Live coverage: Station crew lands in Kazakhstan

United Launch Alliance called off the planned liftoff of a Delta 4-Heavy rocket and a classified National Reconnaissance Office spy satellite from Vandenberg Air Force Base in California on Wednesday after indications of elevated hydrogen concentrations around one of the launcher’s main engines. Three previous launch attempts were scrubbed by technical concerns and bad weather.

SpaceX is likely to land the first stage of the Falcon 9 rocket set for launch April 30 on a drone ship just off the coast of Cape Canaveral, not at the company’s onshore recovery site as originally planned, after a ground test of the company’s Crew Dragon capsule at the landing pad ended in an explosion Saturday.

A Northrop Grumman Cygnus cargo freighter departed the International Space Station Wednesday after delivering more than 7,800 pounds of equipment and experiments, heading for an extended mission with payloads to study fire behavior in microgravity and test a next-generation radio system.