  A technologically mature colony on Mars can produce and deliver at least 1
million tons of liquid hydrogen per year to one or more propellant depots at
Low Earth Orbit (LEO). Production of 1 $kg$ of hydrogen at Marian colony and
its delivery to LEO requires an energy expenditure of 1.4 $GJ$ on Mars. LEO
propellant depot contains hydrogen produced on Mars and oxygen produced on the
Moon or near-Earth asteroids. This propellant is used to deliver payload from
LEO to many destinations in the Solar System including Mars. Delivery of 1 $kg$
payload from LEO to Mars requires an energy expenditure of 3.5 $GJ$ on Mars,
Moon, and near-Earth asteroids. The use of liquid hydrogen produced on Mars to
deliver astronauts and payload to Mars ensures exponential bootstrap growth of
the Martian colony. Martian Colony and delivery of millions of tons of liquid
hydrogen to LEO is the key to Colonization of Solar System. %% Martian Colony
starts transporting liquid hydrogen to LEO only after it grows to significant
size. It should contain about 20 million tons of steel and 3 million tons of
plastic in structures and material as well as several thousand astronauts.
Prior to that time, LEO hydrogen deposit will be supplied by hydrogen from
Lunar poles.
