Strategy for mining an asteroid, part IV

Part I  briefly discussed how to get to the asteroid, how to land, and then how to begin mining operations.
Part II   discussed how to begin construction of the torus. 

Part III discussed masses, what could be done with masses, and values of the masses mined.


Propulsion for the torus?

A solar sail would not provide enough thrust.  This is a different type of craft, obviously.

The link just above describes a fusion based system that wouldn't require breakeven fusion power.  Instead, it would heat the reaction mass via the fusion reaction.  Power would come from solar panels, as the fusion is used to provide thrust, not power.  The article doesn't make it clear enough what the thrust would be, I'm guesstimating from the text that it would be something like 1800 pounds of thrust for the Mars mission thus described.  ( 50 lbs for each MW, 36 MW Jet power claimed).  This is not very much to propel this massive torus structure, so there may be a necessity for multiple engines of this type.  For example, some rough calculations suggest that an array of 12 of these firing continously would take a day or so to get just 1 ft/sec of velocity.  Thus, it would take a long time to get this thing going.  But at 5000 ISP, it wouldn't use nearly as much fuel as a chemical rocket.  A quick look at the rocket equation yields a disquieting observation.  It still requires too much propellant!  Acceleration is also too slow.  It looks like another means of propulsion may be necessary.

Orion, perhaps?  Yes, the torus would be a different type of craft.  Perhaps a world ship that could go to star systems.  But, do we have to be this ambitious?  No, probably not yet.  We just want to buzz around the solar system.

Power for the torus:

Looks like solar power could generate about 80 MW in the center of the torus.  At 1 AU, the distance between the Earth and the Sun, the amount of solar energy available is 1300 watt/square meter.  It so happens that there is a lot of empty space in the middle of the torus.  Fill that empty space with a huge solar panel.  Solar power would be stronger, perhaps by a factor of 4, as the asteroid swings by Venus.

The amount used for the fusion engines would only be a fraction of the amount needed for propulsion, judging by the text of the article linked above.  This leaves plenty for life support inside the torus.

Judging by this Yahoo article, 1 MW could power 80 to 1000 homes on Earth.  In space?  Well, assuming the same ratios, this amount of power, say 50 MW, would be enough for up to 50,000 dwellings.  Plenty of power available.

With this much extra power, I'm convinced that everything can be recycled onboard.  Minimal need for resupply.

Update:

Here's a video where Arthur Clarke says that nuclear propulsion is the only way to get large payloads around the solar system.  I seemed to have stumbled upon that understanding just now.




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