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PASADENA, Calif. -- The Mars Science Laboratory rover, still attached to its drum-shaped interplanetary cruise stage, closed in on the Red Planet on Saturday, steadily accelerating under the increasing tug of the planet's gravity as it streaked toward a precisely targeted plungeinto the martian atmosphere overnight Sunday for a high-stakes descent to the surface. "The spacecraft and ground systems are all healthy and performing as expected," said MSL mission manager Arthur Amador. "The spacecraft is now in the EDL (entry, descent, and landing) approach configuration, in our final approach orientation, pointing our medium gain antenna within a degree of the Earth. We've got a strongtelecom signal, receiving data at 2,000 bits per second. "The power subsystem ishealthy, our rover batteries are charged to 100 percent. The thermaland propulsion systems are nominal with stable temperatures and pressures, and the DSN (Deep Space Network) continues to perform well, tracking the spacecraft continuously and conducting two differential ranging passes per day." As of Saturday morning, the Mars Science Laboratory was just 2.8 million miles from Mars after logging nearly 350 million miles since launch from Cape Canaveral last November.Flight controllers decidedFriday the spacecraft's path toward Mars was accurate enough to forgoa preplanned trajectory correction maneuver. "We're now right on target to fly through the eye of a needle, that is, our target at the top of the Mars atmosphere," said Amador. "The target is a box that's 3 kilometers (1.9 miles) by 12 kilometers (7.5 miles) in dimension. And we're flying right through it." A high-precision atmospheric entry is just the first step in a complex, high-speed series of events designedto get the nuclear-powered Mars Science Laboratory rover Curiosity safely to its landing ellipse on the floor of Gale Crater, within easy roving distance of a 3-mile-highmound of layered rock that represents a record of the Red Planet's enigmatic history. Equipped with a robot arm, a drill, sample scoop, state-of-the-art instruments, and a suite of cameras, Curiosity is the most sophisticated robotic lander ever sent to another planet. Over the course of a planned two-year mission, the rover will search for carbon compounds, one of the key building blocks of life as it is known on Earth, and assess whether habitableenvironments ever existed, or still exist, on the Red Planet. "This is a very complicated vehicle; it's way more complicated than (previous Mars rovers) or other vehicles we've flown in the past, and so it's going to take us a while to first check itout and then get into thescience...that everybody wants to do," said Richard Cook, MSL deputyproject manager. "We're going to spend almost the entire month of August really checkingout the vehicle, getting the first images. We'll obviously be getting science data during that, but we'll also be doing engineering checkouts ofthe instruments, of the sampling system, changing flight software,doing other things. Hopefully by early September we'll be at the point where we can do our first drive and have the vehicle begin tomove around a little bit." But first, it has to get there. Tipping the scales at 1 ton, Curiosity is the largest rover ever sent toMars and it will hit the upper atmosphere at a blistering 13,200 mph. Protected by a massive insulating heat shield, the spacecraft and its computer will fire rocket thrusters to adjust the craft's lift during the hypersonic phase of the descent, dipping or climbing as required and flying through broad S-turns to bleed off speed while keeping the craft on course for a pinpoint landing. After slowing to around 1,000 mph, the craft will deploy a huge supersonicparachute, the heat shield will be jettisoned, and a sophisticated radaraltimeter will begin sounding the surface. After the craft slows to less than 200 mph, the parachute will be jettisoned and Curiosity, bolted to the belly of a rocket-powered descent stage, will fall free for the final drop to the surface. Unlike past landers, Curiosity's jet pack doesn't have legs. Instead, it will act like a flying crane, lowering the rover directly to the surface on the end of a 25-foot-long bridle as the "sky crane" slowly descends. When the flight computer senses"weight on wheels," the bridle will be cut and Curiosity will be ready for initial tests and checkout. Touchdown is expected at 10:17 p.m. PDT Sunday, but it will take radio signals confirming the event 13.8 minutes to cross the 154-million-mile gulf between Earth and Mars. That translates to 10:31 p.m. "Earth-received time." Engineers at the Jet Propulsion Laboratory in Pasadena, Calif., will be relying on NASA's Mars Odyssey orbiter to relay entry, descent, and landing telemetry back to Earth and to confirm asuccessful touchdown. If Odyssey has problems, orif any issues crop up withCuriosity's transmitter, it could take several hours