Astronauts Vande Hei and Acaba at the Arlington National Cemeter

NASA astronauts Mark Vande Hei, left, and Joe Acaba, center, tour the museum at the Tomb of the Unknowns, Friday, June 15, 2018 at Arlington National Cemetery in Arlington, Va. Photo Credit: (NASA/Aubrey Gemignani)

NASA astronauts Mark Vande Hei, left, and Joe Acaba, center, tour the museum at the Tomb of the Unknowns, Friday, June 15, 2018 at Arlington National Cemetery in Arlington, Va. Photo Credit: (NASA/Aubrey Gemignani)

ArlingtonArlington National CemeteryExpedition 54Expedition 54 PostflightJoe AcabaMark Vande HeiTomb of the UnknownsUSAVirginia