Mission Design for the CubeSat OUFTI-1

CHAPTER 55.4 The launch windowThe launch window represents the time gap useful to place the satellite in apredetermined orbit from a specific launch site. As the orbital plane is fixed inthe inertial space, the exact launch instant is the time when the launch site onthe surface of the earth rotates through the orbital plane.The launch is possible only if the latitude of the launch site is smaller than theorbit inclination or equal to it: here comes the importance of having a spaceportas near as possible to the equatorial line.The time to launch depends on the right ascension of ascending node and onthe inclination required.In the OUFTI-1 case, as it will be secondary payload on the launcher, we cannotchoose any of these parameters and therefore we cannot determine the launchwindows.5.5 Earth coverageEarth coverage refers to the surface that a spacecraft instrument or antenna cansee at one instant or over an extended period. The leading parameters are thecovered area and the rate at which new land comes into view as the spacecraftmoves. We can so identify four key parameters:• Footprint Area also called instantaneous Field Of View area(FOV): areathat an instrument can see at any instant• Instantaneous Access Area (IAA): all the area that an instrument couldpotentially see at any instant if it were scanned through its normal rangeof orientations• Area Coverage Rate (ACR): the rate at which the instrument is sensingor accessing new land• Area Access Rate (AAR): the rate at which new land is coming into thespacecraft’s access areaFor an omnidirectional antenna, the footprint corresponds to the access area,as well the coverage rate to the access rate: for OUFTI-1 we need therefore tocalculate only two parameters.We consider a minimal elevation of the spacecraft over the horizon of ɛ = 5 ◦ andwe proceed to the determination of the field of view and of the area coveragerate. The notations are indicated in figure 5.25The first step is to find out the angle θ: for a directional antenna or anoptical payload it represents the beam width and is therefore imposed. In caseof omnidirectional antenna, the directivity diagram has an angle with a loss ofGalli Stefania 50 University of Liège