A novel approach to hybrid propulsion transfers

This paper introduces a hybrid propulsion transfer termed a Hohmann Spiral, incorporating low and high-thrust technologies, analogous to the high-thrust bi-elliptic transfer. To understand this transfer fully it is compared to a
standard high thrust Hohmann and a bi-elliptic transfer. Two critical specific impulse ratios are derived independent of time that determine the point this novel transfer consumes the exact amount of fuel as the two compared transfer
types. It is found that these ratios are valid for both a circular and elliptical starting orbit so long as the apogee of the elliptical orbit coincides with the target orbit radius. An expression representing the fuel mass fraction is derived
dependent of time in order to allow a bound solution space. The final part of this paper investigates two orbit transfer case studies, one is a Geostationary Transfer Orbit to Geostationary Earth Orbit based on the Alphabus platform specification and the other is from Low Earth Orbit to an orbit near the Moon. It is found the thrust required to complete the former transfer in a specified duration of 90 days exceeds current technology and as such provides a technology requirement for future spacecraft. It is found however, for spacecraft of significantly smaller mass, in the region of 1000kg, compared to Alphabus (Max. mass at Launch =8100kg), the transfer consumes the same fuel mass as a standard high-thrust Hohmann transfer with realistic low-thrust propulsion values (150mN, 300mN and 450mN) within the set duration of 90 days. In addition, it is shown that utilising uprated thrusters (210mN, 420mN and 630mN) a fuel mass saving can be made. This could provide a potential transfer alternative for future smaller spacecraft. The second case study is bound to a maximum thrust of 150mN, but the mission duration is not specified to highlight the variation. It is found that the HST offers fuel mass savings of roughly 5% compared to a standard high-thrust transfer and approximately 1.5% compared to a bi-elliptic transfer for different scenarios.