INMARSAT has several services for airliners. The Aero-H and Aero-H+ services both accomodate ACARS and other voicec and data services for airline operation. Aero-H service operates on the INMARSAT I-3 constellation that has global and regional beams. Aero-H+ can operate on either I-3 or I-4 satellites. The I-4 satellites have a global beam as well as multiple small overlapping spot beams, similar to a cellular network. INMARSAT can dynamically assign bandwidth (spectrum) to spotbeams as required, allowing a very high level of frequency re-use. The spotbeams are not steered on the satellite. The system also uses a form of uplink power control. The mobile terminal sets initial transmit power based on elevation angle to the satellite. The network control system keeps track of all terminals logged into the network. The power setting, and therefore approximate elevation angle, are reported back to INMARSAT NCS. If there were two transmissions at large enough differences in reported elevation an approximate bearing and speed could be calculated. That would at least focus the search to a single wide line. However, looking at the arc on the map and assuming it is accurate, this looks to be too big to be in an I-4 spotbeam which means they may be operating on the I-3 constellation which doesn't require as much information as the I-4 does. I'm not as familiar with the H and H+ services as I am with the BGAN service so I don't know the details of how an H or H+ terminal behaves on the two different satellite versions. I truly hope they have more information than is being released. Howie, AB2S
interesting thing is that i am sure that the u.s. as well as other countries have spy satellites that have been taking pictures 24/7 with resolution that can see a person on the ground. that being said, i would further venture to say that none of them will want to show pictures of the jet as it would give away their secret ability. possibly they are fixed on a particular country or city and not the ocean.
73...bruce
At 12:40 PM 3/17/2014, Bruce wrote:
i am sure that the u.s. as well as other countries have spy satellites that have been taking pictures 24/7 with resolution that can see a person on the ground. that being said, i would further venture to say that none of them will want to show pictures of the jet as it would give away their secret ability.
Hey, good to see a post that's on topic. Satellites!
Actually, the capability is not very secret. Its pretty much out in the open. Although every nation keeps the details secret, but you don't need details to understand what kind of a picture is possible. Physics will tell you that.
You can calculate the resolution of a spy satellite. Its just physics. You know the diameter of the aperture (lens or mirror). You know that because dimensions for many classified objects have been published. Also you know the diameter of the space shuttle's payload bay. You know the wavelength of light. Simple formula gives you the resolving power as an angle. To turn that into the size of an object you need to know a distance. You can look up the orbits of many classified satellites, so know how far away they are. But because you get more resolution by being closer, you know the best pictures will come from low orbit, and here the limit is the Earth's atmosphere. No need to know classified orbit data. Just presume there are some spy satellites in low but stable orbits, perhaps 300 to 500 km.
So, yes, they should be able to see something smaller than a person, but here's the kicker... They can't do that everywhere at once. Because they are in orbit close to the earth, they can only see stuff that's under them. This is a tiny fraction of the earth. Also, within that area, you have to tell them where to point. A simple number-of-pixels thing. Looking at the whole footprint at max resolution would be an enormous # of pixels. We would have to guess the limit, but its not hard to guess that the maximum image is way smaller than the footprint. This is great for taking pictures of your opponent's military installations, and maybe even seeing what assets there come and go over time, but it is unlikely to be of help in tracking an airplane that unexpectedly flies some unknown path to some unknown location.
Also, the plane flew at night, in the dark.
I'm sure the big boys are thinking about new capabilities as we speak, and writing them into next year's budget!
nice, thanks antonio. i still think that we have enough of our spy satellites watching that part of the world that they saw it and night should not matter. if we can think outside the box, i am sure we have created it. <br/><br/>73...bruce<a href="https://overview.mail.yahoo.com?.src=iOS"><br/><br/>Sent from Yahoo Mail for iPhone</a>
Finally, (some) technical details, though still not as many as I'd like.
https://www.facebook.com/permalink.php?story_fbid=740971779281171&id=178...
The original analysis was based either on a round trip time measurement or a reported transmitter power, which depends on satellite elevation. Either way, it could only yield a locus of positions that fell on a circle of constant distance (or elevation angle) to the satellite. Erasing the part of the circle that could not be reached with the available fuel left the arcs. I don't understand why there would have been a gap between the two around the equator.
The big problem was to solve the ambiguity -- northern hemisphere or southern?
I believe the answer relies on the fact that Inmarsat 3 F1 is an old satellite launched in 1996. Its inclination has risen to 1.67 degrees, probably because its stationkeeping fuel has run out.
The total measured Doppler would be the sum of the Doppler caused by the plane's motion with respect to the satellite and that due to the satellite's non-zero motion with respect to the earth. Judging from the diagrams on heavens-above.com, I'd say the satellite was moving southward during the flight, which took place between roughly midnight and dawn local time. Since the plane was in the southern hemisphere, the satellite was moving toward it, resulting in a higher net frequency shift than if the plane had been in the northern hemisphere.
Note the shapes of the curves in the plot titled "MH370: Burst Frequency Offset". The southerly track has the Doppler increasing with time, while the northerly track would have it decreasing with time.
The analysis does have to assume a certain fixed speed for the aircraft but it seems to produce consistent results.
It should be possible to replicate Inmarsat's graphs using the three line elements for the satellite and their presumed ground tracks for the aircraft.
Phil
participants (4)
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Bruce -
Franklin Antonio -
Howie DeFelice -
Phil Karn