Mission Design for the CubeSat OUFTI-1

CHAPTER 5.MISSION ANALYSIS5.2 The orbitThe choice of the orbit is an important step in every space mission as it stronglyinfluences the final performances. It’s usually driven by the missions requirementsand therefore it’s specific for each satellite. In this case, as the CubeSatsare secondary payloads on the Vega maiden flight, we couldn’t set anyway theorbit parameter as they are determined by its main payload, the LARES experiment.As above-mentioned, the foreseen orbit is elliptical with a perigee at 350 Kmaltitude, an apogee at 1200 Km and an inclination of 71 ◦ . Concerning the argumentof perigee and the right ascension of ascending node, any input hasn’t beenassigned yet. As the LARES satellite will be placed into a circular orbit, theargument of perigee is the only parameters that can be influenced by the Cube-Sat requirements. Considering that all the CubeSats are european and thatthey necessary have their main ground stations in the northern hemisphere, weexpect and hope to have the apogee over the northern hemisphere: in this case,we could have the longest time to use OUFTI-1 as amateur radio repeater overEurope and to communicate with our ground station. As shown in paragraph5.3.4, the argument of perigee is changing during the satellite lifetime but, asthe D-STAR system has never been used into space and as we still don’t knowhow long it will able to work before breaking down, we strongly hope that itwill be in a convenient position at the beginning.Concerning the possibility of a circular orbit at 350 Km altitude, it’s not thebest solution for OUFTI-1 and , more in general, for the CubeSats: on theone hand, the communication time with the ground stations is short, even ifit’s better than for the case of elliptic orbit with the perigee over the northernhemisphere, and, on the other hand, the lifetime is extremely brief.Anyway, as the most probable orbit is the elliptic one, we will perform theanalysis basing on it, which also represent the more general case.Before describing the OUFTI-1 orbit, we proceed with a recall of orbital mechanics.5.2.1 Orbital mechanicsThe orbital mechanics studies the motion of a spacecraft on a specific trajectory,called orbit, basing on the Newton’s laws of motion and of universal gravitation.Directly from them, come the three Kepler’s laws of planetary motion:- The orbit of every planet is an ellipse with the sun at one of the foci.- The line joining a planet and the sun sweeps out equal areas during equalintervals of time as the planet travels around its orbit.Galli Stefania 33 University of Liège