Peter B. de Selding hit the front page of Space News (subscription only) the other day with a scoop about a Chinese plan to build a 24-satellite navigation network, called Compass, in roughly the same orbit as the American and European sat-nav systems, GPS and Galileo. But theres more: the Chinese are apparently threatening to use an encrypted signal for military ops that would actually overlay and maybe interfere with "M-Code," the Pentagon's GPS broadcast. That's the signal that keeps everything from precision bombs to flying drones on track.You might remember that the Pentagon had a right royal hissy fit when the Europeans proposed to overlay Galileos encrypted signal on the M-code, because under those circumstances the U.S. military wouldnt be able to jam Galileo during any hostilities without blocking its own ability to access the GPS signal. So, you would figure collective hair would be on fire over at the five-sided building at the news of the Chinese plan, right?Well, maybe and maybe not. Turns out this jamming biz is not as simple as it sounds. According to CDIs resident techno-geeks, Haninah, Eric and Ryan, it seems that we could, at least theoretically, jam the Chinese satellites even if the GPS signals are overlain (over-layed? laid over?). It would be difficult, and wed need a lot of jammers to ensure that enough satellites in the network were shut down to degrade the systems functionality. But jamming the signals of individual satellites is a tough challenge, so wed likely end up opting instead for frying in that the easiest way to shut them off would be to them slam them with a pulse that would put the electronics permanently out of commission.That's probably not an option we'd want to take with Galileo constellation -- which, after all, is costing the Euros a serious wad. Considering that the U.S. isnt likely to be at war with Europe anytime soon (perhaps despite the efforts of the French), its probably safe to assume that wed only be talking about stopping up Galileo if some bad guy was using it against us and it is pretty unimaginable that under those circumstances that the U.S. would want to be faced with having to blow (electronically that is) Eurohardware out of the sky.Instead, we'd probably want to use local jammers, to block out a given area's satellite receivers on the ground. GPS signals (and Galileo signals) are weak. So it's pretty dang simple to drown them out using an in-theater jammer putting out a stronger signal over a certain geographic footprint. But that only works if our M-code and their signals aren't crossed-up.But the question of being able to jam the Chinese isnt the only problem raised by the potential Compass signal overlay. The CDI techno-geeks, as well as one of my P-gon buds who actually knows a thing or two about satops, explained that the Compass constellation itself could be used by the Chinese as sort of a giant jammer in space to muck up GPS. The Compass sats could transmit garbage that disabled GPS, or transmit deceptive signals that would not disable it, but cause it to broadcast incorrect data. They could do this intermittently and sneakily to undermine confidence in GPS/Galileo reliability (Beijing to Washington, Were so sorry, bugs in our system.) Or they could equip the Compass satellites with high-powered transmitters linked to a big, red DISABLE GPS button at PLA HQ for use in any conflict with the U.S.Before I get slammed for pretending to be Bill Gertz, it is worth noting, as Gregory Kulacki from the Union of Concerned Scientists pointed out, that there isnt any money in the current Chinese five-year budget plan for such a satnav system, and wed be talking about big, big money. Nor could Gregory find any info in the Chinese-language technical literature in the public domain about the specs for such a potential system. So, maybe the Chinese just want to scare the Euros into letting them in on their signal? Stay tuned, well know more next Monday when Space News will be publishing a follow-up story.-- Theresa Hitchens
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