NASA astronaut Ricky Arnold watches a timer while students conduct an experiment on effervescence, Friday, May 3, 2019 at the Challenger Center in Lanham, MD. During Expedition 55/56, Arnold completed three spacewalks for a total of 19.5 hours outside the International Space Station (ISS), and concluded his 197 day mission when he landed in a remote area near the town of Zhezkazgan, Kazakhstan in Oct. 2018. He also flew to the space station on shuttle mission STS-119 to deliver the final pair of power-generating solar array wings. Photo Credit: (NASA/Aubrey Gemignani)