PM »
Yeah, I wondered about that too, I'm not sure why they propose to do it that way since they give few details. The smaller initial perigee lowering burn might be a reason and they also want reuse of the heavy ITV, which is more efficient from a higher energy orbit. Then again, the difference in energy is small.

What do you imagine they are thinking of? A fairly small burn to lower perigee from SEL-2 altitude to lunar orbit, then a lunar flyby to lower apogee to LEO altitude (becoming the new perigee) and then the TMI at the Earth swingby? Does either the Earth or moon swingby give you an affordable opportunity to change your angle? And since you're free to choose the timing of the lunar flyby doesn't that give you at least some control over the departure angle?

EDIT: hang on, I don't think you're free to choose timing and angle of the lunar flyby freely.
« Last Edit: 09/23/2009 01:33 PM by mmeijeri »
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Offline kfsorensen

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Re: L1/2 spacestation with depot
« Reply #85 on: 09/23/2009 01:29 PM »
Yeah, I wondered about that too, I'm not sure why they propose to do it that way since they give few details. The smaller initial perigee lowering burn might be a reason and they also want reuse of the heavy ITV, which is more efficient from a higher energy orbit. Then again, the difference in energy is small.
I asked Farquhar the same question and the impression I got was that he hadn't considered it, which surprised me, since little escapes that man.

Offline kfsorensen

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Re: L1/2 spacestation with depot
« Reply #86 on: 09/23/2009 01:33 PM »
If you're planning to go to Mars, for instance, and you know the orientation of your HEEO, but that your departure from EML2 is going to be 10 days (for instance) before the perigee departure burn, you can just leave EML2 on the right day, get into your HEEO with the right orientation, and wait for 10 days or so until it's time to do the perigee departure burn.

On the other hand, if you were starting from SEL2, you might need to establish your departure HEEO months before it was time to do the perigee burn (in order to get the HEEO orientation right).  I see that as a major drawback of basing at SEL2, in addition to the transfer time between SEL2 and the Earth's vicinity.

Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #87 on: 09/23/2009 01:40 PM »
Yeah, the transfer time is an issue too. Two weeks each way for reasonable delta-v's. One advantage of the relatively small burns caused by staging and the swingbys is that it allows you to use shorter, higher delta-v trajectories (so less exposure to GCR), but a month extra travel time (and another month between SML-1 and LMO) reduces that advantage. Maybe you could use low delta-v and massive shielding instead, but I'm not sure the numbers add up.
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Offline alexterrell

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Re: L1/2 spacestation with depot
« Reply #88 on: 09/23/2009 01:45 PM »
Just want to add, if all your propellant has to come from Earth, and your using chemical thrusters, is there any advantage in having a depot at L1/2, except for mission size?

If you use VASIMR etc, or better still, a electrodynamic booster or a rotovator, or if your propellant is coming from Phobos or The Moon, then absolutely a L1/L2 depot makes sense.

If coming from Moon / Phobos, then you would want to electrlyse the propellant on demand. Even from Earth, this might be worth considering. Water can be stored as a radiation barrier. 172KW gives you 60 tons of fuel in 3 months. 500KW will refill a Jupiter Upper Stage in 3 months, and that high up, a JUS is a pretty powerful rocket.

Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #89 on: 09/23/2009 02:18 PM »
Just want to add, if all your propellant has to come from Earth, and your using chemical thrusters, is there any advantage in having a depot at L1/2, except for mission size?

I'm not sure what you mean by mission size.

There are a lot of reasons that favour L1/L2 as a staging point to the moon, Mars and beyond. There are even some operational reasons to use it as the first staging point, although I prefer the ISS as the first staging point for strategic reasons. Some reasons are specific to different kinds of depots (deeply cryogenic, mildly cryogenic, storable), other apply to all kinds.

The general reasons include the lower delta-v which would increase the capacity of transfer stages or allow them to take faster routes or some combination of the two. This only increases the capacity of an individual transfer stage, and does not reduce total IMLEO. SEP and ISRU would reduce IMLEO as well. Another advantage that applies to all kinds of propellants is that you would also have less trouble with phasing and nodal regression.

If you have an LH2 depot, then L1/L2 is very interesting because of the more benign thermal environment. If you want to do electrolysis, then continuous sunlight is also valuable.

If you use hypergolics from L1/2 onward as I advocate (at least initially), then you pretty much need L1/2 since LEO would be too inefficient. The L1/2 depot could then be resupplied using commercial propellant launches. This would decouple the emergence of RLVs from the emergence of cryo depots or even full, dedicated depots, as opposed to mere in-flight refueling. In that case you'd use EELV Phase 1 to launch fully fueled upper stages to LEO much like Jupiter, only smaller. The ACES upper stage needed for that would itself be a precursor for a cryo depot. Once that was operational you could dry-launch the ACES EDS and fill it up from the depot. That would make the cryo propellant available for RLV launch as well, perhaps eliminating entirely the need to launch multi-core versions of the Phase 1 EELVs.

A reusable lunar lander, with propellant coming either from Earth or the moon, would also work best with an L1/L2 depot, since it would be wasteful to move the lander back and forth between LEO and the lunar surface every time.

Quote
500KW will refill a Jupiter Upper Stage in 3 months, and that high up, a JUS is a pretty powerful rocket.

That high up pretty much anything is a pretty powerful rocket. JUS would not be very suitable however, since it is so heavy. JUS and L1/2 don't mix well. J-130 + Delta-IV US (or the smaller versions of ACES) would be better, especially if you used them to take advantage of the easier phasing if you use L1/2 as your first staging point. Of course once you have ACES, you have EELV Phase 1 and there's no reason for there to be a J-130.
« Last Edit: 09/23/2009 03:41 PM by mmeijeri »
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Offline alexterrell

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Re: L1/2 spacestation with depot
« Reply #90 on: 09/23/2009 07:45 PM »
What I mean by mission size is being able to transport larger cargos in one go. E.g Altair lander. That is an advantage.

However, as a rule it makes sense to burn your fuel as deep into the gravity well as possible. So from L1, you sweep into a fast fly by orbit and burn at the nearest point to exploit the Oberth effect. But this doesn't give you any fuel saving over just firing up in LEO in the first place.

Unless: You're using something more efficient to get propellant to L1/L2 that the rocket. Such as a rotovator, VASIMR, or a source on the moon.

I agree there are operational benefits - almost permanent sunshine and less radiation pollution.

JUS is too powerful for most things NASA has in mind. I like the idea of using it to take a large capable mission to Phobos, and coming back with 500 tons of water in a spent JUS.

Offline Hop_David

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Re: L1/2 spacestation with depot
« Reply #91 on: 09/23/2009 11:36 PM »
What I mean by mission size is being able to transport larger cargos in one go. E.g Altair lander. That is an advantage.

However, as a rule it makes sense to burn your fuel as deep into the gravity well as possible. So from L1, you sweep into a fast fly by orbit and burn at the nearest point to exploit the Oberth effect. But this doesn't give you any fuel saving over just firing up in LEO in the first place.

Unless: You're using something more efficient to get propellant to L1/L2 that the rocket. Such as a rotovator, VASIMR, or a source on the moon.

I agree there are operational benefits - almost permanent sunshine and less radiation pollution.

JUS is too powerful for most things NASA has in mind. I like the idea of using it to take a large capable mission to Phobos, and coming back with 500 tons of water in a spent JUS.


Experience is a very important factor in bulding reliable, inexpensive vehicles. A high launch rate is desirable.

In building reliable, inexpensive cars, which works better: building a million cars or launching an intensive design study that will attempt to consider every contingency and failure mode?

So I favor many launches of small rockets rather than a rare mammoth launch. LEO fuel depots could provide the market and launch frequency to move us forward in acquiring experience and growing the pool of vendors.

I hope exporting of lunar propellant will become possible. When we're able to extract lunar propellant we'll need to store it in depots. What is the TRL (Technology Readiness Level) of propellant depots? Pretty high in my opinion. We've acquired experience in handling cyrogenics from upper stages of rockets. A number of technologies are maturing to the point where propellant depots are no longer exotic technology.

When we become able to extract propellant from the moon, it would be good if propellant depots were already a mature technology.

A mature propellant depot technology is also desirable if we become able to import Deimos or Phobos propellant.

Offline A_M_Swallow

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Re: L1/2 spacestation with depot
« Reply #92 on: 09/24/2009 01:22 AM »
Just want to add, if all your propellant has to come from Earth, and your using chemical thrusters, is there any advantage in having a depot at L1/2, except for mission size?

Yes, L1/L2 allows the Mars Transfer Vehicle (MTV) to be reusable.  Fuel for a delta-v of 0.14 km/s can be carried.  Where as C3 to LEO is a large 3.22 km/s if you want to keep the spacecraft.

Propellant can be taken to L1 via a SEP, a delta-v of 3.77 km/s.  People can travel to and from L1/L2 in a small capsule that has a heat shield.  A space-dock can be built at L1/L2 to repair the MTV.

The (first) three flights of the reusable MTV could be:

First trip

LEO -> Phobos -> L2

Second trip

L2 -> Phobos -> L2

Third trip

L2 -> Phobos -> L2

Offline infocat13

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Re: L1/2 spacestation with depot
« Reply #93 on: 09/24/2009 02:01 AM »
Quote
- Depots at L1/2 make more sense than depots in LEO - you don't have to store all the EDS propellant

I don't think this is true. For one you couldn't refuel your upper stage in LEO, so you would need a bigger launcher to launch a fully fueled EDS. Now I'm actually in favour of doing it this way in the short run (since it gets cryogenic depots off the critical path), but in the slightly longer run it is a disadvantage. Another disadvantage is that L1 rules out participation in propellant launches by small launch vehicles, which negates most of the benefit of depots. There is a very good case for doing both LEO and L1 depots and gateway stations however.

The ULA EELV proposal says do both LEO and L1 but I think at first a SDHLV would let you use the  ACES tanker system and EELV's together.After you have developed this architecture you finish the cryogenic fuel depot technology as a follow on.The commission stated in a public hearing that cryogenic fuel depots where technologically immature and will cost Development money. ::)
Partially empty ACES tankers would top off at the LEO after launch and at L1 drop any residual fuel.
L1 is a good first place for a long duration shake down cruise for any flexible path mission 
I am a member of the side mount fanboy universe however I can get excited over the EELV exploration architecture fanboy universe.Anything else is budgetary hog wash
flexible path/HERRO

Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #94 on: 09/24/2009 02:15 PM »
The ULA EELV proposal says do both LEO and L1 but I think at first a SDHLV would let you use the  ACES tanker system and EELV's together.After you have developed this architecture you finish the cryogenic fuel depot technology as a follow on.

I don't understand what you mean by that. How do you envisage an ACES tanker system cooperating with SDLV without a cryogenic fuel depot?

Quote
The commission stated in a public hearing that cryogenic fuel depots where technologically immature and will cost Development money. ::)

SDLV probably costs a lot more development money... But the immaturity of cryogenic depots (both perceived and real) is what leads me to hypergolic in-flight refueling as a precursor. Cryogenic depots are not the game changers they are made out to be, it's propellant transfer in general. In-flight refueling is one way to simplify things and using hypergolics is another.

Without cryogenic depots you still need a way to get beyond LEO, because hypergolics are not really suitable for that. Admittedly it's possible to use them for an EDS and the Russians or Indians might want to do it that way, but for the US it is needlessly inefficient. This is where an SDLV could have a niche. You could use J-130 with an existing Delta upper stage to get an Orion to L1/L2, which is indeed an excellent staging point. With the SSME powered J-130 you would even have some extra capacity to LEO, which you could make useful by dropping off excess propellant in LEO. The advantage of SDLV in this case is that you can go to L1/L2 with a single launch and thus avoid EOR with your EDS. This means no boil-off issues, no phasing, no nodal regression. This is the scenario that led me to an initially hypergolic architecture in the first place.

The drawback of this scenario (apart from the fact that team DIRECT wants nothing to do with it) is that you still need to spend >=$2B a year in shuttle fixed costs. There's also the big risk that NASA/politicians/lobby groups will apply pressure for propellant to be launched on the SDLV as well.

To remedy this you could go with EELV Phase 1. It's a smaller HLV, but big enough to lift a fully fueled Delta upper stage to LEO, or a partially fueled ACES that still contains more propellant than the current Delta upper stage. It might just be big enough to do one-launch to L1/L2, though only with solids. On balance I think it's better to do EOR with the EDS and let the crew stage at the ISS. It would also make the ISS more useful.

The main drawback I see in this scenario is that it leaves ULA with a monopoly on EDS launches, which takes roughly half the payload volume away from open competition. While this would be an enormous improvement over a complete NASA monopoly, it would still be undesirable. The good thing however is that once NASA loses its in-house launchers, it will have a vested interest in getting cryogenic depots operational. And conveniently the ACES upper stage is itself a precursor for a cryogenic depot. If development goes as smoothly as its advocates predict, it could be operational not much later than the hypergolic systems.

All in all this scenario allows propellant launches to happen sooner while keeping cryogenic depots off the critical path. And it does so without delaying or risking their eventual development. It even removes the main political obstacle, the shuttle stack, and turns NASA into an ally.

I commend it to the House. ;)
« Last Edit: 09/24/2009 02:44 PM by mmeijeri »
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Offline Hop_David

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Re: L1/2 spacestation with depot
« Reply #95 on: 09/24/2009 10:52 PM »
http://selenianboondocks.com/wp-content/uploads/2009/09/NearTermPropellantDepots.pdf

There are some more on the ULA publications page:

http://www.ulalaunch.com/index_published.html

~Jon

I like the conical heat shield pointing north from the ecliptic plane.

For LEO I had envisioned two heat shields, one protecting the depot from sunlight, the other from earth light. They would have to rotate at different rates, have power and moving parts. The scheme I'd imagined was somewhat of a Rube Goldberg contraption.

The conical shield is a neat and simple solution. The only light this depot endures is from the Southern Cross and other southern constellations.

Offline kkattula

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Re: L1/2 spacestation with depot
« Reply #96 on: 09/25/2009 06:53 AM »
http://selenianboondocks.com/wp-content/uploads/2009/09/NearTermPropellantDepots.pdf

There are some more on the ULA publications page:

http://www.ulalaunch.com/index_published.html

~Jon

I like the conical heat shield pointing north from the ecliptic plane.

For LEO I had envisioned two heat shields, one protecting the depot from sunlight, the other from earth light. They would have to rotate at different rates, have power and moving parts. The scheme I'd imagined was somewhat of a Rube Goldberg contraption.

The conical shield is a neat and simple solution. The only light this depot endures is from the Southern Cross and other southern constellations.

And as it turns out, you need some heat to generate hot H2 for the RCS for station keeping. Zero boil-off is actually undesirable.

Offline robertross

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Re: L1/2 spacestation with depot
« Reply #97 on: 01/31/2010 07:53 PM »
Based on the link Chuck provided us, I would like to push that particular discussion here, if I might. I see some great advantages to push this, especially if we're looking at launching telescopes anyway, but also to enable lunar surface missions, propellant depots, additional radiation experiments, and something BEO.

I'm only partly into the document, but I see some nice things.

From chuck's post:
http://forum.nasaspaceflight.com/index.php?topic=19548.msg531849#msg531849

link to document:
http://history.nasa.gov/DPT/Architectures/Libration%20Points%20&%20In-Space%20Ops%20Libration%20Point%20Gateway%20Final%20Report%20DPT%20Oct_01.pdf
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Offline robertross

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Re: L1/2 spacestation with depot
« Reply #98 on: 02/01/2010 01:05 AM »
Yup, I'm sold on this. Good call chuck to point this out.

It meets many of the objectives I think are fundamental and key to going BEO:

1) International cooperation possible, even using existing ISS module templates like SSRMS, Cupola, maybe Node 3, environmental systems developed so far...
2) COTS components are encourraged (IE: 400Vac 3-phase power)
3) Commercial providers are encourraged for re-supply
4) Makes full use of our (soon to be) new HLV capability
5) Doesn't require many new technologies, but allows close-to-home development of the necessary ones for BEO
6) Can accomplish the task of assembling & repairing telescopes in a more optimal location
7) Enables exceptional location of propellant depots for Mars & other destinations
8. Allows us to test special capabilities like SEP & tugs, proper high impact mmod shielding, effective & accurate radiation shielding requirements, rad-hard electronics, remote operated station
9) Lunar staging point and safe haven, re-supply outpost
10) Staging point for Mars & destinations beyond, for assembly/EVA capabilities.

I've read the whole thread and was really impressed.
I'm half-way through the document linked, which forms the basis of what I've mentioned above. I think the HLV will more than make up for the D4H limitations mentioned within, and can obviously & easily take over the shuttle's role.

The problem I see so far is the Li-ion battery fiber baseline. I see it as too dangerous & fragile for crew from mmod debris impacts. I would rather see this incorporated into a Bigelow inflatable module, forming the inner core for protection that could be removed robotically & jetisoned to the lunar surface for disposal. or something along those lines.

If we are looking for a gateway to the Solar System, this is perhaps the most ideal path to take. A great step forward.
« Last Edit: 02/01/2010 01:05 AM by robertross »
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Offline Bill White

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Re: L1/2 spacestation with depot
« Reply #99 on: 02/01/2010 04:05 AM »
I will quote myself from another thread because it fits here as well:

Quote
I would propose EML Gateway(s) as a vehicle for tying together commercialization and global participation for doing lunar exploration in a sustainable manner.

Deploy an EML Gateway but transfer ownership to a neutral power existing "in between" the world's spacefaring powers and allow that Gateway to do business with everyone - world governments and private entities.

A sort of "Babylon 5" at EML-1 and/or EML-2 to act as a catalyst allowing interface between NASA and other spacefaring nations and private commercial ventures.

This is a link that would allow Bolden's commercialized HLVs to survive future transitions in the occupant of 1600 Pennsylvania Avenue.
EML architectures should be seen as ratchet opportunities

Offline Archibald

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Re: L1/2 spacestation with depot
« Reply #100 on: 02/01/2010 06:27 AM »
I suggest the name Emily for the EML- facility.
If we ever build one at Sun-Earth L1 it might be called Sally;
while a Sun-Mars L1 station might be Samuel :)

There had been a lot of talk about telescope servicing missions recently.

According to this article discussing Belbruno trajectories
http://www.thespacereview.com/article/569/1

Quote
The most fascinating, though, is a way that—theoretically—could allow future servicing of the James Webb Space Telescope (JWST). Unlike Hubble, which is in low Earth orbit, JWST will be located at the Earth-Sun L2 Lagrange point, about 1.5 million kilometers from the Earth. Whereas Hubble was designed to be regularly repaired and upgraded by shuttle missions, there are no plans to make JWST servicable because of its location. However, Folta said there is a way around this by taking advantage of the intersections between Sun-Earth and Earth-Moon dynamics that would allow JWST to maneuver back closer to the Earth. “Because of this intersection we could actually bring the JWST back into the Earth-Moon system. Someone could go out into the Earth-Moon system in three or four days and repair what they needed do, and then we could send JWST back out.” The cost of doing that, in terms of propellant for JWST? Two kilograms, according to Folta.

Offline Robotbeat

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Re: L1/2 spacestation with depot
« Reply #101 on: 02/01/2010 11:49 PM »
...
According to this article discussing Belbruno trajectories
http://www.thespacereview.com/article/569/1

Quote
The most fascinating, though, is a way that—theoretically—could allow future servicing of the James Webb Space Telescope (JWST). Unlike Hubble, which is in low Earth orbit, JWST will be located at the Earth-Sun L2 Lagrange point, about 1.5 million kilometers from the Earth. Whereas Hubble was designed to be regularly repaired and upgraded by shuttle missions, there are no plans to make JWST servicable because of its location. However, Folta said there is a way around this by taking advantage of the intersections between Sun-Earth and Earth-Moon dynamics that would allow JWST to maneuver back closer to the Earth. “Because of this intersection we could actually bring the JWST back into the Earth-Moon system. Someone could go out into the Earth-Moon system in three or four days and repair what they needed do, and then we could send JWST back out.” The cost of doing that, in terms of propellant for JWST? Two kilograms, according to Folta.
That's exactly what I was thinking about, a while back. Why go to ESL2 when you can just go to EML1/2?
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Offline Hop_David

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Re: L1/2 spacestation with depot
« Reply #102 on: 02/02/2010 12:26 AM »
...
According to this article discussing Belbruno trajectories
http://www.thespacereview.com/article/569/1

Quote
The most fascinating, though, is a way that—theoretically—could allow future servicing of the James Webb Space Telescope (JWST). Unlike Hubble, which is in low Earth orbit, JWST will be located at the Earth-Sun L2 Lagrange point, about 1.5 million kilometers from the Earth. Whereas Hubble was designed to be regularly repaired and upgraded by shuttle missions, there are no plans to make JWST servicable because of its location. However, Folta said there is a way around this by taking advantage of the intersections between Sun-Earth and Earth-Moon dynamics that would allow JWST to maneuver back closer to the Earth. “Because of this intersection we could actually bring the JWST back into the Earth-Moon system. Someone could go out into the Earth-Moon system in three or four days and repair what they needed do, and then we could send JWST back out.” The cost of doing that, in terms of propellant for JWST? Two kilograms, according to Folta.
That's exactly what I was thinking about, a while back. Why go to ESL2 when you can just go to EML1/2?

If faulty memory serves, at ESL2 you can shield the scope from 3 major light pollution sources (sun, earth, moon) with a single shade. Those 3 bodies are also sources of infra red light.

As the quoted paragraph mentions, the delta V between EML1/2 and ESL2 is small. But I would suspect it would be time consuming trip.

Offline daveklingler

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Re: L1/2 spacestation with depot
« Reply #103 on: 02/02/2010 07:06 AM »
Without the internet and probably this forum, most people would never have gotten to know propellant depots or the L points really... Everybody would just assume heavy lifters and LOR or EOR-LOR.

As I pointed out in one of the other forums, the original Space Transportation System (the "STS" in shuttle mission names) called for shuttles, a propellant depot/station and a couple of NTR tugs.

Dave Klingler

Offline Robotbeat

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Re: L1/2 spacestation with depot
« Reply #104 on: 02/02/2010 03:37 PM »
...
According to this article discussing Belbruno trajectories
http://www.thespacereview.com/article/569/1

Quote
The most fascinating, though, is a way that—theoretically—could allow future servicing of the James Webb Space Telescope (JWST). Unlike Hubble, which is in low Earth orbit, JWST will be located at the Earth-Sun L2 Lagrange point, about 1.5 million kilometers from the Earth. Whereas Hubble was designed to be regularly repaired and upgraded by shuttle missions, there are no plans to make JWST servicable because of its location. However, Folta said there is a way around this by taking advantage of the intersections between Sun-Earth and Earth-Moon dynamics that would allow JWST to maneuver back closer to the Earth. “Because of this intersection we could actually bring the JWST back into the Earth-Moon system. Someone could go out into the Earth-Moon system in three or four days and repair what they needed do, and then we could send JWST back out.” The cost of doing that, in terms of propellant for JWST? Two kilograms, according to Folta.
That's exactly what I was thinking about, a while back. Why go to ESL2 when you can just go to EML1/2?

If faulty memory serves, at ESL2 you can shield the scope from 3 major light pollution sources (sun, earth, moon) with a single shade. Those 3 bodies are also sources of infra red light.

As the quoted paragraph mentions, the delta V between EML1/2 and ESL2 is small. But I would suspect it would be time consuming trip.

What I was meaning is that any human service mission wouldn't need to go all the way to ESL2. The telescope at ESL2 can send itself to EML1/2 with less than a year's worth of station-keeping propellant. The telescope can take its time to go to EML1/2 if it really needs servicing.
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Offline Archibald

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Re: L1/2 spacestation with depot
« Reply #105 on: 02/02/2010 07:49 PM »
Quote
But I would suspect it would be time consuming trip.

One to three years

Btw, I just love this picture http://forum.nasaspaceflight.com/index.php?action=dlattach;topic=13532.0;attach=86198;image
« Last Edit: 02/02/2010 07:55 PM by Archibald »

Offline butters

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Re: L1/2 spacestation with depot
« Reply #106 on: 02/02/2010 09:14 PM »
I have a number of problems with the L1 Gateway proposal.

1) It doesn't have a propellant depot.

2) It specifies an expendable two-stage lander.

These problems can be fixed by using a docked reusable single-stage lander as a propellant depot.  The lander is the only client for the depot anyway.  The propellant would likely be NTO/MMH or H2O2/RP-1.

3) ISS staging with propulsive braking isn't going to happen.

Maybe a layover at ISS on the way out if the upper stage is to be refilled in LEO for TLI, but return from EML will be direct reentry.

4) Monolithic station imposes unnecessary mass constraints.

The lithium-ion fiber cells to be woven into composite partitions and inflatable skin is a particularly pie in the sky mass optimization.  The station can be launched into three pieces (docking/service module, habitat module, EVA/robotics module), assembled in LEO along with the docked lander (dry), and slowly spiraled out to EML by the SEP.

So you need the station modules, the lander, the SEP tug, the crew transport vehicle, a big enough launch vehicle or cryogenic propellant tankers, storable propellant tankers, and MPLMs.  Piece of cake...
« Last Edit: 02/02/2010 09:18 PM by butters »

Offline A_M_Swallow

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Re: L1/2 spacestation with depot
« Reply #107 on: 02/02/2010 10:28 PM »
Quotes by butters
"So you need the station modules,"
Under development by Bigelow.

"the lander,"
New project.

"the SEP tug,"
A VASIMR SEP tug is probably under development by Ad Astra

"the crew transport vehicle,"
At LEO - Dragon and Dream Chaser.
Else where - New project.

"a big enough launch vehicle"
For people Falcon 9 and man-rated Atlas V under development.
For propellant Falcon 9, Taurus II, Falcon 1, Atlas V and Delta IV.

"or cryogenic propellant tankers,"
New project.

"storable propellant tankers,"
Something for the oil companies to invent.

"and MPLMs."
A Multi-Purpose Logistics Module may or may not exist.


" Piece of cake..."
I will go to the shops.   ;D


The spacestation is also likely to need spacecraft repair facilities like robotic arms.  The same arms may be able to perform cargo transfer between spacecraft.

Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #108 on: 02/02/2010 10:36 PM »
So you need the station modules, the lander, the SEP tug, the crew transport vehicle, a big enough launch vehicle or cryogenic propellant tankers, storable propellant tankers, and MPLMs.  Piece of cake...

You'd want an incremental path towards this.

You could start with the lander itself, which could serve as a mini space station, depot and lander. Then you could add a hab. You could also do this in the reverse order. The hab would likely be a Bigelow hab to avoid unnecessary R&D. Then you could add a SEP tug. If it is only used between L1/L2 and GEO or LLO or in support of exploration to Mars orbit it doesn't have to cross the van Allens repeatedly. This makes it easier to field a first version quickly since that can be done with current technologies. You could also use low energy trajectories and chemical propulsion until the tug was ready.
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Offline butters

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Re: L1/2 spacestation with depot
« Reply #109 on: 02/02/2010 11:42 PM »
To get crew to EML without EOR or LEO refill requires an LV bigger than EELV Heavy, approximately 50mT IMLEO.  Dragon and Dream Chaser don't have the habitable volume and life-support for a 6-day trip (each way) on their own.  So the CTV is an Orion-like 20mT through TLI.

The CTV could be as light as 16mT through TLI with an expendable hab module (e.g. Dragon + Sundancer), launched on two F9s.  That still puts the EDS slightly out of the range of Atlas V 551, and Dragon would be a bit short of the dV to push itself and Sundancer through ROI.

Dragon really needs at least twice as much propellant to play this role.  The tankage may not fit in the capsule, and it may be more appropriate to add another propulsion system in the expendable trunk.  This probably exceeds the performance capability of F9.  It may be able to go on Atlas V 402.

Forget about LEO staging to an exoatmospheric CTV.  The propulsive braking required to return to LEO involves a round-trip dV of at least 7.5 km/s to EML1.  That makes the EDS considerably bigger than it would be for a heavier direct reentry CTV.

So it's not so simple.  Orion (the original reusable spec) was actually close to the ideal CTV because it could get away with not having an expendable hab in this role.  It would be nice to have an LV that could do 25mT IMLEO without any strap-ons (CTV) and up to 40mT with solid strap-ons (EDS).
« Last Edit: 02/02/2010 11:43 PM by butters »

Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #110 on: 02/02/2010 11:46 PM »
To get crew to EML without EOR or LEO refill requires an LV bigger than EELV Heavy, approximately 50mT IMLEO.

EOR is a good option until cryogenic propellant transfer or bigger launch vehicles come along. Single launch is less complicated which is one of the better arguments for a larger launch vehicle. EELV Phase 1 would be the obvious candidate. The complexities of EOR could be mitigated by using the ISS as a staging point and launching the crew first.

EDIT: propellant transfer still requires EOR of course.
« Last Edit: 02/02/2010 11:47 PM by mmeijeri »
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Offline Robotbeat

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Re: L1/2 spacestation with depot
« Reply #111 on: 02/02/2010 11:53 PM »
To get crew to EML without EOR or LEO refill requires an LV bigger than EELV Heavy, approximately 50mT IMLEO.  Dragon and Dream Chaser don't have the habitable volume and life-support for a 6-day trip (each way) on their own.  So the CTV is an Orion-like 20mT through TLI.

The CTV could be as light as 16mT through TLI with an expendable hab module (e.g. Dragon + Sundancer), launched on two F9s.  That still puts the EDS slightly out of the range of Atlas V 551, and Dragon would be a bit short of the dV to push itself and Sundancer through ROI.

Dragon really needs at least twice as much propellant to play this role.  The tankage may not fit in the capsule, and it may be more appropriate to add another propulsion system in the expendable trunk.  This probably exceeds the performance capability of F9.  It may be able to go on Atlas V 402.
Falcon 9 heavy or Falcon 9 with a "Raptor" hydrolox upperstage (or a Falcon 9 heavy with "Raptor" hydrolox upperstage, giving you 45 tons to LEO) are viable alternatives.
Forget about LEO staging to an exoatmospheric CTV.  The propulsive braking required to return to LEO involves a round-trip dV of at least 7.5 km/s to EML1.  That makes the EDS considerably bigger than it would be for a heavier direct reentry CTV.
I _won't_ forget it. If you are using prop depots (and sep tugs), the exponent is broken up. It's not 7.5 km/s, it's 3.7km/s twice. There's a big difference. If using 311s isp propulsion for your exoatmospheric-only crew transport vehicle (would also be a depot/hab and/or a lander), that's a mass-fraction of 7 instead of 12. Almost twice as much. It means you can use a LEO commercial crew vehicle which is already developed, instead of paying billions extra for a new development, money that can be simply spent on propellant (which can help increase launch rates).
« Last Edit: 02/02/2010 11:54 PM by Robotbeat »
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Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #112 on: 02/02/2010 11:58 PM »
Almost twice as much. It means you can use a LEO commercial crew vehicle which is already developed, instead of paying billions extra for a new development, money that can be simply spent on propellant (which can help increase launch rates).

As you know I'm all for commercial propellant launches and SEP, but not to use LOX/LH2 for TLI seems wasteful to me. Why not rendez-vous with a cryogenic EDS in LEO? I can see why you would want to do this while you were waiting for an EDS to be developed on the basis of an existing upper stage. Or if your upper stage is very small like ECA, as was discussed on the man-rated Ariane thread. But not as a general solution.

But hey, if NASA wanted to fund it, I'd not be complaining. :)
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Offline Robotbeat

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Re: L1/2 spacestation with depot
« Reply #113 on: 02/03/2010 12:01 AM »
Almost twice as much. It means you can use a LEO commercial crew vehicle which is already developed, instead of paying billions extra for a new development, money that can be simply spent on propellant (which can help increase launch rates).

As you know I'm all for commercial propellant launches and SEP, but not to use LOX/LH2 for TLI seems wasteful to me. Why not rendez-vous with a cryogenic EDS in LEO? I can see why you would want to do this while you were waiting for an EDS to be developed on the basis of an existing upper stage. Or if your upper stage is very small like ECA, as was discussed on the man-rated Ariane thread. But not as a general solution.

But hey, if NASA wanted to fund it, I'd not be complaining. :)
Good point about the hydrolox. You wouldn't use something with that low of an Isp. I chose a low Isp to highlight what a difference breaking up the exponent makes, something you can do with prop depots and SEP tugs.
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Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #114 on: 02/03/2010 12:06 AM »
Ah, I see. Note that van Allen crossing tugs are still a while away, and they'd be necessary to make this efficient. Aerobraking would be another option, but that needs significant R&D too. I'd be worried about putting all that on the critical path, but eager to see it put on a technology development track. I like frequent small operational milestones. It does increase the risk that further development is terminated early or postponed because sponsors are happy with the initial capability, and that's not good. But then at least it would have been canceled after having delivered an operational capability instead of before it did as with Constellation.
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Offline butters

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Re: L1/2 spacestation with depot
« Reply #115 on: 02/03/2010 12:11 AM »
So you need the station modules, the lander, the SEP tug, the crew transport vehicle, a big enough launch vehicle or cryogenic propellant tankers, storable propellant tankers, and MPLMs.  Piece of cake...
You'd want an incremental path towards this.

You could start with the lander itself, which could serve as a mini space station, depot and lander. Then you could add a hab. You could also do this in the reverse order.

The station is really only necessary for telescope servicing and such.  For the moon, all we need is a lander and propellant tankers in addition to the CTV.  The lander is light enough (and a one-time trip) to use chemical propulsion to get it to EML.  It would be nice to send the tankers (and also cargo landers) using SEP tugs.

Offline Robotbeat

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Re: L1/2 spacestation with depot
« Reply #116 on: 02/03/2010 01:06 AM »
Ah, I see. Note that van Allen crossing tugs are still a while away, and they'd be necessary to make this efficient. ...

I'm not so sure that van Allen belt-crossing is that far away. From what I've read, it involves a thicker coating of radiation-hardening material, which impacts your specific power (not too bad, actually), but specific power isn't so critical at 1 AU from the Sun and if you have enough time and if you already have a quite healthy specific power. I am not convinced this is such a big problem. A radiation-hardened solar array could be demoed on the very first solar-electric tug.
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Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #117 on: 02/03/2010 01:11 AM »
The station is really only necessary for telescope servicing and such.

You might be able to avoid it even for that if you added an optional robotic arm to the lander. Of course, there is no strict reason to avoid a space station since Bigelow modules appear to be close to being a reality. Either way, I'd like the lander to be the cis-lunar and later translunar equivalent of the Shuttle: a jack of all trades while still being a good lander. I'd be perfectly happy with NASA developing this beast in-house, as long as they only used TRL 9 technologies. Commercial players are a long way away from doing anything that is fully commercial beyond LEO and this approach would help them get into LEO faster.

There does not appear to be money for it in the foreseeable future however. Still, it's fun to speculate and fantasise.
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Offline mmeijeri

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Re: L1/2 spacestation with depot
« Reply #118 on: 02/03/2010 01:16 AM »
I'm not so sure that van Allen belt-crossing is that far away. From what I've read, it involves a thicker coating of radiation-hardening material, which impacts your specific power (not too bad, actually), but specific power isn't so critical at 1 AU from the Sun and if you have enough time and if you already have a quite healthy specific power. I am not convinced this is such a big problem. A radiation-hardened solar array could be demoed on the very first solar-electric tug.

There's apparently also a new self healing material that doesn't lose more than 20% of its performance after its initial pass through the van Allens. I'll dig up the link if you want. Stirling engines are apparently also a near term possibility. Note that even so the economics of SEP for LEO to L1/L2 are not obvious. Round trip times are high, which means you have a lot of capital costs. Beyond the Earth moon system they are highly plausible, especially for propellant.
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Offline A_M_Swallow

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Re: L1/2 spacestation with depot
« Reply #119 on: 02/03/2010 01:41 AM »
The radiation hardness of the solar arrays can be tested using a mini tug.  The test tug could spend its time flying up and down through the Van Allen belts.  A mini tug with small solar panels can be launched on a Pegasus or Falcon 1.  There are several small ion engines, one of which may be suitable.

Offline Robo-Nerd

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Re: L1/2 spacestation with depot
« Reply #120 on: 02/05/2010 04:48 AM »
So here is an off the wall thought: An EML-1 / 2 Gateway station may be the first practical location in the solar system for the use of a space tether all the way to a planetary surface. I don't know how practical the capital investment / material science is, but if you could drop a tether from EML-1 to the lunar surface you could achieve a very practical means of potentially getting a lot of mass into an orbital location at very little cost (solar power arrays). Does anyone know if this has been studied at all?

Thanks,
     - Osa

Edit: Answered my own question via wikipedia:

http://en.wikipedia.org/wiki/Lunar_space_elevator
« Last Edit: 02/05/2010 04:54 AM by Robo-Nerd »
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Offline Archibald

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Re: L1/2 spacestation with depot
« Reply #121 on: 06/30/2010 01:24 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.

My spread sheet gives
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


Thread necromancy...

Is the 1.84 km/s one way, thus 3.68 km/s if return included ?
(EML-1 > SML-1 > EML-1)

Offline A_M_Swallow

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Re: L1/2 spacestation with depot
« Reply #122 on: 06/30/2010 03:53 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.

My spread sheet gives
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


Thread necromancy...

Is the 1.84 km/s one way, thus 3.68 km/s if return included ?
(EML-1 > SML-1 > EML-1)

Yes the 1.84 km/s is one way.

Cargo on chemical propulsion is a one way trip.
People return so need to carry return fuel (until ISRU is online).
SEP tugs return to make them reusable.

Offline Bill White

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Re: L1/2 spacestation with depot
« Reply #123 on: 07/14/2010 03:59 AM »
Initially, an EML-1 or EML-2 depot could also be complemented with a smaller reusable lunar lander only large enough to deliver Robonauts to various points on the lunar surface, and then return them to the Gateway.

Perhaps re-use the ascent stage and combine with disposable crasher stages.

How large would a lander need to be to deliver a pair of Robonauts to the lunar surface and then return them safely to EML-1?

Even if a fully functional human lander cannot be funded this decade, why not a Robonaut lander capable of deploying Robonauts to multiple places of interest all over the Moon? 
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Offline FinalFrontier

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Re: L1/2 spacestation with depot
« Reply #124 on: 07/15/2010 04:31 AM »
This spacestation depot seems to be a central idea in the new bill.

I like it :)
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Offline alexterrell

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Re: L1/2 spacestation with depot
« Reply #125 on: 08/01/2010 08:20 PM »
A fuel depot at L1 has no real advantage over LEO except enabling you to use different launch configurations.... unless, you have electric propulsion to transport fuel from LEO to L1.

Consider a 1 MW VASIMR tug, weighing 10 tons, which uses 10 tons of Argon to lift a 60 ton payload to L1 over the course of 12 months. Two such tugs deliver 120 tons per year. If most of this is water, it could be electrolysed "on demand" for a variety of missions.

 

Offline Bill White

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Re: L1/2 spacestation with depot
« Reply #126 on: 08/01/2010 09:02 PM »
A fuel depot at L1 has no real advantage over LEO except enabling you to use different launch configurations.... unless, you have electric propulsion to transport fuel from LEO to L1.

Consider a 1 MW VASIMR tug, weighing 10 tons, which uses 10 tons of Argon to lift a 60 ton payload to L1 over the course of 12 months. Two such tugs deliver 120 tons per year. If most of this is water, it could be electrolysed "on demand" for a variety of missions.

There also are single impulse ballistic trajectories from LEO to various places including EML-1 and EML-2 that are more efficient that more conventional trajectories except that travel times are greatly increased.

100 days from LEO to EML-1, for example, however net payload appears to be substantially increased.

Single impulse also means that conventional upper stages (Centaur for example) can take advantage of these trajectories

See papers linked below

http://ccar.colorado.edu/nag/papers/AAS%2006-132.pdf

http://ccar.colorado.edu/geryon/papers/White_Papers/Lunar-NavCom-WhitePaper-2006-05.pdf
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Offline sdsds

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Re: L1/2 spacestation with depot
« Reply #127 on: 08/01/2010 09:39 PM »
A fuel depot at L1 has no real advantage over LEO

What Bill White said.  Plus (for those looking at cryogenic depots) L1 provides a much more benign thermal environment.  Also, L1 is easier to reach than LEO from the lunar surface or almost anywhere else on the "return leg" of a mission.  Yes, direct return to Earth atmospheric entry is possible, but that doesn't allow "parking" some spacecraft components in a place where they can later be reused.  A depot/station complex near L1 cheaply provides lots of "bang" that would require a lot of "bucks" to provide in LEO.
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Offline Bill White

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Re: L1/2 spacestation with depot
« Reply #128 on: 08/02/2010 12:17 AM »
I do not wish to see EML depots instead of LEO depots and I would advocate for EML depots operating in synergy with LEO depots.

A logistics pipeline, as it were:

Earth < - - > LEO < - - > EML-1/EML-2 < - - > Luna

and

EML-1/EML-2 < - - > GEO

and

EML-1/EML-2 < - - > NEOs

and

EML-1/EML-2 < - - > Phobos / Deimos

etc . . . .
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Offline orbitjunkie

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Re: L1/2 spacestation with depot
« Reply #129 on: 08/02/2010 01:18 PM »
It is often repeated that a station at Earth-Moon L1 or L2 would allow "easy" access to/from anywhere on the lunar surface. Does anyone here know of any good, detailed references on what those lunar landing/launch trajectories look like? I mean something more than spreadsheets with ballpark numbers. Specifically anything that actually integrates trajectories or uses dynamical systems approaches.

I ask because what little "expertise" I may claim is in the area of trajectory design. Although I'm not as experienced with libration orbits, but I have tried to design some landings from a L1/L2 orbit using high fidelity simulations and it was not what I would call simple or easy. I didn't try launching from the surface back to L1 or L2.

While a station/depot at L1 or L2 sounds like a great thing and I really like the idea, I am a little concerned that the practicalities of it will be an achilles heel. Things like limited "launch windows" to certain parts of the lunar surface, or the need to manhandle the trajectory so much as to lose most of the delta-V benefits that are claimed. Too many operational consolations will really dilute the advertised value.

Thanks for any references you may have!

Offline orbitjunkie

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Re: L1/2 spacestation with depot
« Reply #130 on: 08/02/2010 01:27 PM »
So here is an off the wall thought: An EML-1 / 2 Gateway station may be the first practical location in the solar system for the use of a space tether all the way to a planetary surface. I don't know how practical the capital investment / material science is, but if you could drop a tether from EML-1 to the lunar surface you could achieve a very practical means of potentially getting a lot of mass into an orbital location at very little cost (solar power arrays). Does anyone know if this has been studied at all?

Thanks,
     - Osa

Edit: Answered my own question via wikipedia:

http://en.wikipedia.org/wiki/Lunar_space_elevator


One major obstacle in my mind is that putting a satellite "at" a libration point always means it is "orbiting" the point, usually at a very significant distance. Take a look at the graph on page 5 of the below reference:

<snip>
See papers linked below
http://ccar.colorado.edu/nag/papers/AAS%2006-132.pdf

Note the scale. Your satellite could "orbiting" the libration point at a distance of ~50,000 km. You will have very widely varying distances from any point on the lunar surface. The satellite will spend a lot of time far below the horizon of a location on a lunar pole. I suspect you'd have an easier time developing reusable lunar landers and a hydrolox propellant production infrastructure and just use independant vehicles. But maybe someone has actually studied this and found it not be that difficult?

Haha, it also just occurred to me that a Moon-EMLx tether would be a literal bridge to nowhere!

Offline JohnFornaro

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Re: L1/2 spacestation with depot
« Reply #131 on: 08/02/2010 02:58 PM »
Before we go much further, let's get one thing straight:

It is VASIMR, not VASIMIR.
Before we go much further, let's get one thing straight:

It is VASIMR, not VASIMIR.

Variable Specific Impulse Magnetoplasma Rocket
I think they also prefer the case sensitive nomenclature: VaSIMR.

Variable Specific Impulse Magnetoplasma Rocket
« Last Edit: 08/05/2010 02:31 PM by JohnFornaro »
Sometimes I just flat out don't get it.

Offline JohnFornaro

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Re: L1/2 spacestation with depot
« Reply #132 on: 08/02/2010 03:10 PM »
Quote
Your satellite could "orbiting" the libration point at a distance of ~50,000 km.

This is one of the reasons that I don't favor the L2 point; the second being it's distance compared to L1; the third being that a hotel room with one window looking at the Moon and the other widow looking at the Earth would have a higher room rate.

Many around here prefer L2, tho, I believe because it has a better delta-vee budget to elsewhere than L1.

I am printing out this article.  The software available these days makes the analysis of these "families" of orbits much easier, and the graphs are visually very interesting.
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Offline Robotbeat

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Re: L1/2 spacestation with depot
« Reply #133 on: 08/02/2010 04:47 PM »
You could easily change your mind (from a delta-v standpoint) after you launched about whether EML1 or EML2 was a better location. Delta-v between EML1/2 is only ~140m/s... only about a couple years' worth of stationkeeping propellant.
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Offline Bill White

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Re: L1/2 spacestation with depot
« Reply #134 on: 08/03/2010 06:43 PM »
@robotjunkie

It is my non-technical understanding that attaining a low lunar orbit (LLO) is "easy" when starting from EML-1 or EML-2. Thereafter, a surface landing would occur in the same fashion as if LLO were achieved direct from LEO.

Have you attempted to model EML to LLO?

 
« Last Edit: 08/03/2010 06:44 PM by Bill White »
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Offline orbitjunkie

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Re: L1/2 spacestation with depot
« Reply #135 on: 08/03/2010 06:57 PM »
@robotjunkie

It is my non-technical understanding that attaining a low lunar orbit (LLO) is "easy" when starting from EML-1 or EML-2. Thereafter, a surface landing would occur in the same fashion as if LLO were achieved direct from LEO.

Have you attempted to model EML to LLO?


It was a few months ago, but if memory serves my trials included capturing into a LLO rather than direct landing, since I already had a working landing sequence from LLO.

Would still love to see some detailed references if anyone out there knows of some!

Offline sdsds

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Re: L1/2 spacestation with depot
« Reply #136 on: 08/03/2010 10:23 PM »
Have you tried using:
http://astrojava.com/lunar-trajectory-simulation
?

Edit to add:

This simulator can be a bit frustrating at first, but it shows:

If you depart EML-1 with a delta-v of 125 m/s in a direction coplanar with the orbit of the Moon and at an angle of 63.2 degrees (where zero degrees is along the line from the Earth to the Moon) you will reach a perilune of 110.1 km 68.5 hours later.  When there you can insert into an essentially circular LLO with -630 m/s of delta-v.

Sadly that orbit is equatorial.  I can't coerce the simulator to show non-coplanar EML-1 departures, but intuition says there would be a non-coplanar departure with similar delta-v that led to a polar LLO.
« Last Edit: 08/04/2010 03:26 AM by sdsds »
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Offline Bill White

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Re: L1/2 spacestation with depot
« Reply #137 on: 08/04/2010 01:03 PM »
Have you tried using:
http://astrojava.com/lunar-trajectory-simulation
?

Edit to add:

This simulator can be a bit frustrating at first, but it shows:

If you depart EML-1 with a delta-v of 125 m/s in a direction coplanar with the orbit of the Moon and at an angle of 63.2 degrees (where zero degrees is along the line from the Earth to the Moon) you will reach a perilune of 110.1 km 68.5 hours later.  When there you can insert into an essentially circular LLO with -630 m/s of delta-v.

Sadly that orbit is equatorial.  I can't coerce the simulator to show non-coplanar EML-1 departures, but intuition says there would be a non-coplanar departure with similar delta-v that led to a polar LLO.

On page three of the paper linked below the authors assert that "any lunar orbit" (including equatorial and polar orbits) can be attained from EML-1 with essentially the same delta V.

My suggestion would be to contact the authors of this paper and request assistance in tweaking the simulator to achieve the desired results.

http://ccar.colorado.edu/geryon/papers/White_Papers/Lunar-NavCom-WhitePaper-2006-05.pdf
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Offline JohnFornaro

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Re: L1/2 spacestation with depot
« Reply #138 on: 08/04/2010 03:26 PM »
I like the conclusions of the paper; using halo orbits for constellations of com sats, placed in orbit with low energy trajectories.  They could also be power sats for the ISRU facilities as well.  Part of sustainability to me is reducing launch costs.  The long time to orbit these constellations is not a problem, since so much other work needs to be done as well in the interim. 

As to the trajectory app:  It is cool.  But remember: "be sure to propagate sufficiently to reach perilune!"
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Offline Hop_David

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Re: L1/2 spacestation with depot
« Reply #139 on: 08/04/2010 11:57 PM »
I like the conclusions of the paper; using halo orbits for constellations of com sats, placed in orbit with low energy trajectories.  They could also be power sats for the ISRU facilities as well.

L2 power sats would be 64,000 km from the moon's surface, L1 56,000.

This is even further than geosynch from earth's surface (about 36,000)

As with geosynch sats, you'd need big rectennas as well as mammoth satellites.

However, I do think beaming power by microwave has applications on the moon.

If you had a number of solar power plants around the north pole, it's possible each plant could enjoy line of sight with its neighbors. A Japanese power plant on the night side of the terminator could purchase power from a U.S. plant on the day side. 28 days later, vice versa.

« Last Edit: 08/04/2010 11:59 PM by Hop_David »

Offline JohnFornaro

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Re: L1/2 spacestation with depot
« Reply #140 on: 08/05/2010 02:33 PM »
After a few minutes of googoling, I didn't find a straightforward statement: The distance from EML-1 to the Moon's surface is 'x' km.  I did find derivation equations and several other interesting sidetracks.  I choose laziness, and accept the figures given.

What I gathered from the article, after a scan, was the idea of what I would call a heliocentric lunar polar orbit of the constellation of six power sats, whose efforts are coordinated to beam power to the polar ISRU plant.  I realize this morning that wasn't quite what the authors were talking about.

So it's time to fire up the scanner:

First, L1 is not the right place for what I have in mind.  I will be continuing on the lunar mining ice thread, but I point it out here since that's where I am right now.

A fleet of six power/com sats would orbit the Moon in a polar fashion at an appropriate altitude.  The polar axis of the Moon would intersect this orbit, and the orbit plane of the constellation would in turn rotate around the Moon's equator as shown.  The tentative term "heliocentric orbit thing" is posed.  The power sats would always face the sun.  As they rotated above the rectenna in the ice filled lunar crater, they would have to coordinate a choreography of power transmission between themselves and the rectenna. 

The rectenna is designed to accomodate the somewhat greater than 120 degree extremes of the power beams, and the losses from the varying angles of incidence are simply a fact of life.  There is no atmospheric attenuation at least, unlike the schemes which purport to beam power to the Earth.

Additionally, the constellation should provide power to the lunar south pole as well, and should be constructed with this ability from the very beginning, realizing that although one pole will be chosen first, the second pole will happen soon enough.  The first application of course, would be for lunar cracking plants, then for outposts.  I don't know what the eventual settlement pattern of the outposts would be, and that's a field of conjecture in itself, since it would have to accomodate the discovery of gold, for example.  For the moment, assume that they would be polar at first.  Equatorial outposts would not benefit from this scheme, realizing that one power conversion and transmission scheme does not solve all problems.

The constellation would include communication abilities from the beginning, obviously.  In addition, the sats would be designed for expansion, since power needs will always grow.  The expansion capabilities are limited to electrical and structural connections.  These do not have to be designed for all time, but rather only for the next cycle of expansion.  The second group of six expansion sats will connect with these.  Future connection parameters can be designed later on, as well as the future interface required to power equatorial outposts.

One of the interesting articles I did find in this morning's search was this presentation of Lissajous orbits for these constellations:

http://web.mit.edu/egralla/www/research/downloads/AAS_04-248.pdf

Edit:  My isometric-fu is off this morning.  I just noticed I drew only <five> dern satellites.  Fixed the scan...
« Last Edit: 08/05/2010 04:28 PM by JohnFornaro »
Sometimes I just flat out don't get it.

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