A Japanese spacecraft is about to make a close encounter with an asteroid in a mission to recover space dust.
Hayabusa launched in May 2003
The Hayabusa probe is stationed over a giant asteroid some 300 million km from Earth.
On Friday, it will descend to the surface of the 600m-long space rock to carry out observations and release a tiny robotic probe.
Two further descents are planned later this month to collect samples for return to Earth next year.
Japan's Hayabusa spacecraft was launched in May 2003 on a voyage to find out more about the raw materials that made up the early Solar System.
It reached its target asteroid, known as Itokawa, in September, from where it has been mapping the surface and sending back images from a close vantage point.
The Japanese Aerospace Exploration Agency (Jaxa) probe carries the 10cm-tall Minerva robot that will bounce across the asteroid, collecting temperature readings and images.
Friday's planned descent is a practice run designed to survey the landing site ahead of two attempts at sample collection on 12 and 25 November.
It will gather samples by shooting a metal pellet into the asteroid at 300m/s. After the firings, the probe will take off to collect the dust ejected by the impact.
The landings will be controlled autonomously by the spacecraft's software. Mission managers say there is enough fuel onboard to make the landing attempts despite technical problems.
The probe lost one of its three stabilising reaction wheels on 31 July, forcing it into an alternative flight mode. The second wheel failed on 3 October.
Hayabusa will begin its return voyage to Earth in December and is expected to arrive in June 2007. If successful, it will be the first spacecraft to return samples from an asteroid.