Sample Return Missions from Enceladus, Europa, Titan, Ceres, page 1.

Copyright 2014 Robert Clark 

 Gravity measurements from Cassini have provided further evidence that Enceladus has a subice liquid ocean. It is being regarded now as a prime target in the search for extraterrestrial life. The question is how to reach that ocean through what may be 40 km of ice. There have been various proposals for drills. However, NASA has modeled the plumes seen to arise from the "tiger stripes" on Enceladus as coming from vents that attach to the ocean below. Then a simpler method may be to reach the ocean by traveling through these vents. 

This graphic shows how the ice particles and water vapor observed spewing from geysers on Saturn's moon Enceladus may be related to liquid water beneath the surface. The large number of ice particles and the rate at which they are produced require high temperatures, close to the melting point of water. These warm temperatures indicate that there may be an internal lake of liquid water at or near the moon's south pole, where the geysers are present.

http://www.nasa.gov/mission_pages/cassini/multimedia/cassini20080207.html

 In this model the temperatures don't have to be particularly high, just near the melting point.

 This method may work to reach subsurface liquid water for other outer solar system bodies expected to have them such as Europa, Titan and Ceres.

 As a feasibility test we might try it to explore subsurface though deep-sea hydrothermal vents here on Earth. 

Deep-sea vent biogeochemical cycle diagram.

 According to this model the temperatures might reach a maximum of 400 °C. If we can develop a robot to travel through these conditions quite likely it would also work in the conditions for the vent systems of these outer solar system moons.

In an upcoming blog post I'll discuss how the Falcon Heavy at a 53 metric ton(mT) payload capacity and the first version of the SLS at 70 mT could each be used to conduct sample return missions from these outer solar system moons.

     Bob Clark  


Update, April 27, 2014:

 At the Humans 2 Mars 2014 conference it was mentioned "white smokers" during an astrobiology session. These are lower temperature than the "black smokers" so might be easier to explore internally:

White smokers are seafloor hydrothermal vents that are cooler than black smokers. They deposit light-colored silica minerals as well as some sulfides.

https://web.archive.org/web/20130329102456/http://geology.about.com/od/geoprocesses/ig/hydrothermal-features/white-smoker.htm

Since they are smaller however we would need smaller robots to explore them.

UPDATE, February 9, 2015: 

 JPL is investigating robots that can explore fissures in volcanos. They are also considering how they could be used to travel to the subsurface through fissures on worlds such as Europa and Enceladus:

News | January 7, 2015
NASA Robot Plunges Into Volcano to Explore Fissure.

http://www.jpl.nasa.gov/news/news.php?feature=4431