71–80 of 122 posts
Mostly off-topic here, but it seems like the best place to get an answer: several years ago in my lab at Georgia Tech, a technician I worked with said he had a friend who invented a device for doing celestial navigation, but that it 1) worked in the daytime somehow and 2) used digital technology so that it was more precise than a sextant / traditional celestial navigation. The technician was prone to a bit of exagger…
Mostly off-topic here, but it seems like the best place to get an answer: several years ago in my lab at Georgia Tech, a technician I worked with said he had a friend who invented a device for doing celestial navigation, but that it 1) worked in the daytime somehow and 2) used digital technology so that it was more precise than a sextant / traditional celestial navigation. The technician was prone to a bit of exagger…
> Well, how about deliberate dilution of precision or intentionally limiting the speed the GPS chip can be used at? Is that a legal requirement or just done on request? I sort of chuckle whenever I hear of limitations like that being put in place as if someone that can construct an ICBM is going to be constrained by the GPS module.
It was required. But that was gotten rid of by the Clinton administration. See https://www.gps.gov/systems/gps/modernization/sa/ .
Do any of these systems offer a way to cryptographically prove that a signal was received at a specific place and time?
Earlier quoted context omitted.
The speed limit in the US is 1000mph, else it’s a munition. I believe the US used to make their GPS slightly inaccurate, but this was done on the satellite side.
The speed limit in the US is 1000mph, else it’s a munition. Please note: my apologies in advance for a comment that may be perceived as pedantic, but I just wanted to further illuminate this statement. The U.S. regulation, which technically falls under the Export Administration Regulations (Navigation and Avionics), does not exclusively regulate GPS navigation in munitions applications; rather, it serves to regulate…
Earlier quoted context omitted.
China also has strict restrictions on GPS data, including requiring purposeful obfuscation of coordinates for their GCJ-02 geodetic datum, for national security purposes. They don't want accurate maps made.
GCJ-02 used to be a secret way to warp maps to make them less useful for military uses. Now, the GCJ-02 is so well reverse engineered it's practically useless, and just introduces bugs in mapping software when different coordinate systems are used.
Mostly off-topic here, but it seems like the best place to get an answer: several years ago in my lab at Georgia Tech, a technician I worked with said he had a friend who invented a device for doing celestial navigation, but that it 1) worked in the daytime somehow and 2) used digital technology so that it was more precise than a sextant / traditional celestial navigation. The technician was prone to a bit of exagger…
I think all you need is two celestial bodies and local gravity to get a fix on your location.
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I find a bit of humor in imagining NASA rocket launches and atmospheric test vehicles being viewed, in some contexts, as a munition.
I believe "strong" encryption is still viewed as munitions in the US, or at least it used to be.
Mostly off-topic here, but it seems like the best place to get an answer: several years ago in my lab at Georgia Tech, a technician I worked with said he had a friend who invented a device for doing celestial navigation, but that it 1) worked in the daytime somehow and 2) used digital technology so that it was more precise than a sextant / traditional celestial navigation. The technician was prone to a bit of exagger…
That's some kind of flight/operational manual for the astroinertial navigation system (ANS), pretty detailed. Quite amazing that it's been declassified - you can see the link is from the Smithsonian Air and Space Museum. It also discusses details of how missions are loaded and planned with respect to the ANS. It also says that it has planet avoidance information, which gives you some idea of how sensitive it is (obviously the Sun and Moon are avoided).
I've not found any indication of what wavelength was used, but I would imagine the detector is a single infrared photodiode. By blocking visible atmospheric light (scattered), you can see the stars behind. Stars are point sources for all practical purposes, so you can have as large a magnification as you like without resolving them. What that means is if you have an large-aperture telescope, you'll still collect all the light from a star even if your field of view is tiny. Hence why this uses a scanning telescope to sweep around the sky.
Given the technology of the day, it's unlikely they had a multi-pixel detector (maybe a very low res array). So one approach you could use for this is two photodiodes looking slightly apart - by subtracting the signal of one from the other you might be able to correct for local atmospheric light (if the field of view is narrow enough that you don't expect two stars in the same field). Essentially a real-time dark frame. I have no idea how it actually works in practice though. I'm sure nowadays this can be done with a single wide angle camera.
It also seems like it has some strong initial conditions based on e.g. where the aircraft took off as well as references from the onboard IMU, aircraft attitude, etc. And if I read it right, the pilots can also indicate when they've reached waypoints to calibrate the system.
Earlier quoted context omitted.
The speed limit in the US is 1000mph, else it’s a munition. I believe the US used to make their GPS slightly inaccurate, but this was done on the satellite side.
The speed limit in the US is 1000mph, else it’s a munition. Please note: my apologies in advance for a comment that may be perceived as pedantic, but I just wanted to further illuminate this statement. The U.S. regulation, which technically falls under the Export Administration Regulations (Navigation and Avionics), does not exclusively regulate GPS navigation in munitions applications; rather, it serves to regulate…
ICBMs on the other hand, reportedly go ten times the speed of an F22.