Mission Design for the CubeSat OUFTI-1

CHAPTER 8.POWER SYSTEMEectrons/cm 2 . For our mission the fluence over the lifetime, estimated throughthe software Spenvis, is of 8.55 · 10 11 : we can use the values of the third columneven if they are too pessimistic.They give a value for the efficiency of 25.5 %: we will use 25% to be sure of notoversetimating the power.8.3 Power producedWe have now all the elements to calculate the power produced: the directionof sun rays, the eclipse duration and the solar arrays orientation. The programdeveloped calculates the eclipse’s anomalies of entrance and exit. Looping onthe satellite anomaly, it determine whether it’s in sunlight or not: if yes, itcalculate the scalar product between the sun rays direction and the normal toeach face in order to have the incidence angle of sun:cos (β i ) = ˆN s · ˆN i i = 1 : 6 (8.11)where i indicates the face.If cos (β i ) < 0, it means that the face is not watching the sun as it’s turned in theopposite direction: it doesn’t contribute to the power production. Otherwisewe have the power produced by the i-th face:P i = C s A i η i cos (β i ) (8.12)As logical, the maximum power of a face is generated when the sun raysare perpendicular to it. This doesn’t mean that the total maximum power isproduced when one solar array is perpendicular the sun: in fact, in order tohave the total maximum power we need to add the contributions of all thefaces. Indeed, the Delfi-C3 team performed a study to optimize the orientationof solar cells: it came out that the best configuration is when a corner is directedto the sun.Once we have the power generated by each face, we sum the contribution andwe have the total power.8.3.1 Elliptic orbit with starting orbital elementsFor the OUFTI-1 elliptical orbit in case of Ω = 0, ω = 0 and for a simulationstarting at the vernal equinox we have the result represented in figure 8.5.Each vertical line represents one orbit on the moment of the year indicatedby the earth anomaly in abscissa. In blue are represented the eclipses and inthe dark red the maximum power.Galli Stefania 79 University of Liège