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Thread: how do you get supplies from a stationary space elevator while your spacecraft is orbiting the Earth at orbital speed

  1. #1 how do you get supplies from a stationary space elevator while your spacecraft is orbiting the Earth at orbital speed 
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    how do you get supplies from a stationary space elevator while your spacecraft is orbiting the Earth at 17,100 miles per hour
    EDIT: changed question to
    how do you get supplies from a stationary space elevator while your spacecraft is orbiting the Earth at orbital speed


    Last edited by Japith; June 23rd, 2014 at 12:16 AM.
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    Moderator Moderator Janus's Avatar
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    At that speed you'd be orbiting at an altitude of ~550 km, much lower than the top end of the elevator. Servicing these altitudes isn't really in the purview of a space elevator, which is to get payloads to geosync and beyond distances. In fact, if we ever did build them, we would have to most likely do some serious cleaning up of all the stuff presently orbiting at lower elevations to prevent potential collisions.


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    @Janus, Thank you

    Is it possible to be so high you are able to orbit stationary relative to the Earth
    To orbit at the same speed the Earth rotates and to be basically stationary relative to the Earth, still orbiting the Earth but it seems like you are hovering since the Earth is rotating with you.
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    Quote Originally Posted by Japith View Post
    Is it possible to be so high you are able to orbit basically stationary relative to the Earth
    To orbit at the same speed the Earth rotates and to be basically stationary relative to the Earth, still orbiting the Earth but it seems like you are hovering since the Earth is rotating with you.
    Yes. They are known as "geostationary orbits", and are at an altitude of 35786 kilometres.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Thank you Janus and KJW for the replies
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    Is it possible to launch cargo into deep space by using the elevator as a launcher, at the end the cargo will fly away; moreover, build the elevator on a point that most aligns to the moon and catapult cargo into lunar orbit
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    Quote Originally Posted by Japith View Post
    Is it possible to launch cargo into deep space by using the elevator as a launcher, at the end the cargo will fly away; moreover, build the elevator on a point that most aligns to the moon and catapult cargo into lunar orbit

    If you do that then the cargo won't ever escape the lunar orbit due to its gravity pulling at the cargo. Another thing is that cargo doesn't have any power plant to propel it so it wouldn't get very far very fast.
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    Quote Originally Posted by Japith View Post
    Is it possible to launch cargo into deep space by using the elevator as a launcher, at the end the cargo will fly away; moreover, build the elevator on a point that most aligns to the moon and catapult cargo into lunar orbit
    This is one way to use a space elevator. The end of the elevator is actually above the geostationary orbit altitude. (you build the elevator down from the geostationary point, but to keep it in orbital balance you have to counterweight it in the opposite direction.) The top of the elevator can be at 71572 km in altitude.

    At this height, it will be moving at 5.7 km/sec. The orbital speed at this altitude is 2.3 km/sec and the escape velocity is only 3.2 km.sec. Thus a payload lifted to the top and released would escape from Earth's gravity with velocity to spare.

    As far as launch to the moon goes, Any elevator is going to be built at the Equator, and the Moon orbits about 5 degrees away from the ecliptic so the orbital plane of the Moon and the Elevator's plane of the rotation will not line up. The way around this is to launch your payload at just the right time so that it and the Moon arrive at one of the two points where these planes cross each other. Your payload will still need some propulsion system to insert itself into orbit around the moon. The downside to this is that viable launch windows are weeks apart from each other.

    The other method involves changing the orbital plane of the payload after it launches so that it aligns with the Moon's. This involves another engine burn and more fuel, but allows for launch windows about 1 day apart.
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    Malignant Pimple shlunka's Avatar
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    The only way I'd be willing to ride a space elevator... if "Rocket Man" or "Space Oddity" were blaring over the internal speaker system.
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    Quote Originally Posted by shlunka View Post
    The only way I'd be willing to ride a space elevator... if "Rocket Man" or "Space Oddity" were blaring over the internal speaker system.
    Even that could be tiresome after a while. Let's say that the elevator can climb at speeds matching those of the fastest mag-lev trains (500 km/hr), a trip to the end of the elevator would take almost 6 days . Even if we could boost that up to 1800 km/hr ( The theoretical limit for a Chinese prototype), the trip would be still ~24 hrs. IOW, a space elevator would have to be designed more along the lines of a passenger train, with sleeping and dining accommodations, along with room to stretch your legs and possibly entertainment (Beyond the constant looping of the aforementioned songs).
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    Quote Originally Posted by Japith View Post

    Is it possible to be so high you are able to orbit stationary relative to the Earth
    To orbit at the same speed the Earth rotates and to be basically stationary relative to the Earth, still orbiting the Earth but it seems like you are hovering since the Earth is rotating with you.
    Yes, as KJW says, and it was first proposed by the author Arthur C Clarke. That "geo-stationary" orbit is where all the television communications satellites are. Otherwise, your satellite receiver dish would have to move to track them.


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