Keith's note: NASA just flashed this Mars scoreboard graphic again in an effort to lower expectations about MSL's landing chances and to give everyone an appreciation as to how hard it is to land something on Mars. One problem: NASA did not really explain the numbers "Earth: 15 Mars: 24". The U.S. has not tried to send 15+24 or 39 missions to Mars. Not even close. NASA is referring to all missions sent - by everyone - to Mars over the past half century. But they say "we" when they show the chart and refer to previous NASA missions. If you look at this Wikipedia page you can see that 17 or so of the failures were USSR/Russian missions in the 60s and 80s i.e. 30 to 50 years ago. What do half-century-old primitive Soviet Mars probes - many of which never even left Earth - have to do with 21st Century missions? Somewhat misleading to say the least.
'Seven minutes of terror': Mars rover landing will be a nail-biter, Christian Science Monitor
"Humanity's track record for Mars missions isn't stellar, James Green, NASA director of planetary science, suggested ... Since 1960, when the first attempt at a Mars flyby was made by the Soviet Union, "the historical success rate at Mars is only 40 percent," he wrote. That figure, however, includes all space-faring nations, such as Russia, pre- and post-Soviet collapse, which is 0 for 19, most recently with the loss of last year's Phobos-Grunt mission to study the moons of Mars. Out of the 18 mission NASA lists with Mars as the destination or as the main target for a flyby, the agency has a batting average of .730. Of the attempts at landing spacecraft on the surface, beginning with the Viking missions in 1975, the agency is six for seven."
"As you may already know, the historical success rate at the planet Mars is only 40%. Although our landing percentage odds are higher (100%), successful landing with an unproven, next generation, landing system...well, that will be a white-knuckle- experience to say the least."
Keith's note: Jim, how can you say that NASA has 100% landing rates when Mars Polar Lander and DeepSpace 2 crashed into Mars? I guess a "crash" = a "landing" at NASA (who knew). If that's the case we're doing even better than 100% since Mars Climate Orbiter crashed (I mean "landed") on Mars - and it wasn't even supposed to be a lander!