This story was updated at 4 p.m. ET.
A trio of astronauts on the International Space Station are gearing up for their second attempt to return to Earth after an unprecedented glitch prevented their Soyuz spacecraft from undocking from the outpost yesterday (Sept. 23).
The Soyuz crew NASA astronaut Tracy Caldwell Dyson and Russian cosmonauts Alexander Skvortsov and Mikhail Kornienko will try to leave the station again tonight at 10:02 p.m. EDT (0200 GMT).
If all goes according to plan, the spaceflyers will land on the steppes of Kazakhstan in Central Asia Saturday, Sept. 25, at 1:21 a.m. EDT (0521 GMT).
The astronauts' homecoming was delayed by a day as Russian engineers scrambled to correct the malfunctioning microswitch that refused to release a set of hooks and latches on the space station's Russian Poisk docking port.
During their first attempt, Russian flight controllers were unable to command the hooks and latches on the Poisk module to release the Soyuz spacecraft. The Soyuz has its own system of hooks and latches as well, but the ones on the Poisk module must be released first. [ Graphic Inside and Out: The International Space Station ]
The microswitch issue caused hours of delays, and eventually forced Mission Control and the astronauts to scrap undocking and landing plans for a day. The Soyuz crew returned inside the space station, and the 12 Russian recovery helicopters awaiting their landing in Kazakhstan went back to their home airfields.
Overnight, the space station crew rigged up cables to fix the docking port to set the stage for tonight's Soyuz departure.
"Space station crew members installed a series of jumpers, bypassing a failed component that had prevented commands from being received by the Russian Poisk module's docking mechanism," NASA officials said in a status update. "Once the jumpers were in place, the Poisk module hooks and latches were successfully opened."
The hook-and-latch system on the Soyuz remains closed, securing the spacecraft to the station, they added.
The space station's Poisk docking port is on the top of the orbiting laboratory's Russian segment. It was delivered in 2009 and entered use for visiting Russian spaceships earlier this year.
This will be the first undocking conducted at the Poisk module, so Russian engineers will be closely analyzing the problem, said NASA spokesman Rob Navias. The Poisk module will also be the same port that the next three space station crewmembers arrive at on Oct. 10.
"The current plan is to keep these jumper cables in place, so that there is a commanding path that is assured to reclose the hooks after the new Soyuz arrives at the station on October 10," Navias told SPACE.com. "They'll bring up some spare parts and do some troubleshooting so that this problem is alleviated in the future."
The module is just over 13 feet (4 meters) long, about 8 feet (2.5 meters) wide and weighs about 8,000 pounds (17,636 kg). It has about 380 cubic feet (10.7 cubic meters) of living space inside.
- Graphic Inside and Out: The International Space Station
- Video: Astronaut Describes Riding Home on a Rocket
- Gallery - Soyuz Spaceship's Snowy Landing
NASA will broadcast the upcoming Soyuz spacecraft undocking and landing , beginning at 9:45 p.m. ET. Click here for space station mission updates and a link to NASA TV.