NASA engineers are investigating a power issue on the International Space Station, which is delaying an upcoming flight to the orbiting lab. On Monday, a switch failure caused some of the station’s power channels to go down. The ISS still has power, though, and the problem doesn’t pose any threat to the crew, but NASA needs to replace the switch before spacecraft can visit the ISS again.

To generate power, the ISS boasts eight long solar arrays on the outside of the station that convert sunlight into electricity. That electricity is then rerouted throughout the ISS via four switches known as MBSUs. But now, one of those four switches is acting up. As a result, two of the eight power channels that provide electricity to the station aren’t working either.

NASA likes to have redundancy

The six astronauts on board the ISS are safe, but NASA likes to have redundancy, which is why the space agency is pushing back the launch of an upcoming SpaceX Dragon cargo capsule that was supposed to visit station this week. Whenever one of these capsules arrives at the ISS, astronauts use the station’s large robotic arm to grab the incoming vehicle and place it on the outside of the station. The robotic arm needs electricity, and while it is still powered through one of the eight functioning power channels, it also uses one of the channels that is down at the moment.

NASA wants all of the robotic arm’s power channels up and running when the capsule arrives in case an issue arises. If for some extreme reason the robotic arm doesn’t have the power it needs, then the astronauts don’t have a way to grab SpaceX’s capsule.

Originally, SpaceX’s launch was slated for early Wednesday morning, April 30th, with the company’s Dragon capsule arriving at the station on Saturday, May 4th. But now, NASA is delaying the launch so that the space agency has time to replace the switch that’s mucking everything up. “Teams are working on a plan to robotically replace the failed unit and restore full power to the station system,” a NASA spokesperson tells The Verge. “Additional information will be provided as it becomes available.” The earliest launch opportunity is Friday, May 3rd, though it’s unclear yet if the launch will actually happen that day.