Share on Google+Share on FacebookShare on LinkedInShare on TwitterShare on DiggShare on Stumble Upon
Custom Search
4-13 SATELLITE ACQUISITION AND TRACKING An essential operation in communicating by satellite is the acquisition (locating) of the satellite by the earth terminal antenna and the subsequent tracking of the satellite. Initial acquisition depends upon an exact knowledge of the position of the satellite. In combination with the geographic location of the earth terminal, knowing the position of the satellite enables you to compute accurate antenna pointing information. The degree of difficulty in locating and tracking a satellite is determined largely by what type orbit the satellite is in. The locating and tracking of a synchronous satellite is relatively simple. This is because the satellite appears to be stationary. Locating a near-synchronous satellite is also relatively simple because of the slow relative motion of the satellite However, the movement of a near-synchronous satellite is enough that accurate tracking is required to keep the narrow beam antenna pointed toward the satellite. Satellites in medium altitude circular orbits or in elliptical orbits are more difficult to acquire and to track because of the rapid changes in position. Orbital Prediction To acquire and track a satellite in space, the earth terminal antennas must be provided with very accurate pointing information. Antenna pointing information is based upon the orbital prediction of the satellite. This information is derived from an EPHEMERIS table. This table provides the coordinates of a satellite or a celestial body at specific times during a given period. After you know the ephemeris data of a satellite, you can predict for any given location the apparent track of the satellite as viewed from that location. The constants defining an orbit are initially obtained by the process of tracking. At the time of launch, the rocket is tracked by radar from lift-off to orbit and then until it passes out of sight. Tracking data obtained in this way is sufficient for making rough predictions of the orbit. These predictions are made rapidly with a computer and sent to tracking stations all over the world. These other tracking stations watch for the satellite during its first trip and record additional data. During the first week of orbiting, tracking stations all around the world are obtaining progressively more accurate data concerning the Satellite. This data is put into a computer where corrections of earlier estimates of the orbit are made. Once the initial predictions are complete and the satellite link becomes operational, very little change in these calculations is made. The orbits of a satellite will change slightly over a period of time; however, these changes are so gradual that predictions will be accurate enough to be used for weeks or even months without further corrections. When the orbits are known precisely, an ephemeris can be calculated for each satellite of the system. Antenna Pointing Antenna pointing instructions for each satellite must be computed separately for each ground station location. A satellite that bears due south of station A at an elevation of 25 degrees may simultaneously bear due southeast of station B at an elevation of 30 degrees. Antenna pointing instructions are determined by taking into consideration the orbital prediction and the latitude and longitude of each ground station. To establish radio contact with a satellite, the ground station needs to know the bearing and elevation of a satellite. This allows the antenna to be properly pointed.

Electrical News
ARM Gives Peek at Road Map
ARM disclosed new details of its A72, including three functional...
Cypress Expands Error Correcting Code For SRAM
As overall SRAM market shrinks, Cypress sees uptick in automotive,...
EUV Deal Raises Questions
ASML announced it struck a deal to sell 15 EUV...
Make Field-oriented Motor Control Affordable
Shaft sensors and their wiring make field-oriented motor control pricey,...
Why Connect Cars?
EE Times will host a radio show on "Why Connect...
Time Flies Like an Arrow & Fruit Flies Like Bananas
Using a computer to translate something like a technical article...
NXP-Freescale Mega Merger on Track
Five companies, aside from NXP, were in talks with Freescale,...
Basic University Research Key to Industry Progress
A basic, precompetitive research base is required to continue to...
MEMS Seeks its Moore's Law
MEMS provide an alternative route to scaling technology beyond Moore's...
Wireless Charging Gets Universal Antenna
NuCurrent believe the company's 50 patents in areas such as...
Friday Quiz: EMI and EMC
EDN's Designer's Guide to Electromagnetic Compatibility, written by Bill Kimmel...
EEVBlog #736 – World’s First IR Thermal Camera Watch
A quick hack turns a Flir TG165 Thermal camera into...
Wave of 100th Birthday Celebrations Rolls Around the World
Following the party Max's family held to celebrate what would...
Qualcomm Seeking Options Beyond Apple, Samsung
Qualcomm's recent earnings reports suggest significant vulnerabilities. Qualcomm is heavily...
Elvis Sees All in Russia
A Russian company claims it has the first Russian designed...
Smartwatch Uptick in Mobile Slump
Smartwatches could grow to sales of 400 million units a...
8 Views of Security from RSA
Security was in focus at RSA Conference with top cryptographers,...
Electricity, Energy and Global Warming By the Numbers, Part 2
Numerous factors contribute to climate change. In Part 2, we...
10 Trailblazing Companies For Women In IT
On the following pages, we'll take you beyond the tech...
ARM Seeks Energy Harvesting Edge in IoT
With battery lifetimes becoming an increasing preoccupation of some of...

Privacy Statement - Copyright Information. - Contact Us

comments powered by Disqus

Integrated Publishing, Inc.
9438 US Hwy 19N #311 Port Richey, FL 34668

Phone For Parts Inquiries: (727) 755-3260
Google +