![Two astronauts work inside the bottom of Hubble while flying over the earth.](https://science.nasa.gov/wp-content/uploads/2022/05/28024329425-c407a7da5d-o-jpg.webp?w=4096&format=png)
Hubble SM3B RSU Replacement
Astronauts Steven L. Smith and John M. Grunsfeld, appear as small figures in this wide-angle photograph taken during an extravehicular activity (EVA) in December 1999. On this spacewalk they replaced the rate sensor units (RSUs, or gyroscopes) inside the Hubble Space Telescope.
Credits: NASA
Image CreditNASA
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