The main problem was the fact that Discovery shuttle astronauts Steven Swanson and Joseph Acaba installed a restraint pin in the wrong position and this blocked the later attempts to operate a cargo carrier outside the ISS. 

 

Most of the other planned maintenance chores were completed, but the stuck pin left the cargo carrier half deployed and half stowed. It was installed with a few tethers and NASA engineers are currently trying to establish how long the provisionally fix will stay in place. 

 

The mission’s Lead Extravehicular Activity Officer, Glenda Laws-Brown, said that, although it was human error, Acaba had a lot of bad luck. If it would have rotated just a little bit more or maybe a little bit less, the pin might have cleared just fine. 

 

"Some days you're lucky, and some days you're less lucky," she said Laws-Brown who explained that it was an error easy to make because there is no up and down in space. 

 

Swanson and Acaba also installed a second GPS antenna on the Japanese Kibo laboratory. The antenna will be used when the Japanese HTV cargo ship will be there in September. 

 

If NASA engineers find a way the crew could pry or hammer loose the pin, it would be carried out during Monday’s spacewalk. Currently, the crew members aboard the ISS and Discovery space shuttle are taking a Sunday morning off.