The Ultra-violet Sky-Survey Telescope in the TD-1A Satellite

The European satellite TD-1A was launched in March 1972 and carries, in addition to other experiments, a 27-cm ultra-violet telescope which gives low dispersion spectra over the wavelength range 1350–2550 Å and a broad band measurement centred at 2750 Å. The control system causes the telescope to scan the sky in great circles which pass through the ecliptic poles and precess by ∼ 4 arcmin per orbit thus completing a sky survey in ∼ 6 months. The capability of the system is such that a 9th magnitude early-type star can be detected in one scan; this limit is extended where many scans are available. The experiment is described and its performance in orbit fully assessed. Finally, a selection of reduced data extracted from quick-look magnetic tapes is presented and discussed.