To spot NEOs
Last w-e, one of the conferences in Paris was about the threat from NEOs (geocroiseurs).
The current problem is that those inside Earth's orbit around the Sun are very difficult to spot because of the Sun.
That's why a NEO detector (telescope of some sort) should be placed in a sun orbit between Venus and Mercury (perhaps a 6 months orbit) and put several of them. The further from the Earth, the wider the field of view.
Raoul