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Posted by: Shaka Nov 14 2007, 12:18 AM

Does anyone consider it worthwhile to speculate on how we might explore Martian caves or lava tubes for the traces of life - past or present? I have not yet run across any 'official' proposals for "spelunker probes", so perhaps we could have some fun and get in on the ground floor with some feasible early designs. With the engineering and scientific expertise we have at UMSF we should be able to whittle down the possible features for such a rover to a practical core. If the planned surface scrapers and drillers don't turn up conclusive evidence to answer The Big Question, can we justify a search of the Martian Underground?

I can envisage a RTG-powered rover that enters a cave, or rappels down a skylight opening, leaving a base communication stage outside connected to it with a fiber-optic umbilical cable. Some form of laser or other illumination - in the visible and/or infrared - would presumably be required. How many of the MSL instruments could be included? What novel instruments would be appropriate? What is the optimal size and mobility design? 'Do we yet have 'hot' prospects for accessible caves? How should we choose the best candidates?

We can leave this to some JPL bright spark to develop, or we can dive right in. Any takers?

Posted by: nprev Nov 14 2007, 12:52 AM

Cool idea, but I don't think it'd ever fly unless there were some other mission objectives that could be added using the available spelunking features and/or instrumentation. First step here would be requirements development.

Couple of early concerns, here:

1. How much cable would we need? We don't know how deep many of these holes are yet.

2. A lot of the holes look like vertical drops, so the data cable would have to be a hoisting cable (with a hoist, and optocoupled slip rings, and all sorts of mechanical complexity) as well, something similar to that used on maritime vessel winches that have data wiring in the middle of the armor. Not light, and not cheap. Also, the surface vehicle would have to be either heavy enough not to topple or be dragged in, or anchor itself in some way.

3. During remote vehicle traverses, how to avoid cable snagging?

Still a cool idea, but I wouldn't want to try it...

Posted by: dvandorn Nov 14 2007, 01:54 AM

As far as I know, however, all of the lava tube caves we've seen from orbit occur in the Tharsis bulge, many along the flanks of the great shield volcanoes.

Those areas are significantly above "sea level" on Mars. Quite significantly. So much so that you have an even harder time landing anything there -- there's just not enough air to slow you down enough to be able to land anything as heavy as a MER, much less an MSL.

-the other Doug

Posted by: nprev Nov 14 2007, 03:27 AM

Great point, oDoug. Hopefully <wish mode> we'll find some at much lower elevations that might be deep enough to have some significant (>20 mb, which we can probably find in some spots of Hellas with much less effort) atmospheric pressure in their depths </wish mode>. Short of that, hard to see how a caving mission would be worth the expense & risk. Have to be a deep cave indeed on the Tharsis Bulge to make interior conditions interesting enough to investigate.

End of reality check. Think that Shaka's in it for the enjoyment of conjuring up something innovative, and have no wish to rain on his parade! I think that one must-have would be a radar or laser altimeter on the cave-crawler...

Posted by: Shaka Nov 14 2007, 06:20 AM

You get my drift, nprev. Elevation could be a crucial criterion (krikeys! A Crushingly crucial criterion!), but so could be the proximity of geothermal warmth. There must be at least a few caves down amongst all those canyons and rills and badlands and chaotic terrains that could represent a final refugium for the never-say-die remnants of a past Martian biosphere. A refuge from the withering surface assaults of impact barrage, radiation, desiccation, freezedrying, peroxidation etc ad nauseam. Indeed, if there has been the vast underground labyrinth of water/ice systems, subject to sudden outfloods, drainage, rising and falling water tables etc, there MUST be a Martian underground. The remnants of Martian life may have abandoned the hostile surface so long ago that they don't even remember that the surface exists. Drilling down a meter or two may be no more productive than drilling into a Sahara dune. We may have to ferret out the ventilation shafts, the skylights, that offer access to the 'command bunker' of Martian life. (Disable poetic license)

I think it's fair to assume, for the mental exercise, that openings to the underworld have been or will be found. We won't be waiting for the first astronauts to set foot on Mars, and tell them "Just climb down there and see what you find." Even if we wait for man to reach Mars, we will first explore those hazardous nether-regions only with robot probes. So why wait for man? Let's at least put on paper, or the web, a scheme for exploring a cave. (If it's fruitless, Doug can always delete it.)

Happy Thanksgiving Day Parade to all!

Posted by: Cugel Nov 14 2007, 01:20 PM

Elevation is only a problem if you come in on a chute. If you have a nice powerful descent rocket you can land anywhere on Mars. I know this will do something ugly to your budget but powered EDL on Mars must be developed for manned missions anyway. So, in true Zubrinian style, let's just suppose we have that technology and somebody has payed for it.
The good thing is that the landing ellipse will now be down to a few meters or so. We can do a pinpoint landing right next to the hole in the ground.
So, maybe we don't even need a rover type lander (to get to the hole), just a big boom might be sufficient to deploy the probe. (This is the optimistic part)
Also, I don't see the cable problems nprev mentioned before. If you can lower something many miles into an ocean on Earth it surely must be possible to do that in a cave on Mars.
The whole shebang (lander + probe) can be solar powered, so accept for the EDL hardware I don't see why it would cost many billions (MSL class maybe?).

Another idea if you don't like that cable: just drop a battery powered probe into the hole and dangle an antenna which is connected to the lander a meter deep or so in the cave . That would be good enough for a radio link. With airbag technology the fall must be survivable for the probe (which could be pretty small and simple anyway).
Probably carry more than one of these probes anyway. The probes could be deployed into the hole by shooting them out of an airgun, so the lander could actually be quite some distance from the rim.

Posted by: centsworth_II Nov 14 2007, 03:59 PM

If you're looking for microbe-friendly habitats, I think resources would be better
spent developing a means of drilling deep beneath the surface at an area of your
choosing, not limited to specific cave locations. Sending a rover into a cave would
be incredibly cool, but I wonder at the energy budget for providing enough light
to take the cool pictures.

Posted by: nprev Nov 14 2007, 04:12 PM

I was thinking more about what happens after the crawler reaches the bottom & begins to move horizontally. Ocean trawlers on Earth rely on brute force to overcome obstacles, yet still they break cables with tensile strengths well over 10000 lbs & lose gear (been there, done that, with plankton collection gear & scallop survey trawls when I worked for NOAA; reterminating those cables is NOT fun). Cable-linked oceanic ROVs almost always steer well clear of the bottom & are controlled in real time to avoid obstacles. Doesn't take much for a mission-ending snag in the Martian spelunking scenario.

Now, if you're just talking about lowering an instrument package vertically down a hole, that's of course much less risky. Have to ask, though, what sort of useful data would be acquired? Only thing I can think of is to lower a methane-sniffer, and it seems that we'd do better to land a more complete instrumentation suite at other, more accessible surface sites.

Posted by: Shaka Nov 15 2007, 04:56 AM

Thanks, guys, for your input. Clearly this is not in the easy-as-rolling-off-a-log category of engineering challenges!
I'm wondering, for starters, if anyone has yet seen, from orbit, openings like a cave entrance other than the few lava tube skylights at high elevation. Something we can throw a methane probe into. Maybe that's the best available, for now.

Posted by: Cugel Nov 15 2007, 11:59 AM

You're right. The bottom of a cave might not be the ideal surface for a wheeled vehicle. Too much debris, cracks and other nasty things. But as Shaka said, simply characterizing the environment would be very interesting. Temperature, atmosphere composition, radiation levels, some remote spectrometry... it would tell you whether the cave is habitable.

Another question (of a more general nature) is this: when you detect methane in a cave, is it possible to make a distinction between a biologic and a volcanic origin of the gas? I know they did something similar with Huygens on Titan, by comparing isotope ratios or something but I don't know if this would work with the extremely low methane levels on Mars.

Posted by: Shaka Nov 15 2007, 08:21 PM

Good fundamental astrobiological question, Cugel. A quick dip into Google Scholar suggests that the answer is "Yes, maybe." http://www2.ess.ucla.edu/~manning/pdfs/mars_ch4.pdf and see also:http://www.agu.org/cgi-bin/SFgate/SFgate?&listenv=table&multiple=1&range=1&directget=1&application=fm06&database=%2Fdata%2Fepubs%2Fwais%2Findexes%2Ffm06%2Ffm06&maxhits=200&=%22V41G-06%22
Of course the hope would be that if organisms in the underground are the source of the atmospheric gases, the concentrations inside the cave would be significantly higher, hence easier to quantify isotopically. Given the current drive toward miniaturized spectrometers (for military, if not scientific applications!), we may not be far away from an astrobiology lab in a shoebox or better. Weight may not be the challenge.

The bottom of a cave or lava tube may well be a severe challenge to rover mobility. Wheels may have to give way to legs - with snowshoes! - in order to clamber over fallen rocks and dust puddles.

Edit: I just had a spine-tingling mental image of a mechanical SPIDER! Instead of spider silk paying out the back end, you would have fiber-optic cable!

Posted by: dburt Nov 15 2007, 10:22 PM

With regard to moisture and geothermal warmth, why restrict yourself to a cave? The climate inside a cave, unless it is a very deep one indeed, represents the average of the climate at the surface (averaged over day/night and winter/summer) so that any Mars cave is likely to be extremely cold inside, and not necessarily a promising place for life. For me the best refuge for life might be near the vent of one of those very long-lived but largely quiescent Tharsis volcanoes - potentially lots of warmth, moisture, and energy-yielding chemistry, persisting for billions of years at the same spot (no plate tectonics to move it around). Aperiodic eruptions of basalt need not wipe out life for more than a meter or two away from the vent contact, and it could easily re-establish itself afterwards.

Given that drilling to any significant depth is likely to be prohibitively expensive and fraught with mechanical difficulties, why not plan to land our magic rocket in the summit caldera of a volcano (perhaps not one of the tallest ones) and lower our cable of instruments down an old vent or old fumarole, if one could be located? Alternatively, look among the local throat-clearing volcanic ejecta or caldera collapse breccias around the rim for signs of past life. On Earth the closest analog for such a target might be the active biological communities first discovered during the late 1960's near "black smokers" or submarine volcanic vents (above sea floor spreading centers between separating tectonic plates or in regions of extension behind island arcs). Just another idea (one that I've mentioned previously, I believe). What do you think?

-- HDP Don

Posted by: Shaka Nov 15 2007, 11:09 PM

For sure, Prof Don! Any kind of vent or other opening into a volcano would be sweet meat for our 'spelunking spider' (should we name her Shelob ? )
If such openings exist (and I would imagine someone at HiRISE is already looking), then they would be an absolutely top-drawer priority to the geologists as well as the astrobiologists.

Posted by: nprev Nov 16 2007, 01:13 AM

Like the spider, still hate the cable. I wonder if it's technically feasible to build a compact ultrasonic sonar transducer to periodically (and redundantly) vibrate into solid rock with enough juice for it to be picked up by the surface vehicle. The bit rate would be lousy, though, even if we used a combination of modulation methods...maybe a couple of distinct channels would help, like multiple ISDN lines for videoteleconferencing.

EDIT: Ha! Got it! The spider rides down to the bottom on a little descent platform, which is equipped with a simple RF transceiver. The spider calls back to the platform (which stays there), which in turn relays data up to the surface lander and new commands to the lander. Piece of cake, except for all the multipath problems in a cave...redundancy & freq agility should help that a lot, though.

If the cave's just too rough to traverse, you could haul the spider back up again & use it to explore the surrounding territory (always looking for risk mitigation strategies, here!)

BTW, the host platform pretty much has to be a rover...doubt very, very much that we could ever put a fixed lander near enough to a cave/fumarole/vent to get the spider where it needs to go.

Posted by: Shaka Nov 16 2007, 02:39 AM

Don't understand your problem with Shelob's silk. I'm thinking not so much of oceanographic MOCNESS cable, but more like the stuff that pays out behind a guided torpedo or a TOW missile or maybe one of those retrievable towed RF decoys. Think of the bandwidth! And if it can be smoothly payed out and reeled in and support Shelob's weight, then there's no need for a separate lowering platform or limited communication ability. Shelob just walks away from her rover/ lander/base station (which anchors itself with some augers) and heads toward the opening. If the floor drops away, Shelob just pays out cable and drifts down until she regains footing and resumes walking. Equip her with a compact RTG generator, and she should have enough juice to light things up with white or infrared LEDs, take pictures, zap the walls with her chemcam laser, and scare the almighty crap out of Marvin the Martian!

Posted by: nprev Nov 16 2007, 02:48 AM

I keep thinking of the cable getting wedged between two rocks, or wrapped around one from a long-forgotten loop many meters back. If the terrain's rough enough to require Shelob in the first place, then something like those things happening is a near certainty. Wouldn't be such a problem if there was a big power budget & correspondingly powerful motors, response capability, etc., but you just don't get that kind of juice from RTGs.

No worries; an RF link could be designed with a really good bit rate, though considering the bit error rate & multipath effects it might not be adequate for video (think lots of noise & ghost images). Stills would make it okay, though.

Posted by: mchan Nov 16 2007, 03:02 AM

All I gotta say is you guys here have designed descent and comm for a probe to bore thru Europa's ice crust and return data from the submarine ocean. Dropping into and exploring a Martian cave should be a piece of cake!

Posted by: Shaka Nov 16 2007, 04:09 AM

Devilsfood, to be precise.
All we need is to cultivate a techie in the Pentagon.

Posted by: nprev Nov 16 2007, 01:45 PM

Shaka, let's compromise. Shelob can drag a fiber optic line from the descent platform (which goes back up to the rover/lander) till it gets snagged...then either an electrical or pyro-actuated cable cutter on the spider does its thing, and the vehicle switches to its backup RF link to the descent platform.

Thanks for the compliment, mchan! I ain't even gonna discuss the problem of drilling a hole on Europa, though...

Posted by: Cugel Nov 16 2007, 03:09 PM

Thank you for those links. That's very interesting and encouraging news! (And not just for Mars caves)

Posted by: centsworth_II Nov 16 2007, 03:41 PM

The fiber is payed out from the rover/spider as it moves. Once on the ground
the fiber moves no more... no snag worries.

Posted by: Juramike Nov 16 2007, 04:05 PM

Hmmm...I'd worry about possible backtracking. Unlike a TOW missle (which doesn't backtrack - unless it's a really bad day), I'll be our future cave explorer will have to find paths around fallen debris. Some of these paths might be false starts and dead ends, in which case you'll have to backtrack. Getting tangled up underground would be no fun.

I'd assume that lava tubes on Mars are very similar to lava tubes on Earth. Once you drop in, you'll want to go horizontal for as far as the cave will allow. Inside the cave, you could have smooth surfaces but you could also have incredibly rough surfaces as well, especially where debris fell or where lava drips occured. (And don't discount the fact that it is likely that there are multiple levels of tubes, so you may want to rappell down again once inside the first tube). [There is a cave in Lava Beds National Monument where I counted 12 distinct levels - I completely shredded a pair of jeans that day - lotsa twists and turns getting around debris and dropping down tight holes to get to the next level].

Having the ability to drop small radio repeaters as needed might work out best.

-Mike

Posted by: centsworth_II Nov 16 2007, 05:41 PM

The spider will just walk over most debris, but I'm no fan of a dedicated
cave explorer anyway. A cave is a pig in a poke. You don't know what you'll
find until -- after much planning and expense -- you get in there.

I like the idea of going to sites that have been examined as closely
as possible from orbit and show evidence of great science potential
from a ground mission.

Now, if a future orbiter identifies a methane-belching cave....

Posted by: Juramike Nov 16 2007, 06:14 PM

At some point we will need to go in and explore harsh cave environments with robotic exploration.

Suppose we find hydrothermal vents on Europa, I'll bet we'd want to probe the inside the vent itself.

Heck, I bet it'd be pretty neat to sneak a probe down deep inside a hydrothermal vent here on Earth, or deep exploration of crevasses (very cool).

These evironments share the same problems: figuring the route, tight confined areas to maneuver in, communication with the surface, and really harsh physical environments.

-Mike

Posted by: Shaka Nov 16 2007, 09:52 PM

For starters I'll concede that no interplanetary probe could be infallible in the face of sufficiently fiendish challenges from the environment. But if our surface probes don't turn up any incontrovertible evidence for life, we will still have the possibility that it persists deeper underground.

My understanding of living species communities is that they will tend to expand outside of their optimum core area over time. This is because of species competition for resources. The superior competitor will push its inferiors toward the periphery, where they will have to adapt to conditions or go extinct. The process repeats until the community occupies all the habitable space up to the boundary of entirely unsurvivable conditions. This uncrossable boundary could be very deep on Mars (kilometers), in which case our life search will be long and frustrating, or it could be just 10 meters inside a cave, say where radiation levels drop sufficiently. In this case our first cave probe could succeed brilliantly on its first day. You pays your money and takes your chances.

Cents2 understands how Shelob's silk should function, however it would help avoid tangles when backing up if the line can be retracted simultaneously. This complicates the mechanism, of course, but the alternative is to avoid backing up. I'm aware that some of the fiber-optic towed RF decoys (pulled behind war planes to distract radar-guided anti-air missiles) can be reeled in and out again. This implies some kind of small winch at work, but the details are classified, of course. I like the fiber-optic silk because it can combine reliable, high-bandwidth communication/control from earth, with a means to rappel down from skylights or precipices - also because Nature thought of it first . Theoretically Shelob could descend multiple drops, but there are limits to everything.

Cents, where the existence of life is concerned, Mars itself is a "pig in a poke".

Posted by: Del Palmer Nov 16 2007, 10:59 PM

Would a modified version of http://www-robotics.jpl.nasa.gov/systems/system.cfm?System=5 be up to the job?

Posted by: Shaka Nov 17 2007, 01:32 AM

LEMUR How sweet it is! I'm relieved to see that JPL has read the writing on the wall: Build a walking, climbing robot. I suspect that model 2B may still be a number of iterations away from a sufficiently agile climber (the videos don't show climbing over obstacles), but the journey has begun. Goody. Now all we need to do is graft on an analytical lab-in-a-shoebox, a power supply, and a communication link come rappelling line. Devilsfood cake! Actually, we probably have more competition than that. I know the army would like robots creeping through caves in Afghanistan, sniffing out W.M.D.s and U.B.L.'s B.O. We just need the right contacts to bring the technology together.

P.S. I note that the latest issue of Science has a special section on robotics. Soon as it reaches the library, I'll do some homework.

Posted by: nprev Nov 17 2007, 01:57 AM

I was thinking of that, too, but was a bit worried about adding weight to the spider. You're right, though, esp. if the spider is completely self-powered.

As a side note: Hey, Shaka! You know about MOCNESS? God, what a beast that was...I've gone a few rounds with that thing...

Posted by: Shaka Nov 17 2007, 05:21 AM

Helllll, yessss, nprev! It was about 25 years ago when I was proudly shown one of the early models on the dock at WHOI. I never had the budget for MOCNESS, but planktonology was my line! Bongos, Mantas and one-net Tuckers were my stock in trade. I've still got the scars!

Posted by: nprev Nov 17 2007, 11:23 AM

...I was an ET, sailed several times on the Albatross IV out of WHOI, and once on the Ferrel! (1994-1996). We just might know some of the same people...

Back OT here, have we defined a complete instrumentation suite here yet? Also, I'd like to suggest that a 'sample return' (back to the surface lander) capability. In this scenario, Shelob would cut the cable (if necessary) & navigate back to the descent platform using the backup RF comm link, and deliver the sample(s) back to the lander, where the major experiments like a GCMS, atomic force microscope, etc. would reside.

Posted by: Shaka Nov 17 2007, 06:55 PM

"navigate back" Wow, you don't want much! I definitely saw Shelob on a one-way trip. Without her umbilical, how would she get back up all those precipices and skylights? If she finds a community of organisms 10 meters inside, a followup sampler probe would be in the cards, but I wouldn't want the sample brought back to my planet! (Sorry, I watched the Alien movies too many times.)
I prefer the fantasy that all the alphabet soup of instruments have been nanosized into that shoebox in the spider's thorax. No return required.
Choosing what to include as instruments can start with what's going into MSL. I like all that stuff. But maybe the chemcam laser should have a "lethal" setting. Just in case we have to fight for Shelob's life.

P.S. My marine biology career was on the opposite side of planet earth from WHOI, but some of the 'oldtimers' would be known to us both.

Posted by: Shaka Nov 17 2007, 09:25 PM

Expanding further on the subject of Shelob's instrumentation: In contrast to MSL's equipment for identifying organic carbon, we would send an underground probe in the hope that Martian life was surviving there and not just fossilized, so tools to describe living organisms should be a priority. Microscopic unicells would be most probable, so nutrient broths to grow a range of primitive earthly organisms should be offered to rock scrapings, with appropriate chemical and visual sensors to detect metabolism. I use earthly archaea, bacteria and eukaryotes as models, because the most parsimonious assumption is that the evolution of life follows predictable paths in likely environments. The real possibility that Martian life employs a totally 'exotic' alien chemistry opens up a can of worms with too many possibilities to be handled by a first-generation probe. If Shelob Model I produces negative results, Model II may include more exotic chemical broths. (Too many broths spoil the cook! sorry).

I would like to include in Model I tools for the inspection of macroscopic tissue, in the hope that larger organisms are surviving on the tiny stuff. But how to do histology in a crowded shoebox is fairly daunting. Maybe a tool to 'smear' a tissue sample and put it under our microscope would be feasible. Of course at the ambient temperatures underground, things might be frozen solid. Then we would need a nanotech 'cryomicrotome'.
Get to work on that, nprev!

Posted by: nprev Nov 17 2007, 11:29 PM

All over it, Boss! Gonna stick to my guns on Shelob going home, though; these advanced (and delicate) instruments you cite would have a far greater probabilty of surviving long enough to function if they remain on the surface vehicle & the spider comes back. Certainly there should be some in situ instruments: an imager (duh), a light source, a microscope, and maybe a mini-mini-TES. I see the balance of the Shelob payload as collection machinery, though.

EDIT: Just to be perfectly clear: when I say the spider should go home, I mean it should return to the surface & deliver its samples to the rover/lander where all the advanced analytical instrumentation would be. Nohow, no way am I suggesting returning living Martian organisms to the Earth (if found); we got enough trouble in the US with kudzu alone...

Couple of thoughts on ingress/egress methods as well. I can't see Shelob walking up to the edge of a hole & just jumping in (AAAaaahhhhh....splat...or, whack, whack, bang, bang against the sides on the way down...or, even worse, snagged on a projection on the side of the wall, helpless. Crawling down the wall would seem safest, but don't forget that there probably would be some discontinuity in the descent, and gravity sucks...) Seems like you'd have to get the rover VERY close to the rim, extend a good-sized boom, and carefully lower the descent platform with our intrepid spider perched thereupon. Depending on the depth of the hole, you might get a moment arm significant enough to topple the rover...game over. Therefore, the rover would almost certainly have to have some heavy-duty pyro-fired soil anchors to prevent this (added benefit: we could put some chemo or seismo sensors in the anchors!)

A design heuristic emerges: the lighter the spider, the longer the boom, and therefore the better the chance that we can get a straight drop down...

Posted by: tanjent Nov 20 2007, 04:07 PM

Getting any hardware to Mars is going to be expensive for a long time yet. It is hard to visualize a one-shot mission that puts this precious spider-robot into an unscouted hole in the ground. But if the caves are clustered on the flanks of the volcanos, could a lander with MARSIS-type radar be put in a surface location from which it could map several of them at once? Or could a balloon make the rounds, taking snapshots into the cave mouths, and perhaps lowering some kind of radar device on a tether into the entry chambers? Then at least you would have some idea of where your spider would have the best chance to survive and discover something interesting.

Posted by: Shaka Nov 22 2007, 07:25 AM

Scouting is good. Expensive is bad. But good and bad are subjective, and infinitely malleable, so you always have to specify: "Compared to what?"
Scouting from orbit can be very cheap compared to scouting close to the ground, so if possible we scout from orbit. We should be able to see openings to the Underworld bigger than a breadbox, but what else can we scout? Probably not detailed isotopic composition of gases at the opening. For that we need to get closer; a surface rover takes too long to scout more than one opening, and why not send it into the opening? A flyer could visit multiple openings, but how will it fare down low in Mars' atmospheric roller coaster? (I don't like to even think about a balloon!) If we don't scout up any marked gaseous clues, does that rule out life in the caves? What if Martian beasties don't belch out methane? What can subsurface radar tell you about micro-organisms clinging to the walls of a cave?

Scouting is good, but it's not necessarily cheap or easy, nor can it guarantee success. We can select more promising caves on the basis of elevation, probable depth and extent, proximity to geothermal warmth, etc., but in the end we still have to roll the dice and send Shelob on her mission of exploration.