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Super post - I've been trying to find info on the satellite collision..Regards Cormac

No, no, no! You don't want to even think about shooting an obsolete satellite down with a missile. That'll produce as much (or even more!) space junk than a collision between satellites will. The reason it sometimes is done (and mostly works) is because the satellite in question is about to re-enter, and busting it up makes the pieces less aerodynamic, and thus controls where the larger chunks end up reentering at (e.g., over the ocean, instead of over/into a city). But, for high altitude satellites, all a missile collision would do is create LOTS of pieces of high speed debris, something you certainly don't want.

There really isn't any way, short of a (unfunded) space tug, that obsolete satellites can be recovered and deorbited. Even the never satellites that are designed for handling obsolescence don't necessarily deorbit themselves. For geosynchronous satellites, it takes a rather huge delta-V to get them to reenter the atmosphere. So, a lot of these are merely moved to a slightly higher (or lower) parking orbit where they will free up space for a new geosynchronous satellite (and, a huge delta-V translates into an incredible expense for a satellite).

Of course, not all satellites are geosynchronous. There are quite a few LEOs (Low Earth Orbit satellites), such as the Iridium satellite involved in the collision. The reason for this is that geosynchronous satellites have to orbit at a specific altitude (23,000 miles, roughly) over the equator, and that's a long way for a radio signal to propagate (Remember that the strength of a radio signal drops off as the square of the distance.). So, a satellite at, oh, say 400 miles altitude will have a signal about 3300 times as strong as one in geosynchronous orbit (or, conversely, it can receive signals 3300 times weaker, and needs 3300 times less transmitter power)! Of course, the down side of a LEO is that it can't see very far, so the ground access footprint is quite limited, resulting in the need for an array of satellites to cover an area.

Toss into this the fact that quite a few of the Soviet/Russian communications satellites are in what are called Molniya orbits, which are polar, highly eccentric orbits, and you have the makings of an imminent collision between such a satellite and some of the other LEOs in lower inclination orbits (The molniya orbits are useful since they allow coverage of high latitudes, which a large amount of Russia is at.).

Now, for some real fun, since the energy of a satellite collision depends not upon the speed of a satellite, but the velocity [1], consider what will happen when a retrograde satellite hits a non-retrograde satellite.

[1] Velocity is a vector which accounts for the direction, while speed is only a scalar, and does not account for direction.

Fortunately, for all of us, Project Westford was a startling failure, and wasn't repeated.


P.S. I'm not a rocket scientist, but I play one... :*)

Wow, Dave - you should have written this blog entry. The Rocket Scientist was telling me about Molniya orbits, but I didn't have time to mention them. Thanks!

Low sunspot counts don't cause an increase in drag. It's probably better to say that the processes that lead to more or fewer numbers of sunspots also affect the energy density output of the sun, which is ultimately how the sun affects how compressed the magnetosphere gets. The sunspots are more like the speedometer than the driver.

And having established that mental image, I'll commit the cardinal sin of immediately abandoning it in favor of another. Imagine an inner tube mounted on a pole in a stream of flowing water. In fact, imagine a whole series of them nested like Russian dolls. If you make the flow stronger, it compresses the donuts in the direction facing the flow, the way that squeezing balloon animals distorts their shape. If make the flow weaker, external pressure drops, and the donuts can undo some of the shape distortion.

In this case the nested donuts are the earth's magnetosphere and ionosphere. When solar wind reaches the earth, it pushes on the magnetosphere/ionosphere system similar to how the water flow pushes on the nested donuts. If you increase the ram pressure of the solar wind (i.e., it flows faster, or the particle density increases), the magnetosphere shrinks, as does the ionosphere since there are coupling mechanisms that keep the two related. If the ram pressure drops, the opposite happens. If the sun puts out more energy, then ionospheric density rises since more particles are being ionized, and the atmosphere as a whole grows, like when you heat the air in a hot air balloon. (This, coincidentally, is why density drops on the nightside of the earth compared to the dayside. No ionizing sunlight, so ions recombine into neutral atoms and molecules. In fact, no energy input, so atmospheric density drops at any given altitude since temperature drops.)

During solar quiet times, which we know from things like ACE data and counting sunspots and so on, the pressure typically drops compared to active solar periods, the magnetosphere expands, allowing the ionosphere/atmosphere to expand, which means there is an increase in atmospheric density at a given altitude. Greater density, greater drag. I'm told that this is a pretty accurate explanation for why Skylab's orbit decayed significantly faster than was planned, and that a fair amount of what was figured out as a result of learning what happened to Skylab. It also is why the shuttle has been used a number of times to boost ISS into higher-radius orbits.

I know this is off topic, but I have a physics question.
In the game of computer solitaire, does dragging a stack of cards require more energy than dragging one?
At first glance this seems like a frivolous question, but it seems to me that amount of electrons emitted might be different.
I realize there wouldn't be a huge difference.
Thanks for considering this in advance.

Plenty of satellites are in Polar Declining orbit. Most weather satellites and some intelligence satellites are polar. A satellite in polar orbit covers the entire Earth by "flying" directly from pole to pole while the Earth revolves under it.

For U.S. launches it's easy, if it's launched from Vandenberg AFB then it's going into polar orbit; launches from Kennedy Space Center are going into equatorial orbit (geosynchronous or LEO): if it is actually launched from Cape Canaveral AFS then it's a military bird and probably is not going to be covered in the news.

Your local and national news anchor have no clue and refer to KSC as "Cape Canaveral". The shuttle does not take off from or land at Cape Canaveral. There have been no manned launches from the Cape since Gemini.

oops - I meant rotates, not revolves.

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    • Heavy G
      The perfect pick-me-up when gravity gets you down.
      2 oz Tequila
      2 oz Triple sec
      2 oz Rose's sweetened lime juice
      7-Up or Sprite
      Mix tequila, triple sec and lime juice in a shaker and pour into a margarita glass. (Salted rim and ice are optional.) Top off with 7-Up/Sprite and let the weight of the world lift off your shoulders.
    • Listening to the Drums of Feynman
      The perfect nightcap after a long day struggling with QED equations.
      1 oz dark rum
      1/2 oz light rum
      1 oz Tia Maria
      2 oz light cream
      Crushed ice
      1/8 tsp ground nutmeg
      In a shaker half-filled with ice, combine the dark and light rum, Tia Maria, and cream. Shake well. Strain into an old fashioned glass almost filled with crushed ice. Dust with the nutmeg, and serve. Bongos optional.
    • Combustible Edison
      Electrify your friends with amazing pyrotechnics!
      2 oz brandy
      1 oz Campari
      1 oz fresh lemon juice
      Combine Campari and lemon juice in shaker filled with cracked ice. Shake and strain into chilled cocktail glass. Heat brandy in chafing dish, then ignite and pour into glass. Cocktail Go BOOM! Plus, Fire = Pretty!
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      Dr. Strangelove's drink of choice.
      3/4 Triple sec
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      2-3 drops Grenadine
      Fill shot glass 3/4 with Triple Sec. Layer Bailey's on top. Drop Grenadine in center of shot; it should billow up like a mushroom cloud. Remember to "duck and cover."
    • Mad Scientist
      Any mad scientist will tell you that flames make drinking more fun. What good is science if no one gets hurt?
      1 oz Midori melon liqueur
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      151 proof rum
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      Warning: may result in amplified stimulated emission.
      1 oz Southern Comfort
      1/2 oz Amaretto
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      Combine all liquor in a full glass of ice. Shake well. Garnish with orange and cherry. Serve to attractive target of choice.
    • Quantum Theory
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      3/4 oz Rum
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      1/4 oz Grand Marnier
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      Fill with Sweet and sour
      Pour rum, strega and Grand Marnier into a collins glass. Add pineapple and fill with sweet and sour. Sip until all the day's super-positioned states disappear.
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