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Posted by: Paolo Oct 19 2006, 06:23 PM

While researching for my book on solar system exploration two questions have surfaced:
1) In some articles the vidicon sensor of Voyager 2 was said to be 50 per cent more sensitive than that of its sister. Was it just by chance or were the better sensors actually mounted on the probe flying the JSUN trajectory?
2) At the time of the Neptune flyby the Goldstone DSN antenna was arrayed with the Very Large Array, Canberra was pooled with Usuda in Japan. Why wasn't Madrid arrayed with, for example, the Effelsberg radiotelescope in Germany? Was it because Neptune would be very low in the German sky at the time of encounter?

Posted by: tasp Oct 20 2006, 12:22 AM

My recollection of the camera sensitivity issue was that both tubes met specs, one was better though, and fortunately, it wound up on Voyager 2. IIRC, Bruce Murray might have mentioned that in his book. Might have been the Voyager Neptune Travel Guide, too.

I think you are correct about the dish arrays, IIRC, at least for the Uranus encounter, the closest approach and on board tape recorder playback occured when Voyager 2 was over Australia.

Posted by: Analyst Oct 20 2006, 06:31 AM

1) It was known (and hoped) well before launch Voyager 2 could travel to Uranus and maybe Neptune. So I guess they allocated the more sensitive vidicon sensor to Voyager 2. It was hoped to install an improved IRIS on Voyager 2, but it was not finished and tested until after launch.

2) Canberra was arrayed with Parkes, Australia. The antenna in Japan was used for the occultation (radio science), not for data transmission.

Analyst

Posted by: edstrick Oct 20 2006, 09:34 AM

Besides an antenna, you need specific reciever hardware for telemetry reception. It's like trying to read FM signals with an AM receiver designed to operate at FM frequencies <technically bad analogy, but youi get the idea>

Posted by: Paolo Oct 20 2006, 06:14 PM

And in fact the VLA had modifications to receive Voyager's X-band transmissions. But I am wondering why Effelsberg was not used. After all, it had been used to track Helios

Posted by: edstrick Oct 21 2006, 10:44 AM

Helios *MAY* have only had S-band communications, which was the DSN standard for over a decade.

Posted by: edstrick Oct 21 2006, 11:18 AM

Random note on the Voyagers re an above comment on the vidicon sensativities. I don't know about sensativity, but the Voyager 2 narrow angle (I think) vidicon had lower noise levels than Voyager 1's.

Posted by: JRehling Oct 21 2006, 07:15 PM

FWIW, Voyager 2 was launched 16 days before Voyager 1, so the better equipment went up with the first craft launched.

Also, Voyager 1 had a contingency of visting Pluto, which was sacrificed in order to provide a better flyby of Titan. At the time of a putative flyby, though, Pluto was actually closer to the Sun than Neptune, so Neptune "deserved" the better optics more.

I'm not sure *when* the decision was made re: Titan/Pluto. I can't think of any reason why the decision needed to wait until after the craft had been launched, so I guess it was made before launch; anyone know for sure?

Posted by: edstrick Oct 22 2006, 09:43 AM

Titan was a maximum high priority target at Saturn since a conference or workshop focussed on the moon and it's atmosphere about 1975 or so. Voyager 1 ALSO had an absolutely do-not-exclude radio ring occultation sequence that may have precluded a pluto flyby as well.

Posted by: elakdawalla Oct 23 2006, 08:49 PM

I'm not sure about the date, but Dave Seal gave a lot of details about the decision in his guest blog entry.

http://www.planetary.org/blog/article/00000708/

--Emily

Posted by: AlexBlackwell Oct 23 2006, 11:47 PM

You probably already know about this reference but in case you don't, I highly recommend Voyager Tales[i] by David Swift, which I mentioned in http://www.unmannedspaceflight.com/index.php?s=&showtopic=1986&view=findpost&p=34802 several months ago. I think both of your questions may have been addressed in that book.