Astronauts upgrading the Hubble Space Telescope have made a third spacewalk in as many day to make repairs deep inside the orbiting observatory.
Mission chef mechanic John Grunsfeld delved into the interior of Hubble to replace computer circuitry that was never mean to be repaired in space.
He was join by Andrew Feustel to instal a new $88m (£58m ) spectrograph.
The instrument will provide greatter insight into how planets, stars and galaxies are formed.
Mr Grunsfeld, a 50-year-old astronomer, and Mr Feustel, a 43-year-old geologist, also attached a new external power source.
As part of the seven-hours long operation Mr Grunsfeld removed 32 tiny screws using an assortment of hand ratchet and cutters.
On Friday the astronauts struggled to complete a critical repair to the telescop, refurbishing a pair of gyroscopes into the telescope after a new set refuse to go in.
The troubled spacewalk - the second - was the longest yet, lasting eight hours.

From BBC News, Sunday, 17 May 2009.