Sizing of a ramjet/scramjet powered vehicle for mars exploration

The exploration of Mars is an important part of the space exploration programs of the United States, the Soviet Union, Europe, and Japan. Many robotic spacecraft, including orbiters, landers, and rovers have been launched toward Mars since the 1960s. These missions were aimed at gathering data about current conditions and answering questions about the history of Mars as well as a preparation for a possible human mission to Mars. The questions raised by the scientific community are expected to not only give a better appreciation of the red planet but also yield further insight into the past, and possible future, of Earth. In this context, taking into consideration other future means of exploration is a must. Since the Mars atmosphere is about 95.3% carbon dioxide, 2.7% nitrogen and 1.6% argon, the CO2 in the Martian atmosphere may become an oxidizer of unconventional fuelled ramjets such as, in-situ manufactured silanes (Sin H2n+2) [1 , 2]. Compared to a rocket 'hopper', ramjets using the Martian atmosphere may save on-board propellant and thus vehicle mass, a crucial issue, since any such vehicle must either be ferried from Earth, or built in situ. In a previous work [3] by these authors, a preliminary analysis for the feasibility of a hypersonic, CO 2-breathing ramjet using silanes as fuel was demonstrated: in fact, assuming a total structural weight index of 21.0 kgf/m2 (weight index 7.93 kgf/m2 on Mars) and a cruise range of 5,000 km yielded realistic solutions for current industrial materials and fabricating capabilities. In particular, for a 1-metric ton payload, a take-off gross weigh (TOGW) of order 3.2 ton, including the propellants needed to achieve ramjet operation turned out. In this paper, a detailed analysis of the engine flow path and of the cruise CL best conditions has been done. In fact, in order to define the optimal engine cycle (i.e., TBCC, RBCC) and combustor flow speed a Builder [4] analysis is performed. The critical flight speed above which the flow must become supersonic within the combustor is found to be 1600 m/s. The most favourable speed for cruise CL is found to be in the Mach range 6-7. This speed put this vehicle in the class of hypersonic vehicles with supersonic flow through the combustor.