Gregory Chamitoff has been to space twice, spending 6 months aboard the ISS across Expedition 17 and 18 in 2008, and another 15 days as part of STS-134 in 2011.
Head entity: STS-134
Tail entity: Gregory Chamitoff
Relation (head \u2192 tail): astronaut mission
Inverse relation (tail \u2192 head): crew member