<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>to even think about Ceres is a waste of many thingswe need to focus only a few things this centuryMoon.. as stepping stoneMars.. as new EarthEnceladus as possible place where life might be Titan.. because it is a deepfreeze earth and it was discovered by one of the most important man in history <br />Posted by efron_24</DIV><br /><br />OK, let me go down the list of 'challenges' for doing an unmanned sampling return mission:</p><p>Mars requires a heavy heatshield, and a sample return mission is difficult given the high required escape velocity (5.02 km/sec). A return mission requires carrying a lot of fuel instead of science instruments or many samples.. The high surface gravity means that the lander can only sample one location. EXPENSIVE!</p><p>Titan requires a heavy heatshield, and a sample return mission is difficult given the extreme distance from Earth and high required escape velocity (2.65 km/sec), and in addition, the craft also would have to pull itself out of the Saturn gravity well. A return mission requires carrying a lot of fuel instead of science instruments or many samples. This makes a sampling return mission very difficult. Power supply in the thick dark atmosphere would require an expensive and heavy nuclear source, which means less weight for instruments, and solving heat management issues so the craft doesnt sink into the thawing soils. An orbiter would also be required for communication (more expensive). On the positive side, perhaps a balloon could be used to move the craft around to sample different locations. EXPENSIVE!</p><p>Enceladus mission would require a large amount of fuel to decelerate in the Saturnian gravity well and get captured by this tiny moon, and then another large amount of fuel to escape from Saturn's gravity well and get back to earth. On the positive side, at least the Enceladus escape velocity is low (0.24 km/s), so perhaps the craft could be lifted and re-landed at different areas for multiple sampling sites. Power supply in the distance from earth would require an expensive and heavy nuclear source, which means less weight for instruments, and solving heat management issues so the craft doesnt sink into the thawing ices. An orbiter would also be required for communication (more expensive). EXPENSIVE!</p><p>A mission to Ceres would be much easier, given is close proximity, and its tiny gravity (escape velocity = 0.53 km/sec). This means much less fuel is required to land and return. The tiny gravity would allow the craft to hop and reland at different locations for multiple sampling. Also no expensive and heavy nuclear fuel supply is needed. No heat shield would be needed. All told, much more mass could be devoted to instruments. In many ways, Ceres is ideal for an unmanned sample return mission. COMPARTIVELY CHEAP!</p> <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>