NASA officials told reporters at a pre-landing news conference on Sunday that the spacecraft was functioning properly as it sped toward its target.  But Curiosity's most complicated maneuvers are just ahead.

Adam Steltzner is the lead mechanical engineer for the rover's critical entry, descent and landing sequence. "It's a little anxiety provoking, but I will say that I slept better last night than I have slept in a couple of years because she's kind of on her own now.  And when I look back at the hard work that we've done, I believe that the team has done everything that we can to deserve success tonight.  Although, as we all know, we can never guarantee success," he said.

Curiosity will be traveling at about 20,000 kilometers per hour when it hits the thin Martian atmosphere.  It will have only seven minutes to use a parachute, rocket thrusters and a skycrane to reduce its speed and make a safe landing.

Throughout this period, the craft will function autonomously.  NASA engineers will not be able to witness the events in real time because it takes 14 minutes for radio signals to reach Earth from Mars.

NASA's Adam Steltzner says the scientists and engineers overseeing the project are "rationally confident, emotionally terrified" and prepared.  "As far as the amount of control that the team has during entry, descent and landing, it's identical to the control that anybody watching at home has.  We're all along for the ride," he said. 

Curiosity's hazard-avoidance cameras will take pictures shortly after touchdown.  NASA could receive the first low-resolution, black-and-white images within minutes or a few hours of landing. 

Doug McCuistion is the Director of NASA's Mars Exploration Program.  He says the car-sized rover, which has 17 cameras, will soon provide color pictures. "In the days, years, weeks to come, there is going to be an enormous number of images, incredible images, color images, real color this time, too, so kind of like the human eye will see, which will be really exciting.  Those will come, and there will be plenty of those," he said.

But McCuistion stressed that there is no guarantee of a successful mission. "If we don't do it, and we're not successful, we'll pick ourselves up, we'll dust off and do it again.  The science is on the surface.  We need to keep going back, and that's the plan, but I think we're going to stick the landing," he said. 

The main goal of the mission is to see whether Mars ever had conditions that could have supported microbial life.  The nuclear-powered Curiosity is outfitted with instruments to investigate Martian geology, weather and radiation levels during the next two years.  

Curiosity would be the seventh NASA spacecraft to land on the Red Planet.