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Harnessing Solar Energy to Sail to the Stars?
#1
[تصویر:  13469657601.jpg]




It's interesting when you look back at the history of space
exploration and realize that propulsion technology hasn't really changed
very much.


The earliest rocket prototypes were nothing more than elaborate
versions of weapons used during World War 2 and fireworks used during
civil celebrations. Even the Space Shuttle made use of solid rocket
fuel technology in its pair of solid rocket boosters. But, with the
liquid rocket fuel propulsion in the external tank, this combination has
proved to be highly effective and launched hundreds of astronauts into
space.


The approach works -- albeit not very efficiently -- and to get out
of the Earth's gravitational well, it seems for now that the extra punch
from exothermic processes is needed
In deep space, however, there are alternatives receiving very serious consideration -- such as the "eco-friendly" solar sail.


The solar sail concept is simple: any surface exposed to electromagnetic radiation 'feels' a pressure known as radiation pressure
and it's this pressure that exerts a tiny pushing force against the
surface. If the surface happens to be a spacecraft or part of a
spacecraft, it could act against it to provide propulsion through space.


The concept of radiation pressure isn't particularly new. The idea
was first alluded to by Johannes Kepler in 1610 when he suggested the
reason why the tail of a comet points away from the sun was in some way caused
by the sun. Kepler even made reference to using this unknown force for
exploration when he wrote in a letter: 'Provide ships or sails adapted
to the heavenly breezes, and there will be some who will brave even that
void.'
By 1864, it was accepted that light carried momentum and would exert a
pressure on anything it meets. A great demonstration of this can be
seen in the Nichols radiometer, which is a sealed bulb with tiny
silvered glass mirrors attached by a very thin wire inside the glass.
On being exposed to light the mirrors start to rotate, driven by
radiation pressure exerted by photons from the bulb filament.


The technique is already being used in space exploration for course
corrections and fuel savings. For example, NASA's Mercury MESSENGER
probe successfully used solar radiation pressure to make small course
corrections during its journey to the innermost planet To make the most out of radiation pressure for space exploration every
bit of solar energy needs to be eked out. For any useful form of
propulsion, giant solar sails need to be used and exposed to as much
light as possible
The first interplanetary test of a solar sail was conducted by the
Japanese Aerospace Exploration Agency in May 2010 with the launch of
Ikaros. This was the first time a solar sail was deployed and tested in
space and used as its primary propulsion. NASA also launched the
orbital solar sail prototype Nanosail-D in November 2010, successfully
completing its mission after 240 days in Earth orbit. Ikaros, on the
other hand, continues its journey around the sun after passing Venus in
December 2010.


With Ikaros' 27 square meter sail deployed, the full effect of
radiation pressure from the sun on the sail produces about 0.0002 pounds
of force, that's equal to about 0.1 grams -- less than the average
goose feather! The acceleration offered by this method of propulsion is
small but over a long period of time, incredible speeds could be
reached.


The downside to this mode of transportation is that heavier craft
will take longer to accelerate, so larger sails would need to be
manufactured. Ikaros' sail was impregnated with solar cells to power
the electronic equipment and a matrix of liquid crystals around the
outside whose reflectivity could be altered to change the attitude of
the spacecraft.


Future missions will take these tests further from the sun. The
challenge here is that the further away from the sun you go, the weaker
the radiation pressure, so acceleration through interstellar space will
be limited. Innovations in laser technology may extend the range of
solar sails.


The technology is no doubt in its infancy, but new ideas of rotating solar sails in various configurations show great promise.
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 سپاس شده توسط Dash @li ، Hamid Jafary Pooya
#2
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ممنون
در مورد اظهار نظر آقایون در تاپیک دلخوری باید بگم:
آقایون: کم گوی و گزیده گوی چون در// تا ز اندک تو جهان شود پر!!!
هرچند ک کلام گوهر بار از زبان شما جاری نشده، نمیشود و نخواهد شد!!!
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