Press Release

How to drop in on Titan

By SpaceRef Editor
August 28, 2003
Filed under , ,
How to drop in on Titan
titan

You need to have thought of almost every eventuality when landing on a distant
moon in a remote corner of the Solar System. You must have tested your
spacecraft to its limits to be sure it will withstand the extreme conditions
expected on Titan, a moon of Saturn.

Moreover, you have to gather in advance as much information as you can about
the
way your instruments will work in those conditions. It is only when the
scientific instruments work properly that you can say your mission has been
successful.

Descending through poisonous gas

In early 2005, ESA’s Huygens probe will descend through the cloak of noxious
gases surrounding Titan, Saturn’s largest and most mysterious moon. An
Italian-led team of European scientists and engineers have ingeniously tackled
the challenges of testing the reliability, behaviour, and response of some of
the probe’s instruments in actual operation — not simulations.

Using a combination of balloon and parachute, the team had a creative way of
testing a full-scale replica of the Huygens space probe — they dropped it from
33 kilometres above the Earth! The air we breathe on Earth is very different
from the poisonous smog of Titan, but Jean-Pierre Lebreton, ESA Huygens Project
Scientist, says that the way in which the properties of our atmosphere change
are similar to the behaviour of Titan’s atmosphere.

On 6 June 2003, the scientists gathered at the Italian Space Agency’s Trapani
balloon-launch facility in Sicily. To launch the 500-kilogram gondola carrying
the mock-up Huygens space probe, they used a helium balloon that fully inflated
to a diameter of 100 metres (corresponding to a total volume of 400,000 cubic
metres) at its maximum altitude. When the balloon reached a height of 33
kilometres, a release mechanism opened and dropped the probe.

The on-board parachute deployed to slow the probe’s fall from 40 metres per
second to just 4 metres per second. At that speed, the probe floated gently
back
to Earth, taking about 30 minutes to complete its journey beneath the
ten-metre-wide parachute. This parachute was designed to provide a fall speed
very close to the one expected at Titan.

“Altimeter 1, are you receiving me?”

The flight allowed scientists to collect data under conditions which are as
representative as possible in Europe of the future flight to millions of
kilometres away from the Earth. In this way, they can really begin to
understand
the instrument characteristics very well. Scientists call this process
calibration.

Not only are these training exercises important to understand the behaviour of
the instruments and the data, they also contribute to building team spirit for
when the real thrills start at Titan!

This drop was the fourth test flight of the Huygens instruments on Earth (the
first such test took place in Spain during 1995, the following two were done in
Sicily). This flight was the first to have a fully equipped Huygens mock-up,
including the complete Huygens Atmospheric Structure Instrument (H-ASI)
provided
by Italy. Once on Titan, the purpose of H-ASI will be to study the temperature,
pressure, electrical properties, and the winds in this exotic atmosphere.

A mock-up of one of the two Huygens altimeters, mounted on the replica probe
was
also tested during this balloon flight. The altimeters measure the probe’s
height from the ground. “We are still analysing the data but, from what we have
seen so far, the altimeter worked well,” says Lebreton. “The test makes me very
confident that the two altimeters on Huygens will work well at Titan.”

“One of the other exciting and comforting aspects of this test flight was to
see
how good the probe was at stabilising itself during the descent when
atmospheric
turbulences disturbed the fall, thanks to its special parachute design. We can
then confidently expect we will have a flawless drop through Titan’s atmosphere
in early 2005,” says Enrico Flamini, ASI Project Manager for Huygens,
responsible for this test campaign.

The scientists are now considering a final drop during 2004 over Antarctica.
This location is the one on Earth that best resembles Titan’s atmospheric
conditions, in terms of pressure, electrical properties, and temperatures.
Titan’s temperatures can drop to about –180 C!

More about …

* Huygens overview
http://www.esa.int/esaSC/120378_index_0_m.html

Related articles

* Landing on a cosmic iceberg
http://www.esa.int/esaSC/SEM6N12A6BD_exploring_0.html

* Heading for Saturn’s mysterious moon: An interview with Jean-Pierre Lebreton
http://www.esa.int/esaSC/SEMDZ2T1VED_people_0_iv.html

* Splashing down on Titan’s oceans
http://www.esa.int/esaCP/SEMW889YFDD_index_0.html

Related links

* NASA’s “Where is Cassini-Huygens now?”
http://saturn.jpl.nasa.gov

IMAGE CAPTIONS:

Image 1:
http://www.esa.int/export/esaCP/SEMWNPYO4HD_index_1.html

Image 3:
http://www.esa.int/export/esaCP/SEMWNPYO4HD_index_1.html#subhead3

Image 4:
http://www.esa.int/export/esaCP/SEMWNPYO4HD_index_1.html#subhead6
On 6 June 2003, scientists gathered at the Italian Space Agency’s Trapani
balloon-launch facility in Sicily. To launch the 500-kilogram gondola carrying
the mock-up Huygens space probe, they used a helium balloon that fully inflated
to a diameter of 100 metres at its maximum altitude. When the balloon reached a
height of 33 kilometres, a release mechanism opened and dropped the probe.

Credits: ESA

Image 2:
http://www.esa.int/export/esaCP/SEMWNPYO4HD_index_1.html#subhead1
Huygens probe descending through Titan’s atmosphere.

Credits: ESA

SpaceRef staff editor.