Initially, the spacecraft's ADC thrusters would use the same propulsion system as the main thruster. However, it was decided to separate the two systems and select a monopropellant propulsion system for the ADC thrusters. This would lead to a more direct route for the propellant to take to the thrusters, decrease complexity and save on mass and volume by reducing the number of pipes, valves, and flow regulators required for the system. Below are diagrams illustrating the main propulsion system and the ADC propulsion system.

The main propulsion system would be a bipropellant system using hydrogen peroxide - kerosene as a propellant and nitrogen as the pressurant. The propellant would be stored in two separate tanks: one for the hydrogen peroxide and one for the kerosene. Using the valves and flow regulators, the two fuels would mix together to ignite the main engine thruster.

The attitude control propulsion system would be a monopropellant system in blowdown configuration, so only one tank would be required. The tank would be connected to 8 ADC thrusters through its own piping network, which would also include valves and flow regulators. The propellant for this system would be hydrogen peroxide pressurized with nitrogen gas.

Using STK, the entire mission was able to be modeled from the spacecraft’s initial orbit to landing. To get from orbit to the lunar surface, the Hohmann transfer described in the delta V budget was modeled using Astrogator with maneuver and propagate segments. In this simulation, each burn was modeled as an impulsive burn for simplicity. This yielded a total delta V of 2494.36 m/s. Before adding in margin, the total calculated delta V was 2494.77 m/s. Since these numbers matched, there was much more confidence in the calculated budget, and therefore in the propulsion system having the necessary amount of propellant to complete the mission. In the simulation, the spacecraft would touch the surface at a speed of 1.98 m/s, which meets the requirement that the spacecraft must land between 0 and 2 m/s. The transfer from orbit to landing would take 4.83 hours, or around 4 hours and 50 minutes. The graph below shows the spacecraft’s landing trajectory during the last 50 km of the mission. After the second Hohmann burn would be completed, it would only take a few minutes before completing the spacecraft’s landing.

The WIS•DOM thermal analysis was first completed in a MATLAB tool called the Single Node Thermal Analysis tool. The analysis assumes the spacecraft to be an isothermal sphere (one-node) in orbit around the moon. The parameters inputted for WIS•DOM are listed in the table below.

The program allows the user to choose the spacecraft characteristics, the central body around which the spacecraft orbits, and the orbit parameters associated with the chosen orbit. The program pulls information from a “Thermal Library” excel sheet included with the program; the library was compiled from multiple references, though most values are from the New SMAD by Wertz, Everett, and Puschell. The program was written by Samantha Carlowicz (samantha.carlowicz@slu.edu) with assistance and code-snippets provided by Matthew Batchelor (matthew.batchelor@spacex.com).