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Planetary News: Phoenix (2008)Phoenix Closes in on Mars, Ready for "Seven Minutes of Terror"By A.J.S. Rayl
PASADENA -- After traveling for 10 months on a 422-million-mile route – and getting an impressive 2 million miles to the gallon, Phoenix is closing in on the north pole region of Mars and will land today, just before 5 pm Pacific Daylight Time / 8 pm Eastern Daylight Time on Sunday, May 25. There, if everything goes as planned, it will become the world's first mission to dig below the surface of Mars and sample water-ice. "It’s okay so far," Peter Smith, Phoenix principal investigator, of the University of Arizona, told reporters at a press conference earlier today. "We’re going to land safely on Mars. The sky is clear. We’ve been watching the weather. Everything is set for us. We have a sunny day. The rest of the day is watching and waiting. We have sent all the commands we’re going to send to the spacecraft and we’re just going to watch it go in. Mission controllers decided "to waive off the last update we would give the vehicle," reported Barry Goldstein, Phoenix project manager, of NASA's Jet Propulsion Laboratory (JPL) announced at a press conference this morning." That means we have nothing else to do but watch," he confirmed. The decision to forego the final communication with Phoenix comes just hours after a decision made late yesterday afternoon to skip the second-to-last opportunity for adjusting the spacecraft's flightpath even though the spacecraft has "drifted a bit" from its trajectory, as Goldstein put it earlier. Since launching in August 2007, Phoenix's flightpath has been adjusted four times, or in space vernacular, the spacecraft has had four trajectory correction maneuvers (TCMs). These tweaks direct the spacecraft to land inside a specific ellipsoidal area. But since Phoenix hasn't drifted too much and since it has gained the admiration of its crew by being "one of the most well-behaved spacecraft," mission controllers decided to let their bird fly in on its present course. "It’s always tense when you land on Mars," said Steve Squyres, the principal investigator for the Mars Explroation Rover (MER) mission, who is on hand to offer commentary for CNN's news coverage, as well as watch NASA's next landing on the Red Planet. "It’s dangeorus thing to do and a difficult thing to do but I was back in the operations area and talking to a lot of the people on the Phoenix team and they feel good about this," he shared.
"The anxiety comes when decisions are still being made," Squyres continued. "Yesterday they were still deciding about the last trajectory correction manuever and their entry, descent, and landing parameters. Those are crucial decisions and you have to make the right deicisons -- the safety of your mission hangs in the balance and so that’s always tense. Once you have pushed the last button on the last command, it’s in the hands of fate. They’ve done all they can. I remember this from MER – there’s kind of a moment of calm and peace that comes over you when you’ve sent the last commands. They've done that now and right now these guys are just spectators with better seats than you and I have. It’s now up to their spacecraft. It’s just about showtime for these guys and Ido have a good feeling about this." In the final hour before Squyres had to be in the control room for Spirit's landing, he found solace from the anxiety and anticipation by sitting in his office and playing guitar. "I had it and a little amp set up in my office and played guitar for about half an hour and just thought and then packed up my stuff and off we went," he recalled. And Smith's plan? "I got my tattoo, my lucky hat, and my peanuts. That’s what I’m doing,” he smiled. Phoenix is to touch down somewhere inside or perhaps right along the edge of a targeted area about the size of Long Island, 23 kilometers in width by 70 kilometers in length, located in the northern arctic plains of Mars, at 68 degrees north, near the polar cap. The landing area has been thoroughly imaged by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter (MRO) and it is what one would expect of an arctic plain, basically boulder free, with only a few rocks scattered here and there. Even if Phoenix lands slightly outside the targeted area, it shouldn't make much difference.
It will be around -50 degrees Fahrenheit when Phoenix extends is three legs and pirouettes down to the ground, according to Smith, which, given that it's summer in the northern hemisphere of the planet, is actually somewhat balmy. Confirmation of Phoenix's landing could come as early as 4:53 pm Sunday Pacific Daylight Time / 7:53 pm EDT/ 11:53 pm UTC. The landing will have happened 15 minutes earlier on Mars, but at the current distance between Mars and Earth, about 170 million miles, it takes 15 minutes for the confirmation to get "home." Wherever exactly it lands, Phoenix will come to rest farther north than any other spacecraft on the Red Planet and will be the world's first spacecraft to make direct measurements of water on another planet, the first visit the arctic plains on Mars, and the first to experience the up to -100 degrees F temperatures there.
Once it lands and checks in with mission control, Phoenix will open its solar arrays, deploy its camera and weather station mast, then begin taking images. The pictures taken right after landing, which will include images of the solar arrays and perhaps an image of the arctic landscape, may arrive as early as 1.5 hours after confirmation of the landing, Smith said today. If no images arrive then, then the downlink from Odyssey Monday morning will include the first picture postcards from Phoenix. They don't really know how many will be in the first downlink, Smith said. They've planned for 24, but they could get one. It depends, he said, on how long it takes for Phoenix to go through its post-landing motions and check-outs. All images from the mission will be released to the public as they come through the Deep Space Network (DSN) pipeline, he said. At the Jet Propulsion Laboratory (JPL) the anticipation, anxiety -- and "the heebie-jeebies," as Joe Guinn, Phoenix mission manager, of JPL, described it yesterday -- have visibly set in. "This is not an easy thing to do," Smith said yesterday. "We bet the whole farm on a safe landing. We can't do our science without a safe landing, and that's cause for anxiety."
No doubt, team members at Lockheed Martin in Denver where the actual mission control for this mission is, and at the University of Arizona where the mission's science operations center is headquartered, and which is leading the mission for NASA, are feeling the same angst. "The anxiety level is getting high, but we have a team that's well-versed in what we have to do, even in worse case contingencies so we're ready to go," said Barry Goldstein, Phoenix project manager, of JPL. "The team has trained for last five years to do this." Reports from MRO's Mars Color Imager (MARCI) team show that the weather on Mars is looking good for landing today -- and, by some accounts, even better than the unseasonably cold and wet weather in Pasadena. A small dust storm to the northeast of the landing area had already moved across the landing area was downwind as of Saturday and so poses no hazard. If a dust storm should manifest, the Phoenix team can make adjustments "up to three hours before landing," Goldstein said. Winds are not expected to be an issue either. "Unlike the airbag landing system used by Pathfinder and Spirit and Opportunity, Phoenix's retrorocket system is "more robust to wind gusts," Goldstein pointed out. In any case, the dust they've seen "is well within the modeling" of what Phoenix can handle. During entry, descent and landing, data from the Phoenix spacecraft will be relayed to Earth through the Mars Odyssey orbiter. Late this afternoon, MRO and the European Space Agency's Mars Express will also slew their antennas toward Phoenix and monitor the entry, descent, and landing, collecting data that will be played back later to Earth. In fact, MRO's HiRISE camera, also from the University of Arizona, will be attempting to catch a picture of Phoenix as it fireballs into the atmosphere and later as it deploys its parachute. Spirit and Opportunity will be on hand as well. But, as Doug McCuistion, director of the Mars Exploration Program at NASA headquarters put it at the daily press conference, "there's not much they can do, so they're just bringing beer and pretzels to the show."
And, as with all landings on other planets, what a show it promises to be. The entry -- or five or six or seven minutes of terror -- is the most dreaded and feared part of any planetary exploration mission. Phoenix is currently flying in to Mars at 6,100 miles per hour (mph). "At about 18 minutes out, the gravity well will take us in at 12,600 miles per hour," Goldstein said describing the terror. "Then, 14 minutes before touchdown we separate from our cruise stage. At that point, we lose communication, X-band, and we start using our batteries. "We enter the Martian atmosphere seven minutes before touchdown, still traveling at 12,600 mph and the temperatures peaking at the heat shield as it's entering through the not so dense atmosphere of Mars actually reach about 2,600 degrees Fahrenheit," Goldstein continues. That slows the spacecraft down, alleviating 99% of the energy and 90% of the velocity of the vehicle. "We're now traveling at about 1,100 miles per hour, which at the Mars atmospheric density is about 1.5 times the speed of sound. At this point, the parachute will be deployed and we’ll be measuring atmospheric density as we open parachute at about Mach 1.5," slowing Phoenix from 1,100 miles per hour to about 120 mph.
"Then, 15 seconds after the parachute deploys, the heat shield falls away," Goldstein says. "The landing radar antennas are now exposed allowing Phoenix to get the first direct measurement of where the surface is. Then the real fun begins." Phoenix will separate from the backshell and turn on its retro rockets, 12 pulsed thrusters, each putting out 68 pounds of thrust, which will slow down and guide Phoenix to the surface and Phoenix will actually pirouette down to the surface to maximize the solar exposure. For a second by second agenda of the action to come, see chart at the end of this story. "At touchdown we kick up a bit of dust," Goldstein informed. "So before we do anything we have to wait 15 minutes to let the dust settle." The first event after touchdown is to vent, seriously. But for Phoenix that means opening up the pressurization on its propulsion system, "so we have no more pressure on the backside," Goldstein explained. The solar arrays will then begin deploying, but this will happen at a time when the UHF radio is turned off, while Odyssey is orbiting on the other side of the planet. Nevertheless, all of the engineering data from the spacecraft is being recorded for playback. After the solar arrays deploy, the equipment, including the surface stereo imager or camera and the meteorological mast with sensors supplied are deployed. The last element deployed is the Biobarrier, a protective cover around the robotic arm, to assure there are no biological elements that come in contact with our scoop. "All that happens in a short seven minutes," Goldstein reminded. Once sensors on the footpads of the lander detect touchdown, Phoenix will turn off its landing engines. At the same time, the flight operations team at JPL will also be listening for the confirmation signal from Phoenix via the Robert C. Byrd telescope at National Radio Astronomy Observatory (NRAO) in Greenbank, WV. When it lands, Phoenix will deposit a special message from Earth, a silica glass mini-DVD provided by The Planetary Society that contains more than 250,000 names and a collection of Mars-related literature, art, and audio called Visions of Mars. The disk, designed to last hundreds of years, is sent with the hope that future explorers may one day find the message.
From its solitary position in the polar arctic, Phoenix will use its 7.7-foot robotic arm to dig for the first time ever into the ice-rich permafrost and scoop up samples of soil and water-ice from beneath the surface, bring them back to the spacecraft for analysis. It will spend three months investigating the history of the water in the polar ice, looking into whether the subsurface environment in the far-northern plains of Mars has ever been favorable for sustaining microbial life, and assessing the biological potential of the ice-soil boundary. Phoenix also boasts a Canadian-supplied weather station and will be studying the weather in Mars' arctic region. Coordinated observations are planned with the orbiters above to get a top-down analysis of the polar atmosphere. "Six years after Odyssey discovered massive ice deposits surrounding the well-known polar cap on Mars, Phoenix is now prepared to land and explore this exciting region of Mars," Smith said at the press conference Saturday. Phoenix is a lander, not a rover like Spirit and Opportunity, and its three-month mission is tightly focused on the target of water-ice that will lie just beneath it and all around it, and it is just as important to furthering NASA objectives. Smith likened Phoenix's purpose to a quote from Ralph Waldo Emerson he saw hanging in the office of JPL Director Charles I. Elachi earlier that morning: "Do not follow where the path may lead. Go, instead, where there is no path and leave a trail."
"To go where there is no path and leave a trail for others to follow. That's what Phoenix is doing," Smith said. "We're going where there is no path and we're going to leave a trail for others to follow -- not literally a path, but we're going to a place on the planet unexplored," he qualified. "The polar region on the Earth after 100 years of scientific investigation is known to be a place where quiet records are preserved and where you can find a lot of information about the history of life on Earth," Smith continued. "It is preserved in the ice, the deep freezer of the Earth and perhaps this is true of Mars, too. This is what we're going to be finding out." By analyzing the chemistry and mineralogy of the soil and ice using robust instruments, scientists will better understand the history of the Martian arctic and determine whether or not it is habitable. "And that is the business of the Phoenix mission, Smith said. Finding life, if any should exist, will be up to another mission, because they don't have the instruments onboard to detect microscopic life. If, however, there should be sizeable "bugs," clearly their cameras would image them. Part of larger NASA program to look for life on Mars, Phoenix will provide an important contribution to the agency's "Follow the Water" science strategy and will be instrumental in achieving the four science goals of NASA's long-term Mars Exploration Program: 1) determine whether life ever arose on Mars; 2) characterize the climate of Mars; 3) characterize the geology of Mars; and 4) prepare for human exploration. Beyond being the world's first Martian arctic explorer, Phoenix is the first NASA mission being led by a public university and the University of Arizona has the honors. Mission operations are expected to roll over to Arizona's Phoenix Space Operations Center once the spacecraft has landed, stretched out it solar array "wings," and tested its long robotic arm. That shift is expected to occur on Wednesday, May 28.
Although they have no reason to believe the solar arrays won't open up as designed, even if they didn't deploy, the spacecraft will have enough power to last from 28 to 32 hours. If that did happen, Smith said, they would immediately begin imaging, looking at the dust the spacecraft kicked up on landing, and checking out the weather. "There wouldn't be time to get samples and bring them back," he said. The prospect of Phoenix not opening its "wings," is remote, assured Goldstein. "The only possibility for them not opening would be if Phoenix landed between two rocks, like a bulls-eye," and we're landing in an area with almost no rocks. And should for any reason the spacecraft land tilted somehow, "we're very well prepared to deal with a tilted spacecraft," he said. For more information, log back on as coverage of Phoenix flight continues, and be sure to check out Emily Lakdawalla's Planetary Society Planetary Weblog. General Timeline for Phoenix Mission OperationsEvent times are given in Spacecraft Event Time
(SCET), which is the time according to the spacecraft's clock, and also
Earth Received Time (ERT), which accounts for the 15 minutes and 20 seconds
it takes radio signals to traverse the 275 million kilometers (171 million
miles) separating Earth and Mars on landing day. ERT is given both in Universal
Time (UTC) and Pacific Daylight Time (PDT).
The first week following landing will be a "characterization phase," during which the instruments and systems will be ckecked out and tested. Approximately one week after landing, the digging phase will begin, and the first sample of surface soil will be delivered to the Thermal and Evolved-Gas Analyzer (TEGA) instrument. The first analyses will take 10 to 15 days. At the same time as the instruments are being checked out, a parallel effort will be undertaken to determine exactly where Phoenix landed. An approximate location will be known within hours of landing, and two Mars Reconnaissance Orbiter HiRISE images will be taken. However, the knowledge of the location of Phoenix may not be good enough to steer the targeting of HiRISE on the first day. Another imaging attempt planned for the fifth day is more likely to be successful. Digging will proceed in several cycles lasting 8 to 15 days apiece. After each two to three centimeters of digging, new samples will be delivered to TEGA and to the Microscopy, Electrochemistry, and Conductivity Analyzer (MECA). The nominal mission plan accounts for a total of seven cycles of digging and analysis. It is unknown how far Phoenix will have to dig to reach ice, but it is epected to be about two to five centimeters. If the ice is found at the deeper end of the range, the first ice samples may not be analyzed until July or later. The digging phase is expected to last until the beginning of September, 90 sols after landing. Once the digging phase is over, Phoenix will continue to operate essentially as a polar weather station. The mission will end when the Sun travels low enough in the sky that Phoenix no longer receives sufficient power. The spacecraft will conserve power as long as possible. The cameras will search for the first carbon dioxide frost deposits while the Meteorological Station (MET) instrument monitors the weather conditions. The northern autumnal equinox will arrive on Mars on December 26, 2008, bringing winter darkness to the north pole. Phoenix will not survive past this date. In fact, it may not survive beyond November. Emily Lakdawalla contributed this Timeline to this report. For the Phoenix Mars Mission home page, go to: http://phoenix.lpl.arizona.edu/ NASA TV will cover the Phoenix landing events. For information on how to connect: http://www.nasa.gov/multimedia/nasatv/index.html
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