Harvesting fuel from the Saturn system.

[exoscientist]

Nasa scientists are investigating possibilities for follow-up missions <br />to the Cassini mission to the Saturnian moons Titan and Enceladus: <br /><br />Encore For Enceladus! Saturn Moon Ripe For Astrobiology Exploration <br />http://www.space.com/scienceastronomy/060403_mystery_monday.html <br /><br /> Ideal would be sample return missions. A problem would be carrying <br />enough fuel for landing and ascent. It may be we can get the required <br />fuel for the return from the Saturn system itself. <br /> This article in Science gives the estimated amount of molecular oxygen <br />above the Saturn A ring: <br /><br />Oxygen Ions Observed Near Saturn's A Ring. <br />J. H. Waite, Jr., T. E. Cravens, W.-H. Ip, W. T. Kasprzak, J. G. <br />Luhmann, R. L. McNutt, H. B. Niemann, R. V. Yelle, I. Mueller-Wodarg, <br />S. A. Ledvina, S. Scherer <br />Science, 25 February 2005: Vol. 307. no. 5713, pp. 1260 - 1262 <br />http://www.sciencemag.org/cgi/content/abstract/307/5713/1260 <br /><br /> It estimates the number of neutral O2 molecules as 10^4 to 10^5 cm^-3. <br />However, they note it could be much higher than this range because of <br />the limitations of the measurements. I'll take the upper number, 10^5 <br />cm^-3. There are 10^15 cubic centimenters in a cubic kilometer so this <br />amounts to 10^20 molecules per km^3. <br />The article gives the orbital velocity around Saturn at the radial <br />distance of the A ring as in the range of 15 km/s. Actually the article <br />explains there are magnetic effects that accelerate the various ionized <br />molecules even faster which when exchanging momentum with the neutral <br />molecules accelerate these faster as well. I'll use the 15 km/s number <br />for simplicity. Then if we orbit the spacecraft in the opposite <br />direction we would have a relative velocity wi <div class="Discussion_UserSignature"> </div>

 

[barrykirk]

Sorry, but that collection method just won't work for the following reason.<br /><br />You're collecting O2 molocules that are travelling at 30 kM/Sec in the direction opposite your orbital motion.<br /><br />This means that due to action/reaction it's the same as firing a retro rocket with an exhaust velocity of 30 kM/Sec.<br /><br />That reto-rocket will be very efficient at slowing down your orbit, not what you want to do around Saturn.

 

[baktothemoon]

The solution seems somewhat obvious to me but will probably seem very dumb to people here who are experts: <br /><br />For a sample return mission to Titan, carry enough fuel to land on the surface, and the oxygen needed for the return trip. Extract methane from the air or the soil and use it to fuel a LOX-Methane engine to takeoff and return to Earth.<br /><br />For a sample return mission to Enceladus, again carry enough fuel to land, extract water from the ice on the surface or from the geysers, use electrolysis to seperate it into LOX and LH2, use fuel to blastoff and return to Earth. <br /><br />Okay, now tell me why it can't be done.<br /><br />"Ask not what your country can do for you, ask what you can do for your country." John F. Kennedy

 

[askold]

You better be prepared to do all these wonderful things at -290F. Brrrr.

 

[baktothemoon]

Hmmmm....well that makes it a little more difficult, but if a spacecraft can still function in that kind of temerature it might still be possible to do it. <br /><br />"Ask not what your country can do for you, ask what you can do for your country." John F. Kennedy

 

[thinice]

Better be prepared to dissipate a lot of heat from H/OX liquefaction. And to tow fuel tanks and cryogenic hardware all the way from the Earth to Saturn.