When deciding what propulsion system is most appropriate for a mission, thrust and Isp are not the only parameters that need to be considered. A mission planner must balance considerations of mission impact based on a combination of factors, including: mass benefit, complexity, heritage (or flight readiness), and risk ; all of which serve to provide a holistic assessment of a propulsion subsystem choice.
a) using the simplified rocket equation, plot the ratio of propellant of final mass for an Isp range of 100 to 1500s for a Single-Stage-to-Orbit (SSTO) launch vehicle. Use delta V = 9km/s. Based on this graph decide between a solid rocket motor (Isp = 250s) and a bipropellant liquid engine (Isp = 450s) . Justify your answer quantitatively and qualitatively
b) Do the same for a LEO to GEO transfer (delta V = 4km/s). A spacecraft has a thruster with an Isp of 800s. A new prototype, proven to perform with an Isp of 1000s, but which has never been flown, is being considered. Do the mass savings achieved by the new thruster justify its use? Justify your answer quantitatively and qualitatively.