OPAG Reports, Formal proposals/evaluations of future outer SS missions |
OPAG Reports, Formal proposals/evaluations of future outer SS missions |
Nov 9 2007, 08:28 PM
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
http://www.lpi.usra.edu/opag/announcements.html
That's one little URL with a lifetime's worth of reading material. Three detailed studies are available in PDF format. The missing body is Titan, which will be the subject of a forthcoming report. The three focus missions are: Europa Explorer: Fairly detailed description of a mission that is pretty much what Europa Orbiter would have been. Jupiter System Observer: Basically, Galileo 2 (without the antenna mishap!). The craft would start with a 3-year tour of all the Galileans, then spend 1 year in an elliptical Ganymede orbit, then the rest of the mission in a tight, polar Ganymede orbit (like MGS at Mars). That would map the heck out of Ganymede, but also be close enough to the rest of the system to make long-range observations for years. Note that Ganymede would thereby provide a lot of radiation shielding. Enceladus: where three profiles are examined in depth: Enceladus Orbiter only; Enceladus Orbiter with soft lander; Saturn orbiter with Enceladus soft lander. There's more to chew on here than I have had (or may ever have) time for, but I'll throw in my two cents' worth: Seems like a Europa-only mission would only benefit from coming after a JSO. EE would explore Europa much better than JSO would; why even have JSO observations at Europa if EE came first? In many ways, these two missions are competitive. EE would have the big payoff, but JSO seems like basic recon that would prime EE, especially giving specs on radar performance. But if we waited til JSO was 4 years into its mission before completing design of EE, then put EE sometime mid-century. If an Enceladus mission included a Saturn orbiter, then maybe the same orbiter could provide data relay for separate Titan elements. However, a lot of the Enceladus science goals would require an Enceladus orbiter, so I don't think a Saturn orbiter for Enceladus/Titan will win out. Note that Enceladus orbital velocity is low enough that the craft could manage to take lots of hits from ice pellets and survive. Put a bulletproof vest on the craft and let it soar through the plumes endlessly. |
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Nov 20 2007, 12:07 AM
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Member Group: Members Posts: 220 Joined: 13-October 05 Member No.: 528 |
I'm surprised that almost the entire debate seems based on the idea that the only thing interesting about Europa is that there might be life below the ice.
Have any of you looked at the pictures? Or read the articles? There is lot going on down on Europa. Cycloidal cracks. Chaos terrain. Possible periodic geysers spewing up through the cracks, staining the surrounding terrain with various salts and compounds. Even if you throw the whole "life" thing out, here we have a planet sized moon, a huge ice pack covering a global subsurface ocean, with a large diversity of geologic activity. And pretty darn unique. One of the things that makes it so fascinating is that no other object in the solar system looks anything at all like it. Now, as to what can you learn with orbital vs. flyby? There are at least two things you can't do with flybys. A laser altimiter in orbit can measure the flexing of the surface due to tidal forces as Europa moves through it's orbit. That flexure is the most reliable way to determine how thick the ice shell is, the radar system is really unlikely to penetrate the shell if it is more than a couple kilometers thick. The second item is a magnetometer which can measure the induced magnetic field in the European ocean. In all of Galileo's flybys they only detected a change in that induced field on one encounter. That was because you get point samples of the magnetic field, and by unhappy luck all of their flybys occured when the field would have rougly the same alignment. If you put a probe in orbit, you can really milk that information as the moon moves through the Jovian magnetosphere. All the other investigations can be done, if not as well, using multiple flybys. But those two investigations might prove to provide some of the most important revelations. JSO would undoubtably add considerably to our knowledge of the whole Jovian system. But that might be all it did: be a super-Galileo. Might not be a lot of paradigm shifts. EE would at least be an enhanced-Galileo with it's Callisto and Ganymede encounters. But in the case of Europa it has the likely potential to uncover very fundamental disocveries that would completely revolutionize our knowledge of Europa. So in my mind, if you're going to spend roughly the same ammount of money for JSO vs. EE, I'd go for EE. |
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