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Horizon tonight on TV



 
 
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  #1  
Old October 21st 04, 12:13 PM
Steve
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Default Horizon tonight on TV

Thursday 21, 21:00, BBC2 England


Insight into the voyage of the Cassini-Huygens spacecraft, which has
sent back the clearest images of the planet Saturn ever seen




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  #2  
Old October 21st 04, 09:50 PM
James
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"Steve" wrote in message
...
Thursday 21, 21:00, BBC2 England


Insight into the voyage of the Cassini-Huygens spacecraft, which has
sent back the clearest images of the planet Saturn ever seen



Excellent program I thought. Can't wait till January now!


  #3  
Old October 21st 04, 10:16 PM
Jonathan Silverlight
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In message , James
writes

"Steve" wrote in message
...
Thursday 21, 21:00, BBC2 England


Insight into the voyage of the Cassini-Huygens spacecraft, which has
sent back the clearest images of the planet Saturn ever seen



Excellent program I thought. Can't wait till January now!




About the only omission I noticed was the time at Jupiter when they had
problems and lost images, and the only error I caught was that it's been
known for sixty years that Saturn's rings can't be very old.
I still don't know the name of the British astronomer Arthur Clarke
writes about in "2001: A Space Odyssey".
In view of recent events, let's hope there were no errors in Huygens'
drawings!
--
What have they got to hide? Release the ESA Beagle 2 report.
Remove spam and invalid from address to reply.
  #4  
Old October 22nd 04, 10:43 AM
Peter Hayes
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James wrote:

"Steve" wrote in message
...
Thursday 21, 21:00, BBC2 England


Insight into the voyage of the Cassini-Huygens spacecraft, which has
sent back the clearest images of the planet Saturn ever seen



Excellent program I thought. Can't wait till January now!


But surely the ESA and NASA could agree on radio frequencies?

The thought that the Huygens mission could have failed because the
radios were working on different frequencies amazes me. Don't these guys
test things before launch? It sounds like the HST farce where they
didn't test the telescope prior to launch.

--

Peter
  #5  
Old October 22nd 04, 11:38 AM
Jonathan Silverlight
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In message , Peter
Hayes writes
James wrote:

"Steve" wrote in message
...
Thursday 21, 21:00, BBC2 England


Insight into the voyage of the Cassini-Huygens spacecraft, which has
sent back the clearest images of the planet Saturn ever seen



Excellent program I thought. Can't wait till January now!


But surely the ESA and NASA could agree on radio frequencies?

The thought that the Huygens mission could have failed because the
radios were working on different frequencies amazes me. Don't these guys
test things before launch? It sounds like the HST farce where they
didn't test the telescope prior to launch.


A quick Google search throws up an excellent article which explains this
in more detail (there's probably a lot more out there)
http://www.spectrum.ieee.org/WEBONLY/publicfeature/oct04/1004titan.html
There's a FAQ at http://quest.arc.nasa.gov/saturn/qa/cassini/ but it
doesn't seem to cover this.

One more mistake I've just noticed in an excellent programme - the
pictures showed Cassini spinning. Actually, it doesn't normally spin,
because it's three-axis stabilised.

Have there been any documentaries about the politics behind Cassini? The
programme stressed the European collaboration, but it's my understanding
that if it wasn't for Huygens, Cassini would probably have been
cancelled on cost grounds. As it is, they lost the scan platform. And
there was the fuss about the RTGs.
  #6  
Old October 22nd 04, 11:43 AM
Robin Leadbeater
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"Peter Hayes" wrote in message
o.uk...
James wrote:

"Steve" wrote in message
...
Thursday 21, 21:00, BBC2 England


Insight into the voyage of the Cassini-Huygens spacecraft, which

has
sent back the clearest images of the planet Saturn ever seen



Excellent program I thought. Can't wait till January now!


But surely the ESA and NASA could agree on radio frequencies?


That's just the problem. They did! Both are tuned to the same frequency.
Unfortunately, it appears that nobody allowed for the doppler shift which
will put them out of tune relative to each other.

Robin




  #7  
Old October 22nd 04, 11:52 AM
Mike Murphy
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On Fri, 22 Oct 2004 10:43:12 +0100, (Peter
Hayes) wrote:
But surely the ESA and NASA could agree on radio frequencies?
The thought that the Huygens mission could have failed because the
radios were working on different frequencies amazes me. Don't these guys
test things before launch? It sounds like the HST farce where they
didn't test the telescope prior to launch.


I was surprised by this as well. After a little search of the NASA
site I found this press release from June 29, 2001:

http://saturn.jpl.nasa.gov/news/pres...10629-pr-a.cfm

where it says (amongst other things):

--- begin quote ---
After six months of analysis by the European Space Agency (ESA)-NASA
joint Huygens Recovery Task Force, senior management from both
agencies and members of the Cassini-Huygens scientific community have
endorsed the mission modifications. The analysis was undertaken after
the Huygens probe telecommunications problem was identified last
autumn.

The Cassini-Huygens mission was launched in 1997. Engineers last year
identified a design flaw in the Huygens communications system. Without
a change in flight plans, the Huygens receiver would be unable to
compensate enough for the Doppler shift in radio frequency between the
signal emitted by the probe and the one received by the orbiter. A
Doppler shift happens when the distance between a transmitter and
receiver is changing, and Cassini originally would have been rapidly
approaching Titan during Huygens' descent. This would have resulted in
the loss of important data from the probe during its trip through
Titan's atmosphere.

When Cassini arrives at Saturn in July 2004, it will, within the first
seven months, complete three flybys of Titan instead of two as
originally planned. Then, in February 2005, Cassini will resume the
rest of its four-year prime mission as originally planned, studying
the planet and its rings, moons and magnetic environment. The changes
to the mission plan will use about one-fourth to one-third of
Cassini's reserve supply of propellant. The reserve supply is carried
for unforeseen needs such as this and for possible use if the mission
were to be extended beyond 2008.

"This recovery plan will allow us to meet all of the mission's
scientific objectives," said Bob Mitchell, Cassini program manager at
NASA's Jet Propulsion Laboratory, Pasadena, Calif. "It has the
additional advantage of giving us a close look at Titan before
releasing Huygens."
--- end quote ---

Pretty mind boggling stuff Eh?

- Mike

who also thought the Horizon programme was pretty good.
  #8  
Old October 22nd 04, 01:26 PM
Jo
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In ,
Robin Leadbeater typed:
That's just the problem. They did! Both are tuned to the same
frequency. Unfortunately, it appears that nobody allowed for the
doppler shift which will put them out of tune relative to each other.


Nearly...

The article at explains it all
http://www.spectrum.ieee.org/WEBONLY...1004titan.html

Carrier doppler shift had been allowed for. They didn't allow for resulting
changes in the frame rate of the 8192 bit data blocks that modulate the
carrier. I would have expected these blocks to have had proper headers for
data synchronisation, but it looks like they were relying purely on accurate
timing, presumably to keep the electronics simple.

Jo





  #9  
Old October 22nd 04, 09:59 PM
Peter Hayes
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Jo wrote:

In ,
Robin Leadbeater typed:
That's just the problem. They did! Both are tuned to the same
frequency. Unfortunately, it appears that nobody allowed for the
doppler shift which will put them out of tune relative to each other.


Nearly...

The article at explains it all
http://www.spectrum.ieee.org/WEBONLY...1004titan.html

Carrier doppler shift had been allowed for. They didn't allow for resulting
changes in the frame rate of the 8192 bit data blocks that modulate the
carrier. I would have expected these blocks to have had proper headers for
data synchronisation, but it looks like they were relying purely on accurate
timing, presumably to keep the electronics simple.


Thanks for the link, interesting read.

It seems they were using 'off the shelf' equipment designed for Earth
orbit use, equipment that didn't have any major doppler problem.

The 'fix' is neat, though.

--

Peter
  #10  
Old October 23rd 04, 08:59 AM
John Carruthers
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Excellent program I thought. Can't wait till January now!



You don't have to........



SEKAS have Prof. John Zarnecki as one of our speakers.







November 9th TUES Prof. John Zarnecki (OU) “The Cassini-Huygens
Mission to Saturn and Titan”

An exciting and timely talk from the Principal Investigator for the
Surface Science Package

and Co-Investigator for the Atmospheric Structure Instrument for the
Huygens probe/lander

(Joint lecture with Kent Physics Centre) Canterbury, University of
Kent at Canterbury, Physics L.T. 7.30pm


--
http://mysite.wanadoo-members.co.uk/jc_atm/



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