Imagine you want to send a one-ton package to Mars, land it safely on the surface, and have it move around after it lands. First, the package has to survive atmospheric entry on Mars, which heats the package to 1,600 degrees. After this, the package has to deploy a supersonic parachute capable of withstanding 9 gs of force to slow down. The package then has to fire rocket engines, descend slowly to within 20 meters of the surface, and slowly lower a rover into a crater right next to a mountain six kilometers tall via a tether, so that the rockets don’t stir up too much dirt that might damage the rover. All of this in about seven minutes. Oh, and by the way, it takes nearly 14 minutes to send a signal to Mars (too long to allow any realistic form of remote control from Earth), so the onboard computer has to do all of this on its own without any help from mission control. In the early morning hours of August 6, 2012 (Central Daylight Time), NASA will attempt this complex sequence of events and land the newest in its fleet of rovers, called the Mars Science Laboratory (a.k.a. the Curiosity rover).
Various space programs of the past and present have had a number of successes and failures in landing packages on other worlds. In missions past, such missions involved stationary landers or small rovers. In the 1970s, the Soviet Union successfully landed and operated two robotic Moon rovers. Since the Moon is much closer than Mars, this early feat was made easier by the much smaller 1-2 second communication lag that allowed for human controlled operations. Missions to Mars have been numerous over the years–some succeeded, others failed. These missions were a mixed bag of landers, orbiters, flybys, and only more recently, rovers.
The Curiosity rover is a next step, following in the footsteps of previous rovers. The first rover, Soujourner, was a tiny little thing that was only a little over two feet long. It was solar-powered and couldn’t go very far from its lander. This mission was followed by the tremendously successful Spirit and Opportunity rovers, both of which were quite a bit larger than Sojourner. The Curiosity rover is by far the largest of all the rovers on Mars, at about 86 times the mass of Sojourner:
Not only has the mass of rovers increased, but the speed has as well. The Curiosity rover has a maximum surface speed that is about 2.5 times that of Sojourner:
But this is still a relatively slow speed. The maximum surface speed of the Curiosity rover falls somewhere between the speed of a garden snail and the speed of the slowest land mammal.
NASA has produced a dramatic five-minute teaser documentary about the mission to get you hyped about it:
Hopefully nothing goes wrong, but if you want to keep tabs on the landing when it happens, NASA will be providing a number of live feeds while the landing is going on. In addition, local museums and planetariums may run special viewing opportunities, so check your local area for such events.