Flight schools help their students to be familiar with all the aircraft equipment. Student pilots will be hearing about GPS most of the time during training. As a pilot trainee, you must know what GPS means and its use.
GPS stands for Global Positioning System, a satellite-based system that helps in navigation and made up of a network of 24 satellites placed into orbit and transmitting signals to earth. GPS receivers retrieve this information and calculate the exact location of the user by using triangulation. After receiving the signals, GPS receivers determine how far it is from the satellite location. Utilizing the measurements of distance given by a few more satellites, the receiver can easily determine the position of the user and display it on the electronic map of the GPS unit. In order for a GPS receiver to calculate a 2D position and track movements, a GPS receiver must be linked to at least three satellites.
GPS receivers do not only concentrate on determining the location but also other information like the speed, track, trip distance and much more. Even the weather can be calculated by GPS.
GPS receivers are very accurate because of its parallel multi-design. As designed by Garmin, it has 12-channel receivers that are quick to respond onto satellites. They also maintain strong locks that enable it to get all the necessary information that is needed. They are designed with all the advancements in today’s technology so that it can keep pace with all the other latest equipments that we have right now.
Latest versions of Garmin’s GPS receivers have Wide Area Augmentation System (WAAS) capability that can improve the accuracy to less than an average of three meters.
GPS is composed of 24 satellites that are constantly orbiting the earth about 12,000 miles above the earth at roughly 7,000 miles per hour. They are powered by solar energy and have backup batteries in case a solar eclipse occurs. There are two rocket boosters on each satellite for balance and to keep them on track.
There are three different bits of information that a GPS signal has- a pseudorandom code which is commonly known to be the ID code that identifies the satellite that is transmitting the information; ephemeris data which is constantly being transmitted by satellites and contains information that are important for the status of the satellite, the current time and date; and almanac data which tells the GPS receiver where each GPS satellite must be at a certain time of the day.
GPS is representative of the most advanced equipment that is being offered for aircraft like Cirrus.
Coast Flight Training uses Cirrus models that have GPS to enhance safety and situational awareness.
Question by zuestra99: Why are GPS satellites in medium orbit rather than geostationary?
Is there an advantage, other than probably cost, to having the GPS satellites at 12,000 miles rather than in geostationary orbit? Would it work either way?
Best answer:
Answer by SiriusB
Geostationary can only apply to equatorial orbits. With GPS satellites it makes more sense to have them in a polar orbit so that they can cover the entire Earth’s surface over time. Also I presume that putting a satellite at the relatively large distance required for a stationary orbit (22,000 miles) would significantly reduce the precision with which the distance could be measured (GPS doesn’t use triangulation, it works by measuring the distance between satellite and receiver).
Give your answer to this question below!
LightSquared solves GPS interference with new device
“Since we have demonstrated that LightSquared can certainly coexist with the current GPS satellite signals, the coexistence will be even stronger when the new GPS satellites with modern L1C, L2C, and L5 unencrypted codes are launched. …
Read more on CNET
If you enjoyed this article, please consider sharing it!
Geostationary satellites have a hard time covering far north and south regions. Once you are 75 degrees north or south, the satellite is too low on the horizon to be useful. Even at 50 degrees north or south, the satellite would be only 25 degrees above the horizon, and would not cover the far side of hills or mountains, or into valleys.
Plus, the power requirements to send a signal 12,000 miles is only 30% compared to geostationary orbit. That makes a BIG difference in weight, cost, and lifetime.
No, they need to be in a medium orbit.
You want to use GPS even at high latitudes, but geostationary satellites are hard to receive close to the poles. Next, you want to have all satellites in a special constellation or formation. When the satellites are all close together in the sky, for example in a straight line or at the same point, the accuracy of the calculations drops as the signals will get the same disturbances because of the atmosphere. Also, the mathematical calculations inside the receiver will not work well then. Then, you also want this constellation to repeat in a good pattern at regular times. The GPS distance means the constallations repeat every 72 hours, other distances change this. Regular repetition patterns mean, that your receiver will have it easier to find satellites and calculate their position, even when the ground station of the GPS fails to update the orbit information onboard the satellites (The satellites don’t know this themselves, you need ground stations for the required accuracy).
Finally, you also have to consider the launch vehicles you can use. Today this is not such a big problem, but for GPS, there had been the Delta II planned, which has tight mass limitations.
The previous replies about geostationary orbits pretty much answered your questions.
However, there is also some misinformation about GPS given in the previous answers that I’d like to address:
SiriusB said: With GPS satellites it makes more sense to have them in a polar orbit so that they can cover the entire Earth’s surface over time.
Firstly, GPS satellites are NOT in polar orbits. Secondly, a polar orbit doesn’t cover the earth any more efficiently than non-polar orbits. What gives GPS satellites the coverage they do (which is 100% of the earth) is the way the 24+ satellites are distributed in their six orbital planes.
SiruisB said: Also I presume that putting a satellite at the relatively large distance required for a stationary orbit (22,000 miles) would significantly reduce the precision with which the distance could be measured
The presumption is incorrect. The control and space segments of GPS would still monitor satellite positions and update the system accordingly.
urwumpe said: The GPS distance means the constallations repeat every 72 hours, other distances change this.
GPS orbital periods are 12 hrs (11hrs, 56min).