Ted Molczan wrote:

"Clay Blankenship" wrote in message
...
Fred wrote:
A lot of meteorological (and other?) satellites are at about 800-850 km,
in
the range necessary for sun-sychronous polar orbits (every ascending or
descending Equator crossing is at the same local time). For example, all
the NOAA polar orbiters and the DMSP satellites.

The orbital planes of sun-synchronous orbits precess at the rate of
+0.9856 deg/d, negating the -0.9856 deg/d precession due
to Earth's orbit about the sun.

The rate of precession of an orbital plane is a strong function of orbital
inclination, semi-major axis and eccentricity, in that order. As a result,
sun-synchronous orbits can be achieved over a wide range of altitudes.
Generally, the greater the altitude, the greater the inclination required
to be sun-synchronous. This affords satellite designers considerable
flexibility to tailor orbits to specific missions.

Here are some examples of the diversity among sun-synchronous orbits:


You are right--I was misremembering that sun-synchronous orbits needed to
be in a fairly tight altitude range. In fact, the inclination is the
variable that is more tightly restricted (assuming low-earth orbit). I
know a lot of polar-orbiting weather satellites are at around 800 km. I
suppose there is a good tradeoff between fuel requirements, sensor ground
resolution, and other factors there.

Clay
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Clay Blankenship Change 'Z' to 's' to reply
Monterey, CA