One thing that make s the Russians such valuable partners in the international space station program is their extensive experience in low Earth orbit. The list of people with the most cumulative time in space is dominated by cosmonauts, including Sergei Krikalev, the commander of the current space station crew. Krikalev logged his 748th day in space Aug. 16, giving him more time in space than anyone in history.

Those days were accumulated over the course of 17 years and five missions : two to the Mir space station, and three to the international space station . He will continue to add to that record until the current crew’s mission ends in October.

Krikalev broke the record set by Sergei Avdeyev who spent 747 days in space over the course of three flights from 1991-1999. In third place is Valeri Polyakov, a medical doctor who spent 678 days on two missions, including 437 consecutive days in 1994-1995. Anatoliy Solovyov also flew five missions like Krikalev. His total: 651 days.

These cosmonauts and the others who rack up years in space will be key to understanding how the human body is affected by long-term exposure to space, particularly exposure to radiation.

Not enough can be said about the courage of those who continue to be the human guinea pigs for this research. Because humans have been traveling to space for only about four and a half decades, little is known yet about potential problems these pioneers might face as they get older, such as an elevated risk of cancer .

NASA officials have said in recent years that the focus of space station research will be on understanding issues critical to the safety of future crews making long-duration stays on the Moon and traveling to Mars.

The best place to start is to study the data gathered by the Russians while keeping tabs on their cosmonauts as they grow older. NASA officials have commented in the past that the Russian protocols and documentation are different than those used by NASA medical personnel, but that should not stop them from trying to gain insight from the people that have been exposed to the dangers of space for longer than anyone else.