the ships which are pushed by the wind, large solar sails
will some day in the future deploy in Space. With their thin
reflective material, they will react to the weak thrust, a
very weak thrust indeed, given by sunlight to whatever object
it encounters. This
mode of propulsion, using an everlasting source of energy,
will enable the sailcraft to set course through Space beyond
the Moon and further into the Solar System, without limits...
How to travel into Space with the only
energy from sunlight ?.. the idea, which may seem strange at first,
is not a joke. As early as the 17th century, Kepler has noticed
that the tail of a comet did not spread along the direction of motion
as expected, but in the direction opposite to the incoming sunbeams.
He guessed that the fact could be explained by the effect of a pressure
of the light on the particles escaping from the comet. We had to
wait until the end of the 19th century and the work of Maxwell in
the field of electromagnetism, to see the hypothesis confirmed by
mathematical and physical theory.
Today, we know that at the distance of the Earth, the light of the
Sun provides a thrust of 9 micro-newton (the weight of a coin ...)
for each square meter of sail, i.e. the same force as the mere weight
of a 900 gram mass for each square kilometre. This could appear
negligible, but it is not when applied in Space, where there is
no resistance, to thin structures with a good surface to mass ratio.
In the best cases, photonic propulsion will not provide a better
acceleration than a few mm/s2. However, unlike in the case of conventional
propulsion with chemical propellants, the thrust will last as long
as desired, with no limits in time. Quick calculations demonstrate
that a solar sail in Earth orbit could reach escape velocity within
a resonable period of time and then set for interplanetary travel.
Sailing in Space
The first serious considerations about
photonic propulsion came around in Russia in 1915 with the work
of Yakov Pelerman, and then, a few years later, in the 20's, with
Fridrick Tsander, probably inspired by the writings of Space pioneer
Konstantin Tsiolkovsky (see the short history of photonic propulsion).
During the 20th century both engineers and writers were interested
by the concept, and the expression "solar sail" eventually was coined
by the American engineer Garvin in a scientific paper published
in1958. In 1963, Arthur C. Clarke invented a solar sail race from
the Earth to the Moon in his short essay "The Wind from the Sun".
But as early of the mid-fifties the French writer Pierre Boulle
had introduced solar sails in his famous book "The Planet of the
Apes". Unfortunately the film ignored them...
The first operational opportunity for solar sails comes in 1973,
when NASA is considering a rendezvous of a spacecraft with the Halley
comet, and a research program on solar sailing is initiated. For
many reasons, the project is dropped in the late 70's, but several
scientists and technicians from the Jet Propulsion Laboratory decide
to keep the spirit alive as a private venture, and create a non-profit
association, the World Space Foundation, with a goal to prove the
technical feasibility of solar sailing.
In 1981, in Europe, several Space professionals with interest in
solar sails join together to create the Union pour la Promotion
de la Propulsion Photonique (U3P). Originating mostly from ONERA
and from CNES, the French Space Agency, their goal, as an amateur
group, is similar to the goal of the World Space Foundation, with
an additional new idea of racing several solar sails together in
a race between the Earth and the Moon .
The idea of solar sailing is more alive than ever, moving at the
speed of light on the Web. Some future day, soon, a solar sail will
set off into Space !...
Photonic propulsion has already been
investigated in many research projects, sometimes in co-operation
with major universities and several thesis works have been conducted
on the subject of solar sailing trajectories between the Earth and
the Moon( see References). The range is wider than in conventional
Space studies, since original and unexpected solar sail specific
subjects may often pop up :
structure analysis, with physical and mechanical characteristics
unknown on the surface of the Earth : some concepts envision
sails with dimensions in the order of several kilometres, with
a thickness of only a few micrometers.
engineering, for the manufacture of thin aluminium-coated plastic
films, or light and strong booms, made of composite materials,
to stiffen the structure of the sailcraft.
- or in totally
different field, origami, the Japanese art of folding paper,
in order to obtain the optimal packing and unpacking of the
sail, which has to be confined in a small container until the
time of deployment in orbit.
- and many
Use of Photonic
Indirectly, solar sail studies may lead to
many technical applications. We should mention for instance the
folding method developed by Koryo Miura from Japan, which is commercially
applied for a convenient and original way of presenting road maps.
In the field of Space, photonic propulsion has many applications
control for satellites : to prevent the drifting of artificial
satellites from their nominal orbits, frequent corrections must
be applied, usually with small jet thrusters with a limited
propellant supply. Solar sail panels can perform the same corrections
without using expandables. A similar method was used in 1970
to adjust the trajectory of a probe around the planet Mercury.
travel of Space probes : solar sails offer a great method to
travel through the solar system. NASA had considered solar sails
for the Halley comet, today we can think of the exploration
of asteroids or remote objects as Pluto.
- fast transportation
of low mass payloads : a miniature probe with a mass of only
a few hundred grams associated with an ultra-thin solar sail
of a few hundred meters in diameter could reach the orbit of
Jupiter in a matter of a few weeks, to reach in emergency a
far away manned Space colony...
between the dreams of today and the realities of tomorrow,
solar sails are now ready to set off, ready to fly through Space...
Become a member of the solar sail network today !
All your questions, remarks, information are welcome ! ...