Diamond shaped object seen by family of 5 driving near TV transmission tower in South Dakota at Iowa Border.

My family and I (age approximately 8) were nearing the TV transmission tower off Highway 9 at the SD/Iowa border and spotted what we first thought was a helicopter, as we could only see lights moving at first - mostly white, some red, some blue, maybe yellow - don't remember green; the movement was jerkily up, down, and diagonally in random leaps of 50-100'. We thought a helicopter had flown too close to the lines that were supporting the tower, which is what my father, who was driving, initially exclaimed. As we neared, we saw it wasn't a helicopter, but was a dark "kite shaped" object, flattened, with the longer pointed end directed "forward". The lites were underneath and moved around. As we drove even nearer, it began to follow or fly nearer to us, and we saw that it was huge, like maybe the size of a football field! It flew about the length of itself above us, sometimes faster and ahead (so it was visible to the front in the windshield) and sometimes in back, for several minutes as we continued down the road - dad had speeded up but I don't know how fast. At a certain point it was behind us and then suddenly swooped upward and away in seconds shooting into the sky. We were pretty freaked out. My sisters (2 younger) were with me in the back, but only vaguely remember it. My mom is not too willing to admit it either, because of her religious beliefs. Dad remembers it.