Gateway L-2 Mission: Opening Cislunar Space or Dead End?

The L-points of a planetary system. The L-2 point is located on the opposite side of the Moon, about 60,000 km above the center of the far side.

A recent report by the NASA human architecture team has given us a glimpse of the agency’s thinking about future missions beyond low Earth orbit (LEO).  Interest is focused on sending human crews to a “Gateway” outpost stationed at the gravitationally stable Earth-Moon L-2 point.  The facility, built with plans and parts derived from the construction of the International Space Station, would slowly circle the L-2 point in a halo orbit.  From its “hovering” position over the lunar far side, it would be in direct communication with Earth.  Astronauts stationed at the L-2 Gateway would communicate with robotic spacecraft on the surface of the lunar far side – directing rovers to collect samples and emplace geophysical and astronomical equipment.  An L-2 Gateway station could be a staging point for future human missions to the lunar surface, near Earth asteroids, and to Mars and its moons.

The Earth-Moon system contains five libration points (also called Lagrange points, after the astronomer who first described them).  L-1 and L-2 are found 60,000 km above the center of the near and far sides, respectively.  The L-3 point is directly in-line on the opposite side of the Earth, at about lunar distance.  The L-4 and L-5 points also occur at lunar distance (lagging and leading the Moon, respectively).  Because of solar tides and other effects, only the L-4 and L-5 points are stable, though a spacecraft positioned at any L-point can remain there with minimal maintenance.  The advantage of the L-points is that they maintain a constant position with respect to Earth and Moon, so very little energy is required to go from any of the L-points to other places of interest in cislunar space (such as geosynchronous orbit, low Earth and lunar orbit and the lunar surface).  For planetary missions, they offer an assembly point with low departure energies and extended launch windows.

I have described elsewhere the value and potential of cislunar space.  This region of space – the volume of the Earth-Moon system – is where the vast majority of space assets reside. The first step to becoming a true space faring species is the ability to routinely and frequently access various levels of cislunar space.  Occupying these areas solves part of the problem, getting to and from these various places (rocket firings) creates capability.  Rockets need propellant – to fuel and refuel.

How, and from where, would this propellant be supplied?  The idea that we can assemble caches of rocket fuel in space for use by vehicles going to and from LEO has been around for years.  These facilities (propellant depots) would allow the fueling of transfer vehicles and re-fueling for future use upon their return.  Some models call for depot propellant to be supplied from Earth and stored to go beyond LEO.  To work, that vision banks on breakthroughs to lower the current cost to LEO.  Others believe that what really makes a depot system work is the harvesting and use of propellant from off-planet sources, (usually hydrogen and oxygen from the Moon and asteroids).  These fuel sources require much less energy to deliver to depots than propellant delivered up from Earth’s surface, hence significantly lowering overall costs.  The challenge is setting up a system to acquire the propellant and distribute it to the fueling stations of cislunar space – an endeavor that would establish with some certainty, our ability to live and work in space.

The architecture devised by Tony Lavoie and myself was our attempt to design a strategy to set up this propellant delivery system at minimal cost.  In brief, we propose to use robotic assets (operated remotely from Earth) to mine and process lunar polar water, and deliver it to processing stations in cislunar space.  Using non-terrestrial water to make propellant cuts the logistical cord between Earth and space and creates routine access to all of cislunar and interplanetary space.

How does the proposed Gateway L-2 concept fit into such a scenario?  It depends.  In its current efforts, the focus of the NASA architecture team is to design a human mission that goes beyond LEO (using the new Orion/SLS spacecraft currently under development) to demonstrate human “presence” at some destination.  This mission profile does that, but what then?  The initial suggestion is that astronauts at this L-2 station could control robots on the far side of the Moon.  The lunar science community has long desired a sample from the floor of the largest crater on the Moon, the massive South Pole-Aitken basin centered on the lunar far side.  Moreover, certain geophysical and astrophysical measurements can be uniquely undertaken there.  So, one concept has the crew at L-2 Gateway exploring the lunar surface with teleoperated rovers (landed separately) on the far side of the Moon.

In a way, this is “make work” for the crew at L-2.  The use of astronauts to teleoperate surface robots on the far side of the Moon is possible, but offers no real advantage over their remote control from the Earth.  Much is made about the “latency factor” of time delay, but the specific tasks envisioned by these missions (i.e., the retrieval of a few kilograms of rock and soil and the deployment of a long-lived scientific station) could be satisfied by teleoperation with the three-second time lag imposed by the Earth-Moon distance.  In contrast, operation from L-2 will experience a 0.4 second lag – shorter, but worth the effort?  The completely robotic New Frontiers SPA sample return mission was originally envisioned as controlled from Earth.

The extent to which telepresence is needed for effective geological exploration is unclear.  This is a result of both the relatively primitive state of telepresence technology (e.g., still awaiting very high bandwidth visual and tactile sensory systems) and our poor understanding of the “field exploration experience” from a human cognitive viewpoint.  My experience with using remote systems to do geology has been less than edifying.  I find that both poor situational awareness and the diversion of concentration on technical issues of the human-robot interface, results in significantly less time spent conducting true surface exploration.  In other words, as a replacement for human field work, telepresence leaves a lot to be desired.

My sense is that this mission is a hammer looking for a nail.  Manually operating a robot from an L-2 Gateway station – one that could be just as well controlled from Earth – does not add value but rather distracts from the real importance and necessity of creating a cislunar transportation infrastructure.

An L-point outpost needs no special justification if it is part of a complete Earth-Moon cislunar transportation system.  Such an outpost could serve as an extraterrestrial port of call – to fuel and transfer to destinations throughout cislunar space.  To make an L-2 gateway useful, it must be supplied by propellant.  That propellant is present and awaiting harvest only 60,000 km away on the lunar surface.  Unless a facility is on the Moon making propellant for export, we are not creating and operating new spaceflight capability – we are simply flying another mission to give the impression (falsely) that something has been accomplished on the “Flexible Path” and that NASA knows where it is going and what it is doing for long-term human space exploration.

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66 Responses to Gateway L-2 Mission: Opening Cislunar Space or Dead End?

  1. Pingback: Mission: Tomorrow » Gateway L-2 Mission: Opening Cislunar Space or Dead End? | Spudis Lunar Resources

  2. Wouldn’t it also make sense to put a station at L3 for planners who want to pretend the moon doesn’t exist?

  3. Ken Steele says:

    Thanks for the new blog. I’ll be keeping an eye on it. One question: Some years back, when (Mr?Dr?) Zubrin came out with “The Case For Mars”, he pointed out that with a Hohmann orbit to Mars, it made little sense, energy-wise, to choose a side-trip to the Moon first for refueling, but since the rocket in question would be refueled, wouldn’t it be able to go several kps faster than a Hohmann? Would that make a difference, since you wouldn’t have to use a larger rocket launched from Earth to achieve that same velocity?

    Also, wouldn’t an L2 station require several communication satellites to maintain comms with Earth? Gotta figure that price, too!

    Thanks again for your blog.

    • Paul Spudis says:

      Ken,

      Keep in mind that Bob’s goal is Mars and Mars only. He views lunar activity (or activity anywhere else) as a diversion toward that end. My goal is to enable us to travel anywhere we choose to in space. Thus, I make cislunar an important early staging ground to create this new capability. Lunar derived propellant is one aspect that that new capability.

      As for communications at L-2, a spacecraft there would be put in a “halo” orbit, an irregular path that circles the actual L-2 point. This halo orbit would be in direct line-of-sight to both Earth and the lunar far side.

    • Hop David says:

      if there’s no orbital propellant or supplies, it is better to depart from LEO. Trans Mars Injection (TMI) takes about 3.6 km/sec from LEO.

      But propellant and supplies at EML2 would confer an advantage. From LEO and using a lunar gravity assist, it takes 3.2 km/s to reach EML2. Given supplies at EML2, a vehicle can load up on propellant, water for radiation shielding as well as water to drink and oxygen to breathe. From EML2, TMI is about .5 km/s

  4. There are two problems with the L2 scenario.

    The first is that the idea for fully robotic operations on the surface is a bridge too far. If we were able to do this on the Earth today, we would be doing it but we don’t because humans have value in the process. The same is true of the Moon, at least in the early years until we figure out how to build and operate equipment in that environment.

    The second is that L2 is much too far from the lunar surface to enable low cost human landings. The problem that really killed constellation, besides its cost, was the reliance on a massive sortie class lander when we were supposedly building an outpost.

    A scenario where we do land robotic assets to do some simple work, at the lunar north pole rather than the terrain challenged south pole, and then leverage that work with humans on the Moon that focus on resource development will make an L2 outpost actually be worth something as a gateway to other destinations.

    • Ron says:

      You wrote, “If we were able to do this on the Earth today, we would be doing it but we don’t because humans have value in the process. ” Remote Operated Vehicles (ROVs) are a mainstay of the deep-sea oil extraction industry.

      • And who fixes them when they break? A robot?

        You know better.

        • Ron says:

          Deep-sea ROVs can be pulled up to the surface to be worked on by humans. That won’t be the case for robots on the Moon.

          Therefore, there will be a requirement to have maintenance robots on the Moon. It is not asking for unobtanium to consider the idea of having a robot — not autonomous, just tele-operated from Earth— with sensors and end-effectors appropriate for maintenance work.

          Would it be nice to have humans there to do the maintenance work? Sure. But that might cost 10x-100x as much.

          • Robert Clark says:

            With advanced robots such as Robonaut with human-like finger dexterity and with a short lag time much of the repairs could be done without the humans being actually on the lunar surface. However, my understanding of what Spudis plans is that there should also be a human presence on the Moon. I’m optimistic this can be done in the near term with the advent of the SLS and the Falcon Heavy.

            Bob Clark
            http://exoscientist.blogspot.com

      • DougSpace says:

        My perspective on the issue of humans vs robots is two-fold. First, I’m not sure it makes a hill of beans difference in the final analysis. If we use the same landers for cargo and for crew (something I think we should do in the first operations after prospecting) then there won’t be that much of a time-lag between the two. There will be humans on the Moon and their primary job will be fixing telerobots (and building the bulky metal parts for new ones). Second, we can know whether or not robots can repair robots by the time we need to. If we can develop and get them working in a simulated environment then there’s a decent chance they will work on the Moon. For example, if on Earth we can get a dexterous telerobot to pop off the arm of a fellow telerobot and replace it with a spare arm, then perhaps it will work on the Moon. If we are unable to get that to work on Earth, then we just keep sending replacement pieces for the few years until the landers are safe enough to send humans who then repair and get the entire robotic workforce working.

    • Heinrich Monroe says:

      We don’t do this on the Earth not because “humans have value”, but because humans on the Earth are dirt cheap. Humans on the Moon are not.

      L2 is too far from the lunar surface to enable low cost landings?? Huh? L2 is 17% farther from the Moon than the Earth. There is little propulsive cost in descending to the surface from there, and one can actually easily access any site on the surface (unlike in low lunar orbit, where a plane-change might be required.

      • It is three days from L2 to the Moon. This means that you have to have a much more capable lander.

        From lunar orbit all you need is an open cockpit lander for a minimal capability as all you need to do is land people….

        • Vladislaw says:

          couldn’t you still do that? Using a lunar based vehicle, meet the L2 vehicle in lunar orbit transfer passengers and undock, the tug goes back to L2 the lunar cockpit lander returns to the moon.

        • Heinrich Monroe says:

          No, I believe it’s one day. Where do you get three?

          • Hop David says:

            Given an elliptical orbit with a 0 km altitude perilune and 63500 km apolune, orbital period is about 6.4 days. A Hohmann trip would be half this ellipse. Wingo’s 3 days sounds about right to me.

            A Hohmann from 0 km perilune to 300 km apolune is about an hour.

            LLO speed is about 1.6 km/s. A 90 plane change from an equatorial LLO to a polar LLO would cost about 2.3 km/s. In terms of delta v, Plane change expense at EML2 is practically zero. Accessing a polar LLO from EML2 would save a big plane change expense.

    • Hop David says:

      As Ron says there’s BP using ROVs. Also Rio Tinto. There are several markets driving improvements in telerobots and telepresence. Even the entertainment industry. I talk about these at http://hopsblog-hop.blogspot.com/2012/02/puppets-telerobots-and-james-cameron.html

      I’m not sure that cutting light lag latency from ~3 seconds to ~.5 seconds is worth a hab at L2, though. And a halo orbit about L2 will only enjoy line of sight with polar cold traps for only a fraction of the time.

      I’d much rather see a human base on the surface of the moon near a cold trap. Then light lag latency to teleoperated devices would be virtually zero seconds.

      From EML2 there’s not a large delta V penalty for high latitude destinations such as the polar cold traps. Using a lunar assist, EML2 can be reached from LEO with 3.2 km/s. And being distant from the earth and moon, it’s a good thermal environment to store liquid oxygen and hydrogen.

      While I see EML2 as a good place for propellant depots, this proposal for a manned hab at that location has me scratching my head.

  5. Paul:
    I have to agree that this would be sending NASA on a “Mission to Nowhere” as long as it is not a logical and necessary component of a coherent long-term plan. Spending NASA’s limited billions to keep a handfull of robot drivers alive at L2 makes no sense.
    Nelson

  6. Robert says:

    I think L1 would be better. It is closer to Earth. L2 should be used for space telescopes, and for search for alien communications.

    • In terms of delta V, EML2 is better. There’s an 8 day route from LEO using a lunar assist that gets you to EML2 for around 3.2 km/s. For EML1 there’s a 3 day route that takes about 3.8 km/s/

      EML2 is a better thermal environment for storing cryogenic propellant. It’s slightly farther from the moon than EML1 and substantially farther from earth. Moreover, from EML2 these two heat sources (earth and moon) are in the same region of the sky and so can be blocked with a single Multi Layer Insulation (MLI) shade.

      • Heinrich Monroe says:

        The propulsive advantage of L2 over L1 is actually not quite correct. For a simple Hohmann transfer it is, and most of the work has concentrated on such trajectories. But if you include lunar gravity assist trajectories, L1 and L2 become more similarly accessible.

        The thermal environment argument is silly. The MLI shade is going to block the Sun, not the Moon or the Earth. You can’t keep them all in one direction, and so when they’re not, you’re going to be illuminated by Earth and Moon. They are actually pretty far away, so the thermal effect is quite small compared with the leakage from the Sun.

  7. John K. Strickland says:

    Placing a crew at an L2 station would divert funding away from developing the re-usable spacecraft – both robotic and crew-carrying, and the fuel storage facility to refuel them, that would make a station at L1 or L2 truly useful. This also implies that any robots being supervised on the lunar surface would have been placed there by expendable landers. Without re-usable lunar landers, development of fuel production on the lunar surface will be vastly more expensive and much slower. A crew habitat at L2 is just one component of what should be an integrated transportation system. Without lunar fuel available at L1 or L2, the flexible path will be a path to nowhere.

  8. Dr. Manhattan says:

    There are more uses for L2 than a permanently manned base located there. Maybe NASA is a little smarter than you all give it credit for.

  9. gbaikie says:

    “My sense is that this mission is a hammer looking for a nail. ”

    Yes, it seems to be.
    Perhaps L-2 would good place for depot. But the issue seems to be that NASA needs to explore lunar polar regions to establish whether there is minable lunar and try to find where mining water could be most profitable.
    If NASA needs to send robots, it seems rather unnecessary to have a manned station in L-2. Of course in terms of delta-v there little difference between any of the L-points, and it seems if in L-2, one travel to L-1 and then swing around travel back to L-2.

    But let’s suppose that idea is just to have fuel depot in L-2. One could use the depot for robotic mission the lunar surface.
    A manned vehicle at L-2 could also be same a vehicle that sends people to Mars, but that is just later in time line.
    So you start with a fuel depot. The fuel depot can for a number of purposes, and one doesn’t need “The Fuel Depot”, just start with a fuel depot. No one had fuel depot before, probably some thing need to be worked out. A requirement should be that can operated robotically. So one should get to point that docking to it is completely routine, rather than some nail biting adventure.

    So, start with working prototype, and learn stuff, and then build better fuel depots. Think about a whole system refueling everything in Cislunar space. Make telescopes that one can dock with and refuel [even if refueled is cryogenic helium to keep it cold]. Work with satellite makers so birds in GEO can refueled. Consider the possiblity of dragging dead GEO satellites from the graveyard, to used for scrap- NASA should look at helping to start new markets in space [not running these operations but doing stuff that may encourage these markets to begin.

    Also be good to have fuel depot on lunar surface, perhaps that isn’t something that need much in terms technological development, perhaps it could involve some private or public entity. But it seems we might need more lunar exploration before doing something like that.

    • Dr. Manhattan says:

      Or, it’s a fuel depot with engines, shielding, supplies and other exploration vehicle necessities. And it’s only manned when it’s about to go on a long trip and back again to L2. A separate small vehicle shuttles the crew between Earth and it at L2. It’s not a base. It’s reusable space exploration hardware waiting for the next long trip.

  10. DougSpace says:

    Ken, I would also add that there is the issue of sustainability. Mars is not a good initial place for economic productivity. NASA would likely have to spend a lot initially and then continue to spend for an indefinite period as a settlement is established. In contrast, lunar development can start and continue with some telerobotic operations along side people and has the potential for reducing propellant costs for NASA and serve an orbital servicing market. Lunar resources (especially propellant and shielding) can reduce the costs and risks for a Mars mission while giving us experience which could help with later Martian settlement.

  11. Any manned facility located at one of the Earth-Moon Lagrange points (L1, L2, L4, and L5) is going to need mass shielding in order to protect astronauts from cosmic radiation, micrometeorites (water ice protection), and solar events. And the cheapest place to get such mass shielding would be from the lunar poles.

    If NASA is really serious about sending humans to Mars in the 2030s then they have to get serious about exploiting lunar water resources for mass shielding and fueling interplanetary vehicles in order to achieve that goal as quickly and economically as possible.

    NASA’s primary focus in the 2020s should, therefore, be on producing as much lunar water as possible at the lunar poles and exporting as much water as possible to the Lagrange points for storage.

    My only (minor) criticism of your architecture Dr. Spudis is that it should be much more aggressive in its water production capacity.

    You and Mr. Lavoie suggest an architecture that only produces up to 150 tonnes of water on the lunar surface annually(~410 kilograms per day). I think the lunar architecture has to produce at least 1000 tonnes of water annually (nearly three tonnes per day) in order for such a facility to be useful for appropriately mass shielding habitats located at the Lagrange points and for mass shielding and fueling manned interplanetary vehicles headed for Mars.

    I really don’t think NASA can produce too much lunar water since water is a treasured commodity that will always be of value (mass shielding, fuel, air, drinking, washing, growing food, etc.) in extraterrestrial environments.

    Marcel F. Williams

    • Paul Spudis says:

      Marcel,

      My only (minor) criticism of your architecture Dr. Spudis is that it should be much more aggressive in its water production capacity.

      Two points in response. First, we deliberately laid out a water production level that will support a permanent presence on the Moon. We limited our goals to this so as to define a program scope that we could cost. Second, by using small, incremental pieces, our architecture is completely scalable. If more water is desired, we can easily add additional elements to increase the production levels.

      Thanks for coming by and for your thoughtful (as usual) comments.

      • “Thanks for coming by and for your thoughtful (as usual) comments.”

        Thanks! I’m just grateful that a prominent lunar scientist has created a blog on a subject that I believe is so critical to America’s and to the world’s future.

        I have a question about your reusable lunar landing vehicles. I assume that your lunar shuttles and water tankers would utilize restartable engines like the RL-10. But how many times can an RL-10 engine be reliably restarted before it would have to be either replaced or refurbished?

        How many times those engines can be utilized would seem to be a critical component as to how affordable your lunar architecture would be.

        Marcel F. Williams

        • Paul Spudis says:

          I assume that your lunar shuttles and water tankers would utilize restartable engines like the RL-10. But how many times can an RL-10 engine be reliably restarted before it would have to be either replaced or refurbished?

          How many times those engines can be utilized would seem to be a critical component as to how affordable your lunar architecture would be.

          We don’t know the operational lifetime of such an engine, but you are correct, it is a design consideration. In our architecture paper, we make the point that the capability to change out engines on the Moon is essential. Eventually, we would want to install some kind of shop facility at the lunar outpost to be able to strip them down and refurbish them.

  12. DougSpace says:

    > The first is that the idea for fully robotic operations on the surface is a bridge too far.

    There will be a natural division of duties. Teleoperated robots are good for some things but for others, you need humans. Setting up solar panels? If designed well, either telerobotically or even automatically. A hauler taking icy regolith to a solar steamer can probably be done telerobotically. Excavating? Probably could be done telerobotically. Pulling a stuck robot off a rock? Still probably telerobotically. Repairing a robot? Probably best done indoors by an astronaut. Etc. My thinking is that we send some initial telerobotic equipment until the landers have enough of a track record that we can then safely send humans. If some of the earlier telerobots break down. They may have to wait for the humans before they can be repaired and put back into service. Lost time but not lost equipment.

  13. Karl Hallowell says:

    Joseph Louis Lagrange was firstly a mathematician. His considerable work in astronomy is all on the theoretical side (such as figuring out the model of the three body gravitation problem above). Astronomy contains a number of remarkable problems and many mathematical tools have been developed over the centuries, since Newton, to explain astronomical observations and dynamics.

    Lagrange was a key figure in transforming mathematical physics from the rudimentary calculus of Newton and Liebnitz to the sophisticated math and models we have today. A lot of the tools and notation we use today came from his era (such as differential equations and calculus of variations).

  14. Ron says:

    I agree with Paul Spudis’ article in general. Paul has laid out in many previous papers, posts, etc. why developing cis-lunar space is important and I heartily agree that developing cis-lunar space is important for humanity’s future as a spacefaring civilization.

    But overall national commitment to that goal is at best wishy-washy, with VSE casually abandoned and no great upswell of public anger to reinstate it. So we get studies as to an L2 gateway using ISS and SLS components. Maybe good, maybe bad, probably make-work for existing components.

    It will likely never get built. But maybe there will be a lot of studies…

  15. Joe says:

    Hi Paul,

    First of all, congratulations on the new website.

    About the usefulness of an L2 Station (as opposed to an LLO location) to a program aimed at using lunar resources to support the development of Cis-Lunar Space, it would seem to me to be (primarily at least) a matter of orbital mechanics.

    - What is the total Delta-V to move from the lunar surface to L2 to the desired locations in Cis-Lunar Space?
    - What is the total Delta-V to move from the lunar surface to LLO to the desired locations in Cis-Lunar Space?

    I understand the basic principles, but when it comes to detailed calculations I know about enough to be dangerous.

    Can anybody fill in some details on the two questions above?

    • Paul Spudis says:

      Hi Joe,

      Thanks and welcome!

      - What is the total Delta-V to move from the lunar surface to L2 to the desired locations in Cis-Lunar Space?
      - What is the total Delta-V to move from the lunar surface to LLO to the desired locations in Cis-Lunar Space?

      Delta-v from the lunar surface to the L-1 or L-2 point is essentially lunar escape velocity, about 2380 m/s. Delta-v from the lunar surface to to low (100 km) lunar orbit is about 1680 m/s.

      Have a look at this paper by Wendell Mendell and Steve Hoffman, which compares the delta-v requirements for staging localities in cislunar space. Of course, total delta-v is not the only consideration in selecting a staging location; other operational factors (windows, abort possibilities, transit times) must be considered as well.

      • gbaikie says:

        “Delta-v from the lunar surface to the L-1 or L-2 point is essentially lunar escape velocity, about 2380 m/s. Delta-v from the lunar surface to to low (100 km) lunar orbit is about 1680 m/s.”

        And delta-v from earth is lower [can be lowest] to L-points. A depot is where stuff is stored [not necessarily for a long time]. One could take rocket fuel from a depot, and bring it to LLO and provide fuel or boost to the L point or any other location. So with depot in L-2, one leave the moon with enough delta-v to get to LLO, have depot send tanker to LLO, which allows lunar vehicle more delta-v to go another destination.

  16. GCecil says:

    Longer term, isn’t EML2 an end point of a lunar beanstalk (counter-weight a bit farther out)? And current materials are probably up to the task.

  17. Doug says:

    I don’t see it mentioned here that one other key task being discussed for this conceptual outpost is human retrieval and “cleaning” of Mars sample return robotic spacecraft, thus making astronauts a flexible and smart assistant in “breaking the chain” of possible Mars contamination, in the context of planetary protection and reliable landing systems. Your thoughts?

    • Paul Spudis says:

      Doug,

      one other key task being discussed for this conceptual outpost is human retrieval and “cleaning” of Mars sample return robotic spacecraft

      First, there is no Mars sample return mission. Second, assuming that one should eventually fly, there’s no reason you could not “clean” such a sample at an existing LEO space station — or anywhere else in cislunar space, even on the lunar surface. There’s no advantage to being at EM L-2 for that task.

      • Doug says:

        Sorry, Paul, I see your reply as a bit of a knee-jerk response.

        A Mars sample return mission is at least as close in time as the prospects for any human outpost beyond ISS. It is the stated #1 priority of the 2011 planetary science decadal survey, as you well know. Why not connect HEO to this visible support, even if it may fade with time?

        A station at L-2 significantly reduces the chance of any premature Earth re-entry, I would think. And why in the world would you even reference the complexity of landing on the lunar surface (not to mention “contaminating” its surface with Martian dust)?

        • Paul Spudis says:

          Why not connect HEO to this visible support, even if it may fade with time?

          Because I do not see the two efforts as related. For the sample return, it is an unnecessary complication. For the human mission, it is an irrelevancy.

          A station at L-2 significantly reduces the chance of any premature Earth re-entry, I would think.

          Not really. An out-of-control returning Mars sample vehicle would simply burn up in the atmosphere of Earth, about as sterilizing an effect as I can imagine. If it’s not out of control, then it would simply insert into Earth orbit and await retrieval.

          And why in the world would you even reference the complexity of landing on the lunar surface (not to mention “contaminating” its surface with Martian dust)?

          Because in the past, such has been one proposed use of a lunar research laboratory. I’m not advocating it.

  18. Joe says:

    “Deep-sea ROVs can be pulled up to the surface to be worked on by humans. That won’t be the case for robots on the Moon.”

    No it certainly not. Nor that will be the case for Line Replaceable Units (LRUs), the modularized components that the ROVs remove/replace. They are repaired by people living on surface facilities less than a mile from the deep sea facilities in question.

    “Therefore, there will be a requirement to have maintenance robots on the Moon. It is not asking for unobtanium to consider the idea of having a robot — not autonomous, just tele-operated from Earth— with sensors and end-effectors appropriate for maintenance work.”

    But that brings up an interesting question. Are you:
    - Interested in developing the most efficient method of utilizing lunar resources to support the development of cis-lunar space. Or:
    - Are you more interested in using the utilizing lunar resources to support the development of cis-lunar space as a talking point for seeking more money for robotics development?

    If it is the latter, I think you are fighting an unneeded battle. If the development of lunar resources is to proceed, more development of robotics capability will be required (along with more development of human spaceflight capability).

    So what exactly is the argument here?

    • Ron says:

      #1, I’m interested in extending the sphere of economic activity into cis-lunar space.

      UAVs, deep-sea/oil-industry, assembly-line robots, surgical robots, nuclear reactor inspection/maintenance; pigs inside of oil pipelines; hobby robotics, roomba.

      All these things now exist. Robotics will continue to grow and accelerate and will do so independently of any NASA funding. Moore’s Law will drive it’s growth.

      So any cis-lunar development plans — plans that span a decade or more — better put robotics front and center. The Spudis Lavoie plan uses robotics in the early stages and does not rely on SLS/Constellation components for that initial robotic development. I say, “Let’s get going on that aspect now, using existing launchers”.

      No need to wait for SLS.

  19. Pingback: Are you excited about NASA’s L-2 destination? | Alkaon Network

  20. bobpixel says:

    It appears the illustration is for the Earth-Sun L2, so would that be shielded by the magnetotail? It certainly would not be hovering above the dark side of the moon.

    • Paul Spudis says:

      No, that illustration is from Wikipedia and it is meant to show lines of gravitational attraction, not magnetic field lines. However, the L1, L2 and the Moon itself all pass through the Earth’s magnetotail once per month, “downwind” of the Sun.

      • bobpixel says:

        Sorry, I see I need to unpack my comment a bit and decrease the signal to noise.
        1) The picture, showing gravitational attraction lines, is for the sun-earth L points. The L2 in the picture is not the L2 you are discussing, correct?
        2) The L2 in the illustration is within Earth’s magnetotail. Although an outpost in this location is not proposed by anyone currently, wouldn’t this be a place that would be shielded from energetic particles?

        • Paul Spudis says:

          1) The picture, showing gravitational attraction lines, is for the sun-earth L points. The L2 in the picture is not the L2 you are discussing, correct?

          Correct. I just wanted to use a picture that showed the L-points in relation to a body and its orbiting companion. In retrospect, I should have not used this one, but to be honest, I did not notice that it was an image of the Sun-Earth system — I overlooked the presence of the small Moon around the Earth.

          2) The L2 in the illustration is within Earth’s magnetotail. Although an outpost in this location is not proposed by anyone currently, wouldn’t this be a place that would be shielded from energetic particles?

          In reference to Sun-Earth L2, that’s about 1.5 million kilometers from Earth and although it is aligned with Earth’s geotail, it is not protected by it:

          A spacecraft in a L2 halo orbit can expect to encounter all regions of the magnetotail, as well as the free solar wind. This is due to variations in the magnetotail size and direction, which are determined by fluctuations of the solar wind speed, direction, pressure, and density. During its immersion in the magnetotail, the spacecraft will be afforded some protection from energetic particles emitted by the Sun, e.g., by solar proton events, but it may be subjected to bombardment by energetic particles such as heavy ions and relativistic electrons during magnetospheric storms and substorms.

          See this presentation for detailed information about the environment of the Earth-Sun L2 location.

        • The sun-earth L1 and L2 points are about 1.5 million kilometers from earth which is only 1% of an astronomical unit. The earth’s diameter is about 1% that of the sun’s. With a scale drawing, the earth as well as L1 and L2 would be 3 microscopic flyspecks almost right on top of each other.

          For the earth-moon system, L1 and L2 are about 1/6 of a lunar distance from the moon. The moon is about 1/4 of earth’s diameter.

          So far as scale goes, the graphic looks like an earth-moon system. If it’s supposed to be a portrayal of the sun-earth system, the proportions are way off.

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  24. Joe says:

    Paul,

    Thanks for the link.

    Sorry for being so long in responding, but I thought I would break the internet protocol and actually try to read and comprehend the paper before commenting on it.

    The paper does not appear to have a date associated with it, but from its description of the state of development of (what became) the ISS, I would guess it was written in the 1992-1993 time frame.

    Since they state that for the purposes of their analysis “We assume that all materials destined for the space station, regardless of its location, must start from the surface of the Earth”, they do not go into the Lunar surface to L1/L2/LLO and then to other cislunar space destinations. They do however make a good analysis of L1 to either earth or lunar destinations (including launch windows – and I see what you mean by that now). This analysis seems s to make a better case for L1 rather than L2.

    Additionally I noted this comment “The far side of the Moon has been set aside by international agreement as a radio-quiet zone for scientific research since it is the only environment in the solar system completely shielded from terrestrial electronic emissions. Therefore, the Lagrangian point L2, on the far side of the Moon from the Earth, is unsuitable for a space station even though the location is probably better for astronomy.” Is that “international agreement” till in effect? If so that would seem to be a problem for an L2 station one of whose primary purposes would be using tele-robotics to control robots on the lunar far side.

    Am I missing something?

    Joe

    • Paul Spudis says:

      Joe,

      Therefore, the Lagrangian point L2, on the far side of the Moon from the Earth, is unsuitable for a space station even though the location is probably better for astronomy.” Is that “international agreement” till in effect? If so that would seem to be a problem for an L2 station one of whose primary purposes would be using tele-robotics to control robots on the lunar far side.

      There is no “international agreement” to keep away from EM L-2. In any event, a mission there does not permanently contaminate the radio-quiet state of the far side. No one is calling for permanent occupancy there and while people are there, radio equipment operates on frequencies unused by the radio astronomers and in any event, it has an “off button.”

  25. Joe says:

    Paul,

    Check, I had a feeling that is what you were going to say; just wanted to make sure.

    That still leaves the lunar surface to LLO/L1/L2 to other cislunar space Delta Vs as an open issue. I am going to look around and see what I can find. Cannot promise I will find anything, but if I do I will let you know.

    Joe

  26. DougSpace says:

    Political administrations don’t want to change directions within their term because they open themselves up to charges of having made a previous bad decision. So, there is a fair probability that they will continue to a manned L2 station as described because it is along their Path to an asteroid, Phobos, and Mars. Sustainable, cost-effective capability was not part of their plan and is incompatible with their Path and so they won’t develop such capabilities for the duration of the Obama terms.

    So, what needs to be done now to effect a significant change in course? What can we do at a practical level? Blogs and comments have their place. But what action on our part should we do?

    • Paul Spudis says:

      there is a fair probability that they will continue to a manned L2 station as described because it is along their Path to an asteroid, Phobos, and Mars.

      Your assumption is that these are goals that they actually intend to pursue. I am not convinced of that.

      None of us have the power to change policy, but by stating and re-stating the logical path forward, we can eventually make ourselves heard. Spread the word.

      • DougSpace says:

        Spread the word

        Certainly. But I am wondering if there is more that could be done. Although we may not be in a position to directly change policy, perhaps there might be some effective means of indirectly affecting policy (i.e. influencing the policy makers more effectively). For example, it now seems that Romney might actually have a chance. Yet it is not obvious to me that his choice of NASA administrator will support a cis-lunar next policy. Perhaps we could do something now to increase that probability. Also, just how united and organized are cis-lunar next supporters? Certainly nowhere nearly as much as Mars first supporters.

        Your assumption is that these are goals that they actually intend to pursue. I am not convinced of that.

        Since we’re dealing with motivations, none of us can be certain. My guess is that Obama doesn’t want to tangle with space state senators. This is why his administration reversed direction and went along with SLS. I also guess that he doesn’t want to be known as the one who killed BEO HSF. So, he’ll just move SLS forward until the end of his second term and then hand it off to someone else. He’s not going to expend political capital on something that is small and not a priority.

        I’m guessing that it will be close to impossible to get him to make the change to a strategy of a large cis-lunar next program. In such a situation, I think that the best we could do is to advance development of cis-lunar hardware with only about a half billion per year. For example, ULA and Masten’s cryogenic lunar lander could be developed for that amount if funded in an SAA manner. Just an idea.

        • Paul Spudis says:

          Doug,

          just how united and organized are cis-lunar next supporters? Certainly nowhere nearly as much as Mars first supporters.

          True enough, but there’s a big difference between the two pathways: Cislunar Next is affordable and technically achievable. Mars First isn’t.

  27. Matt says:

    I’m curious if an analysis has been done regarding the power system requirements? Specifically considering how often/long the station would be in the moon’s shadow and making solar arrays useless. Or is this even an issue given the minimal amount of time in shadow and the capacity of other power sources?

    • Paul Spudis says:

      how often/long the station would be in the moon’s shadow and making solar arrays useless

      I’m sure this is being looked at, but my understanding is that the Orion will not actually be stationed at the L-2 point, but will be in a “halo” orbit around the L-2 point (if they were AT L-2, communications with the Earth would not be possible). I suspect that this halo orbit will keep the spacecraft illuminated except under rare circumstances.

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