By Dr David Whitehouse BBC News Online science editor

The Stardust probe has successfully completed a close flyby of asteroid Annefrank, according to US space agency (Nasa) engineers.

Although the encounter was viewed merely as an opportunity to test systems, some useful scientific data was obtained.

The craft is to said to have performed well, tracking the small asteroid and taking pictures.

Stardust's primary mission is a rendezvous with Comet Wild 2 in 2004, when it will gather dust samples to return to Earth for analysis two years later.

Good health

The brief encounter with Annefrank was a chance for engineers to carry out a full dress rehearsal of the procedures the spacecraft will use during its 2004 encounter with the comet.

Stardust passed within about 3,300 kilometres (2,050 miles) of the 4-km-wide (2.5 miles) asteroid at 2050 GMT on Saturday.

Radio signals confirming the basic health of the spacecraft after the flyby were received about 30 minutes later via Nasa's Deep Space Network.

Preliminary indications are that Stardust visually tracked Annefrank for about 30 minutes as it flew past the asteroid at a relative speed of about 7 km (4 miles) per second.

Comet dust

Although no dust was anticipated near the asteroid, the spacecraft's dust instruments were in use as they will be at Comet Wild 2.

The dust collector was open and the dust counter from the University of Chicago and dust mass spectrometer from Germany were turned on.

Images and information from the flyby period will be transmitted from the spacecraft through the coming week.

Stardust's scientists and engineers are analysing the data to maximise the chances of success during the 2004 encounter with Comet Wild 2.

The probe will bring samples of comet dust back to Earth in 2006 to help answer fundamental questions about the origins of the Solar System.