STS-134 Mission Specialists Drew Feustel and Mike Fincke will conduct the third spacewalk of the mission Wednesday. They will be trying a new pre-breathe protocol designed to replace the overnight campout in the airlock. The In-Suit Light Exercise (ISLE) is also expected to use less oxygen to prepare the spacewalkers for the higher oxygen environment that is required with the lower pressure inside the spacesuit. They start this ISLE protocol by breathing oxygen for 60 minutes using a mask, followed by depressurization of the airlock to 10.2 psi. They will then put on their spacesuits, followed by a 100-minute in-suit pre-breathe at suit pressure. This includes 50 minutes of light, in-suit exercise using a standard cycle ergometer and 50 minutes of in-suit breathing while resting. This method has been successful in reducing the nitrogen content in the spacewalker’s blood in preparation for the depressurization and repressurization cycle. If it is successful, it might be used for the fourth and final spacewalk.
During the spacewalk, they will complete the external wireless antenna system work Feustel and Greg Chamitoff were unable to finish on the first spacewalk. The remainder of the work of the third spacewalk centers around increasing redundancy in the power supply to the Russian side of the station and extending the reach of the station’s robotic arm to that area. The latter will be achieved by adding a power and data grapple fixture to the exterior of the Zarya module. That will allow the arm to “walk” to the Russian segment, using that grapple fixture as a base.