Kevin Church/BBC News
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。同城约会是该领域的重要参考
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Two years in, he gambled and switched to the Navy Academy at Annapolis, on Chesapeake Bay, in the hope of working with his beloved rockets.
One reason for routinely launching GPS satellites is simply "constellation replenishment," said Col. Andrew Menschner, deputy commander of the Space Force's Space Systems Command. Old satellites degrade and die, and new ones need to go up and replace them. At least 24 GPS satellites are needed for global coverage, and having additional satellites in the fleet can improve navigation precision. Today, there are 31 GPS satellites in operational service, flying more than 12,000 miles (20,000 kilometers) above the Earth.