#110 November 1997
Section 18.104.22.168.110.of the Artemis Data Book
Mission Control™ Workshops, an educational activity of the Lunar Reclamation Soc., Inc.
[The kick off Workshop in this series was held at Duckon in Oak Brook
IL, June 7th, 1997 with Peter Kokh, Mark Kaehny, and Bill Higgins leading
the discussion, along with several other participants. This brainstorming
will come to a head in the Europa Workshop at ISDC '98, Milwaukee, WI,
Just the Facts
The widespread interpretation of the Voyager photographs of Jupiter's 2nd innermost great moon Europa, is that here we have a world with a global ice crust floating on top of a global ocean of considerable depth, covering a rocky crust-mantle-core. Current best guesstimates, reargued from scratch from recent Galileo mission photographs, are amazingly close to those offered a decade or more ago by astronomy "bad boy" John Hoagland. The ice crust is on the order of 1-5 km thick, the ocean beneath it could be a 100 mi. or 60 km deep, likely holding almost twice as much water as all the oceans of Earth. While we have not had on scene the instruments necessary to make direct measurements, it'd be surprising, if this picture is "way off".
Tidal stresses caused by Europa's not quite circular orbit around Jupiter evidently supplies the heat to keep this ocean liquid. In ancient mythology, Rhadamanthus was the son of Europa by Jupiter. So The Rhadamanthic seems an ideally appropriate choice as a name for this hidden global ocean. Water and vacuum do not socialize. But ice and vacuum get along quite well. A thick enough self-derived icy "firmament" can contain an ocean just as effectively as does Earth's thick atmosphere.
The conditions for the formation and maintenance of Europa-like moon worlds seem rather easy to meet in the vicinity of gas giant planets. And gas giants should be quite commonplace throughout the galaxy. It will matter little if the Jove-like primary of the candidate moon does not orbit a sun-like star. The upshot is that there may be far more "Europids" in the galaxy than planets more like "Earth". What we are able to do at / with Europa, may provide the major theme of any human thrust to the stars.
[see MMM # 36 JUN '90, pp. "Oceanids", P. Kokh]What do we, and don't we know about Europa? Maximum elevation differences in the surface are on the order of 100 meters, 300 feet, making Europa flatter than Florida, globe-wide. But ice, even very cold ice, is plastic, so we can argue from the analogy of icebergs that the surface profile is matched by an exaggerated unevenness of the ice crust undersurface. And where we have low spots on the surface, there the ice is correspondingly thicker, being matched with an exaggerated concavity on the underside.
We don't know the amount of impurities in the ice nor of salinity in the ocean. The mechanism that led to Earth's "briny deeps" was /is continual runoff from above ocean continents into the oceans via the river systems. This mechanism does not operate on Europa. There could be some level of salinity, however, if there are, or have been in the past, undersea volcanoes or deep vent ridges. Some of the material from eruptions could percolate into the water and go into suspension or solution. Volcanism is also the only possible source of dissolved gases (e.g. carbon dioxide) in the water.
But we don't know if there is, or ever has been geological activity in this undersea crust. We don't know if it has mountains and undersea continents and basins - or is relatively flat. We don't know a lot. No mission to Europa is now in the works, although a number of missions have been brainstormed to some degree. One cheap and elegant mission proposal would "sample" the chemical content of the ice crust by a simple flyby mission. Upon nearing Jupiter, the probe would aim a "shot" at Europa calculated to splash representative material into space. The probe would then "catch" some of this sample in an aerogel shield as it flew through the splashout cloud. On board instruments would analyze the "catch" and send the information back to Earth by radio.
Our Workshop series aims to ferret out ideas for robotic and follow-up manned missions to Europa, both to its ice crust and through the crust into its Rhadamanthic Ocean.
PRECURSOR ROBOTIC MISSION(S)
At the recent Europa II workshop, as we lacked a critical mass of participants to break up into sub groups, we decided to concentrate on manned mission possibilities. This is perhaps a good thing, because we quickly realized that for a manned assault to be successful a number of questions would already have had to have been decided by robotic missions. So the manned mission is the dog that wags the robotic tail, and any brainstorming of robotic missions without consideration of the needs of follow up manned efforts would be so much irrelevant ivory tower scientific curiosity scratching. Let us hope we will soon graduate to "prospecting mode" following the lead of Lunar Prospector.
Using as a criterion what we'll have to know to mount a human expedition to Europa's ocean, the horseblinders of individual scientific investigators specializing in this or that mini scientific cubbyhole will be off. We won't spend lot's of money learning irrelevant things. What do we need to know? Here are some tasks that need to be done by orbiters and surface missions or rovers.
The following submarine robotic investigations can be carried out either before or in conjunction with a manned landing / submarine expedition. In the former case, a tethered sub-ice mother probe could send out a number of robotic submarine mini-probes reporting back by sonar to the mother probe. These could either have independent active propulsion or, leaving results to chance, be allowed to drift on whatever ocean currents there are.
Jupiter space, inwards of Callisto, is filled with deadly radiation, that is, Io, Europa, and Ganymede, along with the lesser inner satellites (Amalthea and company) orbit the gas giant primary within its vastly stronger more deadly version of Earth's Van Allen Belts. The success of the Galileo mission shows we know how to tackle the problem on the level of short duration robotic missions.
For human expeditions, the challenge is much greater and cannot be underestimated. There are those who have concluded man will never venture inwards from Callisto, the Mercury-sized outermost of Jupiter's mighty four, the Galilean moons known since 1610 and seen by countless millions in small amateur telescopes, even in good binoculars.
Providing material shielding against this radiation would add prohibitive amounts of mass to the manifest. For the purposes of our mission, we assume that it takes place in an era in which the engineering challenges of providing electromagnetic shielding have been mastered.
After a short debate, we assumed that we could land safely on the ice surface without sinking into a pool of fresh water melted by the descent rocket motors. We could use a bevy of smaller scattered rockets (an aerospike configuration?) or simply cut the motors just before touchdown.
On the ice crust surface, where on site material is available, a simple
hanger can be erected to cover the base operations site. This could be
done in modular fashion, by deploying an inflatable to be covered with
shredded ice, which is then solidified into a self-sustaining igloo arch
by microwaves. The inflatable form can then be deflated and moved along
the axis to shape the next section, and so on. The surface base modules,
any fuel storage tanks, vehicles, and other equipment regularly manned
or tended can be regularly housed under this hanger.
Ice-shielded surface base hanger: elevation (L), plan (R).
Through the Ice Crust, Into the Ocean
At the prior (Duckon) workshop, we had discussed thermal melting of a shaft through the ice, using a vertical cabin cylinder of minimum cross-section with a heated (lower) prow cap. This vehicle might be about 10 feet or 3 meters in diameter or whatever the practical minimum. It could have spherical gimbaled rooms that would be stacked one atop the other for the descent and fore and aft of one another horizontally for submarine excursion once through the ice. If a cable winch was employed, it would be best to have the winch reel aboard the descending submarine. That way neither continued descent nor communications would be interrupted if the melted water or slush slurry in the shaft above refroze, seizing the cable.
In the second (First Contact) workshop, we wondered if it might not
be more efficient to equip our vertically deployed submarine vehicle with
a drill head to create a shaft somewhat wider than the vehicle to allow
the crushed ice slurry to pass alongside to the rear (above) the descent
vehicle. We did not do any math at this time to have a basis for comparing
the melt vs. drill methods for energy efficiency and progress speed. We
were simply identifying concepts to put them on the table.
Roaming Free in the Rhadamanthic Ocean
We imagined that upon breaking through to liquid ocean water, the sub would keep descending vertically, reeling out extra communications cable, until it was below the lowest downward protrusions of the ice crust in the area [see illustration, below]. At this point, an antenna would be affixed to the cable, and the cable cut below this point.
The submarine would then be free to roam through the Rhadamanthic, maintaining communications with the surface base by radio or sonar to the antenna suspended below the descent shaft. Joining the antenna at cable's end would be a beacon, to guide the submarine back to the point in the ice crust underside directly below the surface base.
We did not discuss means of ascent, but did wonder if the water/ice slurry in the shaft would not have refrozen in the meantime. In this eventuality, a new parallel escape shaft may have to be bored upwards when the crew's mission was done.
We briefly considered how the shaft might be kept open [percolated bubbles?) to allow routine travel between surface base camp and cable's end, a luxury feature that will probably wait for a second or later follow up manned mission. The writer (PK) personally thinks the ice is to plastic, the cold too intrusive - the hole would quickly freeze solid.
The Submarine Mission
The intra-oceanic mission has already been outlined. It consists of undertaking the deployment of swimming, floating, and ocean bottom probes and science stations (see "Robotic Portion of Manned Mission" above). If an "easier" portion of this science chore list has already been done as part of an especially ambitious precursor robotic mission agenda, then the mission is to continue the work.
Inevitably, findings will pose new questions and if the manned vehicle is equipped to shed light on them, its mission may be expanded accordingly.
Duration of the Manned Mission
Size and Disposition of Personnel
The duration of the overall combined manned mission to Europa, and the division of crew between surface base and submarine vessel, should be figured backwards from the amount of work to be done and the location from which it is to be conducted. Simple as that. We determine the list of tasks to be accomplished, any necessary sequencing, any necessary time-sharing of equipment, and factor in the man-hours, travel time, and crew talents needed in redundancy, toss in a healthy percentage of unassigned time (repairs, recreation, etc. - and then we can sit down and size up the mission. Europa is too far to go not to do the whole job that needs to be done on the first visit. This undertaking will surely dwarf the crew, equipment manifests, and costs of the first Martian Expedition.
Now Just What If? Air, Down Below?
The writer (PK) had wondered if their might be ongoing volcanic outgasing from points along the ten million square miles of Europa's ocean bottom. If so, the likeliest major component would be carbon dioxide, CO2. If so, the ocean would become ever more carbonated (for as long as the volcanism continued) until a saturation point was reached. Beyond that point, free gas might build up in some / all of the concavities of the underside of the ice crust. The gas pressure would have to counterbalance the weight (in Europa's 1/7th Earth standard gravity) of the ice above. Possibly, form time to time the gas pressure would rupture the ice along weak fault lines and escape into space. Could this be at least a secondary source of ice crust fracturing?
There are a lot of ifs here, and the speculation that follows is far less "anchored" than I'd like it to be. Readers are encouraged to give their input, whether constructive or showstopping, and on that basis we'll decide whether continuing brainstorming along the lines that follow should be part of the final workshop in this series, at ISDC '98 next May.
Mentioning all this to my workshop mates, it excited their imaginations, sending them into overdrive. Are such "air" pockets over lagoon like calm ocean surfaces common? How big can they get in area (air-exposed water surface) and volume (air)? How oppressive will be the air pressure? Something that divers on Earth have managed in pressure-equalized sea floor habitats? If there are no naturally occurring gas pocket/lagoons, can we create them by elec-trolosis of the ice? How stable would they be in either case? And in such high pressures, might not the freezing point be on the balmy side? in the 50's?
There is a tradeoff: higher temperatures come with greater pressures. lower with less. We can live with 32° so minimum depth below surface = minimum thickness of ice overburden = lowest atmospheric pressures = the best situation, all else (size/surface/ volume) being equal.
Pitch dark, they could be lit. We could put together a floating outpost in such a pocket, even equipping it with a pressurized dome so the staff could look out on the "cavern" roof and the "lagoon". We could use water heat pumps to maintain interior comfortable conditions through diurnal and seasonal changes, effecting "weather-like" cycles. In these lagoons, we might do high CO2 agriculture on floating platforms, growing some food on the spot. Maybe mini OTEC installations could supply ample power.
Proximity to ocean floor thermal vents could be strategically important. Two possibilities: (1) gas saturation is homogeneous - there might be a real "sea level" above which there are always gas pockets. But what happens if one is breached and vented? (2) if there are pronounced oceanic convection cells, gas saturation may vary accordingly, and "sea" levels may be local or nonexistent.
What is the global distribution of such coves? Are there any clusters of fair sized anchorages? Are there gas pockets large enough to host sizable floating settlements? Cities? If so, such clusters might be where a Europan civilization to be should make its beachhead. Individual outposts could be named after classical harbors of old: New Syracuse, New Carthage, New Tyre, New Alexandria, New Atlantis, and so on.
A big whoa! Are their enough dissolved metal salts in the Rhadamanthic to allow for advanced extraction processing of building and manufacturing materials so that this Europan adventure might become an overture to a very unique Europan settlement and civilization? And if there are deep ocean floor hot vents such as host oases of Earth life not dependent on chlorophyll or sunshine, then aqua culture is possible. If they exist but are lifeless, they could be seeded with specimens from Earth.
How would one transit between coves? By submarine, or by shafts to the
surface and transfer to suborbital surface hoppers? When anchorages are
close by one another or clustered, might man-made tunnels above "sea level"
Could Europa, rather than boring Callisto, become the major human population
center of Jove Space, with active trade to the other Galilean moons? Maybe
there are no such places, and all we have done is to provide science fiction
writers with a new class of venues for their stories. Contents of this issue of Moon Miners' Manifesto
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