NASA Europa Missions, projects and proposals for the 2020s Options

[vjkane]

I'm not complaining, but I'm wondering what this mission will accomplish that the Galileo mission didn't. Both spacecraft have a magnetometer, dust detector, cameras and UV instruments. The Europa mission will also conduct flybys rather than orbit Europa just like Galileo. With the exception of the radar and more advanced versions of the instruments Galileo had, what do scientists hope to get that they couldn't get from Galileo?

You might want to read the following links that address your questions. The last talks about why, given Jupiter's radiation fields, a multifly by mission is better an orbiter:

How Clipper's instruments will study Europa

Europa Clipper design

Why a flyby mission is better than an orbiter

[Decepticon]

I was looking around for some information on Europa mission and noticed the design of the clipper mission has changed.

Looks more compact. http://www.nasa.gov/europa


Sadly I don't see a scan platform. I hope all the science instruments face in same direction.

[nprev]

Cassini doesn't have a scan platform; has not been a problem. After Voyager 2's jammed I think that there's been a shift away from them in order to minimize mechanical complexity and thus reduce the chances of mission-limiting malfunctions.

Cassini also doesn't have a furlable HGA, partially for the same reason & after Galileo. I know that some of the early designs considered one.

[Paolo]

Cassini doesn't have a scan platform; has not been a problem. After Voyager 2's jammed I think that there's been a shift away from them in order to minimize mechanical complexity and thus reduce the chances of mission-limiting malfunctions.

IIRC, Cassini's design had a scan platform up to about 1992, but lost it as a cost reduction move

[Decepticon]

Cassini doesn't have a scan platform; has not been a problem. After Voyager 2's jammed I think that there's been a shift away from them in order to minimize mechanical complexity and thus reduce the chances of mission-limiting malfunctions.

Its all ok with me as long as they have backups for each reaction wheel. Lots of failures as of late.

[nprev]

It's true that Cassini's scan platform was eliminated due to cost constraints, but by now I think it's safe to say that was a serendipitous good move.

There's an old thread that discusses this & other spacecraft moving parts issues here.

[JRehling]

what do scientists hope to get that they couldn't get from Galileo?

One of the quirks of Europa's geography is that the crust preserves a record of tidal stresses on a global scale. The pattern of faults and grooves is like a fingerprint showing the history of fault creation as Europa's crust slowly rotates, decoupled from the sub ocean surface. In this regard, seeing a quarter, half, or even three quarters of the surface leaves our understanding significantly incomplete.

On a world where, say, impact cratering was the only major contribution to surface morphology, that wouldn't be much of a problem. You could assume that the 3/4 you didn't see was about the same as the 1/4 you did see. But Europa's not that kind of place.

Galileo offered a certain level of resolution for very tiny, select regions on Europa, which sampled Europa's terrain types to some degree, but did virtually nothing at global scale. The figures and tables here give you an idea of the coverage.

http://lasp.colorado.edu/JUPITER/CH15/Ch15.html

Where you see tiny rectangles on these maps, for example,
http://lasp.colorado.edu/JUPITER/CH15/EuropaFootprintMap.jpg

…you see how little of the surface was imaged at maximal or near-maximal resolution. In many areas, Europa has not been imaged at better than 5 km/pixel resolution.

In summary, Galileo had the ability to take close-up images of any particular place on Europa, but because of the data limitations, couldn't provide a global survey. Re-flying a Galileo clone with the same instruments but unimpaired data transmission would have been an enormous boost to our understanding. Now, 20 years later, we're only planning the design of the mission that will finally begin to fill those gaps. But, as others have made clear, will be superior to a mere Galileo clone.

[pioneer]

Thanks everyone for all your replies

[vjkane]

Cassini doesn't have a scan platform; has not been a problem. After Voyager 2's jammed I think that there's been a shift away from them in order to minimize mechanical complexity and thus reduce the chances of mission-limiting malfunctions.

Cassini also doesn't have a furlable HGA, partially for the same reason & after Galileo. I know that some of the early designs considered one.

Actually, the lack of a scan platform or independently steerable antenna on Cassini has been considered a continuing nuisance, and one that future missions will want to avoid.

However, that's not so much of a problem for Europa Clipper. Cassini makes observations throughout its orbit, and so scheduling time when remote sensing can be done versus data returned to Earth has been a problem. The Clipper will make observations only in the day or two around each encounter. Almost all of the rest of the orbit will be spent returning the data to Earth. (Presumably there will be some time spent observing Europa from a distance for plumes.) So there isn't the degree of scheduling problem.

Where the lack of scan platform/steerable antenna is a problem is for precise tracking for gravity measurements during closest encounter. The last plans I saw had two small antenna that would point to Earth during the encounters.

[Decepticon]

Found a High Res image. http://www.jpl.nasa.gov/images/jupiter/eur...20150617-16.jpg


Reminds me of the old soviet Mars probes.

[tedstryk]

Actually, the lack of a scan platform or independently steerable antenna on Cassini has been considered a continuing nuisance, and one that future missions will want to avoid.

It has been a mixed bag. The design for Cassini that had one could have done imaging and radar at the same time, which would have been nice. But it wouldn't have been able to do the ultra-stable long exposures that Cassini is known for without smearing them.

[ngunn]

Great article on Europa from Mike Brown with a landing site recommendation, plus link to the new paper with free access:
http://www.mikebrownsplanets.com/2015/10/i-know-i-know.html

EDIT: Coincidentally Van Kane has just posted a couple of Europa entries, also discussing a possible lander, on his futureplanets blog.
http://futureplanets.blogspot.co.uk/2015/1...-accompany.html

[JRehling]

The Europa science and plans are exciting, as Europa news always is.

I'm trying to connect this discussion of Europa to the melt-lens theory of melt-through, in which the water that causes chaos is not arising directly from the ocean, but in lens-shaped zones of liquid water that sometimes contact the surface, but are not in contact with the ocean when they do.

It seems like the dynamics of ocean-surface contact are still way outside our understanding, and of course, the Europa mission would be the step to inform that (further? totally?).

As exciting as a lander would be, it sounds like the risk is very high. Maybe radar could be used to find a flat landing site, but the close-ups from Galileo make it look like Europa may not have a lot of flat landing sites.

[vjkane]

As exciting as a lander would be, it sounds like the risk is very high. Maybe radar could be used to find a flat landing site, but the close-ups from Galileo make it look like Europa may not have a lot of flat landing sites.

John - the purpose of the hi-res imager on the spacecraft is specifically to find the smooth(er) spots in the interesting areas,which all seem to be fractured surfaces.

The ice penetrating radar (they have a surface topography mode as I recall) probably don't have a small enough footprint to safely target a landing site. They should determine whether or not there are lake lenses within the ice.

[JRehling]

The ice penetrating radar (they have a surface topography mode as I recall) probably don't have a small enough footprint to safely target a landing site.

If there's a reflective mode, radar can determine smoothness/roughness at the scale of the wavelength, which is much smaller than the scale of the footprint. But that's ambiguously confounded with other properties of the surface, and I don't know if the data will be useful for that purpose.