The problem with star trail photography is that it renders your camera busy for up to 1-2 hours. This is all good and well if you have just one camera. I shoot with two full frame Nikons. A D3s and a D800. The problem with having two cameras and only one tripod manifested itself during this shot. This shot was the straw that broke the camels back as they say. I was taking this shot and was I half way into the exposure when I looked to my right and seen a great composition of the milky way above the mountains with the international space station(ISS) flying over head. I reached for my second camera to realise that it was useless without the tripod.
After that night I went home, did some research and purchased a second tripod. I have found the second tripod to be very beneficial. I have often left one tripod at work completing a star trail and worked on other local scenes with the second setup.