Russian scientists will remove the frozen sample for analysis in December when the next Antarctic summer season comes. They reached the lake just before they had to leave at the end of the Antarctic summer, when plunging temperatures halt all travel to the region.
Lukin, who made numerous trips to Antarctica, said the physiological challenges of extreme cold and thin oxygen were aggravated by isolation.
"If something happens to you or your colleague, there is no one to help," he said. "It's actually easier to help an astronaut in space."
Martin Siegert, a leading scientist with the British Antarctic Survey, hailed reaching Lake Vostok as "an important milestone ... and a major achievement for the Russians."
The British are trying to reach another subglacial lake, Lake Ellsworth.
"The Russian team share our mission to understand subglacial lake environments and we look forward to developing collaborations with their scientists and also those from the U.S. and other nations, as we all embark on a quest to comprehend these pristine, extreme environments," Siegert said in an email.
Americans scientists are drilling at Lake Whillans, west of the South Pole.
Some voiced hope that studies of Lake Vostok and other subglacial lakes will advance knowledge of Earth's own climate and help predict its changes.
"The clues to how Earth may respond to the continuing impact of humans, particularly fossil fuel emissions and related climate change, are housed in the records of past climate change in Antarctica," said Mahlon Kennicutt II, Texas A&M University professor of oceanography, who leads several Antarctic science groups.
"A view of the past gives us a window on our planet's future," he said.
Russian researchers plan to continue exploring with robotic equipment that will collect water samples and sediments from the bottom of the lake, a project still awaiting the approval of the Antarctic Treaty organization.
The prospect of lakes hidden under Antarctic ice was first put forward at the end of the 19th century by Russian scientist and anarchist Prince Pyotr Kropotkin. Russian geographer Andrei Kapitsa noted the likely location of the lake and named it following Soviet Antarctic missions in the 1950s and 1960s, but it wasn't until 1994 that its existence was proven by Russian and British scientists.
Drilling in the area began in 1989 and dragged on slowly due to funding shortages, equipment breakdowns, environmental concerns and severe cold.
The lake's crystal-clear water may make entrepreneurs sweat just thinking of its commercial potential, but Lukin shot that idea down.
He said his team had no intention of selling any Vostok water samples, but would eventually share the results of their work with scientists from other nations.
AP Science Writer Seth Borenstein reported from Washington.