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At the large table in the Integration Hall of the Institute of
Space Systems, a pump is running, drawing the gleaming silver
solar sail onto the table. There is no other way to pick up this
incredibly fine fabric; even a single quick movement would
cause the material to flap up into the air before slowly landing
again almost weightlessly. It runs across the fingers like water
and is almost imperceptible. The polyimide film is just 0.007
millimetres thick, but is nonetheless remarkably resistant to
tearing. With immense care, Patric Seefeldt and Siebo Reershe-
mius cut the silvery material into strips and then glue them
together to form a sail that will enable a spacecraft to glide
through space.
The first big test for the Gossamer project is scheduled for
2015; then, four masts will unroll in space while sails deploy to
a size of five by five square metres. The spools on which the
masts and sails were wound will be discarded once their work is
done. What is left is a five-by-five-metre ultra-lightweight
Yachts gliding across the water pushed solely by the wind – this is not only an elegant visual spectacle, but also an
extremely effective process. Although there is no wind in space, there is a form of propulsion available round the clock,
365 days a year – the Sun. This is why giant solar sails will propel future spacecraft – slowly, but gradually increasing
in speed and without the burden of a fuel tank. The objective will be to travel across the expanse of space to the very
edge of the Solar System and beyond, or over the Sun’s poles. These regions are not accessible, or only with difficulty,
employing current propulsion systems. Researchers at the DLR Institute of Space Systems in Bremen and the Institute of
Composite Structures and Adaptive Systems in Braunschweig are designing the ultra-fine solar sails that will unfold once
in space on especially lightweight, but nonetheless very sturdy masts.
‘Gossamer’ – using the Sun as a propulsion system
By Manuela Braun
Sailing through space
structure; the combined weight of the sails and masts is less
than 1.5 kilograms. This discard concept distinguishes the Euro-
pean Gossamer project from its US and Japanese competitors.
Once deployed, particles of sunlight – photons – will collide
with the sail and Gossamer 1 will set out on its journey. After
this, Gossamer 2 and Gossamer 3 will embark on their sailing
trips across space at two-year intervals – with larger sail areas,
greater mass, and methods to steer the spacecraft while under
sail.
Thrust with solar power
At least, this is what department head Tom Spröwitz has
in mind. “Gossamer 1 is intended to prove that it is possible to
deploy a structure of this kind in space.” The pressure is on,
because if Gossamer 1, the pilot project, were to fail, prospects
of further attempts would be small. “For this reason, what we
have to do is show that solar propulsion is a technology worth
pursuing and that it works.” The principle is simple – the
photons collide with the aluminium-coated sails, and the colli-
sion and ensuing rebound transfer momentum thus deliver
propulsion. Instead of heavy fuel tanks with a limited capacity,
solar sails enable scientists to leverage the inexhaustible power
of the Sun – and dispense altogether with heavy tanks.
Although the propulsive force is extremely small, by virtue
of acceleration over a period of several months, speeds in excess
of 100 kilometres per second can eventually be reached. That
makes it possible to conduct missions to the very limits of the
Solar System – or even further afield. Since this ‘space yacht’
does not need to gather slingshot momentum from planetary
flypasts, scientists can plan the launch, and indeed the entire
mission, independent of the movements of the planets.
A concept on the test bench
To enable this ultra-lightweight unit to complete its flight
through space without malfunctioning, scientists are conducting
initial implementation tests on the ground. What properties do
Working on the ‘engine’ of the future – Patric Seefelldt holds up a
model of the solar sail.
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