In late 2001, steve Fossett tried to fly a balloon nonstop around the world .
why on his attempted circumnavigation of the globe did Steve attempted to travel at an altitude of approximately 10000 m?
That is a typical stratosphere flight altitude, where the pilot can usually have the benefit of a strong jet stream (west to east) and good fuel economy because of the lower air density. Althought the air density continues to decrease at higher altitude, there is an optimum fuel-economy flight altitude around 10,000 m, for most planes, where the lift matches the plane's weight with the engines operating at efficient thrust levels.