(CNN) -- An undocking glitch has delayed the departure of three astronauts from the international space station aboard a Soyuz spacecraft, NASA said Friday.
The trio -- two Russians and one American -- are now scheduled to return to Earth early Saturday, according to NASA. They are expected to land in Kazakhstan.
The delay means another day in space for Cmdr. Alexander Skvortsov and flight engineers Mikhail Kornienko and Tracy Caldwell Dyson.
NASA said the opening hooks and latches on the docking port would not release. The preliminary evaluation by the Russians was that the micro-switches that interface with the Soyuz malfunctioned.
"Engineers are continuing to troubleshoot the problem," NASA said.
The Russian flight controllers have developed a backup plan, and the resident crew of three is working to fix the malfunction.
According to NASA, a Soyuz space capsule took the first crew to the orbiting laboratory in November 2000. After the February 2003 Columbia accident, the Soyuz became the means of transportation for crew members going to or returning from the international space station.