An update on China's latest satellite launch, and the various types of orbits possible
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- The story: On November 20, 2021, China launched a new satellite called “Gaofen-11 03”, from its Taiyuan Satellite Launch Centre. The Centre is located in the northern province of Shanxi, and the satellite was launched by a Long March-4B rocket, and entered the planned orbit successfully.
- Background: This launch marked the 397th mission of Long March series carrier rockets.
- Long March 4B: This satellite is also called as Chang Zheng 4B, CZ-4B and LM-4B. It is an expendable orbital Launch vehicle of China. The satellite was Launched from Launch Complex 1 of Taiyuan Satellite Launch Center. It is a 3-stage rocket, which is used to place satellites into low Earth orbit as well as sun-synchronous orbits. This satellite was first launched in 1999, with FY-1C weather satellite. It was later used in 2007 Chinese anti-satellite missile test. Its only failed satellite was CBERS-3 satellite, which was launched in 2013.
- Gaofen: It is a series of high-resolution Earth imaging satellite of China, which is used for state-sponsored program China High-resolution Earth Observation System (CHEOS). First Gaofen series satellite, called Gaofen 1 was launched in 2013. The Gaofen-11 03 is an Earth observation satellite, which is operated by CNSA. It was separated in the Sun-synchronous orbit, successfully.
- Types of orbits: There are many factors that decide which orbit would be best for a satellite to use, depending on what the satellite is designed to achieve. Some common orbits are - Geostationary orbit (GEO), Low Earth orbit (LEO), Medium Earth orbit (MEO), Polar orbit and Sun-synchronous orbit (SSO), Transfer orbits and geostationary transfer orbit (GTO), and Lagrange points (L-points).
- GEO - Satellites in geostationary orbit (GEO) circle Earth above the equator from west to east following Earth’s rotation – taking 23 hours 56 minutes and 4 seconds – by travelling at exactly the same rate as Earth.
- LEO - A low Earth orbit (LEO) is, as the name suggests, an orbit that is relatively close to Earth’s surface. It is normally at an altitude of less than 1000 km but could be as low as 160 km above Earth – which is low compared to other orbits, but still very far above Earth’s surface.
- MEO - Medium Earth orbit comprises a wide range of orbits anywhere between LEO and GEO. It is similar to LEO in that it also does not need to take specific paths around Earth, and it is used by a variety of satellites with many different applications.
- Polar - Satellites in polar orbits usually travel past Earth from north to south rather than from west to east, passing roughly over Earth's poles. Satellites in a polar orbit do not have to pass the North and South Pole precisely; even a deviation within 20 to 30 degrees is still classed as a polar orbit. Polar orbits are a type of low Earth orbit, as they are at low altitudes between 200 to 1000 km. Sun-synchronous orbit (SSO) is a particular kind of polar orbit. Satellites in SSO, travelling over the polar regions, are synchronous with the Sun. This means they are synchronised to always be in the same ‘fixed’ position relative to the Sun. This means that the satellite always visits the same spot at the same local time – for example, passing the city of Paris every day at noon exactly.
- GTO - Transfer orbits are a special kind of orbit used to get from one orbit to another. 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. Often, the satellites are instead placed on a transfer orbit: an orbit where, by using relatively little energy from built-in motors, the satellite or spacecraft can move from one orbit to another.
- Lagrange points - Lagrange points, or L-points, allow for orbits that are much, much farther away (over a million kilometres) and do not orbit Earth directly. These are specific points far out in space where the gravitational fields of Earth and the Sun combine in such a way that spacecraft that orbit them remain stable and can thus be ‘anchored’ relative to Earth. If a spacecraft was launched to other points in space very distant from Earth, they would naturally fall into an orbit around the Sun, and those spacecraft would soon end up far from Earth, making communication difficult. Instead, spacecraft launched to these special L-points stay fixed, and remain close to Earth with minimal effort without going into a different orbit.
- EXAM QUESTIONS: (1) Explain the various types of satellite orbits with their applications. (2) What are China's space plans? Explain.
#space #China #Geofen
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