Shuttle Endeavour Astronauts Say Goodbye to Space Station
A digital camera with a fish-eye lens captured this image of NASA astronaut Michael Fincke (top center) during the fourth and last spacewalk of Endeavour's STS-134 mission as construction and maintenance continue on the International Space Station on May 27, 2011. The docked shuttle Endeavour is visible at left.
Credit: NASA

This story was updated at 10:04 a.m. EDT.

HOUSTON – After nearly two weeks parked at the International Space Station, the shuttle Endeavour will leave the orbiting outpost for the last time tonight (May 29) as it nears the end of its final space voyage.

Endeavour will undock from the space station at 11:55 p.m. EDT (0355 May 30 GMT), after delivering a $2 billion astrophysics experiment and a bevy of supplies to the massive, orbiting laboratory. Endeavour's 16-day mission is the orbiter's 25th and final flight before it retires later this year when NASA brings its 30-year space shuttle program to a close. [Photos: Shuttle Endeavour's Final Mission]

"I think it's really going to hit home after Endeavour is sitting on the runway," lead shuttle flight director Gary Horlacher said in a news briefing today (May 29). "It's going to be sad to see her retire, but I can't think of a better mission for her to capitalize her flight with."

A farewell ceremony was held this morning aboard the space station, during which the three station residents – NASA astronaut Ron Garan and Russian cosmonauts Alexander Samokutyaev and Andrey Borisenko – said goodbye to the six visiting astronauts that make up Endeavour's STS-134 crew.

"I just want to say on behalf of the STS-134 crew that we had a very successful mission working with Expedition 28," shuttle commander Mark Kelly said. "It's been a great number of days docked. We're looking forward to getting home and we're going to leave these guys to a little peace and quiet."

Saying goodbye

Garan thanked Endeavour's six astronauts for their hard work during their stay and commented on the teamwork between the two crews.

"It was really great seeing you guys," Garan said. "It was great getting to spend time on the incredible orbital complex. We were just in awe of the finely oiled machine that was STS-134. On behalf of Expedition 27, Expedition 28, we want to thank you for leaving the space station ready for its continued utilization, for at least the next decade. You really left us in good shape."

Station commander Borisenko also took the time to thank Kelly and his crewmates, and wished them well for their journey home.

"[It was good] to see the shuttle crew visiting here when we were working, and I'm happy that the crew has completed the task and I'm glad that they enjoyed staying and working with us as well," Borisenko said in Russian. "Thank you very much and soft landing."

After handshakes and hugs were exchanged all around, the hatches between the station and shuttle were closed at 7:23 a.m. EDT (1123 GMT) after 10 days, 23 hours and 45 minutes.

Wrapping up a long mission

Shuttle commander Mark Kelly, pilot Greg H. Johnson, and mission specialists Andrew Feustel, Greg Chamitoff, Mike Fincke and Roberto Vittori spent almost 11 busy days aboard the space station, performing maintenance and repairs and delivering critical supplies to help outfit the station for the years following the end of NASA's shuttle program.

Four spacewalks were conducted during Endeavour's STS-134 mission. The fourth and final outing also marked the last spacewalk that would ever be performed by members of a shuttle crew. [Amazing Spacewalk Photos by Endeavour Astronauts]

After Endeavour separates from the space station, the shuttle will perform two victory laps around the complex to conduct a special test that will help next-generation spacecraft dock to the International Space Station in the future. 

The Sensor Test for Orion Relative Navigation Risk Mitigation, or STORRM, will test high-definition imagery and laser-based sensor technology that will be used to assist future spaceships, such as NASA's newly announced Multi-Purpose Crew Vehicle in their rendezvous and docking operations at the space station and other potential destinations beyond low-Earth orbit.

"The STORRM test objective there is to basically, analyze and evaluate a sensor system that could be used on a follow-on space vehicle, and so the final missions of any vehicle, aerospace vehicle, typically will be testing stuff that will replace that vehicle," Johnson said in a preflight interview. "We’re going to undock and then instead of departing and coming back home, we’re going to go out several thousand feet and then come back in and re-rendezvous with a totally different sensor."

Endeavour heads home

Once the STORRM test is complete, the shuttle will resume its normal separation procedures to take it away from the space station. Endeavour will then spend two days in orbit before its scheduled landing at NASA's Kennedy Space Center in Florida on Wednesday, June 1.

Endeavour launched on its final mission on May 16, and docked at the space station two days later. As NASA's shuttle program winds down, the remaining flights aim to ferry as much hardware and supplies to the station to take advantage of the enormous cargo-carrying capability of the orbiters.

After the space shuttles are retired and processed, they will be delivered to museums to be put on public display. Endeavour has been promised to the California Science Center in Los Angeles.

NASA has one final space shuttle mission planned after Endeavour lands – the STS-135 flight of Atlantis in July.

You can follow SPACE.com Staff Writer Denise Chow on Twitter @denisechow. Visit SPACE.com for complete coverage of Endeavour's final mission STS-134 or follow us @Spacedotcom and on Facebook.