The propulsion, launch and orbit team have been working on finding a suitable final orbit for our capsule during its 100 years in space. Due to the 25-year orbital lifetime rule to be outside of LEO (Low Earth Orbit) and GEO (Geosynchronous Earth Orbit), we need a propulsion system to get it to Medium Earth Orbit (MEO) for the rest of its journey. To do this, we need the perigee, which is the closest point the CubeSat will be to earth during orbit, to be raised to an altitude of 2100 km and the apogee, the farthest point of the orbit, to be reduced to an altitude of 35000km after being dropped off into a GTO (Geosynchronous Transfer Orbit) by the launch provider.
When deciding which method of propulsion to use we have to consider certain constraints the CubeSat has. We have to compensate performance and total burn duration for the physical constraints, such as the size of the CubeSat, its mass and thermal soak-back issues from the thruster. We are currently deciding between two different methods of propulsion—electric or chemical. Electric propulsion (EP) devices generally have a lower thrust of the two, meaning it will take longer to get into the right orbit, about 140 days as a rough estimate. Alternatively, chemical propulsion systems have a relatively higher thrust and a maneuver would only take about 15 days.
To determine which system will work for the amount of ΔV required, with a mass constraint on propellant, we consider the Isp or specific impulse. For a higher Isp, less propellant is needed to get the capsule into the final orbit, giving EP the upper hand. Given the Isp of a thruster, the orbit team works to simulate the maneuver and determine the ΔV, or the change in velocity, needed to change orbits successfully. From their simulations, we have discovered that the CubeSat needs a ΔV of 250 m/s to perform a successful orbit change and, from there, the team works out how much propellant will be needed based on the method of propulsion used.