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Phoenix spacecraft healthy, on track for Mars landing BY WILLIAM HARWOOD STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION Posted: May 24, 2008 NASA's Phoenix lander closed in on Mars today, healthy and on course for touchdown Sunday evening near the red planet's northern polar cap. Engineers at the Jet Propulsion Laboratory in Pasadena, Calif., decided to forego a course-correction rocket firing late today but left open the option for a final trajectory tweak Sunday eight hours before atmospheric entry. "This is a very exciting day," said Douglas McCuistion, director of NASA's Mars exploration program. "The atmosphere here at JPL is electric. ... The big event is coming tomorrow. It's really just a beehive of activity adding to the excitement and enthusiasm around here." Phoenix will slam into the upper atmosphere of Mars at 7:46 p.m. EDT Sunday, kicking off what JPL Project Manager Barry Goldstein calls "seven minutes of terror." That's how long it will take the spacecraft to make its automated parachute- and rocket-powered descent to the frigid martian surface. Hitting the atmosphere at more than 12,500 mph, the spacecraft will experience a peak deceleration of 9.2 Gs and its heat shield will endure temperatures up to 2,600 degrees Fahrenheit as atmospheric friction slows Phoenix to a relatively sedate 1,100 mph, or about 1.5 times the speed of sound. At that point, the spacecraft will release a parachute to slow it down still more before the lander, now falling to the surface at about 125 mph, is released for a rocket-powered descent to the surface. "And then the real fun begins," Goldstein told reporters today. Firing 12 engines in rapid pulses to control the lander's orientation and descent rate, Phoenix's flight computer will guide the craft to a 5-mph touchdown. The last time NASA tried such a landing with a virtually identical spacecraft in December 1999, the Mars Polar Lander simply disappeared, the presumed victim of a software glitch and a premature engine shutdown. This time around, NASA and spacecraft-builder Lockheed Martin left no stone unturned to find and address potential problems and engineers are optimistic about a successful landing. Even so, Principal Investigator Peter Smith told reporters today he is nervous and "getting butterflies" as Phoenix closes in on its target. "This is not an easy thing to do," he said. "We bet the whole farm on this safe landing and we can't do our science without the safe landing. We've really worked so hard to build our science instruments, our rationale for why we're going, our procedures for doing all the science and yet we have this hurdle to get over before we can do it. And that's what makes me nervous." Touchdown is expected around 7:53:52 p.m., Earth-receive time. The actual landing will occur 15.3 minutes earlier, but it will take that long for radio signals, traveling at 186,000 miles per second, to reach anxious flight controllers on Earth. "All of that happens in a short seven minutes," Goldstein said. "It's a very nerve wracking time. The team has trained for the last five years to do this, the anxiety level is getting high, but we have a team that is well versed in what we have to do in even the worst-case contingencies. So we're ready to go." Quoting the British essayist Samuel Johnson, McCuistion said "'great works are not performed by strength, but by perseverance.' Perseverance is what it takes to get back to the surface of Mars again. The Phoenix team - the University of Arizona, JPL and of course, Lockheed Martin and a number of international participants - has been pushing very hard to get to exactly this point since they were selected about five years ago. ... This is truly the defining moment of this mission." See the May 22 story for a detailed overview of the Phoenix mission.
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SATURDAY STATUS BRIEFING 