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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Jun 20 2008, 05:41 PM
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Member Group: Members Posts: 706 Joined: 22-April 05 Member No.: 351 |
An additional presentation from the Flagship instruments meeting has been posted on the architecture options for the Titan in situ mission. http://opfm.jpl.nasa.gov/community/opfmins...ppresentations/ and scroll down to TSSM In Situ Element Architecture, Flight Systems, & Planning Process, Christian Erd (ESTEC) (Download) (PDF, 31.16 MB).
Some thoughts on the architecture options: First, the in situ elements are released to enter the Titan atmosphere prior to the orbiter's Saturn insertion burn. This means that the availability of the orbiter for data relay for the first ~18 months will be limited to the occasional orbiter flybys of a few hours duration each. When the orbiter is not in place to act as a data relay, then bit rates for direct communication to Earth are very low. (And during any given flyby, the geometry between the balloon or lander and the orbiter may be very poor.) Since Titan is not a friendly environment, having to wait ~18 months for significant data return from the in situ elements is a big risk. The balloon, for example, is being designed for a 1 year lifetime. (In reality, it would probably last longer if it survives the first year, but this is a major mission risk issue.) The in situ mission options discussed consist of a balloon and one or more landers. When NASA did it's billion dollar mission studies for Titan, the balloon option was estimated to have a cost between ~$1.3-1.8B depending on the costing assumptions. Assuming the lower cost (which would have much more development risk), this seems to put the cost of the Titan in situ elements above the budget that ESA is considering (<650 euros). The NASA cost estimate has to be adjusted because it included a launch vehicle that ESA would not pay for (subtract ~$300m) and ESA does not fund instrument development (subtract ~$100M?). (There was also a small carrier craft included in the NASA budget, but it appeared to be pretty minimal. Subtract another $50-100M?) This still leaves the cost of a balloon only element for the NASA study at around $800-850M (assuming the lower end of the price range). At official exchange rates, the 650 euro budget would cover this. However, 1 euro spent in Europe does not seem to buy $1.5 worth of goods or services. (That is, the exchange rate is based more on discrepancies in interest rates than on purchasing power.) If a euro purchases about $1 worth of goods and services spent in Europe, then there seems to be a budget mismatch, even for the most aggressive (and high risk) cost estimate. And the NASA study did not include any landers in the balloon mission. My net take on all this is that the in situ Titan options have significant mission (very limited data relay for the first 18 months) and budgetary risk. I really like these options, so I hope that someone more knowledgeable than I (Ralph...?) shows me the error in my analysis. -------------------- |
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Jun 21 2008, 10:21 PM
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Member Group: Members Posts: 611 Joined: 23-February 07 From: Occasionally in Columbia, MD Member No.: 1764 |
The in situ mission options discussed consist of a balloon and one or more landers. When NASA did it's billion dollar mission studies for Titan, the balloon option was estimated to have a cost between ~$1.3-1.8B depending on the costing assumptions. Assuming the lower cost (which would have much more development risk), this seems to put the cost of the Titan in situ elements above the budget that ESA is considering (<650 euros). The NASA cost estimate has to be adjusted because it included a launch vehicle that ESA would not pay for (subtract ~$300m) and ESA does not fund instrument development (subtract ~$100M?). (There was also a small carrier craft included in the NASA budget, but it appeared to be pretty minimal. Subtract another $50-100M?) This still leaves the cost of a balloon only element for the NASA study at around $800-850M (assuming the lower end of the price range). At official exchange rates, the 650 euro budget would cover this. I'm not a costing expert, but I thought the $1B-box study put the standalone balloon too high. But anyway, 1. I think the cruise stage, plus the cruise operations, add up to way more than the $50-100 you have above 2. Who says ESA is paying for a balloon ? It might be that CNES provides it. Either way, the detailed ESA study of the in-situ elements is just happening now, so tempting as it is to second-guess everything, it may be premature to make assertions of budgetary incompatibility. |
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