What is Satellite: Definition and 685 Discussions

In the context of spaceflight, a satellite is an object that has been intentionally placed into orbit. These objects are called artificial satellites to distinguish them from natural satellites such as Earth's Moon.
On 4 October 1957, the Soviet Union launched the world's first artificial satellite, Sputnik 1. Since then, about 8,900 satellites from more than 40 countries have been launched. According to a 2018 estimate, about 5,000 remained in orbit. Of those, about 1,900 were operational, while the rest had exceeded their useful lives and become space debris. Approximately 63% of operational satellites are in low Earth orbit, 6% are in medium-Earth orbit (at 20,000 km), 29% are in geostationary orbit (at 36,000 km) and the remaining 2% are in various elliptical orbits. In terms of countries with the most satellites, the United States has the most with 1,897 satellites, China is second with 412, and Russia third with 176.
A few large space stations, including the International Space Station, have been launched in parts and assembled in orbit. Over a dozen space probes have been placed into orbit around other bodies and become artificial satellites of the Moon, Mercury, Venus, Mars, Jupiter, Saturn, a few asteroids, a comet and the Sun.
Satellites are used for many purposes. Among several other applications, they can be used to make star maps and maps of planetary surfaces, and also take pictures of planets they are launched into. Common types include military and civilian Earth observation satellites, communications satellites, navigation satellites, weather satellites, and space telescopes. Space stations and human spacecraft in orbit are also satellites.
Satellites can operate by themselves or as part of a larger system, a satellite formation or satellite constellation.
Satellite orbits vary greatly, depending on the purpose of the satellite, and are classified in a number of ways. Well-known (overlapping) classes include low Earth orbit, polar orbit, and geostationary orbit.
A launch vehicle is a rocket that places a satellite into orbit. Usually, it lifts off from a launch pad on land. Some are launched at sea from a submarine or a mobile maritime platform, or aboard a plane (see air launch to orbit).
Satellites are usually semi-independent computer-controlled systems. Satellite subsystems attend many tasks, such as power generation, thermal control, telemetry, attitude control, scientific instrumentation, communication, etc.

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  1. yashboi123

    The velocity of a satellite rotating around the Earth

    Not sure what r would be in this scenario. I tried adding the radius of the earth to the altitude but that wasn't correct either.
  2. N

    I Newton's Second Law - variable mass case

    Dear Experts. In a problem where we need to calculate the acceleration of a satellite in a force free space which sweeps and collects interplanetary dust and a certain rate (dm/dt), I believe that the equation F = m(dv/dt) + v(dm/dt) can be used, by putting F=0 and substituting the function...
  3. D

    I Atomic clock on the Moon

    I learned recently that there are plans to create a dedicated global satellite navigation system (GNSS) for the Moon, so we will have atomic clocks on and around the Moon, but we have at least one there now, in order to compare it with a clock on Earth? You know about such an experiment and its...
  4. jeffinbath

    Is there a serious risk to airliners from satellite debris 12 miles up?

    More and more satellites will be at the end of their lives over the next few years and falling out of orbit. Is there not a risk to the thousands of high flying airliners if these small objects have still not fully burned up by the time they hit the 12 mile high region do you think?
  5. Z

    I Can a Gyroscope on a Satellite Detect Orbit?

    Einstein said, when describing someone falling off a building, that the Earth accelerating up to meet him/her. Without the Earth getting larger in all directions as the paradox goes, it curvature of space-time which is why you can have the acceleration up without the surface moving up as you...
  6. Jade_lowe

    Calculate the Speed of a Satellite Moving in a Stable Circular Orbit

    V = ? m/s V = D/T V = Square root (6.67 * 10^-11)(m)/r
  7. V

    Satellite mechanics: linear and rotational momentum

    [This is a continuation of OP's thread here: https://www.physicsforums.com/threads/satellite-mechanics-linear-and-rotational-momentum.1046963/ ] satellite mechanics: linear and rotational momentum I'm trying to better understand classical mechanics, and came up with a question: Say we have a...
  8. V

    I Satellite mechanics: linear and rotational momentum

    satellite mechanics: linear and rotational momentum I'm trying to better understand classical mechanics, and came up with a question: Say we have a squared satellite weighting 100kg, 1 meter on each side. it has a thruster on it's side, shown in picture thruster quickly ejects 100g of propellant...
  9. Y

    I How to find RAAN and argument of perigee for a satellite?

    I have some values and by using them I need to find the RAAN and argument of perigee of a satellite. I have the period, inclination, apogee and perigee (as values not vectors), found semi-major axis and the eccentricity, but facing difficulty on how to proceed on calculating RAAN and the...
  10. L

    A satellite in orbit in a system with one planet and two moons

    1) Considering the forces on one of the moons, I have: ##\frac{GMm}{(10R)^2}+\frac{Gm^2}{(20R)^2}=m\frac{v^2}{10R}\Leftrightarrow v=\sqrt{\frac{G}{10R}(M+\frac{m}{4})}.## 2) Considering the initial situation in which the satellite is at rest on the surface of the planet...
  11. S

    Calculate Mass of Satellite: Step-by-Step Guide

    I am not really sure what to do to find the mass of satellite. Equation for orbital speed: $$m \frac{v^2}{r}=G\frac{m_1 . m_2}{r^2}$$ $$v_{orbital}=\sqrt{\frac{GM}{r}}$$ Equation for escape speed: $$KE_1+GPE_1=KE_2+GPE_2$$ I tried to take position 1 as the position where the satellite orbits...
  12. seanscon

    I NMR Remote Sensing: Does US Army Detect Buried Weapons?

    Hi I was watching Generally - you can activate use a strong magnetic field on ground, perturb it, and the pick the signal up with a satellite. The result would be in 60 to 1000 MHz ( VHF Television ) by a satellite. But the post also says, that US army is using it to detect burried weapons...
  13. G

    Satellite orbiting the Earth (heat radiation)

    Mass of a satellite is 750g(##m = \rho V = 8,96 \frac{g}{cm^3}\cdot (\frac{4\pi(100cm)^3}{3} -\frac{4\pi(99,9cm)^3}{3}) = \approx 750g =0,75kg##) I am not sure what to integrate. I solved T there but it seems far stretched $$T =\sqrt[4]{\frac{dQ}{dt}\frac{1}{e\sigma A}} $$ How to get the...
  14. X

    B Could satellite be geo-stationary away from equatorial plane?

    I hope this is okay to ask here. I'm working on a sci-fi short story, and for the purposes of the story I want to have a small ship that maintains its position over a specific location on the Earth's surface. Originally, I thought this would be easy. After all, that's what geostationary...
  15. K

    Ensuring Radio Connectivity on a Newly-Launched Satellite

    Any clue how to make sure that the radio is alive on a satellite that has just reached orbit? Can you transmit at full power although you're not sure whether the satellite antenna is deployed or not? What if you do and the satellite antenna turns out to be stowed? How could you have avoided that...
  16. A

    Dish Antennas C/N Problem

    Summary:: I am stuck on a problem on dish antenna C/N and it's relation to frequency. Please see below for thought process. Problem Statement: , Link budget formula in dB form: Pr = Pt + Gt + Gr + 20*log10(lambda/(4*pi*distance)) - Losses [dB] C/N = Pr - Pn [dB], where Pn = 10*log10(k*T*B)...
  17. PainterGuy

    European data relay satellite system

    Hi, I was watching the following video. So, a low Earth orbit continuously transmits data to a geosynchronous satellite via a laser link. The geosynchronous satellite relays the data to a ground station on Earth via a radio link. In case of European Data Relay System (EDRS) laser...
  18. nicolewreyford

    Doppler shift between a moving ship on the ocean and a satellite in LEO

    Summary:: I would like to calculate the Doppler shift for a signal sent by a moving ship to a moving satellite. I want to calculate the frequency observed by an LEO satellite when a signal is transmitted from a moving ship. The LEO satellite has a velocity of 7120m/s and orbits at a height of...
  19. adammish

    Artificial satellite tension

    Hi, I need to prove that the tension for artificial satellite consists of two points of mass m/2 connected by a light rigid rod of length , the tension in the rod is - $$ T=\frac{3}{4}\frac{Gmm'l}{a^3}-\frac{1}{4}\frac{Gm^2}{l^2} $$ the satellite is placed in a circular orbit of radius a>>l...
  20. binis

    I What is the angular velocity of a satellite?

    Angular velocity ω is by definition the runned angle dθ per time dt elapsed: ω=dθ/dt. If the time elapsed in the center of the Earth is dt, the dilated time elapsed on satellite is dt′. What is the satellite's angular velocity? Is it dθ/dt or dθ/dt′?
  21. Tone L

    Satellite Failure: Environmental Causes & Triggers

    I was thinking this past morning of the challenger explosion due to the stiff and cold failed O-rings in the fuel segments. I was trying to think of satellite failures, I couldn't find too much... Do you all know of satellite (components, instruments, etc) failures that occurred while in...
  22. B

    Orbit determination from radar readings of a satellite in orbit

    Hello everyone! This is from The Fundamentals of Astrodynamics Chapter 2 Questions. I'm doing this as a self-study (and never took Linear Algebra) so my "technique" might be a little sloppy 😖😖 Finding specific angular momentum Finding the orbital parameter Finding Eccentricity Vector...
  23. AN630078

    Potential Energy and raising a satellite from Earth into a Circular Orbit

    a. V=-GM/r V=-6.67*10^-11*6.0 x 10^24/6.4 x 10^6 V grav = -62531250 ~ -62.5M Jkg^-1 b. To find the gravitational potential 200 km above the surface of the Earth; r=6.4 x 10^6 +2*10^5 m=6.6*10^6 V grav=-6.67*10^-11*6.0 x 10^24/6.6*10^6 V grav= -60636363 ~ -60.6 M Jkg^-1 Can I check that it is...
  24. S

    A Oddly specific question for help regarding a satellite in a shadow

    Hello fellow Space People, Currently trying to create a function in MATLAB to input an R and V vector and have it spit out all the orbital elements as well as shadow entry/exit locations. I have the Vallado "Fundamentals of Astrodynamics" book and I've used it religiously. I searched on here...
  25. F

    Earth's satellite and its first space speed

    Hello All :) I am a student of mathematics, but I have only one semester of physics in college. I can't solve one with homework. Will there be anyone wise who can solve this? The task is as follows: Calculate: at what height the artificial satellite must move (orbit height): geostationary...
  26. T

    Satellite Orbit Problems

    I just have a question on the problem itself. If I am putting the satellite into orbit 450,000 m above the surface, then would r=6,371,000 m(earth's radius)+450,000 m? And what mass of Earth should I be using, in kg of course.
  27. Y

    Are induced currents of any concern in satellite missions?

    A satellite in an orbit around Earth can be subjected to a changing magnetic field (due to eccentricity or angle of orbit or both) which can induce currents on its envelope. Are these currents negligible or are they of any concern to engineers? Also, as I understand it, the satellites high...
  28. E

    Satellite communications project

    Summary:: Looking for a title and an idea to do a research project on the topic of satellite communications Hello fellow FP, I am in desperate need for an idea to do a project, seminar, call it what you like, on the topic of satellite communications for a course. We covered the basics of...
  29. cwill53

    A Satellite in Circular Orbit

    I know this problem can be solved using energy conservation, but I tried another method that I don't know is correct or not, but yielded a similar result to what my classmates got: $$F_{C}=F_{G}\Rightarrow \frac{mv^{2}}{r}=\frac{GMm}{r^2}$$ $$\frac{v^2}{r}=\frac{Gm}{r^2}\Rightarrow...
  30. G

    Stargazing Satellite grids around other planets

    We send a lot of rovers to Mars, as interesting as the planet could possibly be. But why are we not putting satellite grids around other planets that could transmit superficial probe data at the very least? That along with whatever other prospects satellite grids could possibly bear us. That...
  31. BiggestAfrica

    Gravity problem: determining the period of a satellite in Earth orbit

    Hi! This is a problem from my physics 1 high school course. I've tried using the first and third equations to determine period (answer of 8326.9544s.), however that was incorrect and I never even touched G. I'm not sure where to go from here at all. Any help is appreciated!
  32. B

    Height and Acceleration of a Satellite in Orbit

    a) Eg = Gme/r^2 r = √Gme/Eg r = √[(6.67x10^-11 N*m^2*kg^2)(5.98x10^24 kg)]/(4.5 N/kg) r = 9.41x10^6 m h = r2 - r1 h = 9.41x10^6 m - 6.38x10^6 m h = 3.03x10^6 m that's over 3000 km. Did I not use for right equation? Is Eg not 4.5 N/kg? Also for b), isn't the force of gravity the centripetal...
  33. Andres Padilla

    Problem about orbital mechanics

    I tried it, but I am not getting no of the given answers According to the statement, it is saying that 3 KE (in the orbit ) = ΔUg So, beeing R the radius of the Earth and R2 the radius of the orbit: 3 (1/2)(GMm/r2) = -GMm/r2 - (-GMm/R) Canceling out the GMm: (3/2)(1/r2)= (-1/r2) + (1/R)...
  34. EEristavi

    Universal Gravitation - calculating orbital period of satellite

    I didn't use Kepler's 3rd law and this may be the reason I have a wrong answer. However, I want to know: where I make the mistake. ## ma = \frac {G M m} {R^2}## ## R = (\frac {G M} a)^{1/2}## ##a = \frac {v^2} R## ##V^2 = a R = a (\frac {G M} a)^{1/2} = (G a M)^{1/2}## ##V = (G a M)^{1/4}##...
  35. S

    Two basic questions about satellite communication

    Hi, 1. Is it correct that gateway stations (or teleports?) must be used for spot beam satellite systems? That means, two user terminals cannot communicate directly with each other. 2. Are satellite beacons widely used? Senmeis
  36. S

    I Frozen orbits of the moon

    Quick question for the people to better understand orbital mechanics. Due to large mass concentrations on the moon's surface, there are only four orbital inclinations that a satellite can be at to maintain an indefinite orbit: 27°, 50°, 76°, and 86°. My question is this: If a satellite was...
  37. G

    Satellite Weapons | Dark Rivers of the Heart Spoiler

    Just finished reading Dark rivers of the heart.(SPOILER AHEAD) Personally i found the ending pretty much irrealistic, i don't think that on contemporary tech level, a satellite laser could do any serious harm to a person. However satellites that can identify terrorists and even penetrate the...
  38. mfb

    Satellite internet constellations

    Fast, reliable high-bandwidth internet everywhere in the world - that is the promise of the upcoming satellite constellations. To get a good bandwidth with many customers this needs many satellites; to get a good latency they have to be in low Earth orbit (LEO). Existing satellites providing...
  39. S

    Effect of time dilation on a satellite

    I've got the start of a plot forming in my mind, and I'm wondering if it's likely to be supported by physics at all. My basic understanding: when astronauts go to the International Space Station, due to the speed at which it is travelling, time passes ever-so-slightly slower for them. This...
  40. solarcat

    Where can you not see a satellite

    Homework Statement Where on Earth (what latitude/Longitude) can you not see a geostationary satellite, even if it's in the same hemisphere as you? Homework Equations The height of a geostationary satellite is 35,860,000 meters The radius of Earth is 6,371,000 meters. The Attempt at a...
  41. moonbounce

    (Moonbounce) Can I use moon as a satellite for IOT?

    I am thinking to use the moon as a satellite for my IOT gateway. Let's say I have a gateway that collects data from my sensor nodes but it has no internet access. Using moonbounce(EME), it will send the small data (few bytes) to the moon then reflect it to a ground station with internet...
  42. T

    How much work is done when a satellite is launched into orbit?

    Homework Statement A Satellite is brought up into a geostationary orbit (altitude 35800km measured from the surface of the earth). Satellite weights 1000.0kg. How much work is required to bring satellite from a surface of the Earth to geostationary orbit? Homework Equations Newton's law of...
  43. Zack K

    B Satellite Clocks: General & Special Relativity Time Variations

    Something that crossed my mind recently; I know that satellites have to adjust their clock due to their relativistic time variations in relation to us. I was wondering do they adjust their times in accordance to general relativity or special relativity or both? Or is their speed so insignificant...
  44. S

    Issue in satellite communications as they pass overhead

    Hi, The data sheet of an antenna system can be found at http://www.tcs.la/Portals/0/TCSXY.pdf. This description is taken from it: Our XY pedestal is ideal for tracking satellites in Low-Earth Orbits (LEOS) because it completely eliminates the problem of the overhead keyhole (lost data effect...
  45. Scott Ryals

    Recharge satellite batteries utilizing a ground-based laser?

    Is it feasible to recharge satellite's batteries utilizing a ground-based laser?
  46. shk

    Is the weight of a small satellite in its orbit zero?

    Is the weight of a small satellite in its orbit zero?
  47. alexi_b

    Astronaut forces question

    Homework Statement A 63.8kg spacewalking astronaut pushes off a 678.0kg satellite, exerting a 156.0N force for the 0.870s it takes him to straighten his arms. How far apart are the astronaut and the satellite after 8.67min? Homework Equations The Attempt at a Solution I tried just finding the...
  48. P

    Centripetal Acceleration of Satellite

    Homework Statement Hi, I am stuck on this question: A satellite of mass 1200 kg is in orbit around the Earth at a distance of 22000 km from the centre of the Earth. Calculate the magnitude of the centripetal acceleration of the satellite at this distance. The Attempt at a Solution I did...
  49. N

    I Satellite Orbit synchronization

    Consider a large non-rotating sphere, and one series of satellites, series A, in free fall orbit at the same velocity and altitude slightly above its "equator" going from east to west. Forming a ring in which all the satellites are equal distance apart, and another series of satellites, series...
  50. Romka

    I How to determine the center of gravity of a satellite

    Hello, I am trying to find out how to determine the center of gravity of a CubeSat present in an uniform sphere of radius R, using the initial data given by gyroscopes. The satelitte is equipped with magnetometers, gyroscopes, and accelerometers. By taking into account that the only values I...