Watch the Falcon 9 launch from pad 39A

SpaceX’s next launch with a European-built communications satellite has been delayed to no earlier than March 28 to study a problem with a helium pressurization system on the Falcon 9 rocket, officials said Tuesday.

After four years of brainstorming, custom tool development and training, two astronauts plan to venture outside the International Space Station Friday for the first of four spacewalks to repair a $2 billion cosmic ray detector. The excursions are considered the most challenging since work to service the Hubble Space Telescope.

A Russian Soyuz booster arrived at its launch pad on the Kazakh steppe Sunday, the last stop before liftoff Wednesday with a three-person crew bound for the International Space Station.