Deployment and control of the TALC space telescope
Winner of Best Innovative Paper award
Thinned Aperture Light Collector (TALC) [1,2]
The scientific community has accumulated a string of successes in MIR-FIR astronomy, starting with the IRAS mission in 1983, and culminating with the Herschel Space Observatory in 2009. Europe fared well in this endeavour, with Herschel being internationally recognized as a success. Yet the current approach of monolithic mirrors reached the launcher limits with Herschel. This 3.5m SiC mirror telescope was an extraordinary achievement of the European community, but in its wavelength range, it delivered an angular resolution no better than Galileo’s telescope in the 17th century. The state of the art facility under construction is the NASA-JWST to be launched in 2018. Its 6.5m primary mirror design is however still relying on standard mirror fabrication material and process (Beryllium polished mirrors), simple folding topology, and active optics supported by a stiff structure. The cost and development duration of this program revealed clearly the limits of this approach, in terms of technology and processes. As future science needs will require exceeding the capacities of even the JWST, we need to find a path that escapes this deadlock. The mission concept we propose is based on science requirements derived from Herschel’s advances, and an innovative system approach for the mission implementation leading to the Thinned Aperture Light Collector (TALC) concept. The current design of the TALC telescope features a primary annular mirror of 20 m diameter fitting within mass and volume constraints of the future Ariane 6 fairing. The TALC concept goes beyond the state of the art by changing the system design approach and relying on:
- An innovative deployable mirror whose topology is based on stacking rather than folding, leading to an optimum ratio of collecting area over volume;
- A lightweight segmented primary mirror, based on electrodeposited nickel, carbon composite and honeycomb stacks, built with a replica process to control costs and mitigate the industrial risks;
- An innovative active optics control layer in the mirror rear shell allows controlling the shape by in-plane forces instead of the conventional normal-force actuators that require a rigid support structure.
Fig 1. Deployment of the TALC primary mirror.
Dynamics and vibration control of TALC
Examples of resonance modes are shown in Fig. 2.
Fig 2. Examples of resonances of TALC.
 SAUVAGE M. et al., The science case and data processing strategy for the Thinned Aperture Light Collector (TALC): a project for a 20m far-infrared space telescope, Space Telescopes and Instrumentation 2014: Optical, Infrared, and Millimeter Wave, Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series 9143, p. 91431B, Aug. 2014.
 SAUVAGE M. et al., A development roadmap for critical technologies needed for TALC: A deployable 20m annular space telescope. Proceedings of SPIE – The International Society for Optical Engineering , 9904, 99041L, 2016. doi:10.1117/12.2231867
 DURAND G., AMIAUX J., SAUVAGE M., AUSTIN J., CHESNE S., COLLETTE C., HELLEGOUARCH S. et al. TALC, a far-infrared 20m space telescope and the ELICSIR consortium to reach TRL 3, 37th ESA Antenna Workshop on Large Deployable Antennas, November 2016 (ESTEC, The Netherlands).
 COLLETTE C., CHESNE S., CORREIA S., DURAND G., An active control concept for the TALC space telescope. Mechanics and Industry, 2016. (in press)