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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#1
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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 14 2007, 08:07 PM
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#2
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Senior Member Group: Moderator Posts: 3233 Joined: 11-February 04 From: Tucson, AZ Member No.: 23 |
Yes, if the only difference were which moon was orbited, then yes, I would change my vote to the Europa Explorer. However, keep in mind that another thing that makes JSO interesting is that it can orbit Ganymede for a much longer period than EE could due to the greater radiation exposure at Europa. This provides a much longer opportunity to observe Io and Jupiter which maybe more important than the resolution gained by being at Europa (plus, with a much shorter mission at Europa, more than likely there were would be few if any observations of the rest of the system while in Europa orbit).
-------------------- &@^^!% Jim! I'm a geologist, not a physicist!
The Gish Bar Times - A Blog all about Jupiter's Moon Io |
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Nov 16 2007, 12:39 AM
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#3
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Member Group: Members Posts: 706 Joined: 22-April 05 Member No.: 351 |
I've taken a look through the JSO and Europa Explorer proposals. My take on the choice for the next Flagship mission is that there are two classes of missions being proposed. The first class is to a single moon: Europa, Titan, or Enceladus. (While the Europa Explorer will do some Jovian system science, it's instruments are not optimized for that purpose.) The JSO mission would be a true Jovian system mission with a Ganymede mission in addition. It appears to this arm chair engineer that JSO could be flown to either Europa or Ganymede with fairly few changes.
In my opinion, if the next mission is a focused moon mission, Titan is the most interesting of these three options, and the proposed Titan mission with an orbiter, lander(s), and possibly a balloon (I read somewhere that this may be dropped from the proposal, but am not sure) seems very capable. However, if given a choice between a Jovian system mission that ends orbiting either Europa or Ganymede, I think this is the most science for the buck. -------------------- |
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Nov 18 2007, 10:14 PM
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#4
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
I've taken a look through the JSO and Europa Explorer proposals. My take on the choice for the next Flagship mission is that there are two classes of missions being proposed. The first class is to a single moon: Europa, Titan, or Enceladus. (While the Europa Explorer will do some Jovian system science, it's instruments are not optimized for that purpose.) The JSO mission would be a true Jovian system mission with a Ganymede mission in addition. It appears to this arm chair engineer that JSO could be flown to either Europa or Ganymede with fairly few changes. As described, here are the difference in outcomes: Jupiter: Long-range reconnaisance more frequently and for a much longer time with JSO. Io: Long-range reconnaisance more frequently and for a much longer time with JSO. About four well-distributed close flybys with JSO. No close flybys with EE (several nontargeted flybys about 400K km in distance all with similar geometry). Europa: "Total" mapping with EE. About 7 close flybys with JSO. Ganymede: "Total" mapping with JSO. About 14 close flybys with EE. Callisto: Roughly the same outcome in either mission. (Slightly better with JSO.) Here's my question: How much of the Io long-term observations CAN'T be done from Earth for a ton less money? AFAIK, Io sports about ten major eruptions at any given time, and those are observable from Earth with adaptive optics. For a fraction the cost of JSO, build about 5 tropical observatories dedicated to Io, such that two or three of them can view Io at any time. And, hey, observe Jupiter, Uranus, Neptune, etc., every few hours as well. If you run a program like that, then JSO looks like a distant poor stepchild to EE in science value. Sure, it would provide some nice close-ups of Io, but Galileo didn't totally skimp on those. And the value of those would be more than made up for by the fact that EE would provide "total" mapping of a world of primary interest (Europa) instead of a world of secondary interest (Ganymede). The key with Europa is that a survey with selected, partial coverage at top resolution might miss a landing site of unique value, eg, over a hot spot where the ice shell is thinner/softer. None of the other moons have any potential payoff of that kind, and JSO would only provide a chance at finding such a place if it exists. I'd say that EE is the better mission by far if we do what we should and track Io (and all the gas giants) consistently from here a few AU away. I'd add that I see a lot more value to a few Io flybys than the 14 Ganymede flybys if the EE plan could be tweaked like that. Plan JSO for the distant future, and EE could plan on skipping all Ganymede science except where programmatically convenient (gravity assists). My lone-wolf conjecture on Europa vs. Enceladus is that Europa's ocean is likely more interesting than Enceladus's because it's "dirty". Even if water is key to life, we can also say that 100% pure water is inherently incompatible with life. From what we've seen so far, Enceladus's water is not quite 100% pure, but doesn't feature many complex compounds. I could see it being a reservoir of window-washing fluid of no astrobiological potential. Meanwhile, we can *see* that Europa's innards have some interesting goop in them; otherwise, the triple bands would be white, not tan. Titan deserves a heck of a mission, too, but I think it'll merit waiting for Cassini finishing its reconnaisance before completing that design. Europa had its last close-up about a decade ago; it's due. |
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Nov 19 2007, 01:37 AM
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Member Group: Members Posts: 611 Joined: 23-February 07 From: Occasionally in Columbia, MD Member No.: 1764 |
>Here's my question: How much of the Io long-term observations CAN'T be done from Earth for a ton less money? AFAIK, Io sports about ten major eruptions at any given time, and those are observable from Earth with adaptive optics. For a fraction the cost of JSO, build about 5 tropical observatories dedicated to Io, such that two or three of them can view Io at any time. And, hey, observe Jupiter, Uranus, Neptune, etc., every few hours as well. ..... Interesting question. I think there is a lot of great science to be had from planetary monitoring (20 mins per target per night would do fine in most cases) of io's eruptions and clouds on Titan, Uranus and Neptune, plus Venus nightside, and Jupiter/Saturn by an observatory system like you suggest . But to do a good job these need to be 10m-class facilities with AO...not cheap and NASA is in the business of building spacecraft rather than infrastructure. A lot of that science could be had by more creative scheduling of existing facilities (e.g. allowing 1/20 of a night allocations for months on end..) (A retort question - how much more science would you get by beefing up (or even restoring to higher reliability) the DSN - allowing you to downlink more (and/or lose less) data from existing missions. I bet in terms of science/$ it is a good expenditure, but infrastructure is never a sexy item to sell) As for Io - you can see eruptions are there from the Earth, identifying the location, measuring the total heat flux in a number of bands (allowing area/temperature estimates) but that doesnt give you any of the geomorphology, plume dynamics etc that a JSO would give you. |
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