Assembly, integration, and laboratory testing of the EXCITE spectrograph

Abstract

The EXoplanet Climate Infrared TElescope (EXCITE) is a near-infrared spectrograph (0.8-3.5 µm, R∼50) designed for measuring spectroscopic phase curves of transiting hot Jupiter-type exoplanets that operates off a high-altitude balloon platform. Phase curves produce a combination of phase curve and transit/eclipse spectroscopy, providing a wealth of information for characterizing exoplanet atmospheres. EXCITE will be a firstof- kind dedicated telescope uniquely able to observe a target nearly uninterrupted for tens of hours, enabling phase curve measurements, and complementing JWST. The spectrometer has two channels, a 0.8-2.5 µm band and a 2.5-3.5 µm band, providing a spectrum with a spectral resolution of R≥50. Two Off-Axis Parabolic (OAP) mirrors reimage the telescope focal plane to provide on-axis, diffraction-limited performance, wth a CaF2 prism providing dispersion. The spectrum is imaged with a single JWST flight spare Teledyne H2RG detector, providing Nyquist sampling of each channel. Here, we discuss the spectrograph’s mechanical design, acceptance testing, assembly, and cryostat integration.