TYPES OF ENVIRONMENTAL SATELLITES

perigee, satellites move faster. When at apogee, satellites travel slower. This change in velocity complicates tracking of polar-orbiting satellites. For convenience and ease of orbit calculations, time is referenced to zero when a polar-orbiting satellite passes the equator northbound, and increases through a complete orbital period. Figure 1-4 illustrates the changes that can occur in the perigee and apogee of a satellite over time. Most polar-orbiting satellites also have anomalies in their orbits. An anomaly in an orbit is any change or deviation from a perfectly stable orbit. Some anomalies are planned into an orbit so that the orbit will remain sun synchronous as earth revolves around the sun during the course of a year. Anomalies further complicate satellite orbital predictions. REVIEW QUESTIONS Q1. A satellite with an equatorial orbit would have an inclination angle of how many degrees? Q2. What term is used for a satellite with an equatorial orbit moving with the same speed and direction as the earth? Q3. What term is used to describe the period of time when a polar orbiting satellite is traveling south to north? Q4. What is meant by the term "sun-synchronous" satellite? Q5. Q6. If a satellite has an ascending node time of 1400 local, what would be the approximate descending node time at the same location? What are the major factors that would cause changes in a satellites apogee and/or perigee position? TYPES OF ENVIRONMENTAL SATELLITES LEARNING OBJECTIVES: Recognize the various functions performed by environmental satellites. Identify the major satellite programs operated in the United States. Identify specific types of geostationary satellites, polar-orbiting satellites, DMSP satellites, and foreign satellites. Recognize the advantages and disadvantages of geostationary and polar- orbiting satellites. The first meteorological satellite was launched in April of 1960, and was known as TIROS-1 (Television and InfraRed Observation Satellite). Since that time, numerous satellites with more advanced technology have been introduced, and today there are many different designs of meteorological and oceanographic satellites. Most of these satellites have a variety of sensor packages that survey electromagnetic energy at several different wavelengths. Figure 1-4.—Typical elliptical satellite orbit and changes in the orbital shape over a period of time. 1-4