QUESTION:
I would like to know the altitude of the entry interface and how this is
determined.

ANSWER from Steve Sokol on May 1, 1997:
Sorry for the delay. Had to ask a Fido (Flight Dynamics officer) for the
answer. Waited a couple of days for e-mail response...but ended up cornering
Phil Burley (another Fido) as he walked by my office.

Entry interface occurs and is determined at 400,000 feet above the earth's
surface.

As a weatherman, we have to give a go for weather before de-orbit burn. Had
to ask my rocket scientist friend for help on your question.