Types of Orbit

- Overview

In the early days of the solar system, dust, gas and ice moved through space with speed and momentum, surrounding the sun in clouds. Because the Sun is much larger than these small particles of dust and gas, its gravity draws these small particles into orbit around it, forming clouds into rings around the Sun.

Eventually, these particles began to settle and clump together (or "merge"), growing larger and larger like rolling snowballs until they formed the planets, moons, and asteroids we see today. In fact, the planets are all formed this way, which is why all planets orbit the sun in the same direction and roughly in the same plane.

When rockets launch our satellites, they put them into orbit in space. There, gravity keeps the satellite in its desired orbit—just like gravity keeps the moon in its orbit around the Earth.

The way this happens is similar to throwing a ball out of a tower window - in order to get the ball to fly, you need to first "push" it by throwing it so that it falls toward the ground at a certain speed. While the ball's initial speed is determined by your throw, once you let go, the ball can only rely on gravity to keep it moving toward the ground.

In a similar fashion, a satellite is placed hundreds or thousands of kilometers above the Earth's surface (like in a very tall tower) and is then given a "boost" by a rocket engine to begin its journey into orbit.

The difference is that throwing something will make it fall on a curved path towards the ground – but a really powerful throw will mean that the ground starts to curve away before your object reaches the ground. Your object will fall ‘towards’ Earth indefinitely, causing it to circle the planet repeatedly. Congratulations! You have reached orbit.

In space, there is no air and therefore no air friction, so gravity keeps satellites in Earth orbit with little further help. Putting satellites into orbit allows us to take advantage of telecommunications, navigation, weather forecasting and astronomical observation technologies.

- Earth's Orbit 

Earth's orbit is the elliptical path that Earth takes around the sun, caused by gravity. An orbit is a repeating path that an object in space takes around another object. Earth's orbit is counterclockwise when viewed from above the Northern Hemisphere, and takes 365.256 days to complete. During this time, Earth travels 940 million kilometers at an average speed of 29.78 kilometers per second. 

Ignoring the influence of other Solar System bodies, Earth's orbit, also known as Earth's revolution, is an ellipse with the Earth-Sun barycenter as one focus with a current eccentricity of 0.0167.

Please refer to the following for more information:

• Wikipedia: Earth's Orbit

- Geostationary Orbit

A geostationary orbit, also known as a geosynchronous equatorial orbit, is a circular orbit that circles the Earth's equator at a speed that matches the Earth's rotation. This orbit is 35,786 kilometers above the equator and 42,164 kilometers from the center of the Earth. 

Satellites in geostationary orbit appear to remain stationary over a fixed location on Earth because they orbit at the same rate as the Earth, taking 23 hours, 56 minutes, and 4 seconds to complete one orbit. This position allows satellites to continuously observe the same spot on Earth, which is useful for weather observation and communication. For example, the Geostationary Operational Environmental Satellites (GOES) can provide continuous coverage of specific regions to help locate ships and airplanes in distress. 

As of July 2023, the UCS (Union of Concerned Scientists) Satellite Database lists 580 satellites in geostationary orbit. The first satellite to enter geostationary orbit was Syncom 3, which launched on August 19, 1964. 

- Low Earth Orbit (LEO)

Low Earth orbit (LEO) is the closest orbital range to Earth, with an altitude of 1,200 miles (2,000 km) or less. LEO orbits have an eccentricity of less than 0.25 and a period of 128 minutes or less. Satellites in LEO typically take 90 minutes to 2 hours to complete one orbit around Earth. 

LEO is the most common type of orbit and is considered close enough to Earth for transportation, communication, observation, and resupply. It's also the easiest orbit to reach in terms of rocket power and energy. However, LEO orbits have some disadvantages, including susceptibility to link failures and electromagnetic interference. 

LEO satellites orbit at altitudes ranging from 700 to 3,000 km, but most orbits are between 160 and 2,000 km due to atmospheric drag. The altitude of a LEO constellation is usually determined by the cost of placing satellites at a certain altitude, as well as other factors like: Radiation environment, Space debris, and Intended mission or market. 

- Medium Earth Orbit (MEO) 

Medium Earth orbit (MEO) is a region in space that's between Low Earth Orbit (LEO) and Geostationary Orbit (GEO). MEO satellites orbit the Earth at an altitude of 2,000–36,000 kilometers (1,243–22,300 miles) above the Earth's surface, and orbit the Earth at least twice a day. MEO is also known as intermediate circular orbit (Ico). 

MEO is less expensive to reach than GEO and less fuel intensive to operate in than LEO. It also offers a balance between the costs of higher altitude constellations and the coverage of low orbit satellites. MEO is primarily known as the orbit for GPS and other navigation satellites. MEO HTS constellations have also been deployed to provide low-latency, high-bandwidth data connectivity to commercial companies, government agencies, and service providers. 

MEO is dangerous for humans because astronauts are susceptible to high amounts of radiation. Satellites in MEO are shielded with layers of materials like Kevlar, aluminum, and gold to keep radiation at bay. Satellites and manned space missions that need to pass through MEO should cross it at a high speed with maximum thrust to limit the time spent in the Van Halen radiation zone. 

- Polar Orbit and Sun-synchronous Orbit (SSO)

A polar orbit is a low Earth orbit with an inclination of 90 degrees, where a spacecraft passes over the planet's north and south poles. A sun-synchronous orbit (SSO) is a type of polar orbit where the satellite's orbital period matches the Earth's rotational period around the sun, which is about one year. This means that the satellite's orientation remains constant relative to the sun, and it always visits the same spot at the same local time.

Polar orbits are used for satellites that provide weather tracking, reconnaissance, atmospheric condition measurements, and long-term Earth observation. SSO satellites are used for imaging, weather, and spy satellites. They travel from north to south over the Earth's poles, at altitudes ranging from 200–800 km. 

[Earth Orbit - Niko Lang]

- Transfer Orbits and Geostationary Transfer Orbit (GTO)

A transfer orbit is a special type of orbit that allows a satellite to move from one orbit to another. A geostationary transfer orbit (GTO) is a type of transfer orbit that is used to reach geosynchronous or geostationary orbit. 

When satellites are launched from Earth and carried to space with launch vehicles such as Ariane 5, the satellites are not always placed directly on their final orbit.

A GTO is a Hohmann transfer orbit, which is an elliptical orbit that transfers between two circular orbits of different radiuses in the same plane. The perigee (closest point to Earth) of a GTO is typically as high as low Earth orbit (LEO), while its apogee (furthest point from Earth) is as high as geostationary orbit.

Rockets often drop off their payloads in transfer orbits as halfway points en route to a satellite's final position. From transfer orbit, a satellite can use engine burns to change its inclination and circularize its orbit.

- Lagrange Points

Lagrange Points are positions in space where the gravitational forces of a two-body system like the Sun and Earth produce enhanced regions of attraction and repulsion. These can be used by spacecraft as "parking spots" in space to remain in a fixed position with minimal fuel consumption.

Lagrange points, also known as L-points or libration points, are positions in space where the gravitational forces of two large masses balance out the centripetal force of a smaller object. This means that small objects can remain in a fixed position at these points with minimal fuel consumption.

The five Lagrange points are L1, L2, L3, L4, and L5, and they are all located in the orbital plane of the two larger bodies. L1 and L2 are located on the Sun-Earth axis, L3 is located behind the Sun, opposite Earth, and L4 and L5 are located 60° ahead and behind Earth's orbit, respectively. 

Lagrange points are named after Joseph-Louis Lagrange, an 18th century Italian astronomer and mathematician who discovered them while studying the restricted three-body problem. The term "restricted" refers to the condition that two of the masses are much heavier than the third.

Spacecraft can use Lagrange points as "parking spots" in space, and space agencies often send satellites to L1 and L2 for scientific missions. For example, the James Webb Space Telescope (JWST) has been orbiting at L2 since January 2022, where it has a clear view of deep space.

L4 and L5 are permanently stable Lagrange points, so any objects that exist there will remain. Astronomers call these objects Trojan asteroids, and Jupiter has the most of them. NASA's Lucy mission launched in 2021 to explore Jupiter's Trojan asteroids and is expected to arrive at its first one in 2027.

[More to come ...]