aerostat

noun2

1. •
   An aircraft, such as a dirigible or balloon, that derives its lift from buoyancy rather than from wings or rotors.

   • With its molten temperatures, sulphuric acid clouds, and crushing carbon dioxide atmosphere, Venus has only a handful of aerostat research outposts. — 2008
2. •
   A moored balloon flown in a semi-permanent manner, such as a border patrol monitoring balloon affixed at 18,000 feet (~6 km).