Author Topic: L1/2 spacestation with depot  (Read 64672 times)

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)
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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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Online 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 »
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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 »

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