During a couple of space launches, NASA learned that ionized exhaust from rockets can trigger a lightning stroke if rain clouds are nearby. This happened during one of the Apollo missions, though with no dire consequences. More infamously, in 1987 an Air Force rocket launched from the Kennedy Space Center in Florida was hit by lightning. The rocket was destroyed at a cost of $162 million. Scientists have known about triggered lightning for a long time, and they sometimes attach copper lines to small rockets to attract lightning for research purposes. Lightning caused by rocket exhaust, though, is an unintentional side effect.
NASA discovered that its spacecraft could attract lightning, and so they now build lightning towers around launch pads as a protective measure. (NASA)