[meteorite-list] Radio Astronomers Confirm Huygens Entry in the Atmosphere of Titan

[Ron Baalke]

http://www.esa.int/SPECIALS/Cassini-Huygens/SEMIEPQ3K3E_0.html

Radio astronomers confirm Huygens entry in the atmosphere of Titan
European Space Ageny 
14 January 2005

At 11:25 CET the Robert C. Byrd Green Bank Telescope 
(GBT) of the National Radio-astronomy Observatory in West Virginia, USA, 
a part of the global network of radio telescopes involved in tracking 
the Huygens Titan probe, has detected the probe's 'carrier' (tone) signal.

The detection occurred between 11:20 and 11:25 CET, shortly after the 
probe began its parachute descent through Titan's atmosphere. The extremely 
feeble signal was first picked up by the Radio Science Receiver supplied 
by the NASA Jet Propulsion Laboratory. This signal is an important indication 
that the Huygens probe is 'alive'. However, it does not contain yet any 
substance; the latter is expected to come a few hours later via the Cassini 
spacecraft.

What the Green Bank radio telescope has detected is only 
a carrier signal. It indicates that the back cover of Huygens must 
have been ejected, the main parachute must have been deployed and that 
the probe has begun to transmit, in other words, the probe is "alive". 
This, however, still does not mean that any data have been acquired, nor 
that they have been received by Cassini. The carrier signal is sent continuously 
throughout the descent and as such does not contain any scientific data. 
It is similar to the tone signal heard in a telephone handset once the 
latter is picked up.

Only after having received the data packets at ESOC 
will it be possible to say with certainty whether data were properly acquired. 
The first data set from Cassini will reach ESOC in the afternoon. Additional 
downlinks will follow throughout the evening and night for redundancy.

Further analysis of the signals will be conducted using other three independent 
data acquisition systems at the Green Bank Telescope. In addition to the 
GBT, sixteen other radio telescopes in Australia, China, Japan and the 
USA are involved in tracking the Huygens probe.

The ultimate goal of 
the tracking experiment is to reconstruct the probe's descent trajectory 
with an unprecedented accuracy of the order of one kilometre. The measurements 
will be conducted using Very Long Baseline Interferometry (VLBI) and Doppler 
tracking techniques. This would enable studies of the dynamics of Titan's 
atmosphere, which is considered to be a 'frozen' copy of that of the early 
Earth.

The VLBI component of the tracking experiment is coordinated by 
the Joint Institute for VLBI in Europe (JIVE) and ESA; the Doppler measurements 
are conducted by the Jet Propulsion Laboratory.