Everybody has to have at least one nutty idea. Here's mine: I don't believe in flying saucers but I do believe in the possibility of interstellar travel. I suspect our Solar System has been visited less than 10 times in its entire history by interstellar spacecraft. These spacecraft would be enormous and controlled by machine intelligence (Hollywood examples would be the alien mothership in "Independence Day" or the "Death Star" in "Star Wars"). These vehicles would not travel faster than 5% the speed-of-light and take centuries to travel from one star system to another. When they arrived in a new star system, they would be heavily damaged by collisions with interstellar grains and micrometeors. Their descent stage would be beat up and radioactive from a thermonuclear or antimatter propulsion system. Once these vehicles were "in system", they would jettsion their fuel depleted, damaged and radioactive descent stage. They would then proceed to interesting worlds like the Earth using a low thrust propulsion system. The descent stage from these vehicles would remain in orbit as a recognizable alien artifact. However they would eventually be shredded into dust by meteor impacts (a process taking hundreds of millions of years to complete). I suspect that at least one of the small metallic "asteroids" orbiting the Sun near the Earth is in fact an ancient descent stage.

How would one go hunting for ET's descent stage? First of all, never hint to the politicans or bean counters that this is your actual intention. Your proposal would instantly fail the giggle test, be terminated and you wouldn't get a second chance. Instead, propose to do an asteroid (NEO) inventory. A JIMO type spacecraft architecture would be ideal for this application. In essence, the vehicle would be like a bee collecting nectar from a field of flowers. The JIMO clone spacecraft would first do a fast flyby of the metallic "asteroid" to perform imagery and remote sensing. If it was clear that the "asteroid" was really only an asteriod, the spacecraft would use its ion engines to do an orbit adjust and then proceed to the next interesting "asteroid". If the JIMO clone hit paydirt and the "asteroid" showed promise of being an old artifact, the JIMO clone would reduce its relative speed and close in for a better look. If the JIMO was designed right, it could give hundreds of "asteroids" a nice close look. Obviously if this concept hit paydirt, it would be the most important thing that happened in human history. In essence, we'd have a formerly working starship motor with most of the support technology that we could reverse engineer.

Gary