Alternative GPS System | The Coffeehouse

zzzzz
Yes its an Economy vehicle

One major problem with using lasers Karim is affective range. A laser's range is very limited due lasers being scattered by the atmosphere.

The laser mounted in the Boeing 747 which i think is built or in process of being built is designed to work at 40,000 feet. but the system would need to shoot another 292 miles upward to hit a satellite. Thats slightly outside its range of 200km....

The idea of using lasers to destory a satellite requires lauching another satellite or using ground based missiles

Did you not read those articles????? because one article said its not even being looked at using the ABL for ASAT

Booen wrote:
Though the ABL could point its laser upwards and conceivably use it in some sort of anti-satellite mission, that hasn't been examined. "It's not something we're working on,"

Second problem is

DOD wrote:

Both the United States and Soviet Union developed and tested dedicated anti-satellite (ASAT) weapons in the past, although further development of weapons that physically destroy satellites has been restricted by congressional bans and voluntary Russian moratoria on testing. Both countries retain some ASAT capability, including the ability to disrupt satellite functions without disabling them, such as temporarily blinding them with ground-based lasers or jamming their transmissions (even those in geosynchronous orbits).

When the DOD says "considerable inherent capability"

Does not mean yes it works right now it means Congress give us a few billion so we can use this technology to develop this new application....

Let alone the Missile Defense is still in R&D and building phase.

Karim
Trapped in a world he never made!

zzzzz wrote:
One major problem with using lasers Karim is affective range. A laser's range is very limited due lasers being scattered by the atmosphere.

The laser mounted in the Boeing 747 which i think is built or in process of being built is designed to work at 40,000 feet. but the system would need to shoot another 292 miles upward to hit a satellite. Thats slightly outside its range of 200km....

I'm just going on what the article said:

The ABL is intended to fly at an altitude of about 13 kilometers. While a 300 km-range Scud missile burns out at an altitude of 25 to 30 kilometers, a long-range missile would burn out at 200 kilometers or higher. As a result, if ABL is to be able to attack long-range missiles, the beam director must be able to point the beam upward, which would allow it to target satellites as well.

If the beam director is able to hold the laser beam on an accelerating missile body at a range of several hundred kilometers, it could also hold the beam on a satellite at an altitude of several hundred kilometers. If the beam had sufficient power to destroy missiles, it appears likely that it could physically damage satellites in low orbits, especially since the beam could dwell for longer times than it could on missiles. It would certainly be able to blind reconnaissance satellites temporarily, and could likely damage their sensors and blind them permanently. This mission would require less power than destroying a missile.

There are several points here. One, is that a satellite in low earth orbit is more fragile than a missile. A missile is designed to survive reentry into the atmosphere. A satellite will be a softer target because it will have antennae, solar cells, exposed elements, etc. Here's a picture of the Galileo satellite:

Does that look especially sturdy to you, compared to an ICBM?

Two, a satellite is more vulnerable, because you have a longer dwell time as it passes across the sky, and if you miss it on the first pass, guess what? You wait until it makes another pass and hit it again. Oh, did you only dent it? Well look, it's in orbit, here it comes again.

zzzzz wrote:

The idea of using lasers to destory a satellite requires lauching another satellite or using ground based missiles

There was a footnote to the article you might have missed:

11. Satellite sensors can be temporarily blinded by very low-power lasers. A laser ASAT test in 1997 showed that a 30 watt, ground-based chemical laser was able to temporarily blind an Air Force satellite orbiting at 425 kilometers altitude (John Donnelly, "Laser of 30 Watts Blinded Satellite 300 Miles High," Defense Week, 8 December 1997, p. 1).

Now, if you can temporarily mess up a satellite using a simple 30-watt laser on the ground, what do you think you could do with a megawatt laser that's flying above most of the atmosphere?

Just a thought.

zzzzz wrote:

Did you not read those articles????? because one article said its not even being looked at using the ABL for ASAT

Yeah, I quoted the quote before you did. Big Smile

The second article was from Air Force Magazine -- i.e. this news brought to you by the U.S. Government. My tongue-in-cheek take on it was that just because the government says "we're not actively looking into this" doesn't mean you should take that at face value. My read on the "could be," "possibly," "conceivably but NO" comments was "methinks they doth protest too much."

You're free to take it at face value if you like. Big Smile

Michael Griffiths
Fatalism.

Funnily enough, I found a blog post with some rather good comments testing looking for more information on the F15 antisatellite capability:

http://www.settingtheworldtorights.com/node/106

The comment I found interesting was:

How to Defeat Galileo wrote:

No one has yet (publically) fielded an antisatellite weapon capable of shooting down a GPS or Galileo satellite.

Low Earth Orbit (LEO) satellites, those in orbits of about 1000km altitude or less, are relatively easy to shoot down. There was an F-15 anti-satellite missile, I believe successfully tested several times. The Soviets had a system where they used a guided bomb placed in the same orbit as the target satellite. They could tail any LEO satellite they wanted and destroy it at their leisure. This was also tested several times.

LEO satellites are important targets because almost all the surveilance satellites, both imaging and radar, are kept as close to the ground as they can, to maximize resolution.

Navigation satellites, on the other hand, are a much different problem. Both GPS and Galileo are in (will be in) Medium Earth Orbit (MEO) at about 20000km altitude. It would require a launch vehicle of almost identical capability to the one which originally launched the target to intercept it. This would mean that shooting down a satellite that high is almost as expensive as launching it in the first place.

Probably if we wanted to shut down Galileo, the best way to do it is by spoofing. Spoofing is a process by which an adversary is able to mimic the signal from a real satellite, but with incorrect information, so that receivers on the ground either cannot compute a position at all, which is bad, or compute a wrong position, which is worse.

The whole point of the encoding on the present military system is to prevent spoofing. The GPS transmits two signals simultaneously, one unencrypted and one encrypted, for military use only. The military code is secret. Any satellite broadcasting a military signal without that military code will be completely ignored by the receiver. In fact, the receiver will not even detect that it is there. Since the code is secret, only the military can create that signal, so if your receiver is able to detect it, it must be authentic. The civilian signal on the other hand, since it is published, can be replicated by anybody and therefore easily spoofed.

The Galileo system has a civilian unencrypted signal, a commercial encrypted signal you can buy access to, and a government encrypted signal you cannot. The civilian signal can be easily spoofed, and the commercial signal also if our military buys the keys.

The american GPS satellites are perfectly placed to act as spoofers, and have all the necessary hardware already onboard, to do their main jobs. It would surprise me a great deal if they could not be programmed to spoof either the russian or the new Galileo system, but of course that capability would properly be kept secret

So if the bad guys equip their weapons with civilian or commercial Galileo receivers, those are pretty easy to jam. If they use government receivers, then one of the governments involved is a conspirator and is committing an act of war against whomever the bad guys are targeting. Galileo does not represent a real threat.

On the other hand, a little competition is a good thing. It may be that the american military will be forced to compete against Galileo by providing a better civilian service, thereby causing everyone to buy american GPS receivers which can be disabled in an emergency. This has already begun by the removal of selective availability, an intentional degradation of the civilian signals, and is continuing in the form of new more accurate civilian signals on the next generation american GPS.

As a patriot, I want my military to have as much control over navigation capability as they think they need. As a civilian GPS user, I want as much accuracy as possible. By providing competition, Galileo forces the american military to improve the second to maintain the first.

Shiv
Life is beautiful :)

i am sad that this appeared in a comment . this is good enough to be an article on its own . great work there Michael for posting it here .