JSC2011-E-060140 (29 June 2011) --- NASA astronaut Rex Walheim laughs with his crewmates as STS-135 commander Chris Ferguson gets a refresher on the use of the waste management system on the International Space Station as the crew trains at NASA?s Johnson Space Center June 29, 2011. The day's training marked the crew's final scheduled sessions in the Space Vehicle Mock-up Facility at JSC. Photo credit: NASA Photo/Houston Chronicle, Smiley N. Pool