The SOFIA Telescope in Full Operation

The SOFIA telescope is a 2.5m class Cassegrain telescope with Nasmyth focus. It is the largest telescope ever integrated into an aircraft. The telescope is exposed to the stratospheric environment during the observations and the fact that the telescope’s foundation, which is a Boeing 747 SP, is vibrating and moving in all degrees of freedom (DoF) requires a highly specialized and sophisticated design. Based on the telescope of its predecessor, the Kuiper Airborne Observatory (KAO), the SOFIA telescope design had to evolve to accommodate a telescope 2.5 times the size of KAO. In several hundred successful observation flights, the telescope proved that it performs not only as specified, but is also extremely reliable. Nevertheless, the telescope’s software and hardware are continuously upgraded to optimize its performance without interfering with the observation schedules to reach even more ambitious image size and pointing jitter goals to enable additional science cases. In addition, manufacturing of the line-replaceable units is in process to ensure that the SOFIA telescope can perform without any major interruptions for the envisioned 20 year lifetime. Some of the main features of the SOFIA telescope are its suspension assembly (SUA), which decouples the telescope from SOFIA’s fuselage with air springs and a spherical oil bearing, the extremely stiff Nasmyth tube (NT), which connects cavity and cabin mounted components of the dumbbell design, and the Secondary Mirror Assembly (SMA), which is used for chopping and fast pointing corrections. This paper aims to give an overview of these and all other major telescope subsystems in operation today. In addition, some of the upgrades, either implemented recently or slated for implementation shortly, are introduced.