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Space Forum / Shuttle / April 2007Getting into orbit
getting into orbit. I heard the there's an advantage for a rocket to take off near the equator as the earth is spinning faster there. Why is this, as surely the earth's rotation does not affect a rocket orbiting above the earth? When orbiting the earth your lateral movement must be able to balance the pull of the earths gravity, so does the earths rotation matter? > getting into orbit. > I heard the there's an advantage for a rocket to take off near the > equator as the earth is spinning faster there. This is true if you're going into an orbit that orbits in the same direction as the earth rotates. > Why is this, as surely > the earth's rotation does not affect a rocket orbiting above the > earth? True, but think about what would happen if you tried to go into a retrograde orbit from the equator. That is, you launch the *opposite* direction of the earth's rotation. You've got to expend more energy because you're essentially starting out going the wrong direction with a tangential velocity equal to the velocity at the surface of the earth. > When orbiting the earth your lateral movement must be able > to balance the pull of the earths gravity, so does the earths rotation > matter? You're only in orbit if your velocity is high enough. Getting out of the atmosphere isn't good enough, or you'll just fall back to earth. You spend *a lot* of your energy getting up to the proper orbital velocity. That initial velocity that you get from launching at the equator in the direction of the earth's rotation helps you achieve orbital velocity a bit easier. Jeff  Signature"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety" - B. Franklin, Bartlett's Familiar Quotations (1919) >> getting into orbit. >> I heard the there's an advantage for a rocket to take off near the >> equator as the earth is spinning faster there. > >This is true if you're going into an orbit that orbits in the same direction >as the earth rotates. And if the orbit you are attempting to reach is reasonably close to 0 inclination. D. SignatureTouch-twice life. Eat. Drink. Laugh. -Resolved: To be more temperate in my postings. Oct 5th, 2004 JDL > ><mikejenni...@yahoo.co.uk> wrote in message > >news:1176465413.553096.81790@b75g2000hsg.googlegroups.com... [quoted text clipped - 7 lines] > And if the orbit you are attempting to reach is reasonably close to 0 > inclination. ...and...the launch site is not at a higher latitiude than the desired inclination. Actually, the Earth's rotation benefit varies with the cosine of the inclination, so low inclination works almost as well as 0 degrees. The big advantage of 0 degrees inclination from an equatorial launch site with a latitude of less than 1 degree from the equator is the opportunity for very frequent rendezvous with a station in an equatorial orbit. The equatorial bulge is also a significant factor, since it starts the trajectory further from the center of Earth. This effect is good for about 45 m/s, relative to a polar orbit. Len > D. > -- > Touch-twice life. Eat. Drink. Laugh. > > -Resolved: To be more temperate in my postings. > Oct 5th, 2004 JDL > getting into orbit. > I heard the there's an advantage for a rocket to take off near the [quoted text clipped - 3 lines] > to balance the pull of the earths gravity, so does the earths rotation > matter? Consider this. You need to be going at about 25,000 mph (relative to the center of the Earth) to orbit the Earth at LEO. Now, this doesn't matter if the Earth is spinning or not. Now, at the equator, the earth is spinning West->East at about 1,000 MPH. So, now you only need to accelerate by 24,000 MPH if you launch towards the east. If you launch to the wet, you need to accelarate by 26,000 MPH. SignatureGreg Moore SQL Server DBA Consulting Remote and Onsite available! Email: sql (at) greenms.com http://www.greenms.com/sqlserver.html On Fri, 13 Apr 2007 10:47:20 -0500, Greg D. Moore \(Strider\) wrote (in article <cCNTh.21002$PL.8825@newsread4.news.pas.earthlink.net>): > If you launch to the wet, you need to accelarate by 26,000 MPH. Of course, launching west from the west coast will get you to the wet, as will launching east from the east coast. Launching west from the east coast will get you to the dry, however. ;-) SignatureYou can run on for a long time, Sooner or later, God'll cut you down. ~Johnny Cash How about launching on say a rail gun up the side of a mountain. How much fuel extra capacity would be gained? >>getting into orbit. >>I heard the there's an advantage for a rocket to take off near the [quoted text clipped - 15 lines] > > If you launch to the wet, you need to accelarate by 26,000 MPH. Has any payload ever been launched into a westward orbit over the equator? > Has any payload ever been launched into a westward orbit over the equator? Israel's Ofeq satellites are launched westward (retrograde orbit) over the Mediterranean to avoid flying and dropping spent rocket stages over populated areas in Israel and neighbouring Arab countries. Not quite the equator, but there you have it. SignatureDave Michelson davem@ece.ubc.ca Oh gawd, any minute now someone will bring up the space elevator again.... Brian SignatureBrian Gaff - briang1@blueyonder.co.uk Note:- In order to reduce spam, any email without 'Brian Gaff' in the display name may be lost. >> >> Has any payload ever been launched into a westward orbit over the [quoted text clipped - 4 lines] > populated areas in Israel and neighbouring Arab countries. Not quite the > equator, but there you have it. > Oh gawd, any minute now someone will bring up the space elevator again.... > > Brian Nah, just get Ralph Crandon angry.... "To the Moon, Alice!..." :-) snip > Consider this. You need to be going at about 25,000 mph (relative to the > center of the Earth) to orbit the Earth at LEO. [quoted text clipped - 7 lines] > > If you launch to the wet, you need to accelarate by 26,000 MPH. Not quite true, Orbital velocity is only 17,000 mph. 25,000mph is escape velocity. the "headstart would be about 1125 mph ( circumference 27,000 miles / 24 hours ) So the effect is quite significant, which is why there is lots of talk about setting up a space base at the northern tip of Australia terry > snip > [quoted text clipped - 13 lines] > Not quite true, Orbital velocity is only 17,000 mph. 25,000mph is escape > velocity. Fair enough (I actually was thinking more "Mach 25" which some people say, which to me in space makes little sense :-) > the "headstart would be about 1125 mph ( circumference 27,000 miles / 24 > hours ) Well that one I'll argue I was "close enough" :-) > So the effect is quite significant, which is why there is lots of talk > about > setting up a space base at the northern tip of Australia > terry SignatureGreg Moore SQL Server DBA Consulting Remote and Onsite available! Email: sql (at) greenms.com http://www.greenms.com/sqlserver.html > getting into orbit. > I heard the there's an advantage for a rocket to take off near the [quoted text clipped - 3 lines] > to balance the pull of the earths gravity, so does the earths rotation > matter? Well, look at it this way: All points on the earth (except the geographic poles) must rotate once every day. If you're on the equator, the circumference of the equator is roughly 25000 miles long around the earth. So if you stand on the equator, you're traveling 25,000 miles every day. Just one degree south of the North Geographic Pole, the 89th parallel is only a couple hundred miles long around the earth. So if you stand on the 89th parallel, you're traveling only a couple hundred miles a day. Which rate is faster? SignatureSteven D. Litvintchouk Email: sdlitvin@earthlinkNOSPAM.net Remove the NOSPAM before replying to me. |
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