I don’t think this is correct… a thousand cubic feet of hydrogen is 68lbs of buoyancy at sea level.
A cylinder that was 20’ long, and 5’ in radius (which is a lot bigger than my minivan - would be about 1570 cubic feet.
That could lift about 100lbs at sea level… at flight level 400… that’s going to have to be a huge balloon to lift 100 lbs or the payload has to be tiny tiny - which is possible but I don’t think something the size of a car is adequate.
Your are dramatically underestimating the size of these things:
The Chinese high-altitude balloon shot down over the Atlantic off the coast of South Carolina over the weekend was 200 feet tall and carried a payload the size of a regional airliner, a U.S. Air Force general said in a briefing on Monday.
The balloon's superstructure and hardware weighed "in excess of a couple thousand pounds," said Gen. Glen VanHerck, commander of North American Aerospace Defense Command and U.S. Northern Command.
A cylinder that was 20’ long, and 5’ in radius (which is a lot bigger than my minivan - would be about 1570 cubic feet.
That could lift about 100lbs at sea level… at flight level 400… that’s going to have to be a huge balloon to lift 100 lbs or the payload has to be tiny tiny - which is possible but I don’t think something the size of a car is adequate.