clarke.tcl

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#
# Clarke three-satellite geostationary constellation
#
# based on 'Extra-Terrestrial Relays', Arthur C. Clarke,
# pp 305-308, Wireless World, October 1945.
# http://www.sciencemuseum.org.uk/on-line/clarke/ww1.asp
#
# this script for SaVi 1.2, by Lloyd Wood ([e-mail])
# http://www.ee.surrey.ac.uk/Personal/L.Wood/constellations/
#
# $Id: clarke.tcl,v 1.5 2004/12/26 14:47:19 lloydwood Exp $


# Clarke proposed three geostationary satellites spaced 120 deg at:
#  30E - Africa and Europe
# 150E - China and Oceana
#  90W - the Americas
#
# We duplicate that here. There is slight drift over time even in the SaVi
# model; geostationary satellites need to perform station-keeping against
# perturbation anyway, and this drift is the only motion you'll see.

# It's easiest to give each satellite its own RAAN, so we'll treat them
# as having separate planes even though they're not actually ascending.
set NUM_PLANES 3


# set location of one satellite; the others will be spaced from it
# east is positive.
set sat_longitude 150

# setup orbital elements
set a [expr 35786.1+$RADIUS_OF_EARTH]
set e 0.0
set inc 0.0
set omega 0.0
set Omega 0.0
set T_per [expr 2 * $PI * pow($a,1.5) / sqrt($MU)]

# for illustration purposes, but also a rough guide to practical use;
# although in e.g. Greenland, large dishes point almost to the horizon...
set coverage_angle 5.0

satellites GV_BEGIN

for {set i 0} {$i < $NUM_PLANES} {incr i} {
   # SaVi handles wraparound beyond +/-180
   set Omega [ expr 360.0/$NUM_PLANES * $i + $sat_longitude]
   set T 0
   satellites LOAD $a $e $inc $Omega $omega $T
}

satellites GV_END