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Due to mass and volume constraints on planetary missions, the development of control techniques that do not require fuel are of big interest. For those planets that have a dense enough atmosphere, aerodynamic drag can play an important role. The use of atmospheric differential drag for formation keeping was first proposed by Carolina L. Leonard in 1986, and has been proven to work in Earth atmosphere by many missions. Moreover, atmospheric drag has been used in the Mars atmosphere as aerobraking technique to decelerate landing vehicles, and to circularize the orbit of the spacecraft. Still, no literature was available related to formation flying on Mars. To analyze the use of differential drag on the Mars atmosphere, the researcher accessed the two high resolution models available: NASA's Mars-GRAM and ESA's Mars Climate Database. These models allowed the simulation of conditions that a spacecraft would experience while in orbit around the planet. To explore the feasibility, the researcher first conducted a study where Mars atmosphere density was compared to Earth atmosphere, determining its applicability. Then, a simulation using MATLAB® was conducted, using a Keplerian two-body problem including the effects of Mars zonal harmonics (i.e. J2) and drag perturbations. Two 6U CubeSat were used in the simulation with deployable drag plates of different sizes, giving the possibility of having five differential drag scenarios as means of formation control. The conclusions showed that, although with some limitations, the use of differential drag as means of autonomous formation flying and proximity operations control is feasible using proven techniques previously validated in Low Earth Orbit. Lyapunov control was selected as the control strategy, where three different methods were evaluated and compared. v ACKNOWLEDGMENTS Out of many people that I would like to recognize, there is one who deserves all my acknowledgments for the support, the power, the partnership, laughs, company, and unconditional love, and she is Yanina Hallak. This thesis is dedicated to you. Because of your passion and dedication, we were embraced together in this amazing journey of getting our Master's degree in Aerospace Engineering. Our journey continues now, and there are many great things to come. To Dr. Kira Abercromby, because you are the most brilliant and enthusiastic teacher I have ever had. Your support and dedication to all students, including me, should be an example to follow by all others. I have learned everything I know about orbital dynamics from your classes, and …

Autonomous Formation Flying and Proximity Operations Using Differential Drag on the Mars Atmosphere