SpaceX founder Elon Musk said this weekend that the company is about one month away from launching the first Crew Dragon spacecraft on an unpiloted test flight to the International Space Station, a precursor to a demonstration launch with astronauts later this year. He also warned that early test flights of the commercial crew capsule, built under contract to NASA, will be “especially dangerous.”

SpaceX’s launch director halted a countdown Tuesday to replace a sensor on the upper stage of a Falcon 9 rocket set to blast off with the GovSat 1 communications craft, the product of a joint venture between the commercial satellite operator SES and the government of Luxembourg.

Watch a replay of one of Iridium’s 10 communications satellites launched Sunday deploys from a dispenser mounted on the forward end of SpaceX’s Falcon 9 upper stage.