Three crew members of Expedition 39 returned to Earth from the International Space Station, or ISS, on Tuesday after a 188-day stint in space, during which they orbited the planet more than 3,000 times and traveled nearly 79.8 million miles.

The three astronauts, including Expedition 39 commander Koichi Wakata of Japan Aerospace Exploration Agency, flight engineer Rick Mastracchio of NASA and Soyuz commander Mikhail Tyurin of the Russian Federal Space Agency, or Roscosmos, landed southeast of the remote town of Dzhezkazgan in Kazakhstan at 9:58 p.m. EDT.

During Expedition 39, the crew participated in many research projects related to studying the activation and suppression of the human immune system, the effect of proteins responsible for Huntington's disease, and other conditions that primarily affect neurons in the human brain. The crew also helped install a new plant-growth chamber on the ISS, designed to expand in-orbit food production.

“One of several key research focus areas during Expedition 39 was human health management for long duration space travel, as NASA and Roscosmos prepare for two crew members to spend one year aboard the space station in 2015,” NASA said in a statement.

Mastracchio, Tyurin and Wakata, who arrived at the space station on Nov. 7, also received three cargo spacecraft during their time aboard the orbiting laboratory. And, with the arrival of SpaceX-3 in April, the Expedition 39 crew also unloaded new climbing legs for NASA's Robonaut 2, or R2, humanoid robot, which is designed to take over “routine, dirty and potentially dangerous tasks” from astronauts.

According to NASA, this was the fourth space station mission for Mastracchio, who has now spent 228 days in space. Wakata has spent 348 days in space on four flights while Tyurin has accumulated 532 days in space on three flights.

Expedition 40 is now aboard the ISS with Steve Swanson of NASA and Oleg Artemyev and Alexander Skvortsov of Roscosmos. The trio will be joined by three new crewmates -- Reid Wiseman of NASA, Maxim Suraev of Roscosmos and Alexander Gerst of the European Space Agency -- who are scheduled to launch from Kazakhstan on May 28.