Quoting from NASA warned plan to send humans to Mars may fail news article:

The Obama administration is opposed to another moon landing, saying such a mission would be too costly. It wants instead to focus on capturing an asteroid and placing it into the Moon's orbit for future exploration.

How useful is "placing an asteroid in lunar orbit"? What are implications as a function of research?

  • $\begingroup$ Regardless of how useful such a feat is to humanity, it's cost in comparison to an actual manned lunar expedition is increasingly exorbitant and defeats the purpose of roping in the budget. $\endgroup$ Jun 26, 2019 at 15:16

3 Answers 3


There are entities that hope to mine asteroids, Planetary Resources and Deep Space Industries.

The proposed Asteroid Retrieval Mission is based upon the Keck Report, a paper outlining how a small Near Earth Asteroid (NEA) could be parked in lunar orbit.

Co-authors of the Keck Report include

And a long list of other prominent scientists and engineers whose focus is near earth asteroids.

Many of the co-authors of the Keck Report are also on the staff of Planetary Resources or Deep Space Industries.

Developing a retrieval vehicle with powerful Solar Electric Propulsion (SEP) engines would be a big step towards making asteroid mining plausible. Robust SEP might also be helpful for ferrying massive payloads from earth orbit to lunar orbit, so the technology would also make establishing a lunar base more doable.

Why park an asteroid in lunar orbit? Why not mine it in its heliocentric orbit?

Early asteroid mining will be a process of trial and error. So establishing infra structure will require multiple trips. Trip times to an NEA would be months to a better part of a year. The most accessible asteroids with earth like orbits also have very rare launch windows, on the order of years and decades apart. Light lag latency to a NEA in heliocentric orbit can be 10s of minutes. Since signal strength falls with inverse square of distance.

Let's compare that to an asteroid in lunar orbit. Trips times are less than a week. Launch windows from a given low earth orbit occur each two weeks. Light lag latency is about 3 seconds. Telerobots at ~1 lunar distance can enjoy high bandwidth.

For these reasons lunar orbit is a much better place to develop the fledgling asteroid mining technology.

Placing an asteroid in lunar orbit would be very useful.

  • $\begingroup$ I think both you, the OP, and I fell into a trap here. Look at the quote again. It seems to me it isn't about placing an asteroid into an orbit around the Moon; it's about placing an asteroid into the Moon's orbit around the Earth. $\endgroup$
    – user
    Jun 6, 2014 at 19:16
  • $\begingroup$ The proposed Asteroid Redirect Mission would place an asteroid in orbit about the moon. $\endgroup$
    – HopDavid
    Jun 6, 2014 at 21:09
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    $\begingroup$ Actually the text of the Keck report says "Lunar orbit or possibly regions near the Earth-Moon Lagrange points," so you're both right - both "in orbit around the Moon" and "in the Moon's orbit around Earth" are options. (The reason in both cases is that if something goes wrong it will crash into the Moon and not Earth.) $\endgroup$
    – N. Virgo
    Jun 9, 2014 at 1:17

The Asteroid Retrieval Mission (ARM) is most fundamentally critizied out of disappointment because that's what's left of the envisioned great crewed space mission of our lifetime. Instead of building a permanent lunar base or going to Mars or to a real asteroid, we'll just make a trip back to lunar orbit. That does not inspire. Russian, Chinese and even private entities might do that before ARM completes. This priority will make NASA lose its outstanding place in the imagination of human kind and turn it into an outcompeted second rate space flight organization with recruitment problems.

Even as an asteroid mining technology demonstration it is flawed. Such tiny meteoroids are out of the question when it comes to mining. And Solar Electric Propulsion (SEP) cannot be used to move real asteroids with thousands times the mass.

The science of it is also questionable. Asteroids are likely very diverse. They may have formed in different parts of the solar system at different times in different ways. Some primordial, others more recent impact fragments. A close look at a sample of one will not say much at all about the typical asteroid. Especially since meteoroid sized objects very well may be systematically different from real asteroids. Maybe they are mostly rubble piles which separate easily.

The meteoroid size and propulsion technology is also irrelevant for planetary defence. The Chelyabinsk meteor was larger than what ARM plans to go for.

The political explanation of why the ARM mission exists, seems more logical than any rationale based on science or space economy development. ARM seems to be a political way to motivate the continuation of already ongoing projects like the SLS, Orion and SEP. They all have good potential uses, but the combination is strained and the usefulness limited to keeping those projects financed. Many critics are convinced that ARM will actually never happen, that it will soon be canceled.

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    $\begingroup$ Tunguska and Chelyabinsk are bigger than the ~5 meter asteroid ARM hopes to retrieve. But the delta V to deflect is much smaller than the delta V it takes to park in lunar orbit. $\endgroup$
    – HopDavid
    Jun 8, 2014 at 15:08
  • $\begingroup$ A 5 to 7 meter asteroid would mass from 200 to 500 tonnes. A carbonaceous asteroid could be up to 40% water by mass. A 500 tonne carbonaceous might yield 200 tonnes of water. A 200 to 500 tonne asteroid is more than adequate size to develop ISRU technology on. $\endgroup$
    – HopDavid
    Jun 8, 2014 at 15:39
  • $\begingroup$ @HopDavid Yes, if you know that particular speciment is carbonacious. But still, more is better once you've set up production. Robotic exploration of many asteroids would be scientifically more interesting than a manned mission to a single small one, I think. As for deflection you're of course right about the delta V. But I think that landing and pushing (or bagging and pulling) is more uncertain for planetary defence than to heat/sublime and push on it with radiation pressure such as microwaves. ARM plans to use technologies which are good for the objectives of ARM, but not for much else. $\endgroup$
    – LocalFluff
    Jun 8, 2014 at 15:55
  • $\begingroup$ ARM critic Rand Simberg on the Space Show 22 minutes into the sound clip below, says that the heat shield of Orion is insufficient for returning to Earth after having visited an asteroid in retrograde lunar orbit. thespaceshow.com/detail.asp?q=2259 $\endgroup$
    – LocalFluff
    Jun 11, 2014 at 12:23
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    $\begingroup$ Simberg has been waging jihad on the SLS and Orion for years. Anything falling from an apogee in the moon's neighborhood would re-enter the atmosphere at about 11 km/s. $\endgroup$
    – HopDavid
    Jun 11, 2014 at 16:59

Long term, an asteroid-to-orbit mission has several benefits:

  1. geopolitical value
  2. asteroid defense value
  3. economic value
  4. scientific value

Capture of an asteroid has several geopolitical considerations that give it value, ones which don't require manned missions by anyone.

The proven ability to move asteroids into orbit, especially lunar-coorbit (LaGrange points) or Lunar orbit, would establish definitively a level of fine control over asteroid movement. That level of fine control is a requisite for use of asteroids as weapons of mass destruction, and is directly on par with orbital insertion.

This is undoubtedly a part of the considerations - such a practical capability is bidirectional - if you can put one into stable orbit, you can also crash it, and also send it away from Earth. In other words, by proving you can make a successful insertion, you prove you can prevent one, as well.

The commercial applications, much as with the Apollo program, are a justification, but are probably not the root for the program. (Apollo established that the US could in fact deliver a missile payload anywhere desired within cislunar space.) The mining value of a nickel-iron asteroid as base metal is not worth the effort - it would cost more to recover the metal than the metal is worth. One that has significant other metals would be financially valuable, but the programmatic costs and landing costs may not be viable long term. Planetary Resources thinks they can manage it and make money - but if they had secure numbers, we'd see backers lining up to privately fund it. The risk is too high. (Further, the geopolitical aspects make it impractical to pull it off without it looking like a threat.)

The scientific value of an asteroid to orbit is immense - on par with putting men on the moon, but only slightly so. In addition to the mission itself and its science value as a near-system trans-lunar mission, there is the benefit of it being a platform for a much more radiation-proofed space platform, which would enable truly long-term science missions in microgravity.

The combination makes the asteroid to orbit overall a higher priority for politicians than the pure science of further lunar missions or the science adventure of Mars.

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    $\begingroup$ I think that you overlook the fact that NASA is talking about a tiny rock, not a real asteroid. Crashing it on Earth would only produce a nice bright bolide high in the sky for a second. And the SEP technology is inadequate for capturing any real asteroid. The science value of small space rocks can be gathered in museums where we already have thousands of them. $\endgroup$
    – LocalFluff
    Jun 10, 2014 at 5:11
  • $\begingroup$ The NASA people are talking 3-10m, sure - but the president has been talking bigger. But the fundamental navigational issues are the same whether it's 3m or 3km. Only difference is the engine power and time. Plus, the goal for Planetary Resources is a 100m plus. They need several thousand tons to make the process worth the retrieval from orbit costs. $\endgroup$
    – aramis
    Jun 10, 2014 at 5:20

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