This approach provided a uniform method for computing plant thermal and chemical performance and allowed the different options to be objectively compared on a power and mass basis. Using the results from the chemical and thermal analysis, a trade study for the chemical process for producing both fuel and oxidizer was performed for each of the candidate plants. Each criterion was given a weight of high, medium, or low. Reliability, cost, mass and volume, and power were weighted as high, with reliability being the most critical of the four. The ISPP plant must operate autonomously for 500 days, must produce propellant reliably with no maintenance, and must survive the trip from Earth to Mars.
Cost is always an important factor, and mass and volume affect cost.
The larger the mass, the higher the cost to put a payload into orbit and, eventually, onto the surface of Mars. Additionally, the system with the lowest power requirement would also receive the highest rating. Since the ISPP would be solar-powered, a system with high power demands would require large solar arrays, thus increasing launch mass and volume. Production rate was rated medium, while propellant fuel option and scalability were rated of low importance. All candidate processes produce liquid oxygen and a hydrocarbon, and all candidates have the potential to move from laboratory scale to manned-mission scale.