Adaptive estimation of line-of-sight jitter disturbance

Abstract

Space telescopes equipped with a coronagraph to detect and characterize exoplanets must have the ability to sense and control low-order wavefront aberrations. The line-of-sight (LoS) pointing error due to telecope jitter causes image quality (contrast) degradation, so it must be estimated and compensated for. The LoS pointing error caused by the attitude control system (ACS) and the forces and residual unbalanced momentum from the reaction wheels (RWs) should be estimated and controlled to sub-milliarcsecond (mas) level. The largest errors are due to the RWs’ disturbance and are harmonic in nature. Current LoS estimation and control techniques use the frequency information from tachometer readings as inputs to estimate the LoS pointing error. Inaccuracies in the tachometer readings lead to erroneous estimations and less-effective control. In this paper, we propose a new adaptive technique where we use the low-order wavefront sensor (LOWFS) camera measurements to determine the system parameters and the LoS pointing error, hence removing the dependency of the LoS pointing error estimation on accuracy of the tachometer readings. We present the simulation results where we could estimate and control the LoS pointing error to 0.04 mas.