The goal of this program was the development and qualification of two replacement subunits of the LCT to reduce overall risk in production and LCT cost. The units are the Fame Unit Structure (FUS) and the Telescope Unit (TLU). The target is to maintain the performance of the existing LCT design, but increase design confidence for stable production. This includes reduced TLU delivery times and improved AIT processes.
The developed units are essential for the mechanical and thermal stability of the laser communication system since they provide the interface to the spacecraft as well as to the optical head. Therefore, their achieved stability under launch loads and thermal loads in space were critical. Furthermore, the a thermal optical performance of the telescope as well as high stray light and false light levels were a main driver for the design.
The frame unit structure as interface to the satellite and optical unit provides excellent mechanical stability. Furthermore, the thermal stability is increased compared to previous systems. In addition the unit can be manufactured at decent cost, short lead time at a local manufacturer with short delivery distances. The telescope has in addition to its improved mechanical properties a robust optical design with small wave front errors over the large specified thermal range. The optical throughput at the used wavelength based on transmission and polarization exceeds the required values.
The purely refractive telescope provides high transmission at the specified wavelength range and the range can easily be extended. An unobstructed field of view is provided by the off-axis design. Furthermore, a large field of view for a refractive telescope is achieved. A nearly athermal behaviour of the optical properties over temperature is realized. The telescope features high stray light and false light suppression as well as an integrated sun filter.
The frame unit structure provides a versatile platform to mount optical units and its interface to the spacecraft provides high stability.
For the framework of this project two major units of Tesat’s Laser Communication Terminal are addressed. These are the Telescope Unit (TLU) and the Frame Unit Structure (FUS).
The main activity of this project includes a complete redevelopment and qualification of the Telescope Unit by Hensoldt Optronics GmbH. Due to significant influence of FUS and TLU on mechanical design of LCT the qualification approach of TLU includes a mechanical demonstrator (LMD) to qualify required mechanical loads. The LMD mainly consists of the TLU, FUS, and CPA qualification units to verify their mechanical interaction.
The project has been completed with a successful qualification after a redesign of the first approach for TLU design.