Environmental Engineering Reference
In-Depth Information
small contribution. A prior power satellite design of a generally similar nature [60]
called for a 15 km linear array of 344 combined solar collectors/converters, including
power cables up to 15 km in length. The power satellite was to be launched in 340
segments, each containing rotatable solar arrays and part of the transmitter, which
would be assembled in orbit using on-segment electrical propulsion. Economical
earth to orbit transportation capable of 30 ton payloads would be needed to assemble
one such satellite. A set of smaller geosynchronous satellites, adding up to 1.2 GW
would be possible with laser transmission of energy to earth, avoiding the large
transmitting antenna (http://science.nasa.gov/science-news/science-at-nasa/2001/
ast13nov_1/.). It appears that the reception area for each laser-based satellite, a
eld of
solar cells, would require the same area, 7.5 km in diameter. This hypothetical laser
version has the further drawback that clouds would block the power, unlike the
microwave version that will operate in cloudy weather. It is clear that these designs are
all extremely expensive, and likely unsuitable for an urban power supply, on the basis
of the 7.5 km diameter receiving space requirement.
The reports cited are nearly a decade old and do not re
ect experience from the
International Space Station (http://en.wikipedia.org/wiki/International_Space_Sta-
tion.). ISS is at altitude varying from 400 to 335 km, maintained by onboard power,
and has been manned since the late 2000s and projected to extend at least to 2020. It
has 262 400 solar cells (http://science.nasa.gov/science-news/science-at-nasa/2001/
ast13nov_1/.) located on 8 arrays of dimension 34m
11m, cell area about 2500m
2
,
and delivers about 110 kW. NiH batteries are charged during illumination to provide
power during the 36min of each 92min orbit in which the sun is obscured by the
earth. The cost of the ISS space station has been estimated as $130 billion over 30
years.
The cited studies generally consider neither thin-
lm solar cells nor the
possibility of unfurling thin aluminized mylar mirror surfaces, such as the 10m
2
nanosail (http://science.nasa.gov/science-news/science-at-nasa/2011/24jan_so-
larsail/.), which might be the basis for a less massive structure along the lines of
Figure 5.7.
Progress has beenmade in the private space industry over the past decade. A recent
event is the award, in June 2010, of a $492 million contract (http://www.freerepublic
.com/focus/f-chat/2537487/posts.) to SpaceX, by Iridium Communications, to
launch tens of communications satellites at 666 km altitude, as part of Iridiums
$2.9 billion plan for its upgraded communication satellite network, called NEXT
(http://en.wikipedia.org/wiki/Iridium_satellite_constellation.). This work will in
part use the SpaceX Falcon 9 launch vehicle, capable of putting 11 tons in low earth
orbit.
The Iridium NEXT network to be launched starting in 2015 will deploy 66
communications satellites at 666 km altitude, plus 6 in-orbit and 6 on-ground spare
satellites, approximately 1000 kg inmass. The price $2.9 billion for an in-orbit
fleet of
66 low earth orbit satellites is much below the ISS cost estimated as $130 billion. We
can think of adapting satellites of this type, perhaps out
ttedwith parabolicmirrors to
be unfurled in space, concentrating solar cells, and phased array microwave trans-
mitters to send power to earth.
