Sounding rocket (or Roket Sonda in Indonesian), is a type of rocket that carries instruments to conduct some scientific experiments in suborbital altitudes. Since the use of sounding rockets is constantly increased, there has been an idea to make it reusable. The development of a reusable sounding rockets should includes at least six key technologies, which from those, the development of a proper liquid propellant engine, which thrust can be intermittently controlled, is mandatory. This paper aims to contribute in Indonesia’s own reusable sounding rocket (RSR) development, by presenting an example of preliminary calculation for its liquid-propellant engine. To achieve the intended launch/flight profile to a targeted 120 km maximum altitude, and return safely to the ground, several design parameter is chosen, including the total mass of propellant for the powered ascent and descent that need to be at least 8700 kg, with the mass rate of 60 kg/s, producing 189 kN force. The force is produced by four nozzles to also provide control, where the exit area can be determined to be 0.164 m2. Finally, from these values, a rough estimation of the geometry of the reusable sounding rocket can be determined.