Author Topic: Speed the earth appears to rotate from the shuttle's view  (Read 10922 times)

Offline Cigaboo

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Hi.  I'm pretty new to this.  I think that shuttles orbit Earth at around 7700 m/s and the surface of the earth rotates at about 464 m/s (at the equator).  Does this sound correct?  This is a difference of a factor of about 16, although the shuttle is further away from the Earth's center.  This would seem to suggest that from the shuttle the earth's rotation (the rate that land passes "underneath" you) is very slow, about one visible "rotation" every 1.5 hours?  If you were to stare at the Earth from the shuttle, it would appear almost static at this rate, correct?


Offline ChrisGebhardt

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Re: speed the earth appears to rotate from the shuttle's view
« Reply #1 on: 08/19/2007 06:25 am »
Okay... the "movement" of the Earth observed from either the Space Shuttle or the ISS is actually their own movement over the surface of the Earth. Think about it this way... you're driving your car down the road. You look out the window and you see the ground moving past your car. Now, you're on the Space Shuttle or ISS and you look out the window. You would see the Earth moving by you. It does not look static. Does this help?

Offline SpaceNutz SA

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Re: speed the earth appears to rotate from the shuttle's view
« Reply #2 on: 08/19/2007 06:36 am »
It is a function of both the ISS orbit and the earth rotation.  I think during Apollo or Gemini they differentiated between a spacecraft orbit and spacecraft revolution by saying that a revolution (rev) is a 360 degree angular displacment of the spacecraft where and orbit starts and ends over the same longitude on earth.  Therefore an orbit is slightly longer than a revolution because the spacecraft orbit is posigrade.
"Lets not make things worse by guessing" - Gene Kranz - Apollo 13 Flight Director

Offline Jim

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RE: speed the earth appears to rotate from the shuttle's view
« Reply #3 on: 08/19/2007 01:20 pm »
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Cigaboo - 19/8/2007  1:11 AM
 If you were to stare at the Earth from the shuttle, it would appear almost static at this rate, correct?


You can watch the video and see the earth go by

Offline gavsto2006

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RE: speed the earth appears to rotate from the shuttle's view
« Reply #4 on: 08/19/2007 02:21 pm »
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Cigaboo - 19/8/2007  6:11 AM

Hi.  I'm pretty new to this.  I think that shuttles orbit Earth at around 7700 m/s and the surface of the earth rotates at about 464 m/s (at the equator).  Does this sound correct?  This is a difference of a factor of about 16, although the shuttle is further away from the Earth's center.  This would seem to suggest that from the shuttle the earth's rotation (the rate that land passes "underneath" you) is very slow, about one visible "rotation" every 1.5 hours?  If you were to stare at the Earth from the shuttle, it would appear almost static at this rate, correct?


This would only be the case if you were in a geostationary orbit

Offline SpaceNutz SA

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Re: speed the earth appears to rotate from the shuttle's view
« Reply #5 on: 08/19/2007 05:32 pm »

Think of it in terms of angular velocity. The earth rotation period is 24 hours (0.25deg/min). The ISS rotation period is (more or less) 90mins (3.91deg/min). Becuase of the posigrade orbit (both going in the same direction) subtract the 2 to get the apparent motion of one in the frame of reference of the other (call it about 3.65 deg/min).

Edit:  This of course does not take into account the 51.6deg difference in the roational / orbital planes so a factor of Cos (51.6) would need to be included. 

"Lets not make things worse by guessing" - Gene Kranz - Apollo 13 Flight Director

Offline meiza

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RE: speed the earth appears to rotate from the shuttle's view
« Reply #6 on: 08/19/2007 06:38 pm »
Quote
gavsto2006 - 19/8/2007  3:21 PM

Quote
Cigaboo - 19/8/2007  6:11 AM

Hi.  I'm pretty new to this.  I think that shuttles orbit Earth at around 7700 m/s and the surface of the earth rotates at about 464 m/s (at the equator).  Does this sound correct?  This is a difference of a factor of about 16, although the shuttle is further away from the Earth's center.  This would seem to suggest that from the shuttle the earth's rotation (the rate that land passes "underneath" you) is very slow, about one visible "rotation" every 1.5 hours?  If you were to stare at the Earth from the shuttle, it would appear almost static at this rate, correct?


This would only be the case if you were in a geostationary orbit

No. Geo takes 24 hours. Cigaboo is correct , LEO is 90 minutes per circle. The 24 hours of the earth's rotation is pretty slow compared to that so it doesn't affect that much. The additional distance (300 km) is pretty small too since earth's radius is over 6000 km.

Offline SpaceNutz SA

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RE: speed the earth appears to rotate from the shuttle's view
« Reply #7 on: 08/19/2007 06:46 pm »

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meiza - 19/8/2007 8:38 PM
Quote
gavsto2006 - 19/8/2007 3:21 PM
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If you were to stare at the Earth from the shuttle, it would appear almost static at this rate, correct?
This would only be the case if you were in a geostationary orbit
No. Geo takes 24 hours. Cigaboo is correct , LEO is 90 minutes per circle. The 24 hours of the earth's rotation is pretty slow compared to that so it doesn't affect that much. The additional distance (300 km) is pretty small too since earth's radius is over 6000 km.

The ISS wizzes around the earth at a much faster rate than the earth is rotating.  Obviously there is relative motion between the 2.  Watch NASA TV from the ISS camera and it is plain to see.   Only a Geostationery orbit has no relative motion.

"Lets not make things worse by guessing" - Gene Kranz - Apollo 13 Flight Director

Offline meiza

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Re: speed the earth appears to rotate from the shuttle's view
« Reply #8 on: 08/19/2007 07:55 pm »
What the heck are you saying? Of course there is relative motion, I just said there is, I said earth's OWN rotation is negligible since it's so slow (24 hours per revolution) compared to the ISS/shuttle (90 minutes per revolution).

Offline SpaceNutz SA

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Re: speed the earth appears to rotate from the shuttle's view
« Reply #9 on: 08/19/2007 08:26 pm »
It's a question of which frame of reference you refer to.

I agree that from an inertial frame of reference the ISS orbit is much faster than the earths rotation and the earth does seem mildly 'static' in comparison.  

But the original question (and indeed the title of the thread) is from the ISS frame of reference (ie: if you were sitting on the ISS looking at the earth) in which the earth appears to rotate rather rapidly - approx once every 90 mins.
"Lets not make things worse by guessing" - Gene Kranz - Apollo 13 Flight Director

Offline Cigaboo

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Re: speed the earth appears to rotate from the shuttle's view
« Reply #10 on: 08/23/2007 12:14 am »
Hi, guys.  Thanks for the responses.  I actually started this thread partially in response to seeing how the ISS view of earth appears on tv.  But my question is about a shuttle in orbit, not the ISS because I have a scene in my computer game that takes place from the vantage point of a shuttle in orbit.  If the earth appears nearly static, this means that I can make the earth pretty much a photo of Earth.  But if the earth rotates at a fast clip, I will need to make it a 3D model.

Offline Jim

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Re: Speed the earth appears to rotate from the shuttle's view
« Reply #11 on: 08/23/2007 12:22 am »
It doesn't matter Shuttle, ISS or another spacecraft, it is the same view and it moving fast

Offline HIPAR

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Re: Speed the earth appears to rotate from the shuttle's view
« Reply #12 on: 08/24/2007 03:16 am »
It's an interesting question.

If the earth were not rotating, the speed would be about 25000 miles during the 90 minute orbit period.  When the ISS observes the rotating earth beneath it from orbit, the earth is rotating faster (miles/hour) at the equatorial crossings then it does when the ISS is over its extreme latitudes.  So the relative velocity changes as the orbit progresses.  I would think the observed direction of earth rotation reverses when the station changes its north - south direction.

---  CHAS

Offline Jim

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Re: Speed the earth appears to rotate from the shuttle's view
« Reply #13 on: 08/24/2007 10:20 am »
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HIPAR - 23/8/2007  11:16 PM

It's an interesting question.

If the earth were not rotating, the speed would be about 25000 miles during the 90 minute orbit period.  When the ISS observes the rotating earth beneath it from orbit, the earth is rotating faster (miles/hour) at the equatorial crossings then it does when the ISS is over its extreme latitudes.  So the relative velocity changes as the orbit progresses.  I would think the observed direction of earth rotation reverses when the station changes its north - south direction.

---  CHAS

The crew can not see the earth's rotation..  The earth's rotation is insignificant wrt to the speed of the ISS.  The changes in "ground speed"  would not be preceived  by the observer

Offline Cigaboo

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Re: Speed the earth appears to rotate from the shuttle's view
« Reply #14 on: 08/26/2007 04:43 am »
Jim - thanks for the reply.  I guess I'm a bit confused by your two most recent posts, as I interpret them as contradictions.  In one post you seem to indicate that the view does move fast but in your most recent post you mention "The changes in "ground speed" would not be preceived by the observer".  I think maybe your previous post is the one I should refer to, as you might be speaking about a different issue in the latest post in response to HIPAR's comment.

Offline meiza

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Re: Speed the earth appears to rotate from the shuttle's view
« Reply #15 on: 08/26/2007 07:36 pm »
Look:
Even if earth was tide locked to the sun and did not rotate practically at all and had no nights, days or any 24 hour rhythms, from ISS / shuttle altitude it would seem to rotate since the ISS / shuttle ITSELF goes around the planet every 90 minutes.

The idea is here that the 24 hour planet's OWN rotation is slow, it's not really visible from space. But the 90 minute per rotation flown by ISS / shuttle is fast, and you can see the ground move below you even when you are at 300 km height. Those are two separate things.

24 hours, a long time. 90 minutes, that's one and a half hour, that's a short time. Around the world in 24 hours, that's slow. Around the world in 90 minutes, that's fast.

So what they see when they see a moving earth from low earth orbit, is because of the shuttle's and station's OWN speed, it doesn't have anything to do with the 24 hour rotation of the earth.

Hope this clears up the confusions.

Offline Cigaboo

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Re: Speed the earth appears to rotate from the shuttle's view
« Reply #16 on: 08/27/2007 08:07 am »
Thanks, Meiza.  I was not aware that the shuttle moved around the earth that quickly.

Offline E_ E_ H

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Re: Speed the earth appears to rotate from the shuttle's view
« Reply #17 on: 08/29/2007 12:35 pm »
Cigaboo. Put simply, in order to stay up, the shuttle, ISS, a satellite - indeed any orbital spacecraft - has to move fast enough to go over the horizon before it hits it. It has to move perpendicular, or at a right angle to the direction of the pull of gravity. Therefore, it will move at about 17000mph, relative to it's take off point. Thats about 5 and a half miles per second. At 250 miles altitude, the ground passes by far below (to put it in understandable terms) very quickly. Therefore, looking from a window on the shuttle, you appear to be - indeed you are passing above the surface very fast.

It's like being in permanent freefall inside an aeroplane. Sometimes, if an aircraft hits turbulence, it drops suddenly - sometimes as much as 200 - 300 feet. You are inside it, and it can appear that you are floating. Relative to the aircraft, you are, because gravity is pulling the aircraft down at the same speed that you are falling so you appear to float, well your cup of coffee does anyway! The aircraft is only moving at 650 mph, so that effect never lasts. Eventually, either it flies on as the wings gain lift again, or it hits the ground because gravity pulls it all the way down.

In the same way, the shuttle is moving forwards and gravity is pulling it down. However the shuttle moves so fast forwards that gravity cannot pull it to the ground so objects appear to float and are weightless. NASA training simulates microgravity by flying an aircraft in a big series of dives, each followed by climbs. The dives allow the identical effect to hitting turbulence, but in a controlled and planned manner. The aircraft falls and so do the passengers. They appear to float relative to the aircraft and are therefore weightless.

Edit - Spelling mistakes...
Ground control to Major Chris....

Offline SpaceNutz SA

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Re: Speed the earth appears to rotate from the shuttle's view
« Reply #18 on: 08/29/2007 07:06 pm »

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meiza - 26/8/2007 9:36 PM  So what they see when they see a moving earth from low earth orbit, is because of the shuttle's and station's OWN speed, it doesn't have anything to do with the 24 hour rotation of the earth. Hope this clears up the confusions.

Not really. 

An observer looking at the earth from an LEO satellite sees the resultant of the orbit of the satellite AND the rotation of the earth.  So to say that "it doesn't have anything to do with the 24 hour rotation of the earth" is not true.   The rotation of the earth has a much smaller influence on the observed motion than the ISS orbit but not zero.

"Lets not make things worse by guessing" - Gene Kranz - Apollo 13 Flight Director

Offline Lee Jay

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Re: Speed the earth appears to rotate from the shuttle's view
« Reply #19 on: 08/29/2007 07:19 pm »
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SpaceNutz SA - 29/8/2007  1:06 PM

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meiza - 26/8/2007 9:36 PM  So what they see when they see a moving earth from low earth orbit, is because of the shuttle's and station's OWN speed, it doesn't have anything to do with the 24 hour rotation of the earth. Hope this clears up the confusions.

Not really.  

An observer looking at the earth from an LEO satellite sees the resultant of the orbit of the satellite AND the rotation of the earth.  So to say that "it doesn't have anything to do with the 24 hour rotation of the earth" is not true.   The rotation of the earth has a much smaller influence on the observed motion than the ISS orbit but not zero.


Isn't the influence about a *negative* 6%?  I think the Earth would seem to be going faster if it weren't rotating on its axis (and it would also take more total impulse to get to orbit).

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