Surveillance in space

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Nasa is to build a $600 million space-based telescope to act as an early warning system against asteroids on a collision course with Earth.

The decision to proceed with the “near-Earth object surveillance mission” comes two months after an asteroid large enough to wipe out a city came within 45,000 miles of Earth, the astronomical equivalent of a near-miss. It was detected only the day before, by an observatory in Brazil.

“This one did sneak up on us and it is an interesting story on the limitations of our survey network,” Lindley Johnson, Nasa’s planetary defence officer, told colleagues the day after the 55,000mph fly-by on July 25.

Had the space rock entered the planet’s atmosphere, the resulting blast wave would have devastated an area about 50 miles across, Nasa said.

“This object slipped through a whole series of our capture nets. I wonder how many times this situation has happened without the asteroid being discovered at all,” wrote Paul Chodas, manager of the Centre for Near-Earth Object Studies at Nasa’s jet propulsion laboratory in California.

Emails, obtained as part of a freedom of information request by Buzzfeed News, reveal the depth of alarm at Nasa over the inability to detect potentially catastrophic planetary threats. Whereas an act of Congress 15 years ago tasked Nasa with detecting 90 per cent of near-Earth objects (NEOs) larger than 140m by 2020, no specific funding was attached. More than 20,000 NEOs have been detected and an average of 30 more are added each week.

Ground-based telescopes must be complemented with space-based capabilities to step up progress, a study by the US National Academies of Sciences, Engineering and Medicine concluded in June.

Thomas Zurbuchen, Nasa’s associate administrator for science, estimated in a presentation to a Nasa advisory committee on Monday that the NEO surveillance mission would find 65 per cent of those that remain undiscovered within five years of launch and 90 per cent within a decade. The earliest it could launch would be 2025.

The infrared telescope will be based on a previously conceived mission called NEOCam that was proposed in 2013 but did not move beyond the design phase, a failure that Mr Zurbuchen described as “one of the biggest screw-ups of my job”.

Classifying it as a “planetary defence” mission, instead of a scientific mission, allows the space agency to find funding for the project.

In 2013 a 20m asteroid exploded over Chelyabinsk, Russia, producing a shock wave that damaged thousands of buildings and injured about 1,500 people.

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