Mission Design for the CubeSat OUFTI-1

CHAPTER 5removes energy from the orbit. As a consequence, the semi-major axis is reducedand the orbit leans towards becoming circular. In case of elliptic orbit, the dragacts mainly at the perigee but its effect is a reduction in altitude of the apogee.It generates therefore a force and the acceleration tangent to the orbit trajectory:D = − 1 2 ρv2 Sc Dmms 2 (5.17)where ρ is the atmosphere density, v the speed with respect to the atmosphere,S the satellite cross-sectional area, c D the drag coefficient and mthe mass. The termmc Dis called ballistic coefficient and is often consideredAconstant for a satellite. For small satellites this coefficient is small and thereforethe acceleration is bigger: the situation is therefor particularly critical fornanosatellites.Drag cause a variation of the semi-major axis and of the eccentricity. It hasalso an effect on the argument of perigee ω but unimportant with respect to theeffect of the earth oblateness.For our simulation we consider the cross-sectional area as the surface of a cubeface and c D = 2.2.The atmosphere density varies depending on the solar activity which has a cycleof 11 years: as the solar minimum is happened in 2006, we used a mean densityvalue.Figure 5.14: Aerodynamic drag acceleration for the first day mission.Galli Stefania 42 University of Liège