Nasa Picks "juno" As Next New Frontiers Mission |
Nasa Picks "juno" As Next New Frontiers Mission |
Guest_BruceMoomaw_* |
Jun 1 2005, 10:10 PM
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Guests |
http://www.nasa.gov/home/hqnews/2005/jun/H...rontiers_2.html
Yeah, I know it ain't Saturn, but we don't seem to have any proper slot for Jovian news -- including yesterday's totally unexpected announcement that Amalthea's density is so low as to suggest that it's a highly porous ice object; maybe a captured Kuiper Belt Object reduced to rubble by infalling meteoroids. As Jason Perry says, this might explain those previously mysterious light-colored patches on Amalthea -- they may be its underlying ice, exposed by impacts that punched through the layer of sulfur spray-painted onto it by Io. Scott Bolton has been pretty talkative to me already about the design of Juno. It certainly won't be as good in the PR department as Galileo or Cassini, but it DOES carry a camera -- as much for PR as for Jovian cloud science, according to Bolton. And since the latitude of periapsis of its highly elliptical orbit will change radically during the primary mission, I wonder if they might be able to set up at least one close photographic flyby of Io and/or Amalthea? (I believe, by the way, that this selection is a bit ahead of schedule -- and it certainly indicates that NASA's science program under Griffin won't be a complete slave to Bush's Moon-Mars initiative.) |
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Guest_BruceMoomaw_* |
Jun 15 2005, 10:17 PM
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According to the Space.com article, it will indeed take some movies of cloud patterns -- although I don't know how many there will be. (It's important to keep in mind that Juno's com rate will be much lower than Galileo's was planned to be; and images require MUCH more bits than any other type of data the craft will send.)
I've recently learned that the camera will be a slightly modified version of the descent imager for the 2009 MSL -- which means it will take 2-D images instantanteously rather than using the one-line "pushbroom" technique, and that all three colors will be imaged simultaneously rathern using a filter wheel. This means that -- if the spacecraft's spin axis is simply pointed in the right direction -- it could take very rapid-fire images during a flyby of a Jovian moon, although it could store only a limited number of them. (In any case, Bolton tells me that there are currently no plans for moon flybys -- although he expressed some interest in the idea during our earlier conversations, and I think you might see it during an extended mission after the 32-orbit primary mission is over.) Even a pushbroom camera on a spinning spacecraft, however, could take far better images than the instrument on Pioneer 10 and 11 -- which was simply a single light-meter, equipped with a filter wheel, which could record data during each of the craft's rotations and use (I believe) a tiltable mirror to build up a 2-D image -- VERY SLOWLY, since the Pioneers didn't spin that fast. (By contrast, a 1-line CCD array on a spinning craft can build up a high-res 2-D image during one single sweep of a spinning craft, if of course the CCD line is parallel to the craft's spin axis.) It took 40 minutes for the Pioneers just to build up a 200-line image, which by itself meant that the resolution was limited. It's important to keep in mind that the purpose of the Pioneers was just to serve as scouts of the environmental dangers that would be encountered by later, more advanced Jupiter craft -- dust in the Asteroid Belt, and the intensity of Jupiter's radiation belts -- and so they wer designed to be extremely simple and cheap, since fields and particles and dust detectors don't require complex pointing and have a low bit rate that doesn't require high-speed communcations or a tape recorder. Therefore, any additional science data from the Pioneers was regarded as gravy, and only a few simple instruments capable of working under those conditions were added: the Imaging Photopolarimeter, a UV photometer and an IR radiometer. (The images returned by the IPP, in fact, would have been regarded as successful even if their resolution was no better than that of Earth-based Jovian photos; the instrument's main purposes were to map zodiacal light and study the optical properties of Jupiter's clouds at sunlight angles unavailable from Earth.) |
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