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.)

[Guest_BruceMoomaw_*]

You'll notice that I HAVE backtracked from the Io Observer having "a good chance of being flown in the early 2020s" to "a real chance of being flown before the end of the 2020s" -- having now considered the implications of the newly announced stretchout in the New Frontiers schedule. But beyond that, I refuse to retreat.

[Guest_vjkane2000_*]

You'll notice that I HAVE backtracked from the Io Observer having "a good chance of being flown in the early 2020s" to "a real chance of being flown before the end of the 2020s" -- having now considered the implications of the newly announced stretchout in the New Frontiers schedule.  But beyond that, I refuse to retreat.

By the end of the 2020s, I'll be 75. I'd rather not wait that long, so I'm hoping for a Discovery-class mission to be proposed and accepted. One, called Volcan, was written up several years ago.

One can imagine what such a mission might look like:

Solar powered.
Number of encounters would be limited by cumulative radiation dose. Galileo experienced ~40Krad per encounter. The solar panels will likely be the limiting factor in the number of enounters. I'm not sure how quickly they degrade. The Volcan proposal include something like 3-5 enounters. Perhaps that can be stretched a bit, and/or the radiation per orbit lessened by choosing an encounter point or orbit inclination to minimize radiation.

The instrument compliment could be pretty simple: The Deep Impact Hi-Res and medium-res camera with visible imagers and near-IR spectrometers. A radiometer would need to also use the Hi-Res optics (possibly replacing the near-IR spectrometer). If the encounters will be very close, then a magnetometer would be nice.

The mission would include as many close encounters as the radiation limit will allow (probably at least 5, maybe 10?) spaced 1 or more months apart to allow time series studies of changes. After that limit is reached, perijove would be raised to a safe distance to allow continued observations from a distance (which is why I'd like to see something with the optical capabilities of the Deep Impact Hi-Res on the craft). Long distance time studies would continue as long as funding would allow. During this phase, observations of Jupiter or encounters with Ganymede or Callisto (radiation at Europa is too high) could be possible, but add to mission complexity and cost.

[JRehling]

The mission would include as many close encounters as the radiation limit will allow (probably at least 5, maybe 10?) spaced 1 or more months apart to allow time series studies of changes.  After that limit is reached, perijove would be raised to a safe distance to allow continued observations from a distance (which is why I'd like to see something with the optical capabilities of the Deep Impact Hi-Res on the craft).

A difficulty with eccentric orbit orbiters that zoom in to observe inner satellites at periapsis only is that if the mission is not very long, you observe only a limited range of lighting conditions, and with tidally-locked rotations, you observe a limited range of longitudes. This is why we've seen one side of Io much better than the other (from Galileo) and keep seeing similar longitudes of Titan -- even as late as next spring, we still won't have decent coverage of all Titan longitudes, despite many flybys.

If an orbiter could go into an eccentric polar orbit around Jupiter, it might be able to observe Io (or Europa) both coming and going (when the satellite is nearer to the Sun than Jupiter, or farther). But that's not going to be cheap in delta-v.

I'm not sure what tradeoffs are possible, but getting multiple close flybys of the same hemisphere doesn't get you a lot that a single flyby doesn't. (See Mariner 10.) Of course, the long-duration observations from farther out are all fine and good.

I'll chime in that the capability for continuous observation of Io, at least to the point of observing the several larger hotspots, from Earth had gotten pretty good, although I'm not aware of the details of any such surveys that may be ongoing.