Nano Future 2030

To get back to nanotechnology, I wanted to address the preferred path to a nanotech solution to the asteroid problem.

Let’s assume we have limited nanofactory capability at least. Around 2030, we expect a nanofactory to be capable of converting raw material (carbon, iron, oxygen, etc) into almost any object or tool.  That means we can use a small nano device to mine and fabricate useful structures from the raw materials available on the moon and on the asteroids themselves.  Using those materials we can construct robotic factories to produce much of the fuel, structure and power needed to launch these Asteroid defense spacecraft.

You deliver 100 pounds of technology to the surface of the moon, and two weeks later that device has mined oxygen, magnesium, iron and silicon from the surface of the moon and constructed other nanofactories devoted to hundreds of unique factories.  Slowly solar arrays are assembled to power the mines and factories. This allows more nanofactories and more mining operations to begin work .  In the center of the complex, on the sides of a mountain peak rising from the flat mare of a large crater, a rail gun is assembled for boosting small packages into lunar orbit.  Inside each ten pound package is fuel, parts, structural blocks or electronic devices. 

In lunar orbit, several craft are assembled by robots. Or rather the ships self assemble as if they are made of lego blocks with hands.  After a few weeks, you have a fleet of ships in orbit.  Each ship contains the fuel and rocket systems to boost the entire craft to an asteroid and to catch it and come to rest along side it. Once there, the solar arrays unfold and supply power to build more arrays from the materials on the asteroid. The ship should bring enough material to set up a gravity tractor near the asteroid but by using material from the rock, more systems can be built by the nanofactories on the asteroid. That way you can have ten, twenty tractors all working together to divert a rock faster and with more precision.  If you have ten years to boost, then you may only need on rocket. If you have six months before Earth collision, you might like to have five hundred or a thousand rockets. Nanotech is the only feasible way to ramp up to such large numbers in a short time.

John

I’ve been working on the Belt Buckle idea as an animation but I’m realizing that the gravity tractor can do the job just as well in most cases and, in the case of a rubble pile, it does it better than any other method.

A gravity tractor is the process of hovering a spacecraft close to an asteroid and using the mutual gravity attraction between the ship and the rock to exert a small force on the asteroid over a long period of time to affect its orbit.

The gravity tractor has a few problems.  You can’t let your rocket exhaust hit the asteroid because that exactly cancels some percentage of the thrust used to pull on the rock.  So you have to fire your hovering rockets at an angle to the line between the ship and the center of gravity of the asteroid. That wastes a significant percentage of your thrust.  If the rocket is several diameters away from the asteroid then the angle is small and the loss is small. But then you are too far away from the asteroid (depending on size) to get much gravity effects. So you have to suspend the bulk of your spacecraft from a cable so it rides close to the surface of the asteroid and put the rockets far away from the asteroid to keep them firing almost at the rock. 

Another issue with the gravity tractor is that it can not thrust at maximum thrust because it must have some margin between the average thrust and the maximum thrust since it is an active altitude control system.  If it moved close enough to the rock to use maximum thrust, then it would have nothing left to move further away from the rock when it drifted too close and needed to correct its height.  So you waste thrust one way or the other with a gravity tractor.

The Belt Buckle idea  is more complicated than the gravity tractor. And it needs to de-rotate the asteroid before it can start the orbit change thrust.  That wastes time and fuel compared to the gravity tractor.  I’m not sure at this point if the Belt Buckle idea is viable or needed once you have a gravity tractor.

John