According to Official Guinness Records,
A four-stage rocket sled system accelerated a 87 kg (192 lb) payload to a speed of 2,886 m/s (9,465 ft/s) in 6.031 seconds at Holloman High Speed Test Track, Holloman Air Force Base, New Mexico, USA, on 30 April 2003. This is equivalent to 10,385 km/h (6,453 mph).The sleds carried a package designed to simulate the warhead of a ballistic missile defence system, and despite costing US$750,000 (£465,000 at 2003 rate) to stage, it is cheaper than staging an actual ballistic missile test.
The rocket sleds were of narrow gauge configuration and required 5.046 km (3.13 miles) of track to reach peak speed. The first stage used five rocket motors, the second has six rockets, and the third and fourth each used a single high-performance rocket.
For a complete list of 2003 records, please visit 2003 Guinness Records in United States.