The challenges of propulsion
The challenges of launcher architecture in the context of New Space

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 of propulsion, the heat of reaction released by combustion between an oxidizer and a fuel is transformed into kinetic energy by the expansion of these gases in the nozzle. With chemical propulsion, specific vacuum impulses of the order of 500 s and thrusts of the order of 1,000 kN can be achieved. Chemical propulsion systems are generally grouped into three main categories: solid propellant systems, liquid propellant systems and, more recently, hybrid systems that combine the two.

  Thrust and specific impulse

  According to the momentum theorem, and using the notations in figure 5, the total thrust is $T$ expressed in newtons is given by the following expression :

  $$T=\dot{m}\mathrm{ }{v}_{\mathrm{ej}}+\left(p_{\mathrm{e}}-p_{\mathrm{a}}\right)A_{\mathrm{ e}}$$

  with :

  $p_{\mathrm{c}}$

   : 

  pressure in the combustion chamber [Pa],
  

  $p_{\mathrm{e}}$ ...