Huygens fifth checkout successfully completed during night of 2 February
2 February 2000
The fifth in-flight Huygens checkout was successfully completed during the night of 2 to 3 February. The Probe was switched on at 23:00 UTC on 2February and switched OFF at 02:50 UTC on 3 February. The data came down with a 25 min delay due to the propagation time of the radio signal from Cassini/Huygens to the Earth. The telemetry data were made available to the Huygens Flight Operations Team at HPOC at ESOC in Darmstadt (D). A preliminary evaluation of the data by the Flight Operations Team indicates that all subsystems and experiments performed as expected.The receiver AGC values were expected with some excitement as this was the first checkout to be performed with the HGA turned away from the Sun. The team were in for a nice surprise. The AGC values were even higher than the values obtained during the special off-Sun test performed in May 1998. The values varied between about -92 and -94 dBm.
The Probe and the Probe Support Equipment (PSE) have been switched off to let them cool down. The Probe will now sleep until the next regular checkout scheduled in early September 2000. The PSE will be switched on tomorrow again for the Probe S-band relay test. The Huygens flight control team has prepared the data for distribution to the principal investigators for a detailed analysis. We expect to provide a complete preliminary report within two days.
Probe S-band relay test
Now that the Probe checkout has been completed, over the next 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.
Voyage through the asteroid belt
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.
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 is 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.