2. The challenges of propulsion

2.1 Rocket motors: liquid, solid, hybrid

• How a rocket motor works

  Rocket engines play an essential role in space exploration, providing the energy needed to enable a payload to escape the Earth's gravitational pull and propel vehicles into space, using propulsion systems that can dispense with the presence of air. The propulsion systems currently in use can be classified according to the type of energy stored, and can be divided into three main groups: chemical, nuclear and electric propulsion. Electric propulsion can only achieve very modest thrusts, while nuclear propulsion presents safety problems that have prevented its development for access to space. Launchers use chemical propulsion to put satellites into orbit. In this type...