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Malaysian Airlines MH370 contact lost

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Malaysian Airlines MH370 contact lost

Old 22nd Mar 2014, 12:02
  #7201 (permalink)  
 
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Inmarsat

To put this hypothesis to bed. The satellite has a footprint that covers approximately one third of the Earth's surface. Even though there are lots of empty spaces in the southern Indian Ocean, this satellite also covers a lot of Africa, India, most of Russia and most of Europe. These are not silent areas, there are lots of transmissions to 'listen' to. The only way the satellite can discriminate between 'pings' from aircraft is that these low level protocol 'pings' are actually short messages with a unique 'electronic aircraft address'. It is the INMARSAT business to ensure that these thousands of aircraft transmissions are not mixed up. So the hypothesis that they 'tracked the wrong plane' is just not supportable.

For starters, the satellite doesn't discriminate between anything. It's just a bent pipe retransmitting what it hears in an analogue sense. All demodulation and interpretation occurs on earth.

An end point in such a network would be identified by a DNIC or number, something that looks like an international phone number or an x.25 address. It certainly isn't identified by an aircraft manufacturer's serial number. If the data service isn't paid up and active (there was an early post in this thread indicating the airline didn't use the inmarsat service) who cares about keeping this number-to-plane mapping in sync. Or who cares if the non-useful bit of kit is removed for testing etc.

If the service was not paid up, there would be no polling from the network towards the terminal. There may be polling from the terminal towards the network "->can I logon"...."<-no"... Unless there is a two way flow from the network to the terminal and back to the network timing is going to be very hard to establish. That the range ring lay exactly on the 40 degree contour is telling of the precision the author felt they had. This wasn't 41.5deg, or 42deg, it was more like vaguely in the vicinity of 40deg.

That the inmarsat range calculations were calibrated by the "known" location of the aircraft pre-disappearance is also troublesome. A vague range ring drawn through the place the sat terminal was assumed to be.

Look, I'm accepting that this hypothesis can go right out the window if a few bits of information (like it being and inactive sat service) turn out to be incorrect. There might also be non-public information clearly discrediting this theory. But to me, fire causes loss of comms, then loss of control sounds more plausible than deliberately evades radars to end up in the southern ocean.
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Old 22nd Mar 2014, 12:04
  #7202 (permalink)  
 
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...and the BBC mistakenly have 'Breaking news - China satellite finds debris in the south China sea '
They actually say 'debris' in inverted commas, suggesting it's not actual fact. Besides, whatever it is could well be debris of some sort.
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Old 22nd Mar 2014, 12:08
  #7203 (permalink)  
 
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Originally Posted by Ian W
I think you will find that messages are timestamped probably synched to GPS clock.
I think AT1 in his post https://www.pprune.org/showthread.php?p=7124 explains that the satellite sends out a precise timestamp as part of its ping and the receiver returns it along with the receiver's unique iD, this allowing the lag to be precisely calculated irrespective of how good the clock on the receiver is.
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Old 22nd Mar 2014, 12:11
  #7204 (permalink)  
 
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How satellite pings work.

Rory 166 refers us back to AT1's post no.7124, now on page 357, where a telecoms engineer explains in striking detail how these satellites work and the accuracies involved.

This is dense stuff, but well written and I would like to add my thanks to AT1 for his work in putting that very helpful explanation together.

I've read all 7000+ posts here, but must have skipped this one!
The low data rate inmarsat services that work with omnidirectional antennas are not as sophisticated as the poster may imply. Inmarsat-C is a teletype era service.
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Old 22nd Mar 2014, 12:18
  #7205 (permalink)  
 
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Originally Posted by rh200 View Post
Is it possible that they are taking images at lower resolution to cover more area in each pass?
The 'high quality' Google images are from aircraft not satellites. If you look at GE images in the outback you will see the resolution of the civil satellite images.

On the question of Ping latency, this is not an ip type network ping (which can have lots of reasons for latency), but appears to be a clock synchronisation ping to get the right time division for the TDM to work. As such it will be implemented in hardware not software, so it is unlikely there is anything to influence that latency. It is also likely to be only a rough time synch (say 10 to 100 Microseconds - which would be a 6 to 60 mile precision - so altitude changes would not meaningfully change the time delay.
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Old 22nd Mar 2014, 12:24
  #7206 (permalink)  
 
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Resolution

This is supposed to be a comparison of satellite resolutions

IMINT - Coverage - Resolution

Globalstar images are said to be 1m or 50cm I think.
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Old 22nd Mar 2014, 12:24
  #7207 (permalink)  
 
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Previous posters have incorrectly looked upon the aircraft's Inmarsat receiver clock as if it was a free-running quartz wall clock. It's not free running, its locked synchronous to the incoming bit stream from the satellite (which in turn locks it's own highly accurate caesium or rhubidium clock to other satellites in the constellation and timing sources on the ground).

Once the receiver is synchronised to the bit stream it can start looking for a unique (nearly) repeating pattern of bits to tell it where a frame starts, once it knows where a frame starts it can start to assemble groups of bits into bytes, which will start to assemble into a packet.....etc...

Last edited by catch21; 22nd Mar 2014 at 12:48.
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Old 22nd Mar 2014, 12:26
  #7208 (permalink)  
 
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photos

KH-11 satellite imagery from 30 years ago had a resolution of only a few inches. It is probably even better now. The problem is that thing(s) is usually looking at items of special interest, mostly in the northern hemisphere. They have very little coverage in the south and it is a real bear to retask them. Even then, the targeting can only be changed a slight amount. Satellites don't make right angle turns in orbit.
- Another problem is that the area of coverage is VERY small for each frame of imagery. Some satellite imagery covers many miles per frame, but the trade off is resolution measured in many 10s of feet. The images presented so far in this search appear to be in the latter category.
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Old 22nd Mar 2014, 12:30
  #7209 (permalink)  
 
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Inmarsat know what they're doing. When they say how far the aircraft was from their 64E satellite at 11 minutes past the hours they can be trusted.

They're about the only originator of useful information in the whole saga.

Sadly, it looks like this could remain unsolved, unless someone has a lot of luck with a 43kHz sonar, or some international persons of mystery are willing to stack weather satellite/IR full-disk early warning images from the night of the flight or gets lucky with some archived radar data. Even then, it's going to be hard.

I hope I have to retract that, but two weeks on, it's looking like it'll be a long time before there's any more real news.
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Old 22nd Mar 2014, 12:32
  #7210 (permalink)  
 
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Air Observers

I hear they are sending SES crews from VIC as well now ?

Bloody hell, what a circus.

Must be a few, well connected "wanna be's" in the VIC SES
Airservices Australia trains volunteers they largely source through the SES to be air observers on SAR missions. Commercial aircraft get chartered and the eyeballs come from this pool of trained volunteers. Volunteers are flown on both training and real missions.

When I was in the SES in my younger days I flew on a whole bunch of SAR missions. I personally never saw anything, but whenever something was found, somebody's eyeballs found it.
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Old 22nd Mar 2014, 12:33
  #7211 (permalink)  
 
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Endurance: calling all navigators

Originally Posted by hamster3null View Post
They keep looking further and further south. It's really starting to stretch imagination. Latitude 45 south? MH370 _might_ have run out of fuel close to the spot if it turned due south as soon as it was out of range of Butterworth, passing over a broad swath of Sumatra along the way. If (more likely) it continued at least 30 min. on the original heading before turning, in order to stay clear of Indonesia, it would only get as far as latitude 36 by the last ping, latitude 40 if it stayed airborne for another 30 minutes after that.
Interesting, Hamster... Has anyone here determined a reasonably accurate range/endurance given we know:


49.1 metric tons of fuel, TOW 223.5 tons, air temp & meteo/wind, rate of climb, cruise speed (to loss of comms), & we have an idea of flight path (radar) & descent to 5000ft AMSL from LKP to LEP.


From that info some here must be able to ascertain a reasonably accurate estimated max range based on a couple of scenarios:


A> 2nd climb back to FL350, cruise until flame out + glide
B> no 2nd climb, continue at 5000ft until flame out + glide
C> assume no descent from IGARI & FL350 maintained until flame out + glide


Any navigators here with the appropriate knowledge & skills willing to post some calcs/estimates???


Might prove helpful for the crowd ;-)
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Old 22nd Mar 2014, 12:39
  #7212 (permalink)  
 
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UnreliableSource
The satellites are digital launched in 1995
You may be thinking of the original Satcom A satellites launched in 1979
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Old 22nd Mar 2014, 12:40
  #7213 (permalink)  
 
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Slight correction to previous post



Last radar plot is R285/250NM from Butterworth.

That the Chinese twitter image shows R295/200NM is irritating again. If this is the quality of investigation how can we believe what they say else.
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Old 22nd Mar 2014, 12:41
  #7214 (permalink)  
 
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Quality of satellite images

What am I missing here?

My garden is 5 metres x 12 metres and even on the standard Google Maps satellite view you can see my garden shed, footpath, fruit trees and a 2m x 3m vegetable patch. Standard Google Earth will even show the 20cm x 40cm steps on my grass.

So why are we being shown these very low resolution satellite photos anytime anything is found? I know the operators of these satellites don't want to reveal capability but come on, I'm sure a resolution at least as good as to that of Google Maps is no big military or commercial secret.
Google maps pictures might be updated once a year; this is because it takes that long to get around a photographing every place of interest at high resolution. If you look at google maps images away from metro areas the resolution gets quite poor.

Trying to quickly cover huge areas of oceans that may never have been photographed before is challenging.
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Old 22nd Mar 2014, 12:47
  #7215 (permalink)  
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Originally Posted by deadheader View Post
49.1 metric tons of fuel, TOW 223.5 tons, air temp & meteo/wind, rate of climb, cruise speed (to loss of comms), & we have an idea of flight path (radar) & descent to 5000ft AMSL from LKP to LEP.

. . .

A> 2nd climb back to FL350, cruise until flame out + glide
B> no 2nd climb, continue at 5000ft until flame out + glide
C> assume no descent from IGARI & FL350 maintained until flame out + glide


Any navigators here with the appropriate knowledge & skills willing to post some calcs/estimates???
Deadheader, as with everything else here, not enough information.

Would need the operating data manual, did it descend to 5000ft and only C applies. Did it cruise climb so have a longer descent? What met winds at all heights and over a whole postulated route?
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Old 22nd Mar 2014, 12:48
  #7216 (permalink)  
 
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If located this is what they would use

This is a video regarding "who to" find objects in deep water.
Belive this company was part of the recovery of Air France black boxes.

F-1 Engine Recovery | Bezos Expeditions
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Old 22nd Mar 2014, 12:50
  #7217 (permalink)  
 
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onetrack,a different set of protocols apples to visiting foreign airforces.
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Old 22nd Mar 2014, 12:51
  #7218 (permalink)  
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Lost in translation

I am an ATC and the transcript also surprised me.
I guess the problem is that it is a translation from English to Chinese and then to English. However, the lack of read back is not explained by incorrect translation.
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Old 22nd Mar 2014, 12:59
  #7219 (permalink)  
 
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Google's "satellite" images

In populated areas, Google's "satellite" images aren't from satellites. They're taken from planes flying over at 800-1500 feet altitude.

See Google's description

To get a sense for Google's true satellite resolution, zoom in on a remote area, say, rural Newfoundland. Even buildings look blurry there.
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Old 22nd Mar 2014, 13:11
  #7220 (permalink)  
 
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fg32 :-

The plane flew steadily away from the satellite over the equator while pinging, McLaughlin said.
are you interpreting this as ( note the comma)

The plane flew steadily away from the satellite over the equator, while pinging, McLaughlin said.
or

The plane flew steadily away from the satellite, over the equator while pinging, McLaughlin said.
At least one of those interviews is on here I will see if I can find it

Last edited by oldoberon; 22nd Mar 2014 at 13:13. Reason: add last para
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