24 Sep 2001

Checking out a spacecraft when it is in deep space and moving away from Earth at a relative speed of 79200 km/h is a rather complex operation that requires a lot of advance planning. However, after seven similar procedures since the launch of Cassini-Huygens in October 1997, the mission operations team at the European Space Operations Centre (ESOC) in Darmstadt, Germany, and their colleagues at the Jet Propulsion Laboratory (JPL) in California are used to dealing with these situations.

Claudio Sollazzo, Head of Huygens Operations Unit at ESOC explained how the eighth check-out was conducted.

"We agreed with the principal scientific investigators the sequence of activities to be carried out and put together a coherent set of operations," he said. "We then created a command sequence which we tested on the ground with our Huygens engineering model at ESOC. It's like a twin sister of the actual space probe and if it works on the engineering version, we know it will be fine on Huygens."

"We then passed this information on to JPL," he explained. "This is because the probe is attached to the Cassini spacecraft and all of our commands have to be passed on to Huygens via Cassini."

The command sequence was sent to Cassini several weeks ago via one of the Deep Space Network antennae in Goldstone, California. On Thursday 20 September, at 11:20 UTC (12:20 CET) Cassini instructed the probe to switch on so that its computers could conduct the necessary test sequence.

For the next 4 hours 18 minutes, the results of this remote diagnosis were transmitted back to Earth in real time. However, the spacecraft were so far away that the first radio signals took 52 minutes 41 seconds to arrive at Goldstone, even though they were travelling at the speed of light (over one billion km/h).

The information was rapidly passed on by satellite link to ESOC, where the operations team eagerly awaited the results.

An initial assessment of the telemetry indicates that all sub-systems and payloads on Huygens performed as expected. The science data have already been distributed to all Huygens principal investigators and preliminary reports from each instrument team are expected within the next week.

"Everything went perfectly," said a delighted Claudio Sollazzo.

The next regular check-out of Huygens is scheduled for March 2002.

For further information please contact:
Claudio Sollazzo
Head of Huygens Operations Unit
European Space Operations Centre, Darmstadt, Germany
Tel: +49-6151-902824
Email: claudio.sollazzoesa.int