The Dutch Nuna vehicle which will participate in the 3010 km World Solar
Challenge rally through Australia this November is not just special because
it is solar powered. This racing car also benefits from the most recent
European space technology and expertise.
The World Solar Challenge 2001 will be a tough race. Driving from Darwin to
Adelaide at the end of November means traversing 3010 km of Australian desert
during the hottest season. It will be a four day battle against the elements
and yet forty racing cars are still keen to enter the competition. Among
these is the Dutch vehicle ‘Nuna’ that will be driven by students. Place
your bets on Nuna as the winner — it is much more than a ordinary solar
powered racing car.
Nuna is fitted with solar cells which have actually been in outer space, as
part of the Hubble Space Telescope. The Alpha Centauri Team, which built the
Nuna, is supported by Dutch astronaut and Delft University of Technology
(TUD) Professor Wubbo Ockels.
“If Nuna wins the race, it will be due in part to the use of space
technology” explained Ramon Martinez, a mechanical engineering student at
TUD and leader of the Alpha Centauri Team, which also includes another five
TUD students and two students of Amsterdam University. “Solar cells with
such a high efficiency have never before been used in the race. They are
dual junction and triple junction gallium arsenide cells, with two or three
layers. The sunlight that passes through the top layer, which would normally
be wasted, is now used by the second or even third layer.”
The solar cells are such a recent development that the European Space Agency
(ESA) has yet to use them in space. Their first space application will be at
the end of next year when the SMART-1 lunar mission is launched. One of the
jobs of SMART-1 is to test a solar powered ion engine.
“Nuna is fitted with 36 solar panels” explained Martinez. “Their output is
optimised by 11 Maximum Power Point Trackers.” Maximum Power Point Trackers
(MPPT) have been used in satellites for years. They optimise the output of
the solar panels when they are in the shade, for example when the attitude
of the satellite changes relative to the sun. ESA’s Rosetta mission to
comet Wirtanen, to be launched in January 2003, will also be equipped with
MPPTs.
Martinez continued “Nuna will also occasionally be in the shade, which
reduces the efficiency of solar cells. But the MPPTs will ensure that the
solar cells supply a lot of power and will also stabilise the power. A chip
measures the voltage supplied by a solar panel, compares it with the fixed
battery voltage, and then determines the best voltage to charge the battery.
In this way we can get an efficiency of no less than 97%. Of course, we
also need a high-performance battery to operate effectively in poor weather
conditions. Depending on the speed, we will be able to travel 250 to 500 km
on a full battery.”
The batteries are also based on space technology. The 48 large Li-ion cells
are connected in series and can supply the solar racing car with 5 kWh of
electrical energy. They are specially developed for use in satellites, where
high reliability is essential.
“I think the whole car could easily be launched into space.” jokes Koen
Boorsma, who studies aerospace engineering at TUD. He was responsible for
the construction of the aluminium frame around the driver, as well as Nuna’s
bodywork. “The whole car has to be light and strong. That’s why we built the
bodywork in carbon fibre, reinforced on the outside with Kevlar. The Kevlar
layer will protect the Nuna against the impact of gravel during the race.”
Kevlar is extremely strong and is used not only in bullet-proof vests but
also in spacesuits, for protection against micrometeorites. Some walls of
the International Space Station (ISS) are also reinforced with Kevlar to
protect the astronauts.
The Alpha Centauri Team even considered the use of real space suits. Air
cooling would adversely affect the aerodynamics of the racing car. As the
temperature in the cockpit can be as high as 70 C, a space suit might help.
However, in the small cockpit it would be too restrictive. Instead, the
pilot will wear a cooling vest with ice cubes.
“Will we win? With this car we stand a pretty good chance.” concluded
Martinez. “In theory, we should be able to reach a speed of 190 km/h. In
practice it will probably be around 160 km/h, which would still be a record
for a solar powered racing car. However, we will only reach that speed on
a special test circuit, before the race. During the race on public roads
the normal Australian speed limits will apply. The Nuna will be followed
by a support vehicle with Wubbo Ockels, captain of communications, and
the rest of the team. The support vehicle will collect data about the
temperature and current from the solar panels. This information will help
the pilot to determine the strategy. Should you try to drive away quickly
from under cloud cover? Or should you try to save energy in that situation?
Selecting the best racing strategy should help us to gain on the other
teams.”
To power the GPS navigation system of the Nuna and the equipment to
stay in contact with the support vehicle, two strips of solar cells of
32.5 x 9.1 cm are fitted on each side of the cockpit. These solar cells
are the most exotic component of the vehicle as they have actually been in
space. They were part of the solar panels of the Hubble Space Telescope.
In 1993, after performing maintenance on Hubble, ESA astronaut Claude
Nicollier took them back to earth. They were analysed to study
micrometeorite impacts. These solar cells still have such a high
performance that they can now be used to make the Nuna a real solar powered
racing car from outer space.
For further information about ESA’s contribution to the Nuna, please contact:
ESA’s Communications Office at ESTEC in Noordwijk
tel. + 31 (0) 71 5653006, fax: + 31 (0) 71 5655728.
Related News
* Hubble gets new ESA-supplied solar arrays
http://www.esa.int/export/esaCP/Pr_50_1993_p_EN.html
* ESA press release: A unique test for Hubble’s new solar arrays
http://www.esa.int/export/esaCP/Pr_61_2000_p_EN.html
Related links
* Alpha Centauri Team
* World Solar Challenge
* Hubble European Information Centre
http://sci.esa.int/hubble/index.cfm
* SMART-1
IMAGE CAPTIONS:
[Image 1:
http://www.esa.int/export/esaCP/ESA5U72VMOC_index_1.html]
Space technology and expertise in the Dutch solar powered racing car ‘Nuna’.
[Image 2:
http://www.esa.int/export/esaCP/ESA5U72VMOC_index_1.html#subhead1]
Wind tunnel tests performed on a scale model of the Nuna.
[Image 3:
http://www.esa.int/export/esaCP/ESA5U72VMOC_index_1.html#subhead3]
>From start to finish the World Solar Challenge is 3010 km.
[Image 4:
http://www.esa.int/export/esaCP/ESA5U72VMOC_index_1.html#subhead4]
Astronaut Claude Nicollier, mission specialist from the European Space Agency
(ESA), works at a storage enclosure, using one of the Hubble power tools,
during the second of three STS-103 extravehicular activities (EVA). (NASA)
