Re the other pings. I have read elsewhere that the trip time for the ping is an implementation detail which is stored in some kind of routing table on board the

Re the other pings. I have read elsewhere that the trip time for the ping is an implementation detail which is stored in some kind of routing table on board the satellite. It's used to calculate an efficient time division multiplexing strategy for the RF transmission protocol used. Hence only the trip time from the last ping is cached. There are records of previous successful pings, just not with any trip time data. The trip time data is what give you the diameter of circle to search on. The remaining arcs are the parts thought to have been within range given the fuel and flight time so far. Pings apparently occur every hour. The 'thickness' of the line of the arc is up to 1 hours flight time depending on how much longer the plane flew on after the last ping. Edited to clarify stuff about arcs and pings.