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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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"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! |
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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. |
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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 |
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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. |
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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 |
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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. |
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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 |
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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 |
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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/ --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.782 / Virus Database: 528 - Release Date: 22/10/2004 |
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