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Bringing an Asteroid to Lunar Orbit

Long before Planetary Resources was a gleam in the eye of its founders, John Lewis (University of Arizona) wrote a book that put asteroid mining into the public consciousness. Mining the Sky: Untold Riches from the Asteroids, Comets and Planets (Perseus Books, 1996) contains no shortage of wonders, as in the well publicized idea that a single one-kilometer asteroid could produce enough gold and silver to equal world production for a century. David Brin writes about this on George Dvorsky’s Sentient Developments site, noting that while that would produce a collapse in gold and silver prices, it would also produce incalculable benefits in terms of raw materials production that could change the economic paradigm entirely.

Lewis is a natural fit with Planetary Resources, the highly buzzed-about startup that plans to make asteroid mining a reality, and it’s no surprise to see that he serves as one of its advisors. But remembering Mining the Sky, I was startled to discover that the idea of using asteroid resources goes all the way back to Konstantin Tsiolkovskii, who wrote about it in The Exploration of Cosmic Space by Means of Reaction Motors in 1903 — it was in this same work that the Russian rocket scientist and visionary first proposed multistage rockets using liquid hydrogen and liquid oxygen for space exploration. It seems fitting that there is an asteroid with a Tsiolkovskii connection, the object 1590 Tsiolkovskaja being named for his wife.

Image: An artist’s concept of a fragmented asteroid laden with resources. Image: NASA/JPL-Caltech/Handout , Reuters files.

A New Study on Asteroid Retrieval

Caltech’s Keck Institute for Space Studies has examined asteroid possibilities in the just released Asteroid Retrieval Feasibility Study, whose April 12 appearance was timed to perfection by the powers behind Planetary Resources. What the Keck study is interested in is returning an object not to low-Earth orbit but a high lunar orbit, allowing the project to be conducted with far more relaxed propulsion constraints than would be applied deep in Earth’s gravity well. A corollary to this is the fact that larger asteroids can be captured. The study authors settled on an asteroid 7 meters in diameter with a mass on the order of 500,000 kg. This was a 6-month study enlisting a wide range of space-minded talent (see the contributor list on p. 6 of the report).

The Keck report meshes with NASA’s current goals of sending a manned expedition to a near-Earth asteroid halfway into the next decade, though given the mutable nature of NASA’s funding, that’s the least of the reasons to make this happen. Even so, an asteroid retrieval has definite consequences for manned flight. What Keck has in mind is robotic, unmanned missions that culminate in a scout mission, also robotic, to enable detailed mission planning. The full retrieval mission is seen as a precursor to subsequent human missions to this and other NEAs. An NEA in high-lunar orbit then becomes an obvious and accessible target for astronaut visitation.

Again, no astronauts on the retrieval mission, which is robotic. But:

Taken together, these attributes of an ACR [Asteroid Capture and Return] mission would endow NASA (and its partners) with a new demonstrated capability in deep space that hasn’t been seen since Apollo. Once astronaut visits to the captured object begin, NASA would be putting human explorers in contact with an ancient, scientifically intriguing, and economically valuable body beyond the Moon, an achievement that would compare very favorably to any attempts to repeat the Apollo lunar landings.

Reasons for Snatching an Asteroid

Why retrieve an asteroid in the first place? Here’s a distilled rational from the executive summary, one that begins with a focus on the effect of spurring manned spaceflight:

It would provide a high-value target in cislunar space that would require a human presence to take full advantage of this new resource. It would offer an affordable path to providing operational experience with astronauts working around and with a NEA that could feed forward to much longer duration human missions to larger NEAs in deep space. It would provide an affordable path to meeting the nation’s goal of sending astronauts to a near-Earth object by 2025. It represents a new synergy between robotic and human missions in which robotic spacecraft retrieve significant quantities of valuable resources for exploitation by astronaut crews to enable human exploration farther out into the solar system.

All true, of course, but it’s only after this spadework has been done that the report turns to what has electrified the space community about Planetary Resources and its own asteroid plans, and it’s nothing like an Apollo-style effort to get people to particular destinations. The goal is broader and much longer-lasting. Once we have an asteroid, either by traveling to it or by inducing it into a lunar orbit for further exploitation, we have the ability to extract materials from it. All this gets into the real infrastructure-building components of asteroid mining:

…water or other material extracted from a returned, volatile-rich NEA could be used to provide affordable shielding against galactic cosmic rays. The extracted water could also be used for propellant to transport the shielded habitat. These activities could jump-start an entire in situ resource utilization (ISRU) industry. The availability of a multi-hundred-ton asteroid in lunar orbit could also stimulate the expansion of international cooperation in space as agencies work together to determine how to sample and process this raw material. The capture, transportation, examination, and dissection of an entire NEA would provide valuable information for planetary defense activities that may someday have to deflect a much larger near-Earth object. Finally, placing a NEA in lunar orbit would provide a new capability for human exploration not seen since Apollo.

Aspects of the Retrieval Mission

Two aspects of the asteroid retrieval campaign are immediately obvious. Before retrieving anything, we need an extended effort to identify objects that fit the bill physically and offer up orbital parameters that would make them good candidates for the return mission. We also need a transportation method, and here what the Keck study advocates is a ~40-kW solar electric propulsion system with a specific impulse of 3,000 seconds. It’s interesting to see by the report’s figures that, given a single launch to low-Earth orbit aboard an Atlas V-class vehicle, the ultimate plan would be to retrieve 28 times the mass launched to LEO and bring it into high lunar orbit.

The mission plan is fascinating and fodder for science fiction writers. The solar electric propulsion system would be used to spiral the vehicle into high-Earth orbit and a lunar gravity assist would then put the vehicle on a trajectory to the NEA. The report allocates 90 days for studying the NEA and capturing and ‘de-tumbling’ the asteroid, transporting it back to the Earth-Moon system for a second lunar gravity assist that would be used to capture it. Transfer to a stable high lunar orbit would take place about 4.5 months after the first gravity assist.

All of this presupposes mechanisms for stabilizing and moving the asteroid, which the report says could be done with a high-strength bag assembly, deployable and inflatable arms and cinching cables, the bag being 10 meters by 15-meters in diameter looking like this:

Image: The capture mechanism deployed and in operation. Credit: Rick Sternbach/KISS.

But before any such mission can be flown, we also need improved ways of studying potential targets. Planetary Resources has the idea of launching inexpensive telescopes that could sample a wide variety of NEAs, while the Keck report notes the value of the solar electric propulsion system for sending multiple-target robotic precursors that would precede any human missions. As opposed to the upcoming (2016) OSIRIS REx mission, which will return 60 grams of surface material, a robotic precursor like this would be used to bring back large boulders and regolith samples from any human targets prior to sending manned crews there.

The report’s focus on resource acquisition in space is heartening. Check this:

The asteroidal material delivered to cislunar space could be used to provide radiation shielding for future deep space missions and also validate in-situ resource utilization (ISRU) processes (water extraction, propellant production, etc.) that could significantly reduce the mass and propulsion requirements for a human mission. The introduction of ISRU into human mission designs could be extremely beneficial, but until the processing and storage techniques have been sufficiently tested in a relevant environment it is difficult to baseline the use of ISRU into the human mission architecture. Bringing back large quantities of asteroid materials to an advantageous location would make validation of an ISRU system significantly easier.

Well said — the whole notion of in situ acquisition and utilization is critical as we look toward building a true human future in space. Part of the Planetary Resources plan is to extract water from asteroids not only for human needs (much better than launching from deep within the gravity well) but also for the creation of rocket fuel. The report’s emphasis on the need to bring back asteroid materials to study the prospects in detail is wise, because we need to learn how effectively we can go about extracting these materials and turning them around for space use.

But there are other areas where moving into the asteroids, first with robots and then human crews, makes abundant sense. Tomorrow I want to examine asteroid deflection as one major area that will benefit from these activities, and we’ll also look at the ramifications of all those telescopes Planetary Resources plans to put into space. We may only be scratching the surface of how useful our future ability to move tools and crews to asteroids — or to move asteroids themselves — may turn out to be in building the next phase of human civilization.


Comments on this entry are closed.

  • Marcel F. Williams May 2, 2012, 13:20

    Technically, this would be a meteoroid mission. Meteoroids are rocks in space that are less than 10 meters in diameter. Under their scenario, it would take several years to place a 500 t0nne plus meteoroid into lunar orbit.

    However, a large reusable IVF (Integrated Vehicle Fluids) LOX/LH2 based lunar tanker about the size of the SLS CPS (Cryogenic Propulsion Stage) and deployed by the SLS and refueled using polar lunar water resources could easily lift more 500 tonnes of material (water or regolith) from the Moon to the Lagrange points after 5 round trips (10 starts of its RL-10 engines) in less than a year.

    A permanent outpost at one of the lunar poles would probably already be producing water and fuel for astronauts on the lunar surface and for their reusable lunar shuttles.

    Marcel F. Williams

  • Michael May 2, 2012, 16:11

    Slowing and stopping the rock’s rotation can be as simple as exposing it to a magnetic field (most rocks if not all will contain traces of iron or magnet materials) then using thrusters on the craft to cancel the momentum. A 500 ton rock rotating at a few rpm will have energy in the low megajoules range.

  • bill May 2, 2012, 16:35

    While I admit this sounds awful good, I can’t help but wonder just how practical it will be to achieve in reality, my reason for saying that is that an asteroid is an highly irregular object probably with a high variational density. While the science of dynamics is well-defined and in theory can handle any situation, in reality there could be a considerable problem being able to accurately define the trajectories to move the object into lunar orbit.

  • Steven Rappolee May 2, 2012, 17:20

    to prevent resource price collapse you meter the amount of that resource you sell every year, a “asteroid cartel” I will have to Google this to see if this term has been used before :)

  • Alex Tolley May 2, 2012, 18:47

    @Steven Rappolee
    Like the central banks’ gold holdings are a “cartel”? Control of the flow of a product shouldn’t an issue, especially as futures markets can be used to hedge prices and demand delivery of the underlying commodity on contract expiry.

    Joy’s point in the previous thread is more important. Is there a profitable business to be made, and are the returns worth the risks? While Joy is skeptical, I think it is pretty clear cheap water would be a huge economic benefit for the [as yet unborn] space tourism industry. The key is to determine if water extracted from asteroids or short period comets can be delivered at a price well below that of water lobbed into space on even the dumbest of boosters. I suspect the answer is yes, because water can be delivered very slowly, using the mass as the propellant (or possibly using a solar sail) making it potentially much easier and cheaper to deliver from space than from earth. I’m more sanguine about the prospects for bulk volatiles than I am for precious metals delivered back down a gravity well.

  • James May 2, 2012, 20:53

    Paul, can you interview someone from Planetary Resources, Inc from Centauri Dreams or let us have a life chat with them on the site?

  • Eniac May 3, 2012, 1:24

    500 tons is not much, and will not be worth the cost, I suspect. Unless the whole thing is pure ice, there will be a lot of dead weight carted around at high cost. The platinum in particular is at 5-20 ppm, so 99.98% of the mass moved would be tailings.

  • Laura May 3, 2012, 1:30

    Getting a rough dollar value of a pound of water extracted from an asteroid against water brought up from Earth is pretty straightforward. You’d have to price it “advantageously” below the cost to get a pound of payload to orbit – say a few thousand to ten thousand dollars per pound, depending on the launch vehicle. Then figure in the value added of breaking it down into LOX and LH2 and there’s your price. (Details are left to the reader.)

    If the cost of prospecting, retrieval to Moon orbit, extraction, and processing can come in below that several thousand dollar price per pound that the end product might be worth, you could have a business (if there’s enough continuous demand).

    I assume some serious calculations have been done on this, but to this casual observer it seems getting the costs down that level that could be a challenge. I do hope I’m wrong.

  • Securis May 3, 2012, 5:47

    Whenever i read something about mining in space the first science fiction story that comes to my mind is “Dead Space”. The horrors on the USG Ishimura are still haunting me.



  • A. A. Jackson May 3, 2012, 7:28

    I am somewhat dubious of the costs.
    These things are always underestimated.
    Off the top of my head I would guess the DDT&E at 4 billion, and that may be under running it.
    I don’t see how recurring costs can be as low .34 billion, but maybe.
    I am supposing they are thinking of very cheap ground control and mission planning?
    Man 2025!
    We are not talking about a tiny tiny infrastructure here.

    “Fifth, the public would clearly see the results from human exploration once astronauts begin the
    lengthy, challenging task of examining and “dissecting” a ~ 500 metric ton asteroid.”
    Not the public I would worry about it’s Congress.
    If even with international partners we are in cis-lunar space by 2020….
    I’ll be cow kicked!

  • torque_xtr May 3, 2012, 8:45

    It’s fascinating to see the asteroid mining topic finally gaining attention, and disappointing to see all the economical constraints for bringing an asteroid to lunar orbit, but here is a question: why doing the asteroid mining so carefully and not bringing them straight to Earth in most natural way?

    A 20m metal object generates the impact explosion on the scale of megatons, but without radioactive fallout, and does not disperse much after the impact. The Earth has plenty of remote desert locations to make such an impact safe, if the precise targeting is provided! So all the miners would have to do is to find a metal asteroid on the appropriate orbit, give it a calculated nudge, then wait several years, watch the fireworks (much more harmless than nuclear explosions of the same scale) and extract the resources with conventional equipment. With a gravitational maneuver in Mars’ field, the possible delta-v’s could be on the order of 100 m/s. If the electrical propulsion with the exhaust velosity of 200 km/s is used, then to move a 20m asteroid, several tens of tons of fuel would be needed, and since the tractor can fly to the target using the same fuel, the total cost is on the order of bringing the tractor, the fuel and the energy source to LEO. For the price of bringing ~50 tons to LEO, several tens of thousands tons of iron and nickel, and several tons of mixed platinum metals could be obtained here on earth in form of easily extractable concentrate. This doesn’t sound profitable with current prices, but may become more so as the prices for platinum metals increase and the costs of bringing cargo to LEO decrease… If the fuel for electrical propulsion is extracted from the Moon, and the tractor launching station is based there, then the total price possibly could be an order of magnitude lower!

    And compare that to delta-Vs on order of 1 km/s to stabilise NEOs on the lunar orbit and to costs of bringing many hundred tons of non-conventional mining equipment to the same orbit…

  • Paul Gilster May 3, 2012, 10:27

    James writes:

    Paul, can you interview someone from Planetary Resources, Inc from Centauri Dreams or let us have a life chat with them on the site?

    I’m on the case, James, and will hope to have an interview in the near future.

  • Wishful May 3, 2012, 15:34

    Capture an asteroid or maybe a few, use it a a nice new weapon. Launch it towards your target (Country, city) of choice and watch the colourful fireworks. What we would call “natural weapons”.

  • philw1776 May 3, 2012, 16:38

    Can’t help but think that Luna will have justification for getting really nervous with asteroids in lunar orbit.

  • Stan May 3, 2012, 17:37

    I expect in the future, when robotic systems become more autonomous, we will simply orbit with the asteroids, mine them any distance away in orbit, and then just transport the finished material to lunar orbit. Then asteroid sized won’t be a problem, nor will cost of moving it to lunar orbit.

  • Rob Henry May 3, 2012, 19:29

    I am sorry, but occasionally someone plants one of those ideas in your head that just won’t go when it really should – exactly analogous to an annoying but catchy tune.

    Eniac once pointed out, that the energy required to move objects around the solar system (at least those that are not locked in stable orbital resonances), has no minimum if we play pinball starting with much lower mass objects and cascade upwards to perturb ever higher mass objects. The problem of chaos is fixed by ever smaller (proportionately) adjustment mechanisms on each subsequent body. Will we ever be daring enough to add potentially Earth sterilising (if we get it wrong) icy moons to our double planet (which, as such, allows much higher capture potential and alleviates us of having to look at Pluto/Charon type systems).

    Will that be the real way that we one day boost our space economy to critical mass and ignite the next phase in our development?

  • Murgatroyd May 5, 2012, 5:03

    torque_xtr wrote:
    A 20m metal object generates the impact explosion on the scale of megatons, but without radioactive fallout, and does not disperse much after the impact. The Earth has plenty of remote desert locations to make such an impact safe, if the precise targeting is provided!

    Nature has performed this experiment countless times, yet you won’t find any 20-meter hunks of nickel-iron meteorite just lying around. Daniel Barringer had the same idea you had, but never found a main body to the 50-meter impactor that produced Meteor Crater. An impactor in that size range pretty much vaporizes.

    We do mine the ores that resulted from one impact event, the Sudbury Basin structure. But that bugger was 10 to 15 kilometers across and hit almost two billion years ago, creating a crater about 250 kilometers wide. Not an experiment we’d want to recreate in the modern era.

  • Murgatroyd May 5, 2012, 5:08

    An anal-retentive observation: I’m a little disappointed in Rick Sternbach, unless someone altered his artwork after he created it. Look at the illumination on the capture structure and on the asteroid. Now look at the shadow of the asteroid on the capture structure. Un-possible!

  • Eniac May 5, 2012, 21:48


    Look at the illumination on the capture structure and on the asteroid. Now look at the shadow of the asteroid on the capture structure. Un-possible!

    I cannot see the inconsistency you speak of. What specifically do you see wrong with the picture?

    Nature has performed this experiment countless times, yet you won’t find any 20-meter hunks of nickel-iron meteorite just lying around.

    Then again, NASA and the Russians have performed this experiment many times as well, in a more controlled fashion. With live human beings in many cases, who where able to walk away from their singed, but intact capsule.

  • ljk May 7, 2012, 10:20

    philw1776 said on May 3, 2012 at 16:38:

    “Can’t help but think that Luna will have justification for getting really nervous with asteroids in lunar orbit.”

    As I recall from the data that the ALSEPs recorded from the time they were placed on the Moon by the Apollo missions until their premature shutdown in 1977 to save money (a whole million dollars there – then again Carter and Mondale were never friends of space exploration, just ask Carl Sagan), our natural satellite gets lots of natural hits from space rocks.

    In addition to probably having to put a lunar base/colony under the surface, this might be an incentive to set up a Space Watch system in lunar orbit or perhaps at one of the more stable Legrange points. Mars gets hits by cosmic debris too, so this system may have to be standard around all the non-atmospheric worlds we colonize.

  • TAHempel May 14, 2012, 4:01

    Interesting ideas, really, but highly inefficient. Return the materials to the planet would have adverse effects on the economy. Returning only a very small portion to Earth would be much more economical. People would pay a (rightly-so) premium for “space gold”. The far more valuable scenario is to not return it to Earth at all. A manufacturing base should be created to create material and goods for the space-based endeavor.

    Current methods to do so are horribly expensive. Perhaps it is time to revisit the mode/method of the Orion Engine. We could create 4 large heavy payload rockets of such size as to jump-start space exploration/resource gathering. One ship for NEO as a space dock, one for a ship to travel back and forth from dock to dock located in lunar orbit, one ship for the space dock there, and the largest of these to be located on the surface of the moon itself. The amounts of titanium there should be more than sufficient to create the massive resource gathering ships that will eventually travel to the belt and beyond. The moon would also be a logical location for manufacturing and tourism. Recall that it was only a few short years ago that $9B USD was spent on a casino. Who and how much woukd be spent on the first casino on the moon? Who would pay to control the gaming interest on the transport ship between NEO and Lunar orbit?

    I think we do indeed need to review unmanned launches of orion engine craft…

  • David Claughton May 15, 2012, 9:51

    > Return the materials to the planet would have adverse effects on the economy

    That’s a very short-sighted viewpoint if you don’t mind me saying so. Yes it’s true that an asteroid containing large quantities of gold and platinum brought back to Earth would likely cause the gold and platinum markets to collapse in the first instance.

    However look beyond that and there are plenty of manufacturing processes which are currently either very expensive or completely unfeasible due to the rarity of certain metals on Earth. Some of these processes could potentially revolutionise industries and boost the economy in ways that more than make up for the initial drop in the precious metal markets.

    One example that springs to mind, is the idea that batteries in mobile phones, laptops and electric cars could be replaced by mass-produced fuel-cells. This is a potential development that is severely hampered by the current price of platinum. Similarly efficient solar panels require multiple different semi-conductor materials, for which the current market price of Gallium and Germanium is a problem.

  • Tom June 15, 2012, 22:09

    A lot of folks have some unusual ideas on the ‘economics’ of precious metals.
    250 megatons of gold will not necessarily ‘meltdown’ the commodity index value of this particular resource. Restocking Ft. Knox structures the trade.
    Space resource utilization isn’t going to be like the ‘silk roads’ or ’18th Century Merchant fleets’; rather it will be effective management of refining, manufacture and transport that will be the bulk of the work. More like automotive or aircraft manufacture doesn’t automatically make you a billionaire? Energy, volatiles and life support logistics are crucial components to ‘human in space’; think of the old children’s story of ‘king midas’….. his golden touch lead him to death of famine & thirst.
    There will be a market, but right now its the competition of lowering the cost of launching versus the costs of conventional mining. Space being desirable for the environmental non-impact of mining & construction.
    For now, its easier to do it here… if you have no problems getting the ‘jobsites’ & ‘quarries’? Considering the resource ‘exploitation’ that is cursing the developing world, Space offers an alternative route that might be more desirable.