Nasa's space craft Genesis, which has been collecting dust from the sun, is heading back to Earth on Wednesday.
The precious particles have to be returned to Earth in one piece, so Hollywood stunt pilots have been enlisted to help them land safely.
The dust will be ejected from the probe in a special capsule as the craft enters the Earth's atmosphere.
Helicopters will be waiting to snatch the capsule's parachute in midair to prevent it hitting the ground.
Four chances
The helicopter pilots have had 17 rehearsals for the task and haven't dropped a capsule yet.
When it happens for real they'll have four shots each at getting it right.
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