The transponder only pings when it is queried by a proper signal from the active radar on the proper signal. That signal swept the plane about every 4.64 seconds. The missile, if there was one, was traveling at Mach 2 or greater. At that speed, the missile would travel almost a mile in the 4.64 seconds and there would only be time for any such missile to get just two transponder returns during the flight, not enough to use for any lock on the plane for guidance. Most of these MANPAD missiles are heat seekers and would then average the center of the heat sources when they get close enough.
Flight TWA-800 at 13,800 feet was visible by the naked eye at 8:31 PM on that July evening from the range this theoretical missile could be fired. It was at the extreme altitude range that could be reached by some tripod launched missiles, but not by any shoulder launched missiles.
TWA-800 was also being tracked by two passive radar stations, but the records of those radar stations were taken to the White House the next day and have never been seen since. One of them was a much more rapid sweep. Those records could have told us a lot of the missing distance data and possibly some altitude data and certainly would have shown data on any bogeys that might have been in the area. The Active Radar return pings do not record any data not related to transponders, unfortunately. The air traffic controllers do not need to have their screens cluttered up with data they are not concerned about so their systems are designed to exclude everything except air traffic data.
Which was happening from that radar station in Pennsylvania as was indicated in the link I previously submitted.
Beyond that, I do not think it is too technically difficult for anyone to ping it if they want to. It's made to automatically respond to the correct sort of query on the correct frequency of microwave radiation. You could design a missile so that the missile will continuously ping it.
It would be effectively guiding the missile to itself. That would actually be a pretty easy guidance system to build.
Flight TWA-800 at 13,800 feet was visible by the naked eye at 8:31 PM on that July evening from the range this theoretical missile could be fired. It was at the extreme altitude range that could be reached by some tripod launched missiles, but not by any shoulder launched missiles.
If I remember correctly, Jack Cashill said it was bigger than a shoulder fired missile. If you have it mounted on a large boat, it likely can have a pretty good reach.