A pair of spacewalking astronauts wrapped up a hastily planned repair job on Saturday to replace a suspect coolant pump needed to keep the International Space Station at full power.

NASA astronauts Chris Cassidy and Tom Marshburn put on spacesuits and left the space station’s airlock shortly before 9 a.m. EDT to attempt to stem an ammonia coolant leak that cropped up on Thursday.

Over the next four hours, they installed a spare pump, then positioned themselves to check for signs of escaping ammonia ice crystals when the system was turned back on.

“No flakes,” Cassidy reported to flight controllers at the Johnson Space Center in Houston.

Engineers will monitor the system over the next several days and beyond to make sure the pump replacement fixed the problem.

“We certainly have come a long way in identifying a potential source,” said NASA mission commentator Rob Navias as the astronauts returned to the station’s airlock. The entire spacewalk lasted 5-1/2 hours.

The station crew discovered a steady stream of ammonia flakes flowing away from the far left side of the station’s exterior frame on Thursday. Flight controllers spent the next 48 hours diagnosing the problem and coming up with potential solutions.

Engineers believed the leak most likely was coming from in or around a 260-pound (118-kg) pump that pushes ammonia throughout the system. The coolant dissipates heat from electronics in space station’s solar-powered electrical system.

The station can be reconfigured to compensate for a system shutdown, but if a second problem should occur, that likely would mean a cutback in power available for the experiments.

The $100 billion station, which flies about 250 miles above Earth, is a research laboratory for biomedical, physics, astronomical and other experiments, as well as for technology development and demonstrations.

On Sunday, station commander Chris Hadfield, the first Canadian to lead the international outpost, turns over the helm to Russian cosmonaut Pavel Vinogradov. Hadfield, Marshburn and cosmonaut Roman Romanenko, who have been aboard the station since December, are scheduled to depart on Monday.

Their replacements – NASA’s Karen Nyberg, Italy’s Luca Parmitano and Russian Fyodor Yurchikhin – are due to launch on May 28.

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NASA released an amazing image of New York City that its astronauts captured from outer space.

According to the space agency, a member of Expedition 35 aboard the International Space Station took this photograph of the city’s metropolitan area March 23.

The space station orbits the Earth, and the crew member was able to capture the 400-millimeter image at night.

The photo shows Manhattan glowing nearly completely amber, ringed by New Jersey, Brooklyn and Queens.

As NASA pointed out, Central Park is just to the left of the center of the frame.

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The 5 miles per second rock shooting through the Eastern sky Friday could unlock vast wealth, or spell destruction. The 150-foot wide asteroid 2012 DA14 is the largest to ever be detected passing this close and will provide lessons for space exploration.

“This is a unique opportunity,” Dwayne Brown, a spokesman for Nasa’s science department, told Metro. “This can tell us about asteroid trajectories, how the Sun affects them, and their origin in nature.”

2012 DA14 will pass just 17,000 miles away – within communication satellite orbit – and although it is not considered a threat, it will influence disaster preparation. “If we can better understand the approach, that helps us with an asteroid on collision course,” says Brown, adding that a strategy already exists based on deflection. “You can nudge it onto another course with even a light touch.”

Nasa have made asteroid study a top priority, and an army of robotic telescopes and sky surveyors helped to spot 2012 DA14 in February 2012. It is significant progress given that many asteroids are only seen as, or after, they pass.

Citizen astronomers have key to the advance, and thousands of enthusiasts will be watching the skies Friday. “Some amateur astronomers have observatories that would make a university jealous,” said David Dickinson, editor of the Astroguyz website. “Websites allow you to calculate co-ordinates for accurate location, how to watch and monitor events – and we’re constantly exchanging information live on Twitter.”

Civil society groups are increasingly partners in asteroid exploration and have been heavily involved in the 2016 launch of the OSIRIS-REx satellite, the first mission to mine samples from moving asteroids. 2012 DA14 has an estimated value of $200 billion in precious metals, hinting at a lucrative future in asteroid mining.

Yet over half of all Near-Earth Objects (NEO) remain undetected and a threat. “We need to find objects down to at least 100m, the vast majority of which we haven’t found yet,” Richard Crowther, chief engineer at the UK Space Agency, told Metro. A sudden, catastrophic event remains a possibility.

How to watch

2012 DA14 will be closest at 1924 GMT Friday and will be visible from parts of Europe and Africa. David Dickinson recommends being somewhere as dark as possible with telescope or binoculars and a wide field of vision. Calculate its route beforehand and focus on one position, the asteroid will resemble a shooting star and will be clearest when passing in front of the Moon. Check out Astroguyz.com or b612foundation.org to find out more, or http://www.nasa.gov/ntv to watch live.

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