money is in short supply

From: Brad Walsh

> Here's another advantage of developing robotic on-orbit construction--
> no matter what the dominant human space activity is 100 years from now,
> whether it's tourism, Chinese collectives, squared-jawed American
> explorers, solar power, permanent habitats, or just what we've got now,
> mostly robotic exploration, the one thing that they would all want is
> to buy some of the materials they need to complete their jobs from
> storehouses already in orbit, so they can cut down on what they have to
> lift out of the gravity well.

To a certain extent, I agree with this, but an important point is that we have to get to some activity involving many mega-tonnages in orbit in order to invoke ET materials as an advantage. For any activity not requiring many mega-tons of some material or product, use of ET materials cannot be economically justified.

That's why SPS has remained so popular over the years among the space materials crowd. SPS needs to be large scale in order to be efficient.

Regards,

Mike Combs