MemoryTale
Good with a stick
The scenario I've used is that barrels of flour were fired into the enemy ranks with catapults, before the airborne flour was detonated using a rudimentary explosive. Is that feasible for causing damage?
How powerful is an explosive based on flour mixed with air? In my WIP, a beseiged castle uses flour barrels as an improvised defense. The intended result is the destruction of incoming seige equipment and the first couple of lines of the enemy army. The more traditional route of oil vats + fire isn't really an option in this scenario.
You can have Neutrinos or Radio as beacon. Ordinary Radioactivity won't work.
andabout half an hour. On average, Jupiter is 5.2 AU from the sun and Earth is 1 AU from the sun, So its about 4 AU from Earth to Jupiter on the average. Light crosses 1 AU in about 8 minutes - so maybe 32 minutes.
Right now, about 35-40 minutes, give or take. But that changes every second, because Jupiter is now moving away from Earth.