Europa Orbiter, Speculation, updates and discussion Options

[Redstone]

There has been lots of discussion of a mission to Europa in the excellent thread on the Juno mission. I thought that since a Europa mission seems to be once again becoming a possibility, it deserved its own thread for news, updates and discussion. I thought I'd kick things off with a summary of past efforts on a Europa mission, and on where things stand now. If I make a mistake, please correct me!

In the course of its prime and extended missions, Galileo found evidence of liquid water under the icy surface of the planet. Planning began on a Europa Orbiter mission, with a projected arrival date of 2008, to confirm the presence of the ocean, characterize the thickness of the icy crust and identify places for a future landing. One thing to note about these earlier plans: they included a direct trajectory to Jupiter, presumably to minimize mission duration and qualms about RTGs re-entering Earth atmosphere after some (highly unlikely) targeting mishap. But NASA lacked a nice category of missions to place the Europa Orbiter in. Eventually it got lumped together with Pluto Express and Solar Probe in a Outer Solar System program labelled "Fire and Ice", a term which also got applied to the Galileo Europa Mission extension. Without a solid program to support it, (like Mars Exploration, Great Observatories, or Discovery) the mission looked like an orphan.

As Bruce Moomaw has well documented, attempts to kill off the Pluto mission led to a tug of war between NASA, the planetary scientists and the public, resulting in Congressional directives to NASA. Pluto Express became the Pluto/Kuiper Belt Explorer and then New Horizons and New Frontiers 1. (New Frontiers 2 is of course Juno.) But the cost for the Europa mission continued to rise, and the launch date recede, as the difficulty of radiation shielding and the large delta-v requirements hit home, and the mission's public profile fell. The launch date moved to 2010 and the costs moved over a $1b. Then along came Sean O'Keefe and JIMO, a justification for the Prometheus program through developing nuclear electric propulsion, not with RTGs, but with an in-space fission reactor. Launch got moved to 2011, then 2012, while the cost went even further through the roof.

With the arrival of Mike Griffin, JIMO was cancelled. As Griffin said to Congress, "It was not a mission, in my judgment, that was well-formed." But interest in a Europa mission remained and remains strong. In 2003 the National Academy of Science's Decadal Survey flatly stated that a Europa Orbiter was the top priority for the next Large scale (aka Flagship) mission. (See page 196 of the report.) NASA's current Solar System Exploration Roadmap reaffirmed a Europa orbiter as the next flagship mission. The question as always is money. As Administrator Griffin said, "The Science Mission directorate wants to do a Europa mission, the National Academy of Sciences wants to do a Europa mission, I want to do a Europa mission. When we can afford it in the budget, we'll do it."

Evidence of that support beyond rhetoric and reports trickled out with a letter from Andy Danzler, NASA's Solar System chief, to the Outer Planets Assessment Group (OPAG). He reported that he had "funded a team to take a quick look at the boundary conditions of a mission to Europa, that is, how much power, mass, travel time, etc. for various realistic scenarios. For planning purposes, this group is looking at launch dates in the 2012-2015 range, although the later dates are more likely in terms of funding." For funding details however, we have to wait for the FY 2007 budget.

OK, now the good stuff.

The latest meeting of OPAG included reports on a Reference Design for the mission. A kind of first draft which establishes a baseline which can be tweaked and modified to extract the best science return.

There are many things to like about this draft design:
* The mission is now permitted to use Earth flybys, and uses a proven trajectory, the same as used by Galileo (Venus-Earth-Earth Gravity Assist). This allows a BIG increase in the available mass.
* The orbiter uses RTGs, but not super advanced ones that require further years of development.
* The orbiter is similar to Cassini in appearance, with 2 engines, a cylindrical tank structure, RTGs at the base, the magetometer boom at the top, and space for a lander bolted to side. The similarities may make it easier to convince Congress that this is something NASA knows how to do. The most obvious configuration change is with science payload and HGA having switched places, and the addition of a radar array. And there looks like a camera the size of MRO's HiRISE!
* The mission is definitely Flagship in scope with a launch mass of over 7000 kg on a heavy lift launch vehicle. For comparison Cassini was 5712 kg at launch on a Titan IV, and Galileo was 2223 kg when launched using the Shuttle and an Inertial Upper Stage.
* There is a good opportunity for ESA participation with the lander and science instruments. NASA/ESA co-operation is on the agenda for the next OPAG meeting.
* The mission does not assume big upgrades to the Deep Space Network. If the Next Generation DSN does come along, that's just gravy.
* Despite the Europa focus, the mission appears to give at least part of a Galilleo II style tour with multiple flybys of the outer Galileans over 18 months. Only Io will have to wait.

The OPAG Europa working group is also expected to present further work at the next meeting in October. More details will emerge then. I think there is room for cautious optimism on this mission. While we won't be seeing a mission launch for at least another 7 years, the combined weight of the planetary science community does tend to get it's way in the long run. I think the momentum is finally starting to build.

[Guest_BruceMoomaw_*]

Very nice work. (My saying this, by the way, has no connection whatsoever with your praising my work on the Great Pluto Probe War...) Absolutely the only error I can detect -- and I've long been obsessed with Europa exploration -- is that the original design for Europa Orbiter DID have a big radar array that in fact looked very much like this new one; it was just located at a different place on the craft.

And, yep, they seem determined now to add a very big HiRISE-type camera, in addition to the much smaller one they planned from the start. Not only are high-res shots of Europa important for understanding its surface processes; they're crucial for figuring out how to safely land spacecraft on what looks like a VERY rugged surface. While I'd love to see a small lander (if properly designed) added to this mission, however -- as would Jack Farmer -- it is very much up in the air whether they'll have the money to do so. (I'm currently planning a future article arguing that the best possible design by far for a small lander on this mission would be a penetrator rather than a surface lander.)

[Decepticon]

(I'm currently planning a future article arguing that the best possible design by far for a small lander on this mission would be a penetrator rather than a surface lander.)

I'm all for the Penetrator.

[Bob Shaw]

I'm all for the Penetrator.

Yeah. We could use the spare ones the Japanese have...

[infocat13]

45% to 50% of the cost of the Europa orbiter mission is the cost of mission design and test.I would build 4 more space craft of identical design except for the mass set aside for the lander/probe.this mass would be used by a payload best suited for the target planet. targets? saturn(a cassini follow on) uranus and neptune. the 4th spacecraft would be insurence or a mission of oppertunity.

[tedstryk]

45% to 50% of the cost of the Europa orbiter mission is the cost of mission design and test.I would build 4 more space craft of identical design except for the mass set aside for the lander/probe.this mass would be used by a payload best suited for the target planet. targets? saturn(a cassini follow on)  uranus and neptune. the 4th spacecraft would be insurence or a mission of oppertunity.

It might be neat to buffer one up and put a more appropriate instrument sweet on it, and send it on a tour like that of Galileo's later years (in other words, flying by Io repeatedly and occasionally other moons). With a Hirise likecamera, it could study Io's temporal activity, with closeup coverage every few weeks.

[Decepticon]

Europa/Io complete mapping is a must.


What a disappointment with mapping from Galileo. Even with the extended mission Europa is still poorly mapped.

[JRehling]

And, yep, they seem determined now to add a very big HiRISE-type camera, in addition to the much smaller one they planned from the start.  Not only are high-res shots of Europa important for understanding its surface processes; they're crucial for figuring out how to safely land spacecraft on what looks like a VERY rugged surface.  While I'd love to see a small lander (if properly designed) added to this mission, however -- as would Jack Farmer -- it is very much up in the air whether they'll have the money to do so.  (I'm currently planning a future article arguing that the best possible design by far for a small lander on this mission would be a penetrator rather than a surface lander.)

The thing that worries me is that we are, by necessity, playing a game of Twenty Questions with Europa, and a big, battlestar-galactica craft asks a lot of questions at once, meaning that some of them may be mis-asked. (Like the fluid-probing instruments on Huygens.)

A big camera plus a possible lander could serve purposes, for sure, and if they came for free, who could complain? But look at how many missions we're using to pursue Mars exploration... Given that Europa is also going to take a lot of missions to crack (surely spread over a much longer span of time), a smaller scope might be called for.

Note that with a powerful camera, not much of the surface gets mapped: MOC on MGS will end up mapping only a few percent of Mars's surface (it was have been about 1.5%, IIRC, in the nominal mission). The kicker is, a Europa Orbiter won't live for a decade like MGS, but a month, so *very* little of Europa's surface will benefit from the camera's work. Granted, an attempt to image representative sites (both typical and the odd, atypical feature) should return a weighty fraction of the scientific knowledge that a comprehensive high-res mapping would, but the value of the camera still has to be weighed against that. I suppose the idea would be to produce *final* imaging of potential lander sites, and you have to do that sooner or later, so why not now? Well, the answer might come once the other instruments have had a look.

For a lander, that goes in spades. If we find something out from the hi-res camera, that could really affect lander design.

I think it'd be wiser to launch a probe with radar, a good-not-great camera, no lander, and have a quicker turnaround til the next mission. Europa's not going anywhere. Let's be methodical instead of extravagant.

[tedstryk]

The thing that worries me is that we are, by necessity, playing a game of Twenty Questions with Europa, and a big, battlestar-galactica craft asks a lot of questions at once, meaning that some of them may be mis-asked. (Like the fluid-probing instruments on Huygens.)

A big camera plus a possible lander could serve purposes, for sure, and if they came for free, who could complain? But look at how many missions we're using to pursue Mars exploration... Given that Europa is also going to take a lot of missions to crack (surely spread over a much longer span of time), a smaller scope might be called for.

Note that with a powerful camera, not much of the surface gets mapped: MOC on MGS will end up mapping only a few percent of Mars's surface (it was have been about 1.5%, IIRC, in the nominal mission). The kicker is, a Europa Orbiter won't live for a decade like MGS, but a month, so *very* little of Europa's surface will benefit from the camera's work. Granted, an attempt to image representative sites (both typical and the odd, atypical feature) should return a weighty fraction of the scientific knowledge that a comprehensive high-res mapping would, but the value of the camera still has to be weighed against that. I suppose the idea would be to produce *final* imaging of potential lander sites, and you have to do that sooner or later, so why not now? Well, the answer might come once the other instruments have had a look.

For a lander, that goes in spades. If we find something out from the hi-res camera, that could really affect lander design.

I think it'd be wiser to launch a probe with radar, a good-not-great camera, no lander, and have a quicker turnaround til the next mission. Europa's not going anywhere. Let's be methodical instead of extravagant.

Well, actually, in its low resolution channel, MOC has mapped the planet many times over at resolution of a few hundred meters. If the big camera comes with something like CTX, it could be quite useful. I also think that we are in a bit of a better positon with regard to a priori knowledge at Europa than at Titan. With a lander however, that is not the case. I don't think we know about the surface at a fine scale well enough for good site selection, although a relatively simple penetrometer wouldn't hurt - I just think it is early.

[Redstone]

I think you have to balance the size and capability of the spacecraft against the permissible frequency of visits. Because of Europa's distance, and the large delta-v required to go into orbit, a sequential program like that for Mars is not going to be feasible. So there is more demand for the number of question-answer cycles to be kept to a minimum, even if that means more capable, and hence more expensive missions.

When it comes to any form of lander, I think anything complex will send mission risk and cost too high. But penetrometers may be vulnerable to being axed once the squeeze begins for spacecraft resources and funding, even if we are looking at 7 tonnes for the mission. The Decadal Survey *did* identify a Europa orbiter and lander as separate missions, after all. If the lander is an international contribution, that would make it more secure.

The HiRISE style camera is interesting. Certainly the 30 day prime mission is way too short a time to return the amount of data involved in mapping at that kind of resolution. Since the mission will have a wide angle camera for the global mapping, the question would be where to aim the big mirror. One aspect of the mission that would help is the many flybys and steady final approach to Europa before orbit insertion, which would give lots of opportunities for preliminary surveys. Also, if the mission carried a lot of onboard memory, then once in orbit thumnails could be sent, and then selected detail returned. But at that point the mission team would have to make up its mind *fast* (i.e. on a daily basis) on what was to come back in high resolution.

[edstrick]

With a HiRISE style camera, you can do an enormous amount of high quality "raster" style mapping of moons from a distance. Either with a framing camera or a pushbroom sensor (I'd go with framing cause of low light levels), you couild build up low-distortion gigapixel mapping mosaics before the spacecraft moves a lot or the moon rotates a lot.

Somebody do the math and tell me for Galileo-type orbits, what resolution you get 6, 12, 24 and 48 hours from a flyby of the 3 ice moons, and what resolution <km/pixel> you get on Io.

[Marcel]

I'm all for the Penetrator.

Would a soft lander be possible given the allocated space (and mass) for it on the craft ? I assume there's no real atmosphere to parachute into, so i'm afraid the answer is NO.

[Marcel]

http://www2.jpl.nasa.gov/galileo/europa/hst.html

"Europa's oxygen atmosphere is so tenuous that its surface pressure is barely one hundred billionth that of the Earth,"

I guess my dream of having a stereo camera with 360 PAN capability on Europa shatters here. A soft lander seems impossible for now......

[antoniseb]

Even a simple very small lander (a kilogram of instruments) would be useful for learning some things that we'll need to know for a more complex lander/rover. The Hi resolution camera won't be able to resolve things better than a few meters, and will be unable to actually test the surface composition.

[Marcel]

Even a simple very small lander (a kilogram of instruments) would be useful for learning some things that we'll need to know for a more complex lander/rover.

But soft landing without an atmosphere isn't possible. At least not for the allocated mass of the lander.

[Decepticon]

I was thinking more in the lines of a Melt its way threw type probe.


Or how about this!

[Marcel]

I was thinking more in the lines of a Melt its way threw type probe.
Or how about this!

What the h... is that ?

[ljk4-1]

What the h... is that ?     

Ever seen the sequel to 2001: A Space Odyssey?



It actually looks both plausible and Soviet.

[Bob Shaw]

But soft landing without an atmosphere isn't possible. At least not for the allocated mass of the lander.

Marcel:

Let's think outside the box...

...Ranger-A plus airbags?

Bob Shaw

[Marcel]

Marcel:

Let's think outside the box...

...Ranger-A plus airbags?

Bob Shaw

I suppose that IF we could make airbags that strong, it would easily thump! back into space far beyond the escape velocity of 2,2 km/sec.....it would buy us about a nanosecond on the surface

[Decepticon]

I'm 30 now, I hope that before I kick the bucket that I'll know for sure if there is a Subsurface ocean or not.

Life or No life.

Just the fact that a ocean other than our own is out is very cool.

A subsurface/orbiter probe should be Top Priority. *Ducks at Tomato's*

[antoniseb]

I suppose that IF we could make airbags that strong, it would easily thump! back into space far beyond the escape velocity of 2,2 km/sec.....it would buy us about a nanosecond on the surface 

If the orbiter released a craft from low orbit and the craft had a small rocket to de-orbit and layers airbags intended to pop on impact you might sufficiently decelerate a fairly hard set of instruments (perhaps 60 to 100 g's).

I'll have to do a few quick calculations to see if this is reasonable. The big doubt item is whether anything useful can be put in a small enough lander.

[ljk4-1]

If the orbiter released a craft from low orbit and the craft had a small rocket to de-orbit and layers airbags intended to pop on impact you might sufficiently decelerate a fairly hard set of instruments (perhaps 60 to 100 g's).

I'll have to do a few quick calculations to see if this is reasonable. The big doubt item is whether anything useful can be put in a small enough lander.

They had airbags on Luna 9.

[JRehling]

I think you have to balance the size and capability of the spacecraft against the permissible frequency of visits. Because of Europa's distance, and the large delta-v required to go into orbit, a sequential program like that for Mars is not going to be feasible. So there is more demand for the number of question-answer cycles to be kept to a minimum, even if that means more capable, and hence more expensive missions.

An alternative is to be resigned to the fact that Europa exploration is going to take a lot longer than Mars exploration. The trade-off, simply put, is: Do we want to get the most bang for our buck but have it take more time to fly all the missions we want, or do we want to get the science sooner and risk some missions/instruments that end up missing the point due to some yet-unknown characteristic(s) of Europa?

Don't kick me out of the enthusiast club, but I can't fabricate a case for urgency here. If it takes 8 billion-dollar missions to reach a certain level of understanding, vs a quartet of 3-billion-dollar missions completed in half the time, how do you explain (to the public??) that getting the answers sooner is worth the extra $4 billion? Assuming a fixed budget for exploration, this also means the rest of the solar system gets gyped out of many missions. There is opportunity cost.

When it comes to any form of lander, I think anything complex will send mission risk and cost too high. But penetrometers may be vulnerable to being axed once the squeeze begins for spacecraft resources and funding, even if we are looking at 7 tonnes for the mission. The Decadal Survey *did* identify a Europa orbiter and lander as separate missions, after all. If the lander is an international contribution, that would make it more secure.

I think a smash-and-grab mission that uses an impactor to blast some ice up to a collector that is on a free-return trajectory to Earth has to be considered.

As I see it, the lander concept comes down to two main investigations: What is the composition of the non-H2O stuff? Is there a seismic/thermal/magnetic indication of the structure/activity of the crust and subcrust?

An orbiter can start to speak to the magnetic and probably thermal (by scanning the nightside and eclipsed-dayside in IR) issues. Smash-and-grab would give us a point sample of composition.

I think a very strong candidate plan for the first two missions would be an orbiter that performs detailed surfacing mapping, including scrutiny of whether or not the non-ice component is the same compositionally everywhere. This mission would screen for the best possible locations for any future surface mission, whether it be smash-and-grab, a Pathfinder-style lander, or a penetrator-lander. It is certainly risky to launch a lander of any style without having that basic reconnaisance completed.

The case for the second mission being a lander seems elusive to me. The magnetic and thermal questions will be addressed in part by the orbiter (of course, note: the conditional nature of that statement is already evidence that the second mission should be designed around the results of the first). A smash-and-grab mission would not provide the seismic data of a lander, but would provide infinitely better analysis, in earthly labs, of surface samples -- for far less delta-v.

The combo strategy I have mentioned before for the first landed mission would be to have a lander with seismic capabilities touch down (or penetrate) first, then have an impactor (with its own camera, of course) strike the surface nearby shortly thereafter, providing a known seismic event that would probe the crust fantastically. That same impactor could be the one spraying particles up to the catcher's mitt on the free return trajectory. In all, three elements involving the surface, designed according to the results of the orbiter mission, with a broad wealth of returned data: seismic, magnetic, and thermal data from the landed probe at one location, closeup imagery of a second location, precise seismic data which would give excellent data on one location in the crust, and samples for earthly labs!

Seen this way, the great upside is not to link Mission 1 and Mission 2 to the same launch, but Mission 2 and Mission 3.

The HiRISE style camera is interesting. Certainly the 30 day prime mission is way too short a time to return the amount of data involved in mapping at that kind of resolution. Since the mission will have a wide angle camera for the global mapping, the question would be where to aim the big mirror. One aspect of the mission that would help is the many flybys and steady final approach to Europa before orbit insertion, which would give lots of opportunities for preliminary surveys. Also, if the mission carried a lot of onboard memory, then once in orbit thumnails could be sent, and then selected detail returned. But at that point the mission team would have to make up its mind *fast* (i.e. on a daily basis) on what was to come back in high resolution.

I agree that sophisticated regimes for selecting imagery returns are called for. I don't see why such a mission could not have truly massive memory (cmon, that's light), and the ground crew would have the entire duration of the mission to request imagery for downlink -- imagery taken the first day should still be available for downlink on the last day. Store everything, or at least a heck of a lot. It's a nice thought that the orbiter could have a great set of high resolution imaging in its memory, and the ground crew could peruse the low resolution map, and then request detailed observations in terms of a downlink, as opposed to in terms of a new, future observation.

[ljk4-1]

I think a smash-and-grab mission that uses an impactor to blast some ice up to a collector that is on a free-return trajectory to Earth has to be considered.

Such a mission was developed called Europa Ice Clipper. A 50-pound ball would be slammed into Europa by a flyby probe, which would fly through the debris cloud, grab some samples of Europa, and return them to Earth.

http://www.astrobiology.com/europa/ice.clipper.html

[Guest_BruceMoomaw_*]

I've been thinking for some time about a modified version of Ice Clipper, in which the spacecraft would be based not on Stardust (with a small impactor) but on Deep Impact (with a much bigger Impactor kicking up a much larger amount of debris, and kicking up almost all of it from depths far below the radiation-modified upper layer). The Impactor's camera could also get extremely high-res final photos which could provide additional valuable information on small-scale surface ruggedness for the purposes of lander design.

I've even wondered if it might be advisable to launch such a mission BEFORE the Orbiter; a high-res camera and near-IR camera on the main craft, coupled to a very high-capacity and high-speed data recorder, could get high-resolution terrain and compositional data on quite a respectable part of Europa's surface just from a flyby (like the "Firebird" Io flyby once proposed as a Discovery mission). One possible motivation for such a mission flying first has disappeared, though: Janus Eluszkiewicz's argument that Europa's upper layers might be riddled with large cavities that would seriously interfere with the depth penetration of a radar sounder -- making it advisable to test the effectiveness of Europan radar sounding from a flyby first -- has come under very serious fire on the grounds that he simply assumed that such cavities could exist when the physical evidence is against it: http://www.lpi.usra.edu/meetings/lpsc2005/pdf/2346.pdf .

And the big problem with a smash-and-grab mission remains: given the very small amount of surface material that it would collect, could even supersensitive Earth-based labs properly inspect the sample for biological evidence? (Especially since it's quite possible that the heating the samples would inevitably undergo as they plowed through the aerogel collector layer would break down organic compounds.) if so, it might be preferable to initially analyze Europa's ice using in-situ instruments, even given their greatly reduced sensitivity and flexibility, simply because they could analyze much bigger amounts of material. JPL's own design study for an initial lightweight Europa soft lander ( http://www.lpi.usra.edu/opag/jun_05_meetin...ssion_Study.pdf ; http://www.lpi.usra.edu/opag/jun_05_meetin..._Trace_OPAG.pdf ) calls for such an organic-isotopic analysis -- using a combined liquid chromatograph and mass spectrometer -- as one of the two top priority instruments for a Europa lander, the other being a seismometer for data on ice-layer total thickness. I myself would regard organic analysis as even more important.

The problem is collecting a big enough sample for such analysis on a small lander -- and collecting it from a fair depth, below the radiation-scrambled surface layer, using a lightweight sample-collection system. The JPL study (which focuses on a surface lander, just because that's the one design it was contracted to examine) expresses concern about this, but doesn't mention specific solutions. A penetrator would seem to be the logical solution. The "Polar Night" Discovery mission proposed to analyze lunar polar ices -- which could well end up as the second in the new series of US lunar exploration probes -- called for three penetrators, each weighing only 30 kg, surviving a crash into the surface at 75 meters/sec and burying themselves 1-2 meters deep ( http://www.nrl.navy.mil/techtransfer/exhib.../PolarNight.pdf ; http://www.mae.usu.edu/faculty/tmosher/Gen...edia/Mosher.pdf ). They would each carry a neutron spectrometer (not necessary for Europa) and a mass spectrometer, and impact tests in which these instruments were fired into a 2-meter layer of plywood and exposed to 1200 Gs (four times their planned load) showed them surviving just fine.

Again, though, if interesting compounds are seriously diluted in the Europan ice, the problem is acquiring enough of them to analyze -- which might require a heated probe to melt its way down through several dozen meters of ice and filter diluted compounds out of the resulting large amount of meltwater ( http://lasp.colorado.edu/icymoons/europacl...ps_EurAbode.pdf ). But such a probe would almost certainly be too big to carry as a piggyback on Europa Orbiter.

If a small penetrator COULD have a chance of analyzing enough material to be worthwhile, however, it would seem vastly preferable to a surface lander as a piggyback on Europa Orbiter in almost every way. It would easily dig below the radiation-modified surface layer (unlikely to be more than a meter or so deep); it would be much lighter than a surface lander; it could land on virtually any terrain, no matter how rugged; it would bury itself and thus provide its own shielding from Jupiter's radiation (which is otherwise a major problem for a moderately long-lived lander); and it would couple its seismometer to Europa far more rigidly than a surface lander. It would probably be unable to obtain post-landing terrain photos, but it could record descent photos during the last few seconds before impact and play them back later for almost equally good imaging data.

[Guest_BruceMoomaw_*]

Stop press! While poking around on the Web for the above note, I've just found that Paul G. Lucey -- the Principal Investigator for "Polar Night" -- is also working on "Thunderbolt: In-Situ Detection of Biotic Compounds on Europa" ( http://www.higp.hawaii.edu/cgi-bin/higp/di...ame=PaulG.Lucey ). This is surely a Europa penetrator, and I intend to talk to him about it immediately.

[deglr6328]

Not being familliar with Luna-9, I checked it out and.....did the engineers include something of an easter egg in this image?

[Bob Shaw]

They had airbags on Luna 9.

I don't think so... ...there was a big insulating cover over the lander - is that what you're thinking of?

[Guest_vjkane2000_*]

If a small penetrator COULD have a chance of analyzing enough material to be worthwhile, however, it would seem vastly preferable to a surface lander as a piggyback on Europa Orbiter in almost every way.  It would easily dig below the radiation-modified surface layer (unlikely to be more than a meter or so deep); it would be much lighter than a surface lander; it could land on virtually any terrain, no matter how rugged; it would bury itself and thus provide its own shielding from Jupiter's radiation (which is otherwise a major problem for a moderately long-lived lander); and it would couple its seismometer to Europa far more rigidly than a surface lander.  It would probably be unable to obtain post-landing terrain photos, but it could record descent photos during the last few seconds before impact and play them back later for almost equally good imaging data.

Penetrators have been proposed for many missions, but they always suffer from the same problems: very limited room for sophisticated instruments (big difference between a spectrometer that can detect water and one that can unambiguously classify organic molecules) and the need for entry into the surface to be near vertical. At the same time, there are some nice features to penetrators for Europa: they did beneath the surface ice (good for sampling) and have a meter or two of ice shielding them from the radiation (good for a longer life). A potential issue: if the Europeans do the lander, I don't think they have much experience with penetrators, but could be quite wrong on this.

[Jeff7]

Someone mentioned an impactor - how about using a small stream of impactors to blast successive craters, and at the end of the stream would be the instrument-laden lander itself? It might still need to drill, but not nearly as much.

[Guest_BruceMoomaw_*]

Uh-uh -- you'd need a huge weight in impactors to blast a hole of any significant depth, whereas you could achieve much greater penetration for tremendously less weight just by making the probe a melt probe (or giving the surface lander a longer drill). To say nothing of the gargantuan targeting difficulties...

[ljk4-1]

Back in 1998 I initiated a discussion list for landing a probe on Europa to explore its subsurface global ocean. Named Icepick, the discussion lasted until just a few months ago.

http://www.klx.com/europa/

You can read the discussions here. I think we hit on many if not most of the scenarios for making this mission plan a reality.

http://www.mail-archive.com/europa%40klx.com/

If someone wants to revive the Icepick list and get discussions going again, I would be most grateful. Jeff Foust ran the intial list and Web site.

[Guest_BruceMoomaw_*]

Yep, that's the site where I got my start as a space commentator -- and where Simon first ran into me. Sad to see that it's finally disappeared. Maybe I should have hung around there, but I've been juggling several plates at one time for the last few years and just never got around to dropping back in. It starts to look as though the discussion site for Europa exploration may migrate over here.

[Redstone]

Apologies if this has already been discussed, but on the OPAG site, there's a fascinating report on Europa Surface Science options. It runs to 86 pages and covers radiation issues as well as landing methods. It was based on the JIMO as the mothership, but much of the discussion is still relevant, I think. I haven't had the chance to go through it in detail, but one point caught my eye: for 375 kg, you can soft land 167 kg on the surface using powered descent. For comparison, the Huygens probe had a mass of 320 kg.

[Jeff7]

Uh-uh -- you'd need a huge weight in impactors to blast a hole of any significant depth, whereas you could achieve much greater penetration for tremendously less weight just by making the probe a melt probe (or giving the surface lander a longer drill).  To say nothing of the gargantuan targeting difficulties...

Ok, a melt probe. RTG powered I assume? Just did a quick search.....one page says this of Cassini's RTG's:
"The alpha particles naturally heat the pellets to 572 degrees Fahrenheit (300 degrees Celsius)."
Not too bad at all, more than I expected actually. That'd definitely make a hole....though I'm just thinking now, it'd encase itself beneath the ice. The water above would likely refreeze fairly quickly, even with a toasty robot beneath it. So the little meltbot would be sealed under the ice rather quicly. What would it use for communication? A fiber optic line would be risky (might get tangled), and would add weight. And I don't know how well radio waves penetrate ice.

[hendric]

So the little meltbot would be sealed under the ice rather quicly. What would it use for communication? A fiber optic line would be risky (might get tangled), and would add weight. And I don't know how well radio waves penetrate ice.

A fiber optic cable is probably the best bet, using a floating transmitter/receiver at the end of the line to keep it above the meltwater until it refreezes. Radio would require repeaters to go through the ice, which is possible, but you'd have to power them somehow, and keep them from melting down (or up!) when they activate.

[Guest_BruceMoomaw_*]

Jeff: I saw that OPAG report -- and the two more recent papers att the OPAG site that I mentioned previously elaborate on it somewhat.

Hendric: The idea of a fiber-optic line for communications -- originally the favored idea -- got the boot several years ago, both because of weight problems and becuase the slow but steady ductile sliding of Europa's ice layers would almost certainly snap it. The current plan is to have the probe carry a stack of tiny disk-shaped radio repeater packages powered by tiny RTGs, and release one every kilometer or so that it descends -- so that they're close enough to pick up each other's radio signals through the ice and thus chain-link the signal from the melt probe all the way to its surface carrier.

[Guest_BruceMoomaw_*]

I should add that the heat from the extremely tiny RTG that each such package would require would not be nearly enough to melt the surounding ice and make it sink deeper.

[deglr6328]

Wouldn't it? Let's say you want a 10W transmitter. You will need at least, I don't know, ~15W total for electronics and losses and such..? The abysmal efficiency of RTGs meas you will need at least a ~100W heat source to power the thing......ice is a very good insulator.....

I would very much like to see a plot of EM wave attenuation vs frequency for ice so that any "windows" could be identified and the necessary transmitter power could be constrained with higher confidence.

Hmm this looks interesting...

[Guest_BruceMoomaw_*]

There are two relevant JPL Technical Reports on this design. Unfortunately, JPL's technical-report server seems to be offline for now, so I've attached both reports.

Actually, each transceiver would use a mere 0.12 W power source, hooked up to a capacitor to allow periodic bursts of 1.3 W transmission power. So that's why there's no RTG ice-melting problem.

Attached File(s)

 CDAR____Europa____JPL_TR_01_2122____Bryant.pdf ( 477.38K ) Number of downloads: 1958

 

[Guest_BruceMoomaw_*]

And here's the other JPL report.

Attached File(s)

 CDAR____Europa____JPL_TR_99_2051____Zimmerman.pdf ( 832.18K ) Number of downloads: 446

 

[deglr6328]

hmmm! very interesting thank you!

[Roly]

Was anyone at the recent (October) OPAG meeting where the new Europa Orbiter was due to be discussed?

The October report and documents aren't up yet, but surely it can't be too long now. Wonder how the talks with ESA went? Hope there was some more support for the 2013 opportunity, given the extra dry mass that could be delivered (probably enough for the soft lander studied by Balint, Nov. 2004).

Roly

[Guest_BruceMoomaw_*]

I wasn't able to make it to OPAG, and have been monitoring their site for news on the presentations and final report from the October meeting. They haven't turned up yet, but I expect them soon.


http://www.lpi.usra.edu/opag/meetings.html
http://www.lpi.usra.edu/opag/reports.html

[Guest_Richard Trigaux_*]

Jeff: I saw that OPAG report -- and the two more recent papers att the OPAG site that I mentioned previously elaborate on it somewhat.

Hendric: The idea of a fiber-optic line for communications -- originally the favored idea -- got the boot several years ago, both because of weight problems and becuase the slow but steady ductile sliding of Europa's ice layers would almost certainly snap it.  The current plan is to have the probe carry a stack of tiny disk-shaped radio repeater packages powered by tiny RTGs, and release one every kilometer or so that it descends -- so that they're close enough to pick up each other's radio signals through the ice and thus chain-link the signal from the melt probe all the way to its surface carrier.

Why not ultrasonic communication? Sounds transmit well and far in solid mediums, and there would be no need of lines, repeaters and the like. I see well the penetrator having an array of piezoelectric crystals on its top, it would even be directive. On the countrary a radio link could not work if there is a fault or ice layer at 0°C soaked with salty water.
After, if the penetrator has a density between water and ice, it would float at the bottom of the ice and collect many molecules with a filter.

And with no added cost this sonar (call it by its name) would be a wonderfull mean to probe the ice crust, faults and galeries, and above all to probe the ocean itself, its depth, eventually layers and currents, floating objects, and the ocean floor...

fascinating: an ultrasonic "image" of volcanoes from the rocky core of Europa... "black smokers" (thermal vents) would be already fine.

More and more: the penetrator abandons its floater, and sinks to the rocky floor itself, and takes photos of it, eventually showing weeds and living forms...

Wow!



And on the surface?
A repeater left on the surface could send enough power (like Huygens did) to be picked from Earth (with a slow bit rate. Of course if there is an orbiter to relay data it would be better). If the repeater is buried in ice, just its radio antenna out, it could work for months and years, much compensating for the slow bit rate.

[Guest_BruceMoomaw_*]

The presentations from the third OPAG meeting have just arrived: http://www.lpi.usra.edu/opag/oct_05_meeting/agenda.html . (The final report from the meeting isn't available yet, though.)

[ljk4-1]

Though this may sound terribly obvious, any Europa landers/ocean explorers had better be designed to last a long time if their main goal is going to be the search for life on that Jovian moon.

Unless the ice crust is encrusted with dead microbes or such similar creatures and their alien jellyfish counterparts are saturating Europa's ocean, I do not want to end up with the same situation as the Viking landers, who were stuck on two tiny spots on Mars and had scientists and the media declaring the Red Planet a dead world (again) when a few scoopfuls of dirt revealed no native microbes. Europa will require a long exploration.

To add: The global ocean on Europa is estimated to be *60 miles* deep. Thankfully in one sense the moon's much smaller mass makes the bottom water pressure on Europa no "worse" than that found in the deepest parts of the Pacific Ocean (7 miles down), but if there are black smokers and alien versions of red tubes worms and giant crabs living around them, can we design a probe that could make it all the way to the bottom of the Europan Ocean and return the data to Earth?

Another question: Life may be able to survive on Europa in its present state, but based on what we know, could it ever have gotten off to a start in the first place?

[Guest_BruceMoomaw_*]

The reply to the second question is simply: we don't know. We don't know whether life could have evolved out of prebiotic molecules on Earth had the water been as acid and/or saline as Europa's appears to be; there has been at least one abstract I've read expressing doubt, but given our stupefying continuing level of ignorance about how the chemical process occurred on Earth itself, we just don't know.

As for the first question: even if we don't get all the way down to isolated "smokers" on the floor of Europa's ocean, we should be able to detect microbes (or their remnants) from such locations spread uniformly through the ocean water -- after all, that's how life on Earth gets transferred from one isolated smoker to another and so survives after the first smoker finally goes out. And if the alternative theory is true that Europan microbes may derive their nourishment instead from chemicals manufactured by radiation in Europa's upper ice layer and then gradually transferred down to the ocen by geological processes in that ice layer, the principle is even more true -- in fact, in that case the life would probably be concentrated at the TOP of the liquid-water layer.

This also leaves the question of whether we can find evidence of microbes in Europa's liquid ocean without even having to bore down through the ice layer to the ocean, by instead analyzing the surface ice itself to look for such remains transported up to the surface by those same slow geological processes in the ice layer. The consensus seems to be that this is a real possibility -- but, since there's a thin layer of brittle supercold "nonconvective" ice 1-3 km thick on top of the warmer main ice layer which slowly convects (and which even perhaps carries pockets of still-liquid brine upwards), we are going to have to be careful to choose landing sites that look likely to have had buried material erupted all the way up to the surface. (There are several types of Europan surface features that show promise of this, which is another reason why we do need a Europa orbiter first to pick out good landing sites.)

[Guest_Richard Trigaux_*]

This also leaves the question of whether we can find evidence of microbes in Europa's liquid ocean without even having to bore down through the ice layer to the ocean, by instead analyzing the surface ice itself to look for such remains transported up to the surface by those same slow geological processes in the ice layer.  The consensus seems to be that this is a real possibility -- but, since there's a thin layer of brittle supercold "nonconvective" ice 1-3 km thick on top of the warmer main ice layer which slowly convects (and which even perhaps carries pockets of still-liquid brine upwards), we are going to have to be careful to choose landing sites that look likely to have had buried material erupted all the way up to the surface.  (There are several types of Europan surface features that show promise of this, which is another reason why we do need a Europa orbiter first to pick out good landing sites.)

Yes, good approach in a first time, before trying to reach the bottom of the ocean (what I think possible but more complicated). But the very upper layer of ice (about 1m) is exposed to strong radiations, and thus sterilized, and anyway not representative of the global ice chemistry. So we need to drill from the very first landing, even if only 1-2m. For this reason penetrators were proposed (sticking themselves in ice like an arrow, which solves the problem of soft landing) or using a more classical drill, or a heat source able to melt ice. (RTGs were proposed, but RTGs are weak, a chemical source would perform better for this very purpose). A tip would be to place all the electronics into the drill, so that it is protected from radiations and it can last for much longer, very useful if it carries a seismometre.


Also a RTG was proposed to melt the ice down the ocean. But are RTGs powerfull enough for this? I would rather see a bot with a screw-shaped nose and a body with fins, like in sci-fi novels, running with a high gear rate, it would be much more power-efficient and faster than just melting ice. We have plenty of places on Earth to test this, in the Antarctic ice shelds. If there are interesting results from a surface examination, there will be a strong support for the idea of looking at the botton of the ocean.

[Ames]

The beauty of an RTG is that it creates a LOT of "waste" heat that can be put to use here for "free".
Also the electricity generation efficiency can be increased if there is an effective cold sink.

So an RTG probe is Perfect - as long as you don't hit a buried rock/meteorite.

Nick

[Guest_BruceMoomaw_*]

If they do add a small lander to the first Europa orbiter -- and that is a very big "if" -- I've been a fan for some time of making it a penetrator rather than a surface lander, for a whole swarm of reasons:

(1) Such a penetrator can punch down a meter or two into the ice just by impact, giving it a good chance of getting below the radation-modified upper layer. (As far as I'm concerned, no lander that doesn't drill down that far is worth sending.)

(2) It could couple a seismometer -- the second most important instrument for a Europa lander, according to the science working group -- to the crust far more firmly than a surace lander.

(3) It would bury itself in the ice deeply enough to be shielded from Jupiter's radiation -- a very serious problem for an exposed surface lander.

(4) It could land on virtually any kind of terrain, no matter how rugged.

As far as I can tell, its ONLY disadvantage is that it would have more trouble getting post-landing surface photos -- but it could carry a descent camera and memory buffer to record and later play back the last few images before impact to get imaging data almost as good.

Sure enough, Paul G. Lucey -- the Univ. of Hawaii scientist who has proposed the "Polar Night" Discovery-class penetrators to look for lunar ice (they would weigh only 65 kg, penetrate 1-2 meters into the surface, and carry mass spectrometers which have already survived impact tests at four times the planned landing speed) -- is now proposing "Thunderbolt", a mission to look for Europan surface organics. He hasn't yet described it -- and I'm still waiting to hear any details from him -- but it is surely another penetrator mission.

However, there's another problem, as Chris Chyba pointed out in "Europa As An Abode of Life": the probe may have to process one hell of a lot of meltwater to filter out enough organics for study -- quite possibly 100 times more than any pentrator or small surface lander could possibly collect. We may have instead to fall back on a larger and later surface lander with an attached heated melt probe capable of melting down at least 100-200 meters, and filtering all the large amount of meltwater which it produces in the process. And while the waste heat from an RTG would do just fine to generate the melting heat -- that's been the plan from the start -- if Europa's ice is as highly saline as many think, a salt crust would build up ahead of any simple melt probe. It may need both a melting head AND a rotating drill head to chew through the accumulated salt. In any case, I don't see any way to put either of these on a penetrator.

[ljk4-1]

Here's a use for an Europa Ocean Probe - as a neutrino detector!


Paper: astro-ph/0511243

Date: Wed, 9 Nov 2005 17:14:51 GMT (304kb)

Title: Development of Acoustic Sensors for the ANTARES Experiment

Authors: Christopher Lindsay Naumann, Gisela Anton, Kay Graf, Juergen Hoessl,
Alexander Kappes, Timo Karg, Uli Katz, Robert Lahmann and Karsten Salomon

Comments: 5 pages, 3 figures. Proceedings of the ARENA 2005 Workshop
\\
In order to study the possibility of acoustic detection of ultra-high energy
neutrinos in water, our group is planning to deploy and operate an array of
acoustic sensors using the ANTARES Neutrino telescope in the Mediterranean Sea.
Therefore, acoustic sensor hardware has to be developed which is both capable
of operation under the hostile conditions of the deep sea and at the same time
provides the high sensitivity necessary to detect the weak pressure signals
resulting from the neutrino's interaction in water. In this paper, two
different approaches to building such sensors, as well as performance studies
in the laboratory and in situ, are presented.

\\ ( http://arXiv.org/abs/astro-ph/0511243 , 304kb)

[ljk4-1]

Anyone know if clay minerals exist on Europa, or could exist?

http://www.spaceref.com/news/viewpr.html?pid=18272

[Roly]

I know this has come up before but is it possible to do a Europa fly-by within a Discovery cost-cap?

Given that the Europa Orbiter is going to be 2012 at the earliest, surely there is scope for someone to propose something for Europa at the next Discovery AO.

I don't know that much about the design of orbiters, and this may
demonstrate (and probably does) some fundamental misconceptions, but I was
curious about a return to fly-by missions instead of orbiters like Galileo,
Cassini, EO etc. From what I have gathered, for many missions, the largest
problem is the energy required to brake into science orbit, particularly
where there is no potential for aerobraking, meaning a huge percentage of
the mass budget must be spent on a powerful engine and the requisite
propellant. I was under the impression that these problems were vastly
reduced in fly-by trajectories (?) With VEEGA trajectory perhaps this would be possible on a very economical LV (though it seems everything going forward is flying on Delta IV and Atlas now, not Delta II?) Okay so not a Taurus but there must be something in between Taurus and Delta/Atlas EELVs.

So instead of spending mass on an large engine with enough fuel to get into
a science orbit, couldn't the spacecraft instead focus on acquiring a huge
amount of data over a very short period of time in a low-altitude fly-by?
It would then sample a small area of the target at high-resolution.

It could carry (and I'm only guessing, the exposure/integration
times/pointing accuracy might make it truly impossible) stereo cameras and a
high
resolution imaging spectrometer on a motion compensation
scan-platform. All would operate
simultaneously, with power from advanced Solar arrays (Rosetta heritage?) lithium-ion batteries,
which would be charged during the cruise phase by the array to make up for any
power deficit during the very short and high-demand encounter phase. They could even be augmented with lithium primary batteries if required. The
spacecraft would be equipped with extremely wide and fast data busses,
caching the acquired data to memory and writing it out to solid-state disks
for later playback. No-RPS, easier admin. burden, compatibility with Discovery AO.

It would record this to high-capacity solid-state data recorders (multi-100s
GB), and then replay it once it had left its target, potentially over a
period of months or even years, depending on how much power was available,
local limits on the downlink and so on. This eases DSN management perhaps? Offline compression would be helpful, especially given that there might be issues with heavy compression in the Jovian environment (I'm suprised ICT did so amazingly well).

As an added bonus some of the
radiation hardening requirements would be reduced, as the spacecraft would
not be remaining in the most dangerous areas for a prolonged period,
repartitioning mass away from shielding and to the science payload. Lithium polymer batteries might be decent for providing some incidental shielding in any case.

I suspect I am heavily overestimating the ability of the scan platform to
provide adequate motion compensation, and the amount of time needed for the
instruments to acquire data - but I was curious about the idea because it
leverages some of the things that have become much better and cheaper over
time, like bus bandwidth, memory, disk write performance, processing power,
detector resolution/sensitivity - to replace things that have not, like
putting large amounts of propellant and engine mass into orbit.

I read a bit about Firebird recently, which seemed to utilize a similar approach. Perhaps there is geometry which would make possible a "Fire and Ice bird" (like the old JPL 'Fire and Ice' theme) ?

I've wondered out loud about this on other forums but no-one ever seems to have any ideas (other than Orbiters are better, which of course they are...)

Roly

[dvandorn]

It's not just that orbiters are better (though that rather goes without saying, in many ways).

First, there is the issue of time-and-change-dependent observations. If one of your goals at Europa is finding places where the ice crust is thin enough to provide some form of access to the ocean below, you need to observe Europa over a matter of weeks and months and track the movements of the crust.

Second, there is the issue of coverage. No matter how you design your approach trajectory, you're going to be able to observe only a tiny fraction of the surface during a fast fly-by. And there will only be one side sunlit during that snapshot. So no matter how capable a fly-by probe might be, its choice of what it can view is severely limited.

Lastly, there is the politics of funding. We are *barely* to a point where we can think about getting Congress to fund a Europa Orbiter mission -- a mission that we really need, in order to answer fundamental questions and set up a possible landing mission (and, more ambitiously, a mission to explore the subsurface ocean). Because of the points I raised above, a fly-by mission is far less likely to provide those answers, no matter how much data it returns about a very small portion of Europa. And now, *in addition* to funding an orbiter for a billion or more dollars, we're going to ask them to fund an interim fly-by mission for another half a billion dollars? If we were to do that, we'd end up with either the less-useful fly-by and NO orbiter, or (more likely) just getting laughed off the Hill for trying to get them to fund *two* different missions to the same chunk of ice millions and millions of miles away -- a chunk of ice most of them think is worthless in the first place.

Is that a little better answer than a simple "orbiters are better" statement?

-the other Doug

[JRehling]

Second, there is the issue of coverage.  No matter how you design your approach trajectory, you're going to be able to observe only a tiny fraction of the surface during a fast fly-by.  And there will only be one side sunlit during that snapshot.  So no matter how capable a fly-by probe might be, its choice of what it can view is severely limited.-the other Doug

Something that the continued Cassini imaging of Saturn's many moons has made me aware of is the value of terminator observations, which are even more severely limited than observations intended merely to map albedo. A single flyby will show a world in 50% illumination, but only a small fraction of the surface in the low sun angles near the terminator. When Cassini's mission is done, we will be able to generate low-resolution DEMs for all of Saturn's inner icy moons, which would be very hard to achieve by performing direct measurements of altimetry for so many worlds (JIMO comes to mind).

Amateur astronomers know how dull an object the full Moon is, and Mariner maps of Mercury show how much more detail is seen at the terminator than mid-disk. An orbiter (even a Jupiter-orbiting craft) would provide not just twice the imaging of Europa -- in terms of terminator observations, it would provide perhaps 100 times as much imaging.

Any flyby of Europa better be a sample return.

[Guest_Richard Trigaux_*]

Anyone know if clay minerals exist on Europa, or could exist?

http://www.spaceref.com/news/viewpr.html?pid=18272

At rough guess, it is possible, if there are basaltic rocks at the bottom of the ocean. clay is the usual result of slow chemical attack of such rocks by water. But perhaps the chemistry of Europa water is very different of Earth rainwater, so the result may be different. And if Europa has a carbon layer around its rocky core, clay becomes unlikely.

That this clay may arrive at the surface is another question. Europa shows strong evidences of the ice layer being broken is small icebergs and turned upside down, from some catastrophic events. So things in the ocean can reach the surface. That some clay from the bottom of the ocean could reach the surface needs a double transfer, first into the ocean, second into the ice layer. Maybe the catastrophic events can achieve both in the same time.

So a lander could search for such particles in the molten ice. From them it could give clues about the core of Europa

[Guest_Richard Trigaux_*]

I don't know that much about the design of orbiters, ... the largest
problem is the energy required to brake into science orbit, particularly
where there is no potential for aerobraking, meaning a huge percentage of
the mass budget must be spent on a powerful engine and the requisite
propellant.

Would not an economic trajectory achieved with a ship in orbit around Jupiter, using the moons as a gravitational assistance, until getting a nearby circular orbit at the level of Europa, which provides the most economic way to brake and land?

The only inconvenience of this is that it would require some months, and also staying into radiation belts for a long time. So what is gained in fuel may be lost in hardening the electronics.

[Guest_BruceMoomaw_*]

That is exactly the plan that has ALWAYS been written for Europa Orbiter -- it will make, first, about 6 flybys of Ganymede and about 3 of Callisto, and then (in the so-called "Tour Endgame") as many as a dozen close flybys of Europa itself to almost match orbits with that moon before orbital insertion. (For a drawing of a typical such tour, see page 10 of http://www.lpi.usra.edu/opag/jun_05_meetin...ssion_Study.pdf .) The whole process will take roughly 18 months, during which EO will soak up about 900 kilorads of radiation -- equal to the dose it will get during its 1 month in orbit around Europa itself.

As for aerocapture for EO, it's been considered, but -- besides the fact that aerocapture technology won't even nearly be ready for an EO launch by 2014 -- I was told at the COMPLEX meeting that studies indicate that aerocapture doesn't provide much of an advantage for this particular mission. (The plan, by the way, is also to use a flyby of Ganymede to help brake the craft into orbit around Jupiter initially, as Galileo used a flyby of Io for that purpose.) But -- even with all this gravity-assist -- half of EO's weight must be propellant. This is simply a difficult mission.

[Guest_BruceMoomaw_*]

Another description of the "Tour and Endgame" can be found on pg. 23-26 of the most detailed description of the original Europa Orbiter concept at http://outerplanets.larc.nasa.gov/outerpla.../Europa_MPD.pdf . (One nice recent development: calculations now indicate that the total radiation dose that EO will get during this mission is less than half of the originally estimated 4 megarads. This by itself lops 200 kg off the needed shielding weight, and thus about 400 kg off the total spacecraft weight.)

[Guest_BruceMoomaw_*]

Also, you'll notice that the Endgame involves only about half a dozen Europa flybys, rather than a dozen as I stated above.

[ljk4-1]

Perhaps this will require a separate topic, but what will it take to put a lander on Io? Just imagine what surface images will look like from there!

[Guest_BruceMoomaw_*]

That will be a while coming -- the radiation level at Io is 30 times that at Europa!

[Roly]

Thanks for the replies about the orbiters - the constitute the most compelling explanation yet of why you don't bother with fly-by missions unless the target is exceptionally hard. I can see the political point is also important when there is a [F]lagship class mission looking for money (that's a capital 'F' for the large clas flagship that EO will doubtless end up being).

Counting the days until EO arrives. I wish Juno could do some science on the Galilean moons, but I guess that's totally not the point, given the orbit. New Horizons Jupiter encounter should be great.

Roly

[Guest_BruceMoomaw_*]

Yeah, it's been made clear to me by Scott Bolton that they don't WANT to fly Juno close to any of the Galilean moons, even if they get the chance. (Although I would presume that its camera could make some observations of Io's continuing activity.)

In fact, he's now made one interesting point that I had never thought of: Juno is definitely NOT going to have a long prolonged mission. It will have taken a considerable radiation dose by the end of its one-year primary mission, and they want to make sure it doesn't break down before they have a chance to deliberately crash it into Jupiter to make sure it doesn't eventually hit Europa. He's talking about an extended mission of -- at most -- one month, and they will in fact be monitoring its behavior carefully on the chance that they may have to end its mission a little ahead of schedule. (A landslide majority of its useful science will have been done by the first 6 months.)

This one is scientifically aimed at Jupiter -- period -- and (like Mars Climate Orbiter had it succeeded) it's going to do very little that will be of interest to the general public.

By the way, its launch has definitely been bumped now into July 2010 or August 2011.

[Marslauncher]

Is the Europa Orbiter Still on? on was it replaced by Juno?

Just saw a program on Science Channel that mentioned it

[Decepticon]

You know this is very confusing lately. I was gonna suggest a area on this board with a listings of approved missions and future mission as well as canceled/on ice missions.

[Guest_BruceMoomaw_*]

No, Juno AND the Europa orbiter (under its new name, "Europa Geophysical Explorer") are both planned, although EGE won't get its official program start until 2007.

However, one thing that is on hold for now is the previous plan for a Deep Jupiter Multiprobe mission, for which they won't give any go-ahead until they examine the Juno results -- that is, not for quite a while (since Juno won't arrive till 2016). There has recently been a very dramatic, but apparently firm, change in the science community's attitude toward the giant-planet entry probe program, which is yet another item in my "Astronomy" article that I must leave dangling for now.

[odave]

which is yet another item in my "Astronomy" article that I must leave dangling for now.

"Astronomy" needs to pay you a sales commission, Bruce

Any news on what issue your article will appear in?

[Guest_AlexBlackwell_*]

"Astronomy" needs to pay you a sales commission, Bruce 

Or deduct from what they've paid him since he's dropping so many hints

Seriously, though, it's a good thing he didn't submit the article to Science or Nature because his comments here, as helpful and useful as they are to the forum, might constitute "prior publication," which both journals use as grounds for rejection or refusal to publish.

[Guest_BruceMoomaw_*]

My article will be appearing in either the February or March issue. Unfortunately, I ended up with enough material to write a 9.5 page article (AFTER extensive trimming), and so the editors will be hacking it down to 4 pages -- and I'm not sure what complete sections they're going to cut out to do so. I will, at any rate, try to get "SpaceDaily" to publish whatever info "Astronomy" doesn't; and anything relevant that gets cut out there will get put into this blog at some point, rest assured.

[mars loon]

My article will be appearing in either the February or March issue.  Unfortunately, I ended up with enough material to write a 9.5 page article (AFTER extensive trimming), and so the editors will be hacking it down to 4 pages -- and I'm not sure what complete sections they're going to cut out to do so. 

Too bad about the extensive cuts. did you learn that after it was already written?

[Bob Shaw]

My article will be appearing in either the February or March issue.  Unfortunately, I ended up with enough material to write a 9.5 page article (AFTER extensive trimming), and so the editors will be hacking it down to 4 pages -- and I'm not sure what complete sections they're going to cut out to do so.  I will, at any rate, try to get "SpaceDaily" to publish whatever info "Astronomy" doesn't; and anything relevant that gets cut out there will get put into this blog at some point, rest assured.

Bruce:

Perhaps it was a slip of the keyboard, but the word 'blog' caught my attention. Do you produce one? Do you have *time* to produce one?

I'm sure we'd all be fascinated, were you to do so - even when we (quietly) disagree with you, your comments on the unmanned spaceflight scene are without peer!

Bob Shaw

[Guest_BruceMoomaw_*]

Nope, no blog -- I've never quite had the time and/or the nerve. (One recent "New Yorker" cartoon shows one dog telling another: "I considered starting a blog, but I finally just decided to go in for pointless barking instead.")

As for the article, they told me from the start that 4 pages was the length. The trouble is that whenever I attend one of these damn conferences, I get enough interesting material for SEVERAL articles, and then go through the torments of hell trying desperately to hack a 12 to 15-page article down to a few pages while the article bleeds and screams piteously. As with my 2004 article on the MER-A landing for "Astronomy", I finally just had to throw myself on the mercy of the editors by submitting an oversized article and letting them do the dirty work. (A far cry from those bright college days when I was straining desperately to inflate puny term papers.)

[Decepticon]

And I've always wondered why the articles are so fricken short.

[mars loon]

As for the article, they told me from the start that 4 pages was the length.  The trouble is that whenever I attend one of these damn conferences, I get enough interesting material for SEVERAL articles, and then go through the torments of hell trying desperately to hack a 12 to 15-page article down to a few pages while the article bleeds and screams piteously.  As with my 2004 article on the MER-A landing for "Astronomy", I finally just had to throw myself on the mercy of the editors by submitting an oversized article and letting them do the dirty work.  (A far cry from those bright college days when I was straining desperately to inflate puny term papers.)

Bruce, what month in 2004 was that?

Also, hard to say if you used the best approach with the editors. Did you consider 2 versions? one short, one long.

In your opinion did they retain the best stuff? or would you have preferred alternate surgery?

I/we can sympathisize with your pain and torment.

[mike]

Editors are evil. They should be outlawed.

[Rob Pinnegar]

And I've always wondered why the articles are so fricken short.

I guess that, if they weren't short, there'd be no room for the pretty pictures. That was something that _did_ bother me about Astronomy when I was a kid. But I guess that full page images of Saturn are probably a big selling point to the general public.

[Bob Shaw]

Bruce:

I dunno what the copyright issues are (hopefully, you'd be paid *twice*), but perhaps the editors of Astronomy could be persuaded to do a web-only version of your articles, perhaps a month or two after the print version, and which would be somewhat longer? It'd be the sort of thing which might drive us guys to their website, thus giving them a double-whammy on the advertising...

There are publishing imperatives in print media which don't always suit in-depth articles, but there's no reason these days not to claim back the high ground on the WWW!

Bob Shaw

[dvandorn]

Editors are evil.  They should be outlawed.

Reminds me of an old Isaac Asimov short story in which a writer had been cursed by Satan such that he was incapable of writing anything except pact-with-the-devil stories. The upshot is that, after the writer died and went to Hell, the only thing he could end up submitting to the publishers in the Underworld were........


.....wait for it.....


.....pact with the Editor stories!

:::ducking:::

-the other Doug

[mike]

Heh. I dare say almost everything is a pact-with-the-editor story.. and I dare also say that almost everything is dulled down and bland-ized so that it won't 'confuse anyone'. Yeah, why make people think when they can just read pap that reinforces their already long-held beliefs.. WHERE'S MY PAYCHECK SO I CAN WATCH MORE 'FRIENDS'

But I digress...

[Guest_BruceMoomaw_*]

Bruce, what month in 2004 was that?

Also, hard to say if you used the best approach with the editors.  Did you consider 2 versions?  one short, one long. 

In your opinion did they retain the best stuff? or would you have preferred alternate surgery?   

I/we can sympathize with your pain and torment.

My MER story -- along with a 1-page piece on Stardust's comet flyby, during which I expressed my belief in a theory of the craters which I gather is still not proven, but still seems to me probable -- is in the April 2004 issue.

Both then and this time, from the very first they warned me that the final article wouldn't be allowed to go over about 2000 words. I never dreamed I'd have such trouble deciding what to cut out. I was somewhat disappointed that the finished product for MER-A simply didn't include any news you couldn't have gotten from other articles on the subject, but with that short length you just couldn't do much else. The only thing that made me really grind my teeth was that the editor took it on himself to insert a passage in which he listed a bunch of elements and described them as "minerals", thus leaving me holding the bag for looking like a scientific illiterate.

On the bright side, while I hung around JPL for the first 11 post-landing days, I finished the article just before Spirit's computer crisis, which would probably have led me to include a gloomy passage on how the mission was Certainly Doomed.

[Guest_Richard Trigaux_*]

Here
Russia Plans "Long-Lived" Venus Probe
was dicussed the idea of using unconventionnal electronics to sustain the high temperatures (460°C) at the surface of Venus.

There was mainly three methods proposed:
-unconventionnal semiconductors
-micro-sized vacuum tubes implemented witht he techniques of integrated circuits
-micro-sized electrostatic relays

I note that the two latest proposals are also suited to resist to high radioactivity levels, so that they will be a good solution for a Europa orbiter (and even a Io orbiter) by increasing reliability and removing the weigh of shielding.

Developing such techniques will need only a series of small scale test, and then after a relatively short period of large scale development, in a total duration which is not uncompatible with the launching of the mission.

[JRehling]

Another description of the "Tour and Endgame" can be found on pg. 23-26 of the most detailed description of the original Europa Orbiter concept at http://outerplanets.larc.nasa.gov/outerpla.../Europa_MPD.pdf .  (One nice recent development: calculations now indicate that the total radiation dose that EO will get during this mission is less than half of the originally estimated 4 megarads....

It's seemed to me that if we found a way to transform the radiation from charged particles into energy, we'd solve two problems at once for Jupiter missions. Surely if the particles were segregated, this would be possible. I imagine the problem is that the net charge of any stream would be neutral and trying to segregate them would require more energy than you would get out of them... although I'm not *sure* that is so. If you could "split the beam" and get a net negative hitting a cathode and a net positive hitting an anode, you could run a current strong enough to power the beam splitter... in principle. Then you'd have a mission that would would *want* to fly, eg, near Io/Europa orbit. (And a generator that wouldn't much work anywhere else.)

[Guest_BruceMoomaw_*]

Uh-uh. Back when I was posting to the Europa Icepick website, I once did the actual calculations on the energy flux from Jupiter's radiation belts -- which turned out to be pathetically small: about five orders of magnitude less than you need to power a spacecraft! The belts are splendid at poisoning solid-state electronics (or biochemistry), but as a power source they stink.

However, running a long conductive tether from a spacecraft and letting it plow through Jupiter's intense magnetic field is a very different matter -- for an orbiter of Jupiter or one of the moons, that will work beautifully, if you're willing to put up with the tether.

[Guest_Richard Trigaux_*]

However, running a long conductive tether from a spacecraft and letting it plow through Jupiter's intense magnetic field is a very different matter -- for an orbiter of Jupiter or one of the moons, that will work beautifully, if you're willing to put up with the tether.

There was such an attempt by the NASA to fly a tethered satellite around Earth using this system, and it worked very well, providing a good power, except that the mechanical forces acting on the cable were stronger than expected, breaking the cable. Around Jupiter it would work well, and perhaps too around other giant planets. That will be safer than using a RTG, and potentially it could yeld more power. (RTGs too are good at poisoning electronics, although around Europa their action is smaller than the indigenous radiations)

[edstrick]

"except that the mechanical forces acting on the cable were stronger than expected, breaking the cable"

Actually, they had undetected flaws in the insulation on the conductive tether, possibly some grit in the insulation or between it and the wire (not sure working from memory). It electrally shorted through to one of the pulleys or guides on the deployment mechanism, and the considerably higher ELECTRIC CURRENT than expected burned through and severed the tether. That part of the experiment worked too well... oops!

[Guest_BruceMoomaw_*]

Yep. In fact, when I finally read about that incident in detail, I was startled to learn that it was due to a completely unexpected phenomenon that they still can't explain: they had an electrical arc run from the cable to the end of the deployment boom that -- amazingly -- continued to flow for several seconds after it had melted through the cable, while the end of the cable was drifting away from the boom. Apparently some kind of gas leaked out of the Shuttle to allow the arc, but they have never solved the mystery. This makes me a bit more inclined to forgive the Italians for having us fly that Shuttle mission twice and have it fail both times.

[Guest_Richard Trigaux_*]

Yep.  In fact, when I finally read about that incident in detail, I was startled to learn that it was due to a completely unexpected phenomenon that they still can't explain: they had an electrical arc run from the cable to the end of the deployment boom that -- amazingly -- continued to flow for several seconds after it had melted through the cable, while the end of the cable was drifting away from the boom.  Apparently some kind of gas leaked out of the Shuttle to allow the arc, but they have never solved the mystery.  This makes me a bit more inclined to forgive the Italians for having us fly that Shuttle mission twice and have it fail both times.

This is really odd, and cannot explained by the static charge of the shuttle: it had to receive current from somewhere else, to form a circuit with the cable. And the arc had to be pretty long, to be still sustained seconds after breaking.

There may have be some halo of gaz around the shuttle. Weren't emptying their toilets at that time? Letting some ice block stuck at the shuttle sending high flow of steam all around? This could be the origin of many "unexplained" phenomenon, water steam being especially conductive.

With my opinion this experiment should be made again, using two technological satellites, not the shuttle.

[mars loon]

Some bad news about the prospects for a Europa Orbiter have just been posted by Lou Friedman of The Planetary Society

see this link:

http://www.planetary.org/programs/projects...e_12142005.html

first 3 paragraphs:

By Louis Friedman
December 14, 2005

In the recently passed NASA Appropriations bill, the US Congress directed NASA to begin work on a Europa orbiter and to make a request for a new start for a Europa mission project in fiscal year 2007. This was welcome news to NASA, who lost their focus on Europa when the nuclear propelled Jupiter Icy Moon Orbiter mission was cancelled last spring.

But now word has it that there will be no Europa proposal in the 2007 budget proposal that will be made to Congress early next year. The Washington Aerospace Briefing, a respected newsletter publication of Space News, is reporting that the Administration’s Office of Management and Budget is denying the Europa request on budget grounds.

The Planetary Society will fight for a Europa mission. Whether or not is in the budget request, we will lobby in Congress for its inclusion in the NASA program. Our Explore Europa Campaign is already in full swing. Having Congress insert funds in the ’06 budget was a good start, but we need to ensure support in 2007 and beyond.

[Guest_vjkane2000_*]

NASA's science budget is a mess -- too many missions, several with large overruns. It would be irresponsible to add a $1B+ mission into the pie until everything else gets straightened out. What might be useful, though, is some early development money next year to get things moving again.

[Guest_BruceMoomaw_*]

The plan was to just insert about $10 million this year for initial design studies -- including making absolutely sure that they DO want to fly Europa Orbiter before any of the other possible Flagship-class missions. Once again, we have a case of the idiotic manned program eating the rest of NASA alive.

[Decepticon]

Once again, we have a case of the idiotic manned program eating the rest of NASA alive.

I could have not said that better!

[Guest_AlexBlackwell_*]

Once again, we have a case of the idiotic manned program eating the rest of NASA alive.

Not that I don't think that NASA's manned space program is becoming a larger and larger money pit, but I'd like to see hard evidence that money not spent by NASA there would be transferred over to space science. A great many legislators appropriate funds for Shuttle/ISS because the money is spent in their districts for that specific purpose. It's amazing how many people believe that eliminating billions of dollars from the NASA EMSD would automatically result in an increase for NASA SMD.

This post has been edited by AlexBlackwell: Dec 16 2005, 08:09 PM

[Guest_BruceMoomaw_*]

The very fact that Congressmen fund NASA as pork to their home districts indicates that if the manned-program budget was cut, SOME of the money thus saved would get transferred to the unmanned program.

[mars loon]

The very fact that Congressmen fund NASA as pork to their home districts indicates that if the manned-program budget was cut, SOME of the money thus saved would get transferred to the unmanned program.

I dont see how you can make that connection. Your suggestion may or may not be true

Hopefully this truly worthy mission does get funded somehow, despite the gloomy outlook.

[scisys]

I dont see how you can make that connection. Your suggestion may or may not be true

Hopefully this truly worthy mission does get funded somehow, despite the gloomy outlook.

It has always seemed to me that the problem with the manned program is not that allocated funds are coming at the expense of the unmanned programs. The problem is that *cost overruns* in the manned program are carved out of the hide of the unmanned program. This nails you every year even after a mission is scoped and funded. Heck it even nails you during ops.

Still, this argument has been going on since forever. The reality is that the unmanned program has to live within the boundries defined by the, admittedly excessive, needs of the manned program. I don't like it but I don't see a way to change it. It is inlikely that money cut from the manned program will end up in the unmanned program. However, a reined-in manned program would be less of a yearly threat to the unmanned program and cause fewer 're-engineerings', 'budget exercies', 'descopes', 'stand-downs', 'development deferrals' ... pick your favorite euphemism for feeding the beast that is the manned program.

My personal feeling on a Europa mission is that it needs to focus on two questions: "is there (still) liquid water (for sure)?" and "where are the thinnest parts of the ice?". One has to hope the answers will be such that the justification for follow-on missions will lead to penetrators and landers, etc. The tendency towards a Galileo style tour must be avoided at all cost. It should be a Europa only tour. Otherwise the flight ops budget alone would kill the mission when you start adding all the systemic requirements for mission planning and resource allocation. I know we don't go out there very often and Jupiter ain't Mars, but I don't see any Galileo/Cassini style missions coming along anytime soon (or long term to be honest).

Perhaps a Europa mission should become a near term component of the Origins Program (would that be a good thing or more likely to kill it?)

[Guest_BruceMoomaw_*]

Actually, the Europa Orbiter is a good deal more complex as a mission than a replay of Galileo would be, given the technology and experience we now have. Indeed, a Jupiter orbiter that makes dozens of Io flybys is one of the second-rank candidates for a New Frontiers mission -- which means, given NASA's likely change to the NF proposal rules, that they'll accept ideas for it in the next round of NF selections in 2008. Such a craft would make Ganymede and Callisto flybys anyway to keep modifying its orbit to fly over different parts of Io's surface and at different phase angles, so it could easily be turned into a mission to study all three of the remaining Galilean moons. Indeed, it could be a virtual duplicate of the Europa Orbiter but with much less onboard fuel -- the radiation shielding for EO would allow such a craft to make at least 25 close Io flybys (maybe 50; I've got to recheck my records).

In fact, since EO itself will have to make a total of about a dozen Ganymede and Callisto flybys to get into position for Europa orbit insertion, it is virtually certain to make major observations of those moons -- and Jupiter itself -- during the 18 months or so before it goes into orbit around Europa itself.

[scisys]

In fact, since EO itself will have to make a total of about a dozen Ganymede and Callisto flybys to get into position for Europa orbit insertion, it is virtually certain to make major observations of those moons -- and Jupiter itself -- during the 18 months or so before it goes into orbit around Europa itself.

I guess this is one of the tendencies I think probably dooms a Europa Orbiter. I really do understand the forces which would drive the desire for such observations (particularly given the loss of atmospheric dynamics data from Galileo) but such observations do not come for free. Building this into a reference mission plan will lead to instrumentation choices driven partially by such observations. It is expensive to develop such observation plans. Would there now be a scan platform? That costs in many ways (hardware design, assembly and test; ops planning software; constraint checking; etc.). No scan platform? Then you have the attendant fights over spacecraft orientation. An S/C designed to be an orbiter can be purely a nadir look design with perhaps a side look radar.

Allowing for 'cruise science' grows the flight team during what could be quiescent time. Getting into orbit aroudn Europa *is* complex. It just seems to me that a mission design that avoids any additional complexity or design drivers would have a greater chance of approval. By allowng cruise science you now require an S/C that is part fly-by and part orbiter. Throw in serviing as a delivery bus for a lander and you are starting to talk real money. As more is added, there is a non-linear increase in integration costs.