Canadian Astronaut Bob Thirsk completed a 6 month tour of Earth's upper orbit while on the International Space Station. Mr. Thirsk had written a letter prior to coming home on a Russian space craft with two other members of the crew saying, "If asked to do so, I could remain aboard the Station and continue to perform well. But I feel a fatigue setting in that even weekends and a good night's sleep cannot relieve. It is now time to return home."

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