I think that many people in this forum would agree that somebody's going to have to land on Europa someday before the rather elaborate schemes to penetrate the outer ice layer will ever fly, if for no other reason than to get some relevant ground truth before committing to such an elaborate, expensive, and risky mission.

EO seems to have ruled out any surface science package for that mission (though it would be nice to change their minds! ), but I think that there is a valid requirement at some point to directly assess the surface properties of Europa in an inexpensive yet creative way. Some candidate instrument payloads might be:

1. A sonar transducer/receiver set embedded within a penetrometer to determine crust density and examine the uniformity of the ice layer within the operational radius of the instrument (looking for cracks and holes, in other words).

2. A conductivity sensor again embedded inside a penetrometer to measure the native salinity of the surrounding material and possibly derive some constraints on the composition of metallic salts in the European crust (saltiness has a major effect on ice properties, in addition to the obvious need to derive the salt content of any underlying ocean).

3. A seismometer for all sorts of reasons.


How does this sound? Any critiques, additions, or subtractions? I omitted a surface imager not only because of bandwidth/extra complexity considerations but also because it seems desirable to penetrate the crust in order to minimize as much as possible reading any contaminants from Io during surface measurements. The orbiter data could be used to sense and subtract this from the penetrometer readings.

The all ice surface would facilitate the use of penetrators instead of more complex landers. Ideally, look for vented material that came to the surface from a fissure, and maybe there would still be some organics left over. But yes, I would want a seismometer!

JPL's study of useful instruments for a small Europa lander listed, in order of priority:

(1 & 2): A surface GCMS (or, better, a mass spectrometer combined with some kind of liquid chromatography) to look for organics and other interesting compounds; and a seismometer to try to sound the thickness of the total ice layer.

(3) A magnetometer to make induced-field measurements simultaneously with an orbiter to obtain data on the thickness of both the ice layer AND the underlying liquid-water layer.

(4) A surface panoramic camera.

There was, as I've noted, a knockdown debate on this subject at the November COMPLEX meeting -- including an unbelievably dreary and nitpicking debate over the usefulness of seismometers and magnetometers, culminating in the general conclusion that you'd need at least 1 or 2 weeks of data from them, which requires powering the lander with a small RTG rather than batteries.

But the trouble, again, is that the most important measurement by far would be a search for possibly biological organic compounds buried deeply enough in the ice that Jupiter's radiation won't have scrambled them unrecognizably -- and such a small lander probably can't drill the 1 or 2 meters necessary for that purpose. Any of the other measurements that a small lander could make can just as well be delayed and then put on the first dedicated larger Europa Astrobiological Lander mission to look for near-subsurface organics, at a site selected by Europa Orbiter.

The obvious possible solution to this problem would be a penetrator, and in fact at the meeting I spoke up and suggested just that. (It has other major advantages, too -- elimination of the need for a heavy final braking or shock-absorption system, shielding of the lander from Jupiter's destructive radiation by the ice itself, and better coupling of the seismometer to Europa's surface.) Unfortunately, Torrance Johnson was one step ahead of me. He said that just this possibility was examined in depth by the JIMO science definition team, and it turned out that penetrators on airless worlds have one huge Achilles heel -- there's no airflow to keep their nose pointed straight in their direction of travel when they hit the surface. So you need to add a big and complex attitude-control system to do this, or your penetrator will hit the surface slightly skewed, at which point you're screwed.

Still, Paul Lucey of the University of Hawaii is proposing "Thunderbolt" -- a Europa penetrator to look for subsurface organics (a descendant of his "Polar Night" Discovery proposal that would launch three small penetrators from a lunar orbiter to look for polar ice). The COMPLEX people actually suggested that I should get in touch with him to see if he's found a possible solution to the attitude-control problem, and while I haven't been able to contact him yet I intend to do so after New Year.

By the way, I'm telling you guys all this because every crumb of it had to be cut out of the shortened version of my upcoming article on the COMPLEX meeting for "Astronomy".

An interesting factoid is that penetrating into lunar ice would be operationally very similar to penetrating into Europan ice -- if there is lunar ice on the surface of comparable purity (I suspect it's dirtier). That is, the orbital-->impact delta-v would be very similar. The main difference is that a lunar ice mission would end up in darkness. Of course, the instrument selection might be quite different as well.

as Bruce points out.. hit the surface slightly off dead-on, and you're screwed.. and slightly off is very damn little, I think. NOT trivial.

Regarding the lunar polar ice. I think the best evidence is fairly clear. Despite the weak claims of a signal of ice in bistatic-radar data using the prospector or clemantine (forget which) data, earthbased radar reveals no trace of depolarized backscattered signals from low attenuation, thick ice deposits in the lunar cold-traps. They see it on Mercury's polar ice, the martian poles, and icy galillean satellites. Not the Moon.

This agrees with (I dont' remember who's) model for lunar volatile sources and sinks, combined with models for loss mechanisms from polar ices, including radiation sputtering, UV photodissociation (interplanetary and interstellar Lyman Alpha), impact gardening etc. The conclusion was that the most plausible model had many percent but not tens of percent ice mixed with regolith in the polar cold traps to depths of meters or more. This would be rather hard to spot optically, except maybe by scanning with infrared lasers, one in a strong ice absorption band, the other just outside the band.

A real resource, but not one you'd want to squander as hydrogen for rocket fuel, etc., except on the shortest term.

There are *natural* penetrators as well as man-made ones. All we do, is look for a nice fresh impact, fissure, mini tiger-stripe or whatever, and land there. Turn a few ice boulders over, and there's your reasonably deep, reasonably fresh sample.

An orbiter with *good* imaging would be required, plus a smallish lander (perhaps attached to the orbiter, or not - the orbital dynamics might make it cheaper to have survey orbits/descent profiles which are best served by two vehicles).

Bob Shaw

I think it is going to be pretty difficult to argue for/design a complex lander on Europa without establishing ground truth with a simpler lander. If there is no lander on the next mission, then I suspect it will be two missions beyond before we see a very capable lander.

Re the penetrometer descent alignment problem: Wouldn't a "nose-heavy" penetrometer with an elongated body tend to align itself to local vertical during descent regardless of the presence of an atmosphere? If I'm not mistaken, a variation of this sort of tidal stabilization is used on terrestrial comsats for attitude stabilization up at GEO. Even though Europa's gravity gradient is much gentler, a penetrometer launched with a sufficiently low delta-V with respect to Europa should therefore have enough time to align itself properly during the descent.

Uh-uh. An object that short would take weeks -- and maybe months -- to align itself, and then it would point itself straight downward instead of in the direction of motion. There is no simple solution to this problem.

As for a smaller lander to provide ground truth for the later bigger ones, there are two possible ways in which this could be useful -- but there are cheaper alternatives to both. First, of course, we need really high-resolution pictures of Europa's surface to see what kinds of landing hazards exist -- especially since the data we have up to now suggests that the surface may be extremely rugged, laced with crevasses and small ridges. But Europa Orbiter is now virtually certain to carry a big MGS-type camera for very high-res photos of some patches of the surface from orbit.

Second, it might be wise to get a measure of the salt content of the ice before sending a big lander that would probably obtain its data by releasing a short-distance Cryobot to melt its way 100 meters or more into the surface. (We want to be sure of getting below the upper layer of radiation-modified surface material -- which may have been gardened by impacts a fair distance into the surface if we're unlucky -- and Chris Chyba has also pointed out that a Cryobot may be the only way of gathering and filtering enough meltwater to have a good chance of detecting small amounts of biochemicals.) But high salt content might jam up a Cryobot by causing it to build up more and more concentrated brine in front of its nose until you had a block of salt which it could not melt through -- so it may be necessary to add a mechanical grinding head to chew down through this at the same time that you melt the ice. However, EO is virtually certain to carry a good near-IR spectrometer -- and a mass spectrometer to analyze the molecules of Europa's surface sputtered into the space above it by Jupiter's intense radiation -- and these together should be able to answer that question. (They may even add an X-ray spectrometer for direct element measurements.)

I've wondered, though, if it might be worthwhile to put a small sterilized impactor on EO, equipped with a camera, to be released during the last flyby of Europa which the craft will make to almost match orbits with the moon before it finally fires its rocket engine on the next pass to enter orbit around it. This could provide us with very close-up pre-impact photos that might provide more data on surface roughness -- and the Orbiter might be able to fly through the cloud of debris thrown up by the impact (Ice Clipper-style) to do a better mass spectrometric analysis of Europa's main surface constituents. And such an impactor would of course be much lighter than a flat-out lander, especially since EO wouldn't need to carry the fuel to brake its mass into Europa orbit. I still imagine the data from this would not be worth the monetary and mass cost, but I DO intend to ask the mission's designers about the possibility.

Hmm. How about a "semi-hard" lander al a Ranger instead? (...without the balsa wood, of course!)

Seriously, if the velocity differential is small enough during the final flyby, maybe something like a minature version of the MER EDL system without chutes but augmented by a retro could drop a nice little instrument suite on the surface with a high probability of success.

Two wild ideas:

1) Europa has an atmosphere though it is extremely thin. Might some kind of large drag chute or balloon give enough drag to stabilize a penetrator? A penetrator would be long and thin, so it would not require much drag to align it.

2) Armor piercing projectiles use a "sleeve" of softer material (e g lead) to hold and align the penetrator on contact with the armor.
However the ice may be to soft to "strip" the sleeve and in any case I think it would only work if the penetrator comes in more or less vertically.

tty

Europa's atmospheric pressure is something like 10^-7 bar... which, according to Wikipedia, is 10 times less than the pressure on Earth at which aerodynamic surfaces cease to function. (Europa's atmosphere is oxygen gas, so density for a given pressure should be similar). The drag is enough that you couldn't orbit at 1 m above the surface for too long, but methinks it would be a little low for penetrator alignment.

Perhaps a future mission would drop an impactor at high velocity to vaporize some ice and a carefully timed following craft would decel in the plume . . . .


{dramatic to watch, but would it work?}

It was called the Europa Ice Clipper:

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

It's too bad there is no GPS system on Europa. The new US/Swedish Excalibur guided artillery shell actually has a miniaturized GPS/INS guidance package and solid rocket attitude control system that is not only ruggedized to survive being shot out of a 155 mm gun and small and light enough to fit inside a 155 mm shell, it's also dead cheap compared to normal space hardware and built to stand long-term storage without maintenance.

tty

I don't know how much GPS would really help, but a good, cheap minaturized INS is a must-have, along with that solid-rocket attitude control system...maybe add a radar altimeter in the nose of the penetrometer & have the steering algorithm just hunt for the max rad alt return amplitude that's closing in correspondence with the descent rate, which would presumably wash out side-scatter....? Hmm, this sounds more do-able...

AlexBlackwell posted the fact that the 2006 Discovery Ao window is now open:

http://www.unmannedspaceflight.com/index.p...t=0&#entry34412

Anybody feel brave enough to submit a proposal for a Discovery ridealong penetrometer for EO based on what we've chewed over so far? I have no academic or industry affiliation, nor am I a scientist, so all I can do is instigate...

I think it is the best solution. A mission of two steps: 1) simpler lander to ascut the surrondings in order to identify the required characteristics for the second mission. 2) The second mission will be properly designed according to the 1st mission to get the a more detailed mission such as a kind of penetrator.

The best experience is : Advance slow but as firm as possible.

Rodolfo

Tell me this wouldn't be useful for an Europan ocean probe:

A SUBMERSIBLE HOLOGRAPHIC MICROSCOPE. A new device allows
scientists to form 3D images of tiny marine organisms at depths as
great as 100 m. The device allows the recording of behavioral
characteristics of zooplankton and other marine organisms in their
natural environment without having to bring specimens to the
surface for examination. Scientists at Dalhousie University in
Halifax, Canada, used the hologram arrangement originally invented
by Denis Gabor: light from a laser is focused on a pinhole that acts
as a point source of light if the size of the hole is comparable to
the wavelength of light. The spherical waves that emanate from the
pinhole illuminate a sample of sea water. Waves scattered by
objects in the sea water then combine at the chip of a CCD camera
with un-scattered waves (the reference wave) from the pin hole to
form a digitized interference pattern or hologram. The digital
holograms are then sent to a computer where they are digitally
reconstructed with specially developed software to provide images of
the objects. The Dalhousie researchers packaged their holography
apparatus in such a way that the laser and digital camera parts are
in separate watertight containers, while the object plane is left
open (see figure at http://www.aip.org/png/2006/255.htm ). One
difficulty was to get container windows of optical quality that are
thin enough for high resolution imaging but thick enough to resist
sea pressure. The new submersible microscope can also record the
trajectories of organisms in the sample volume so that movies of the
swimming characteristics of micron size marine organisms can easily
be produced. Holograms with1024 x 1024 pixels can be recorded at 7
to 10 frames/s. This requires a large bandwidth for data
transmission to a surface vessel and was accomplished with water
tight Ethernet cables. Imaging volumes can be several cubic
centimeters depending on the desired resolution. The Gabor geometry
allowed the Dalhousie researchers to design a very simple instrument
capable of wavelength limited resolution of marine organisms in
their natural environment. Past generations of submersible
holographic microscopes had lower resolution, weighed several tons,
had to be deployed from large ships, and used high-resolution film
as the hologram recording medium. This meant that only a small
number of holograms could be recorded. In contrast, the Dalhousie
instrument only weighs 20 kg, can be deployed from small boats or
even pleasure vessels, and can record thousands of holograms in a
few minutes so that the motion of aquatic organisms can be captured
in detail. (Jericho et al., Review of Scientific Instruments,
upcoming article; contact M.H. Jericho, Dalhousie University,
jericho@fizz.phys.dal.ca, and also the Universidad Nacional de
Columbia)

***********
PHYSICS NEWS UPDATE is a digest of physics news items arising
from physics meetings, physics journals, newspapers and
magazines, and other news sources. It is provided free of charge
as a way of broadly disseminating information about physics and
physicists. For that reason, you are free to post it, if you like,
where others can read it, providing only that you credit AIP.
Physics News Update appears approximately once a week.

Karl Hibbitts describes a proposed hyper-velocity impactor that would
smack right into Europa’s outer ice shell.

http://www.astrobio.net/news/article1944.html

It seems that at the November 2005 COMPLEX meeting there were
4 options presented for a Europa Lander that could be included as part
of the Europa Explorer mission.

Each of these options assumes the same plan for initial descent.
First, the lander arrives, eventually, with the Orbiter in a circular 100-km orbit
around Europa.
Second, after separation, the lander fires a thruster to
decrease velocity by 22 m/sec. This puts the lander into a 100 x 1.5 km orbit
around Europa.
Third, a large rocket burn takes place at periapsis to decrease velocity by 1,500 m/sec.
This essentially stops the lander cold and it begins to free-fall the last
1.5 km to the surface. This is the Stop and Drop maneuver. The remainig descent
to Europa's surface is where the designs diverge.

These are details of each of the 4 proposed lander designs.

1. JMI - Jovian Moon Impactor - This probe falls all the way to the
surface, impacting it at 62 m/sec. It is designed to withstand 5,000 - 10,000 g's and
looks to heritage from the Deep Space 2 Mars penetrators. This is where a precursor
mission like DS-2 has its payoff.
JMI Mass = 65 Kg

2. EPF - Europa PathFinder - After the Stop and Drop, EPF free falls to the surface, but
cushions its landing with 3 airbags, similar in size to the Beagle 2 design. The EPF itself
is desinged to withstand 600 g's and is saucer-shaped.
EPF Mass = 220 Kg

3. ESSP - Europa Surface Science Package - After the Stop and Drop, the ESSP utilizes
thrusters to slow its descent. The thusters cut-off at about 10 meters and ESSP freefalls
to semi-soft landing at about 40 g's or somewhat greater.
ESSP Mass = 350 Kg

Each of these first 3 landers is designed to have payload masses of about 7 - 8 Kg,
a lifetime of 3 days, power levels of about 10 W,
with a total science data transmission of 200-300 MBits.


4. IML - Icy Moon Lander - A true soft lander, using thrusters all the way to the surface
after Stop and Drop. Landing at less than 40 g's and using an RTG.
TMI Mass = 825 KG
The TMI is designed to last for 30 days, to have a power level of 100 W, to have a payload
mass of 40 Kg, and to transmit a total of 7 Gbit of data.

I think that the IML and/or the ESSP may use crushable materials to cushion the
landing on Europa. Also, these landers are able to be considered since the new
mission design for the Europa Explorer envisions using the Delta 4 Heavy as the launch
vehicle and the use of a VEEGA trajectory. The VEEGA trajectory design utilizes 1 Venus
and 2 Earth flybys and enables 7,000 Kg to be sent on the way to Jupiter.
This contrasts with the original Europa Orbiter design that contemplated
a payload of only 1,500 Kg to Jupiter.




Another Phil

Why to limit the life time of a surface lander? if it has no RTG, it is understandable that the battery limits the lifetime (when it is exhausted). But a RTG has a theoretical lifetime of 30 years or more.

I know what the limiting factor is: radioactivity, which will quickly destroy any electronics. However there would be some strong interest into having a long lived probe on Europa surface:

-long run seismometre recording (a lone seismometre is not very useful, but a further mission may bring another one, so that they could work as a network and explore inner Europa structure, provided that the first is still working 10 or 20 years later).
-use it as a beacon or GPS emitter for a further mission or landing
-detecting underground SOUNDS on Europa, which may help to understand the oceanic properties.



So what I propose would be that the lander may have a pod, which would use the excess RTG heat to bury a small emitter/seismometre deep enough into the ice, so that it would be protected against radiations and could work for 20 or 30 years.

Could there be alternative power sources other than RTG?

-solar panels could still have some efficiency on Europe, but they would quickly degrade with radiations.

-a long wire left on the ground may gather enough electricity to feed a small circuit, with an emitter working in burst mode. On Earth, during magnetic storms, continuous currents can appear into power lines, strong enough to disturb their normal operation. On Europe, which moves into Jupiter magnetic field, a large copper loop laid on the ground may gather enough energy to feed a small aparatus, without all the hassle and problems of a RTG, insensitive to radiations, and for a virtually infinite time. A large capacitor battery would store the energy for emission bursts, of during magnetic storms (the current may be sometimes zero), without a limited lifetime like batteries.

Mainly with an eye towards the mass budget. There are time-varying phenomena on Europa, and there are non-time-varying phenomena (at least, on cycles of greater than 30 Earth days). Only a magnetometer and seismograph would be useful over long time scales; other than the diurnal changes in light and those two experiments, the only requirement for a long lifetime will be to grab samples near the craft... and that might be rather homogeneous itself. Some of the time variation the magnetometer will go looking for would repeat many times in 30 days anyway. So the question is how much mass is it worth (taking it away from surface composition instruments, or orbiter instruments) to get a long life out of a seismometer?

I would say that a long-lived seismometer would be worth quite a bit. Consider all the variables (potentially) involved: sub-shell oceanic tidal effects on the crust, undersea vulcanism, crustal structural failure events, resonance flexing from the other big moons...the seismic environment on Europa might be quite complex indeed, and thus would require long-term data acquisition.

Of course, you really need a lot more than one seismometer in one location to get a really useful dataset.

and also very difficult to read, as whatever comes from the rocky core would have to pass through a liquid layer (eventually not continuous) and an ice layer (eventually not heterogenous). Worse, the water layer would play as a wave guide, bluring the origins of vibrations.

So with my opinium we should send a simple mission with one seismometre which would:

1) give an idea of rocky quakes (long term), to give an idea of how do do for a future cluster.

2) estimate the depth of ice and water layers. (a very useful step for a further lander/driller)

The best place on Earth to test the 2) would be on Ross ice shield, which is freely floating over water.

1) would work with a small lander,using a wire loop to sustain a long-term activity.

2) would be a one-shot, in the litteral meaning: a small shell impacts the surface at a (relatively) high speed, which produces seismic waves. Then it waits for the return from the ice bottom and ocean floor. Shortest mission than on Venus! This seems to be the simplest mission we can imagine, with yet an important result: the thickness of ice and water. Only hitch: it seems that most of Europa surface would rather be a layer of rubbles than plain ice. So this shell should aim at places where ther is plain ice, in the chaotic regions. This is a problem of a homing missile relying on a stored image of the target.

A panoramic camera plus an astronamic telescope to observe closer to Jupiter changing clouds would be a MUST! It is for observating for any change phenomena that might happen on Europa moon.

Rodolfo

I don't see that reasoning. Europa is in the thick of radiation belts, and any telescope would be a lot of mass that would have to be gently landed on Europa. You would get better and longer-term imagery of Jupiter by having a bigger telescope orbiting Jupiter outside the radiation belts. There's no reason to take a Jupiter-aimed instrument and waste rocket fuel putting it on the surface of Europa.

Just in terms of Jupiter distance, there must be an optimal radius for a telescope in terms of fuel needed to put it into orbit vs. resolution vs. radiation-limited lifetime. I don't expect that optimum to be at Europa, where anything not underground is going to die in months from radiation.

Why? If you want to observe jupiter - have a jupiter orbiter. Spending the time, volume, mass, energy and data to do it from the very very very harsh surface of Europa is just stupid.

Doug

Considering the deliverable mass potential, and our recent experiene with MER, I think it would be silly to send a fixed lander rather than a rover. Seems like the MSL design ought to be nearly ideal for Europa, and it already has radioisotope generators integrated. I suspect that mission planners are assuming that the surface will be dull and homogeneous, so that one spot is as interesting as another. This may be a mistake, so why not use off-the-shelf technology and provide some options. At the very least, a rover would be a handy means of deploying a seismic network.

I'm sure everyone would love a massive long life rover on the surface of Europa....who wouldn't. Every scientist, every engineer would LOVE to have a rover on Europa.

And we'd all like New Horizons to be a Pluto Orbiter, and DAWN to be sample return, and Messenger to be a lander......

But you have to do what is feasable given time, money, and in this case technology. I would wager that if you put MSL on the surface of Europa - it would be dead with a week due to radiation, MC might be able to comment, but I'd think Mastcam would just get quietly fried. 'Shield it' you might say....that would requrie so much shielding the thing would never get off the pad. (because every kg of shielding requires kg's of fuel for landing, and THAT required multiple kg's of payload capacity )

A comparatively simple impactor / hard lander, perhaps with a decent imager, short life etc...that's currently feasable in a sensible time frame and budget and would tell us a hell of a lot about Europa.

MSL will be ( hopefully ) the 7th succesfull landing on Mars. 4 of those were/will be static landers.

If we were talking out 4th Europan lander..I'd be going 'hell yeah - let's go for wheels' - but for our first effort....one needs to be modest in requirements.

As Alan has said w.r.t. NH.....better is the enemy of good enough.

Doug

Yes I agree with djellison and others.
To give the Europa lander plan the chance to get trough the budgetary squeeze it will have to be the lightest and in some ways simplest kind of lander imaginable. So the actual landing might not even be a 'soft' one but actually take advantage of getting buried to ensure that the lander doesnt die from radiation prematurely.

Then again about radiation, would there be any advantage of landing on Europas trailing side?

A buried or semi-buried lander might also include a simple sampling system.

Imagine adding a radiactive heating element of a similar kind to those the MER are using, such would melt a bit of ice which would pour inside to any choice of sensors the designers could fit into such an instrument package. This one could answer some basic questions such as:

Have the ice on the landing spot ever been circulated in the interior or Europa? Does it contain any gasses? If so which ones?

Have the contents of the sample been changed in any way by radiation?

Lastly: Does it contain anything else but lighter elements? If not, which ones and what are their origin?
Yes I think of possible volcanic matrial from Io of course, if we're very lucky we might get one small peek at an Io sample for free.

I don't think we can bet that a Europa rover wouldn't land in a hopelessly craggy "warzone" of infinite overlapping crevasses that make roving impossible. A bouncing lander would have an increased chance of settling into such a cranny. Remember that in the case of Mars, smooth at low resolution has tended to mean rough at high resolution and vice versa. On Earth, that's not quite true. So we can't bet on landing on what seems to be a smooth frozen pond and getting a slick, smooth surface: it could be bad news at rover-wheel scales.

I did a quick web-search to see if there are any results from terrestrial radar on the roughness of Europa, but it's clear that terrestrial radar is not well disposed to answer the question: a 2001-published study using 70cm wavelengths didn't even *find* Europa. The icy Galileans are very bright at shorter wavelengths. We know from the best Galileo images that some of Europa looks very rough at 6m/pixel. That is already an important answer for a rover that would want to travel more than 12 m!

Simply put, we can't bet the bank there there exists any Europan terrain that a wheeled vehicle can traverse, so we're not going to invest billions on one and hope for the best.

Furthermore, we don't know if anyplace on Europa is interestingly diverse at rover scales. If we did land on a big smooth homogeneous ice sheet, why rove at all?

DISadvantage! Jupiter rotates much faster (~7x) than Europa orbits, so it's precisely the trailing side that gets the most radiation. This generates obvious effects on Callisto, at least, where the pattern of CO2 deposition shows lead/trail effects.

To make good on your idea, landing smack in the middle of the leading side would block some radiation. I imagine a bouncing lander that ended up in a "hollow" would get some additional help. The radiation exposure of a well-placed lander might be a factor of a few less than something orbiting Jupiter as a Europa trojan.

Now I understand that it is very expensive to send a spacecraft around Jupiter due to the high radiation exposition. That is the factor that leads to build a more expensive spacecraft in having a good radiation hardened on many eletronic parts (camera, pancam, navcam, telescope, sensors and others electrical parts) and also shielding on these components externally. At the end, that will add much weight to the spacecraft and also increase even further the weight for propulsion landing combustible.

In spit of the fact of high radiation on Europe, there will be any kind of camera shoothing on the surface?

Rodolfo

We have no actual mission in place - so we don't know

Doug

Harkening back to the origin of this thread, I completely agree that the first Europa lander should be as simple, inexpensive, and rugged as possible in order to mitigate risks and maximize science return, particularly since it would almost certainly be a piggyback on EO or some other Flagship-class mission.

With that in mind, I just don't see a feasible way to get a camera on the surface given the implicit constraints imposed by likely landing methods unless some variation of the Pathfinder/MER balloon system is employed...and even then, would this instrument provide truly critical science data in comparison to other possible instruments?

Don't get me wrong--I'm a pic junkie like everyone else! --but investigating as many of the geophysical questions about Europa as possible during the first surface mission has to be priority #1 in order to justify the expenditure. If it ever comes to a choice between a cam or a seismometer, conductivity sensor or a GCMS, I have to go with any of the latter three.

My rationale behind sending a rover initially is that, unlike with Mars, missions to the outer solar system are rare and expensive, and you may as well invest a little extra in versatility. Choosing to use an existing rover design which just happens to be good enough to be appropriate to the destination means minimal required investment in R&D (a big part of the price of MSL and other missions), so all you need to do is build a copy from the existing plans and launch it. Heck, build an assembly line and just get in the habit of sending a stanardardized rover out every year or two with incremental inprovements; we could in short order have rovers on every body of interest in the solar system (Ceres, Vesta, the other Galilean satellites, Titan, Triton, Mercury, and some of the other icy satellites). Note that I'm recommending the MSL design, not MER, so no airbags and bouncing would be involved. Sure it might get there and immediately get stuck in a crevice... but it might not, it might be able to rove for hundreds of kilometers and see amazing things. As to the radiation on Europa... I don't know enough about it to determine whether it's a show stopper. And yes, realistically I know that with the current diversion of resources to the manned program [a rant I won't go into here...], this isn't going to happen any time soon. Just wishful thinking. More generally, I think that we need to start developing some standard plug-in compatible components for orbiters and rovers so that putting a mission together is more like building a PC... pick the parts you want, put 'em together, and send them somewhere, with no need for a big engineering project that reinvents the wheel for every mission. Okay, rant over...

Ah, the good old Soviet method, eh? The US always built a few Cadillacs, while the USSR built Ladas by the thousand...

Bob Shaw

I would guess that a panoramic camera of some kind would be landed. Other than shifting conditions of lighting as Europa rotates, there would not be any expectation of any change in the scenery, so a single panorama taken as soon as possible after landing would be just about as good as extended coverage over a longer lifetime. If nothing changes, why keep photographing it? That does a lot to blunt concerns about radiation, because it's fine then if the camera dies a few hours after landing. If it survived to take a second panorama as daylight shifted, that would be nice, but not crucial.

There may be tradeoffs between camera longevity, power sources and data transmission rates - all of these will have to be just right.

Bob Shaw

Perhaps the cunning technique that would have been used with Beagle 2 for the first couple of sols.....a parabolic mirror with a single camera under it.

Make it a 2k x 2k CCD, and a good sharp mirror - and you'd have the equiv of something like a 1000 x 500 pixel 360 degree panorama. You also could seperate the camera electronics from the actual field of few - tuck it down in the body of the spacecraft, shielded, looking up through some think optics to the mirror at the top.

Doug

I like this kind of thinking, on how to get a camera on landers as part of the challenge. Each place we send a spacecraft to which has anything to see should be looked at.
Video is the next frontier of visual documentation of at least selected targets. If there is expectation of dynamic visual events, such as in landing near an active volcano on Io, basing a rover design on the MSL landers would presumably include their video capability which would greatly enhance the public sense of 'being there'. Just as launch cams are becoming a standerd practice in major launches, landing videos will be seen as an opportunity not to be missed once the first Mars landing video is seen. Bandwidth issues are part of the hurdle to overcome and recieve due attention over time.


Don

The visual science might means more than any other sensor science. With a good picture, we can interpret many applied sciences such as geology, minerology, biology, astronomy, glacialogy, vulcanology, and much more what you can count!, pa!

Rodolfo

There are three ways to protect electronics from radiations:

-shielding. An overal shield is out of question, due to its weight. But some crucial parts could be shielded with some very local shields, like power transistors in a DC-CD converter (which can break from a single event, and are critical). A CCD camera chip can also be shielded, classical shield behind, and lead glass optics in front

-short working time. As JRehling and Bob Shaw say, there is no need of a camera working for months, at least not on a static lander.

-hardened electronics. This is about a variety of techniques used to make electronic parts, especially semiconductors, less sensitive to radiations. But this is difficult, and not much can be gained, say one or two orders of magnitude, and that is not enough on Europa. So I suggest to use completelly different methods, such as triodes or electrostatic microrelays, as I already explained on the Venus lander thread.


An alternative to a simple lander would be a very low orbiter. Its orbit could be set to decay little by little, so that it would graze the ground, allowing to send quantities of very high resolution images, showing things like pebbles on large regions. Of course, it would impact the ground sooner or later, with too much speed o survive. But by letting a rope hang to the ground, we could obtain some free braking, before using a rocket to end braking.



Europa ground looks smooth from altitude, but it is likely a kind of ice regolite, with large blocks, pebbles, and much sand. Worse, it seems that there are many equilibrium slopes, so that climbing them would result in avalanches. A rover nightmare!

So, rather than wheels, it would require a kind of large spider, working with some hydraulic system, like scorpio legs. This could make very long legs with a reasonable weight.

But I think that, fortunately, the most interesting regions are the reddish chaotic regions, which formed with breaking and melting of the ice crust. As there was liquid water on the surface, it frozen hard, not in blocks. So, between the small hills if the chaotic regions, there must be flat hard regions, the most interesting place to find chemmicals or biological particules into the ice. The best place to search, and the best place to land...

Three techniques:
-the homing missile, using a high resolution picture to land on a selected place. Variant 1, with a rocket to land at small speed
-same, but variant 2, lands at high speed and buries itself in ice.
-the airbags, which we can expect they will bounce toward a bottom, precisely where we want to go.

Eventually a cluster of small landers with only such crude guidance, have much chances to land, at least one, in the right place. It would be short lived landers, but with analysis tools, microscope, etc. A small chemical heater could melt some ice.


A lander with a long lived seismometre could land in the same way into the same place, where it would find solid ice to operate properly. The variant with a high speed landing is prefered, because it would provide a shielding against radiations.

In the outer solar system, we have tended to find that higher albedo objects have more active, self-cleaning (due to activity) surfaces. These surfaces tend to be the roughest on a meter scale, while the cratered-to-hell-and-gone iceballs like Rhea or Callisto have relatively block and rubble free undulating but smooth meter-scale surfaces. They've been hit so much you just make the rubble bounce and pound it finer.

I'm overstating this, but it's a clear trend.

Richard:

I quite like the idea of an ACME ™ Space Science Corporation tether being used as a brake - presumably without an anchor at the end, though...

Bob Shaw

Just offhand and without checking I dont think any tether would work, orbital speed are simply to high. It would merely snap when it hits any outcrop or block of ice.
Perhaps something could be made by some exotic material, but dont say carbonfiber, its very stong along the length but the force would be applied as much from the side for such a tether.

The atmosphere of Europa are also to thin for any aerobreaking, well perhaps you might get some small amount but nothing significant. Anything that takes time will be one disadvantage here.

So im still advocating the idea of one impactor, get it trough Jupiters radiaiton belt fast, perhaps not without any orbit at all at first.
If its piggyback on one Europa orbiter then it would of course have to separate early since its approach would be somewhat different than for the orbiter.
Fly it down via a swingby capture by Europa, a breaking burn and then down to the surface in very short order. That way one might buy a few days of precious science on the surface.

Addendum: I know its a pipedream, and against the suggestion of a simple Europa probe, but imagine having one instrument to detect Cherenkow flashes on one such lander/impactor.

Besides the ACME-ish imagery conjured up by this concept, the smear control will be a challenge. Without compensating for imager to target relative motion, the images will probably look like something out of the trip fantastique from the film 2001.

Pushbroom?

Doug

Of course, there is the problem of motion blur. But I am in the business of electronics. So I think it is possible to get data out of a CCD in such a way to avoid motion blur. But I won't tell it, unless some mission team hires me!

a smear-controled camera would be much lighter and smaller than a telescope, for the same resolution. But grazing Europa ground would require more fuel. So it is a trade-off, as usual. About radioactivity, it is about the same, wherever we are close or far from the ground. Perhaps a close orbit would allow to spend some time in zones which are shielded by Europa.

About a theter cable trailing on the ground, I realize it would be difficult, the part touching the ground would simply explode, transmitting little effort to the main probe. Such a cable would be heavy too, and it would not really "hang" to the ground from orbit. So it is not sure it could really work.