| Popis: |
The paper deals with the preliminary design of a new system for Telescience operations of microgravity experimentation on-board the International Space Station. The system represents an innovative implementation of new telecommunication system that combined with on-board computer, is able to provide complementary link between the investigator on-ground and the facilities on-board. This new concept is aimed to carry out the following tasks: • to reduce as much as possible the period of loss of the signal, so as to guarantee an almost continuous and real-time control of the experiment; • to reduce the complexity of the network which routes the signal from ISS to the Investigator and vice versa; • to simplify the access procedure to the scientific payloads. In order to obtain such results the system has been designed to be operated with the existing commercial telecommunication satellites for mobile users. The selection of these platforms imposed the utilisation of low bit rate channels, that, however, using data extraction techniques, are compliant with large part of the planned experiments. This scenario has been defined also taking into account a comparative analysis of the possible constellation suitable for this utilisation. A major problem due to the installation on a space platform of a transponder conceived for Earth mobile users is the magnitude and the rate of Doppler shift between the platform and the satellites of the constellation. The required modifications to the transponder have been analysed and a solution is proposed. Utilisation of low bit rate channels represents a strong constraint for data stream, since for a certain number of microgravity experiments the most relevant information is carried in video images. A video link, on the other hand, is an extremely demanding resource, often not available during the complete mission, but only during very limited periods of coverage. From these considerations stems the idea to implement on-board a system able to extract most significant scientific information from experiment images and to transmit only this information over the link (available during all the mission time). In addition, other systems on-ground receive the data and are able to reconstruct a “virtual” image on the basis of the extraction algorithm used. In this paper, techniques that can be applied to this process of “video information extraction” are analysed and discussed. As a test case two algorithms of data extraction from video images of Fluid Science experiments have been developed, together with the on-ground reconstruction software. The algorithms have been tested using images of an experiment carried out during Spacelab LMS mission and the results obtained are presented. Their implementation has shown that this system is suitable for the real-time experiment control, also taking into account that the scientific images can be stored on-board and analysed post-flight for a more accurate scientific evaluation. |
Full Text from ScienceDirect