7.3.2 Propellant budget

The Deep Space Propulsion system requires enough fuel for Jovian insertion. The rocket equation was used to find out how much fuel was needed. A reserve fuel of %20 was added. The final bipropellant fuel mass for the Deep Space system is 987.4 kg. The Lander Propulsion system must perform a landing, meaning that it is subject to gravity loss. The gravity loss was estimated by defining and effective I_sp of the lander engines:

$$I_{sp_{eff}} = I_{sp} \times \frac{\vert\vec T-\vec W\vert}{\vert\vec T\vert}$$ (3)

Here, $\vec T$ is the thrust vector, $\vec W$ is the spacecraft's weight, and I_sp is the true specific impulse of the engines. Then, the gravity loss at the landing can be estimated. Using the $\Delta V$'s for a Hohmann transfer, the rocket equation is used to calculate the required fuel mass for the landing. The effective I_sp is used to calculate the fuel needed for the landing half of the transfer. The lander (monopropellant) fuel required turned out to be 712.8 kg. Finally, the Attitude Control propellant mass is based on a percentage of the bipropellant mass: 170.02 kg.