ESA's Huygens probe, now orbiting Saturn on board the NASA/ESA/ASI Cassini spacecraft, is in good health and successfully passed its fifteenth 'In-Flight Checkout' on 14 September 2004.

An artist's concept shows Huygens parachuting to Titan after deployment from the Cassini orbiter. Credit: EADS Astrium

This in-flight checkout procedure was the last but one planned before separation of the Huygens probe from Cassini in December this year, and it included some specific activities that were intended to prepare for the separation. The main difference in this procedure from previous checkouts was that there was a test of the Master Timer Unit (MTU).

Because Huygens will spend three weeks coasting towards Titan following separation from the Cassini orbiter, its systems and instruments are powered down.

The MTU is the 'triple-redundant' alarm-clock that has the most important job of waking up Huygens a few hours before its entry into Titan's atmosphere.

The checkout also included some specific payload activities required to configure the Huygens instruments before separation.

The procedure was carried out live, with Cassini transmitting the data to Earth in real-time. However the data arrived on Earth with an 80-minute delay as this is the time taken for light, and therefore radio signals, to travel the distance between Saturn and Earth.

The preliminary analysis of the real-time data received, performed within 12 hours after the test, indicates that the MTU test was successful, and that all instruments performed as expected.