NASA Releases Details of Titan Submarine Concept

Zothecula writes: Now that NASA has got the hang of planetary rovers, the space agency is looking at sending submarines into space around the year 2040. At the recent 2015 NASA Institute for Advanced Concepts Symposium, NASA scientists and engineers presented a study of the Titan Submarine Phase I Conceptual Design (PDF), which outlines a possible mission to Saturn's largest moon, Titan, where the unmanned submersible would explore the seas of liquid hydrocarbons at the Titanian poles.

"At its heart, the submarine would use a 1 kW radiothermal Stirling generator. This would not only provide power to propel the craft, but it would also keep the electronics from freezing. Unfortunately, Titan is so cold that it's almost a cryogenic environment, so the waste heat from the generator would cause the liquids around it to boil and this would need be taken into account when designing the sub to minimize interference. However, NASA estimates that the boat could do about one meter per second (3.6 km/h, 2.2 mph)."

Comments

Re:25 Years from now?

[Rei]

You joke, but the ability to reconfigure spacecraft on the fly even on the smaller scale has proven itself valuable time and time again. I love how they came up with a trick after New Horizons was launched to nearly double its communication rate. It has two radio transmitters, one primary and one backup, and one dish. When they launched, it seemed obvious that only one could be used at a time - but en route someone figured out that if you have one transmit with right-handed polarization and the other with left-handed, they can both transmit at the same time, and then on Earth the two signals can be separated out. But since the spacecraft wasn't designed for enough power to use them at once (that was never supposed to be necessary), they needed to find a trick to get more power. And it's not easy, given that there's not a lot of things running when the probe is just drifting in deep space - what are you going to do, shut down your guidance computer? Well... yes, that's exactly what they came up with - when they've filled up their memory, they align the antenna, then spin up the spacecraft, shut down the guidance computer, transmit at double speed until the memory is free, then restart guidance and stop the spin so that they can resume data collection.

While 3d printing and robotic arms for assembly is a stretch at present, the importance of having hardware flexibility is increasingly being demonstrated in space missions.

Re:Drop it on Europa

[Rei]

Hmm, just another thought which I haven't seen anywhere else. Orbital velocity through Titan's ionosphere would be about 1500 m/s, if my calculations are right. Exhaust velocity on ion engines ranges from tens of thousands to millions of meters per second. So a ram scoop to refill propellant is plausible, your drag should be well less than your ability to reboost with the propellant you acquire, even if efficiency is low; in practice you should be able to capture much faster than your burn rate. While all ion engines have certain elements which are "optimal" in terms of performance, you can generally use whatever ions you want without too dramatic of a sacrifice in terms of isp and thrust (so long as there's no corrosion problems or the like).

So, for a sample return mission:

1) A probe with detachable, flying lander (each RTG-powered) is boosted to LEO. As for the lander, I personally like the tilt-wing design, as it allows easy of landing and requires only a small RTG (it can fly in short hops, replenishing batteries on the ground while during surface science), but allows the high speed and range of travel of a fixed-wing plane.

2) The probe begins a decade or more ion-propelled journey to Saturn, with only enough propellant to reach a stable orbit in Titan's upper atmosphere (and possibly some minor exploration of the Saturnian system en-route).

3) The lander drops off, aerobrakes over the course of a few weeks, and then explores the planet for a year or so while the orbiter replenishes itself. A tilt-wing aircraft could probably explore all of the most interesting places on the planet in that timeframe and take numerous small samples). The lander only needs a small antenna, as the orbiter can act as a repeater to Earth.

4) When exploration and propellant refill are done, the lander then flies back up through the atmosphere to as high and fast as it can, then activates a rocket stage (1500-2000 m/s delta-V) to re-rendezvous with the probe. The spent stage is ejected.

5) The probe returns to Earth on ion power using its propellant from Titan (possibly with some minor exploration of the Saturnian system en-route). Upon return to Earth, the leftover propellant could itself be studied as a sample return in its own right (it could even be gathered into different tanks from different altitudes via an elliptical orbit if so desired).