Nick writes:

> It kind of boggles my mind with our advances in technology there are no
>  foreseeable successors to the Concorde.  Wouldn't a 400 passenger SST
>  that could make four round trips a day between America and Europe be
>  economically viable?

The environmental problems associated with high-altitude flight are not to be
minimized. There is already a great deal of accumulated evidence that current
tropospheric flight traffic is significantly increasing the cloudiness at
that level, and thus not insignificantly modifying the weather (see, e.g.,

     http://hyperion.gsfc.nasa.gov/AEAP/98minnisabs.html
     http://asterix.essc.psu.edu/fieldcamp/success/success1.html )

The problems of hypersonic flight at very high altitude (upper stratosphere)
are much worse, which is highly chemically photoreactive. For a reasonable
review (written 30 years ago) of the problems, see:

     http://www.magma.ca/~jdreid/uv.htm

The few Concorde flights a day that are now conducted can be tolerated. Heavy
SST/HST traffic probably can't be.

Wirt Atmar