May 31, 2011 — After more than 15 days in orbit, space shuttle Endeavour is headed home to Earth for its final time. The youngest of NASA's winged orbiters, Endeavour is returning with an empty cargo bay — its payload, the final U.S. components for the International Space Station delivered and installed.

Packed inside its crew cabin, sharing space with its six astronauts, is Endeavour's final delivery: several thousand pounds of science experiment results and spent supplies from the station. Also onboard, having made the round trip with the shuttle, is a special stash of souvenirs — the mission's Official Flight Kit (OFK), packed with mementos for the many organizations that supported the astronauts and made the flight a success.

The duffle-bag sized flight kit, together with the astronauts' individual personal preference kits, continues a tradition of astronauts flying mementos dating back through all of the 134 shuttle missions to date and the earlier U.S. manned space flights. Hundreds of thousands of small U.S. flags, crew patches, medallions, and lapel pins have flown over the course of the past five decades.

Endeavour's empty cargo bay (with the station's Dextre robot in the foreground) as seen before undocking from the ISS. (NASA)

Endeavour's STS-134 flight kit is no exception, with nearly 500 of the crew's embroidered patches — as designed by commander Mark Kelly's mother-in-law, Congresswoman Gabrille Giffords' (D-Ariz.) mother, Gloria — alongside more than 5,000 4-inch by 6-inch U.S. flags and more than 2,000 of Endeavour's own orbiter flags.

Endeavour's 25th and final mission is also the next-to-last for the space shuttle program, which is represented in the OFK by 2,700 "end-of-mission" lapel pins and hundreds of similarly designed bookmarks, decals and emblems to be distributed after the flight to shuttle program workers.

Not everything in the flight kit however, is packed in mass. Many are individual mementos flown at the request of the crew members for organizations that they support and that supported them.

For example, a two-inch gold bar from the U.S. Merchant Marine Academy made the trip on behalf of Kelly, who graduated from the academy in 1986.

A poem from the Tucson Poetry Center in Arizona is also on board, along with an Archie Comics comic book cover.

Another cartoon character, a Czech mole named Krtek, is aboard Endeavour in the form of a stuffed toy.

"My wife's mother is Czech and so we have strong ties to the Czech Republic," mission specialist Drew Feustel told collectSPACE. "They're actually building a whole science and education outreach program around this character and we hope to be able to go back to visit the country and tour around with Krtek and try to get the schools involved and see a lot of the students and excite them about math and science and technology."

Mementos ranging from a metal disk borrowed from the National Institute of Nuclear Physics in Rome to a pennant from Tuscany are in the OFK representing Italy, the home nation of European Space Agency (ESA) astronaut and STS-134 mission specialist Roberto Vittori.

The Mary Rose Museum in Portsmouth, England, loaned a 3-inch wooden ball from the 16th century ship "Mary Rose" so it could sail in the vast ocean of space. The "Mary Rose" was one of the first purpose-built warships and was raised in 1982 after more than 400 years underwater. The ball, called a "parrel," was part of the mechanism used to raise sails up the masts.

The "Mary Rose" has an additional connection to NASA: astronaut Michael Foale worked as a volunteer diver on the ship's excavation in 1981.

Another museum-sponsored piece is the five-star insignia worn by General Henry "Hap" Arnold, an architect of the modern Air Force. The insignia belongs to the National Museum of the U.S. Air Force in Dayton, Ohio.

Endeavour's pilot Greg H. Johnson and mission specialist Mike Fincke are Air Force officers.

More than 100 robotics merit badges are inside the flight kit for the Boy Scouts of America. The newly introduced badge was developed in cooperation with NASA but also shares a connection with STS-134 mission specialist Greg Chamitoff, who was an Eagle Scout.

Chamitoff also flew a patch designed by the Boy Scouts' Santa Clara County Council in California, where he was a scout.

"When this flight came up, they got very excited about making a space patch for the council and so they did, and I'm flying it for them," Chamitoff told collectSPACE.

Robotics in space is also manifested by a hand and arm flying on Endeavour. Robonaut 2, the first humanoid robot in space, was delivered to the station during the previous shuttle mission and its extra appendage was packed on Endeavour to salute the work done on Earth to deploy the robot in space.