On the eve of the return to Earth of three crew members after six months in space, the International Space Station's Expedition 39 crew tackled spacesuit maintenance as well as a full morning of biomedical research for the station's departing commander on Monday.

Commander Koichi Wakata of the Japan Aerospace Exploration Agency, Flight Engineer Rick Mastracchio of NASA and Soyuz commander Mikhail Tyurin of Roscosmos, the Russian Federal Space Agency, will wrap up 188 days in space when they depart Tuesday aboard the Soyuz TMA-11M spacecraft that brought them to the station back in November. The trio will undock their Soyuz from the station at 6:36 p.m. EDT for a landing southeast of the remote town of Dzhezkazgan in Kazakhstan at 9:58 p.m. (7:58 a.m. May 14, Kazakh time).

NASA Television will provide complete coverage of the Expedition 39 crew's return to Earth, from farewells to landing.

Expedition 40, under the command of NASA astronaut Steve Swanson, will formally begin aboard the station when the Soyuz carrying Wakata, Mastracchio and Tyurin undocks. Swanson and his crewmates, Flight Engineers Alexander Skvortsov and Oleg Artemyev of Roscosmos, will operate the station as a three-person crew for two weeks until the arrival of three new crew members. Reid Wiseman of NASA, Max Suraev of Roscosmos and Alexander Gerst of the European Space Agency are scheduled to launch from the Baikonur Cosmodrome in Kazakhstan on May 28.

Wrapping up his tour of duty as the first Japanese commander of the orbital complex, Wakata passed the station's helm to Swanson during a change of command ceremony Monday afternoon.

Wakata spent much of his final full day in space working inside the station's Columbus laboratory as he participated in the BP Reg experiment. This is a Canadian Space Agency medical study that seeks to understand the causes of fainting and dizziness seen in some astronauts when they return to Earth following a long-duration mission.

Results from this experiment will not only help researchers understand and mitigate these unwanted effects for returning astronauts, but it also will have direct benefits for people on Earth - particularly those predisposed to falls and resulting injuries, as seen in the elderly.

Meanwhile inside the Quest airlock, Mastracchio and Swanson replaced a fan pump separator inside one of the U.S. spacesuits. Contamination of the fan pump separator in a different suit worn by Flight Engineer Luca Parmitano during a July 2013 spacewalk resulted in an incident that brought an early end to that excursion. This contamination clogged several small holes that prevented water from flowing properly, causing water to back up and flow into the space suit's air system and enter the helmet.

On the Russian side of the complex, Tyurin completed his final session of Lower Body Negative Pressure Training to condition himself for Tuesday's landing. Artemyev assisted the veteran cosmonaut as he donned a special outfit that simulates the effects of gravity by drawing fluids to the lower half of the body. In addition to conditioning cosmonauts for the return home, this device provides Russian researchers with data to predict how cosmonauts will react to the full force of Earth's gravity at the end of their mission.

Afterward, Tyurin focused on packing crew items and science cargo inside his Soyuz spacecraft for return to Earth.

Artemyev meanwhile initialized and deployed new dosimeters for the Matryoshka experiment. Named after the traditional Russian nesting dolls, Matryoshka analyzes the radiation environment onboard the station.

Skvortsov downloaded data from an earthquake-monitoring experiment known as Seismoprognoz. He also photographed samples from the Struktura protein crystal growth study.