Page 112 - Satellite Communications, Fourth Edition

92 Chapter Three

Equation (3.22) gives:

M 2e sinM
3.32104 rad 2 .0000613 sin190.2817°
190.28044°

Equation (3.20) then gives:
SS GST
59.4313° 311.0487° 190.2804° 201.764°
358.996°
and Eq. (3.21):

SSmean M GST
59.4313° 311.0487° 190.2804° 201.764°
358.996°

From Table 1.3 the assigned spot for INTELSAT 10-02 is 359° east.
Modified inclination and eccentricity parameters can be derived from
the specified values of inclination i, the eccentricity e, and the angles w
and Ω. Details of these will be found in Maral and Bousquet (1998).

3.6 Earth Eclipse of Satellite

If the earth’s equatorial plane coincided with the plane of the earth’s
orbit around the sun (the ecliptic plane), geostationary satellites would
be eclipsed by the earth once each day. As it is, the equatorial plane is
tilted at an angle of 23.4° to the ecliptic plane, and this keeps the satel-
lite in full view of the sun for most days of the year, as illustrated by posi-
tion A in Fig. 3.8. Around the spring and autumnal equinoxes, when the
sun is crossing the equator, the satellite does pass into the earth’s
shadow at certain periods, these being periods of eclipse as illustrated
in Fig. 3.8. The spring equinox is the first day of spring, and the autum-
nal equinox is the first day of autumn.
Eclipses begin 23 days before equinox and end 23 days after equinox.
The eclipse lasts about 10 min at the beginning and end of the eclipse
period and increases to a maximum duration of about 72 min at full
eclipse (Spilker, 1977). During an eclipse, the solar cells do not function,
and operating power must be supplied from batteries. This is discussed
further in Sec. 7.2, and Fig. 7.3 shows eclipse time as a function of days
of the year.
Where the satellite longitude is east of the earth station, the satellite
enters eclipse during daylight (and early evening) hours for the earth
station, as illustrated in Fig. 3.9. This can be undesirable if the satellite