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Huygens 6th Probe Checkout

Huygens 6th Probe Checkout

The 6th Huygens in-flight checkout was executed on Friday 28 July from 16:00 UT to 20:00 UT. The Huygens activities were carried out while Cassini was in view of the Goldstone Deep Space Antenna. The Huygens telemetry data was routed via the Jet Propulsion Laboratory, Pasadena, California, to the Huygens Probe Operations Centre (HPOC) at ESOC, Darmstadt, Germany.

Summary of the Probe temperature since early February 2000

Like the previous checkout, this one was also performed while Cassini's High Gain Antenna (HGA) pointed at Earth. The Sun was at about 10 degrees away from the axis of the HGA, well outside its main lobe. Only a small amount of radio noise was picked up from the Sun, therefore the radio environment was excellent for another calibration point of the Huygens receivers.

Since Cassini's HGA is nominally pointed at the Earth, Huygens large heatshield helps the HGA to shadow the rest of the spacecraft. The probe temperatures are continuously monitored by the Orbiter when the Probe is sleeping.

The temperature of the batteries is currently about 12 °C, which is well within the range acceptable before executing a checkout. The battery temperatures are expected to increase by about 20-22 °C during a checkout, which will bring them to < 35 °C, well within the acceptable upper limit of 45 °C.

The first data arrived at ESOC at 16:39 UT as it took 38 min for the radio signal to travel from Cassini/Huygens to Earth at the speed of light, and less than 1 min for JPL to pre-process and forward them to HPOC. The first signs of life from Huygens were acclaimed with some relief at HPOC. "A Huygens checkout will never be a routine activity. It's the end step of several months of careful preparatory work for the Huygens Flight Operations Team. There is always some emotion when we hear from our little Probe which is now so far from us", said Jean-Pierre Lebreton, the Huygens Project Scientist.

A preliminary evaluation of the data indicates that the checkout was nominally executed and that the Probe and its payload performed as expected. The data were pre-processed at HPOC and sent to the experimenter teams for a detailed evaluation. The results of the checkout will be reviewed in details at HPOC in mid-October.

Radio receiver performance during the checkout.

Position of Cassini-Huygens spacecraft at the time of the checkout

The position of the spacecraft at the time of the checkout is illustrated in the figure on the right, which was composed by using the Solar System Simulator tool from JPL. (

At the time of the checkout Cassini was pointing its High Gain Antenna (HGA) at Earth and the Sun was about 10 degrees away from the antenna boresight (axis) as illustrated in the images below.

Pointing of Cassini-Huygens at the time of the checkout

As expected the radio noise level at the input of the Huygens receivers was low, at about the same level as during the previous checkout. Hence, the Huygens receivers were operating in a very good signal-to-noise ratio environment. This is confirmed by the high AGC level returned in the Huygens telemetry as shown in the figure below.

Huygens receivers AGC values history


Last Update: 1 September 2019
21-Sep-2021 23:10 UT

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