Here is an article that may be of intrest
http://www.straitstimes.com/breaking-news/se-asia/story/missing-mh370-how-satellites-communicate-plane-malaysia-airlines
It certainly sounds as if they have a method but it may have been simplified for the media. Certainly would be interesting to find out what was done.
Thanks for the link. Extra interesting in that even an article purporting to explain, still contains massive internal contradictions. Quote from the text:
"4. Through the hourly "handshakes", the satellite can determine the approximate location of the plane so that it can relay messages efficiently. A plane that is flying directly under a satellite would be at a 90-degree angle to the satellite. An aircraft flying at the poles would be at 0 degrees, the CNN report said. The last message sent by MH370 was at 40 degrees.
5. A satellite can “see” in an arc that stretches north and south of its fixed position, but without global positioning system (GPS) on the plane, the satellite can say only how far away the electronic "ping" from the aircraft is, not where it is coming from, a source told The New York Times."
You see that these two points directly contradict each other? #4 is the version supporting the 'arcs chart', while #5 is what I'd expect to be true. Except that there's a difference between 'ping' and 'handshake', and it's important since you can't get ranging time-of-flight from a one-way ping from the plane. If the satellite pings the plane and the plane responds, that's a handshake, and gives you some ranging info, albeit with an uncertainty due to the potentially variable response lag at the plane.
The media are using the terms as if synonymous.
Then there's a reader comment:
"RocketRob
The initial handshake is established when the plane powers up (on the ground) -- perhaps around 12:11 am based on the approximate one hour ping cadence. Flight took off at 12:41 am so first in-air ping would have occurred around 1:11 am -- about 10 minutes after the plane reached its cruising altitude of 35,000 feet, and only 4 minutes after the final ACARS transmission was sent. (As a reminder, we don't know when the ACARS was disabled, other than it happened sometime after 1:07 but before 1:37.)
So there should be a total of 8 in-flight pings from MH370 -- from 1:11 am to 8:11 am. The Inmarsat-5 F1 satellite (located at 63 degrees east longitude in geosynchronous orbit)
cannot determine the azimuth from which it receives pings from the aircraft, only the range (which can be calculated from speed-of-light roundtrip time between the satellite and the plane, assuming you know the response latency by the plane). For the final ping, the roundtrip speed-of-light time appears to have been around 252 milliseconds, implying a range to the plane of about 37,800 km. That works out to a circle on the ground, centered on 0N, 63E, of radius 4850 km, or a little over 3000 miles.
Of course, much of that circle can be ruled out based on the impossibility of the plane reaching it from its last known position. This is why NTSB and other authorities have plotted an arc (actually a pair of them) where the plane could have been at 8:11 am. I'm assuming the gap between the two arcs must be based on information gleaned from the prior pings which would provide a series of hourly range-rates. I would rather have *all* the arcs so that I could draw my own conclusions. I'd also like to know the measurement uncertainties in the computed ranges, which are a function of satellite clock accuracy (presumably excellent) and aircraft response latency (probably the main source of uncertainty)."
Emphasis is mine. Notice he calls it 'Inmarsat-5 F1'. My satellite almanac is old (1997) which is where I got 'Inmarsat-3' from. But it would have reached EOL by now.
So, we still have the awkward situation where the assumptions of that official 'arcs' chart may be invalid - and all that means.
Really need to find some accurate, definitely have not been fiddled with, technical information on the capabilities of the Inmarsat-5 F1. Anyone have anything that's in physical print form, or files they've had in their possession since at least a year ago?
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