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Old 02-08-2015, 11:30 AM   #31
K_Jameson
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 [SIZE="3"]The Planetary Society: "It's Official: We're On the Way to Europa"
Forum Orbiter Italia is already on the way...

http://orbiter-forum.com/showthread.php?t=32148



(sorry for the broken links in the images)
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Old 02-08-2015, 03:55 PM   #32
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 In the spirit of Galactic Penguin, I have changed the titles of the Europa Clipper and JUICE mission threads to something more creative.

Now, about a year ago, evidence of geysers coming from Europa was discovered by Hubble. Unfortunately, recently analyzed data from the Cassini Jupiter Millennium Flyby shows that if Europa has geysers, they erupt only on occasion and may be less powerful than thought. This has implications for trying to sample Europa's ocean without landing on the surface and how much interaction the ocean has with the surface.

JPL: "Signs of Europa Plumes Remain Elusive in Search of Cassini Data"
Dr. Caroline Porco prefers making a mission to Enceladus instead since it is virtually certain now the plumes there extend to the subsurface ocean:

https://www.facebook.com/carolynporc...794158414387:0

Bob Clark
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Old 02-08-2015, 11:19 PM   #33
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 Dr. Caroline Porco prefers making a mission to Enceladus instead since it is virtually certain now the plumes there extend to the subsurface ocean:

https://www.facebook.com/carolynporc...794158414387:0

Bob Clark
An Enceladus sample return (with a better mass spectrometer than Cassini) can be flown within the Discovery budget.

A flagship mission to Europa was already chosen over one to Saturn in the Planetary Decadal Survey for reasons, I recall, including the relative maturity of the proposals. But exploration of Enceladus can be done along with Europa, the only problem I see with a sample return is that it would be a Category V Restricted in terms of planetary protection.

To be clear, I still absolutely agree that Enceladus (and Titan) also deserve more attention. Unfortunately funds are pretty limited.

I just recalled the other Discovery proposal to Enceladus.

Last edited by Unstung; 02-08-2015 at 11:43 PM.
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Old 02-09-2015, 04:58 PM   #34
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Originally Posted by Unstung View Post
 An Enceladus sample return (with a better mass spectrometer than Cassini) can be flown within the Discovery budget.
A flagship mission to Europa was already chosen over one to Saturn in the Planetary Decadal Survey for reasons, I recall, including the relative maturity of the proposals. But exploration of Enceladus can be done along with Europa, the only problem I see with a sample return is that it would be a Category V Restricted in terms of planetary protection.
To be clear, I still absolutely agree that Enceladus (and Titan) also deserve more attention. Unfortunately funds are pretty limited.
I just recalled the other Discovery proposal to Enceladus.
Thanks for those links to the http://futureplanets.blogspot.com site, a very informative blog on planetary science I hadn't seen before.

Bob Clark

---------- Post added at 11:58 AM ---------- Previous post was at 10:41 AM ----------

Sunday, February 8, 2015
Let’s Send a Private Mission to Europa, Expert Says.
http://www.astrowatch.net/2015/02/le...to-europa.html

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Old 02-23-2015, 02:28 AM   #35
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SpaceNews: "Europa Clipper Team Seeking Earlier Launch"
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The team working on the leading concept for a mission to Europa believes it can be ready for launch as soon as 2022, several years ahead of the schedule NASA officials recently stated.

In a Feb. 19 presentation to NASA’s Outer Planets Assessment Group (OPAG) at the Ames Research Center, Barry Goldstein, Europa Clipper pre-project manager at the Jet Propulsion Laboratory, said they are taking advantage of additional funding provided by Congress to accelerate work on the mission.

“It’s our responsibility to drive as hard as we can to launch as early as we can,” he said. “Our best-case scenario is launching in an opportunity that opens up in May to June of 2022, and we’re holding to that.”

That schedule is more aggressive than what NASA officials said Feb. 2 when they released the agency’s 2016 budget proposal. That proposal included $30 million for a Europa mission, with the projected budget gradually increasing to $100 million per year by 2020.

“For the first time, this budget does assume a five-year funding profile for a mission to Europa,” NASA Chief Financial Officer David Radzanowski told reporters in a Feb. 2 conference call. “The current funding profile would assume a launch in the mid-2020s.”

Congress, though, has been more generous with funding for a Europa mission, appropriating about a quarter billion dollars in the last three years, including $100 million for 2015. That has allowed NASA to accelerate risk reduction work on the Europa Clipper mission design and seek proposals for instruments the spacecraft will carry.

“Congress has really been quite generous,” said Jim Green, director of NASA’s Planetary Science Division, in a separate presentation at the OPAG meeting. “We’re forward funding a lot of work.”

[...]

It has been determined that solar panels will degrade less in the Jupiter environment than plutonium degrades naturally. So a mission that uses solar will be able to run longer extended missions and will conserve NASA's precious plutonium supply.

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Old 02-23-2015, 04:43 AM   #36
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 It has been determined that solar panels will degrade less in the Jupiter environment than plutonium degrades naturally. So a mission that uses solar will be able to run longer extended missions and will conserve NASA's precious plutonium supply.
Whoa. I wouldn't have expected that, especially considering how harsh the Jupiter environment is. It's good to know, though, and makes the scarcity of plutonium seem less dire.
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Old 02-23-2015, 08:17 PM   #37
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The problem with solars at Jupiter is that such a large array can make the spacecraft far less manoeuvrable and poses potential limitations on the image sharpness because of vibrations from those huge panels. Also, the array must be almost constantly pointed at the sun, posing constraints on the liberty of pointing the instruments at the targets. A steerable scan platform would be welcome, but adds complexity and costs.

Last edited by K_Jameson; 02-23-2015 at 08:20 PM.
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Old 02-24-2015, 12:13 AM   #38
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The Europa Clipper will have a rechargeable battery so it can point away from the sun and survive in Europa's shadow during each brief flyby. But the spacecraft has to turn its entire body to make observations with different instruments.

I did not think that large solar arrays will make the spacecraft less maneuverable and more susceptible to vibrations, good point. I'm just confident that the scientists and engineers know what they are doing and will design a spacecraft that can complete all of its objectives, if not more. They are working on a shoestring budget compared to previous proposals.
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Old 02-24-2015, 09:52 AM   #39
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 The Europa Clipper will have a rechargeable battery so it can point away from the sun and survive in Europa's shadow during each brief flyby.
Even the batteries degrades over time... anyway i agree with you: surely the engineers will make a great work with the solar-powered Europa Clipper, although some drawbacks remains from my point of view. Maybe the claims about the small degradation of the solar cells are a little optimistic and "propagandistic"... they must advocate the mission and achieve consensus..

...I'm perhaps a little biased because RTG are the "iconical" power sources for the outer planets probes...
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Old 02-24-2015, 01:39 PM   #40
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RTG's simplify the design of the whole vehicle. The power subsystem has fewer parts, you don't need to worry about sun-pointing or tracking, and the vehicle is lighter, as well as steadier pointing. And the degradation rate of the plutonium is easy to model, whereas with batteries and solar cells there are various ways to manufacture them so it's harder to anticipate exactly how fast they'll break down.

But the reality is that plutonium is in short supply, and solar powered space tech is fairly advanced at this point, so it's certainly not a show-stopper.
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Old 02-24-2015, 01:52 PM   #41
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I agree.

What about a non-plutonium RTG? I heard something about Americium-241. It is far less efficient than plutonium, but cheaper and easiest to produce.
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Old 02-24-2015, 02:07 PM   #42
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 I agree.

What about a non-plutonium RTG? I heard something about Americium-241. It is far less efficient than plutonium, but cheaper and easiest to produce.
And also far less suitable for spaceflight applications, since it produces only 1/4th of the power of Pu and generates more harmful radiation that must be shielded for not disturbing science.
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Old 02-24-2015, 02:14 PM   #43
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Indeed. Is what i said. Nevertheless, Americium is taken into account for space applications.

http://www.lpi.usra.edu/meetings/nets2012/pdf/3043.pdf

"While the specific power of a 241Am fuelled RTG is unlikely to match that of 238Pu fuelled units (except perhaps at small size) the design work undertaken provides confidence in the capability and performance of potential 241Am systems for future space mission opportunities."
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Old 02-24-2015, 02:41 PM   #44
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Yeah, but the feasibility for spaceflight does not mean that they are automatically better than other energy sources. It just means that they are qualified to be even considered as alternative.
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Old 02-24-2015, 02:50 PM   #45
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 Yeah, but the feasibility for spaceflight does not mean that they are automatically better than other energy sources.
I don't say that Americium is automatically the better alternative... only that is AN alternative... ;-)

Last edited by K_Jameson; 02-24-2015 at 02:53 PM.
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