QUESTION:
If there is no constraint in launch azimuth and we have 2 launch sites
available, at equator and at 35 deg latitude, if we have to launch a
satellite into orbit with 30 deg inclination, which launch site would be the
best? Why?

ANSWER from Andrew Petro on December 4, 1997:
That is an interesting question.  To go to a 30 deg inclination it is better
to use the launch site at the equator.  If you picture a satellite in a 30
deg inclined orbit, its ground track will cross the equator often but it
will never pass over anywhere above 30 deg North or below 30 deg South and
so it never passes over 35 deg N or S.  If you launch from 35 deg you will
have to do a plane change to reach a 30 deg inclination and that type of
maneuver is very expensive in terms of rocket performance.  From the equator
you can just launch into the proper azimuth with no plane change.  That is
one reason why the new Space Station will be in a 51 degree orbit instead of
28.5 deg (which we typically use).  Our launch site is at 28.5 deg latitude
and the Russian site is at about 46 deg (but they typically use 51 deg
orbits because of launch azimuth restrictions).  It is easier for us to get
to 51 deg than for them to get to 28 deg.  (A 51 degree orbit is also more
useful for Earth observation.)

Andrew Petro
Johnson Space Center