As he landed in a puff of dust on the Kazakh steppe on September 6, Jeff Williams broke the record for the longest time a NASA astronaut has spent in space. Williams was traveling aboard the International Space Station, helping to upgrade the orbiting laboratory with an inflatable habitat, docking station, and high-definition camera.

The 172-day voyage, his fourth trip to space, brought his total number of days living and working in orbit to 534. Previously, famed astronaut twin Scott Kelly had bragging rights with 520 days. (See 15 amazing photos from Scott Kelly’s year in space.)

“It is an incredible experience to see the details of the Earth from that vantage point and to see the Earth is uniquely suited for life,” Williams told National Geographic during an interview at Johnson Space Center in Houston shortly after his return to Earth. (Watch the full interview above.)

Williams holds the U.S. title by a relatively narrow margin: Peggy Whitson could soon best him with up to 560 cumulative days. What’s more, Russian cosmonauts remain the world champions of spaceflight duration: Gennady Padalka has spent a whopping 879 days in space, over five missions to the ISS and its predecessor, the Russian space station Mir.

These kinds of spaceflight milestones are of great interest to NASA as the agency explores the challenges of sending humans much, much farther from home—say, to Mars. According to NASA’s current vision, a mission to the red planet could last for up to 1,100 days, so it's important to figure out how humans respond to prolonged low gravity, cosmic radiation, and confined quarters (among other things).

Right now, our best proxy is to look at how seasoned astronauts are faring after long hours in Earth’s orbit, and how simulated space missions affect Earth-bound volunteers, such as the participants of Hi-SEAS, a year-long mock mission to Mars that recently concluded in Hawaii. (Find out more about what it felt like to spend a year isolated in a harsh, Mars-like environment.)

Here are a few of the most extreme human spaceflight records, and how they stack up to the needs of a mission to Mars.

Longest Single Spaceflight

Since 1995, cosmonaut Valeri Polyakov has held the record for the longest time any human has spent consecutively in space. He lived and worked aboard the Russian space station Mir from January 1994 until March 1995, racking up 437 days on one mission. According to Wired, Polyakov says that he volunteered to stay in orbit for so long to prove that humans can endure extended periods in zero G and thus are able to handle a trip to Mars. The record-breaking adventure seems to have left him not much worse for the wear—Polyakov is still an active member of the space biomedical community at the age of 74.

View Images The Soyuz spacecraft drifts to Earth carrying Jeff Williams and two Russian cosmonauts after a 172-day mission on the International Space Station. Photograph by Bill Ingalls, NASA, Getty Images

Farthest Distance Traveled From Earth

Astronauts Jim Lovell, Fred Haise, and Jack Swigert are probably best remembered for their heroic, if harrowing, slingshot around the moon during Apollo 13. While the trio may have been disappointed that they never made it to the lunar surface, they can boast a different accomplishment. The maneuver that brought their troubled spacecraft safely back to Earth also took them the farthest from home that any human has ever been. In April of 1970, the three astronauts were a staggering 248,655 miles away from our planet. Still, Martian hopefuls face a journey of around 250 million miles.

Longest Spacewalk

Working in space means taking the occasional trip outside to repair or upgrade your vehicle or habitat, and that means donning what is currently a bulky pressurized spacesuit. In March 2001, NASA astronauts Jim Voss and Susan Helms conducted the longest single spacewalk on record, spending eight hours and 56 minutes outside the ISS. Crews on Mars will also need to roam outside the relative safety of a habitat module for prolonged periods, so NASA is working on various ways to improve spacesuit designs, such as making them more flexible and easier to get on and off.

Longest Time on Another World