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Unmanned Spaceflight.com _ Exploration Strategy _ Outer Planet Flagship Selection & Definition
Posted by: vjkane Sep 5 2008, 04:03 PM
Given the renaming of the forum to Exploration Strategy to discuss mission selection and definition, I thought I'd create this new discussion thread to continue the discussions that had previously been in the Outer Solar System > Jupiter forum. Since the options are either Jupiter or Saturn as targets, this seems to be a more suitable place.
I repeat here a previous post to the old forum with a link to the latest status report on the selection and definition:
An August update on the two possible outer planet missions has been posted at: http://www.lpi.usra.edu/opag/flagshipOPF08.pdf
Both concepts are maturing and both look very feasible with compelling science. (I'm glad that I don't have to decide!) Report is only on the U.S. orbiter elements.
Some highlights:
Mission costs are being allowed to increase by a few hundred million dollars to enable more capable instrument packages.
Selection between Jovian and Saturnian system destination is now Feb 2009.
Risks for the Saturn mission are much lower (but appear to apply only to the orbiter element). Europa mission appears to have higher risk elements (assuming same scale used for both) because of the radiation environment.
Current plan for the Titan in situ elements is to release them early in the Saturn Titan tour, which means a long period (12-18 months?) with only periodic relay by the orbiter and direct communication with Earth used in between.
Posted by: djellison Sep 5 2008, 04:06 PM
That was part of the motivation in the name change
Posted by: JRehling Sep 8 2008, 05:32 AM
[...]
Posted by: vjkane Sep 9 2008, 07:54 PM
I think that the risk in the presentation refers to the risk that the capabilities can be implemented within the schedule and dollars allocated and then perform as expected.
John brings up another source of risk -- will our goals change? I think the Titan people would say that we already know enough to know what the high priority goals are short of the truly unexpected.
Posted by: Mariner9 Sep 10 2008, 06:07 PM
I certainly expect new discoveries to keep coming in from the Cassini data, for years to come. But how signifigant will those discoveries be? Impossible to be certain, that's what makes it a 'discovery', but you can at least hazard a guess based on history. The more data you have, the less signifigant new findings tend to be. (a huge generalization, to be sure)
I think it is a fairly low risk that we will find something new and fundamental in Cassini Titan data (either previously collected and unanalyzed, or found in the upcoming extended mission) so important that it completely overshadows all other questions and goals for the currently defined Titan Orbiter mission.
I think we are just as far along on the learning curve as we were when the Europa orbiter was identified as the main Jupiter system target following Galileo. Keep in mind, that decision was made in 1999 (3 years into the Galileo mission), and nearly ten years later Europa is still the main target of interest, and the goals of the Europa flagship mission today are not all that different from the goals of 1999.
Posted by: JRehling Sep 10 2008, 07:44 PM
[...]
Posted by: Mariner9 Sep 10 2008, 08:17 PM
I think all your points are good ones, but I would come to a slightly different conclusion.
I agree with you about Mars being a fascinating and complex world. But in the Mars Exploration Program they are not flying a mission, analyzing all possible data, and then starting planning for the next mission. They are identifying the most important goals based on the current knowledge, and using that information to prepare for later (and not the next) mission(s). Meanwhile, the current sets of missions are still returning data (or in some cases haven't even flown yet). The discoveries they make might be the basis for a later mission, but 6-10 years down the line.
You cite a good example with the gullies that MGS discovered, they were indeed found after a great deal of information about Mars had been returned. But would anything have changed in MER, MRO, Phoenix, or MSL if we had waited until after 2000 to start planning them? In fact, even though the genesis of Phoenix started long before 2000 (since it is based on Mars 98 mission plans), we still flew it. The MER landing site selection occured long after the discovery of the gullies, and yet we didn't choose to land next to one (largely because of engineering limitations I will grant you).
I'm reminded of something I heard a lecturer say about the field of archeaology. Every generation they learn better ways of examining sites, and they cringe when they look back at previous generations and think about what might have been lost because (based on modern standards) the sites were damaged as they were examined. He said that they always wonder if they should wait, and let things mature more before they continue digging things up. But that would mean stopping everything dead in its tracks, and the damage done to the advancement of science by stopping seemed much worse than waiting for the day that they know how to do it perfectly.... because for one thing, that day will never come. There will always be better and better methods over the horizon.
I think the opportunity lost with Titan would be waiting until all information possible has been extracted from each mission before even planning and starting on the next one. I don't think it is necessary.
Posted by: JRehling Sep 10 2008, 08:53 PM
[...]
Posted by: Mariner9 Sep 10 2008, 09:20 PM
Really? I didn't realize that there were some concerns in advance about the Gusev landing site. Clearly it didn't turn out to be an ancient lake bed as hoped, but I thought that was completely determined after the fact and no one had raised concerns before hand. I'm not excluding the possibility, I just hadn't heard that before now (which is why I love this site, I'm always learning things). If you run across a resource for that debate I'd love a link to it. If it was covered on this board, I probably missed it because there is so much to follow over on the Mars forums.
Posted by: vjkane Sep 10 2008, 10:15 PM
I think that the Titan orbiter science is pretty well understood at this point, and the chances of future Cassini discoveries making a major change are probably acceptably small.
Similarly, the knowledge of the atmosphere is sufficient to design a balloon probe.
The problem that I see is that we know only course information about a small fraction of the surface. Therefore, optimizing the landing site is unlikely given the plan to release the in situ elements before the orbital studies from a Flagship craft begin. I believe that's why a lander has been targetted for either the widespread dune areas or one of the lakes (large, homogeneous areas that are interesting in their own right). Also, long term studies of seismology and weather can be done from almost any location (or put another way, if you get only one lander, then where you put it is less important for these kinds of studies).
On the other hand, my programmatic management experience suggests to me that we are still very early in the architecting of the optimal in situ mission elements. (1 lander or two? big balloon payload or smaller? etc.)
Both Titan and Europa are hard to study from orbit. Titan because the haze limits optical instruments, the atmospheric depth makes subsurface radar sounding hard, and SARs eat up a lot of budget and data bandwidth. Europa, on the other hand, sits in the middle of a literally killing radiation field.
Still, given all this, I come down on the side of Titan if the Europeans contribute a meaningful in situ element. We can hypothesize a lot about the internal structure of these large icy moons. A seismometer on Titan could increase our knowledge by several orders of magnitude and that isn't possible for Europa (with current technologies and budgets). (Although the proposal for the lake lander would eliminate this instrument.) Similarly, we can use a balloon to explore the atmospheric chemistry, wind patterns, and surface/subsurface. So Titan wins on the grounds of being in the top 3 most interesting solar system bodies and the ability to do long term in situ studies.
However, if the Europeans don't contribute the in situ elements, then the Europa orbiter studies more interesting bodies with a modern set of instruments than does the Titan orbiter. (While the Titan orbiter will increase our knowledge of Enceladus, it won't add much to our knowledge of Saturn itself or the other moons. A Europa mission would make up for the Galileo antenna problem and bring modern instruments to bear vs. Galileo's mid-1970 technology instruments.)
Posted by: JRehling Sep 10 2008, 10:16 PM
[...]
Posted by: Vultur Sep 13 2008, 12:40 AM
Would a Europa mission be reasonably able to detect sub-ice life? If not, I think we'd learn more from Titan; if so, then I personally would make that target #1 in the solar system. Isn't it the most likely place to find life?
Posted by: ngunn Sep 13 2008, 07:05 PM
The short answer is no. It's not one of the currently proposed mission's objectives and probably couldn't be attempted yet even if unlimited funds were available.
Posted by: ugordan Sep 13 2008, 07:18 PM
It's nitpicking, but if unlimited funds were available... well, let's just say people in 1961 didn't believe landing a man on the Moon was possible either;)
Posted by: Vultur Sep 13 2008, 07:49 PM
OK. Then what would the Europa mission's objectives be? I thought Europa was mostly interesting because of the possibility of life...
Posted by: Mariner9 Sep 13 2008, 08:16 PM
It is true that Europa's (almost near certain) subsurface ocean has the very strong potential to harbor life.
Even if it did not have life, Europa is geologically unique. Its surface is mostly water ice and is very active, showing very few craters. The composition of the different ices on its surface is unclear, particularly in the areas nearest to the more recently active ridges (somewhat inaccurately called triple bands). The Chaos regions show what look like iceburgs floating in a sea which melted, then froze again. It is now thought those Chaos regions did not have a liquid surface, but were instead a type of tectonic feature not seen on earth.
There are huge ridge features called cycloids which span hundreds of kilometers, and at least one article I read speculated that when they form that the major faulting takes place over a span of hours or days (as opposed to years).
It goes on from there.
I think Europa's potential as a life bearing world is what puts it to the top of the list over other bodies like Io, but even if you take away the life element it is still a most interesting place.
Posted by: JRehling Sep 13 2008, 08:47 PM
[...]
Posted by: Greg Hullender Sep 13 2008, 10:54 PM
I know at least one who did. :-)
http://history.nasa.gov/moondec.html
--Greg
Posted by: ugordan Sep 14 2008, 04:48 PM
That's exactly why I put in 1961.
The majority of other people at that point in time felt it couldn't be done.
Posted by: vjkane Sep 16 2008, 02:26 AM
John -
I find your arguments about the nth question compelling. I wonder if a New Frontiers class mission could significantly improve our ability to target a follow on flagship mission. If not, then we'll be stuck in this "we don't know enough to optimally target a Titan flagship mission" loop forever.
Posted by: vjkane Sep 23 2008, 09:01 PM
Could we end up with a mission to both Europa/Jovian system and Titan out of the flagship definition process?
The possibility occurred to me as I was reading through the EuroPlanet abstracts. A bit of background. For Titan, ESA is looking at a balloon and lander, with the current emphasis apparently on a short-lived lake floater. The plan of record (to the extent there is one, but this is what's in the abstracts) is for the in situ elements to be released before the orbiter does the insertion burn. The orbiter then does 18 months of an orbital tour around Saturn before finally entering into a 1,500 km high circular orbit.
There are a lot implications to this plan. First, the lake floater needs a relay only for a few hours, which will presumably be done by the orbiter as it passes by Titan. Then the balloon is largely on its own and dependent on direct communication with Earth to send its data home except for brief periods when the orbiter flies by for the first 18 months. (Nominal lifetime of the balloon is given as "months.") Even after the orbiter is circling Titan, most of the balloon's data will have to be sent directly to Earth. The orbiter will have relay coverage only over a fairly thin strip along its orbit track. The movement of Titan around Saturn then will bring the balloon into this track just twice each 16 day orbit.
The net of all this long discussion is that the ESA elements of the Titan mission would be designed to operate without the orbiter. Given that, ESA could send the balloon and a short lived lander to Titan on a flyby carrier craft. This would be somewhat similar to the approached used for landers to Mars except that the carrier craft would need to have the ability to receive and relay the lander's data. NASA would still need to provide the RTG power source, and based on current launch policy for nuclear power sources, provide the launch.
Can anyone spot a flaw in this argument (especially Ralph L)?
Here are links to the relevant Europlanet abstracts:
http://cosis.net/abstracts/EPSC2008/00182/EPSC2008-A-00182-1.pdf
http://cosis.net/abstracts/EPSC2008/00202/EPSC2008-A-00202-1.pdf
http://cosis.net/abstracts/EPSC2008/00625/EPSC2008-A-00625-1.pdf
Posted by: rlorenz Sep 24 2008, 04:36 AM
There are a lot implications to this plan. First, the lake floater needs a relay only for a few hours, which will presumably be done by the orbiter as it passes by Titan. Then the balloon is largely on its own and dependent on direct communication with Earth to send its data home except for brief periods when the orbiter flies by for the first 18 months. (Nominal lifetime of the balloon is given as "months.") Even after the orbiter is circling Titan, most of the balloon's data will have to be sent directly to Earth. The orbiter will have relay coverage only over a fairly thin strip along its orbit track. The movement of Titan around Saturn then will bring the balloon into this track just twice each 16 day orbit.
Can anyone spot a flaw in this argument (especially Ralph L)?
Yes.
You are substantially understating the ability of the orbiter and balloon to communicate outside close Titan
flybys - for those months, the orbiter will still only be a million km or less away. So direct-to-Earth is not
the main conduit (although that helps fill in gaps when orbiter and balloon are on opposite sides of Titan)
You (and NASA and ESA) will hopefully be making your judgements on the final reports when they are
complete rather than meeting abstracts, though I know that's all there is right now. I could believe
there might be a presentation at the November OPAG meeting that might be the next public release of
information.
Posted by: vjkane Sep 24 2008, 05:35 AM
I had wondered about long distance relay from the balloon to orbiter. That is one big antenna on the orbiter...
Still, if NASA decides on a Jovian mission, I'd still want ESA to select a Titan in situ mission over a Ganymede orbiter. That is, unless I have again substantially misunderstood how little data could be returned by a balloon at Titan without a relay.
Thanks for the clarification, Ralph. I was hoping it wasn't this dire, but after several OPAG presentations and abstracts ignoring the issue, I got to thinking...
Posted by: ustrax Feb 12 2009, 09:42 AM
Got e-mail from Athena Coustenis:
"The Final and Joint Symmary Reports of the Europa Jupiter System Mission (EJSM) and the Titan Saturn System Mission (TSSM) are now posted in their Public Release version on the OPFM website:
http://opfm.jpl.nasa.gov
From what we know, the NASA ESA Decision Board meeting will be taking place as scheduled today. The joint announcement may be made early next week."
Posted by: volcanopele Feb 12 2009, 10:29 AM
Thanks for the update on when the downselection will be announced. I will try to post some summaries of the main final report for JEO on http://gishbar.blogspot.com (with a focus on Io science) while Van Kane will summarize the Titan Orbiter report on his blog, http://futureplanets.blogspot.com
Posted by: volcanopele Feb 12 2009, 11:56 PM
The ESA Assessment reports for the Jupiter Ganymede Orbiter and the Titan In-Situ Elements are now online:
Jupiter Ganymede Orbiter: http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=44188#
Titan In-Situ Elements: http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=44185#
I have also posted a second part of my look at the potential for Io science with the Europa/Jupiter System Mission on my blog: http://gishbar.blogspot.com/2009/02/io-science-with-ejsm-part-deux.html . Don't forget to check out some of my previous posts on the Flagship Mission selection process at http://gishbar.blogspot.com/search/label/Flagship%20Mission .
Posted by: ngunn Feb 18 2009, 02:32 PM
Time is running out to vote for your favourite at 'futureplanets':
"Europa Jupiter System Mission
Titan Saturn System Mission
Show results
Votes so far: 263
Hours left to vote: 6"
What does Van Kane know?? 
Posted by: remcook Feb 19 2009, 08:30 AM
Jupiter it is then...
http://www.spaceflightnow.com/news/n0902/18outerplanets/index2.html
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