(This belongs with the other messages below)

Amazingly, when I first set out my ideas, some astronomers actually thought that I was literally proposing using the Terrestrial Planet Imager to find threatening asteroids and comets. Clearly, the instruments of the Terrestrial Planet Imager would have to be greatly modified to be able to cover the wider field of view necessary for a comet and asteroid search.

After I set out my thinking on using lunar based instruments for dealing with the problem, several proposals were made for using free space based telescopes. While one of these free space based telescopes would certainly offer at least initially a better area of search, multiple telescopes mounted on the Moon could also provide this capability. Also, free space based telescopes would provide no capability in the radar frequencies, which may be easier to work with than the optical ones foe dealing with this hazard.

The question then comes down to capabilities and cost. Since the amount of damage the next one of these that hits will do eliminates the consideration of cost as a factor, the question then comes down to capabilities...

If you have ever looked at a high resolution image of space, you will understand that looking for threatening asteroids and comets is roughly equivalent to looking for particular grains of sand in a sandbox. The imaging CCDs provide output, which you can either transmit to earth, which requires an incredible bandwidth, or these images can be processed by parallel computers as they are taken, with only information of concern shipped back to the Earth.

If you use parallel computers in orbit they will require a large amount of energy (mass) and storage (more mass). Besides raising launch costs, this in turn makes pointing the instrument much more difficult. Difficulties in pointing the instrument in turn then limit the area of survey. Also, the more parts there are, the more likely it is that one of them will fail, and then you run into problems of servicing or replacing the telescope.

Many of the information and communication problems which any free space based asteroid and comet detection system will face could first be identified and worked on if the NESS telescope is launched as an engineering test item.

EP