The 25th flight of the Space Shuttle launched to deploy the second TDRS satellite for NASA, conduct "Teacher In Space" lessons, observe Halley's Comet, and carry out biomedical experiments. This was the 10th and final flight of Space Shuttle Challenger and marked the last time civilians (who were not members of the Astronaut Corps) flew on a NASA rocket. Launched in near-freezing conditions after a devastating temperature drop overnight, both O-ring seals between the two Solid Rocket Booster segments failed at the instant of launch. A temporary seal was formed by O-ring debris but was knocked loose when Challenger encountered upper level wind shear greater than she should have been launch into. The broken seal allowed hot gasses to escape the rocket booster and destroy the base of the External Tank. Challenger was ripped apart by aerodynamic forces 73 seconds after launch as the External Tank failed. Contrary to public memory, Challenger did not explode. All seven crewmembers lost their lives in what is still considered the worst spaceflight accident in history. It is the only fatal space accident that was broadcast live on TV. Over her short, three year career, Challenger spent a total of 62 days in space, travelled 41,527,414 km, and carried 60 cremembers.