Nasa Picks "juno" As Next New Frontiers Mission Options

[Guest_BruceMoomaw_*]

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.)

[edstrick]

Why is it spinning?
Field and Particles instruments and gravity measurements really like spinning spacecraft. You cross-calibrate magnetometer data perpendicular to the spin axis, and get "whole sky" coverage with the particles instruments you simply can't get with 3-axis controlled spacecraft. Cassini (before program de-scoping) was going to have two scan platforms: One for the imaging and remote sensing spectrometers, One (or was it two?) for scanning the charged and neutral particle spectrometers across the sky. Voyagers and the gutted Cassini had to do special maneuvers to orient particle detectors in desired look-directions. With a scan platform, Voyager still could do remote sensing. Cassini is so crippled by the descoping that it has to constantly trade-off between science investigations as there is no scan platfor at all, and it has to stop all remote sensing to replay data back to Earth, then not transit 2/3 or so of the time while it's taking data. We'd have far more pictures from the mission (better mapping coverage, etc) if they hadn't lost the scan platform to bad management and radical surgery mandated by bean counters.
Oh.. Gravity studies are much helped by the stable attitude and no thruster firing of spin stabilized spacecraft. Note that the "Pioneer Effect" (teeny sunward directed apparent acceleration of the Pioneers in deep space) is utterly undetectible on the Voyagers, due to trajectory peturbations by attitude control thruster firing.