TopHat series of top mounted balloon-borne telescopes

We describe the engineering design and operational concept for a series of three complementary top mounted balloon- borne experiments to measure the Cosmic Microwave Background Radiation anisotropy, culminating in a two week circumpolar flight from McMurdo Station, Antarctica. Each experiment is designed to provide a maximum science return in addition to acting as a pathfinder to the successor flights of top- mounted balloon-borne experiments. The experiment program, named TopHat, will involve the launch and operation of the first far-infrared and microwave telescope flown entirely from the top of a 28 million cubic foot balloon. It utilizes a two axis gimbal pointing system, a one meter Cassegrain optical system with a chopping secondary mirror, and a 3He evaporation cryostat designed to maintain a bolometer detector temperature of 0.25 K for 30 days without cycling. The series of flights will begin with an engineering test flight scheduled for launch in July 1996 from Palestine, Texas, followed by a pointing experiment to be flown from Ft. Sumner, New Mexico in April 1997. A spinning experiment will be launched from Ft. Sumner in April 1998 and Antarctica in December 1998.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.