International Space Station astronauts carried out an overnight spacewalk in order to install an electromagnetic energy probe and perform other experiments. The operation took them more than five hours and they completed it at 1:29 a.m. Eastern time Tuesday.

ISS commander Mike Fincke and flight engineer Yuri Lonchakov worked together and managed to install a Langmuir probe on the space station’s Pirs docking compartment. The device will be used to measure the effects of electromagnetic fields on pyrotechnical separation bolts.

Mr. Lonchakov was at his first spacewalk.

The electrical charges on the separation bolts are believed to have caused difficult landings of the Russian space capsules that have returned home from the ISS in October 2007 and April 2008 (expeditions 15 and 16 of the Russian Soyuz spacecraft).

"There's an electron cloud flowing around the station at all times. And then the station itself generates electricity," said deputy program manager Kirk Shireman last week.

All went almost as planned. The astronaut and cosmonaut completed the first stage of the spacewalk, and then installed the two science experiments, but the testing of the gear proved to be tricky because it was not sending data to the mission specialist on Earth. The time was running out, sot the two astronauts were told to retrieve one of the experiments and head back to the airlock.

"We've done everything we could," said Fincke, speaking Russian through a translator.

Fincke and Lonchakov returned to Pirs, reentered the airlock and closed the hatch.

The ISS is an international project of 16 nations. Its construction has started more than 10 years ago and cost about $100 billion.