This is added to the output table right after the spacecraft reaches orbital velocity at its altitude. Sometimes this altitude is below the low drag altitude and in any case maneuvering fuel is needed, so it is good to have an extra one twentieth fuel compared to the empty mass of the spacecraft. The orbital velocity at its altitude is calculated using the altitude, ground orbital and radius.

orbital velocity = ground orbital * sqrt( radius / ( radius + altitude ) )
 

This is used in the trajectory tables in atmospheric spacecraft, multi stage spacecraft, and spacecraft cost.
 

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