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Author
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Topic: How far up is Zero G?
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Aztecdoug
Member Posts: 1405
From: Huntington Beach
Registered: Feb 2000
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posted 06-25-2003 02:25 PM
   
Here is a question directed to the more technically minded. I am curious how far up you really have to go to reach zero gravity?Certainly you can be weightless in the Vomit Comet. The X-15 flew some flights that were weightless. I understand those are simply a function of their parabolic flight profile. Even orbital flight is termed as micro-gravity. Is orbital flight weightless just because the vehicle is going real fast? Sort of like dropping in an elevator real quick? If the ISS simply stopped its orbital speed wouldn�t it just fall straight down to the Earth like the first two Mercury Redstone flights? So, back to my question, where does real weightlessness begin in relation to the Earth? Or is this more of a Cosmological thing where there is always some form of gravity tugging you here or there?
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Warm Regards Douglas Henry Enjoy yourself and have fun.... it is only a hobby! |
nasamad
Member Posts: 2121
From: Essex, UK
Registered: Jul 2001
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posted 06-25-2003 02:35 PM
My guess would have to be, to be in zero-g you would have to be outside the gravity field of any planet or body. Even if you were past Pluto in a spacecraft you would still be in microgravity I think.
I think if you delved deeper you would find that anything that has a mass exerts a pull (gravity) upon objects around it. Just my two penneth, .... Adam (I'm just know someone is gonna put me right somewhere, lol ) |
Rizz
Member Posts: 1208
From: Upcountry, Maui, Hawaii
Registered: Mar 2002
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posted 06-25-2003 03:30 PM
I don't know the answer but....these links may help. http://www.msnbc.com/news/218291.asp?cp1=1
http://www.glenbrook.k12.il.us/gbssci/phys/Class/circles/u6l4d.html Rizz
http://lifesci3.arc.nasa.gov/SpaceSettlement/Video/Weightlessness.html
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Ben
Member Posts: 1896
From: Cape Canaveral, FL
Registered: May 2000
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posted 06-25-2003 04:01 PM
There is no "zero g". It can only be created by the falling of two objects at the same time, in relation to one another.Even going far enough away from the planets or the sun, the galactic center still has an enormous pull on things. You are weightless in space because you are always moving. Maybe my logic is wrong, but I don't think there is anywhere in space where you could stay still and not be pulled towards something. My two cents. ------------------
-Ben http://www.geocities.com/ovcolumbia/ |
Ben
Member Posts: 1896
From: Cape Canaveral, FL
Registered: May 2000
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posted 06-25-2003 04:03 PM
And yes, if the ISS were suddenly stopped, somehow, it would fall straight down to earth, vertically. If the earth were stopped, it would fall into the sun. If the sun were stopped, right into the center of the galaxy. Etc, etc. |
spaceheaded
Member Posts: 147
From: MD
Registered: Feb 2003
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posted 06-25-2003 04:10 PM
Isaac Newton's Universal Law of Gravitation says that every particle of matter in the Universe attracts every other particle with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them.I think that's the answer, but my head hurts when I think about it. Bill
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STEVE SMITH
unregistered
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posted 06-25-2003 04:37 PM
As an example to some of the above points, remember the Apollo's velocity kept slowing as it pulled away from the earth. It slowed as I recall to about 2,00 MPH, then accelarated as the Moon gravitational pull increased and became more than the earth's. I believe it got up to about 4.500 MPH as it entered Lunar orbit |
BLACKARROW
unregistered
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posted 06-25-2003 05:29 PM
I'm not a scientist or a mathematician, but I think the best way to answer this is to imagine an infinitely long ladder rising up from the Earth's equator into deepest space. Imagine an astronaut in a pressure suit with an endless supply of air. He starts climbing up the ladder, mile after mile. The "inverse square law" tells us that as he doubles his height above the ground, the pull of gravity exerted by the increasingly distant Earth reduces to a quarter. At a certain height, he will experience 1/2 of normal gravity. If he then climbs twice as far, the pull of gravity will drop to 1/8. When he doubles his height again, gravity will drop to 1/32. Then 1/128. Then 1/512. Then 1/2048. Then 1/8192. And so on. However many times he doubles his height, getting billions of miles up the ladder, that fraction of one gravity will get smaller and smaller, but it will never reach ZERO. In practice, our tireless climber will eventually reach a point where the gravitational pull of the sun, or a distant planet, will exceed the Earth's gravity, but Earth will still be exerting an almost vanishingly small gravitational pull. |
Aztecdoug
Member Posts: 1405
From: Huntington Beach
Registered: Feb 2000
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posted 06-25-2003 05:40 PM
Thanks everyone for your thoughts. Rizz, those links hit the nail on the head.You do lose weight with altitude. One article mentioned a man would be a couple of ounces less at the top of Mt. Everest versus Sea Level. But, that is very minor. The real key is freefall. Orbital flight is just a balanced free fall. Like those amusement park rides that drop you. You and your seat both fall at the same velocity thus you don't feel the seat contacting your body anymore. But in the case of orbit you fall in a circle around the Earth. I have recalled a space walker commenting somewhere that there is a tremendous sensation of falling once you leave the capsule. Ben I think your comments illustrate the big picture very well. "And yes, if the ISS were suddenly stopped, somehow, it would fall straight down to earth, vertically. If the earth were stopped, it would fall into the sun. If the sun were stopped, right into the center of the galaxy. Etc, etc." Interesting stuff. Thanks again everyone for your thoughts and input this has been bugging for some strange reason the last few days! ------------------
Warm Regards Douglas Henry Enjoy yourself and have fun.... it is only a hobby! [This message has been edited by Aztecdoug (edited June 25, 2003).] |
Ben
Member Posts: 1896
From: Cape Canaveral, FL
Registered: May 2000
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posted 06-25-2003 05:56 PM
The ISS orbits about 200 miles up. If you could stop the ISS in place, but not let it fall: i.e. if you had a platform above the earth at 200 miles, the gravitational force would be nearly the same on earth's sufrace. Maybe a few pounds less, but not much.I tried to explain this to my dad a few months go, and he didn't get it :-) so it's not the easiest concept to understand. People think that if you go into space, you "just" float. |
Ben
Member Posts: 1896
From: Cape Canaveral, FL
Registered: May 2000
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posted 06-25-2003 05:59 PM
I can add one more thing:Take the ISS or any satellite. The station is falling towards earth, simple as that. The difference is, at precisely 17,450 miles per hour, the station is falling towards earth at the same rate that the earths surface curves. The station is falling towards earth, but the earth is curving away under it. So, it will never hit the ground, but just constantly keep falling "around" it; constantly falling towards the earths surface. [This message has been edited by Ben (edited June 25, 2003).] |
chet
Member Posts: 1506
From: Beverly Hills, Calif.
Registered: Nov 2000
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posted 06-25-2003 07:52 PM
FWIW, I invested a few thousand dollars in Enron; I hit Zero G pretty rapidly after freefall.-Chet |
music_space
Member Posts: 1179
From: Canada
Registered: Jul 2001
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posted 06-26-2003 12:17 PM
Technically, you are experiencing microgravity as soon as you are falling, or flying through the air unpropelled. So in essence, you are under microgravity when you jump off a three-feet ladder, just as you are each time you briefly arc through the air between each steps while running.Microgravity labs, including some at NASA, achieve a few seconds of microgravity by dropping experiments down a tower. You too can have close to four seconds of microgravity in a dropping-tower-type ride in amusement parks -- once at the Six-Flags of Denver, I rode their dropping-ride 16 times in a row, which added up to about 60 seconds of micro-g total. (by the way, if you visit Las Vegas, while the Stratosphere hotel has, on top of its tower, something that looks like a dropping tower, which they call "Big Shot", it is not a dropping tower. This thing shoots you up, pulls you down with negative G's, shoots you up again some more. While the view is outstanding, this is the fastest ticket I know to nausea!) And it's not so much a function of altitude either. In fact, if there was a tube running down from the surface to the center of the earth and if you fell into it, you'd experience a form of reduced gravity, I guess. Besides, if you had a aircraft which could zip through ground-level atmosphere at proper speed, you could simulate an orbit and its microgravity effects. What an air-controller nightmare though! ------------------
Fran�ois Guay
Collector of litterature, notebooks, equipment and memories! [This message has been edited by music_space (edited June 26, 2003).] |
Carrie
Member Posts: 225
From: Syracuse, New York, USA
Registered: May 2003
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posted 06-26-2003 06:49 PM
And isn't it true you weigh (very slightly)less at the equator than the poles, due to greater forces (centrifugal, I _think_, though it's been a while since I took physics) lifting you off the surface?Complicating matters, Carrie 
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Ideals are like the stars...we may never reach them, but we can set our course by them. |
derek
Member Posts: 297
From: N.Ireland.
Registered: Jul 2002
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posted 06-27-2003 04:52 AM
I'm reading these posts with great interest as I'll be weightless 13 days hence....------------------
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Rizz
Member Posts: 1208
From: Upcountry, Maui, Hawaii
Registered: Mar 2002
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posted 06-27-2003 05:04 AM
derek-Are you going for a ride in a Mig-25??? Rizz |
ALAIN
Member Posts: 355
From: GENT, Belgium
Registered: Apr 2001
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posted 06-27-2003 02:16 PM
The first question is not 100% clear ... there're many aspects to Zero-g ...
But the topic-opener should read something on Lagrangian points |
Aztecdoug
Member Posts: 1405
From: Huntington Beach
Registered: Feb 2000
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posted 06-27-2003 03:45 PM
Alain,You are right. That is a good point. I realized after the data started coming in that the topic was sort of open for two directions. I did get an email off-line regarding lagrange points. In fact I had read some years ago in Discover magazine a great article on the topic. I think one topical application is to build a space station at one for true Zero G. Another is to use them for space travel using less fuel. Here a couple of links I dug up on them. http://www.genesismission.org/mission/lagrangepoints.html http://map.gsfc.nasa.gov/m_mm/ob_techorbit1.html
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Warm Regards
Douglas Henry Enjoy yourself and have fun.... it is only a hobby! [This message has been edited by Aztecdoug (edited June 27, 2003).] |
derek
Member Posts: 297
From: N.Ireland.
Registered: Jul 2002
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posted 06-27-2003 04:37 PM
Yes,Rizz,I'm catching the MIG express the day after I experience zero G,see my recent post under,"It will happen this summer" in News and Events.------------------
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Rizz
Member Posts: 1208
From: Upcountry, Maui, Hawaii
Registered: Mar 2002
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posted 06-28-2003 12:59 AM
God Speed derek!!!You are in for the ride of your LIFE  |
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