INTERNATIONAL SPACE STATION --

Its try, try again for astronauts on board the International Space Station today.

Two astronauts are making another attempt to boost power to the space station during a spacewalk this morning. They began the spacewalk just after 7 a.m.

They tools the astronauts are using are unusual -- a tooth brush and some wire cleaners, along with other equipment. Their goal is to clean stuck bolts that prevented them from installing a new power unit to the exterior of the space station.

Suni Williams of NASA and Akihiko Hoshide of the Japan Aerospace Exploration Agency will try to complete installation of a spare Main Bus Switching Unit. Its one of four boxes thats on the outside of the space station that helps route power from solar arrays to different parts of the station.

It is key to making sure the space station has the power it needs. In last weeks attempt, a stuck bolt prevented astronauts from properly installing the power unit. Last weeks attempt clocked in at eight hours, 17 minutes, the third longest spacewalk in history.

Todays spacewalk is only supposed to last six and a half hours. At the four hour mark, if the astronauts cant get the unit installed, they will start to bring it inside the quest airlock and work on the box inside the space station.

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Astronauts to repair power unit on International Space Station