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While we may not
get to that earth-like planet around Proxima Centauri anytime soon, NASA
scientists are proposing all kinds of ways to explore the planets, moons,
asteroids and various other rocky and icy things floating in and around our own
solar system.
Checking in at
the NIAC Symposium
The plan to head
to Titan was laid out at NASA's annual Innovative Advanced Concepts (NIAC)
Program Symposium held this week. The NIAC program is intended to fund
visionary ideas that go way beyond things as mundane as going back to the moon
or putting a colony on Mars. In fact, some of the ideas on display seem like
science fiction, but this is all real, and while the missions and concepts can
boggle the mind, they show just how deep into space NASA is looking.
But first, a bit
about Titan. It's the second largest moon in our solar system, behind Ganymede,
which orbits our largest planet, Jupiter. It is a beautiful moon, at times
looking positively earthlike with its cloud-filled skies. It is unique in that
it has a dense atmosphere composed almost entirely of nitrogen with clouds of
carbon-rich methane and ethane. Its surface is mostly ice and rocks. We only
learned that in 2004, when the Cassini-Huygens spacecraft got close enough to
peer through the yellowy nitrogen-carbon smog.
But Cassini also
found liquid on Titan -- a lot of it, in the form of giant lakes of
hydrocarbons. In fact, according to Jason Hartwig from NASA's Glenn Research Center,
Titan is “the only other body, other than earth in our solar system, that has
stable accessible seas.” Hartwig is part of the team, called COMPASS, that NASA
funded and asked to figure out a way to get to Titan and explore its great
lakes.
Titan? Yes
Titan!
There are three
main seas on Titan -- Punga, Kraken and Ligeia Mare -- and together they are
about as large as the Great Lakes here in the U.S. They are composed entirely
of hydrocarbons, primarily methane and ethane. Hartwig says that's “about 100
times more liquefied natural gas on Titan than the whole planet earth
combined.” Exploring those seas, seeing what's in them, and perhaps more
importantly, what's at the bottom of them, is what NASA's Titan Submarine
project is all about.
That's right. Submarine.
Team leader Steve Oleson, along with Hartwig and the rest of the COMPASS team,
wants to send an autonomous submarine to Titan that would roam around, up and
down these giant lakes. They have a proposed launch date of 2038, a 7-year
transit time and then a full year of this as-yet-unnamed sub cruising around on
Titan. Why 2038? That's to make sure Saturn doesn't get between Titan and the
earth, so NASA can talk to its little explorer.
Details,
details, details
The submarine
will be about 6 meters long, equipped with a small plutonium engine in the back
called a Stirling radioisotope generator (SRG). The heat from the engine keeps
the electronics in the front of the sub warm. That's vital because the
hydrocarbon seas are a frigid minus 180 degrees celsius.
And the sub also
has a potentially retractable sail that runs along its length. After 8 hours
under Kraken Mare, it would resurface, Hartwig says, "and have 16 hours to
communicate and recharge and all that." From a layman's point of view this
may seem a bit like a thought exercise. And to some extent it is. But so was
going to the Moon until we did it. The level of detail that the team has
drilled down to makes it clear they think this is something we can actually do.
One strategy
they've put together to make this real is an exercise called a COMPASS run.
Hartwig calls it "very intense." Basically, he says, "it's a
bunch of people sitting together for 4 - 5 days straight trying to update the
design." They bash through every
imaginable problem. “We are finding that the terrain around some of these seas
is really quite treacherous,” Hartwig explains, so if the sub is, for instance,
piggybacking on a probe that is exploring Titan's surface, they have to make
sure it's sturdy enough to get to the water's edge. The more likely scenario is
for the sub to be dropped directly into Kraken Mare from low orbit for a safe
submarine splashdown.
Another COMPASS
problem? Bubbles, caused by the hot sub hitting the cold hydrocarbons.
"That waste heat we’re dumping into the liquid may be enough to cause
bubbles," Hartwig says. Those bubbles can get in the way of cameras or
even "coalesce at the aft end and cause our propellers to cavitate,"
which could stall the sub in the water.
Whether the
project actually happens though is still uncertain, NASA has a notoriously
tight budget. But it's fun to realize that we are in fact capable of achieving
such an audacious voyage of discovery.
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