EP who is going to believe you know squat about the differences in shielding properties of materials when you don't even know the basics about radiation shielding? That was a rather obvious copout to avoid admitting your errors and discussing the issue further. Now if you want me to tell you the difference, I have plenty of references from which to look it up.

Can a rover do your job EP? If it can't do yours I doubt very much it can do the work of a highly trained scientitst. I'll put 6 million years of evolution against a decade of engineering any day. There isn't an engineering project yet that matches the flexibility of any living complex organism let alone human intelligence. That last 6 million on top of the previous 4 billion is one killer ap.

Here's some math of the type you are familiar with: the top two people involved with NASA's manned space program (Griffin, Horowitz) were Mars Society Steering Committed members from its founding until they took their present positions.

You might want to visit NASA's NEO site sometime to get an update on real impact risk estimates. Actual probabilities rather than statements like the vicinity of Earth.

see ya