>> Landing "somewhere" on the moon is hard enough. Navigating to >> within a >> few 100's of metres of a preselected spot is far far harder. > You still have to aim for "somewhere" on the moon, might as well > make > the dart an interesting place ;-> Not the point, alas. You definitely aim "somewhere" but if eg your TLI (translunar insertion) burn produces a less than 100% intended "good enough" result, if the imprecisely known mascons in the lunar surface on your final orbit perturb you not too much, if your descent stage comes up to power a little more slowly than expected, or if .... BUT the net result is that you are liable to be able to complete the basic mission, then you probably go with what maximises the probability of not failing totally. In the early days of nuclear standoff the reason that they could build "The Hole" under Cheyenne mountain and hope that it would survive an attack was that targeting accuracy was low. A direct hit of a suitably large megatonnage would always have killed it but the chances of achieving this were low. When it comes to sending rovers to the moon on a $25M total budget you are closer to the good old days than to laser guided fly-down-your-chimney munitions. None of the Apollo landers arrived precisely at intended target and AFAIK there is now some uncertainty where some of them actually are. Both locating something on the lunar surface which is lost to modern science AND going there is a vast challenge. The sites whose locations are precisely* known are that of Apollo 11, 14, 15 and the Soviet Lunokhod 2, so if one were going to visit an earlier landing site, those would be the best choices. Incidentally, those 3 Apollo sites also make utter rubbish of Fox TV's otherwise utterly rubbish documentary that claims that the US never landed men on the moon. Russell * Finding the reason is left as an exercise for the student :-) -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist