Passive isolator design for jitter reduction in the Terrestrial Planet Finder Coronagraph

Abstract

Terrestrial Planet Finder (TPF) is a mission to locate and study extrasolar Earthlike planets. The TPF Coronagraph (TPF-C), planned for launch in the latter half of the next decade, will use a coronagraphic mask and other optics to suppress the light of the nearby star in order to collect visible light fkom such planets. The required contrast ratio of 5e-11 can only be achieved by maintaining pointing accuracy to 4 milli-arcseconds, and limiting optics jitter to below 5 rim. Numerous mechanical disturbances act to induce jitter. This paper concentrates on passive isolation techniques to minimize the optical degradation introduced by disturbance sources. A passive isolation system, using compliant mounts placed at an energy bottleneck to reduce energy transmission above a certain frequency, is a low risk, flight proven design approach. However, the attenuation is limited, compared to an active system, so the feasibility of the design must be demonstrated by analysis. The paper presents the jitter analysis for the baseline TPF design, using a passive isolation system. The analysis model representing the dynamics of the spacecraft and telescope is described, with emphasis on passive isolator modeling. Pointing and deformation metrics, consistent with the TPF-C error budget, are derived. Jitter prediction methodology and results are presented. Then an analysis of the critical design parameters that drive the TPFC ~ jitter response is performed.

Design Methodology of a Passive Vibration Isolation System for an Optical System With Sensitive Line-of-Sight

“…Vibration can be classified in two categories: translational vibration and rotational vibration [14,15]. Some optical systems such as astronomical telescopes, laser communication devices, and long focal length airborne cameras have very sensitive line-of-sight (LOS) and require very high pointing accuracies [16][17][18][19][20][21][22]. For example, the National…”

A Numerical Study on the Performance of Nonlinear Models of a Microvibration Isolator

“…In particular, the high resolution remote sensing satellites are one of the research hotspots of high precision spacecraft; for example, the American KH-13 surveillance satellite achieves an observational resolution of 0.05 meter, and the commercial remote sensing satellite GeoEye-1 launched in September 2008 acquires a resolution of 0.41 meter [2]. Due to the effects of bearing disturbance, static and dynamic imbalance of momentum/reaction wheels, the high frequency jitter may propagate to spacecraft body structure and then to optical payload; thus the image quality and the resolution performance will probably be affected seriously [3]. In order to satisfy the strict line-of-sight performance and stability requirements of high precision spacecraft, the amplitude of vibration should be reduced to the order of micrometers or even nanometers [4], and a commonly used method to solve this dilemma is inserting oil microvibration isolators between the jitter source and spacecraft or/and between the optical payload and spacecraft [5].…”

The imaging stability enhancement of optical payload using multiple vibration isolation platforms

“…For example, the Hubble Space Telescope (HST), launched in 1990, required pointing stability to be less than 0.007 arcsecond within periods up to 24 hours (Davis et al, 1986). The allocation for line of sight (LOS) motion on the James Webb space telescope (JWST) (Bronowicki, 2006) and the terrestrial planet finder coronagraph (TPF-C) is less than 4 milli-arcseconds (Blaurock et al, 2005).…”

“…Based on the above description, it is known that multiple vibration isolation platforms are commonly employed to enhance the imaging stability of the optical payload on satellites. When the jitter performances using these multiple vibration isolation platforms are predicted in some space missions, the structures of the spacecraft are all modeled using the finite element method, where some use the vibration isolation system consisting of six decoupled second-order lowpass filters to approximate the effect of a passive fly wheel mount (Liu et al, 2005;Miller et al, 2007;Gary et al, 1998;Liu and Maghami, 2008). These accurate finite element models are necessary to predict the jitter performance of the spacecraft.…”