It's go time for NASA's Phoenix Mars Lander.
After nearly 10 months speeding across 422 million miles (679 million km), the Phoenix spacecraft is just days away from plunging into the Martian atmosphere on Sunday to land near the north pole of Mars.
"We've been working quite hard all the way along," said Deborah Bass, Phoenix's deputy principal investigator at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. "The feeling around here is that we are cautiously optimistic."
Phoenix is slated to land on the Martian arctic plains in a region called Vastitas Borealis, where it will use a robotic arm to dig for water ice in the hopes of determining whether the site may have once been capable of supporting primitive life.
NASA's Phoenix mission machine kicked into high gear Thursday at 2:30 p.m. EDT (1830 GMT) with the first in a series of status briefings leading up to the first hoped-for signal from the probe at 7:53 p.m. EDT (2353 GMT) on Sunday.
Because of the 171 million miles (275 million km) between Mars and Earth during Phoenix's red planet arrival, it will take signals about 15 to 20 minutes to reach NASA's control center at JPL once they're sent.
"We're working at night, because that's when the spacecraft is going to land," Bass told SPACE.com, adding that the entire Phoenix team should now be in place at JPL and at a primary mission control center at the University of Arizona, Tucson. "This will be just an absolutely thrilling experience."
Phoenix is the first spacecraft to attempt a powered landing on Mars since the crash of NASA's ill-fated Mars Polar Lander in 1999.
It follows the 2004 airbag-cushioned arrivals of the agency's Spirit and Opportunity — which are still active today — and would mark the first successful powered landing on Mars since NASA's two Viking spacecraft arrived in 1976.
Red planet rundown
While mission engineers and researchers have worked diligently over the last 10 months to rehearse Phoenix's landing day, the pace will definitely pick up leading into this weekend.
On Saturday, Phoenix researchers and engineers will hold another mission update at 3:00 p.m. EDT (1900 GMT), which like Thursday's will be broadcast live on NASA TV.
Later that night, at about 10:46 p.m. EDT (0246 May 25 GMT), Phoenix may fire its thrusters to tweak its approach toward the Martian arctic.
Another course correction is available on Sunday — landing day — at 11:46 a.m. EDT (1546 GMT), followed by a 3:00 p.m. EDT (1900 GMT) mission briefing before NASA kicks off continuous live coverage at 6:30 p.m. EDT (2230 GMT).
For cable television subscribers without NASA TV or computer access for NASA's Sunday webcast, the Science Channel will also provide live Phoenix landing coverage and commentary from 7:00-9:00 p.m. EDT (2300-0100 GMT).
Phoenix, itself, will bounce signals off NASA and European spacecraft orbiting Mars to send data and telemetry back home.
Crunch time for the Phoenix Mars Lander comes at 7:39 p.m. EDT (2339 GMT) on Sunday, when the spacecraft separates from its cruise stage and is only 14 minutes away from its planned touchdown on the Martian surface.
"There are a lot of events," said Barry Goldstein, Phoenix project manager at JPL. "We fire 26 pyrotechnic events in the last 14 minutes of this vehicle, and each of those has to work perfectly for this mission to come off as we've planned."
Phoenix is due to slam into the Martian atmosphere at 7:46:33 p.m. EDT (2346:33 GMT) while traveling at 12,600 mph (20,277 kph), beginning a seven-minute descent that will be over well before mission controllers on Earth get their first hint that it even began.
The probe is expected to deploy its parachute about four minutes later, then drop free at 7:50:15 p.m. EDT (2350:15 GMT), then drop free a few minutes later to fire its pulse rocket engines for the final landing approach.
If all goes well, the first hint of a successful landing will come at 7:53:52 p.m. EDT (2353:52 GMT), though Phoenix will have to wait 15 minutes for the dust to settle before deploying its vital power-generating solar panels, mission managers have said.
"Our highest goal is to see if this might form a habitable environment on Mars," said Peter Smith, Phoenix's principal investigator at the University of Arizona, Tucson. "There's no signpost today that tells you where to land, and that will be life. So we're taking a chance."
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