If we did manage to create aircraft capable of the speed of light, it would render them invisible to every form of detection available at the present time until they had passed. Some time in the future, maybe we will create some sort of super radar or something, but I do not see how.
The speed of light is calculated to be 670,617,629 mph or 1,079,254,458 kph. To put this into proportion, The Space Shuttle's re-entry speed is 17,322 mph or 27877 kph. If we were going to be trying this speed in the atmosphere, things would not end well. In space however,I can't see how we could not do it. Since there is no friction from an atmosphere in space, we theoretically should be able to reach an unlimited speed as long as we can be propelled for a long enough time, and we can dodge around asteroids and planets and whatnot. If this is true, we should be able to reach the speed of light with technology we have already, we just haven't bothered to try yet
Scientists have also been looking at the possibility of "wrinkling" space to essentially create a shorter distance to travel. You would not feel anything inside the aircraft, but it would appear that stars are streaking by outside the ship, sort of like warp drive in Star Trek.
This is as much as I know on the subject of light speed. There are probably a few holes in my knowledge, and I would appreciate it if you guys can correct me, as I like to learn.