ISS Star Trail Photography By Donald Roy Pettit

International Space Station
Pettit's first space mission was as a mission specialist on ISS Expedition 6 in 2002 and 2003. During his six-month stay aboard the space station, he performed two EVAs to help install external scientific equipment. During free time on his stay aboard the International Space Station, he conducted demonstrations showing how fluids react in an extremely low gravity environment in a series he called "Saturday Morning Science".
Pettit was Mission Specialist 1 on the STS-126 mission to deliver equipment and supplies to the ISS. He spent 15 days 20 hours 29 minutes and 37 seconds on board Endeavour.
Pettit also performed experiments on board ISS related to clumping of solid particles in microgravity. The experiments showed that particles of various materials which varied in size between 1 micrometer and 6 mm naturally clumped together in microgravity when confined to a volume of 4 liters that included a few grams of the materials. The cause was theorized to be electrostatic. This presents a plausible mechanism for the initial stages of planetary formation, since particles of this size do not have sufficient gravity to cause this phenomenon.