Back Telescope Assembly (BTA)

Back Telescope Assembly for Meteosat Third Generation spacecraft

The Back Telescope Assembly (BTA) is an optical subsystem of the IRS instrument that will embark on the Meteosat Third Generation spacecraft. The MTG IRS is part of the MTG-S satellite. MTG (Meteosat Third Generation) a collaborative project between EUMETSAT and ESA. The task of the BTA is to provide a relay optics from the interferometer assembly to the cold optics.

The Back Telescope Assembly consists of an afocal reflective telescope that images and transfers an entrance pupil to an exit pupil plane; both pupil locations being specified as interface requirements. The precision required imposes the use of an active thermal control of the telescope assembly structure. This is achieved with the integration of two operational and one survival thermal lines for thermal regulation purposes. The structure and the mirrors are made of high-grade Aluminium.

The development of the BTA implies:

Structural design and analysis: quasi-static, random, shock;
Thermal design and analysis: The main functions of the BTA thermal design are as follows:
- To ensure strict thermal stability (0+0.5°C), during operational mode
- To keep temperatures in survival range, during survival mode
- To limit thermo elastic deformation, in relation to mechanical desig, the BTA has to be decoupled to the optical bench on which it is integrated and is cool down thanks to a radiator. The control is achieved by heater lines.
Thermo-mechanical analysis and impact on the optical performance;
Optical design and analysis;
Opto-mechanical analysis: sensitivity with respect to manufacturing tolerances;
Manufacture, integration and tests;
Environmental tests performed at CSL