Balloon spaceship
 

I am collecting information now for a project i will undertake in the spring of 2019 (my plate is way too full until then.) I want to make a balloon type flying vehicle that is shaped like a flying saucer. the helium balloons inside will give it the lift that it needs (I am researching the feasibility of installing a small compressor to reduce the helium in some of the balloons to make it go up and down). The low profile will help make it not only travel, but stay put because there will be less wind resistance so hopefully will not be blown around so much. I am looking for help on the following right now:

The material to use for the "space ship". Must be very strong and ultra-light. The low profile of the flying saucer will limit the amount of balloon I can carry, thus limiting the amount of lift.
The material used to make the balloons. I am considering using 5 so that if one or two fail the ship will fall gracefully, like a feather, rather than like a lead balloon.

The space ship will be used for surveillance, photography and possibly some form of communication/relay station. I am hoping to cover the roof of it with solar cells, so that it will be able to stay up for an extended time, days if not weeks. This is all a dream phase now....weight is going to be a big issue, but as I said, I am collecting data about two points now and will mull on it for the next year before taking action.

If in US don't forget to get FAA approval. And surveillance is one of the key things people are PO'd about drones.

But it is only going to be 5 feet across. Do I still need FAA approval?