PASADENA, Calif: After a lull of more than 20 years, NASA is poised to resume exploration of the Red Planet as the Mars Pathfinder spacecraft prepares for a July 4 touchdown. Making a whimsical entry, the half-ton lander will approach the surface at 1pm EST at about 55 miles per hour, whereupon a bubble pack will absorb the brunt of the impact, sending the lander bouncing like a basketball up to the height of a four-story building until it settles safely on the planet surface. A small rover named Sojourner (24.5 inches long by 18.7 inches wide) will then emerge to study the planet's geological characteristics. Pathfinder will land at the dry mouth of an ancient channel called Ares Vallis. The site was picked for its relatively flat surface and the variety of rock and soil samples it may present. While the mission has ambitious scientific objectives, a more crucial goal is to show the system can do the job faster, better and cheaper than the pricey missions of the past. And if it has an amusing way of making an entrance, can't hurt.