If you are going to do anything in space, it would have to make money. Otherwise, what's the point?
That's what this series is all about. In my peregrinations on the web today, I found one item that could be manufactured on the moon: aluminum mirrors. These need not be heavy, since there isn't any weather, nor is there a need to support a lot of weight. A mirror of significant enough size may be powerful enough to lift itself off the moon and into orbit. Impossible?
Okay, so lets make this a speculation alert worthy post.
Before coming across that story on the web today, I had some more thoughts about the coaster, and how it may work. In previous posts, I posited that it may be worth it to spin the tungsten up so as to spread the heat evenly. In this post, a better idea would be posited--- to just move gases around in order to do that. It would be like a heating element- it would wrap around in concentric circles from a focal point where it is the hottest. The gas would recirculate around and around and heat up the entire tungsten heater so that the reaction mass can obtain its energy from it in a heat exchanger.
You could use the hydrogen reaction mass as a preheater of a sort in order to acquire heat from the recirculated gas and make a type of Stirling Engine that would work in the capacity of a pump. The pump would have a hot side and a cold side--- meaning the two gases. The piston would pump the hot gases through the heating element so as to keep it uniformly hot. The reaction mass would pass around the heating element at its hottest point. It is hoped that it would get up to 2700 degrees centigrade so as to gain enough energy for thrust and Isp of a nuclear thermal rocket. The advantage is that you could do this without the mass of a nuclear reactor.
Now, if you had large enough mirrors--- manufactured on the moon--- that you may be able to set up a transportation system that gets you to the asteroids and to mine them profitably.