Astronaut John M. Grunsfeld

Astronaut John M. Grunsfeld, STS-109 payload commander, participates in the third of five spacewalks to perform work on the Hubble Space Telescope (HST). The extravehicular activity (EVA) was the second of three for Linnehan and Grunsfeld, payload commander. In a "first" for the HST mission, power to the telescope was completely turned off in order to replace the Power Control Unit (PCU), the heart of HST's electrical power system.

Credits: NASA