Like many people I have been rather skeptical of the data produced by
Inmarsat in which they claimed that the a/c flew along or near to the
"southern" arc produced by signal levels of the hourly pings.
I could see how they might deduce the arc , but not how they could tell if
the signals were north or south of the equator.
Of course all this assumed that , as was mentioned in the media Inmarsat at
63 degs was used [ 5 Flight 1 ]....but the system aboard MH370 was older and
didnt use GPS.
Then I suddenly realised that not only was the system old , but so was the
satellite.
These non GPS signals are sent via Inmarsat 3F1 at 64.18 east....not 62.7
east.
Not only that , but 3F1 launchedd in 1996 , is inclined by 1.6697
degs....so wobbles above and below the geo arc in an extended figure of 8
pattern every 24 hours.
INMARSAT 3-F1
1 23839U 96020A 14082.92914473 -.00000008 00000-0 10000-3 0 2891
2 23839 1.6697 73.1023 0005489 286.4812 220.7448 1.00274299 65821
At the time the flight took off the sat was 1 deg 11 mins N of the equator
.Three hours later it was at the top of its wobble one deg 40 minutes....and
by 2240 GMT it was back around one deg 11 minutes....having travelled around
the top of the figure of eight.
This gave Inmarsat the third refrence to allow a very approximate idea of where
the signal was coming from....and put it in the southern corridor , not the
northern.
Ref 1 the signals from MH370
Ref 2 the doppler from the wobbling satellite and the moving aircraft
Ref 3 the calculated behaviour of a signal from a "known" a/c within the
footprint of Inmarsat
Hardly cutting edge science...more basic orbital mechanics , but probably
the first time they have used the technique
All geostationery satellites move around a bit but are kept in position by
the operators station keeping.
As they get older they start to wobble more as the fuel runs out and to
extend their life , the operators carry out fewer regular burns.
Even the most stable geo sats. those we get our tv from , move
You can see this movement in the 80 minute time lapse video I took about
ten years ago of a group of TV satellites
The dots are the satellites 36,000 km out in space the streaks are stars
which appear to move due to the rotation of Earth
So there we are....thats probably how they did it.
No doubt someone from Inmarsat will correct me on some of the finer points....but these are the basics.
Of course , Inmarsat tracked the device emitting the ping....not
necessarilly MH370......but odds are the two were together.