Just as motor vehicles need fuelling before long journeys,
so spacecraft require full tanks before they set off to
visit other worlds. But whereas a typical car may carry
40 or 50 litres of petrol and then be refuelled after
travelling a few hundred kilometres, there are no filling
stations in space.

As a result, interplanetary explorers such as ESA’s Rosetta
comet chaser have to carry vast amounts of both fuel and
oxidiser for their extended trek to other worlds.

In the case of Rosetta, the cube-shaped Orbiter has recently
been filled with more than 1.7 tonnes of propellant for its
6.5 billion kilometre expedition to explore Comet Wirtanen.
More than half of its weight on lift-off will be accounted
for by 1060 kg of oxidiser (nitrogen tetroxide) and 660 kg
of fuel (monomethyl hydrazine).(*)

Once Rosetta is boosted out of Earth’s gravitational grasp
by an Ariane 5 launcher, the spacecraft will rely on this
supply for manoeuvring and attitude control throughout its
10.5 year space odyssey to the depths of the Solar System
and back.

The task of transferring such a huge amount of propellant
was entrusted to a team of six skilled engineers from
Astrium-UK. Wearing protective suits, the team worked in
shifts over three days to prepare the spacecraft for its
January 2003 launch.

Team leader Chris Smith described the well-rehearsed
procedure.

“We worked on two shifts for each propellant tank — two
men on each shift and two more in the control room,” he
explained. “Each shift lasted a maximum of 4.5 hours
because that is the lifetime of our radio batteries.”

“On shift one, we made all the connections between the
tanks and started the filling operation. Later, we
stopped the operation, closed the valves and handed over
to our colleagues on the second shift to complete the
fuelling. The men in the control room monitored the
entire procedure by video, giving directions by radio
to the fuelling team.”

Every precaution was taken to ensure that there was no
spillage or exposure to the toxic fuel.

“We have to wear special pressurised SCAPE suits. (SCAPE
stands for Self-Contained Atmosphere Protective Equipment.)
These are quite difficult to put on, so we always have a
radio man and a safety officer standing by to assist us,”
said Smith.

“First, we put on a pair of ‘long johns’ that cover us
up to the neck. After our oversocks and silk gloves are
taped to the long johns, we put on a heavy waistcoat
that carries our radio equipment. Next, we put on the
rubber-impregnated suit. We squeeze the left leg in
first, then the right leg, before curling into a ball
and pushing the head into the top of the suit. Then
the arms go in and the suit is zipped up. Finally, the
helmet is fitted and the airline is connected.”

“We breathe normal air, but the temperature of the suit
is controlled by an air conditioner. The suit weighs
about 40 pounds (18 kg) and the helmet is very heavy,
so it presses on your shoulders and gives you a backache.”

“We were transferring nearly 4000 pounds (1700 kg) of
fuel — essentially a 4000 pound bomb — so while we
were working, everyone was cleared from the site for a
distance of one third of a mile (0.5 km) and blast walls
were in place in the building. ‘Sniffers’ monitored the
air in the room to detect any release of vapours.”

So what was the outcome of this protracted procedure?

“It all went very smoothly,” said Smith. “It is always
difficult connecting the fuel lines to the spacecraft
while wearing a SCAPE, but there was only one leaky
valve and that was spotted immediately.”

For a veteran of 10 ESA missions, isn’t Smith ever
concerned about working in such a hazardous environment?

“We always worry about the safety side, but if we didn’t
then it would be time to quit,” he said. “Things can
happen that we can’t predict, but everyone on the team
is confident in each other’s abilities.”

The success of this fuelling operation brings to an end
a hectic three-month pre-launch campaign at the Kourou
spaceport for the engineers from ESA and industry. The
Rosetta comet chaser now rests inside building S5B
awaiting the go-ahead for mating with its Ariane launcher.
“This was the last major activity on the spacecraft, and
the most dangerous,” said Fleming Pedersen, the Rosetta
System and Payload AIV Engineer. “We are now looking
forward to ‘babysitting’ the spacecraft for a few weeks
before the final launch preparations in January.”

(*) Petrol or diesel fuel used by cars will burn in the
presence of oxygen in the air. However, since there is
no air (or oxygen) in space, Rosetta has to carry its
own oxidiser, which enables the fuel to burn when it
fires its 24 rocket thrusters.

USEFUL LINKS FOR THIS STORY

* More about Rosetta
http://sci.esa.int/rosetta/

* Rosetta launch site
http://www.esa.int/export/esaMI/Rosetta/index.html

IMAGE CAPTIONS:

[Image 1:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=13&cid=12&oid=31251&ooid=31255]
Chris Smith and Robert Lenaghan of the Astrium Propulsion
team ready for scape suit training.

[Image 2:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=13&cid=12&oid=31251&ooid=31253]

[Image 3:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=13&cid=12&oid=31251&ooid=31254]
Scape suit training is given by the CSG safety.