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#247217 - 07/15/09 03:31 PM what goes up?
Luke Luke Member Registered: 07/05/01 Posts: 241 Loc: Missouri	Ok science guys, perhaps you can help this ole hillbilly figure this out. When a spacecraft enters earth orbit it is enveloped in an ionspheric cloud cutting off radio communication. Yet when a spacecraft is launched it does not. Why? Isn't the speed needed to obtain orbit a constant, thereby when the speed is decreased one deorbits? _________________________ What a long strange trip it's been.
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#247223 - 07/16/09 03:57 PM Re: what goes up? [Re: Luke]
Darby Darby Administrator Senior Investigator Registered: 05/15/01 Posts: 4583 Loc: Santa Barbara, CA	Luke, When the vehicle is launched it doesn't obtain orbital velocity until the very end of the insertion event. During that phase the atmosphereic pressure (density) is decreasing and is at its minimum when orbital velocity is reached. It retains that velocity throughout its orbital period. When it comes down, leaves orbit, it is traveling at ~17,000 mph when it hits the atmosphere. That's the difference. The density of the gas (air) is increasing as it descends. Remember, density can be defined as the number of particles encountered per unit of time. If you're traveling very slowly in an otherwise dense gas you won't encounter radiant energy. But if you're traveling at a very high speed in an otherwise thin gas you can encounter many more particles per unit of time than when you were in the original situation. The "thin" gas becomes a very dense gas from your perspective. Imagine traveling at near the speed of light in the inter planetary regions of the Solar System. Sure, its "outter space" but when you're colliding with trillions of hydrogen atoms per second with the relativistic mass of plutonium its a brick wall. The situations are not mirror reflections of each other. In the end, however, you will discover that energy is conserved. It just presents itself in diffrent forms. On the upleg a good portion of the chemical energy is converted to gravitational potential energy. On the downleg a good portion of the gravitational potential energy is converted to radiant energy (heat) due to friction. On the upleg the vehicle just didn't have sufficient velocity, when the gas was dense, to form a significant plasma envelope around it. _________________________ E. W. "Darby" Darbyshire Administrator - Anomalies.net DarbyII@COX.net
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#247224 - 07/16/09 06:53 PM Re: what goes up? [Re: Luke]
Luke Luke Member Registered: 07/05/01 Posts: 241 Loc: Missouri	(Doh) Thanks Darby, I guess I just wasn't able to follow the process through. Very good explanation by the way. Any time you can get through a nogging thick as mine you have accomplished something! You should consider teaching. Somehow I was leaving the atmosphere thinning out of my thought process. So I would suppose it would take as much fuel/thrust to reenter the atmosphere as it would to leave in my universe, highly prohibitive. Hillbilly logic will normally get me in trouble. _________________________ What a long strange trip it's been.
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#247228 - 07/17/09 01:40 PM Re: what goes up? [Re: Luke]
Darby Darby Administrator Senior Investigator Registered: 05/15/01 Posts: 4583 Loc: Santa Barbara, CA	Originally Posted By: Luke (Doh) Thanks So I would suppose it would take as much fuel/thrust to reenter the atmosphere as it would to leave No problem. And thank you. Leaving and returning don't consume the same amount of fuel but if you broaden the definition to "energy" then you're absolutely correct. From launch to recovery you will use the same amount of energy (in various forms) on both legs. You might have to dig deep to find all of it but it will be there. In one sense the system obeys Hooke's Law - springs, rubber bands, pendulums, harmonic oscillators - conservation of energy. Take a pendulum. Make it a nice large one so you don't have to worry too much about friction with the air or the lever. Make the arm 4-5 meters long and hang a 10 kg weight on it so that its near the floor. Let it hang until it comes to a stop. Drop a plumb bob down to the floor and mark the spot below the weight where it is at rest. Now pull the weight back 15 or 20 degrees. Drop the plumb bob and mark the spot on the floor below it. Let it go. How far will it swing in the other direction? Exactly the same distance. Switch out the weight with a 20 kg weight (double the weight). Pull it back to the same mark and let it go. You doubled the weight so how far will it swing on the other side? Exactly the same amount as the 10 kg weight. Galileo did the same experiment with falling weights (though its doubtful that he actually dropped them off the Tower of Pisa). They accelerated at exactly the same rate no matter what the difference in weight between the objects. The rate of acceleration depends only on the local gravitational field not the mass of the objects being accelerated. The space craft is the pendulum. It swung up into orbit on one half phase and swung back down to land on the other half phase. Same energy on both half phases of the "oscillation". _________________________ E. W. "Darby" Darbyshire Administrator - Anomalies.net DarbyII@COX.net
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#247229 - 07/17/09 03:21 PM Re: what goes up? [Re: Darby]
Mr.P. Mr.P. Member Registered: 08/03/04 Posts: 2886 Loc: Atlanta	What comes down musta gone up? _________________________ Before morning constitutional, "Dear goD, for the shit yoU are about to receive, yoU are welcome."
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