Preliminary Screening of Multimode Spacecraft Propulsion Systems for Interplanetary Missions

Multimode spacecraft propulsion combines two or more propulsive modes into a single system and has been shown to be beneficial for geocentric missions and for specific interplanetary missions. This study develops an analytical method for preliminarily screening all-chemical, all-electric, hybrid, and multimode propulsion systems for small spacecraft (100 kg class) completing interplanetary missions. Key parameters of comparison include payload mass delivered, transfer time, transfer rate, and excess propulsion capability for a given required payload mass. It is shown that present term multimode propulsion systems with a chemical mode specific impulse of 170 seconds and 16% electric mode efficiency provide lower transfer rates than all-electric and hybrid architectures for multiple concepts of operations for Earth-Mars missions. Increasing the multimode chemical specific impulse to 230 seconds and electric mode efficiency to 30% results in transfer rates greater than any other architecture considered can provide. It is also shown that multimode electric mode specific impulse values between 1,000 and 1,500 seconds produce the greatest multimode transfer rates across the scenarios considered. For a fixed payload mass of 40 kg, it is shown that multimode and hybrid systems have the potential for significant propulsive capability at the target planet. Although all-electric, hybrid, and multimode architectures can complete the considered transfers, multimode propulsion provides mission designers increased operational flexibility that may be compelling for some applications with present technology despite lower transfer rates. Future improvements in multimode performance and system dry mass reductions will provide transfer rates greater than all-electric or hybrid architectures in addition to flexibility.