How can I catch an asteroid?

Question

I'm interested in asteroid mining, but don't have the infrastructure in place to process ores and the like in space. However, I've got a nice planet-based refinery setup where I could easily process an asteroid, except for one problem: it's on a planet, and my asteroids are in space.

I'd like to get my asteroids, which vary in composition, but are generally between 50 and 300 meters in radius, from their high-speed orbits around the sun onto the surface of my planet, which has a similar size, gravitational pull, and atmosphere to Earth. I'd also like to do so without destroying huge tracts of land, causing tsunamis, triggering extinctions, or any of the other general badness that usually comes when asteroids deorbit themselves into the ground.

What's the best way for me to go about doing this? How can I deorbit and 'catch' an asteroid without anything horrible happening?

Answer 1

Capturing an asteroid would consist of several steps...

Identify The easiest asteroids to capture are going to be the closest, slowest rocks with the least amount of rotation, so these will be prime candidates. You will also want rocks with relatively soft surfaces for the next step.

Capture Capturing a rock is fairly simplistic if you think about it, assuming you've identified good rocks. This will be easiest with at least three ships or drones, each equipped with harpoons. The harpoon will need to propel an anchoring hook into the surface of the rock, with the cable fitted to a swivel between the cable and the ship. Ships could then control velocity and rotation, so that the rock can be towed back to the home planet.

Delivery Once the home planet is reached, the ship(s) place the rock into geosynchronous orbit with a space elevator specifically designed to handle the weight of the rock. A traditional elevator for ferrying people would not suffice, as the descent mechanism would need to be much stronger, possibly even rocket or anti-gravitation assistance to slow down descent.

Most of this could be plausible with a slight leap in current technology, eliminating the need for any explosives in space.

Answer 2

You could try to destroy the asteroids in space and collect the fragments. Smaller parts are easier to transport and process.

You could also send spaceships with roof-mounted thrusters to the asteroid and basically attach them as thrusters to the asteroid. You can also construct standalone thrusters on the asteroid's surface. This might enable you to steer the asteroid and slow it down. This option requires a pretty high technological development and also a good amount of resources to start with.

Another option (for civilizations with even higher technological development) could be using eddy currents to slow the asteroids down (at least the metallic ones). I am not sure how and whether this would work with objects as heavy, big, fast and irregular as an asteroid though. You would probably need tremendous amounts of metal and energy to build and power a device that can create a magnetic field this strong. It might also destroy your planet, so you better build it very far away from it or go with one of the less crazy options.

Answer 3

By high speed orbits, you mean they orbit closer to the star than your planet, right?

Getting machinery there is the costlier part, in terms of energy. A lot of delta-V involved. You have to match their orbital speed in order to dock to them.

This involves two problems:

• it is a huge change of speed;
• due to the former problem, it takes a lot of fuel... But in order to take large amounts of fuel anywhere in space, you have to burn more fuel (every bit of fuel is a payload until ou use it).

Essentially your problem is similar to that of catching the Voyager and bringing it back home, as seen on XKCD. Only you want to go to a lower orbit and back, instead of going through a solar escape trajectory and back.

There are ways in which you can solve those problems. Mining done exclusively by drones keeps weights needed to operate low, and it means you can use an acceleration rate that could kill humans. You can also sacrifice your miners with less ethical implications if they are disposable drones.

As for fuel, Nasa is testing an engine that does not require the ejection of mass in order to accelerate in space. That's witchcraft to many scientists, but just goes into showing that you probably don't need to handwave at all to have mining ships of reasonable sizes to reach those asteroids (really, go read that XKCD article and check the figures!).

One last thing. Keep your masses as low as possible. Don't bring the asteroids whole back home. Have the drones separate ore from useless rock. Bring only the ore back home. If your ships launch from the surface of the depleted asteroids, they will also push whatever's left into lower orbits, potentially making the "mining orbits" safer.

To bring the ore to the surface, put it in orbit of your planet first, then have space shuttles take it in chuncks to the planet surface - make it a regular service, just like Space X takes payloads to and from the ISS on a schedule. It then turns into a matter of having enough ships to keep your business productive.

Answer 4

The fastest and quickest way would be to plant a few nuclear weapons on the surface and detonate then timed to decelerate the asteroid so that it can get caught in the planets gravitational field instead of flying off into oblivion. You do run the risk of catastrophic failure with some ill-timed blasts, but hey, story options and plot devices abound with this method. Just remember, who controls the WMD's required for asteroid moving?

The second option is to have specialized spaceships with either reinforced noses or payloads of rockets and mass drivers to serve the same purpose. Have the spaceship chose an asteroid to move, dock with it, and either brace itself and fire the engines to push it into orbit, or deploy the rockets and mass drivers to push it into orbit. It could all be manned, or automated.

Further reading on AtomicRocket can get you more information about this issue.

Hope it helps.

Answer 5

You need a space elevator. Break the asteroid into pieces and send loads in the down cars. Furthermore, these will act as ballast to use in lifting up cars for free.

More generally, you have a problem with energy. If you use the planet to slow and stop the rock, even using controlled aerobreaking rather than a messy impact, you are transferring all that energy onto the Earth. It doesn't matter if it's one rock or dust, the result is the same.

You can start by reducing its orbital velocity to zero while still in space, using means where the re-action (e.g. rocket exhaust) misses the Earth. Then you still have to lower it to the ground, and that has an inherent amount of potential energy which is converted to heat. If it drops to the ground it leaves a big crater, but if you use a parachute (or whatever) it still impresses the same amount of energy onto the air and eventually the Earth as a whole. If done on an industrial scale, this could be the future's equivilent of burning fossil fuels.

Before a full space elevator is built, you can consider a mere 80 mile long tether. Well, since the platform above will have difficulty thrusting in a manner which doesn't just transfer the exhaust to the air below, it will actually need a much longer tether to lower the rock as the platform continues to speed by at orbital speed.

Importing material will be expensive, and this will drive more industry into space. Your postulated situation is unrealistic: the rock will be (far preferentially) be mined and refined in space or on the Moon. Asteroids can be found that are made of metal, so start with those and you don't have ore that needs refining as with Earthly mines; not at all. Metal foundries can work on the Moon and provide stock and finished parts for space-based industry. I'm sure they will still like steel for something even though they mostly use carbon and composites.

The real profit will be for platnum and other rare metals that are used in industry but in much smaller quantities. Landing this will be much less of a problem because of the orders of magnitude smaller quantity and the high price of the material.