By its very nature, spaceflight is very challenging and very wasteful. As Tsiolkovsky's famous Rocket Equation establishes, propellant accounts for the majority of a rocket's mass, which is burned off during launch. The process also introduces large amounts of greenhouse gases, such as carbon dioxide, water vapor, and black carbon, as well as ozone-depleting chemicals, into the upper atmosphere. On top of that, the disposal process for satellites once they are no longer operational (deorbiting and burning up in the atmosphere) is also wasteful, with no materials retrieved or reused.