The Ariel payload consists of an integrated suite comprising the telescope assembly (TA), the Ariel infrared spectrometer (AIRS), and the Fine Guidance System (FGS)/photometer module, along with the necessary supporting hardware and services. All these units are accommodated inside the cryogenic payload module, while warm payload units are accommodated inside the service module (the FGS Control Unit, the Instrument Control Unit, and the cryo-cooler and Cooler Drive Electronics).
TA — Telescope Assembly
The TA is an off-axis Cassegrain telescope followed by a third parabolic mirror to recollimate the beam, passively cooled to a temperature of ~55 K. It has an elliptical main mirror with dimensions of 1.1 m × 0.7 m — equivalent to 0.9 m circular — a diffraction limit of about 3 µm, and a focal ratio (f) of 13.4.
AIRS — Ariel IR Spectrometer
AIRS is a broad-band, medium-resolution near-infrared spectrometer operating between 1.95 µm and 7.8 µm. The spectrometer is a single module incorporating two dual Offner channels covering the 1.95–3.9 µm and 3.9–7.8 µm wavelength bands, and provides a resolving power of R~30–200 across its spectral range. The proposed detector is a fine-tuned version of the Teledyne MCT (Mercury-Cadmium-Telluride) array developed for NEOCam (the Near-Earth Object Camera). The operating temperature for the detectors is below 42 K, AIRS is mounted on the optical bench alongside the FGS and telescope interface.
FGS (Fine Guidance System) module & Near-infrared Photometer
The FGS module provides three narrow-band visible to near-infrared photometer channels (two used as guidance sensors as well as for science) and a low-resolution near-infrared spectrometer. The four-channel FGS/photometer will include a Gregorian telescope, and covers three narrow spectral bands spanning 0.50–0.55 µm, 0.8–1.0 µm and 1.0–1.2 µm, and a low-resolution 1.25–1.95 µm spectrometer. Both the FGS and NIR-photometer are mounted on the optical bench.