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No. 11 - 15th Huygens Probe Checkout

No. 11 - 15th Huygens Probe Checkout

The fifteenth Probe In-Flight Checkout was successfully executed on Tuesday 14 September 2004. As it is the last but one in-flight checkout planned before separation, it included some specific activities that are intended to prepare for Probe separation around Christmas this year.

The checkout consisted of two parts: A nominal type 1b checkout (as run during the 13th checkout), followed - in the same power cycle - by a Mission Timer Unit (MTU) Redundant Load Test. The checkout included specific payload activities as required to configure instruments before separation. The MTU Load Test checked the triply-redundant alarm-clock that will get the most important job of waking-up Huygens a few hours before entry in Titan's atmosphere at the end of the 3-week coast phase following separation from the Cassini Orbiter.

The checkout was carried out live, with Cassini transmitting the data to Earth in real-time. The data took nearly 80 minutes to travel to Earth due to the large distance between Saturn and the Earth, giving the One-Way-Light-Time of 1 hour 19 minutes 28 seconds. The data were received on Earth via DSS-15 at Goldstone (34m antenna) and transmitted directly to the Huygens Probe Operations Centre (HPOC) at ESOC, Darmstadt, Germany, over NASA's Jet Propulsion Laboratory (JPL), in Pasadena, USA, using a dedicated JPL-HPOC data line. As usual, the data were also recorded on board Cassini for later playback for redundancy reasons. The real-time data-stream indicated that the Huygens Probe System remains in good health, after its 7-year journey through space from Earth to Saturn, riding on the Cassini Orbiter.

The preliminary analysis of the real-time data set, performed within 24 hours after the test, indicates that the checkout was nominal, the MTU load test was successful, and that all instruments performed as expected.

Upcoming Activities

19 September 2004 - Battery Depassivation sequence #1
Huygens carries 5 non-rechargeable LiSO2 batteries which will provide power after separation from the Orbiter. The Huygens batteries have been inactive for more than 7 years. The purpose of the battery depassivation activities is to remove the thin passivating chemical layer that forms within the lithium battery cells, on the surface of their electrodes, when no current flows. This layer, which builds up naturally over time, enables the cells to retain their charge during the long Cassini-Huygens cruise phase but would prevent to use the full capacity of the batteries if it were not removed before use.

Huygens Power Conditioning & Distribution Unit (PCDU)

In principle, depassivation is achieved by simply discharging each battery against a sufficiently high load for a short period of time. In practice, it first requires the Probe and its instruments to be powered-on using the Cassini bus, via its Solid State Power Switches (SSPSs), in order to establish a sufficiently high load on the Probe's bus. Each of the Probe's five power sections, as illustrated in the figure, is then configured individually to connect the associated battery to supply the Probe bus in parallel to one of the Cassini power lines for a period of 5 minutes. The sequence ends once all five battery modules have, in turn, been depassivated. A second battery depassivation sequence is planned end of November.

The battery depassivation sequence has been fully tested before launch and recently re-validated using the Huygens Probe Engineering Model located at HPOC/ESOC.

A report on the outcome of the battery depassivation activity will be published early next week.

For further information, please contact

Jean-Pierre Lebreton
Huygens Mission Manager/Project Scientist
ESTEC, Noordwijk, The Netherlands
Tel: +(31) 71 565 3600

Claudio Sollazzo
Huygens Mission Operations Manager
Huygens co-located Team
JPL, Pasadena, USA
Tel: +(1) 818 393 3811

Joe Wheadon
Huygens Local Operations Manager
ESOC/HPOC
Darmstadt, Germany
Tel: +(49) (0) 6151902233

Last Update: 1 September 2019
20-Jan-2021 09:28 UT

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