<p>ISS is travelling with about 8 km/s around Earth. At that velocity the centrifugal force on the circular orbit is strong enough to cancel out gravity. The parts ISS is made of, needed to be accelerated to that speed by rockets.</p>

CC BY-SA 3.0
2014-03-03T15:33:24.030Z
It doesn't really annihilate gravity, it just provides an opposite and equal force (almost) that keeps the satellite at a near constant altitude.
christopherlovell
CC BY-SA 3.0
2014-03-03T20:30:37.313Z
@ChrisLovell Now used 'cancel out' instead; hope that's less misleading.
Gerald
CC BY-SA 3.0
2014-09-22T06:01:27.247Z
Centrifugal force is completely out of place here.  In a centrifuge, the objects inside it are driven against the outside walls. No object onboard the ISS is being driven against the outside walls -- they are orbiting with the station.  In other words, they and the ISS are falling around earth, entirely subject to gravity (which is NOT cancelled out).
Cyberherbalist
CC BY-SA 3.0
2014-09-22T12:59:46.490Z
@Cyberherbalist The fictitious [centrifugal force](https://en.wikipedia.org/wiki/Centrifugal_force) (the apparent force in the non-inertial reference frame rotating with the ISS around approximately the center of Earth) plays a role here. It is balanced by the gravitational force of Earth which acts as a [centripetal force](https://en.wikipedia.org/wiki/Centripetal_force) here. That is the reason why the objects inside ISS **and the whole ISS** do not fly away from Earth.
pabouk - Ukraine stay strong
CC BY-SA 3.0
2014-03-01T21:01:32.637Z
2014-03-03T20:28:33.320Z
2014-03-03T20:28:33.320Z
Gerald
<p>Centrifugal force is too small to cancel gravity. The ISS, as all the satellites, are actually "always falling", but the horizontal component of their speed will always take them over the horizon line, keeping the distance to Earth constant. You have a very good explanation here</p>

<p><a href="http://www.lasalle.edu/~smithsc/Astronomy/Orbits/orbits.html" rel="nofollow">http://www.lasalle.edu/~smithsc/Astronomy/Orbits/orbits.html</a></p>

CC BY-SA 3.0
2014-09-22T14:32:35.493Z
Why do you say that the "centrifugal force is too small"? The centrifugal force is a so-called [fictitious force](http://en.wikipedia.org/wiki/Fictitious_force) that is only defined in rotating reference frames, but from the perspective of such a frame, it is perfectly correct to say that the centrifugal force is equal and opposite to the gravitational force for a circular orbit. But of course, it is also correct (and more fundamental) to explain the orbit in the context of an *inertial* frame where there is no centrifugal force, invoking the horizontal component of velocity as you did.
Hypnosifl
CC BY-SA 3.0
2014-09-22T05:17:46.353Z
2014-09-22T05:17:46.353Z
Andrei
<p>Your question presumes that the ISS is beyond Earth's gravity, that it has escaped earth's gravitational pull. This is not correct. All objects with mass in the universe affect all other things with mass in the universe, the effect just gets weaker with distance. So the ISS is feeling the effect of gravity from Earth significantly more than the moon is.</p>

<p>The reason the ISS doesn't just fall to the earth, either directly or gradually spiralling towards the earth, is that it is travelling fast enough around the earth that it is continually "missing" earth. It is sometimes described as 'falling' constantly around earth.</p>

<p>If I am to be properly correct though, the reality is that ISS <strong>is</strong> in fact falling towards the earth, <a href="http://www.heavens-above.com/IssHeight.aspx">getting closer and closer to Earth all the time</a>. It needs occasional boosts to push it further back out in it's orbit.</p>

<p>Just to blow your mind a little bit: The ISS is pulling on the Earth with the same force that the Earth is pulling on ISS.</p>

CC BY-SA 4.0
2021-01-20T03:09:55.540Z
That the orbit is not stable and gradually decreasing is not an effect of gravity, but of the drag of earth's atmosphere even in 400km height
planetmaker
CC BY-SA 3.0
2014-03-02T22:58:49.790Z
2014-03-02T22:58:49.790Z
Jeremy
<p>How do they make International space station to orbit the earth beyond Earth's gravity acting on it? We all know that ISS is rotating at an altitude of just 350km away. How could the ISS escape Earth's gravitational pull?</p>

CC BY-SA 3.0
2014-03-01T18:50:51.207Z
And what is the speed of ISS? I think that is the answer - the closer you are the faster is your speed (while angular velocity remains the same).
Tomáš Zato
CC BY-SA 3.0
2014-03-01T21:03:41.917Z
The question might to be migrated to the Space Exploration site.
Gerald
CC BY-SA 3.0
2014-03-03T14:04:47.907Z
Praveen - it is not rotating. It is orbiting - which means it is entirely within the action of Earth's gravity. It is not escaping - as you can see by the fact it keeps orbiting.
Rory Alsop
<orbit><gravity><astrophysics>
Earth's gravitational pull on ISS
Praveen Kadambari
# Earth's gravitational pull on ISS

(Asked by: username_0 on 2014-03-01)

How do they make International space station to orbit the earth beyond Earth's gravity acting on it? We all know that ISS is rotating at an altitude of just 350km away. How could the ISS escape Earth's gravitational pull?

**Tags:** orbit, gravity, astrophysics

> **Comments:**
> **username_1**: And what is the speed of ISS? I think that is the answer - the closer you are the faster is your speed (while angular velocity remains the same).  
> **username_2**: The question might to be migrated to the Space Exploration site.  
> **username_3**: Praveen - it is not rotating. It is orbiting - which means it is entirely within the action of Earth's gravity. It is not escaping - as you can see by the fact it keeps orbiting.  

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## 3 answers

### Answer by username_9 on 2014-03-02. Score: 11 | Accepted answer

Your question presumes that the ISS is beyond Earth's gravity, that it has escaped earth's gravitational pull. This is not correct. All objects with mass in the universe affect all other things with mass in the universe, the effect just gets weaker with distance. So the ISS is feeling the effect of gravity from Earth significantly more than the moon is.

The reason the ISS doesn't just fall to the earth, either directly or gradually spiralling towards the earth, is that it is travelling fast enough around the earth that it is continually "missing" earth. It is sometimes described as 'falling' constantly around earth.

If I am to be properly correct though, the reality is that ISS **is** in fact falling towards the earth, [getting closer and closer to Earth all the time](http://www.heavens-above.com/IssHeight.aspx). It needs occasional boosts to push it further back out in it's orbit.

Just to blow your mind a little bit: The ISS is pulling on the Earth with the same force that the Earth is pulling on ISS.

> **Comments:**
> **username_10**: That the orbit is not stable and gradually decreasing is not an effect of gravity, but of the drag of earth's atmosphere even in 400km height  

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### Answer by username_2 on 2014-03-01. Score: 0

ISS is travelling with about 8 km/s around Earth. At that velocity the centrifugal force on the circular orbit is strong enough to cancel out gravity. The parts ISS is made of, needed to be accelerated to that speed by rockets.

> **Comments:**
> **username_4**: It doesn't really annihilate gravity, it just provides an opposite and equal force (almost) that keeps the satellite at a near constant altitude.  
> **username_2**: @ChrisLovell Now used 'cancel out' instead; hope that's less misleading.  
> **username_5**: Centrifugal force is completely out of place here.  In a centrifuge, the objects inside it are driven against the outside walls. No object onboard the ISS is being driven against the outside walls -- they are orbiting with the station.  In other words, they and the ISS are falling around earth, entirely subject to gravity (which is NOT cancelled out).  
> **username_6**: @username_5 The fictitious [centrifugal force](https://en.wikipedia.org/wiki/Centrifugal_force) (the apparent force in the non-inertial reference frame rotating with the ISS around approximately the center of Earth) plays a role here. It is balanced by the gravitational force of Earth which acts as a [centripetal force](https://en.wikipedia.org/wiki/Centripetal_force) here. That is the reason why the objects inside ISS **and the whole ISS** do not fly away from Earth.  

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### Answer by username_7 on 2014-09-22. Score: 0

Centrifugal force is too small to cancel gravity. The ISS, as all the satellites, are actually "always falling", but the horizontal component of their speed will always take them over the horizon line, keeping the distance to Earth constant. You have a very good explanation here

<http://www.lasalle.edu/~smithsc/Astronomy/Orbits/orbits.html>

> **Comments:**
> **username_8**: Why do you say that the "centrifugal force is too small"? The centrifugal force is a so-called [fictitious force](http://en.wikipedia.org/wiki/Fictitious_force) that is only defined in rotating reference frames, but from the perspective of such a frame, it is perfectly correct to say that the centrifugal force is equal and opposite to the gravitational force for a circular orbit. But of course, it is also correct (and more fundamental) to explain the orbit in the context of an *inertial* frame where there is no centrifugal force, invoking the horizontal component of velocity as you did.  

---

