Couldnt we use a non vital part of the spaceship (i.e. engines etc) looking at the sun all the time as shield; what are the exact requirements for a shield like this;

The idea of using an asteroid (or several, pushed together) for radiation shielding is a sensible one, and not new. And the mass requirements for shielding of various sorts are well known, so I’m not sure why a paper has been written about it. Perhaps to report on those asteroid orbits?

But it makes a lot more sense to pick it up already in space than try to ship all that mass up from Earth. Getting out of Earth orbit is about 90% of the way to Mars, in fuel terms.

By the time we get around to building that space-elevator, I expect we’ll solve it by genetically engineering radiation-resistance into the colonists.

- You are going to generate huge amounts of dust that will be very slow to settle;
- Mining is an activity that uses heavy tools and lots of them. Heavy is the enemy of spacecraft;
- This isn’t just a simple 10 cm borehole. You have to hollow out a seriously large cavern because the crew has to live there. You might even want to park the entire spacecraft inside;
- asteroid composition is highly variable. Hollowing out a rubble pile is basically impossible unless reconceived along different lines;
- tunnelling an iron asteroid? Really? The energy requirements alone will probably nix that idea;
- tunnelling an ice asteroid. Now that, it seems to me, might have a chance. Still challenging, but less so than the other possibilities. You could use lasers or other heat sources to carve the asteroid.

Thanks for the question–I asked Gregory Matloff the same question, and I’ve clarified the article. It turns out he was picturing the asteroid as a sphere, and the spacecraft in the center. So the thickness of protection is roughly 16.4 feet, meaning a 33-foot-wide asteroid would be needed. Here’s his entire response:

“This is easily clarified. From a standard NASA reference (Space Settlements: A Design Study, NASA SP-413, p. 45), the cosmic-ray shielding by Earth’s atmosphere amounts to the equivalent of 10 tons of material per square meter. This is 20,000 pounds or about 10,000 kilograms per square meter. If we assume that the NEO has a density between that of asteroids Ida and Mathilde, which have been visited by flyby spacecraft, the NEO’s density is 2,000 kilograms per square meter. If our space crew digs in 5 meters, they have enough shielding from asteroid material. For a spherical asteroid, they will be at the center of a 10-meter or 33-foot sphere. As the NASA reference states, these numbers are conservative. We could probably work with a smaller NEO. Also, if it is a porous NEO, it will be larger or if it is an iron NEO it will be smaller to provide the same shielding.”

Thanks for asking!
Patrick