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?
Cigaboo - 19/8/2007 6:11 AMHi. 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?
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.
gavsto2006 - 19/8/2007 3:21 PMQuoteCigaboo - 19/8/2007 6:11 AMHi. 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
meiza - 19/8/2007 8:38 PM Quotegavsto2006 - 19/8/2007 3:21 PM Quote 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.
gavsto2006 - 19/8/2007 3:21 PM Quote 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
If you were to stare at the Earth from the shuttle, it would appear almost static at this rate, correct?
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.
HIPAR - 23/8/2007 11:16 PMIt'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
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.
SpaceNutz SA - 29/8/2007 1:06 PMQuotemeiza - 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.