We have radar and people watching our borders 24/7. They know whenever something enters our airspace. They track it and if it can't be identified, they go out to check it.
The U.S. government, after Roswell, has become extremely adept at picking up on crashed alien spacecraft. They have a huge incentive: after Roswell, they received a huge technological bonanza from that spacecraft that they reverse-engineered and which led to the major jump in technology that we have been experiencing in the last few decades. Corsi's book explains how they did it. Corsi, the person in charge of this project, tells how they carefully covered their tracks, using military defense contractors to develop the technology. Examples of what was developed are fiberoptics and Kevlar.
Ever since Roswell, the U.S. government has been very fast at recovering crashed alien spacecraft. It's almost as if they are just waiting for it to happen. They have even gone into other countries to retrieve a downed spacecraft. How they get away with this is amazing to me, but they do it. This is how aggressive they are about it.
Howard Blum's book ("Far Out") exposes the fact that contrary to what they say, the U.S. government is highly involved in tracking UFOs. They even have a collection of downed spacecraft which is secreted in a highly guarded facility known as Area 51.
My point is that the posters on that thread wanted to automatically assume it was a U.S. gov't failed experiment. That is not necessarily so as anyone who is familiar with this topic will tell you that UFOs are tracking everything we do in regard to space, nuclear, etc. The spacecraft that went down could just as easily have been an extraterrestrial spaceship.
Cher