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Cape Canaveral, Fla., 14 July 2005--The space shuttle Discovery, which was due to launch at 3:51 p.m. Eastern Daylight Time yesterday, will remain on the ground until at least Sunday, though it is more likely to launch several days after that, NASA says. Yesterday, at about 1:30 p.m., as the Discovery's seven-person crew sat strapped into their seats, ready to launch, an automatic test of a sensor in the liquid-hydrogen fuel tank showed that the sensor had stopped working. The sensor is one of four "low-level" sensors that watch out for an abnormally low amount of fuel in the tank. They would never normally come into play during a flight, as NASA budgets for a generous fuel margin. The purpose of the sensors is to give the shuttle's computers enough time to shut down the spacecraft's three main engines before the last drop of fuel is exhausted. NASA doesn't know exactly what would happen to an engine that ran out of fuel while operating, says Wayne Hale, deputy shuttle program manager for NASA. "We never tested it," says Hale, but he believes it would cause "serious damage."

NASA spotted the sensor problem when a simulation signal was sent to the electronics box that controls the sensor. Immersed in the hydrogen tank, all four sensors were reading "wet," but the simulation signal commanded them to temporarily read "dry." However, one sensor continued to read "wet." It took about 5 minutes of discussion for launch controllers to scrub the launch after that, says Hale.

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Economics Drives Ray-Gun Resurgence

Laser weapons, cheaper by the shot, should work well against drones and cruise missiles

4 min read
In an artist’s rendering, a truck is shown with five sets of wheels—two sets for the cab, the rest for the trailer—and a box on the top of the trailer, from which a red ray is projected on an angle, upward, ending in the silhouette of an airplane, which is being destroyed

Lockheed Martin's laser packs up to 300 kilowatts—enough to fry a drone or a plane.

Lockheed Martin

The technical challenge of missile defense has been compared with that of hitting a bullet with a bullet. Then there is the still tougher economic challenge of using an expensive interceptor to kill a cheaper target—like hitting a lead bullet with a golden one.

Maybe trouble and money could be saved by shooting down such targets with a laser. Once the system was designed, built, and paid for, the cost per shot would be low. Such considerations led planners at the Pentagon to seek a solution from Lockheed Martin, which has just delivered a 300-kilowatt laser to the U.S. Army. The new weapon combines the output of a large bundle of fiber lasers of varying frequencies to form a single beam of white light. This laser has been undergoing tests in the lab, and it should see its first field trials sometime in 2023. General Atomics, a military contractor in San Diego, is also developing a laser of this power for the Army based on what’s known as the distributed-gain design, which has a single aperture.

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