BED II
The Balloon Experimental Twin Telescope for Infrared Interferometer (BETTII) was an interferometer for astronomy in the far infrared . Since this spectral range is absorbed by the earth's atmosphere , the twin telescope was attached to a stratospheric balloon in order to overcome most of it at an altitude of 40,000 m. BETTII consisted of an interferometer with a base length of 8 m, which enabled observations in the wavelength range from 30 µm to 90 µm with an angular resolution of 0.5 arc seconds . Using a Fourier spectrometer , this area could be examined with a frequency resolution of 1: 100.
BETTII was destroyed at the end of the first technical test flight in Texas on June 9, 2017, when it detached itself from the balloon and parachute when the landing was initiated and therefore fell unchecked to the ground from a height of 40,000 m.