Mission Design for the CubeSat OUFTI-1

CHAPTER 9.THERMAL-CONTROL SYSTEMCombining the precedent expressions, we obtain:T2 4 − T14 Q 1→2 = qA = −1−ɛ 1ɛ 1 A 1+ 1F 1,2 A 1+ 1−ɛ 2ɛ 2 A 2R eq = 1 − ɛ 1+ 1 + 1 − ɛ (9.11)2ɛ 1 A 1 F 1,2 A 1 ɛ 2 A 2In this case the equivalent resistance is composed by three terms that canbe divided as shown in figure 9.3.Figure 9.3: Radiative equivalent resistanceWe need now to identify the view factors.All the faces see the cold space with a view factor F i,99 = 1 except for the facesdirected towards sun and earth that have a lower factor. We start with theface which sees the earth and the cold space: it can be treated as the radiativeexchange between a square (the satellite’s face) and a circle with radius r (theearth projected) separated by a distance h (the altitude). The correspondingformula for an average altitude of 775 Km give the following result:F face,earth =1( hr) 2+ 1= 0.98 (9.12)We can say that practically the face can see only the earth. Anyway wemaintained the link with the cold space too.Applying the same formula for the face regarding the sun and using the sun’sradius and the sun’s distance from earth, we have the view factor:F face,sun = 2, 27 · 10 −5 (9.13)The hypothesis of modeling the sun as a visible flux on the satellite is definitelyacceptable as the face practically sees only the cold space but collects thesun rays.Galli Stefania 91 University of Liège