Today, NASA remembers the sacrifice of the crews of Apollo 1 and space shuttles Columbia and Challenger. Mission Control Center in Houston and the crew aboard the International Space Station observed a moment of silence and Commander Scott Kelly sent down a few words memorializing the lost astronauts. The six residents aboard the space station kept up their pace with spacewalk preparations, Cygnus cargo transfers and advanced space science. The orbital laboratory also completed two of a series of reboosts on Wednesday ahead of a crew swap and a cargo delivery planned for March. Cosmonauts Yuri Malenchenko and Sergey Volkov checked out their Russian Orlan spacesuits and tools before next week’s spacewalk.