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 The 10-meter South Pole Telescope and the BICEPTelescope at the Amundsen-Scott South Pole Station in 2008. (Keith Vanderlinde/National Science Foundation via Reuters) 
 
 A medical rescue plane took off from Amundsen-Scott research station at the South Pole Wednesday morning, en route to complete only the third evacuation during the dark Antarctic winter in the station's 60-year history. 
 
 Flights to the pole are risky and rare during the six-month polar night, temperatures can sink below minus 100 degrees Fahrenheit and the only light comes from the moon and stars. 
 
 Kelly Falkner, the director of polar programs for the National Science Foundation (which runs the South Pole station), said that two workers were airlifted out of the station Wednesday. One was a seasonal employee for contractor Lockheed Martin who requires medical treatment not available at the station; the NSF has not identified the second patient. Falkner couldn't provide further details about the medical motivation behind the rescues for privacy reasons. 
 
 The rescue effort was launched early last week after consultation with outside medical experts and agency officials. 
 
 "We try to balance our decisions with all of the risks involved," Falkner said, noting that the safety of the flight crew and the needs of all 48 people overwintering at the station were also taken into account. "It's a very serious decision that we take to move in this direction." 
 
 Dozens of people spend the winter at the Amundsen-Scott station each year, many of them employed by the NSF or lead contractor Lockheed Martin. They help maintain the station, oversee long-term monitoring of the atmosphere and climate change, conduct research on the early history of the universe via two radio telescopes, and observe the behavior of subatomic particles at the station's IceCube Neutrino Observatory. 
 
 But evacuation efforts such as this are exceedingly uncommon. The brutal cold and near-total darkness that blankets Antarctica during the austral winter make flights in and out of the station all but impossible. In 1999, a doctor who discovered a cancerous lump in her right breast treated herself — even performing her own biopsy and administering her own chemotherapy — for almost six months until the weather thawed enough for a rescue plane to arrive. A decade later, when a manager for the station suffered a stroke in August, the question of whether an airlift was possible led to a tense standoff. She was ultimately flown out in mid October. 
 
 [The stunning results of a photographer’s epic journey to Antarctica] 
 
 "We were stuck in a place that's harder to get to than the International Space Station," said Ron Shemenski, a former physician for the station who in 2001 became the first person to be evacuated during the dark winter months. "We know we're on our own." 
 
 In this 2003 photo, a Twin Otter flies out of the South Pole on a previous medical flight. (Jason Medley/National Science Foundation) 
 
 Between February and October, only one type of aircraft can fly to, land at and take off again from the South Pole: the tiny Twin Otter. Two of these hardy, winter-proof bush planes, operated by Canadian polar service firm Kenn Borek, landed at the British-run Rothera research station on the Antarctic coast Monday, each of them carrying a pilot, a co-pilot, an engineer and a medic. 
 
 One plane and its crew remained at Rothera to provide search-and-rescue capability as needed. The second was prepped for a journey and equipped with skis to allow it to land on snow and ice. 
 
 On Tuesday morning, as soon as the weather allowed, the plane took off toward the pole, flying into the deeper cold (temperature at Amundsen-Scott on Tuesday was minus-73 degrees Fahrenheit) and impenetrable night. It arrived that evening, and after a 10-hour stop to rest and refuel, left for Rothera early Wednesday morning. 
 
 Only a half dozen people on Earth know what that journey is like; Alberta bush pilot Sean Loutitt is one of them. 
 
 "It's a 10-hour flight, and you only have 12 or 13 hours of fuel on board," he said. "You're monitoring the weather the whole time, but eventually you get to a point of no return. Then you're committed to the pole, no matter what." 
 
 Loutitt was the chief pilot for Kenn Borek during the mission to evacuate Shemenski in 2001. Before that rescue effort, no one had flown to Amundsen-Scott through the polar night. It was assumed that it couldn't be done. 
 
 That belief is part of the mythology of the pole, Shemenski said. "It was like a macho thing," he recalled. "At that point when the last plane left, you were there for six months. That was it." 
 
 [At the South Pole, BICEP2 astronomer is upbeat as he hunts for elusive Big Bang signal] 
 
 But about a month and a half after the last flight out, in April 2001, Shemenski started suffering stomach pains and throwing up repeatedly. As the physician for the station, he diagnosed himself with pancreatitis. 
 
 The doctor was determined not to leave the pole, arguing that he could treat himself on his own (indeed, by the time rescuers arrived, he was on his way to recovery, he said). But a medical expert consulted by the NSF said that Shemenski had a 50 percent chance of dying in the six months until regular flights to the pole resumed. Officials pointed out that, though Shemenski could take his own chances, they couldn't risk the possibility that his 49 colleagues would be left at the station without a doctor. 
 
 "It's like being in the military," Shemenski said. "I was ordered off. So I left." 
 
 
 
 The last sunset of the summer at the South Pole, on March 20. (NOAA) 
 
 The initial call went to the the U.S. Air Force, which began to assemble dozens of military personnel and three C-130 Hercules planes for the rescue mission. But the temperatures at the pole were already too cold for the C-130s. The mission was scrubbed and the NSF sought an alternative: Kenn Borek's Twin Otters. 
 
 The planes are certified to fly at temperatures as low as minus-75 degrees Celsius (minus-103 degrees Fahrenheit), according to Falkner. Their systems are a good deal simpler than the C-130's, and they require less fuel — essential when every ounce of fuel has to be warmed for flight. At the pole's low temperatures, fuel freezes into an unusable jelly. So does the grease in a plane's hinges and gears. Winter storms can flare up in a heartbeat. And if anything goes awry, pilots may need to land on unknown terrain in total darkness. 
 
 All of this was on Loutitt's mind as he prepared for the mission south. He'd flown to Amundsen-Scott before, and had done countless flights into the Arctic Circle during the northern polar night. But this was different. 
 
 "You're the only plane flying on an entire continent," he said. "You have to be prepared to be totally self-reliant if something goes wrong." 
 
 [British explorer Henry Worsley dies attempting solo crossing of Antarctica] 
 
 Luckily, the trip in 2001 was relatively smooth. After hours of flying in darkness, Loutitt and his crew finally glimpsed a glimmer of light below them: Barrels of gasoline were burning along the makeshift runway the South Pole station workers had prepared. They'd reached the bottom of Earth. 
 
 The replacement doctor for the station disembarked, and the ailing Shemenski clambered onto the plane. But as they started up the engines, the crew realized they couldn't take off. The Twin Otter's skis had stuck to the ice beneath them, and the grease on the wing flaps had frozen them in the fully extended position. While the station workers hacked at the ice on the skis, the plane's mechanic jerry-rigged the controls to allow it to take off. It was one of the longest, slowest take-offs any of them had ever attempted, but eventually, they were in the air. 
 
 The journey back to Rothera was unlike anything Shemenski had experienced. 
 
 "During the initial part when you’re in the darkness it's hardly a sensation of moving at all because you can't see anything," he recalled. "Everything's black." 
 
 But then a thin line of pink appeared — sunlight on the horizon. 
 
 "It was really beautiful to watch it grow," co-pilot Mark Cary told Canadian broadcaster CTV for a documentary about the mission. "It was like a gift and a sign to say everything’s going to work out and you guys are going the right way." 
 
 
 
 A U.S. Antarctic Program participant enjoys a walk under a full moon at Amundsen-Scott South Pole Station. The South Pole has continual darkness during the winter. (Calee Allen/National Science Foundation) 
 
 Cary and Loutitt would repeat the flight two years later, when Barry McCue, an environmental health and safety officer employed by contractor Raytheon Polar Services, developed a serious infection in his gallbladder. This time, Shemenski was the medical director for Raytheon and helped coordinate the rescue. 
 
 McCue and his rescuers made it off the frozen continent safely, and McCue recovered fully from a successful surgery to treat his infection. 
 
 "You can tell they’re getting better at the planning of it,” McCue told the Antarctic Sun, a newspaper run by the NSF. “For me it was just take the plan off the shelf, blow the dust off and then just figure out what the people should do.” 
 
 Still, any mission to the darkest and most distant place on Earth is risky. That the NSF decided that an evacuation is its best option, Shemenski said, means that those at the pole must be seriously ill. 
 
 After they land at Rothera, the patients will be taken to Punta Arenas in Chile, and then to a hospital that hasn't been disclosed. The flight covers 1,500 miles and lasts about 10 hours. 
 
 The trip back to the coast is just as dark and perilous as the journey to the pole. But, this time, the Twin Otter will be flying toward daylight. 
 
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 Save ||||| Two sick workers were evacuated from the National Science Foundation's (NSF’s) Amundsen-Scott South Pole research station today and taken to the British Antarctic Survey’s Rothera station on the Antarctic Peninsula. They are now awaiting transport off the continent to receive medical care, either today or tomorrow, depending on weather conditions. NSF is not releasing the workers’ identities and medical conditions, citing privacy. 
 
 Here is our previous coverage, from 15 June: 
 
 Two propeller-driven planes took off today from Calgary, Canada, on a perilous rescue mission to the U.S. research station at the South Pole. If all goes well, one of the planes will arrive in 6 days to pick up a member of the winter-over crew suffering from an unspecified medical emergency that requires treatment at a hospital. 
 
 Every February, after the scientists have left, a few dozen people hunker down to spend the long, dark austral winter at the Amundsen–Scott South Pole research station operated by the National Science Foundation (NSF). Medical problems do occur, but most can be handled with medical personnel on site or in consultations with stateside doctors. The decision to evacuate someone is not made lightly because such a rescue operation is both dangerous and elaborate. Medevacs require planes that can operate in the extreme cold and are equipped with skis. The South Pole station has no tarmac, so the planes must land in the dark on compact snow. 
 
 The Twin Otter aircraft are operated by the Canadian firm Kenn Borek Air, Ltd., which contracts with NSF to provide logistical support to the U.S. Antarctic Program. The aircraft will fly via South America to the British Antarctic Survey’s Rothera Research Station on the Antarctic Peninsula. One will remain there as a backup for search-and-rescue operations; the other will travel another 2400 kilometers to the South Pole. 
 
 The planes are based year-round in Canada because they are used during the summer months to transport scientists working in the Arctic, says Kelly Falkner, head of NSF’s Division of Polar Programs in Arlington, Virginia. NSF doesn’t own its own aircraft, and “the program’s demand for the planes is almost nil” during the austral winter, she says. In recent decades, Kenn Borek’s Twin Otters have conducted perhaps a handful of emergency rescues. 
 
 The plight of overwintering researchers garnered national attention in 1999, when South Pole physician Jerri Nielsen learned she had breast cancer in late May. The only medical professional on hand, she enlisted untrained technicians to help her perform a biopsy and remained on station until her evacuation in October. And in August 2011, when 58-year-old Renee-Nicole Douceur, winter manager at the station, suffered a stroke, NSF deemed it unsafe to send in a rescue plane. Despite pleas from family members, a petition to the White House, and numerous media stories, Douceur remained at the South Pole for 2 months until she finally caught a ride out on a scheduled cargo plane. 
 
 NSF officials have not identified or released any information about the medical condition of the crew member, who is employed by Lockheed Martin Antarctic Support Contract (ASC). ASC is the prime contract for operations and research support contractor to NSF for the U.S. Antarctic Program. 
 
 *Update, 15 June, 4:47 p.m.: You can track the progress of the rescue mission here.
– At least one worker is seriously ill at the US South Pole station, and because it is winter in Antarctica, it would be easier to reach the unidentified person if he or she were anywhere else on the planet—or even on the International Space Station. The worker is one of 48 people wintering at the National Science Foundation's Amundsen–Scott South Pole research station, and two planes have been sent from Canada to carry out a very unusual and risky rescue mission, reports Science. Only two other such rescues have been carried out in the 60 years the station has been operating and, until the evacuation of physician Ron Shemenski in 2001, it had been thought that the relentless cold and dark made it impossible to get people away from the South Pole in winter, reports the Washington Post. Shemenski had pancreatitis and the NSF feared he would die. Two Twin Otter bush planes, each with a pilot, a co-pilot, an engineer, and a medic, are carrying out the mission, with one plane remaining at a British research station on the Antarctic Peninsula in case crew from the first plane need to be rescued. They hope to carry out the rescue by the middle of next week. (You can track progress here.) "It's a 10-hour flight, and you only have 12 or 13 hours of fuel on board," pilot Sean Loutitt, who was chief pilot during the 2001 rescue mission, tells the Post. "You're monitoring the weather the whole time, but eventually you get to a point of no return. Then you're committed to the pole, no matter what." He also took part in a rescue in 2003, when a worker had a gall bladder infection. The currently ill worker's medical situation has not been specified. (In 2011, the NSF balked at sending a plane after the station's winter manager had a stroke.)