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| The submersible could extract cores from the seabed to unlock a rich climatic history |
Excerpt from bbc.com
But one concept mission being studied by the US space agency could top even that.
Scientists are proposing to send a robot submarine to the
oily seas of Saturn’s moon Titan. The seas are filled not with water,
but with hydrocarbons like methane and ethane.
These compounds exist in their liquid state on the moon, where the temperature averages -180C.
The plan is funded by an initiative called Nasa Innovative
Advanced Concepts (NIAC), where researchers are encouraged to think out
of the box.
“That’s quite liberating,” says the scientist behind the
project, Dr Ralph Lorenz, who is outlining the concept here at the Lunar
and Planetary Science Conference (LPSC) in Texas.
Titan’s north pole is a land of hydrocarbon seas and lakes
“You can take a step back and really let your imagination run riot.”
But Dr Lorenz believes the mission is eminently achievable with the right resources, timing and technology.
Unmanned underwater vehicles (UUVs) are now widely used for
military purposes, by search teams, in oil exploration and scientific
investigation. So existing technologies could be adapted for use on
another world.
One of the most striking aspects of the proposal is a plan to
deliver the sub in a variant of the US military’s secretive mini-space
shuttle, the X-37B.
The sub would fit in the payload bay of the unmanned shuttle,
with the stack then launched on a rocket. Once at Titan, the shuttle
and its payload would glide down through the moon’s soupy atmosphere.
Deep-freeze
The sub could be deployed in one of two ways. The X-37B could
open its payload bay doors whilst in flight, jettisoning the robotic
sub.
The submersible would then open a parachute and splash down
in the sea. This method has been used before by the US military to
deploy a bomb called the MOAB.
Alternatively, the shuttle could ditch in the sea, opening its doors to deploy the sub before sinking.
Titan resembles a deep frozen version of Earth, making it an
attractive target for exploration. It was visited by the European
Huygens probe, which touched down on the surface in 2005.
A mission called the Titan Mare Explorer (TiME), in which
Ralph Lorenz was involved, would have returned there with a floating
lander that gathered data from the sea surface.
The X-37B military mini-shuttle could be used to deliver the sub to Titan
TiME was one of three finalists in the selection process for a
Nasa low-cost Discovery mission, but eventually lost out to a Mars
proposal called InSight. The new Titan concept combines some of TiME’s
science objectives with others enabled by the use of a submersible.
“You can do everything that a mission like TiME could do,
particularly at the shoreline and measure the weather and the
composition at the sea surface, measure the waves,” Ralph Lorenz tells
me.
“But it also lets you carry out detailed mapping of the sea
floor, where there’s a rich buried record of Titan’s climate history.”
Fizzy drink
Around shorelines on Titan are sediments left behind when
liquid hydrocarbons evaporate; they suggest sea levels on the moon have
periodically risen and fallen.
Indeed, while the seas are today concentrated in the moon’s
far north, natural cycles determined by the properties of Titan’s orbit
may cause these bodies of liquid to jump between poles every 30,000
years.
A sub could shed light on the basin in which the seas lie, including the possibility that it’s a giant eroded impact crater.
The mission might see layering in the liquid column like that
seen in Earth’s Black Sea, where a salty, oxygen-poor layer exists
beneath fresher (though still brackish) surface waters.
The TiME mission would have performed the first investigation of an extra-terrestrial ocean
“One could imagine that kind of compositional layering in
Titan’s seas; you may have more ethane-rich liquid at the base and a
‘fresher’ methane rich layer at the surface. But maybe tidal and
wind-driven currents are enough to stir everything up and mix it.”
The $100,000 Niac study didn’t identify instruments to be
carried by the torpedo-shaped vessel. But sidescan sonar, a camera, and a
seafloor sampling system are obvious candidates.
However, operating a sub in Titan’s same-but-different
environment presents unique challenges. For example, military submarines
face a problem called cavitation, where the propellers cause bubbling
that’s audible to sonar. This can give away their presence to the enemy.
If Titan’s seas are methane-rich, and have nitrogen dissolved
in them (as scientists think), changing the temperature of the liquid
hydrocarbon by just a few Kelvin could cause the nitrogen to come out of
solution. This means the sub’s system for getting rid of waste heat
would cause fizzing that might interfere with sonar measurements.
But Dr Lorenz says tweaking the design of the heat rejection
system, or using the sonar when the sub is at rest could help mitigate.
Above us the waves
Communications are also a vital consideration. TiME would have
taken advantage of a geometric window of opportunity when Titan’s north
pole was pointed towards Earth, allowing direct communication with our
planet.
But as the end of the decade approaches, Earth gets lower and
lower on the horizon – making it more difficult to send data directly.
So the submarine mission is being targeted for 2040 – the next point
when the direct mode becomes possible.
To save everyone the wait, an orbiting spacecraft could
accompany the sub to Titan in order to relay data to Earth. This would
enable the mission to launch at any time, but also add considerable
cost.
Another crucial factor is power. Spacecraft that stay within
the inner Solar System can use solar panels to generate electricity.
But missions venturing beyond the asteroid belt need
radioactive power generators, usually fuelled by the decay of
plutonium-238. However, the US stopped production in the 1980s and
supplies have been running out, causing consternation within the
planetary science community.
Without this radioactive fuel, outer Solar System destinations like Titan are shut down to exploration.
TiME was to have used a novel power system called an Advanced
Stirling Radioisotope Generator, which would have made the most
efficient use of valuable remaining plutonium-238.
But its development was hit by delays, and the project was
eventually placed on ice in 2013 – when the US officially re-started
plutonium production.
“If TiME had been selected, we’d be launching 13 months from
now. It was on the path to implementation… it was a real thing,” says
Dr Lorenz.
He estimates that between $5m and $10m were spent on its
development. But there’s now the potential to send a lander that can
dive as well as float.
Saturn’s biggest moon will continue to fascinate and inspire,
making a return inevitable. And when we do go back, it may just be with
a submarine.
Source Article from http://feedproxy.google.com/~r/AscensionEarth2012/~3/Yv0su_qiCv4/is-titan-submarine-most-daring-space.html
Is Titan submarine the most daring space mission yet?
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