From Bryn Glover, Kirkby Malzeard, North Yorkshire, UK
Your story on using moon dust to create a sunshield for Earth implies that the 1 million tonnes of dust needed would have to be replaced at the rate of 200,000 tonnes a day. While you mention the possible use of a railgun to propel the dust into space, there would need to be infrastructure for other aspects of this(18 February, p 18).
Presumably, actual dust sources would soon be exhausted, and so machinery to mine and crush 200,000 tonnes of moon rock a day would be needed. All of this must be built and transported to the moon, probably within a few decades. Has anyone calculated the carbon footprint of doing this?
