A hypersonic glider launched by the US military from California seems to have vanished during a test flight over the Pacific this week.
The Falcon HTV -2 glider is an unmanned, rocket-launched vehicle that travels thousands of miles per hour and was programmed to land near Kwajalein missile range in the Marshall Islands.
Our correspondent Giff Johnson says the fate of the aircraft is unknown.
"Nobody including the US Defense Department seems to know where it came down, or in fact if it came down. All I can really report from the Marshall Islands is that nobody here has complained of bits of the sky falling on their islands, at least not so far."
Giff Johnson says the incident has stirred up talk of the expense of such US military projects compared to rents paid to local land owners.
He says about 40 years ago a missile crashed into an inhabited island in the region.
