1. Introduction

Communications Satellite

21 May 1998

The Galaxy 4 communications satellite failed. The satellite, shaped like a nine-foot cube with a solar panel stretching 100 feet, remained in a stable orbit above the Equator, but the system that kept it pointed at the Earth malfunctioned, causing it to spin. A backup system also failed.

29 August 2000

The Spacecraft Control Processor aboard the Mexican Solidaridad 1 communications satellite malfunctioned, wiping out television, radio and pager services for Mexico.

AMOS-5 Communications Satellite

21 November 2015

All communications with the Amos-5 satellite were lost. It provided coverage over the continent of Africa, as well as Europe and the Middle East.

USS Essex and other ships

As a society we have become dependent on satellite communications. But space is not a friendly place and satellites fail with alarming frequency. So if our satellite communications fail and we’re miles at sea, what do we do?

Radio Antennas on the USS Bairoko

Before the advent of satellites, long distance communications were carried out with high frequency (HF) radio transmissions.

NOAA weather fax showing significant wave height and wind

Some important communications still use HF radio, including NOAA Weather Fax transmissions.

Composite image showing military applications of low frequency radio communicaitons

Other communications continue to use low frequency (LF) transmissions, including time stations and some military communications.

Sky, space, and surface waves

In this lesson, we look at the factors that control long-distance radio communications, with an emphasis on refraction in the ionosphere, frequency selection, and solar radiation.