Environmental Engineering Reference
In-Depth Information
24 h. The orbit is nearly polar (within 8.6 ), with
100.7min period. The inclination of the orbital
plane is 98.594 from the equatorial plane. The
Radarsat track presumably goes over Ottawa,
Canada, say at noon, and this condition repeats
at Ottawa every 24 days. A constellation of 24
such satellites could put one satellite above
Ottawa at noon each day.
Figure 5.8 (Radarsat-2, 2200 kg, launched in
2007) Imaging capabilities [61] of Radarsat-2.
The synthetic aperture radar antenna is the
rectangular slab at the bottom (15m1.5m,
mass 750 kg), an array of C-band (5.405GHz)
transmit and receive modules. The solar arrays
are each 3.73m
1.8m. The full cycle of orbits
repeats after 24 days, with 14 7/24 orbits each
same side of the satellite continues to face the sun. This is a sun-synchronous orbit,
a special type of polar orbit.
All of the orbits go through points close to the north and south poles, and the orbits
are most widely spaced, about 2860 km
1780 mi, at the equator. At 40 N latitude,
this spacing is 1363 mi.
One can imagine a power satellite version of the Radarsat-2 satellite whose orbit
passes over New York City. Distinct rectenna locations within a swath of 1000 km
¼
621.5 mi width could then be provided power, while the satellite is overhead. The
antenna would have to be larger (our previous estimate was 500m diameter) to
reduce the minimum swath from 45 km, to focus only on our chosen rectenna area,
139m in diameter. ThemaximumRadarsat-2 power is 5 kW, and the antenna mass is
750 kg. The Radarsat antenna is 15m
21.705m 2 , and contains 10 240
radiating elements [61], which are organized in 2 wings, each with 2 antenna panels.
If we assume that each radiating element is 1 / 2 wavelength, spaced longitudinally by
l /2, and columns of elements are spaced laterally by 1 wavelength l , then the area of
the antenna would be 10 240
¼
1.447m
27.7m 2 , which is similar to
the stated area, 21.705m 2 . The whole satellite is rotated along its direction of motion,
in a roll maneuver taking 10min, to switch from a right view to a left view. So the
rapidly accessible addresses on the ground are in a single 500 kmswath on one side or
the other of the orbital ground track.
But the time above a given location turns out to be insuf
l 2
(0.052) 2
¼
10 240
¼
cient for useful power
delivery, on this model. If we take the longitudinal addressable length as the satellite
altitude, A
807 km (which would allow angles up to 45 from the vertical), then the
¼
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