Satellite
A satellite or artificial satellite
Except for
Satellites are placed from the surface to the orbit by launch vehicles, high enough to avoid orbital decay by the atmosphere. Satellites can then change or maintain the orbit by propulsion, usually by chemical or ion thrusters. As of 2018, about 90% of the satellites orbiting the Earth are in low Earth orbit or geostationary orbit; geostationary means the satellites stay still in the sky (relative to a fixed point on the ground). Some imaging satellites chose a Sun-synchronous orbit because they can scan the entire globe with similar lighting. As the number of satellites and space debris around Earth increases, the threat of collision has become more severe. A small number of satellites orbit other bodies (such as the Moon, Mars, and the Sun) or many bodies at once (two for a halo orbit, three for a Lissajous orbit).
The first artificial satellite launched into the Earth's orbit was the Soviet Union's Sputnik 1, on October 4, 1957. As of December 31st 2022, there are 6,718 operational satellites in the Earth's orbit, of which 4,529 belong to the United States (3,996 commercial), 590 belong to China, 174 belong to Russia, and 1,425 belong to other nations.[1]
History
Early proposals
The first published mathematical study of the possibility of an artificial satellite was Newton's cannonball, a thought experiment by Isaac Newton to explain the motion of natural satellites, in his Philosophiæ Naturalis Principia Mathematica (1687). The first fictional depiction of a satellite being launched into orbit was a short story by Edward Everett Hale, "The Brick Moon" (1869).[2][3] The idea surfaced again in Jules Verne's The Begum's Fortune (1879).
In 1903,
In a 1945
In May 1946, the
In 1946, American theoretical astrophysicist Lyman Spitzer proposed an orbiting space telescope.[8]
In February 1954, Project RAND released "Scientific Uses for a Satellite Vehicle", by R. R. Carhart.[9] This expanded on potential scientific uses for satellite vehicles and was followed in June 1955 with "The Scientific Use of an Artificial Satellite", by H. K. Kallmann and W. W. Kellogg.[10]
First satellites
The first artificial satellite was
In the context of activities planned for the International Geophysical Year (1957–1958), the White House announced on 29 July 1955 that the U.S. intended to launch satellites by the spring of 1958. This became known as Project Vanguard. On 31 July, the Soviet Union announced its intention to launch a satellite by the fall of 1957.
Sputnik 2 was launched on 3 November 1957 and carried the first living passenger into orbit, a dog named Laika.[11]
In early 1955, after being pressured by the
In June 1961, three and a half years after the launch of Sputnik 1, the United States Space Surveillance Network cataloged 115 Earth-orbiting satellites.[15] Astérix or A-1 (initially conceptualized as FR.2 or FR-2) is the first French satellite. It was launched on 26 November 1965 by a Diamant A rocket from the CIEES launch site at Hammaguir, Algeria. With Astérix, France became the sixth country to have an artificial satellite and the third country to launch a satellite on its own rocket
France is the third country to launch a satellite on its own rocket, the Astérix, on 26 November 1965 by a Diamant A rocket from the CIEES launch site at Hammaguir, Algeria.
Early satellites were built to unique designs. With advancements in technology, multiple satellites began to be built on
Later Satellite Development
After the late 2010s, and especially after the advent and operational fielding of large
By the early 2000s, and particularly after the advent of
In different periods, many countries, such as Algeria, Argentina, Australia, Austria, Brazil, Canada, Chile, China, Denmark, Egypt, Finland, France, Germany, India, Iran, Israel, Italy, Japan, Kazakhstan, South Korea, Malaysia, Mexico, the Netherlands, Norway, Pakistan, Poland, Russia, Saudi Arabia, South Africa, Spain, Switzerland, Thailand, Turkey, Ukraine, the United Kingdom and the United States, had some satellites in orbit.[22]
Japan's space agency (JAXA) and NASA plan to send a wooden satellite prototype called LingoSat into orbit in the summer of 2024. They have been working on this project for few years and sent first wood samples to the space in 2021 to test the material's resilience to space conditions. [23]
Components
Orbit and altitude control
Most satellites use chemical or
Chemical thrusters on satellites usually use
Power
Most satellites use
Communications
Applications
Earth observation
Earth observation satellites are designed to monitor and survey the Earth, called remote sensing. Most Earth observation satellites are placed in low Earth orbit for a high data resolution, though some are placed in a geostationary orbit for an uninterrupted coverage. Some satellites are placed in a Sun-synchronous orbit to have consistent lighting and obtain a total view of the Earth. Depending on the satellites' functions, they might have a normal camera, radar, lidar, photometer, or atmospheric instruments. Earth observation satellite's data is most used in archaeology, cartography, environmental monitoring, meteorology, and reconnaissance applications.[citation needed] As of 2021, there are over 950 Earth observation satellites, with the largest number of satellites operated with Planet Labs.[25]
Communication
A
Spy satellites
When an Earth observation satellite or a communications satellite is deployed for military or intelligence purposes, it is known as a spy satellite or reconnaissance satellite.
Its uses include early missile warning, nuclear explosion detection, electronic reconnaissance, and optical or radar imaging surveillance.
Navigational satellites are satellites that use radio time signals transmitted to enable mobile receivers on the ground to determine their exact location. The relatively clear line of sight between the satellites and receivers on the ground, combined with ever-improving electronics, allows satellite navigation systems to measure location to accuracies on the order of a few meters in real time.
Telescope
Experimental
Weapon
Since the mid-2000s, satellites have been hacked by militant organizations to broadcast propaganda and to pilfer classified information from military communication networks.
Environmental Impact
The environmental impact of satellites is not currently well understood as they were previously assumed to be benign due to the rarity of satellite launches. However, the exponential increase and projected growth of satellite launches are bringing the issue into consideration. The main issues are resource use and the release of pollutants into the atmosphere which can happen at different stages of a satellite's lifetime.
Resource use
Resource use is difficult to monitor and quantify for satellites and launch vehicles due to their commercially sensitive nature. However, aluminium is a preferred metal in satellite construction due to its lightweight and relative cheapness and typically constitutes around 40% of a satellite's mass.[36] Through mining and refining, aluminium has numerous negative environmental impacts and is one of the most carbon-intensive metals.[37] Satellite manufacturing also requires rare elements such as lithium, gold, and gallium, some of which have significant environmental consequences linked to their mining and processing and/or are in limited supply.[38][39][40] Launch vehicles require larger amounts of raw materials to manufacture and the booster stages are usually dropped into the ocean after fuel exhaustion. They are not normally recovered.[38] Two empty boosters used for Ariane 5, which were composed mainly of steel, weighed around 38 tons each,[41] to give an idea of the quantity of materials that are often left in the ocean.
Launches
Rocket launches release numerous pollutants into every layer of the atmosphere, especially affecting the atmosphere above the
Rocket emissions in the stratosphere and their effects are only beginning to be studied and it is likely that the impacts will be more critical than emissions in the troposphere.[38] The stratosphere includes the ozone layer and pollutants emitted from rockets can contribute to ozone depletion in a number of ways. Radicals such as NOx, HOx, and ClOx deplete stratospheric O3 through intermolecular reactions and can have huge impacts in trace amounts.[42] However, it is currently understood that launch rates would need to increase by ten times to match the impact of regulated ozone-depleting substances.[45][46] Whilst emissions of water vapour are largely deemed as inert, H2O is the source gas for HOx and can also contribute to ozone loss through the formation of ice particles.[45] Black carbon particles emitted by rockets can absorb solar radiation in the stratosphere and cause warming in the surrounding air which can then impact the circulatory dynamics of the stratosphere.[47] Both warming and changes in circulation can then cause depletion of the ozone layer.
Operational lifetime
LEO Satellites
Several pollutants are released in the upper atmospheric layers during the orbital lifetime of LEO satellites. Orbital decay is caused by atmospheric drag and to keep the satellite in the correct orbit the platform occasionally needs repositioning. To do this nozzle-based systems use a chemical propellant to create thrust. In most cases hydrazine is the chemical propellant used which then releases ammonia, hydrogen and nitrogen as gas into the upper atmosphere.[42] Also, the environment of the outer atmosphere causes the degradation of exterior materials. The atomic oxygen in the upper atmosphere oxidises hydrocarbon-based polymers like
Night sky
Given the current surge in satellites in the sky, soon hundreds of satellites may be clearly visible to the human eye at dark sites. It is estimated that the overall levels of diffuse brightness of the night skies has increased by up to 10% above natural levels.[49] This has the potential to confuse organisms, like insects and night-migrating birds, that use celestial patterns for migration and orientation.[50][51] The impact this might have is currently unclear. The visibility of man-made objects in the night sky may also impact people's linkages with the world, nature, and culture.[52]
Ground-based infrastructure
At all points of a satellite's lifetime, its movement and processes are monitored on the ground through a network of facilities. The environmental cost of the infrastructure as well as day-to-day operations is likely to be quite high,[38] but quantification requires further investigation.
End of life
When satellites reach the end of life they are intentionally deorbited or moved to a graveyard orbit further away from Earth in order to reduce space debris. Physical collection or removal is not economical or even currently possible. Moving satellites out to a graveyard orbit is also unsustainable because they remain there for hundreds of years.[38] It will lead to the further pollution of space and future issues with space debris. When satellites deorbit much of it is destroyed during re-entry into the atmosphere due to the heat. This introduces more material and pollutants into the atmosphere.
Pollution and interference
Issues like space debris, radio and light pollution are increasing in magnitude and at the same time lack progress in national or international regulation.[55][54] Space debris pose dangers to the spacecraft[56][57] (including satellites)[57][58] in or crossing geocentric orbits and have the potential to drive a Kessler syndrome[59] which could potentially curtail humanity from conducting space endeavors in the future.[60][61]
With increase in the number of satellite constellations, like SpaceX Starlink, the astronomical community, such as the IAU, report that orbital pollution is getting increased significantly.[62][63][64][65][66] A report from the SATCON1 workshop in 2020 concluded that the effects of large satellite constellations can severely affect some astronomical research efforts and lists six ways to mitigate harm to astronomy.[67][68] The IAU is establishing a center (CPS) to coordinate or aggregate measures to mitigate such detrimental effects.[69][70][71]
Some notable satellite failures that polluted and dispersed radioactive materials are Kosmos 954, Kosmos 1402 and the Transit 5-BN-3.
Generally liability has been covered by the
Due to the low received signal strength of satellite transmissions, they are prone to jamming by land-based transmitters. Such jamming is limited to the geographical area within the transmitter's range. GPS satellites are potential targets for jamming,[73][74] but satellite phone and television signals have also been subjected to jamming.[75][76]
Also, it is very easy to transmit a carrier radio signal to a geostationary satellite and thus interfere with the legitimate uses of the satellite's transponder. It is common for Earth stations to transmit at the wrong time or on the wrong frequency in commercial satellite space, and dual-illuminate the transponder, rendering the frequency unusable. Satellite operators now have sophisticated monitoring tools and methods that enable them to pinpoint the source of any carrier and manage the transponder space effectively. [citation needed]
See also
- High-altitude platform station
- Solar aircraft
- Satellite refuelling
Notes
- natural satellites.
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External links
- Satellite at Curlie
- EO Portal directory Archived 23 September 2013 at the Wayback Machine