"This is a bit melodramatic. The space elevator concept is essentially a vertical pole; very few of those orbits would even come within a hundred miles of the elevator."
Not true. Every satellite in Low Earth Orbit (LEO) crosses the Equator twice on each orbit --once on the ascending node and once on the descending node and there are 16 orbits per day. The Space Elevator proponents suggest it's possible to literally swing that "pole" through the orbits of every object out to a distance of 64,000 miles all day everyday without hitting anything. I don't think it can be done and I stand by my statement. But, don't take my word for it, call NORAD and ask them how many objects they're tracking out to 64,000 miles.
"That said, yes, junk is a serious issue. Given that the US military has just run recent successful tests zapping mortars out of the air with lasers, and given that US aircraft carriers have automatic heavy-bore machine guns which can cut enemy planes in half in flight, I should think that a series of automated defense points along the cable, paired with redundancy not only in defense but in the cable itself, should provide a reasonable basis for extrapolation."
This statement is just silly. Like You'd want to make matters worse by shooting at an object in the first place (adding 6000 rounds per minute, moving at a thousand meters per second, to the debris field), and making little pieces out of bigger ones that you might be able to track and avoid. Anything that breaks an object apart in orbit is going to make matters worse not better.
"This is called a straw man. Just because you're aware of one bone-headed project doesn't mean that this one is any less realistic. This is a fallacy. This is a bit like saying that hybrid cars can't be done, because look at the Yugo, what a dismal failure, and it's a car too."
No it's not. My original point was that the space elevator is a waste of money, like MADMEN is a waste of money. And yes, it's your money too.
Orbital velocity is 17,551mph minimum for low earth orbit. That's Los Angeles to New York in a little more than 9 minutes and it gets you 16 orbits in a day --that's crossing the Equator on an ascending and descending node (that's where the cable would be) on every orbit.
And you're right, relative velocities are the bigger problem, and not all of them are moving at the same speed.
For small objects in near circular orbit it's bad enough, but not all objects are in near circular orbits. Some are in highly elliptical orbits --they travel slower at aphelion than at perihelion (these were called apogee and perigee when I took orbital mechanics 20 years ago) -think "screaming along" (Kepler's equal area in equal time law)
If you want exact numbers of objects in orbit at specific altitudes you'll have to call NORAD or NASA --it's Saturday and they're probably bored so they won't mind. You might find a NASA site that has specifics, but I'd call NORAD (they own the radars).
I wouldn't suggest that reducing the total cost to low earth orbit is a bad idea --it's a great idea, that needs to be considered very carefully. I don't think raising a valid criticism or reasonable doubt constitutes jumping to conclusions either.
I was stationed at NORAD in the early eighties and junk in low earth orbit was a major concern as the shuttle program transitioned from idea to reality. I expect the problem is much worse now. I think "cloud" is a more apt description of the debris field. Yes, stuff re-enters the atmosphere all day every day, so I guess you could say it's a self healing process, but it's a long process.
The trouble with ideas is that they cost taxpayer dollars even if it turns out to be a bust.
I don't think most people have any idea what it would take to successfully swing a cable through maybe 20,000 objects at various altitudes, all travelling at 17,000 MPH or so, all day every day without hitting anything.
There's a long ugly road between this idea and reality.
Maybe it wouldn't be so bad if NASA didn't fund the programs. It would be O.K. with me if someone with an idea wanted to fund the research themselves or recruit funding from corporate types.
MADMEN is a similar boondoggle. But, don't take my word for it, ask Duncan Steele, PhD. In 1995 Steele published a book called "Rogue Asteroids and Doomsday Comets" addressing this particular option (throwing material off an dangerous asteroid using a mass driver). Thomas Ahrens and Alan Harris at the California Institute of Technology looked at this very system (page 229). They dismissed it in 1992 because the ejection requirement was "...many thousands of tons..." over a lot of years. What did they come up with in answer to that? A "fleet" of mass drivers throwing stuff off. MADMEN indeed.
Remember that satellites in LEO make 16 revolutions per day (once every 89 minutes) and cross the equator twice on each (ascending and descending). Multiply that by nearly 10,000 objects big enough to track (~5cm) and many more they can't see. NASA has a good description of the problem that explains the physics and gives examples of high velocity impacts.
Before this gets too far, somebody should call NORAD and ask them how many of the 2500+ satellites and other odd bits of junk traveling at 17551mph (LEO) cross the Equator (ascending and descending nodes) and might present a collision hazard. I could be wrong, but shouldn't the answer should be "Almost all of them."
This reminds me of the asteroid/comet problem, the probability of a significant impact might be low, but it only takes one.
It seems to me that Microsoft, after many years of poor performance and an anti-trust conviction and a multimillion dollar fine in Euroland, may already be dying.
Doesn't anyone with more than a couple of years of computing experience already hate them?
I've been working with computers for 25 years and I started using Linux when it finally had a reasonable set of desktop applications and resolved some of the hardware compatability issues.
Many US companies are dying --but it's from the inside so many don't see the decay until it far along.
Can a company really survive in an environment where the potential customer base hates them, when they write crappy code that any 14 year-old can break into, and their business practices send even normally sedate government bureaucrats into a frenzy? Do they really have that much money?
I'll bet the executives are clueless about what's really happening on the shop floors too --another common problem in companies these days.
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"This is a bit melodramatic. The space elevator concept is essentially a vertical pole; very few of those orbits would even come within a hundred miles of the elevator."
Not true. Every satellite in Low Earth Orbit (LEO) crosses the Equator twice on each orbit --once on the ascending node and once on the descending node and there are 16 orbits per day. The Space Elevator proponents suggest it's possible to literally swing that "pole" through the orbits of every object out to a distance of 64,000 miles all day everyday without hitting anything. I don't think it can be done and I stand by my statement. But, don't take my word for it, call NORAD and ask them how many objects they're tracking out to 64,000 miles.
"That said, yes, junk is a serious issue. Given that the US military has just run recent successful tests zapping mortars out of the air with lasers, and given that US aircraft carriers have automatic heavy-bore machine guns which can cut enemy planes in half in flight, I should think that a series of automated defense points along the cable, paired with redundancy not only in defense but in the cable itself, should provide a reasonable basis for extrapolation."
This statement is just silly. Like You'd want to make matters worse by shooting at an object in the first place (adding 6000 rounds per minute, moving at a thousand meters per second, to the debris field), and making little pieces out of bigger ones that you might be able to track and avoid. Anything that breaks an object apart in orbit is going to make matters worse not better.
"This is called a straw man. Just because you're aware of one bone-headed project doesn't mean that this one is any less realistic. This is a fallacy. This is a bit like saying that hybrid cars can't be done, because look at the Yugo, what a dismal failure, and it's a car too."
No it's not. My original point was that the space elevator is a waste of money, like MADMEN is a waste of money. And yes, it's your money too.
Orbital velocity is 17,551mph minimum for low earth orbit. That's Los Angeles to New York in a little more than 9 minutes and it gets you 16 orbits in a day --that's crossing the Equator on an ascending and descending node (that's where the cable would be) on every orbit.
And you're right, relative velocities are the bigger problem, and not all of them are moving at the same speed.
For small objects in near circular orbit it's bad enough, but not all objects are in near circular orbits. Some are in highly elliptical orbits --they travel slower at aphelion than at perihelion (these were called apogee and perigee when I took orbital mechanics 20 years ago) -think "screaming along" (Kepler's equal area in equal time law)
If you want exact numbers of objects in orbit at specific altitudes you'll have to call NORAD or NASA --it's Saturday and they're probably bored so they won't mind. You might find a NASA site that has specifics, but I'd call NORAD (they own the radars).
I wouldn't suggest that reducing the total cost to low earth orbit is a bad idea --it's a great idea, that needs to be considered very carefully. I don't think raising a valid criticism or reasonable doubt constitutes jumping to conclusions either.
I was stationed at NORAD in the early eighties and junk in low earth orbit was a major concern as the shuttle program transitioned from idea to reality. I expect the problem is much worse now. I think "cloud" is a more apt description of the debris field. Yes, stuff re-enters the atmosphere all day every day, so I guess you could say it's a self healing process, but it's a long process.
The trouble with ideas is that they cost taxpayer dollars even if it turns out to be a bust.
I don't think most people have any idea what it would take to successfully swing a cable through maybe 20,000 objects at various altitudes, all travelling at 17,000 MPH or so, all day every day without hitting anything.
There's a long ugly road between this idea and reality.
Maybe it wouldn't be so bad if NASA didn't fund the programs. It would be O.K. with me if someone with an idea wanted to fund the research themselves or recruit funding from corporate types.
MADMEN is a similar boondoggle. But, don't take my word for it, ask Duncan Steele, PhD. In 1995 Steele published a book called "Rogue Asteroids and Doomsday Comets" addressing this particular option (throwing material off an dangerous asteroid using a mass driver). Thomas Ahrens and Alan Harris at the California Institute of Technology looked at this very system (page 229). They dismissed it in 1992 because the ejection requirement was "...many thousands of tons..." over a lot of years. What did they come up with in answer to that? A "fleet" of mass drivers throwing stuff off. MADMEN indeed.
Remember that satellites in LEO make 16 revolutions per day (once every 89 minutes) and cross the equator twice on each (ascending and descending). Multiply that by nearly 10,000 objects big enough to track (~5cm) and many more they can't see. NASA has a good description of the problem that explains the physics and gives examples of high velocity impacts.
This is not a trivial problem.
Before this gets too far, somebody should call NORAD and ask them how many of the 2500+ satellites and other odd bits of junk traveling at 17551mph (LEO) cross the Equator (ascending and descending nodes) and might present a collision hazard. I could be wrong, but shouldn't the answer should be "Almost all of them."
This reminds me of the asteroid/comet problem, the probability of a significant impact might be low, but it only takes one.
It seems to me that Microsoft, after many years of poor performance and an anti-trust conviction and a multimillion dollar fine in Euroland, may already be dying. Doesn't anyone with more than a couple of years of computing experience already hate them? I've been working with computers for 25 years and I started using Linux when it finally had a reasonable set of desktop applications and resolved some of the hardware compatability issues. Many US companies are dying --but it's from the inside so many don't see the decay until it far along. Can a company really survive in an environment where the potential customer base hates them, when they write crappy code that any 14 year-old can break into, and their business practices send even normally sedate government bureaucrats into a frenzy? Do they really have that much money? I'll bet the executives are clueless about what's really happening on the shop floors too --another common problem in companies these days.