In 1903 he published “Investigation of outer space rocket appliances” where he mathematically proved that space flight was possible. He also developed early ideas of liquid rocket engines.
The formula he used to prove space flight was possible was:
Where:
V= Speed of the rocket at any time
I0=Specific impulse fuel
M0 & M1=Mass of the rocket in the initial and final time.
In his studies Tsiolkovsky researched ways of flight control, methods of cooling the rocket in re-entry, the optimal descent trajectory and a pump system for the fuel components. He also looked into different fuel sources such as liquid oxygen, hydrogen and oxygen with hydrocarbons. He was very ahead of his time proposing things such as “Space rocket trains”.
Other work he did was correctly determining the escape velocity from Earth’s orbit at 8kms-1 and stated that it could be achieved by using a multi-staged rocket fuelled by liquid oxygen and hydrogen. He predicted the use of liquid oxygen and liquid hydrogen or liquid oxygen and kerosene for propulsion, spinning space stations for artificial gravity, space suits, the problems of eating, drinking, and sleeping in weightlessness, as well closed cycle biological systems to provide food and oxygen for any space colonies that could have developed as he believed was probable at this time.
In total he published over 500 works about space travel and related subjects including publications, designs for various rocket components