7
$\begingroup$

I think the question needs very little clarification - specific asteroids and/or their asteroid orbit type would answer it. My own interest is in what would best suit targeting for asteroid mining on the basis of delta-v requirements to reach known objects with known orbits.

Near Earth Objects and Earth orbit crossing ones would seem to be easier to reach - less delta-v - but I don't know it is actually the case: Atiras asteroids are inside Earth's orbit around the sun without crossing it, Atens are inside but do cross it, Apollos are outside and cross it and Amors are outside and don't.

$\endgroup$
5
  • $\begingroup$ Actually, what you plan to do with them has an impact: if you just want to land on them, then it only matters that the asteroid gets close to Earth at a specific time. If you want to mine them, you probably want them to remain close to Earth for a more or less prolonged period. $\endgroup$
    – jcaron
    Jun 30 at 9:28
  • $\begingroup$ Of course, there have already been instances of spacecraft landing on asteroids and comets (NEAR Shoemaker, Hayabusa, OSIRIS-REx, Hayabusa2, Deep Impact, Rosetta/Philae) and even some that have come back to Earth with samples (Hayabusa2). 5.4 grams "mined" :-) $\endgroup$
    – jcaron
    Jun 30 at 9:38
  • $\begingroup$ But wouldn't getting to some other part of the earth's orbit take much more delta-v than to reach a higher or lower orbit? There's no periodic time when the other side of the earth's orbit aligns with us. $\endgroup$ Jun 30 at 23:50
  • $\begingroup$ I was thinking about asteroids with known orbits and the periodic "windows" to get to and return materials from them - and that is about delta-v, not distance per se. $\endgroup$
    – Ken Fabian
    Jul 1 at 3:51
  • $\begingroup$ @KenFabian I've added a bounty; let's get you some mineable asteroids! $\endgroup$
    – uhoh
    Jul 2 at 9:53
13
$\begingroup$

note: This is a historical answer, and explains how to find tiny asteroids close by. The OP has clarified they want a profitably mineable-sized asteroid so there is room for more answers.

Previous wording:

...specific asteroids and/or their asteroid orbit type...

As discussed in Have there been any documented mini-moons since 2006 RH120?, "mini-moons" are predicted to regularly enter temporary chaotic orbits within the Earth-Moon system for months to years, and for meter sizes and below there should usually be one available, if you can find it! (see below). From the last half of the abstract of the 2012 preprint The population of natural Earth satellites:

At any given time there should be at least one NES of 1-meter diameter orbiting the Earth. The average temporarily-captured orbiter (TCO; an object that makes at least one revolution around the Earth in a co-rotating coordinate system) completes (2.88 ± 0.82) rev around the Earth during a capture event that lasts (286± 18) d. We find a small preference for capture events starting in either January or July. Our results are consistent with the single known natural TCO, 2006 RH120, a few meter diameter object that was captured for about a year starting in June 2006. We estimate that about 0.1% of all meteors impacting the Earth were TCOs.

For planning and launching such a mission you do not even need a significantly positive geocentric $C_3$; your mission takes place in high Earth orbit though you will need some more delta-v for maneuvering into the asteroid's chaotic orbit, coming along side it, and station-keeping against differential solar pressure and tidal forces from Earth and Moon.

Note: you will need very tiny, precision thrusters for these maneuvers as your velocity adjustments may be measured in microns per second rather than millimeters per second!

You may also want to scrap those large, flat solar panels which in this case will feel like solar sails, and either just cover your surface with them (allow for ways to radiate heat as well!) or use an RTG.

It is worth noting that in chaotic three-body motion (Earth + Moon + negligible/essentially massless object) you can't really say for sure if the energy is positive or negative; if the orbit is bound or unbound. If you know state vectors exactly you and predict if it has a chance of escape or not and roughly when. For more on that see @MarkAdler's answer to Was the Apollo spacecraft always gravitationally bound to the Earth-Moon system? which begins:

Hmm. This question is trickier than it sounds. To know whether a body in a three-body system is always gravitationally "bound", you have to look into the future.

For a model of what the mission might be like, look at missions that insert into 3-body halo or Lissajous orbits, like SOHO, DSCOVR, JWST... "and the rest."

You will likely need a little more delta-v reserve to catch up to and match the particular mini-moon's trajectory exactly since with a mass of only a few ton's entering orbit about it will not be practical; solar pressure is probably the main problem here.

You will also need a lot of fancy thermal infrared imaging and radar work from Earth, from other spacecraft and from your spacecraft to nail down the asteroid's exact position and velocity because:

  1. Chaotic motion means that small errors tend to amplify exponentially with time; if you're off by a few tens of meters in position or even a few millimeters per second in velocity, a month later it could be surprisingly far away from where you predict. SOHO's doubling time was two weeks and it was in a nice, well-behaved halo orbit! See also Roberts 2002 The SOHO Mission L1 Halo Orbit Recovery From the Attitude Control Anomalies of 1998.
  2. The visible light reflected by a 1 meter astroid is pretty tiny, and the amount of radar power you can illuminate 1 square meter at 500,000 km is tiny as well (remember that your return signal scales as $1/r^4$), but this low-albedo, high-emissivity body is constantly radiating hundreds of watts of thermal infrared being heated at by the Sun at 1 AU, against a pretty black background.

Happy hunting, there's probably one out there right now!


Here is an example of one theoretical orbit from here or here:

example of a mini-moon trajectory

$\endgroup$
5
  • $\begingroup$ Informative, interesting, but not quite the answer I was expecting or looking for. Problem with the question(er), not your answer. I hadn't considered objects so small but these do seem to be the nearest in distance as well as delta-v terms. I was thinking of delta-v getting to and from known asteroids with known orbits - most of which will be a lot bigger and might contain both nickel-iron and carbonaceous material to extract water to make fuel. $\endgroup$
    – Ken Fabian
    Jul 1 at 3:45
  • $\begingroup$ @KenFabian yes there would probably not be much excitement nor forthcoming wealth mining a 1 meter diameter asteroid, despite the scientific value. The size distribution of asteroids is inverse, the smaller the size, the most numerous, so maybe you can add a size limit to your question? There are lists of asteroids, so if you say > 1 km or > 10 km then people can start looking for those with low delta-v. Usually we shouldn't change the question too much, but I obviously missed "mining" in your question so it's fine if you edit to emphasize the minimum size you would consider worthwhile. $\endgroup$
    – uhoh
    Jul 1 at 6:23
  • $\begingroup$ @KenFabian It's fine with me, and if you've got a minimum size in place maybe I can add a bounty to attract some new answers. $\endgroup$
    – uhoh
    Jul 1 at 6:26
  • 1
    $\begingroup$ I reworded the question slightly, not specifying a size, but asking about known objects. Even a 1km diameter will mass a LOT. Not that it isn't possible something as big as that can become a mini-moon - but it would be down to luck and the ability to be opportunistic if it comes within reach. $\endgroup$
    – Ken Fabian
    Jul 1 at 7:12
  • $\begingroup$ @KenFabian okay thanks for the update. I've added a note at the top of this answer and I'll add a bounty as soon as I can. $\endgroup$
    – uhoh
    Jul 1 at 7:32
4
+100
$\begingroup$

I don't have the time right now to post a comprehensive answer, so I'll do a provisional one with some resources that might help you out. At some point I will might edit this into a full answer.

Here's a couple of papers that you'll be interested to read:

https://dspace.mit.edu/handle/1721.1/73467

https://planet4589.org/jcm/pubs/sci/papers/2018/Taylor18.pdf

https://www.researchgate.net/publication/263280808_Low_Delta-V_Near-Earth_Asteroids_a_survey_of_suitable_targets_for_space_missions

So that this is not a link-only answer, here are some takeaways from skimming through the texts:

  • Most near earth asteroids require a delta-v around 6-8 km/s
  • Very few asteroids have a delta-v smaller than 4 km/s

List item

  • 2006_RH120 has the smallest known delta-v at 3.8 km/s. However it is only about 3m in radius, so not what you're after.
  • Finding low delta-v objects is hard. Not only are they small, but they'll share a very similar orbit to earth, which means they'll precess very slowly, meaning they'll stay in very similar apparent positions relative to the sun. Assuming a uniform distribution around earth's orbit, most will be on the sunward side, in areas seldom observed by telescopes. -Looking through lists of near earth orbits isn't particularly helpful, as in order to be one of those, you just have to cross earth's orbit.
  • I don't have a close 'good' target for you, but looking at the OSIRIS-REx mission to (101955) Bennu will give you a good idea of what that might be, by virtue of the mission sharing many of the constraints as your question.
  • There's a bunch of other factors that influence whether an asteroid is a good target for mining. One that has already been mentioned is size. Another is rotation, some of these objects spin at close to their maximum theoretical speed. Another is the presence of moons, and yet another is the presence of hidden pockets of volatile ices. Finally, you want to make sure your asteroid has the minerals/ ores you actually want, and isn't just composed of rock.
$\endgroup$
2
  • $\begingroup$ just for clarity, the numbers are for (minimum) delta-v between LEO and object? With 3.9 km/s between LEO and geostationary it sounds like a lot of acceleration to get to NEO's is still getting out of Earth's gravity well. FYI I would target carbonaceous material; it should have water in it for making fuel - sounds like a LOT of that is needed - plus should contain nickel-iron (the target mineral) as nodules and grains in that softer material. $\endgroup$
    – Ken Fabian
    Jul 2 at 23:06
  • $\begingroup$ @KenFabian Yes, these are minima. It takes about 3 km/s of delta-V to get from LEO to escape velocity, which is a big chunk of the total, yes. $\endgroup$
    – Ingolifs
    Jul 6 at 21:36
0
$\begingroup$

I was looking at something like this (asteroid mining) but I was more concerned with the size of the asteroid. I use the small body ferret database to get a smaller list of asteroid names. Then I looked at the orbits and more data on the JPL Small-Body Database Browser.

After looking at several asteroids orbital diagram I starting to wonder about their speed and quickly realized that there is no fixed delta-v. The asteroid speeds up as it gets closer to the sun and slows down as it travels away from the sun (apsis).

Then ... there is the how close is it going to get and when. I was surprised to see some asteroids get really close to Earth's orbit but at the wrong time, meaning Earth is in the other side... and depending on the asteroid's orbit, it may take years/decades to come back.

Regardless ... it takes time to find good candidates. Good luck.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.