INFLUENCE OF INTERPLANETARY TRAJECTORY SELECTION ON EARTH ATMOSPHERICENTRY VELOCITY OF MARS MISSIONS

Many current manned Mars mission studies are using low lift-to-drag ra tio vehicles to aerobrake at both Mars and Earth. This paper will demo nstrate that if entry velocity constraints are incorporated into the i nterplanetary analysis of aerobraking Mars missions, more opportunitie s can be achieved for only a small increase in initial mass in low-Ear th orbit (IMLEO). These additional opportunities result from varying t he initial launch date and the encounter dates and possibly using a po wered Venus swingby on either the inbound or outbound transfer. This p aper not only presents unconstrained entry velocity missions but also includes results for entry velocities below 12.5 and 14 km/s on Earth return and between 6.0-8.5 km/s at Mars arrival. The results indicate that, regardless of the Mars entry velocity range selected, an Earth e ntry velocity below 14 km/s is easily attainable for a minimal IMLEO i ncrease. Although there are fewer 12.5 km/s Earth entry velocity missi ons possible, both Mars entry velocity constraint cases have over 50% of their missions requiring a negligible IMLEO increase.