Satellite Communications Payload and System

Chapter 2

Payload's On-Orbit Environment

This chapter describes the payload's on-orbit environment and the general effects of the environment on the payload. How the payload units are affected in detail is addressed in Chapters 3–4. The sections in this chapter are as follows:

• Section 2.1: What determines the on-orbit environment, namely the orbit, the spacecraft's general layout and orientation, and the payload's general layout on the spacecraft bus
• Section 2.2: On-orbit environment itself and how the spacecraft bus mitigates it for the payload. General aspects of the environment are thermal, aging, radiation, and attitude disturbances
• Section 2.3: General effects of the mitigated environment on the payload.

2.1 What Determines Environment

The payload's on-orbit environment is determined, at the highest level, by the spacecraft orbit, the spacecraft's general shape and configuration, the spacecraft's orientation on orbit, and how the payload is laid out in the spacecraft.

2.1.1 Orbit

Communications satellites can be found in various orbits. The satellite revolves about the center of the earth in either a nominal circle or a nominal ellipse. The nominal shape is characterized by the eccentricity, which is zero for a circle and positive for an ellipse. The circle or ellipse is only nominally the motion because it is perturbed by the nonspherical shape of the earth, local variations in the earth's density, the gravitational pull of other heavenly bodies, and other effects. The ...