Photos: Atlas 5 rocket aims for International Space Station

SpaceX test-fired a Falcon 9 rocket for the second time Saturday after replacing a valve following an earlier static fire test Wednesday. The move has postponed the Falcon 9 rocket’s launch with the Amos 17 commercial communications satellite to no earlier than Tuesday.

NASA has purchased two seats on Russian Soyuz capsules launching later this year and in early 2018 to expand the crew on the U.S. segment of the International Space Station from three to four, and reserved options to fly astronauts on Soyuz spacecraft in 2019 if commercial rides are not available in time.

Bound for the International Space Station with a max load of fresh supplies, a commercially-operated cargo ship was mounted atop its booster rocket today for liftoff from Cape Canaveral on March 22.