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At Forest last year I was inspired by the hot air balloons located near the hangar. Their enormous size and the way they lit up the sky with their propane burners seemed like a great opportunity for projection mapping.
With the cooperation and permission of the balloon owner, I'd design and build an aluminum rig that would noninvasively attach to the basket and mount an array of 6-9 projectors. Six projectors would aim upwards towards the envelop and the remainder would point down lighting up the forest floor. Power and data lines would be run up one of the guy wires as to reduce weight and allow for more passengers. I estimate the total weight of the rig and projectors to be ~100 lbs.
To add an interactive element, the generative visuals can be driven by an audio input. This could be a wireless signal sent from the nearest audible stage or a microphone located in the basket. Passengers could shout and sing into the mic and see an immediate response in projected light. Also riding in a projection mapped balloon should be a first for just about anyone.
My initial concept used programmable lasers because they are brighter and more effective over a long distance, but they are also significantly more expensive, considering the budget, and there is some safety concerns regarding laser light hitting people in the eye. It's doable, but I'd want to do it safely and would need to consult with a licensed expert.