Malaysian Airlines MH370 contact lost

[ana1936]

Thanks TelecoAg. It does make much more sense to me that the satellite initiates the ping each hour.

In any case, the satellite has to send a message and get a return message as part of the ping exchange in order to be sure of the identity of the plane. Typically it would encrypt a random number using the specific plane's public key and check that the supposed plane was able to decrypt that message and return it encrypted with the satellite's public key.

The satellite's accurate clocks can then record timestamps for the sending and receiving parts of that message.

The journey of the message each way would take about 130 millseconds while it would only take 1-2 millseconds for the plane's equipment to process the incoming message and send a response back. Thus most of the 262 milliseconds difference in timestamps would be travel time.

This gives a pretty good estimate of distance between satellite and plane.