A Russian rocket launch failure, followed by the safe emergency landing of a capsule intended to carry an American astronaut and his Russian counterpart into orbit, could prompt major disruptions for U.S. human space exploration.

The problem with the Soyuz booster, roughly two minutes after blastoff from Kazakhstan’s Baikonur Cosmodrome, caused an automatic abort that sent the crew — NASA astronaut Nick Hague and Russian cosmonaut Alexey Ovchinin — back to earth in a wild ride of more than 32 minutes.

There were huge sighs of relief following the first such in-flight crisis on a Russian vehicle affecting a NASA astronaut. But the failure also raises difficult scheduling issues for replacing the three crew members currently occupying the space station, along with a host of questions about the safety and reliability of Russian boosters and spacecraft that are now the only way to take people to the orbiting laboratory.

At the very least, Thursday’s developments ratcheted up pressure on NASA to certify new U.S. vehicles able to ferry crews to and from the space station. It adds urgency to efforts by two competing contractors — Boeing Co. BA, -2.55%   and Elon Musk’s Space Exploration Technologies Corp. — to conduct unmanned test flights so they can begin human missions around the middle of 2019.

An expanded version of this report appears on WSJ.com.

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