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jms4
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What is the lowest altitude for a satellite to orbit?
Single, un-boosted, complete (though decayed) revolution?DaveC426913 said:boosting continually
Based on the data for Tiangong-1, the orbital decay gets that severe right about 140 km. The graph of altitude versus time gets steep there at the end.Bystander said:Single, un-boosted, complete (though decayed) revolution?
It looks steep based on the scale, but it is only losing about 1-2 km per orbit at that point, which is slower than walking speed (it's about 0.4 m/s). Google tells me an ISS orbit maintenance burn might be 1.3 m/s delta-V over 12 minutes (not sure how typical that is). Yes, if you burned continuously you'd run out of fuel fast, but in terms of the decay rate, at that point it was only about 5% of what a continuous burn could reverse in one orbit.jbriggs444 said:Based on the data for Tiangong-1, the orbital decay gets that severe right about 140 km. The graph of altitude versus time gets steep there at the end.
http://www.satflare.com/track.asp?q=37820#TOP
You're being generous.russ_watters said:This is common fodder for sci-fi movies
I did check that page, and It doesn't say anything about it, only examples of low Earth orbiting satellites like ISSjim mcnamara said:Can you clarify a bit?
Does the orbit have to be stable?
Did you try google first? I did:
https://en.wikipedia.org/wiki/Low_Earth_orbit
Thank you, but at what altitude will it be stable, like it requires extremely low amount of boostingDaveC426913 said:Virtually any satellite in LEO is slowed by friction with rarefied atmosphere, causing it to lose altitude. They need the ability to boost themselves back up occasionally.
How low an orbit can be depends on how broadly you apply the term 'occasionally'.
At some altitude, its speed will be slowed so much that it needs to boost continually, just to stay at altitude.
In practical terms this too has a limit, due to a limited supply fuel as well as friction/shock heating destroying the craft.
Presumably, if boosting continually, it should no longer be considered 'orbiting'.
altitude where boosting is required very little far lower than the ISS for exampleBystander said:Single, un-boosted, complete (though decayed) revolution?
jms4 said:Thank you, but at what altitude will it be stable, like it requires extremely low amount of boosting
The ISS requires monthly boosting. Does that satisfy "extremely low" or "very little"? Feels like a fair amount to me...jms4 said:altitude where boosting is required very little far lower than the ISS for example
I'm sorry if I'm being unfair, i just need an approximate value of range like periodic monthly boosting or something, so I could put in a minor part of project, not serious, so don't spend too much time thinking about it, but thank you anyway for helping out.Vanadium 50 said:I don't think you're being fair to us. You seem to want an exact answer from us, but are only willing to vaguely specify the problem. "altitude where boosting is required very little" and "extremely low amount of boosting". How long is a piece of string?
The Wikipedia article has examples. You're not going to do any better than that.
Ok, fine that is fair enough for me, thank you.russ_watters said:The ISS requires monthly boosting. Does that satisfy "extremely low" or "very little"? Feels like a fair amount to me...
This article is light on numbers but does mention the use of ion thrusters at an altitude of 235 km. https://en.wikipedia.org/wiki/Orbital_station-keepingjms4 said:I'm sorry if I'm being unfair, i just need an approximate value of range like periodic monthly boosting or something, so I could put in a minor part of project, not serious, so don't spend too much time thinking about it, but thank you anyway for helping out.
That seems like a great application for in engines; I hadn't heard that had been done.jbriggs444 said:This article is light on numbers but does mention the use of ion thrusters at an altitude of 235 km. https://en.wikipedia.org/wiki/Orbital_station-keeping
For a smooth planet with no atmosphere, yes.Kyle Gonterwitz said:Is this a trick question? I think the lowest possible altitude of a satellite orbiting the Earth would be just above sea level. The satellite would have to achieve escape velocity, have thrust available to overcome drag, and have to be able to navigate around landmasses, but technically that should qualify as a satellite in orbit.
Post #13 clarifies the purpose of the question. It is a practical matter -- roughly how high does one need to go so that the station keeping requirements are manageable.Kyle Gonterwitz said:Is this a trick question?
Yes. The ISS for example is particularly draggy and a google/eye all tells me it is much worse, losing about 7m/orbit or accelerating at 14m/s/orbit.glappkaeft said:And even if you can find a number for one satellite, the answer for other satellites depends on the orientation of that satellite and drag vs mass in that orientation.
And even for the same satellite, varying solar activity can have an effect on the Earth's atmosphere, which will cause the drag to change.glappkaeft said:And even if you can find a number for one satellite, the answer for other satellites depends on the orientation of that satellite and drag vs mass in that orientation.
I don't understand where you are going with this. What is practical? We have craft operating at 60,000 or even 160,000 feet, but they don't use orbital mechanics to stay aloft, they use normal aerodynamic lift or buoyancy. Craft that rely primarily on orbital mechanics to stay aloft are not possible in that altitude range for a couple of reasons: they'd quickly burn up or run out of fuel.Kyle Gonterwitz said:Flight level 600 is at 60,000 ft which is the upper boundary of controlled airspace, that would be the practical, lowest possible altitude. Search for the relationship between altitude and atmospheric pressure to find that relationship, then go as high as needed to optimize a design based on propulsion energy needed to achieve the desired altitude at orbital/escape velocity with minimum thrust to overcome atmospheric density/drag for the duration of the mission.
I am in complete agreement but we can say that the stratopause is about the lowest we can have a LEO satellite.DaveC426913 said:Virtually any satellite in LEO is slowed by friction with rarefied atmosphere, causing it to lose altitude. They need the ability to boost themselves back up occasionally.
How low an orbit can be depends on how broadly you apply the term 'occasionally'.
At some altitude, its speed will be slowed so much that it needs to boost continually, just to stay at altitude.
In practical terms this too has a limit, due to a limited supply fuel as well as friction/shock heating destroying the craft.
Presumably, if boosting continually, it should no longer be considered 'orbiting'.
As previously pointed out, if it is continually thrusting - whether to maintain altitude or overcome drag - then it can't be considered 'orbiting'.Kyle Gonterwitz said:Is this a trick question? I think the lowest possible altitude of a satellite orbiting the Earth would be just above sea level. The satellite would have to achieve escape velocity, have thrust available to overcome drag, and have to be able to navigate around landmasses, but technically that should qualify as a satellite in orbit.
The stratopause (circa 60 km) is a more appropriate altitude for sounding rockets than for satellites.Tom Kunich said:Well it depends on its purpose. If I remember correctly they intend to launch very low Earth orbit weather satellites that require continuous replacement as their orbits rapidly decay and they fall out of the sky.
If you could really do that that on earth, like you said, just above sea level and make the satellite orbit just 1 circular orbit around earth, I will give you 100 trillion dollars of Zimbabwe. It is not practical but theoretical, and it's not possible on Earth but on a theoretical planet without any elevation and no atmosphere.Kyle Gonterwitz said:Is this a trick question? I think the lowest possible altitude of a satellite orbiting the Earth would be just above sea level. The satellite would have to achieve escape velocity, have thrust available to overcome drag, and have to be able to navigate around landmasses, but technically that should qualify as a satellite in orbit.
Thank you very much, but I'm not an aviation engineer, so if you could help or just show a few simple formulas that would be more than helpfulKyle Gonterwitz said:Flight level 600 is at 60,000 ft which is the upper boundary of controlled airspace, that would be the practical, lowest possible altitude. Search for the relationship between altitude and atmospheric pressure to find that relationship, then go as high as needed to optimize a design based on propulsion energy needed to achieve the desired altitude at orbital/escape velocity with minimum thrust to overcome atmospheric density/drag for the duration of the mission.
The mass of the satellite does not enter in (*). One can obtain the orbital velocity by equating the centripetal acceleration for a circular orbit ##a=\frac{v^2}{r}## with the centripetal acceleration provided by gravity ##a=\frac{GM}{r^2}##.Tom Kunich said:v = sqrt /Gravity x mass of satellite / actual radius of orbit
The lowest possible altitude for a satellite depends on its purpose and orbit. For a low Earth orbit (LEO) satellite, the lowest possible altitude is around 160 kilometers. For a geostationary orbit (GEO) satellite, the lowest possible altitude is around 35,786 kilometers.
The altitude of a satellite affects its speed, coverage area, and communication capabilities. A lower altitude means a faster orbit and more frequent coverage of a specific area. It also allows for better communication with ground stations.
The lowest possible altitude for a satellite is determined by its intended purpose, orbit type, and launch capabilities. Scientists and engineers use mathematical calculations and simulations to determine the optimal altitude for a satellite to achieve its objectives.
Yes, a satellite can orbit at an altitude lower than the lowest possible, but it may not be able to maintain a stable orbit. The Earth's atmosphere and other factors can cause drag on the satellite, making it lose altitude and eventually fall back to Earth.
Yes, there are risks associated with a satellite orbiting at the lowest possible altitude. The Earth's atmosphere and space debris can pose a threat to the satellite, potentially causing damage or destruction. Additionally, a lower altitude can also make a satellite more vulnerable to atmospheric drag and radiation, potentially shortening its lifespan.