How Do Satellites Orbit Earth? Principles, Technology & Everyday Uses
The term ‘satellite’ refers to a natural object such as a moon or spacecraft which is an artificial satellite orbiting a larger astronomical body. Most of the known natural satellites orbit planets, the Earth’s Moon is the most obvious example of it.
All the planets in the solar system generally except Venus and Mercury have natural satellites. More than 160 such objects have so far been discovered in the solar system with Saturn and Jupiter together contributing about two-thirds of the total.
The planets’ natural satellites vary greatly in size and shape as well as colour. A few satellites are larger than Mercury, for example, the planet Saturn’s Titan and Jupiter’s Ganymede each of which is more than 5,000 km that is about 3,100 miles in diameter.
The satellites also usually differ significantly in composition. The satellite moon for example generally consists almost entirely of rocky material. On the other hand, we see that the composition of Saturn’s Enceladus is 50 percent or more ice. Some asteroids are said to have their own tiny moons.
Natural and Artificial Satellites
A natural satellite is a moon that orbits a planet or a star. For example, the moon is a satellite because it orbits the earth. Usually, the word that is "satellite" refers to a machine that is launched into space and moves around the planet Earth or another body in space.
The planet Earth and the satellite moon are examples of natural satellites. There are thousands of artificial or man-made satellites that are orbiting Earth.
In the context of spaceflight, a satellite is said to be an object that has been intentionally placed into orbit. These objects are known as artificial satellites to distinguish them from natural satellites such as planet Earth's Moon.
Some satellites take pictures of the planet earth that helps meteorologists predict weather and track hurricanes. Some of the satellites take pictures of other planets, the sun and the black holes and the dark matter or faraway galaxies. These pictures generally help scientists to understand the solar system and the universe as well.
Still, we can say that the other satellites are used mainly for communications such as beaming TV signals and phone calls that are around the world. A group of more than 20 satellites make up the Global Positioning System or the GPS. If we have a GPS receiver, these satellites can help figure out our exact location.
Satellite Composition
The satellites come in many sizes and shapes. But most have at least two parts in common - that is a power source and antenna. The antenna usually receives and sends information which is often to and from Earth. The power source can be a panel or solar panel or battery. Solar panels generally make power by turning sunlight into electricity.
Many satellites of NASA carry cameras and scientific sensors. Sometimes these instruments usually point toward the planet Earth to gather information about its land, air and water. Other times they face toward space to collect data from the universe and the solar system.
Satellite Uses
Satellites can collect more data, more quickly than instruments present on the ground.
The satellites also can see into space better than telescopes at planet Earth's surface. This is because satellites usually fly above the clouds and the dust and molecules in the atmosphere that can block the view from ground level.
Before satellites TV signals didn't go very far. The TV signals only travel in line which is straight. So they would quickly trail off into space instead of following the Earth's curve. Mountains or tall buildings would block them. Phone calls to places which are faraway were also a problem. The setting up of wires of telephone over long distances or underwater is difficult and costs a lot.
With satellites, the signals of TV and phone calls are sent upward to a satellite. Then almost instantly the satellite can send them back down to different locations on Earth.
Satellites Launched into Space
On 4 October 1957, the Soviet Union Russia launched the world's first artificial satellite named Sputnik 1. Since then there are 8,900 satellites from more than 40 countries have been launched. According to the estimates of 2018, there are some 5,000 remaining in orbit. Of those who are about 1,900 were operational while the rest have exceeded their useful lives and become debris space.
In terms of countries with the most satellites, the country USA has the most with 859 satellites. China is said to be the second with 250 and Russia third with 146. These are then followed by India at 118, Japan at 72 and the UK at 52.
A few large stations of space including the International Space Station has been launched in parts and then it is assembled in orbit. Over a dozen probes of space have been placed into orbit around other bodies and become artificial satellites of the Moon, and Mercury, Venus, Mars, Jupiter, Saturn, a few asteroids, a comet and the Sun.
FAQs on Satellites: Composition, Functions & Types in Physics
1. What is a satellite in the context of physics?
In physics, a satellite is any object that is in orbit around a larger object (a primary body) due to the force of gravity. Satellites can be categorised into two main types: natural satellites, such as the Moon orbiting the Earth, and artificial satellites, which are human-made objects launched into orbit for specific purposes.
2. What are the main components that make up an artificial satellite?
An artificial satellite is a complex system composed of several essential parts. The main components include:
The Bus: This is the structural frame of the satellite, which holds all the components together.
Power System: Typically consists of solar panels to generate electricity from sunlight and rechargeable batteries to store power for when the satellite is in Earth's shadow.
Communication System: Includes antennas and transponders to receive signals from and transmit data back to Earth.
Attitude Control System: This system keeps the satellite correctly oriented in space, ensuring its antennas point towards Earth and its solar panels face the Sun.
Payload: This refers to the specific equipment the satellite carries to perform its mission, such as cameras, sensors, or scientific instruments.
3. What are the different types of satellites based on their function?
Satellites are classified based on their intended mission. The most common types include:
Communications Satellites: Used for telecommunications, television broadcasting, and providing internet services (e.g., Intelsat, Starlink).
Navigation Satellites: Form constellations to provide precise location and time information for Global Positioning Systems (GPS).
Earth Observation Satellites: Monitor the planet for environmental changes, mapping, and surveillance (e.g., Landsat series).
Weather Satellites: Help in forecasting weather by monitoring cloud patterns, temperature, and atmospheric conditions.
Astronomical Satellites: Function as space-based telescopes to observe distant planets, galaxies, and other celestial objects without atmospheric interference (e.g., Hubble Space Telescope).
4. What are the primary functions and importance of satellites in modern life?
Satellites are vital to modern technology and science, serving several crucial functions:
Global Communication: They enable long-distance telephone calls, television broadcasts, and internet access across the globe.
Navigation and Positioning: Systems like GPS rely entirely on satellites for accurate location tracking for vehicles, ships, and aircraft.
Weather Forecasting: They provide essential data for accurate weather prediction and tracking of storms, cyclones, and other natural disasters.
Scientific Research: Satellites collect data about Earth's climate, oceans, and atmosphere, as well as observe the universe, expanding our scientific understanding.
Remote Sensing: They are used in agriculture, city planning, and managing natural resources by providing detailed imagery of the Earth's surface.
5. How does a satellite stay in orbit and not fall back to Earth?
A satellite stays in orbit by maintaining a delicate balance between two forces: its forward velocity (or inertia) and the gravitational pull of the Earth. The satellite is launched with a very high tangential speed. While Earth's gravity constantly pulls the satellite downwards, its high forward speed ensures that as it falls, the Earth's surface curves away beneath it at the same rate. This continuous state of 'falling around the Earth' is what constitutes an orbit. If it were to slow down, gravity would win, and it would fall back; if it were to speed up too much, it would escape Earth's gravity altogether.
6. What is orbital velocity and why is it crucial for a satellite?
Orbital velocity is the specific, constant speed that a satellite must have to maintain a stable orbit around a celestial body like Earth. This velocity is crucial because it directly determines the stability and altitude of the orbit. If the satellite's velocity is less than the required orbital velocity, it will be unable to counteract gravity and will spiral back towards Earth. Conversely, if its velocity significantly exceeds the orbital velocity and reaches the escape velocity, it will overcome Earth's gravitational pull and fly off into space. Thus, achieving the precise orbital velocity is fundamental for a satellite's mission success.
7. Why are geostationary satellites placed at a specific altitude directly above the equator?
A geostationary satellite must appear stationary from a point on Earth's surface. This is achieved by meeting two strict conditions:
Orbital Period: Its orbital period must be exactly 24 hours, matching the rotational period of the Earth. According to the laws of physics, this specific period is only possible at a precise altitude of approximately 35,786 kilometres above the Earth's surface.
Equatorial Orbit: The orbit must be in the same plane as the equator. This ensures that the satellite moves in sync with the Earth's rotation without drifting north or south. This fixed position is essential for applications like TV broadcasting, where ground antennas must remain pointed at the satellite constantly.
8. What is the fundamental difference between a natural satellite and an artificial satellite?
The fundamental difference lies in their origin and purpose. A natural satellite, like the Earth's Moon, is a celestial body formed through natural processes and orbits a larger body due to gravity. It does not have a human-defined purpose. In contrast, an artificial satellite is a human-made machine, constructed from materials like metals and composites, and deliberately launched into orbit to perform specific tasks such as communication, navigation, or scientific observation.
