sprints seven miles per second ‘round his captor -
the massive puffed, yellow-buff gas balloon
but wobbles as if hooked by a one-clawed raptor.
He whips past his sister moons, scarred Dione
and pocked Tethys in a frenzied orbital race.
Saturn's affectionate attendant cronies
pull with a fly-by, gut-churning embrace.
Ice-shelled Enceladus roils at the core;
fissures and resurfaces his shining skin.
From chasms, cryovolcanic geysers soar
and paint the nebulous ice-crystal E ring.
He's wrenched, twisted and warped - the treatment’s rough,
but renders heat through internal commotion.
Enceladus has all the fundamental stuff
to foster life in an under-ice ocean.
- Diane Hine, Enceladus
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Figure 1: This image was captured by NASA’s Cassini
spacecraft in orbit around Saturn. Shown here is Titan together with the icy
moon Dione. The bulk of Saturn fills the background. Here, Saturn’s rings are
viewed nearly edge-on and the dark bands at the bottom are shadows cast by Saturn’s
rings onto the planet’s cloud-tops. Saturn is also home to Enceladus - an icy
moon with active geysers at its south pole. Credit: NASA/JPL-Caltech, Space
Science Institute.
Creating large volumes of habitable space is a key
requirement for manned exploration of the numerous and diverse worlds found
throughout the solar system. On many of these worlds, water in the form of ice
exists as a relatively abundant resource. A paper recently published on arXiv
investigates the idea of using water ice to construct domes housing large
volumes of habitable space on places with abundant water ice and where
temperatures are low enough such that water ice always stays solid. These
places include the cold permanently shadowed crater floors at the poles of the
Moon and Mercury; the Galilean satellites - Europa, Ganymede and Callisto; the
icy moons of Saturn and Uranus; and the Kuiper Belt Objects. The construction
of ice domes from locally available water ice will allow manned exploration and
colonization of these worlds without having to transport large amounts of
construction equipment from Earth or elsewhere.
An ice dome basically consists of a shell of water ice of
some thickness which forms the main structure. Enclosed within the dome is a
large habitable volume with an Earth-like atmospheric pressure. The temperature
within this habitable volume will depend on the properties of the thermal
insulation covering the internal surface of the ice dome. This temperature
should not be too high so as to prevent melting of the ice dome from inside out.
An ice dome can be constructed to a very large size, containing thousands to
millions of cubic metres of habitable volume. Its construction begins with the
deposition of water vapour directly onto the internal surface of a thin, weakly
inflated and dome-shaped film of material. Ethylene tetrafluoroethylene (ETFE) can
serve as a possible film material. It can be prefabricated on Earth and then
transported to site where it is weakly inflated to achieve its desired dome-shape.
Since the outer surface of the film is exposed to the cold vacuum of space, any
water vapour that gets deposited onto the film’s inner surface quickly freezes
into a layer of solid ice. Over a period of time, the layer of ice thickens and
eventually forms a dome of ice with sufficient strength to support an Earth-like
atmospheric pressure within it.
As a result, the only equipment required for the
construction of an ice dome is a thin film to serve as a deposition surface and
a device that can spray water vapour. This alleviates the need to transport
large amount of construction material and equipment from Earth. In fact, a
number of other benefits can be derived from constructing ice domes as
pressurized habitats. The huge amount of habitable space enclosed within an ice
dome will improve living conditions and enable new possibilities such as large
scale agriculture and recreational sports. Water ice also possesses good radiation
shielding properties. A one metre thick layer of water ice can effectively
attenuate incoming gamma radiation to less than one percent its original
intensity. The ice layer of a typical ice dome is likely to be on the order of
a few metres thick. Although very large quantities of water are required to construct
an ice dome, all the water can be derived locally and is 100 percent
recyclable. If the ice dome needs to be scrapped for any reason, it can be
slowly sublimated and the water vapour pumped to construct another ice dome
nearby.
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Figure 2: Halving thickness (cm) of various shielding
materials versus gamma radiation energy. Source: Gamma Ray Attenuation
Properties of Common Shielding Materials by Daniel R. McAlister, Ph.D., January
2012
An ice dome offers excellent protection against incoming meteoroids.
Due to the thickness of the ice layer and the high strength of ice on the
dome’s external surface, meteoroids are expected to cause nothing more than minor surface
damage. Such damage can be easily repaired by spraying liquid water into the
crack where the water will quickly freeze and restore the ice to its original
strength. In the unlikely event that a meteoroid is large and/or energetic
enough to punch a hole through the ice dome, venting of atmosphere through the
hole can cause moisture to freeze around the hole and eventually plug it.
Liquid water can also be sprayed into such a hole to quickly seal it.
Reference:
Stefan Harsan Farr (2013), “Ice Dome Construction for Large
Scale Habitats on Atmosphereless Bodies”, arXiv:1303.5356 [physics.pop-ph]