Friday, October 23, 2009

A Choice of Asteroids

I began researching this post believing that Apophis (with its April 13, 2029 close approach) was our best opportunity to capture the resources of an asteroid for humanity and the space program.

Soon I realized that the selections are bountiful (or frightening, depending upon your point of view).

NASA maintains several valuable web sites and services, including

As I described in my post Capturing Apophis, these objects are far too large for us to simply man-handle. We must use finesse, or more precisely, we must use the gravitational influence of a body such as the Earth to do most of the work for us. We can nudge small to medium size bodies a bit given months or years of head start. So, we need objects that pass close by, perhaps within the orbit of the Moon.

Plus, I’m interested in objects we can capture in my lifetime.

Here is a list of potential asteroids. Their distance of closest approach is given in Earth radii (1 Er = 6400 km). For reference, the Moon averages 60 Er (Earth radii) away. This list is in order of close approach date.

  • 2005 YU55 passes at 25 Er on 8-Nov-2011. It’s 120 meters across, masses 3 million tons. I wish it passed later – it would make a wonderful practice asteroid but we’re not likely to be able to launch a deflection mission in time.
  • 2008 UV99 passes at 7.16 Er on 30-Mar-2019, is 400 meters wide and masses 87 million tons.
  • 2001 FB90 passes at 13 Er on 24-Mar-2021, is 349 meters wide and masses 58 million tons.
  • 2007 RY19 passes within 0.89 Er on 12-Mar-2024, is 110 meters wide, masses 1.8 million tons.
  • 2001 CA21 passes at 6.41 Er on 9-Oct-2025, is 677 meters wide and masses 422 million tons.
  • 2001 WN5 passes at 37.5 Er on 26-Jun-2028, is 780 meters wide, massing 646 million tons.
  • Apophis 99942 passes at 5.86 Er on 13-Apr-2029, is 270 meters across and masses at least 25 million tons.
  • 2007 FT3 passes at 22 Er on 03-Oct-2030, is 340 meters wide, masses 54 million tons.
  • 2009 UN3 passes at 19 Er away on 09-Feb-2032, is 919 meters wide massing just over a billion tons.

Note that the sizes are estimates based upon the apparent brightness of the asteroid. None of these have been imaged and measured. The masses are estimates based upon a spherical body of that size with a density of 2.6 tons per cubic meter (partly porous). A solid body would mass more, nickel-iron much more.

This list is not exhaustive, and some of these asteroids may be moving too fast (or not have suitable advance rendezvous orbits) for our purposes. But all 9 of these pass close enough to the Earth that their subsequent orbits are changed by the Earth’s gravity, and a relatively small nudge can be used to control a gravitational slingshot and choose its subsequent path. Some may require multiple slingshots and many elapsed years before they can be parked in a suitable orbit, but even the smallest of these (2007 RY19 at 1.8 million tons) contains enough resources to pay for the effort many times over.

There are many other asteroids from which to choose. A number of asteroids are in horseshoe or spiral orbits near the Earth, and may make suitable low delta-V rendezvous targets. Many more are easier to reach (in terms of required delta-V) than the surface of the Moon. Some of these are nickel-iron asteroids, others may be extinct comets containing huge amounts of ice. One estimate is that 6% of asteroids may be extinct comets.

We need better observations of all of the above objects. If one were a carbonaceous chondrite or an extinct comet, its value would be immensely greater due to the high content of carbon and water – the stuff of life. If one was nickel-iron then that, too, would have extra value. But all asteroids have great value once they’ve been captured into a stable Earth orbit, as all of them contain oxygen, silicon, magnesium, and iron.

Clearly, we don’t need to fight over these trillion-dollar resources. There are enough potentially valuable asteroids to share.


michael Hanlon said...

we are to influence the path of an asteroid and insert it in some orbit we choose, The proximity to the E/M L3, mostly but also L2, is paramount to the decision of which to attempt a grab at. It may take a little longer to get to those points, but the least amount of E for delta x,y,z and v would be required there. Can your modeling focus on the L pts and still consider the Earth in the model?

Stephen D. Covey said...

Without the Earth, there are no L points, so it is always part of the picture. Actually, it's the most important part, as an asteroid already having a close approach to the Earth is key to controlling a huge slingshot maneuver with the small amount of delta-V we can impose on a large asteroid.
If the asteroid passes sufficiently close to the Earth (how close depends upon its relative velocity as it passes), then we can control its subsequent path.
And a genius (or twisted, or both) orbital engineer (such as the genius who thought up the Cassini path) can find a way to end up with the desired final orbit, always keeping the limits of physics and orbital mechanics in mind.
Personally, I don't really care what the final orbit is, so long as it is close enough to the Earth to be convenient (in time and delta-V to reach), and safe and stable (we don't want it crashing into the Earth or Moon for the next hundred years). I'd love for it to be in a low Earth orbit (say a thousand miles up), or possibly just outside of geosync orbit (24,000 miles up), but I don't see how that's possible.
There is some possibility of ending up with an orbit near a Lagrange point, or possibly one of those horseshoe or other odd orbits.

michael Hanlon said...

You paid attention to Apophis when you found out about it. You formed a plan when you found it would passnear the E/M L3 point. But, it took your investigating to realize that L3 had importance. I just want a new column put into the JPL dB which indicates proximity to the L pts, especially three and two. One reason for this data: theremay be NEOs which pose no danger of Earth collision but which do pose a great opportunity if they are at a managable spot in the heavens for altering their orbits, such as the Lagrange points. If we are to capture the easiest to get, then the data I request is most important. If anything shows up as coming within 100 kilometers (the actual d should be arrived at by analyzing the ratio of mass to proximity)(A small mass 25clicks away may be easier to harvest than a huge one ten clicks awat)

michael Hanlon said...

I apologize for the incomplete thought. If it comes within that magnitude of distance it should be 'grabbable'. I am making a presumption, of course. I look at the gravity wells associated with the E/M and expect that anything getting to L4,5 will automatically drop into the wells. But still, the table of proximities should list approaches to all of those points.

Stephen D. Covey said...

Choosing an asteroid based upon how close it passes to a Lagrange point is not quite right. We want to choose it based upon how slowly it approaches the Earth, and how closely it passes to the Earth. Then we can tune its subsequent orbits so that it can end up at or near one of the Lagrange points or another desirable location.
But your point that NASA should provide another table is an excellent one. There are some near-misses that are not in their Hazardous Object Database for precisely the reason you mention: they won't strike the Earth. Yet these are still excellent choices for orbital tuning and eventual capture.
And your second point is excellent, also, in that the smaller objects are easier to deflect to where we need them.
Another consideration is less well-known, and that is the asteroid's composition. A low metal, low iron ordinary chondrite is much less valuable than an iron asteroid or a carbonaceous chondrite. At present, we guess at size and composition based upon poorly known albedos and spectra. We should do a better job of characterizing our resources.

michael Hanlon said...

Naturally orbiting objects have equal velocities if their orbital radii are equal. Fact of celestial mechanics. Deviations from the perfect path (a circle) account for differences in velocities as does eccentricity of the center(s) of the path. Any object going near any of our E/M L-pts are going o have a relatively equal velocity (yes, that velocity may be thousands of miles per minute, but so won't ours) An approach near one of the points should take weeks of proximity. Plenty of time to travel and perform horsepower acts, be it strap ion pulse engines or fix a laser push receiver or a microW target or mass ejector, or to position a "tractor to lead or lag it in a direction or just plain old grunt push it.
Using JPL's Feedback system, I have requested that they add to their calculations about NEOs the proximities to the L-pts. After all, If the data is not needed it is already there in their calc's about E approach. they just have to make the program line that calls for that point to be added. I did complicate the request though when I asked that they include a "Harvest Benefit Co-efficient" to the list which would be a combination of mass, distance and (just now realized) composition (Dam me & my mistakes). That way the computer should rank the probability of an economically successful mission.
They did respond when I used this avenue before when asking if the 99942 Apophis encounter with Venus in 2016 (or was it 2012?)impacted the risk assessment of the 2035(or '36?) event. They said absolutely no impact but I don't have the facility to disprove it. Anyway, they do talk anonymously.