ESA Science & Technology - 5th Huygens in-flight Checkout tonight

Yesterday, the spacecraft was successfully re-oriented so as to point its High Gain Antenna (HGA) towards Earth. This makes it possible to get high-rate telemetry in real time. The Probe checkout will be executed in direct visibility from the Goldstone Deep Space Network (DSN) station and thus data will arrive in quasi-real time (at 300 000 kms^-1 radio waves take about 20 minutes to reach in Earth) at the Huygens Probe Control Centre at ESOC, Darmstadt (D) through the Cassini Control Centre at JPL.

On completion of the Probe checkout activities, the following two nights a sequence of Probe S-band relay tests will be conducted to exercise and calibrate the Huygens radio receivers on board the Orbiter. The S-band relay test will be performed by transmitting from the Goldstone DSN an S-band signal (2.040 and 2.098 GHz) to the Orbiter's HGA. The Probe itself will remain OFF during the Relay test. The Huygens Probe Support Equipment - the piece of Huygens equipment that remains permanently attached to the Orbiter after the Probe release - will see this signal and process it as if it were coming from the Probe itself during its descent in through Titan's atmosphere. This will provide a complete end-to-end test of the radio link between the Probe and the Orbiter.

Schedule of activities for the fifth checkout

The Cassini/Huygens spacecraft is currently flying through the asteroid belt, on its way to Jupiter. A distant observation of Asteroid 2685 Masursky was performed on 23 January (see related link "Asteroid Masursky flyby").

By 2 February, it had reached a distance of 2.7 AU from the Sun. The distance to the Sun is now continuously increasing, which provides some relief for the spacecraft thermal control systems. Up to now, the spacecraft has been flying with its HGA pointed to the Sun to allow the 4-m diameter dish to shadow the spacecraft from the Sun's heat in the inner Solar System. On 1 February at 12:00 UT, a manoeuvre reoriented the spacecraft so as to point the HGA to Earth. The spacecraft has been rolled such that the Probe is slightly exposed to the Sun to help provide shadow for the sensitive instruments onboard the Orbiter.

The HGA-to-Earth attitude will be Cassini/Huygens' nominal attitude until it reaches Jupiter at the end of this year. The pointing of the HGA to Earth opens the gate for high data rate telemetry, making it possible to communicate much more easily with the spacecraft than has been possible up to now. A downlink data rate capability of up to 248 kbit/s will become available; making it possible to dump the solid state memory (2 gigabit capacity) in one single DSN pass or to provide real-time high-data rate capability.

Soon after pointing the HGA to Earth, a number of activities took place. The data obtained during the observations of Asteroid Masursky on 23 January were transferred to Earth. Other activities in preparation for the Probe checkout were also performed. We intend to keep our readers informed as the activities proceed during the rest of the week. Stay tuned!

Schedule of the Huygens 5th checkout activities