It is launched initially by parachute, but as it deploys, the Inertial Navigation System and Global Positioning System take over.

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Using an approach known as "inertial navigation", modified from military and industrial applications and Dr Donikian's own work with firefighters and first responders, Navisens' algorithms process raw data gleaned from low-cost motion sensors on smartphones.

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The decision to bring the shuttle down came after one of the orbiter's three key navigation tools -- an inertial measurement unit -- stopped working.

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Like most prototypes, the the SWAN (System for Wearable Audio Navigation) is pretty bulky in its current form, with a laptop, GPS, inertial sensors, pedometer, RFID tags, RF sensors, a compass, and other gear all stuffed into a backpack, although they're apparently already working on a smaller version.

ENGADGET: SWAN: System for Wearable Audio Navigation