TPF-Interferometer: a decade of development in exoplanet detection technology

Abstract

The last decade has seen great advances in interferometric nulling technology, propelled at first by the SIM and KECK nulling programs and then by the Terrestrial Planet Finder Interferometer (TPF-I). In the infrared at N-band (using a CO 2 laser at 10.6 micron wavelength) the first million to one nulls were reported on a KECK testbed in 2003. For TPF-I, nulls needed to be both deep and broadband, and a suite of testbeds was designed and built to study all aspects of achromatic nulling and system implementation, including formation flying technology. Also, observatory designs were drawn up and studied against performance models. Modeling revealed that natural variations in the alignment and control of the optical system produced an "instability noise" signal and this realization eventually led to a redesign of the layout to a rectangular formation. The complexity of the early TPF-I spacecraft design was mitigated by the infusion of ideas from Europe and produced the current X-Array design which utilizes simple reflectors to form the apertures together with a stretched three dimensional formation geometry. This paper summarizes the main achievements of the infrared nulling technology program including the development of adaptive nulling for broadband performance and the demonstration of starlight suppression by 100 million to one.

Science enabled by high precision inertial formation flying

“…Both NASA and ESA have studied infrared nulling interferometers based on a cluster of spacecraft flying in a rigid formation. Both concepts, TPF-I (NASA; Martin et al, 2011) and Darwin (ESA; Cockell et al, 2009) are based on several 'collector' spacecraft redirecting radiation to a common 'combiner' spacecraft (Fig. 7).…”

Introduction

“…Indeed, a space based interferometer, albeit a small one, has been used for many years in the form of the Hubble Space Telescope Fine Guidance System, for example McNamara et al, 2007. Space based interferometers have been proposed for direct planet detection (Martin et al, 2011;Cockell et al, 2009), astrometry (Coughlin et al, 2010), and more recently for the detection of gravitational waves (Danzmann & Rüdiger, 2002). In the longer term, more general purpose astronomical facilities will make imaging of objects from stars to deep-field cosmology possible using baselines of thousands of kilometers (Labeyrie et al, 2009).…”

Investigating nearby exoplanets via interstellar radar

“…Instead, a combination of techniques will be needed (Shao et al 2010), almost certainly including direct imaging techniques such as those proposed for the Terrestrial Planet Finder (Levine et al 2009;Martin et al 2011). These are aiming at 10% accuracy on systems up to 30 pc distant (Beichman et al 2006), and should provide the required accuracy on the nearer systems considered here.…”