You must have heard of an orbit if you are not a flat-earth believer. Earth, as a round planet, essentially has 3 types of orbits: the high earth orbit, the medium earth orbit, and the low earth orbit.
Today, we focus on the low earth orbit and how satellites in the low earth orbit work, other types of orbits, and everything you need to know about them. So, what is low earth orbit, how far is it from the earth’s surface, and what is it used for?
Keep reading to find out.
But first, let us define an orbit.
What is an orbit?
An orbit is a path. It is a curved path in which objects, ranging from planets, asteroids, stars, or spacecraft, travel due to gravity. Gravitational pull keeps the revolving mass attracted to nearby objects.
Usually, the smaller object orbits around the larger object. Consider an example of the sun, the earth, and the moon.
The earth goes around the sun, while the moon orbits the earth. Note that the sun is bigger than the earth, while the moon is smaller.
The same thing happens when we launch satellites into space. A group of scientists sit and design the best path to keep the satellite orbiting the earth while resisting the earth’s gravitational forces.
When you launch a satellite, depending on its purpose, it can settle in one of the orbits we have.
Types of Orbits
Different orbits have different eccentricities- a measure of how circular or elliptical they are. Earth has several orbits, each with its advantages and capabilities. The different levels of orbits also give satellites on these paths a different perspective of the earth.
Earth has 3 basic classes of orbits, which are classified according to their altitude. And depending on high they are, their speed of orbiting the earth also changes.
These orbits include:
1. High earth orbit
The high earth orbit is home to most weather and communications satellites. These orbits are about 35,780km from the earth’s surface.
When satellites that orbit the earth at the high earth orbit reach exactly 42,164km from the center of the earth into the HEO, they travel at the same speed as the earth.
Since both bodies are moving at the same speed, the satellites at this altitude appear stationary on a single longitude.
The satellites might drift north or south; these special orbits are called geosynchronous orbits.
There is another group of high earth orbit which is geosynchronous but orbits the earth directly over the equator. This type is called geostationary orbit.
Satellites launched into the GEO circle orbit the earth from west to east, around the equator. Usually, it takes the satellite about 23 hours and 56 minutes to complete one rotation of the earth, which is almost similar to the orbiting speed of the earth.
This orbit is very valuable in weather monitoring since they provide a constant view of the same area.
2. Medium earth orbit
Medium-earth orbits are closer to the earth’s core compared to high-earth orbits. There are two main medium earth orbits: the Molniya orbit and the semi-synchronous orbit.
The semi-synchronous orbit is a near-circular orbit. It is located 26,560km from the earth’s center or about 20,200 km from its surface.
Satellites in the semi-synchronous orbit take about 12 hours to go around the earth, so in 24 hours, the satellites in the medium earth orbit cross over the same 2 spots over the equator.
Most global positioning systems (GPS) satellites orbit the earth on the medium earth orbit.
On the other hand, the Molniya orbit was introduced by the Russians, who found that using geostationary satellites was ineffective in monitoring areas further north or south of the equator.
The Molniya orbit is extremely elliptical, with one end closer to the earth than the other. So, when it moves closer to earth, it is accelerated by gravity and slows down as it moves away.
So, even if the satellites on the Molniya orbit take 12 hours to orbit the earth, it takes about one-third of the time to go around one hemisphere and two-thirds of the time to go around the other hemisphere.
3. Low earth orbit
The low earth orbit, known as LEO, is closest to the earth’s surface. It is nearly circular, and satellites travel at very high speeds.
Depending on what the satellites in the low earth orbit are monitoring, they may have different inclinations.
NASA’s earth-observing satellites are on LEO and are highly inclined. Due to this, they orbit the earth in a nearly polar orbit, moving from pole to pole in 99 minutes.
The theory behind the LEO
Do you know how you jump into the air and land on your feet? That’s all thanks to gravity. The satellites in LEO experience a stronger drag compared to satellites in the HEO.
Satellites in the LEO regime go around the earth at speeds of about 7.8km/s or 17,500mph.
At higher altitudes, the speed decreases, but the efforts of pushing a satellite into the high and medium earth orbit are huge. Hence the constellations of satellites on LEO, with about 55% of all satellites in the low earth orbit.
If the satellite on LEO moves at speeds greater than 11,2km/s, or 25,000mph, they reach the earth’s escape velocity and veer off its orbit.
Interesting facts about LEO
A satellite in LEO takes about 90-120 minutes to revolve around the earth, depending on its altitude. This means that an LEO satellite could complete about 16 revolutions every day. So, these satellites only appear in view for a few seconds before speeding off.
Thanks to their short orbital periods and closeness to the earth, LEO satellites are ideal for remote sensing applications.
They are also great for communication, so Space X launches their Starlink satellites into the LEO.
Of the 4,550 satellites actively orbiting the earth as of 18th January 2022, 3,790 operated from the LEO. Most satellites are for communication, earth observations, and technology developments.
What is a low earth orbit satellite?
A low earth satellite is a spacecraft that orbits the earth in the low earth orbit. These satellites are launched 400-2,000km from the earth’s surface.
Most satellites deployed to this level are for broadband communication since they have an added advantage in countering inter-satellite latency. They also have a short round-trip time,
Space X has now sent over 3,000 satellites into space for communication.
The LEO satellite constellation has an advantage over traditional communication systems as it offers increased user performance.
Thanks to many satellites launched into orbit; satellite operators can provide global coverage and visibility, which is Starlink’s goal.
And while they are amazing at offering latency-free internet to the most rural areas in the world, these low-orbit satellites have their share of disadvantages.
How do LEO satellites work?
As mentioned, LEO satellites go around the earth about 12-16 times a day. That means they are not fixed on a single point like the geostationary satellites. Instead, they go around the earth, as it also orbits about its axis.
While most of these satellites are used for communication, imaging, and spying, they have different designs. Nonetheless, LEO satellites share some common features.
Some common features of LEO satellites include the following:
- Standard L- frequency band – This L-band radio frequency is particularly common in maritime and long-range communications. Due to their compatibility with this radio frequency, LEO satellite owners need smaller ground equipment to receive signals from space. Most importantly, this radio frequency band is less susceptible to distortion due to weather conditions.
- They orbit the earth at very high speeds – The international space station, located in LEO, completes a complete revolution around the earth in 93 minutes. And due to the fast speeds, most of the satellites in LEO fall in and out of range frequently.
- They only work in constellations – Since these satellites are always in motion, it is nearly impossible to rely on only one satellite to monitor or communicate to a single point on the earth’s surface. For this reason, satellite operators opt to send constellations of LEO into space for better coverage. Also, since these satellites are closer to earth, their coverage distance is smaller. That means you would need many similar satellites to provide uninterrupted coverage.
In short, one satellite sends data links to a base station on earth, and the next satellite in range receives the return signal.
Advantages of LEO satellites
Consider the most prevalent satellite provider in LEO orbit today, Space X. With their Starlink satellites, a constellation of over 2,000 active satellites; they can provide uninterrupted communication over America and Europe.
Their integration allows LEO satellites to communicate where traditional communication systems are unavailable.
Another advantage of the LEO satellites is their low latency rates. Their closeness to earth makes it easy for these satellites to offer stable and reliable connections. And since the signal has to travel shorter distances, each LEO satellite can hangle greater bandwidth, which is ideal for mobile communications.
Disadvantages of low earth orbit
One of the main disadvantages of deploying satellites into LEO is the shorter life span of these space crafts. The satellites also experience a higher atmospheric drag, often leading them to lose orbit.
Due to their exposure to atmospheric drag, these LEO satellites do not stay in space for long. In turn, their maintenance and replacement cost becomes very high.
Also, the satellites on the low earth orbit move at extremely high angular velocities, which means shorter dwell time. So, if you plan to observe them from the earth, you only have a few seconds to see the satellites as they speed past your location.
Another drawback of LEO satellites is their complexity. Operators must match thousands of settings for the satellites to provide seamless coverage. Synchronization becomes even more complex when the operators work with thousands of satellites in space.
Low earth orbit is home to thousands of satellites and millions of pieces of debris. And while satellite operators are pushing more LEO satellites into orbit, there remains the high risk of collision in space.
However, you must recognize the benefit that these satellites serve. With them, it is now possible to connect the unconnected parts of the earth. Areas that have never seen the light of the internet will soon have a seamless, latency-free, and fast internet connection, thanks to the constellation of satellites in low earth orbit.