The Mars Science Laboratory "Curiosity" will land on Mars in about 4 hours -- at 10:31 p.m. Pacific (Aug 5), 1:31 a.m. Eastern (Aug 6).
You can watch events unfold live here.
The landing method is very complex and has never been done before. The final step involves lowering the rover on a "sky crane" from the rocket-powered descent vehicle -- which is firing its rockets as this is happening -- cutting the cables when the rover touches down, and then flying the descent module away from the rover.
If this works, it will make the Apollo landings look like child's play.
Watch it. It might be America's last feat of engineering.