It takes a lot of resources to put a vehicle into space. Not all of those resources are harmless. Hydrazine, used in rocket fuel, is a powerful propellant. But it's also toxic and corrosive. Organizations like NASA are now looking into green propellant alternatives to hydrazine.
Ideally, the new propellant would be less hazardous to handle than current rocket fuel, reducing the costs of organizing a space voyage. It should also break down into harmless components, eliminating the risk of polluting the environment.
Wishing for a green alternative to hydrazine doesn't make a new propellant magically appear. That's why NASA has invited companies and organizations to present technological demonstrations of alternative propellants. In February 2012, NASA announced that it would accept proposals until the end of April. A winning proposal could earn up to $50 million.
Reducing the environmental impact of launches is a big job. To launch a space shuttle into orbit, NASA used two solid rocket boosters, each carrying 1 million pounds (453,592 kilograms) of propellant. The shuttle itself carried an additional half-million gallons (1.9 million liters) of liquid fuel [source: NASA].