Satellite Basics for Everyone: An Illustrated Guide to Satellites for Non-Technical and Technical People

by C. Robert Welti Ph.D.

Overview

Satellite Basics for Everyone intends to stimulate a wide interest in engineering and science sorely needed to overcome our educational deficiencies to compete in the global economy. It offers a laypeople portal to the amazing world of satellites; indispensable to our everyday life and security. Something for everyone: come away with a level of new knowledge commensurate with your level of education to date.

Learn about satellites that affect us every day, how they work, and how we can place and keep them on orbit by integrating science, technology, engineering, art, and mathematics (STEAM).

Satellite Basics for Everyone presents an introduction and overview to satellites. Its written as clearly and understandably as possible for a wide audience. It provides a learning tool for grade school students. High school and college students can use it for helping them decide on career fields. Its for people with curious minds who want to know about satellites that affect their daily lives. And, it provides a training tool and an overview for people who build, operate, and use data collected by satellites.

Satellite Basics for Everyone describes satellite missions, orbits, population, closeness, debris, collision risk, builders, owners, operators, launch vehicles, and costs. Focus then turns to describing the orbit, components, environment, and operation of the geostationary communications satellite because it affects our daily lives the most by providing television, radio, commercial business, Internet and telephone services. A description of satellite motion prepares for the included Mission Planning Example of how to place and keep this satellite on orbit and keep the antennas pointing in the right direction to perform its mission.

Product Details

ISBN-13:	9781475925937
Publisher:	iUniverse, Incorporated
Publication date:	06/04/2012
Pages:	148
Sales rank:	724,697
Product dimensions:	6.00(w) x 9.00(h) x 0.32(d)

About the Author

C. Robert Weltis career spans over fifty years in aerospace and software systems working on satellite and telecommunications programs. Bob has a PhD in Engineering from UCLA. He now enjoys retirement living on a golf course with his wife Kem in the foothills of the California Gold Country.

Read an Excerpt

SATELLITE BASICS FOR EVERYONE

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By C. Robert Welti

iUniverse, Inc.

Copyright © 2012 C. Robert Welti
All right reserved.
ISBN: 978-1-4759-2593-7

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Chapter One

Artificial Earth Satellites

Satellite missions dictate their design and orbit. Satellites consist of a mission payload and a support platform or bus. The mission payloads perform their primary mission functions, including: making measurements, providing communications, providing navigation, and special military operations. The bus transports the mission payload around in its orbit and provides: electrical power, attitude control, payload pointing, temperature control, orbital position control, and orbital changes.

Origin of Artificial Satellites

The Soviet Union launched the first artificial satellite Sputnik 1 shown in Figure 1-1 on October 4, 1957. Sputnik 1 triggered the Space Race between the Soviet Union and the United States during the Cold War.

In early 1945 the United States started the Vanguard Rocket development to launch a satellite. After several Vanguard explosions on the launch pad, as witnessed on TV, the United States launched its first artificial satellite, Explorer 1 shown in Figure 1-2 on January 31, 1958 with the Vanguard. The Explorer's scientific payload included instruments to measure: cosmic rays, temperatures, acoustics of cosmic dust impacts, and micrometeorite impacts.

Major Satellite Types

Satellite missions dictate their design and orbit.

Major satellite types include:

• Astronomical

• Communications

• Navigation

• Reconnaissance

• Earth Observation

• Space Station

• Scientific

Astronomical satellites are satellites used for observing distant planets, galaxies, and other outer space objects. Payloads include telescopes and antennas and sensors sensitive to radiated energy at various wavelengths. The Hubble Space Telescope shown in Figure 1-3 is an example of a famous astronomical satellite.

The Hubble Space Telescope (HST) is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 7.9 ft. aperture telescope in low earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared. Hubble's orbit outside the distortion of earth allows it to take extremely sharp images with almost no background light. The United States space agency NASA built HST with contributions from the European Space Agency. The Space Telescope Science Institute operates HST. Hubble's expected lifetime is until at least 2014.

Communications satellites are satellites stationed in space for the purpose of telecommunications. Modern communications satellites typically use 24 hour geostationary orbits, 12 hour Molniya orbits, or low earth orbits.

The most common orbit is the geostationary orbit where the satellite is placed on orbit above a point of the equator and orbits around the earth at the same rate as the rotation of the earth around its axis, thereby keeping the satellite on station above the equator.

Figure 1-4 shows a simplified drawing of a typical geostationary communications satellite. In Chapter 3, focus is on the Geostationary Communications Satellite because it affects our daily lives and our security.

The Geostationary Communications Satellite provides global television, radio, business, Internet, and telephone services. Communications satellites are critical for national security because they provide global command and control of military resources and dissemination of vital intelligence information.

Navigational satellites are satellites which use radio time signals transmitted to enable mobile receivers on the ground to determine their exact location. The relatively clear line of sight between the satellites and receivers on the ground, combined with ever-improving electronics, allows satellite navigation systems to measure location to accuracies on the order of 10 feet in real time.

The Global Position Satellite (GPS) shown in Figure 1-5 is part of the constellation of satellites that provides global satellite signals for determining the position of receivers on the land, sea, and in the air.

GPS receivers also provide position information for missiles, lower earth orbiting satellites, drones and other weapon delivery systems. Position accuracy improves as the number of received satellite signals increases.

Reconnaissance satellites are earth observation satellites or communications satellites deployed for military or intelligence applications. Figure 1-6 shows an artist's concept of one of these satellites. Governments keep gathered information from these satellites classified.

The first generation type reconnaissance satellites took photographs and ejected canisters of photographic film, which would descend to earth. Later satellites had digital imaging systems and downloaded the images via encrypted radio links. Examples of reconnaissance satellite missions include: high resolution photography (IMINT), measurement and signature intelligence (MASINT), communications eavesdropping (SIGINT), covert communications, monitoring of nuclear test ban compliance, and detection of missile launches.

Earth observation satellites are satellites intended for non-military uses such as environmental monitoring, meteorology, map making, and topology. They take measurements at various wavelengths.

The Geostationary Operational Environmental Satellite (GOES) shown in Figure 1-7 is operated by the United States National Environmental Satellite, Data, and Information Service (NESDIS) and supports weather forecasting, severe storm tracking, and meteorology research.

Spacecraft and ground-based elements work together to provide a continuous stream of environmental data. The National Weather Service (NWS) uses the GOES system for its United States weather monitoring and forecasting operations and scientific researchers use the data to better understand land, atmosphere, ocean, and climate interactions.

Space stations are man-made structures that are designed for human beings to live on in outer space. A space station is distinguished from other manned spacecraft by its lack of major propulsion or landing facilities. Space stations are designed for medium-term living in orbit, for periods of weeks, months, or even years. Figure 1-8 shows the International Space Station.

The International Space Station (ISS) provides a platform to conduct scientific research that cannot be performed in any other way. The primary fields of research include astrobiology, astronomy, human research including space medicine and life sciences, physical sciences, material science, space weather, and weather on Earth. Medical research improves knowledge about the effects of long-term space exposure on the human body, including muscle atrophy, bone loss, and fluid shift. The ISS provides a location in the relative safety of Low Earth Orbit to test spacecraft systems that will be required for long-duration missions to the Moon and Mars.

Scientific satellites perform space environment experiments in the fields of biology, chemical processes, metallurgy, botany, and medicine.

The Upper Atmosphere Research Satellite (UARS) shown in Figure 1-9 was a NASA-operated orbital observatory whose mission was to study the earth's atmosphere, particularly the protective ozone layer.

Measurements included: the concentrations and distributions of nitrogen and chlorine compounds, ozone, water vapor and methane; thermal emission from the earth's limb (edge of earth's disc as seen from space); hydrogen chloride, hydrogen fluoride, nitric oxide, nitrogen dioxide, temperature, aerosol extinction, aerosol composition, the emission and absorption lines of molecular oxygen above the limb of the earth, wind, and temperature and emission rate from airglow and aurora.

Satellites in Orbit

Objects in Orbit

Who keeps track of the objects orbiting the earth? The United States Space Surveillance Network (SSN) does. Its mission involves detecting, tracking, cataloging, and identifying artificial objects orbiting earth, including: active and inactive satellites, spent rocket bodies, or fragmentation debris.

The SSN tracked space objects since 1957 when the Soviet Union opened the space age with the launch of Sputnik I. Since then, the SSN tracked tens of thousands of space objects orbiting earth. Currently, the SSN tracks thousands of orbiting objects. The rest have re-entered earth's turbulent atmosphere and disintegrated, or survived re-entry and impacted the earth. The space objects now orbiting earth range from satellites weighing several tons to pieces of spent rocket bodies weighing only several pounds. A small percentage of the space objects are operational satellites, the rest are debris.

Numbers of Satellites

How many satellites are in orbit? As of October 1, 2011, there were 966 operating satellites in orbit. The United States, Russia, and China are the three countries with the most satellites owned outright. These three countries among them own 613 or about two-thirds of the active satellites. Who owns the other third? A number of other countries and partnerships own between 10-20 satellites, but at least 115 countries in total own a satellite or share in one.

The four types of satellite orbits are: Low Earth Orbits (LEO) between 100 and 1,240 miles altitude, Medium Earth Orbits (MEO) between 1,243 and 22,236 miles altitude, Elliptical orbits' altitudes vary significantly between LEO and MEO altitudes during one orbit revolution, and Geostationary Orbits (GEO) at 22,236 miles altitude.

The total of 966 operating satellites is distributed into the following type of orbits:

• Low Earth Orbit (LEO): 470

• Medium Earth Orbit (MEO): 64

• Elliptical: 34

• Geostationary Orbits (GEO): 398

The total of 966 operating satellites is distributed by country as follows:

• United States: 443

• Russia: 101

• China: 69

• Others: 353

The total of 443 of U.S. satellites is distributed as follows:

• Commercial: 194

• Government: 128

• Military: 121

Out of the 398 total number of Geostationary Orbits (GEO) satellites, 355 are Communications Satellites which are distributed as follows:

• Commercial: 266

• Government: 30

• Military: 59

The 355 communications satellites in GEO orbit are distributed by country as follows:

• United States: 154

• Russia: 18

• China: 28

• Others: 155

Satellites in a geostationary orbit occupy a single orbit zone above the equator. Each satellite in geostationary orbit must be kept in its position within a sufficient distance so that it does not collide with other satellites.

Absent any other limitations on the availability of orbital positions, 1,800 satellites could be placed in a geostationary orbit at about 90 miles apart without posing a navigational hazard to others; however, as you shall see in the next section geostationary communications satellites group together over high population regions of the earth. To avoid harmful radio-frequency interference during operations the International Telecommunication Union assigns them an orbital slot (assigned longitude and radio frequency). This has led to conflicts among different countries wishing access to the same orbital slots and radio frequencies. These disputes are addressed through the International Telecommunication Union's allocation mechanism.

Satellite Longitudes and Separation

How are satellites distributed and separated? Appendix B presents the number of geostationary (GEO) satellites in orbit and major cities that are within 15° longitude ranges. Table 1-1 presents a summary of Appendix B.

Satellites group together above the high density regions such as above North America and Europe because of the high demand for communications in those regions.

Satellites that are close to each other have to maintain their longitude orbit positions very accurately to prevent a collision that could be caused by a thruster malfunction. Table 1-2 shows examples of satellite clusters that are closely grouped satellites in the same orbital slots.

Table 1-2 shows that eight satellites have no separation, but we know that there has to be some separation otherwise there would be a collision. The database provided this information and research did not reveal the amount of separation. Given the distance around the geostationary orbit is 164,619 miles; there is 457 miles per degree of longitude.

Table 1-2 also shows that there are sixteen satellites that are only separated by 0.01° which equates to 4.57 miles. In addition, the database shows that there are 15, 8, 10 and 7 satellites that are separated by 0.20° (9.14 miles), 0.03° (13.72 miles), 0.04° (18.28 miles) and 0.05° (22.85 miles), respectively. Fortunately, the geostationary satellites are not exactly at the same altitude so they are also separated in altitude. What is the probability of a satellite collision in the geostationary orbit? Barring a control failure, collision probability for satellites in the geostationary belt is very small due to the fact that the satellites are moving in the same direction at a relatively low velocity (to each other).

Debris in Orbit

How much debris is in orbit? Debris consists of everything from spent rocket stages and defunct satellites to erosion, explosion, and collision fragments. As the orbits of these objects often overlap the trajectories of newer objects, debris is a potential collision risk to operational satellites.

The vast majority of the estimated tens of millions of pieces of space debris are small particles, less than half an inch. Impacts of these particles cause erosive damage. Solar panels and optical devices (such as telescopes or star trackers) are subject to constant wear by debris and to a much lesser extent by micrometeorites.

Figure 1-10 shows the space debris populations seen from outside geostationary orbit (GEO). Note the two primary debris fields, the ring of objects in GEO and the cloud of objects in low earth orbit (LEO). In 2011, NASA said approximately 22,000 different objects were being tracked. More than 20,000 pieces are larger than a softball and it is estimated that 500,000 are larger than a marble. These objects travel around the earth at speeds up to 17,500 mph.

The only protection against larger debris is to maneuver the satellite in order to avoid a collision. If a collision with larger debris does occur, many of the resulting fragments from the damaged satellite will be in the two pound mass range and these objects become an additional collision risk.

As the chance of collision is a function of the number of objects in space, there is a critical density where the creation of new debris occurs faster than the various natural forces that remove these objects from orbit. Beyond this point a runaway chain reaction can occur that reduces all objects in orbit to debris in a period of years or months.

The 2009 satellite collision was the first accidental hypervelocity collision between two intact artificial satellites in earth orbit. The collision occurred on February 10, 2009 at 490 miles above the Taymyr Peninsula in Siberia, when Iridium 33 and Kosmos-2251 collided.

The satellites collided at a speed of approximately 26,170 mph, faster than escape velocity on earth. NASA reported that a large amount of debris was produced by the collision. As of March 2010, the U.S. Space Surveillance Network has cataloged 1,740 pieces of debris from the collision, with about 400 additional pieces waiting to be cataloged.

Events where two satellites approach within several miles of each other occur numerous times each day. Sorting through the large number of potential collisions to identify those that are high risk presents a challenge. Precise, up-to-date information regarding current satellite positions is difficult to obtain. Calculations had predicted these two satellites to miss by approximately 639 yards. An Iridium spokesman reported that they experienced close approaches, which numbered 400 per week (for approaches within 3 miles) for the entire Iridium constellation. He estimated the risk of collision per conjunction as one in 50 million.

This collision and numerous near-misses have renewed calls for mandatory disposal of defunct satellites (typically by deorbiting them), but no such international law exists as of yet.

(Continues...)

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Excerpted from SATELLITE BASICS FOR EVERYONE by C. Robert Welti Copyright © 2012 by C. Robert Welti. Excerpted by permission of iUniverse, Inc.. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Table of Contents

Contents

Preface....................vii
Introduction....................ix
Artificial Earth Satellites....................1
Origin of Artificial Satellites....................1
Satellites in Orbit....................10
Satellite Ownership Costs....................18
Satellite Launch....................19
Satellite Launch Vehicles....................19
Other Launch Systems....................26
Vehicle Configurations....................27
Launch Costs....................28
Geostationary Communications Satellite....................29
Geostationary Orbit....................31
Satellite Communications Services....................32
Ground Stations....................36
Satellite Components....................36
Mission Payload....................41
Satellite Bus....................47
Sample Communications Satellites....................61
Satellite Motion....................63
Kepler's Laws....................64
Elliptical Orbits....................65
Orbit Equations....................66
Eccentricity....................68
Simplifying Calculations....................69
Mission Planning Example....................71
The Mission....................71
Parking Orbit....................72
Geostationary Orbit....................73
Transfer Orbit....................74
Transfer Orbit Injection....................75
Geostationary Orbit Injection....................76
Achieving Longitude Station....................77
Orbits Summary....................78
Mission Planning Refinement....................79
Orbit Inclination....................80
Multiple Transfer Orbits....................83
Station-Keeping....................90
Propellant Requirements....................93
Rocket Equation....................93
Orbit Insertion Maneuvers....................95
Station-Keeping....................98
Attitude Control....................98
Propellant Mass Summary....................99
Total Mass Summary....................100
Mission Optimization....................101
Conclusions....................103
Appendices....................107
A - Unit Conversions....................107
B - Longitude Distribution....................109
C - Operators/Contractors....................111
D - Launch Vehicles and Sites....................115
E - Sample Communications Satellites....................117
F - Earth Parameters....................121
Glossary....................123
References....................129
Index....................131
About the Author....................135