Space dust, particles, meteors, and the like

[knlwtchr 0]

OK, I think we have the Black hole debate hashed out. How about space debris? I imagine most things burn up in the atmosphere (which I dont really fully understand yet), but what about those things that make it through? Why aren't meteors landing on garages? Or making craters in national parks? Or whatever? Do things bounce off the atmosphere?

 

Just had a thought, too. When the space shuttles come back and they re-enter the Earths atmosphere, I know they come down on a curve to match rotation (Is that right?), is there a point when, like a piece of space debris, it is no longer flying towards Earth, but being pulled, or is it always being pulled? The velocity and strength/force it must take to slow down any object coming to Earth must be incredible. It messes with your head!

[Tachyon 0]

what about those things that make it through? Why aren't meteors landing on garages? Or making craters in national parks? Or whatever? Do things bounce off the atmosphere?

To put it simply, space is very big. Hugely, amazingly, mind-bogglingly big. While the Earth may seem like a large target, it's relatively small compared to the amount of "empty" space around the Earth. Moreover, the Earth itself is in motion relative to any object with which it might collide, so an object's trajectory has to take it to where the Earth will be in its orbit around the Sun, not where it is right now. So statistically speaking, more objects are going to miss the Earth than collide with it. We've been lucky so far and avoided hitting anything large enough to cause mass extinctions.

 

I'm sure there are others on this board more qualified to answer questions regarding atmospheric entry/re-entry, so I won't touch on how the space shuttle re-enters the atmosphere. On the subject of "flight" versus "pull": everything "orbiting" Earth is actually in constant free-fall around the Earth. Every object with mass in the universe exerts a gravitational pull on every other object; the strength of that pull decreases drastically with distance. The Earth exerts a gravitational pull on all the objects that orbit it, but these objects are travelling fast enough that instead of falling into the Earth, they fall around it constantly, hence "constant free-fall." Eventually these objects' orbits may decay, which means their velocity decreases to the point that they can no longer maintain that state of free fall, and the object crashes back toward Earth's surface.

[Sorehl 0]

How about space debris? I imagine most things burn up in the atmosphere (which I dont really fully understand yet), but what about those things that make it through? Why aren't meteors landing on garages? Or making craters in national parks? Or whatever? Do things bounce off the atmosphere?

I assume by space debris, you mean matter that falls to Earth rather than orbital debris like satellites. The latter topic is discussed elsewhere on this board, so I won't treat it here. By far, the vast majority of material that falls to Earth burns up in the atmosphere. This is due to the tremendous decelleration involved in an object moving at several km/sec (yes, that's kilometers per second) in a vacuum hitting a comparatively dense wall of atmospheric gases. And there's a lot of it, mostly grain sized. The Earth is estimated to gain about 40 tons of mass each day in interplanetary material.

 

Meteors do land on garages, but this is rare because: 1) Sizable meteors that can survive re-entry are less common than grain-sized ones, and 2) Not much of the Earth is covered by garages, and 3) People don't always see or recognize a meteor when it does hit something. A meteor capable of making a crater would have to be quite large. The largest, recent one was the Tunguska blast of 1908, even though it appears to have vaporized before hitting. No crater, but it was like a 10 megaton blast and knocked down forest trees 15 miles outward.

 

Things do skim the atmosphere and bounce off. There's a famous film of a 3m-8m meteor doing this over the Grand Teton National Park - you can find more information about it by searching The Great Daylight 1972 Fireball.

 

Just had a thought, too. When the space shuttles come back and they re-enter the Earths atmosphere, I know they come down on a curve to match rotation (Is that right?), is there a point when, like a piece of space debris, it is no longer flying towards Earth, but being pulled, or is it always being pulled? The velocity and strength/force it must take to slow down any object coming to Earth must be incredible. It messes with your head!

The Space Shuttle operates in low-Earth orbit (~200mi up) and it moves in a trajectory that matches the Earth's rotation. Orbits that move against the Earth's rotation are called retrograde and take extra fuel to get up there in that direction - you're actually having to fight against the spin and still reach orbital velocity.

 

Tachyon hit all the right points about gravity and orbits. If you're in orbit, you're still being pulled by the planet. You're just moving so fast that you're falling over the edge of the Earth's curve. (The weightless effect is because you're all falling together, like riders on the Vomit Comet.) Imagine firing a cannonball so fast that during the time it falls downward, the Earth's surface curves away from it. If you can keep that speed up, you just keep falling around the planet. Satellites and shuttles work by not just rocketing up to space where there's little atmospheric drag, but also by rocketing sideways so they are moving fast enough to fall around the Earth. That's why launch columns curve away and don't go straight up.

[Jorahl 0]

Understanding why things burn up in the atmosphere is like thinking about slamming on your brakes. You do that at high enough speed and your tires leave a black skid mark on the road. A random space rock tumbling through the emptiness of space hitting the atmosphere does about the same thing.

 

It's nice and happy in the vacuum between the planets with not much of anything ever getting in it's way. Then it comes racing towards Earth and hits the atmosphere. Right now where I'm at we've got a nice wind going at about 15 miles an hour and it's kinda hard to keep your hat on if we get a gust. The kinds of speed the rock is going will take more than your hat off. Find a big ball of mud and shoot it with your water hose. That's kinda what happens to any space debris traveling at speed through the atmosphere. The object has to be big enough to have something left of it by the time it reaches the surface or be made of something hard enough to survive reentry.

[knlwtchr 0]

The Earth exerts a gravitational pull on all the objects that orbit it, but these objects are travelling fast enough that instead of falling into the Earth, they fall around it constantly, hence "constant free-fall."

 

Interesting, but I guess those objects are moving at the same speed in the same direction? Or are there objects moving faster than others, therefore creating a danger of rear ending each other?

 

2) Not much of the Earth is covered by garages,

 

I like that! =0]

 

The Earth is estimated to gain about 40 tons of mass each day in interplanetary material.

 

40 TONS of mass per day? Holy cow! Is there some sort of exchange? In that I mean, is the atmosphere losing mass in other ways to balance out this accumulation? Incredible!

[Sorehl 0]

Interesting, but I guess those objects are moving at the same speed in the same direction? Or are there objects moving faster than others, therefore creating a danger of rear ending each other?

To quote Tachyon quoting Douglas Adams, space is mind-bogglingly big. The orbital space above the Earth is, well, larger than the surface of the Earth. Then you have to add that third dimension, up. (But don't fret - even Khan had a problem using it.) Objects can orbit at one of various orientations, called inclination. They can orbit at any height. The orbits can be roughly circular, or wildly elliptical like a Molniya orbit. (For a look at a previous discussion of orbits and what's where, see the topic Ringed Earth.)

 

You can't actually rear-end someone in the same orbit. An artifact of orbital mechanics is that the geometry, and where you are along the path, determines your speed. If you change your speed or direction, the orbit itself changes.

 

The key is that, even when orbital paths cross, the satellites aren't there at the same time. We have collisions at intersections on Earth because: 1) We have much more traffic, 2) We're usually limited to two-dimensions (note that overpasses solve this), and 3) we tend to be further restricted to specific trafffic corridors (flight paths or roads) and popular destinations. None of these are true in orbit (although the congregation of GEO satellites comes close).

[knlwtchr 0]

To quote Tachyon quoting Douglas Adams, space is mind-bogglingly big. The orbital space above the Earth is, well, larger than the surface of the Earth. Then you have to add that third dimension, up. (But don't fret - even Khan had a problem using it.) Objects can orbit at one of various orientations, called inclination. They can orbit at any height. The orbits can be roughly circular, or wildly elliptical like a Molniya orbit. (For a look at a previous discussion of orbits and what's where, see the topic Ringed Earth.)

 

You can't actually rear-end someone in the same orbit. An artifact of orbital mechanics is that the geometry, and where you are along the path, determines your speed. If you change your speed or direction, the orbit itself changes.

 

The key is that, even when orbital paths cross, the satellites aren't there at the same time. We have collisions at intersections on Earth because: 1) We have much more traffic, 2) We're usually limited to two-dimensions (note that overpasses solve this), and 3) we tend to be further restricted to specific trafffic corridors (flight paths or roads) and popular destinations. None of these are true in orbit (although the congregation of GEO satellites comes close).

 

Neat! I know that as you gradually move away from Earth, things become more and more dimensional. Things are that way now, but, its like you say, its comparable to driving a car (two dimensions) or flying a plane (more than two dimensions).

 

If there is no air in space, is there also no vacuum? Would it also stand to reason that when a ship or an object flies by something, it doesn't effect it, like it wouldn't cause a gust of wind or any other kind of displacement?

[knlwtchr 0]

I have another question for this string, though it may be a little off topic. Why is this satellite issue with N. Korea such a problem? Don't other Countries launch satellites regularly? Why worry about N. Korea?

[Sorehl 0]

I have another question for this string, though it may be a little off topic. Why is this satellite issue with N. Korea such a problem? Don't other Countries launch satellites regularly? Why worry about N. Korea?

 

Because it wasn't a satellite launch. It was a test of their long-range missile capability, which the U.N. told them not to do since they are also a nuclear power. We see how effective that was.

 

The "satellite" in question didn't even separate from the final stage and went splash in the Pacific. Even if it had made it, all it was designed to do was broadcast a signal hailing their "Great Leader".

 

So this was just a bit of belligerent saber-rattling to get attention, frighten the Japanese, and provide some negotiation leverage for their next blackmail attempt. Upside: maybe it'll remind the new U.S. administration why we continue to need a missile defense program. And why our European allies actually don't want us to trade it away.

 

Bias Alert: I should note my RL involvement in the aerospace community, currently employed in the missile defense sphere, so you may feel free to consider my bias in the above statements.

[knlwtchr 0]

The "satellite" in question didn't even separate from the final stage and went splash in the Pacific. Even if it had made it, all it was designed to do was broadcast a signal hailing their "Great Leader".

 

They still keep saying their rocket made it into space. That Jong Ill is a nut case!

 

Hey Sorehl, do you know of any way I can figure out the information on Heavens-above.com without going through a year of calculus? Its giving me positional data of certain objects in longitude and latitude, but I still have no idea where that would be relative to my position on the Earth.

[will_marx 0]

They still keep saying their rocket made it into space. That Jong Ill is a nut case!

That's the problem with Third World dictatorships. They can never separate fact from fiction.

 

Hey Sorehl, do you know of any way I can figure out the information on Heavens-above.com without going through a year of calculus? Its giving me positional data of certain objects in longitude and latitude, but I still have no idea where that would be relative to my position on the Earth.

Well, most satellites wouldn't remain over one fixed location. But if you have a handy-dandy GPS receiver, you can get your local coordinates from it, and that will give you a rough approximation on where their orbital paths cross over you. Unless you happen to be on the equator, where geostationary and -synchronous orbiting satellites orbit at 22,236 miles from the Earth.

 

A geostationary orbit is one in which a satellite orbits the earth at exactly the same speed as the earth turns and at the same latitude, specifically zero, the latitude of the equator. A satellite orbiting in a geostationary orbit appears to be hovering in the same spot in the sky, and is directly over the same patch of ground at all times.

A geosynchronous orbit is one in which the satellite is synchronized with the earth's rotation, but the orbit is tilted with respect to the plane of the equator. A satellite in a geosynchronous orbit will wander up and down in latitude, although it will stay over the same line of longitude. Although the terms 'geostationary' and 'geosynchronous' are sometimes used interchangeably, they are not the same technically; geostationary orbit is a subset of all possible geosynchronous orbits

http://www.wisegeek.com/what-is-geostationary-orbit.htm

[Sovak 0]

That's the problem with Third World dictatorships. They can never separate fact from fiction.

 

 

Third world? Perhaps you have missed practically everything that ever came out of Washington D.C.?

[will_marx 0]

Third world? Perhaps you have missed practically everything that ever came out of Washington D.C.?

I tend to ignore what comes out of Washington, Sovak, except for my military pay raises (as pathetic as they are) and any deployment orders

[eagle 0]

Well, most satellites wouldn't remain over one fixed location. But if you have a handy-dandy GPS receiver, you can get your local coordinates from it, and that will give you a rough approximation on where their orbital paths cross over you. Unless you happen to be on the equator, where geostationary and -synchronous orbiting satellites orbit at 22,236 miles from the Earth.,...or deep within a multi-layered canopy jungle...that really tubes on a covert mission,from a 1971..ish experience.,even most recent as of 1982.!,... :o

[Sorehl 0]

Do you know of any way I can figure out the information on Heavens-above.com without going through a year of calculus? Its giving me positional data of certain objects in longitude and latitude, but I still have no idea where that would be relative to my position on the Earth.

Not a problem.

 

Positional data for Iridium flares or satellite overpasses is given in relative Azimith and Altitude. That is, assuming you've input your position in latitude and longitude (via their city locator or GPS), they tell you when to look in terms of relative Azimth (which direction, in 360 degrees starting with north as 0) and relative Altitude (how high in 90 degrees, with the horizon at 0). (Sometimes they simpifly Azimuth by saying N, NNE, NE, etc.) So 90 degrees Az is due East, and 45 degree Altitude is halfway up from the horizon. Actually, this is how they plots bearings on Star Trek: The Next Generation - although they would say 90 mark 45. In Trek, zero Azimuth is measured either relative to the front of the ship or absolute toward the galactic center.

 

Back to satellites, if you wanted to know when you can see the International Space Station, you'd have to first type in your current coordinates (or sign up for a free account which will remember your position). You click the ISS observations, the website makes the calculations, and says:

 

Date: 15 Apr

Mag(nitude): 0.1 (a measure of the apparent brightness on a Greek-designed exponential scale - lower is better and subzero is best)

Start Time: 05:00:25

Alt(itude): 10

Az(miuth) S

Max Time: 05:02:40

Alt(itude): 30

Az(miuth) SE

Stop Time: 05:04:55

Alt(itude): 10

Az(miuth) E

 

Which means at your location on the 15th of April at 5 a.m., the ISS will appear due south near the horizon (10 degrees is the lowest "mask angle" they'll claim, since there's usually a house or a billboard or a mountain on the horizon). A little over two minutes later, it will reach its highest point about a third of the way up the sky toward the Southeast, then descend until it disappears in the East at the horizon a little over two minutes after that. That's a bright view lasting nearly five minutes. I actually find it cooler to see it disappear much higher in the sky, which means it's passing into the Earth's shadow and no longer illuminated by the sun. One way to prove you're not looking at a mere airplane.

 

For essentially fixed objects like stars, nebulae, and galaxies, as well as slow moving objects like planets and comets, the site provide a more cryptic method known as Geocentric data using Right Ascension and Declination. Not impossible to figure out, but its much easier to just look at the Whole Sky Chart and see what's visible on a particular night and time.

 

Hope this helps. If you've never tried, there's usually several good satellite observations available on any given night or early morning. As I've said before, Iridium flares are my favorite. I'd be interested if anyone takes the challenge and sees something.

[knlwtchr 0]

Cool! Thanks, Sorehl! I actually didnt think there would be a way to understand the scientific gabbilty-gook, but I completely understood what you wrote here. I dont think there is anything going on in my area until the 13th, but Ill keep my peepers open and let you know! =0]