After five days of extensive tests, engineers and scientists on both sides of the Atlantic are confident that ESA’s Huygens Probe will be able to fulfil its exciting mission to explore Saturn’s giant satellite, Titan. The tests, which took place 16 – 21 November, were required to check out the all-important communications link between Huygens and NASA’s Cassini spacecraft.

This communications link, which will be used to send back the first images and in situ data from the mysterious, smog-covered moon, is the key to the success of the Huygens mission. If the scientific bonanza from Huygens is to be realised, it is imperative that the radio signal between the Probe and Cassini remains unbroken during the descent through Titan’s dense atmosphere.

However, avoiding any breaks in the Huygens transmission is far from easy, since the two spacecraft will be more than 65,000 kilometres apart and travelling at high speed in different directions. The descending Probe may also drift hundreds of kilometres off course if it encounters strong winds during its descent to the surface of Titan. All of these motions will cause significant shifts in the strength and frequency of the radio signals that arrive at Cassini.

In order to ensure that a continuous transmission can be achieved, teams from ESA and NASA decided to carry out a complex test procedure, using NASA’s Goldstone antenna in California to send a series of signals to Huygens, via Cassini. These signals were intended to simulate the stream of data that will be sent back by the Probe during its parachute descent through Titan’s atmosphere in January 2005.

“The tests lasted 5 days- more precisely 5 nights for us in Darmstadt,” said Claudio Sollazzo, Huygens Mission Operations Manager at the European Space Operations Centre (ESOC) in Germany.

“We tested a nominal mission scenario and several deviations from it,” he explained. “About 1 gigabit of data per day was sent back, so it will take a few months to fully analyse this data set. However, I am very pleased to say that we seem to have successfully met all of our objectives.”

“This test campaign was also a very beneficial exercise for the Huygens Flight Operations Team on its way to get ready for the real mission in three years from now,” he added.

Jean-Pierre Lebreton, ESA’s Huygens project scientist, also expressed his delight with the outcome.

“The test clearly confirms that the Probe’s radio signals will fall within the narrow bandwidth of the Huygens receivers on board Cassini,” he said.

“Even under the worst case conditions tested, with significant deviations from the nominal parameters, we have shown that we will retrieve all data that the Probe will send to Cassini during its descent, and for at least 15 minutes on the surface,” he added.

The widespread satisfaction with the way things went was reflected equally by staff at the Jet Propulsion Laboratory in California.

“We have taken major steps towards the validation of the Huygens Recovery Task Force design,” said Earl Maize, Cassini Spacecraft Operations Office Manager.

“The whole test was very smooth and went exceedingly well,” added his deputy, Julie Webster, who was responsible for the interfacing between the JPL and Huygens teams. “It looks like the results are going to be in the range of what we were hoping for on the recovery mission.”

“We have come a long way since we discovered the communications problem last year,” concluded Lebreton.


Claudio Sollazzo
Huygens Mission Operations Manager
European Space Operations Centre
Tel: +49 6151 902824

Dr Jean-Pierre Lebreton
Huygens project scientist
ESTEC, The Netherlands
Tel: +31 71 565 3600

Earl Maize
Cassini Spacecraft Operations Office Manager
Jet Propulsion Laboratory
Tel: +1 818 393 1062

Related Links

  • Huygens operations
  • More about Huygens
  • What is the Doppler effect?