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NASA Warns of Cluttered Space
Ant wrote to mention a National Geographic article looking at the cluttered nature of Near-Earth Orbit. From the article: "Since the launch of the Soviet Union's Sputnik I satellite in 1957, humans have been generating space junk. The U.S. Space Surveillance Network is currently tracking over 13,000 human-made objects larger than four inches (ten centimeters) in diameter orbiting the Earth. These include both operational spacecraft and debris such as derelict rocket bodies. 'Of the 13,000 objects, over 40 percent came from breakups of both spacecraft and rocket bodies,'Johnson said."
Space.com has a breakdown of responsibility by country of some of the larger debris in space.
And if you're really hardcore into space debris (it's hard to even type that without laughing), Orbital Debris Quarterly News is your magazine!
My work here is dung.
Java based orbit tracker courtesy of NASA:
3 D.html
http://science.nasa.gov/Realtime/JTrack/3D/JTrack
Coding with assembly is like playing with Legos. Coding an application in assembly is like building a car with Legos.
check out http://www.tethers.com/ They have a net thingie for grabbing space debris, and tethers for dragging debris out of orbit!
LEO's pretty fast (hours to years), but for specifics, it really depends on the orbit and the object. A lightweight object with a large cross section at a 180km orbit may take only a day to reenter. A heavy object with a small cross section at 450 km may stay up for a decade.
;)
Unfortunately (assuming my simulations are correct), orbits tend not to decay circularly. Rather, they tend to become more elliptical until the orbit finally intersects the atmosphere enough that it can't escape. Thus, you can't count on them being in too low of an orbit for you to collide with them as their orbit decays.
Now, GEO's a whole different story. Things in GEO tend to stay up, but they tend to not stay where you want them to stay
Son, a woman is a lot like a refrigerator. They're six feet tall, 300 pounds... they make ice... umm...
etc to put their own systems in place to ensure GPS access during troubled times?
Correct me if I am wrong, but GPS satellites are in geosynchronous orbit a couple earth radii (radiuses?) out. That makes a sphere with one heck of a huge "surface", and I am sure there is a heck of a lot of room for oodles more junk out at that range before it ever becomes a problem. The problem is low earth orbit, which has a considerably smaller "area" (or volume if you include a chunk of height).
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Drag forces (yes, there's drag even at LEO) for objects of the same cross-section would be the same regardless of mass, so a lighter objects would slow faster. So, the rate of decay is proportional to cross-section (larget cross-section->higher drag) and inversely proportional to mass (larger mass->drag force causes smaller acceleration).
"Because Science" is one step from "Because old book". Try "Because of my experiment testing my falsifiable assertion".
Correct me if I am wrong,
:-)
Ok. Although, luckily, not everything you said is wrong.
GPS satellites are in geosynchronous orbit a couple earth radii (radiuses?) out.
Well, no. The current United States GPS system consists of 24 satellites (plus spares) orbiting in 6 equally-spaced orbital planes at an inclination of 55 degrees and an altitude of 20,200 km, which is right in the region of space between low Earth orbit (LEO - generally between 100km and 1000km altitude) and geosyncronous Earth orbit (GEO - 35,786km altitude). The Earth's radius is 6,378km at the equator. Getting a GPS coordinate reading requires receiving signals from at least 4 satellites in the constellation. There is very little space debris in this band of space.
Yes, "radii" is a correct plural.
That makes a sphere with one heck of a huge "surface", and I am sure there is a heck of a lot of room for oodles more junk out at that range before it ever becomes a problem.
Yes, the sphere has much more area, but when we talk about geosynchronous or geostationary orbits, we're really only talking about a small band of that sphere, centered on the equator. The physical space available to satellites out there in the GEO band is quite large, it's true, and the danger of collision from debris is very small. However, GEO is still rather crowded, from an angular perspective. Satellites that are 75km apart in the GEO band (which is plenty of buffer; lots of LEO satellites are closer than that) are only 0.1 degrees apart when viewed from the Earth. With a finite amount of angular space and radio bandwidth available and lots of different satellite systems competing, this is something that will have to be addressed in the near future.
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While I don't want to belittle the seriousness of a bolt traveling at 35,000 km/h striking a manned space vehicle, a little perspective is due. A conservative definition of low earth orbit is anything between 100km and 1500km in altitude, simplifying this as a spherical shell that is a volume of space equal to 1.41329782 × 10^19 m^3
Now even giving the NASA estimates of hundreds of thousands of objects (including those under the 4in size for tracking) a fudge factor of 100 giving on the order 50,000,000 objects in LEO that gives a debris density of 3.53782475 × 10^-12 m^-3... or 1 object in every 2.82659564 × 10^11 m^3 or 1 object per 282.659564 km^3.
Even if we assumed that every piece of junk was concentrated in the lowest kilometer of LEO (100 to 101 km in altitude) that still gives us a volume of space equal to 1.26924532 × 10^14 m^3
With the same fudge factor of 50,000,000 pieces of deride we have an object density of 3.93934878 × 10^-7 m^-3 or 1 object per 2538490.64 m^3 to put this in perspective, the Empire State Building has a volume of just over 1000000 m^3.
Have you thought for yourself today?
No, it doesn't. If there was no atmosphere, the apple would fall faster than the feather.
;) LEO, while many orders of magnitude less dense than at sea level on Earth, is orders of magnitude more dense than interplanetary space, which is likewise orders of magnitude more dense than interstellar space, which is again orders of magnitude more dense than intergalactic space. Thus, there is a constant light resistance that steadily saps your delta-V, and you have to reboost if you want to maintain orbit.
Of course, there's *some* atmosphere even in intergalactic space
GEO faces a different problem. The atmosphere is much thinner up there, so resistance isn't a big problem. The problem, however, is that the moon tries to pull you into a harmonic orbit with itself, and you have to counter that. You also have to deal with Earth's irregular gravitational field (it's pretty even, but not completely even, and effects build up), radiation and solar wind pressure, and other problems.
Son, a woman is a lot like a refrigerator. They're six feet tall, 300 pounds... they make ice... umm...