Do you like Chemistry

For this project, you will evaluate two chemical processes which are used to lift rockets from the ground into space.  Lower stage rocket fuel is the reaction of hydrogen gas with oxygen gas to create water.  This is used in the troposphere to avoid adding toxic gasses to the environment in which we live.  However, once safely above the tropopause (what's that?!  And where is it?), another reaction is useful: that of hydrazine and nitrogen tetroxide are used.  Why aren't these used in the troposphere?  Why are they able to be used in the stratosphere and above?  Describe these processes, provide balanced chemical equations for each, and detail the energetics of both.  Please cite all credible sources, and avoid the use of wiki sites.  Your project should be 3-5 pages in length.