На - On on the hot air balloon

okay ,I realize:))Thx!

I think you need to take into account some important details: what is the main thought of the sentence? Somebody flies using the balloon (in = "в корзине воздушного шара" ), or just something is painting on it (on = на воздушном шаре).Usually, of course, in Russian language we think about the travel by ballon. The word "Big" emphasises size of ballon.

thanks

На большом воздушном шаре - into the basket of air balloon - it's means of transport - like an airship. на in this case means into the means of tranposrt.