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.
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