The European Space Agency says it will attempt to land the first spacecraft on a comet on Nov. 12.
It says the maneuver will take about seven hours starting from the moment its unmanned probe Rosetta releases the 100-kilogram lander at 0835 GMT (0335 EST).
Because of the 28 minutes it takes the signal to travel back to Earth, confirmation of a successful landing won't arrive until about shortly after 1600 GMT (1100 EST).
ESA said in a statement Friday that it has a backup plan in case of a problem with the preferred landing site.
Scientists hope the decade-long mission to examine comet 67P/Churyumov-Gerasimenko will help them learn more about the origins and evolution of objects in the universe.
"If the attempt is successful, this will mark the first time humans have ever landed a spacecraft on a comet," the Monitor's Pete Spotts wrote shortly after NASA selected a landing site earlier this month.
As with lander sites on other solar system objects, the team needed to find a location with few boulders. And if the site has any slope to it, the slope has to be gradual enough to prevent the lander from landing and rolling legs up, like a helpless turtle.
The team is playing a cosmic version of "Beat the Clock." The comet is en route to its closest approach to the sun next August. But as it makes that approach, it will heat up and spew ever larger amounts of dust and gas from the surface. Planners hope to place Philae on the surface in November, before the fireworks begin in earnest.
Putting the craft on the surface – and keeping it there – is no small feat given the comet's weak gravity. On Earth, a craft has to reach speeds of about 25,000 mph to break free of the planet. On 67P/Churyumov-Gerasimenko, merely attempting to saunter across the surface would launch an comet-walking astronaut back into space.