How Satellite Company Inmarsat Tracked Down MH370

mdsolar (1045926) writes "Malaysian Prime Minister Najib Razak has announced that, based on satellite data analysis from UK company Inmarsat, Malayian Airlines flight MH370 ended in the southern Indian Ocean, and no one on board survived. 'Effectually we looked at the doppler effect, which is the change in frequency, due to the movement of a satellite in its orbit. What that then gave us was a predicted path for the northerly route and a predicted path the southerly route,' explained Chris McLaughlin, senior vice president of external affairs at Inmarsat. 'What we discovered was a correlation with the southerly route and not with the northern route after the final turn that the aircraft made, so we could be as close to certain as anybody could be in that situation that it went south. Where we then went was to work out where the last ping was, knowing that the aircraft still had some fuel, but that it would have run out before the next automated ping. We don't know what speed the aircraft was flying at, but we assumed about 450 knots.' Inmarsat passed the relevant analysis to the UK Air Accidents Investigation Branch (AAIB) yesterday. The cause of the crash remains a mystery."

Comments

Executive summary...

[Last_Available_Usern]

We still have no idea exactly where the aircraft is, how it went down, or what to do now.

Re:Some questions

[Strider-]

How come the frequency information of the signal received by the satellite was saved? What is the purpose of saving all that data in normal operations?

The communications system in question is likely based on TDMA (Time Division Multiple Access). While I have not worked with Inmarsat systems, all the other satcom systems I have worked with log each connection, and various pieces of information regarding the connection. One of these parameters that is logged is the frequency offset (ie the difference between the expected and actual frequency). This is useful from a troubleshooting perspective as it allows you to spot transmitter and receiver components that are drifting out of specification. Some of the more advanced satellite systems (iDirect) will actually log the geographic coordinates of the uplink site, as this plays into the timing requirements for the network. Unfortunately, Inmarsat isn't this aggressive with their timing, so time of flight isn't an issue).

And why did it take three weeks to do that analysis?

This is pure speculation on my part, but I would wager they had to go back through significant amounts of logs in order to characterize the transmitter and receiver components on that particular aircraft. The doppler effect is going to be subtle compared to the thermal drift of the transmitter, so they need to factor that out before they can get at the thermal drift. Also every oscillator and transmitter is different, so they would need to characterize the transmitter that is on that specific aircraft (which is now of course missing).