An electrical distribution unit aboard the International Space Station was disrupted on Monday and two of the laboratory's eight power channels were disrupted. The crew was in no danger while the engineers were fixing the problem, officials said. However, if the problem can not be solved, it may be necessary to replace the electrical container with a replacement device, possibly causing NASA to delay the launch of a SpaceX Dragon supply ship Wednesday. Assuming a punctual launch on a Falcon 9 rocket, the kite cargo box, loaded with nearly 5,500 pounds of equipment and supplies, is expected to overtake the station early Friday and then stand by during the lab's robot arm snaps in and pulls him in to put on.
The Canadian-built robotic arm can be powered by a single power source, but NASA flight rules require two for redundancy. As it turned out, one of the two circuits that assisted the arm operation was turned off by the problem of the main bus switching unit that came on Monday.
A NASA official said the energy from the two channels fed by the Main Bus Switching Unit (MBSU) or MBSU could be redirected using jumpers. NASA flight rules require redundant power for robotic arm operations. If the secondary force to the arm can not be diverted or otherwise reconstructed in any way and the flight rule remains in effect, the launch of the kite is likely to be delayed until the MBSU can be replaced either by robots or during a spacewalk.
The primary solar power system of the space station consists of four rotating solar wings, two to the right of the pressure modules of the outpost and two to the left. Four MBSUs mounted in the center of the station's solar cell framework distribute the power from the downstream arrays to different circuits. The faulty MBSU has shut down the current channels 3A and 3B. The system has been designed so that the channels can be "crossed" if necessary to correct errors.
In 2017, a MBSU feeding channels 2A and 2B malfunctioned, requiring air traffic controllers to replace the station's robotic arm. Another MBSU was replaced in 2012 during two spacewalks.