High resolution images of the Earth surface in the visible wavelength are useful in a variety of human activities, from agriculture, to urban area monitoring, but the utilization is often limited by the high cost of the images and the relatively small number of satellites equipped with high resolution telescopes. In order to encourage the utilization of high resolution images, Italian Space Agency (ASI) funded a project aimed to investigate the possibility of utilization of microsatellites for this task. The objective of the project MITAR (MIcro Telescope, high Resolution) is to realize a prototypal telescope, capable of a 1m resolution from 400Km altitude, compatible with a microsatellite platform.
The necessity of a compact, lightweight and highly performing payload has been achieved designing a Cassegrain configuration with composite material mirrors and an innovative deployable structure.
The feasibility analysis and preliminary design have been presented at the SPIE Remote Sensing Europe 2003 congress in the paper titled "High resolution deployable telescope for satellite application".
Present paper focuses on the activities developed by Second University of Naples. In the university it has been designed a structure capable of a smooth deploy, without active control systems. The structure is deployed by lenticular tape springs (LTS), damped with viscoelastic polymer.
In the paper it is quickly described the optical system, then the peculiarity of the lenticular tape springs are shortly described. The characterization of the visco-elastically damped LTS (VEDLTS), and the description of the efforts aimed to have numerical and analytical instruments for the prediction of this innovative elements are exposed with more details.
We report then some relevant detail of the deployable structure and the realization related aspects.
The paper is concluded with the results of the very preliminary tests, aimed to verify the ability of the structure of performing a correct deploy and the accuracy of the deployed configuration.
The tests have evidenced that the structure does not easily deploy spontaneously, then it has been necessary to use some conventional springs in order to trigger a correct deploy, obtaining a structure with the needed characteristics.
CO.RI.S.T.A. is involved in a research project funded by ASI (Italian Space Agency), named MITAR, to realise a very compact, lightweight deployable telescope in visible wavelength range to get earth images from microsatellite. The satellite considered for the study is SMART, an Italian academic multi-mission microsatellite operating on circular sun-synchronous orbits. The telescope has a Cassegrain configuration with a parabolic primary mirror and an hyperbolic secondary mirror. This configuration guaranties the best aberrations corrections and the best compactness. The primary and the secondary mirror are 40 cm and 10 cm in diameter respectively, while their relative distance is 52cm. Mirrors will be realised with innovative composite material to obtain lightweight optical elements. Thanks to its limited size and light weight, the system can be easily deployed. The deployable structure will keep the secondary mirror close to the primary one during launch phases. Once in orbit, a system of lenticular tape springs and dumpers will extend the structure. The structure will be enclosed in multilayer blankets that will shield the sensor from light and will thermally stabilize the structure, preventing excessive thermal deformation. The images will be detected by a very high resolution CCD camera installed onboard the satellite.