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What happens when a GPS satellite fails? Or if you have an earthquake? Seems like precisely in those times of national need that one's most sophisticated techno
by toufka 13y ago
What happens when a GPS satellite fails? Or if you have an earthquake? Seems like precisely in those times of national need that one's most sophisticated technologies might be sorely out of commission. A seemingly pretty nice way to inflict 'collateral damage' on one's self. Especially if such a precautionary set of rules were put into more and more machines.
- superuser2 13y agoThe interlocks aren't permanent - they can be bypassed by the manufacturer.
- Udo 13y agoI'm not sure you actually meant it as a joke, but that's hilarious in a cynically-detached kind of way. So these machines are not bought but licensed and they will fail as soon as the manufacturer becomes unable to continually grant usage rights, i.e. during a region-wide catastrophe.
- superuser2 13y agoI'm merely pointing out that GPS outage would be no more than an annoyance. . If the machinery experiences significant acceleration in an earthquake, it's not necessarily intact or safe to operate afterwards. The enclosing machine shop is also not likely to be in any state to continue operations if something as large as the pictured CNC machine has been thrown across the room. I don't buy that this issue is a big deal either. From a software freedom standpoint, yes, this is terrible. But I don't think it's as much of a problem for the owner as the parent suggests.
- yaddayadda 13y agoI have no idea how many of these machines are in a given area, but assuming it is an IMU [1] triggered lockdown, an earthquake could lock down many (10?, 100?, 1,000?) in a single geographic area very, very quickly. That seems like a big problem. If the lockdown mechanism is GPS, then it should be clear where the actual machine is, so there shouldn't be any need to lock it down unless it's in a black zone. And what happens if the manufacturer goes belly-up? [1] https://en.wikipedia.org/wiki/Inertial_measurement_unit https://en.wikipedia.org/wiki/Inertial_measurement_unit
- AlexDanger 13y agoConsumer GPS devices have some interesting lock-down rules built into them. They shut themselves down if they detect you are travelling around Mach 2 or above 18000 metres altitude. The reasoning is fairly obvious - they dont want to see dumb missiles getting upgraded to a DIY guided ballistic missile thanks to a $100 Garmin gaffa taped to the side and a cheap flight control computer. http://en.wikipedia.org/wiki/CoCom http://en.wikipedia.org/wiki/CoCom
- mct 13y agoThey shut themselves down if they detect you are travelling around Mach 2 or above 18000 metres altitude The intention was for a GPS device to disable itself if it was traveling faster than 1k knots AND above 60k feet, not traveling faster than 1k knots OR above 60k feet. Unfortunately, many GPS devices improperly implement this as an OR condition, rather than an AND condition. This becomes problematic when using a GPS in a high-altitude weather balloon to determine altitude and location, which a few friends and I did a couple years ago. We had to be very careful when selecting the GPS we used to avoid this pitfall.
- AlexDanger 13y agoInteresting, I did not know that. Which GPS did you end up using?
- wyager 13y agoWhich GPS units are acceptable for this? I'm working on a HAB and I'm worried about this CoCom bullshit. The one I'm thinking of uses a SiRFstarIII or IV; any idea of those use || instead of the proper &&?
- nknighthb 13y ago> What happens when a GPS satellite fails? The receivers use other satellites. They have to anyway: You can't get a fix with only one satellite.
- baddox 13y agoI would imagine you normally need three. If I'm visualizing the geometry correctly, the intersection of three spheres is two points, and it should be easy to guess which of the two is the more likely location of your device.
- mutagen 13y agoBecause relatively cheap GPS receiver clocks drift, typically 4 satellites are needed for a position. You can assume an elevation, especially at sea level, and solve a position with three satellites but this introduces other factors (ellipsoid vs geoid, satellite constellation geometry, etc) that can make a good position difficult to obtain. In practice there are enough satellites that these considerations are theoretical. Most situations that would involve limited satellites also introduce stuff like multi path reflections that further degrade position accuracy.
- tinkerdol 13y agoHere is a graphic to add to that explanation if anyone is curious: http://gis.stackexchange.com/questions/12866/why-does-gps-positioning-require-four-satellites http://gis.stackexchange.com/questions/12866/why-does-gps-po...
- avn2109 13y agoIn North America your GPS probably connects to between five and twelve satellites.