WASHINGTON (AFP) - Two astronauts on Friday embarked on the first space walk of the Endeavour shuttles final mission to the International Space Station (ISS), according to NASA. Andrew Feustel and Greg Chamitoff, wearing spacesuits with solid and broken red stripes, respectively, floated out of the station at 0710 GMT to retrieve two science experiments that had been delivered in November 2009. Feustel, who is on his fourth lifetime space walk, will then retrieve a similar experiment brought up aboard Endeavour and install it. The excursion was to last six and a half hours, according to NASA, and will be followed by three more space walks over the course of the 16-day mission, the penultimate journey of the decades-old US shuttle program. On Thursday Endeavours astronauts installed a massive physics experiment, part of a 16-nation collaboration that aims to discover how the universe began. The Alpha Magnetic Spectrometer-2 is a $2-billion, 15,000-pound (7,000-kilogram) particle detector that will remain at the ISS to scour the universe for hints of dark matter and antimatter over the next decade. It is expected to send data to scientists on Earth for the next 10 years. NASA managers at mission control in Houston were meanwhile inspecting the shuttles heat shield after seven tiles appeared to have been damaged during its ascent, but officials have said there is no reason to be alarmed.