Washington, Sep 7 (IANS): Three Expedition 48 astronauts safely returned to the Earth on Wednesday after completing a 172-day mission aboard the International Space Station (ISS).

The Soyuz TMA-20M spacecraft carrying astronaut Jeff Williams of NASA and cosmonauts Alexey Ovchinin and Oleg Skripochka of the Russian space agency Roscosmos landed near the town of Dzhezkazgan, Kazakhstan.

Veteran NASA astronaut Williams has now spent 534 days in space, making him first on the all-time NASA astronaut list.

"From his first flight in 2000, when the station was still under construction, to present day where the focus is science, technology development and fostering commercialisation, Williams even helped prepare the space station for future dockings of commercial spacecraft under NASA's Commercial Crew Programme," said Kirk Shireman, ISS programme manager at NASA's Johnson Space Centre in Houston.

"We're incredibly proud of what Williams has accomplished off the Earth for the Earth," he added.

The first International Docking Adapter was installed during a spacewalk by Williams and fellow NASA astronaut Kate Rubins on August 19.

Outfitted with a host of sensors and systems, the adapter's main purpose is to connect spacecraft bringing astronauts to the station in the future.

Its first users are expected to be Boeing's CST-100 Starliner and SpaceX's Crew Dragon spacecraft, now in development in partnership with NASA.

Together, the Expedition 48 crew members contributed to hundreds of experiments in biology, biotechnology, physical science and Earth science aboard humanity's only orbiting laboratory.

The crew members also welcomed five cargo spacecraft during their stay.

Expedition 49 continues operating the station with Anatoly Ivanishin of Roscosmos in command until the arrival of three new crew members.

Shane Kimbrough of NASA and cosmonauts Sergey Ryzhikov and Andrey Borisenko of Roscosmos are scheduled to launch from Baikonur, Kazakhstan, on September 23.