# Moving an asteroid into Earth orbit

Count Iblis
Suppose we want to use an asteroid to build a large space station. We could alter the course of a asteroid so that it will come very close to Earth, but the velocity relative to Earth will then be more than the escape velocity of 11.2 km/s. Presumably we must use aerobraking to let it lose enough energy to be captured. But then this must be done such that perturbations by the Sun or Moon will then change the orbit so that it doesn't move inside the atmosphere anymore.

Can we capture a 10 km diameter asteroid this way?

Gold Member
Suppose we want to use an asteroid to build a large space station. We could alter the course of a asteroid so that it will come very close to Earth, but the velocity relative to Earth will then be more than the escape velocity of 11.2 km/s. Presumably we must use aerobraking to let it lose enough energy to be captured. But then this must be done such that perturbations by the Sun or Moon will then change the orbit so that it doesn't move inside the atmosphere anymore.

Can we capture a 10 km diameter asteroid this way?
Yes. The real engineering question is: where will you house the 7 billion occupants while Earth is under construction?

(I'm not just being facetious, there's an underlying ... risk ... inherent in your proposal.)

Staff Emeritus
Can we capture a 10 km diameter asteroid this way?
Absolutely! Jupiter captured several this way, all at once, in July 1994. The Earth captures several smallish asteroids this way frequently, and captured a larger one in 1908, and a very large one 65 million years ago.

The idea of aiming a 10 km asteroid at the Earth's atmosphere is rather foolish.

Perhaps using the Moon as a gravity slingshot might be a better idea. Perhaps.

Gold Member
... If you consider an impact as a capture! :)
But Jupiter actually did capture SL-9 into an orbit probably about a century prior to impact. But as the impact illustrated, it was not a stable orbit. Likewise, using the moon as a slingshot can work. In fact it did, in 2006: http://www.orbitsimulator.com/cgi-bin/yabb/YaBB.pl?num=1182030550
But it was also an unstable orbit, and after completing a few orbits, our temporary moon escaped. So to capture and keep an asteroid in a stable orbit requires a large amount of delta-V on our part. You won't want to use the atmosphere, because you will broil the surface.
If we had the technology to produce the necessary delta V, then we would have the technology to mine the asteroid in its solar orbit, returning only the finished product to Earth.

EngineeredVision
I actually have an entire profession dedicated to asteroid wrangling in a science fiction story I'm developing. This profession plays an integral role in terraforming because it allows for large ice-laden objects in the outer systems to be brought to the inner terrestrial planets to deliver large quantities of water. In this case the asteroid wranglers actually want the captured body to strike the terraforming candidate. It’s been theorized that much of Earth’s water actually came to our planet in this way.

The second and more difficult function of the asteroid wranglers is to, as you suggest, capture a very large asteroid object and draw it into orbit around a terraforming candidate, essentially turning it into a small moon. This offers many benefits to the developing biosphere such as providing tides and stabilizing the planet’s rotation over time, thereby fostering more stable climate conditions.

Because there are inherent dangers with either of these operations they are only ever done on non-inhabited terraforming candidates.

Mentor
In SF world military applications of such a profession seem to be promising

Staff Emeritus