Maxime J. Rizzo

Far-Infrared Double-Fourier Interferometers and their Spectral Sensitivity

Double-Fourier interferometry is the most viable path to sub-arcsecond spatial resolution for future astronomical instruments that will observe the universe at far-infrared wavelengths. The double transform spatio-spectral interferometry couples pupil plane beam combination with detector arrays to enable imaging spectroscopy of wide fields, that will be key to accomplishing top-level science goals. The wide field of view and the necessity for these instruments to fly above the opaque atmosphere create unique characteristics and requirements compared to instruments on ground-based telescopes. In this paper, we discuss some characteristics of single-baseline spatio-spectral interferometers. We investigate the impact of intensity and optical path difference noise on the interferogram and the spectral signal-to-noise ratio. We apply our findings to the special case of the Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII), a balloon payload that will be a first application of this technique at far-infrared wavelengths on a flying platform.

The balloon experimental twin telescope for infrared interferometry (BETTII): An experiment for high angular resolution in the far-infrared

The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII) is a new balloon-borne far-infrared interferometer, being designed to provide spatially-resolved spectroscopy in the far infrared (30–90 μm). The combination of an 8-meter baseline with a double-Fourier Michelson interferometer allows the identification and separation of closely-spaced astronomical sources, while also providing a low-resolution spectrum for each source. In this wavelength range, BETTII will provide subarcsecond angular resolution, a capability unmatched by other far-infrared facilities. This paper provides an overview of the entire design of the BETTII experiment, with a short discussion of the predicted performance on flight.

Tracking near-infrared fringes on BETTII: a balloon-borne, 8m-baseline interferometer

We present the design of a fringe tracking system for the Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII). BETTII is a balloon- borne, far-infrared, 8 m-baseline interferometer with two 50 cm siderostats. Beams from the two arms are combined in the pupil plane to enable double-Fourier, spatio-spectral interferometry. To maintain the phase stability of the system, we need to actively correct of the optical path difference (OPD) between the two arms. The fringe-tracking system will work in the near-infrared and will use a reference star within the field of view to achieve two goals: overlap the beams coming from the two siderostats, and track the location of the central fringe packet, which is a measure of the OPD. The fringe tracker will share most of the optical train with the science instrument. This system is part of the overall control architecture that feeds fast steering tip/ tilt mirrors and a warm delay line to ensure proper beam combination and OPD control for the science instrument. This paper investigates the different sources of perturbations that are expected at float altitude, and derives the sensitivity of the fringe-tracking system. We show progress on validating our design using a visible light, broadband Mach-Zehnder interferometer that was developed at NASA/GSFC. This system demonstrates the viability of our OPD determination approach and provides a means of testing and characterizing several OPD determination and control algorithms.

Design and status of the Balloon Experimental Twin Telescope for infrared interferometry (BETTII): an interferometer at the edge of space

The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII) is an 8-meter baseline far-infrared interferometer designed to fly on a high altitude balloon. BETTII uses a double-Fourier Michelson interferometer to simultaneously obtain spatial and spectral information on science targets; the long baseline permits subarcsecond angular resolution, a capability unmatched by other far-infrared facilities. Here, we present key aspects of the overall design of the mission and provide an overview of the current status of the project. We also discuss briefly the implications of this experiment for future space-based far-infrared interferometers.

Building an interferometer at the edge of space: pointing and phase control system for BETTII

We propose an architecture for the control system of BETTII,1 a far-infrared, balloon-borne interferometer with a baseline of 8 meters. This system involves multiple synchronized control loops for real-time pointing control and precise attitude knowledge. This will enable accurate phase estimation and control, a necessity for successful interferometry. We present the overall control strategy and describe our flight hardware in detail. We also show our current test setup and the first results of our coarse pointing loop.

The balloon experimental twin telescope for infrared interferometry (BETTII): interferometry at the edge of the atmosphere

The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII) is an 8-meter baseline far-infrared interferometer designed to fly on a high altitude balloon. BETTII uses a double-Fourier Michelson interferometer to simultaneously obtain spatial and spectral information on science targets; the long baseline permits subarcsecond angular resolution, a capability unmatched by other far-infrared facilities. This program started in 2011, and is now in the process of building and testing components of the mission, aiming for first flight in fall of 2015. This paper will provide an overview of the BETTII experiment, with a discussion of current progress and of future plans.

The Space High Angular Resolution Probe for the Infrared (SHARP-IR)

The Space High Angular Resolution Probe for the Infrared (SHARP-IR) is a new mission currently under study. As part of the preparation for the Decadal Survey, NASA is currently undertaking studies of four major missions, but interest has also been shown in determining if there are feasible sub-

The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII): towards the first flight

1B missions that could provide significant scientific return. SHARP-IR is being designed as one such potential probe. In this talk, we will discuss some of the potential scientific questions that could be addressed with the mission, the current design, and the path forward to concept maturation.

Precision attitude control for the BETTII balloon-borne interferometer

The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII) is a balloon-borne, far-infrared direct detection interferometer with a baseline of 8 m and two collectors of 50 cm. It is designed to study galactic clustered star formation by providing spatially-resolved spectroscopy of nearby star clusters. It is being assembled and tested at NASA Goddard Space Flight Center for a first flight in Fall 2016. We report on recent progress concerning the pointing control system and discuss the overall status of the project as it gets ready for its commissioning flight.

The path to interferometry in space

The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII) is an 8-meter baseline far-infrared interferometer to fly on a high altitude balloon. Operating at wavelengths of 30-90 microns, BETTII will obtain spatial and spectral information on science targets at angular resolutions down to less than half an arcsecond, a capability unmatched by other far-infrared facilities. This requires attitude control of the gondola at the several arcsecond level, and phase correction of the gondola attitude at a level of less than a tenth of an arcsecond, great challenges for a lightweight balloon-borne system. We have designed a precision attitude determination system to provide gondola attitude knowledge at a level of 2 milliarcseconds at rates up to 100Hz, with accurate absolute attitude determination at the half arcsecond level at rates of up to 10Hz. A multi-stage control system involving rigid body motion and tip-tiltpiston correction provides precision pointing stability to the level required for the far-infrared instrument to perform its spatial/spectral interferometry in an open-loop control. We present key aspects of the design of the attitude determination and control and its development status.