At 06:19 PM 06/21/2002, Henry Spencer wrote: >There is one class of PHAs which will have to be seen as they approach: >long-period comets simply don't come around the Sun repeatedly in any >reasonable amount of time. They are a particularly ugly case: short >warning times, awkward orbits which render rendezvous-based deflection >methods unworkable, and some possibility that one could have an orbit >which would put it near or behind the Sun in our sky until it was quite >close.
You left out random course changes, from outgassing. For a small, active comet, it could be just a few weeks before impact until we knew for sure whether we were going to get clobbered or just get a great light show. Niven and Pournelle demonstrate this well in _Lucifer's Hammer_, as the odds against impact fall from 300:1 to 20:1 to 1:1 to where will it hit and what will it do? By coincidence, I'm rereading _Mote in God's Eye_... >The level of resources currently >invested in this stuff is really ridiculously small. Morrison used to complain that the number of people working on PHA detection was only just sufficient to staff a McDonald's. It's gotten a little better, but it needs to get a lot better. The Air Force sat up and took notice a few years ago; I forget the details, but some USAF study concluded that with the Soviet Union out of the picture, the greatest single catastrophic threat to American lives was from PHAs. I believe USAF is doing PHA detection with some of their old satellite cameras, now that CCDs are so much better. -R -- No electrons were harmed in the creation of this message PETE - People for the Ethical Treatment of Electrons Randall Clague [EMAIL PROTECTED] _______________________________________________ ERPS-list mailing list [EMAIL PROTECTED] http://lists.erps.org/mailman/listinfo/erps-list
