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GPS and space debris...

4K views 32 replies 16 participants last post by  Valiente 
#1 ·
Wondering if we may want to dust off our sextants in the coming months and years. A derelict Russian satellite and a functioning American satellite collided a few days ago, creating a debris field 500 miles above the earth. Apparently this is a popular orbit for the satellites that give sailors, airmen and drivers coordinates for our navigational devices. Once you have a collision like this, it's like a chain reaction, causing more collisions and more debris, so on and so forth. And it apparently takes a little time for gravity to clean up the mess (10,000 years, according to some sources). I'm wondering when space is going to be all but inaccessible to us...

Read it and weep:

Space crash debris to orbit Earth for 10,000 years - Yahoo! News
 
#2 ·
Well, this is why I keep up my CN, not because I'm a Luddite, but because I understand physics and probability.

Kessler Syndrome - Wikipedia, the free encyclopedia

From a launch perspective, a thin, wildly dispersed field of coin-sized spalls is much worse than chunks of dead satellites here and there. It's like dioxin: a barrel of the stuff in one place is bad enough, but a few micrograms in everybody is deadly.
 
#4 ·
Maybe not, but the phrases "clear and present danger" and "law of unintended consequences" come to mind.

Space is very, very big, but time is very, very long. See "what was that container doing there?" for the yachting equivalent.

Anyone who's evolved on a planet like this one that's had two and possibly more major extinction events due to fairly modest space rocks slamming into us with gigatons of TNT equivalent explosive power has no right to be smug about the rapidly moving crap they've left in a can't decay fast enough orbit.
 
#7 ·
You have to remember that the GPS Satellites are 11000 miles above the earth. The debris field should not be of any worry. Unless that debris is flung outwards toward the GPS orbits. Then you can worry abit about it.
 
#9 ·
True, but the intervening space between LEO and HEO can be covered by flying debris in under an hour...heh heh.

Seriously, it's not the satellites in HEO I worry about, but the fact that they eventually fail or otherwise go out of service. If a thin layer of debris exists between the surface of the Earth and that altitude, for lack of a better term, and the debris is randomly moving at 10X bullet speed, the problem becomes "how do you fly a great big rocket full of rocket fuel through that to reach high orbit?"

The situation is analogous to motoring through the Great Pacific Gyre without trapping a plastic bag against your raw water intake. The ocean is very big, but the plastic bits and pieces in the water column are numerous and randomizes once inside the gyre.
 
#13 ·
But....but...but

I thought GPS couldn't be threatened. I thought it was impervious to attack. I thought we didn't need all that antiquated, old school, neanderthal-era navigation stuff. Glad I saved the Loran and sextant. All this time, the Chinese were the concern, and look, it's just an accident that's showing how vulnerable the whole deal could be. Well, they say it was an accident. Maybe the Ruskies did it on purpose. OOOoohhhhh!!!! ...........
 
#17 ·
Funny, that's not what I got from the report to Congress here:

http://pnt.gov/public/docs/2008-biennial.pdf

It seems at least vulnerable, if not marginal. Anyway, my point is this: the prudent mariner relies on a suite of navigational aids, and that GPS is only one. It is a very good one, admittedly, but there are shortcomings to it due to the nature of space itself.

I suspect the best course would be to get a GPS receiver that can receive ALL the "constellations" either in use now or shortly to be in use. Seamless switching from the U.S. system to the European Galileos to GLONASS to COMPASS...whatever. This would greatly reduce the chance of outages in service or coverage for the average boater.
 
#18 ·
Question and answer time

Q) What is the longest single voyage I'm likely to do?

A) Probably 4 weeks at sea.

Q) How many satellites does my GPS log onto at any one time?

A) Mmmmm - normally 9, sometimes 11

Q) How many does it need to give me a fix?

A) I think it's 3

Q) What are the chances of any 6 satellites getting taken out by space debris in four weeks?

A) Very, very remote.

Q) What are the chances that all 6 will be in my sector of the sky?

A) None at all.

Q) Should I be worried?

A) I don't think so.
 
#22 ·
Q) Should I be worried?

A) I don't think so.
So you would think, but this isn't about total failure, it's about gaps appearing in less-travelled parts of the world due to, as SD points out, the number of functioning satellites falling below the 24 needed for full coverage.

It's not that it might not be there, but it might not be there if you need it in mist at night near the sketchier sort of reef.

I'm not trying to be alarmist here, but simply realistic that GPS is a system reliant on a certain minimum number of functioning elements. Reduce or remove those elements, and coverage is also reduced along with accuracy. Three satellites is good (but not if they are also at 20 degrees above the horizon), but more locks are better, because of this very interconnectivity of the signal processing.

The way people talk about GPS, it's as permanent as the stars and as reliable as the sunrise. Actually, it's more like the electricity grid: 99% fine, but parts of it are pretty old and prone to failure, which is why you keep candles and flashlights in a drawer. Also, to extend the analogy, if the GPS constellation is missing a few functioning satellites, does this impair accuracy? Would the average sailor be aware if his "circle of confidence" went from five metres to five hundred because there were just 21 satellites and not 24 working? A subtle or intermittent degradation is in some ways worse than a straight outage.

Even if they did, how many voyagers today have such "candles and flashlights" aboard and can use them? Half the people here can't heave to.

My wife's first CN class is this evening...purely coincidental, I assure you.;)
 
#20 ·
Being a plumber and knowing how much I get for scrap metal I would suggest in the not so distant future when space travel is more the norm the returning space ship's could do what the early sailing ship's did in a Australia we'd send our WOOL to England and they'd return to Sydney full of what ever the colony needed Iron roofing etc the returning ship's could return full of space junk ready to be recycled its just a thought cheers Kerry
 
#21 ·
I'd also point out that currently 20 or so of the 31 satellites used for GPS are beyond their expected working life, and 8 or 9 of those have no redundancy in critical systems. The GPS system requires 24 satellites to be working for the system to function properly... If only the 8 or 9 that have seriously compromised systems fail... GPS is down for the count...
 
#24 ·
I would think that there is the real possibility that there will one day be so much debris in low earth orbit that high earth orbit becomes all but inaccessible. When a nav. satellites come to the end of its service life, there may not be a way to foist another one up to replace it.
 
#25 ·
Maybe it is time to break out the Star Wars stuff for a little target pratice.

A nuke test in the desert along with a ICBM long range test might remind some countries of some things they may have forgoten.
 
#26 ·
Maybe it is time to break out the Star Wars stuff for a little target pratice.

A nuke test in the desert along with a ICBM long range test might remind some countries of some things they may have forgoten.
Indeed it might; but be careful what you wish for. ;)
 
#27 ·
If GPS was out in certain areas, how far would a person travel while they were taking a fix using a sextant and time ticks before they actually got their fix?

We know that a fix by sextant is not all that accurate, but it will get you in the ball park...but the ball park could be pretty big in rougher conditions.

Sailing in reefy areas using a sextant could land you on a reef by the time you figured out where you thought you should be, but the sextant is better than nothing.
 
#28 ·
You can always stop, or nearly so, and confirming latitude with a noon sight is a matter of seconds. Confirming latitude and longitude is less than 20 minutes with current methods, and a lot less than that if you are in practice.

So say you are in a light current of about two knots, and you are drifting with it in a 10 knot wind toward the suspected reef. With all sail down (or better yet, sailing to windward with reduced sail to get you practically treading water), you might move at worst 1 NM.

A good sight will give you accuracy of 1-2 NM, so yes, some planning is involved, but as some charts (including electronic ones) have an error of 1 NM or greater (especially the ones last done by Capt. Cook (!) although he was surprisingly good), I would hope you would be keeping a dead reckoning and start trying to determine your location a lot farther away than that.

Seeing discoloured water or breaking waves from five miles off with binoculars from halfway up a mast shouldn't be that hard in daylight, especially if you have a bearing in mind down which to look.
 
#29 ·
By the time GPS fails from old age and is inaccessible due to the LEO minefield, somebody will have produced a sufficiently realistic sailing video game, so that the electroboaters who relied solely on GPS can enjoy sailing without ever leaving their homes, while mariners who practiced CN will have our sextants to fall back on.
 
#30 ·
Also, I'd point out that CN techniques are primarily for use when in the open ocean, and that a mistake of even up to 5 NM is generally not a big problem given that you're hundreds of miles from land. If you're within sight of land, you should be using coastal pilotage skills, not celestial navigation.
 
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#31 ·
I think the "special case" is nominally mid-ocean places like the Tuamotus, and so on, an area both sometimes inaccurately charted, or inherently dangerous due to charted but awash reefs and atolls.

Sable Island comes to mind, as do places like the Torres Strait, the Barrier Reef and like this: Pacific Ocean - Elizabeth & Middleton Reefs (this whole site is great for weird little islands and reefs.)

If you chart a course and keep a running fix from CN, divergences due to current or steerage (like XTE with GPS) will eventually appear and can be corrected. Sailors used to plot courses to avoid land, but GPS sailors will, by contrast, tend to want to sail past land for the visual confirmation or because it's a more direct route. "Waypointers" don't always keep a prudent offing, in my view, because so much of the navigation is left to the plotter and the AP.

Because of its greater "circle of uncertainty", by contrast, CN encourages caution and land other than the destination is ideally avoided altogether.

How do I know this? From the changing nature of boating accidents and groundings...people are very precisely hitting the same damn rocks four feet below the surface of the ocean! We've all heard about people piling into breakwalls, huge buoys, piers and the like, sometimes at speed. It's sheer carelessness, aided and abetted by precision instrumentation that itself doesn't have a stake in staying dry.

I have to wonder if some sort of cutting and pasting of lat/lons goes on instead of looking at the right charts, and manually plotting a course that gives a good offing that is clear of fringing reefs and yet close enough to get into a viable anchorage promptly.
 
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