What is Satellites: Definition and 176 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. D

    Why can't satellites be equipped with radar systems so that they can detect (and then avoid) impending collisions?

    Why can't satellites be equipped with radar systems so that they can detect (and then avoid) impending collisions?
  2. A

    I Very bright geo satellite in my night sky?

    Something strange! There is a very bright geostationary satellite visible in our nigh sky quite recently. It was there at 10 pm and was there at 6am at the same position which means it is stationary above a fixed position relative to the earth. But the internet says we cannot see geostationary...
  3. halfapizza

    How Does Satellite Technology Intersect with Ham Radio Experience?

    I'm an electrical engineer of 35 years. I've been in multiple industries, but now work with satellites, LEO specifically. I'm also a Ham Radio operator, AC7DN. My favorite quote is from Leonardo daVinci - "Simplicity is the ultimate sophistication."
  4. berkeman

    B Exploring Attitude Control of Satellites & ISS

    I tried a Google search on this question, and got mixed results. I was curious if satellites (and the ISS) have to burn power to stay pointed at Earth, or if any were able to use passive tidal locking instead. I did find that satellites in geosychronous orbit are less likely to use tidal...
  5. Amaterasu21

    I Why are Saturn's moons so bright?

    Hi all, In the Jovian system, Callisto is extremely dark (albedo 0.22) because its ancient surface is covered with meteoritic dust. Ganymede is brighter (albedo 0.43) as its surface has been resurfaced more recently and hasn't had as much time to accumulate dust; that's confirmed by the younger...
  6. J

    B Gas planets with solid satellites

    I assume that planets and their satellites are created more or less at the same time. Why gaseous planets like Saturn have solid rings and satellites?
  7. H

    Which sub-forum would be suitable for asking Q. related to rockets?

    If I need to ask doubts about very basics of rockets and satellites, for example about what basically Ramjet and Scramjet are, which sub-forum should be suitable.
  8. MiSTSiM

    Given two Earth satellites, A and B, find the potential energy/kinetic energy

    = -3.7298538168*10^13, -2.0594767123*10^13 Ive tried this equation with both masses and my homework keeps coming back with the wrong answer. I've tried checking my arithmetic but I cannot find anything wrong with it please help haven't gotten the chance to try B but I am pretty sure it will be...
  9. P

    B What gives satellites their tangential velocity?

    What gives satellite a tangential velocity?
  10. L

    Next Generation CMB satellites?

    Hi,this one as my new guy post! Any news on the next generation satellite?NASA?
  11. H

    B Extraterrestrial Object Orbits

    I am thinking about an extraterrestrial object like Oumuamua but say volume 750 E+9 (=750,000,000,000 I think but not sure of density although not solid rock) that takes orbit near Space to Earth. 1. Would the magnetic field of this object disturb the balance of local orbits or operation of...
  12. guyvsdcsniper

    Geosynchronous Satellites: Distance & Formula Analysis

    My work is attached. I did get the answer right using the formula V=√(G*me/r). Im just confused as to why I can't use V=2pi*r/T to also get the right answer? With this equation I would assume T=86400s. I was able to use both equations to get the correct answer for a problem relating to...
  13. DaveE

    The Unwise Idea of Wooden Satellites

    I can't even count how many reasons this is a stupid idea. But then, what do I know? https://gizmodo.com/japanese-researchers-are-making-wooden-satellites-becau-1845967973?fbclid=IwAR1Gf70ByB991GnkkDxSetcsgWyW8sJ81-JMHjl3_j65KKEh9kYry2-32Gs
  14. S

    What effect will SpaceX's 42K satellites have on astrononical viewing?

    There has to got to be some effect.
  15. checkerboard

    When do I include the Earth's radius in questions involving satellites?

    The answer is 5.29 x 10^3N and I used r=7 380 000m to get it. However, in a different question like this one "If the mass of Earth is 5.98 x 10^24kg and the radius is 6.38 x10^6m, the gravitational potential energy of a 1.2x 10^3-kg satellite located in an orbit 230 km above the surface of Earth...
  16. M

    Investigating Motion of Rockets & Satellites: Advanced Mechanics Depth Study

    Homework Statement: Hi, I just got my first year 12 assignment which is a depth study of advanced mechanics. I had one idea of investigating the motion of rockets and satellites. I could even do something with circular motion or projectile motion, taking air resistance into consideration. I...
  17. L

    Are these birds, planes or satellites, or meteors?

    Dear experts, What are these things (dozens of them): Are these birds, planes or satellites, or meteors? Has anyone seen anything like these?
  18. S

    Ka vs. Ku communication satellites

    Hi, I’ve heard Ku communication satellites have a broader coverage while Ka satellites only support spot beams. Is it correct? Senmeis
  19. S

    SpaceX's 5K Satellites: A Risk of Man-Made Meteors?

    I was reading about SpaceX wanting to put up 5K satellites, with these put in a low enough orbit that they would need to be periodically boosted to stay up, and simply falling out of the sky within a few months if they malfunction or run out of fuel. This makes me wonder about how small a...
  20. O

    Area covered on Earth by geostationary satellites

    My question is, given that the height of geostationary satellite to be 35786 Km and radius of about 6378km determine the area covered by a geostationary satellite Or deteremine minimum number of geostationary satellites requires to cover whole earth. Regards thanks a bunch :)
  21. mfb

    SpaceX Starlink launch - first 60 satellites

    Starlink launch in 20.5 hours, live coverage here. 80% chance that the weather will be good, backup launch date is the following day. The deployment of the satellites could be very interesting.A lot of new information about Starship: They are building two of them - one in Texas (that one was...
  22. J

    B Earth Orbits of Geostationary Satellites

    Do geostationary satellites move with the Earth's orbit or do they not move at all?
  23. M

    Two manned satellites approaching one another

    Homework Statement I have tried this several times, though I am going wrong someplace along the way. I have tried using these equations below but I cannot seem to get anywhere with it. I left the attempts below so that you may see what I have done, and maybe someone can tell me what I am doing...
  24. S

    Kinetic energy and momentum of two satellites colliding

    Homework Statement Two satellites in space collide inelastically. What happens to the kinetic energy and momentum? a. both are conserved b. KE conserved but momentum reduced c. KE reduced but momentum conserved d. both are reduced e. KE reduced but momentum increased Homework Equations elastic...
  25. Scott Ryals

    I Repurposing Satellites: Maximizing the Lifespan of Space Technology

    With the new blackjack spy sats coming, what happens to the existing ones? Could they be repurposed for astronomy?:
  26. H

    I Do trojan satellites follow migrating planets?

    Some or all of the planets are thought to have migrated long ago under the gravitational influence of Jupiter. Would the trojan matter at their L4 and L5 points have followed during their migration to new orbits? In other words, while the L4 and L5 points are approaching or receding from the...
  27. F

    Solar radiation for the stabilization of satellites?

    Hi, I'm new here. I have a doubt regarding solar radiation, I heard in an astronomy class on the use of this solar radiation for the stabilization of satellites in orbit due to mechanical problems with their stabilizers. Electromagnetic waves emitted through solar radiation stabilize such a...
  28. YMMMA

    Physics: Circular motion and the orbital speeds of satellites

    Homework Statement Satellite 1 has mass m1 & radius R1 and satellite 2 has mass m2 and radius 2R1 Which satellite’s speed is greater? Question and my attempt are shown in the attached file. Homework Equations V= √GM/R The Attempt at a Solution I am not sure if my steps are correct, but if...

    Launching satellites using electromagnet power

    Why can't we launch satellite by using electromagnet power?
  30. W

    B Why don't man-made satellites drift away from the Earth?

    What is the difference between man-made satellites and the moon that causes the former to drift towards the Earth but the latter drift away?
  31. Merlin3189

    Iridium flares end with replacement satellites

    For a long time I'd heard about Iridium flares, but not taken much trouble to see one. This week I took advantage of the uncommon spell of clear nights to pop out and look at a couple. Not quite what I'd expected, so I went to look into them a little more. One of the things I discovered is...
  32. A Alex P

    I Are Stars and Planets Differentiated by Nuclear Processes in the Solar System?

    In solar system, we have sun and planets revolving around it. We have satellites orbiting around some of planets. Are all of these are same thing, just differentiated on the basis of size and nuclear processes occurring inside them? I mean, if nuclear processes occurring inside their core its a...
  33. A

    Satellites and the Earth's Magnetic Field

    So i was just wondering if a satellite's circuitry could be affected by the Earth's own magnetic field inducing a current, if it was moving through it quickly enough (the space station for example), and how it might mess with it? Also considering a satellite is a big hunk of metal, could passing...
  34. RUTA

    Insights The Schwarzschild Metric: Part 1, GPS Satellites - Comments

    Greg Bernhardt submitted a new PF Insights post The Schwarzschild Metric: Part 1, GPS Satellites Continue reading the Original PF Insights Post.
  35. I

    B We could lose electricity and satellites due to solar flares

    Hello, all! I found several sources which say that humanity could be in trouble because of solar flares! Scientists said that the Earth could be hit by solar flare within the next 100 years! Current costs of repair in the US could be up to 2.5 trillion dollars! It seems like Sun will punish...
  36. C

    B Uranus's Moon Cressida is Doomed

    The first measurement of the mass of a small Uranian moon suggests it will be obliterated by smashing into another moon in a mere million years. By Ken Croswell Full story: New Scientist
  37. V

    Calculus in the velocity and acceleration of satellites.

    Homework Statement I am working on a project dealing with the velocity and acceleration of satellites based on their distance from Earth. I was recommended to include some calculus in this project. Originally I thought I could just take the derivative of the orbital speed equation to find...
  38. N

    I Why is time dilation not symmetric for satellites and Earth?

    Hello, I read that satellites is effected by the time dilation caused by gravity and also by that one from special relativity. And so there is a need to prepare the onboard clock to ensure that the time is synchronized with a clock on Earth. But why is this effect not symmetric? The...
  39. I

    B If Earth moves at 500,000 mph then why don't satellites stay behind?

    If Earth moves at 500,000 MPH then why don't satellites get left behind? The solar system is orbiting the galaxy's central black hole, so, if you push a satellite in 1 direction while it attracts to Earth it will orbit Earth but should be left behind big time still. Also, if we were to place...
  40. C

    B Uranus May Have Two Dark Unseen Moons

    And astronomers will be examining Hubble data to try and find them. Full story at New Scientist
  41. M

    A Need help with satellite navigation? Any textbook recommendations?

    Hey guys, looking to get some advice on satellite navigation. Can anyone recommend a nice textbook covering Newton, Kepler, Lagrange etc and their contributions to orbital motion. Also any textbooks on MATLAB or Maple examples of orbits - relativistic or Newtonian it doesn't matter. Not put off...
  42. petrushkagoogol

    A Could Earth Support Two Moons in Different Orbits?

    Could we have a stable gravitational system with 2 Moons : * In the same orbit * In different orbits ? :wideeyed:
  43. O

    A satellite, the sun and the satellites heat protector

    Homework Statement A spacecraft is protected from the Sun’s radiation by a planar baffle whose size is much greater than that of the spacecraft itself. The baffle is aligned perpendicular to the direction of the Sun. Show that the equilibrium temperature of the baffle is...
  44. i_hate_math

    Satellites Orbits and Energy Problem

    Homework Statement Two small spaceships, each with mass m = 2000 kg, are in the circular Earth orbit of the figure, at an altitude h of 440 km. Igor, the commander of one of the ships, arrives at any fixed point in the orbit 81.0 s ahead of Picard, the commander of the other ship. What are the...
  45. S

    Is 4G LTE Compatible with Satellites?

    Hi,can 4G LTE be used on LEO satellites to provide a base station on space?Senmeis
  46. M

    How often do satellites pass the moon?

    So, I have really no background in astrophysics (other than touching on some areas in general physics and calculus). I understand that asking questions such as the one in my title, that I would need to be more specific, and I will attempt to be as specific as I can. I understand that most...
  47. king yasin ally

    Can I Build My Own Deep Space Antenna Network for Receiving Planetary Probes?

    I am trying to build my own communication / listening dish, multi frequency antenna, basically my own deep space antenna network. how to get the needed supply for such endeavour? help with any info on this, a new field for me. thanks!
  48. mfb

    SpaceX SpaceX: First stage landed Satellites in orbit

    A great launch, everything worked as expected, delivering 11 OrbComm satellites to Earth orbit (they all got deployed in the minutes after reaching orbit). But that was the routine part... although it was the first flight of an improved version of Falcon 9 1.1 ("Full thrust" version). The first...
  49. Y

    Comparing Total Energy of Satellites in Different Orbits: Magnitude vs. Sign?

    Homework Statement If two satellites A and B are orbiting the Earth out of which A is closer to the Earth then the total energy of which Earth plus satellite system is lesser?Homework EquationsThe Attempt at a Solution Should I consider only the magnitude while comparing using the formula total...
  50. Y

    Two satellites A and B move around earth in a circular orbit

    Two satellites A and B move around Earth in a circular orbit. The mass of B is twice the mass of A then I agree that kinetic energy of B is greater than that of A. But what I couldn't understand was that why are speeds of A and B equal as given in the book. Shouldn't they differ according to the...