Constraints for the Performance of Large-Deployable Reflectors based on Surface Deformations simulated for Tandem-L

Abstract

Based upon the needs of the scientific community, the next generation of earth observation radar satellites will focus on comparatively longer wavelengths such as L- or even P-band. Due to operational constraints, instruments currently under development will likely be constructed as a phased antenna feed array paired with a large deployable reflector (LDR) / boom assembly. Compared to traditional planar array based instrument designs, this leads to a series of novel challenges which have to be addressed. Serving a plethora of different scientific applications, LDR based missions such as Tandem-L have been designed to carry a highly versatile instrument which results in rather stringent requirements on the instrument performance, especially in terms of pointing performance and phase stability. One major concern is the necessary performance such LDR/boom assemblies in terms of tolerable thermo-elastic deformations of the reflector mesh and mechanical pointing stability, especially in conjunction with the state-of-the art digital beamforming methods which are to be employed on-board. Hence, using the S/C and instrument geometry currently foreseen for the Tandem-L mission, in this presentation we specifically analyze and discuss the impact of both expected intra-orbit thermo-elastic deformations (TED) and a series of shifted and tilted LDR configurations on simulated far-field antenna patterns before and after digital beamforming. Based upon this analysis, we derive constraints for the necessary operational performance of such an LDR-boom assembly in terms of acceptable limits on the resulting variation in antenna gain and phase as well as pointing stability. Finally, this analysis is extended to a shaped, no longer fully paraboloid version of the LDR. Such a shape has been proposed to improve the Tandem-L performance in the case of a potential Transmit-Receive-Module failure.