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Post by Moon Man on Nov 16, 2005 8:58:41 GMT -4
These tables may help with the atmosphere question. As you can see, the Earth's atmosphere extends thousands of kilometers into space, however it becomes extremely thin. The International Space Station orbits at about 400 km at which the air is only 1/468,000,000,000 as thick as at sea level. Even at this low density the atmosphere stills causes the ISS orbit to slowly decay, requiring occasional propulsive boosts to keep it in orbit. Good morning everyone. The ISS was raised 5 mile just last week by the Russians.
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Post by Moon Man on Nov 16, 2005 9:16:26 GMT -4
To me it does. But does it to MM? It didn't have any effect the last time we tried that argument, he just ignored it and kept on pushing the same old line. Ha! I accept and agree that temps cannot be measured. I have agreed with you folks on this since I was on BA, however, I still believed that it is hot or cold out in empty space, despite the temps not being measurable.
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Post by echnaton on Nov 16, 2005 9:20:37 GMT -4
It didn't have any effect the last time we tried that argument, he just ignored it and kept on pushing the same old line. Ha! I accept and agree that temps cannot be measured. I have agreed with you folks on this since I was on BA, however, I still believed that it is hot or cold out in empty space, despite the temps not being measurable. On what facts about nature do you base this believe?
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Post by sts60 on Nov 16, 2005 9:49:12 GMT -4
Good morning everyone.Good morning, and some apologies for being rather snippy on the other thread. The ISS was raised 5 mile just last week by the Russians.This can be done with chemical rockets (as has been done to the Station by the Shuttle and the Russian Progress vehicle which you indicated), which is cool, by ion thrusters (now in commercial use on satellites) - even cooler, or by electromagnetic tethers - the coolest of all. Using the planet's magnetic field for a step. Therefore, since we agree that a shadow on earth would be very short, if at all, in the summer,Remember, it's not just a function of it being summer (which raises the highest point in the sky for the Sun's path), it's also a function of time-of-day: shadows are always shorter at noon than in morning or everning. The Apollo lunar activities took place during lunar morning. and since we agree that the sun on the moon and earth shine equally as bright, for the most part, then why are there major shadows on the moon during the summer missions..?Bu "major", I assume you mean fairly elongated. As above, they were there during lunar morning, so the Sun was relatively low in the sky. Outer space is a vacuum. Earth is not. The vacuum bgins just beyond our atmosphere. What is our atmosphere made of that prevents the vacuum from penetrating it..?The air is pulled down by gravity, just like everything else. It's squashed towards the ground. Of course, individual air molecules (nitrogen, oxygen, water vapor, etc.) whiz around up, down, and sideways so everything doesn't all just settle down; but the overall effect means that the air just thins out as you go higher. There's no sharp transition from "air" to "vacuum"; it's fairly arbitrary. The density profile of the air is pretty well modeled by the logarithmic function you get when you apply ordinary kinematics to it; not perfectly, but pretty well. So air it keeping the vacuum out and the vacuum is not keeping the air in our atmosphere..?
Is it air pressure that keeps the vacuum out..?
Why is the atmosphere ceiling at the height it is and not, say, another 100 miles into space before the vacuum begins..?Air doesn't "keep the vacuum out"; the vacuum is just that part of the Universe from which you've excluded air by pumping it out of a chamber, or by hugging it down towards the planetary surface with gravity. But in the latter case, again, the transition is gradual. If the atmosphere was made of different stuff, if it was a different average temperature, or if the gravitational pull of the Earth was different, then it would extend a greater or lesser amount into space. One of the interesting effects of the second item is how increased solar activity during the 11-year solar cycle heats the upper atmosphere, expanding it, and causing greater drag on low-orbiting satellites, which makes their orbits decay faster. Where is the ozone layer located..? Right outside our atmosphere or further out..? If it is further out is it beyond the height of the space station..?Upper atmosphere, below "space" and the ISS orbit. If it is below the space station our we not creating holes in it by flying through it over and over again..? even if we're only penetrating it for a few seconds each time given the speed the shuttle is doing..?No hole, no more than an airplane makes flying through the air, but there has been some argument about Shuttle SRM (solid boosters) exhaust products having some depleting effect on ozone. Also, the ozone layer protects us from harmful rays from the sun, so what protects the spacestation and the astronauts (yeah I know they are inside it and not outside) if there is no ozone layer inbetween the earth and the moon..?The structure of their vehicles or space suits, and the coatings on their windows or visors, keeps the ultraviolet light out. Heck, my contact lenses block 98% of UV-A or -B or whatever.
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Post by Moon Man on Nov 16, 2005 10:26:51 GMT -4
Ha! I accept and agree that temps cannot be measured. I have agreed with you folks on this since I was on BA, however, I still believed that it is hot or cold out in empty space, despite the temps not being measurable. On what facts about nature do you base this believe? It is said temps cannot be maesured, but I based my theory on it still being cold in space because Apollo 13 astronauts complained of being cold. It was also mentioned that they dump their human waste in space and it froze. We had also discussed the fact that only an object in space gets heated up to temps of +250 degrees F from the sun rays, however, cold is not created by cold rays, or night rays, it is cold because of the lack of sun rays, in my opinion. sts60, no need to apologize. I like the bickering smart@$$ comments. You're extremely smart, no doubt, but you're also funny and I like that. I'm not only here to learn I'm also here for some laughs, or else it would get boring really quick. Thanks for your answers above.
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politik
Venus
on a crusade against ignorance
Posts: 83
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Post by politik on Nov 16, 2005 10:41:12 GMT -4
We had also discussed the fact that only an object in space gets heated up to temps of +250 degrees F from the sun rays, however, cold is not created by cold rays, or night rays, it is cold because of the lack of sun rays, in my opinion.
Did you read my post on the moon/Mercury comparison?
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Post by Moon Man on Nov 16, 2005 10:56:04 GMT -4
Yes, I read every message, however, there is so many messages and so much information to absorb that it doesn't all register at once. I'm a lay spaceman after all. Thank you for joining in and sharing your wisdom.
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Post by Jason Thompson on Nov 16, 2005 11:09:31 GMT -4
Apollo 13 astronauts complained of being cold.
That's because their spacecraft radiated its heat into space faster than it could generate it once all the systems were closed down. That does not mean it was cold in space.
It was also mentioned that they dump their human waste in space and it froze.
An effect that has been explained in this thread as being due to pressure (or rather lack of pressure), not temperature. Some water first boils, then the remainder freezes and then sublimes. This is not a temperature related phenomenon. As I explained earlier, with the right equipment you can get water to freeze and boil at room temperature.
We had also discussed the fact that only an object in space gets heated up to temps of +250 degrees F from the sun rays, however, cold is not created by cold rays, or night rays, it is cold because of the lack of sun rays, in my opinion.
Right. let's see if we can clear this up.
You have asked, on many occasions, how hot or cold it is in space. We all got very frustrated because it seemed to take an inordinate amount of effort to explain to you that you cannot define how hot or cold space is because space is simply an absence of matter, and hence cannot have properties such as temperature. There is simply nothing there to be hot or cold.
How hot or cold an object in space gets depends on what it is and how it behaves thermodynamically. I guess at a pinch you could say it is cold in space because an object in unilluminated space will eventually get very cold as it radiates its heat away.
What you must remember in these conversations, however, is that you are largely dealing with scientists and engineers, and tackling scientific and engineering subjects. You can say it is cold in space, but you cannot then use that seriously oversimplified generalisation to argue points about the thermal behaviour of things like spacecraft and spacesuits, and it certainly doesn't apply to the behaviour of liquids thrown into space.
To give you an example, the crew cabin inside Apollo 13 got very cold. However, for some part of the flight after the accident one side of the exterior got rather warm because the spacecraft was not performing the slow roll that it would have been performing in a normal flight. As such one side was exposed to the sun for an extended period and one side was in continual shadow. Moreover, because the different parts of the spacecraft were made of different materials, different parts of the sunlit side warmed up at different rates, and different parts of the shaded side cooled at different rates, and when the crew were able to roll the stack again different parts of the spacecraft had reached different temperatures, despite being exposed to the same environment for the same period of time (this was a major engineering concern because of the physical stress it placed on the systems). The question is, which part would you use to say how hot or cold it was in space? Do you see where the problems are with this?
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Post by AstroSmurf on Nov 16, 2005 11:13:15 GMT -4
Aquarius (the Apollo 13 LM) got cold because it was designed to lose heat if left to its own devices. With the electrical equipment running and heating it, this would normally result in a comfortable temperature inside. Since they had to conserve power, this equipment was turned off as much as possible. Ergo, the generated heat no longer compensated for the designed heat loss, and it got cold.
Skylab had the exact opposite problem - IIRC, part of the external shielding had fallen off, so temperatures rose higher than intended. They finally rigged a sheet of metal outside to keep temperatures down.
You can have ten temperature readers sitting side by side in space, all reading different (and correct) values at the same time. There is no one true temperature value - it can be more or less anything; you have to study the exact conditions to be able to tell.
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Post by sts60 on Nov 16, 2005 11:26:37 GMT -4
We had also discussed the fact that only an object in space gets heated up to temps of +250 degrees F from the sun rays,
Think of it this way. The Moon has been around for billions of years, constantly toasting in the sunlight (the tiny percentage of area occasionally shadowed by the Earth is negligible for this purpose). It has had waaaay more than enough time to come to thermal equilibrium.
Why, then, isn't the entire Moon 250 deg. F?
The Moon, after all, is an object in space. Sure, it's a large object, but it's had all those billions of years to heat up. There's no atmosphere to reflect solar heat away. Just a chunk of rock - an object - in space, heated by the Sun.
Moon Man, what do you think?
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Post by Moon Man on Nov 16, 2005 11:42:19 GMT -4
Thanks Jason and astro.
New question.
If you had a battery operated go cart or golf cart on earth and you climb a hill it's going to discharge the battery quicker than driving it on level ground.
When the rover was ascending a hill on the moon does it also drain the battery quicker..?
Apollo 17 was in a valley so I am assuming they climbs some hills, even if it was gradual.
Also, there is no atmosphere on the moon and the rover had a top speed of 8 mph. There is, however, 1/6 gravity, as compared to earth. Lets say they were doing 8 mph and began climbing a long hill, would they maintain that 8 mph speed going up a hill or would they slow down a bit..?
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Post by Moon Man on Nov 16, 2005 11:48:40 GMT -4
Moon Man, what do you think? I think it's all very interesting, but I don't pretend to grasp and understand all of it as of yet.
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Post by Jason Thompson on Nov 16, 2005 12:07:25 GMT -4
If you had a battery operated go cart or golf cart on earth and you climb a hill it's going to discharge the battery quicker than driving it on level ground.
When the rover was ascending a hill on the moon does it also drain the battery quicker..?
Almost certainly. But do bear in mind that the rover was designed to cope with hills and valleys as well as level ground.
Apollo 17 was in a valley so I am assuming they climbs some hills, even if it was gradual.
Also, there is no atmosphere on the moon and the rover had a top speed of 8 mph. There is, however, 1/6 gravity, as compared to earth. Lets say they were doing 8 mph and began climbing a long hill, would they maintain that 8 mph speed going up a hill or would they slow down a bit..?
They would slow down a bit, since they would now be working against the gravity of the Moon. However, the rover went on circuits, not one-way trips. The extra work done going uphill would be balanced by the effort saved going downhill when they returned to the LM.
This sounds like you're heading to the battery debate again. I thought that was confined to the other thread.
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Post by Moon Man on Nov 16, 2005 12:16:18 GMT -4
Thanks Jason. It was just a general question that I wondered about, and you're right, I should've asked it in the battery debate thread. Sorry.
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Post by sts60 on Nov 16, 2005 12:17:22 GMT -4
The idea was to extrapolate from your notion that an object in space at the Earth's distance from the Sun must heat up to 250F in the sunlight. But the Moon is an object in space, and has been in direct sunlight for billions of years. By your thinking, the entire Moon should be at 250F.
Of course, it's not. The Moon is in "dynamic equilbrium" - that is, as a whole it doesn't get hotter or cooler over time due to (roughly constant) solar heating. The parts of it exposed to the Sun heat up, unevenly because of optical properties, composition, size, and view factors; this heat is radiated out to deep space all the time. As parts of the Moon rotate into night, the heat radiation (not to be confused with ionizing "radiation" like gamma rays) continues to reject heat away, but since there is no more heat input from the Sun, those parts get cooler - again, unevenly - until lunar morning comes and the cycle repeats.
The same thing is done with spacecraft, except that we can precisely control the rates at which they absorb external heat, generate internal heat, and reject (via radiation) heat to their surroundings (i.e., cool themselves). Balancing these factors keeps spacecraft thermal engineers busy, but obviously it works, because otherwise DirecTV would be charging people a hundred bucks a month for 637 channels of static.
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