Abstract
We present the expected performance for a ground-based terahertz (THz) radiometer, a plan to be launched on the TERahertz EXplore-1 (TEREX-1) Mars exploration microspacecraft. The small THz passive radiometer has been developed for the TEREX series of future microspacecrafts. This spacecraft is an opportunity for organizations with limited resources and technology to conduct frequent missions to Mars well suited for resource exploration in contrast to all of the current and past Mars missions of large/giant class missions with fully government lead. The observation frequencies of the TEREX-1 radiometer are 474.64–475.64 and 486.64–487.64 GHz with a 100-kHz resolution, and the double-sideband noise temperature less than 3000 K. A theoretical error analysis is performed with the instrument characteristics to assess for the first time up-looking observations of atmospheric oxygen molecules (O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) and water vapor (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O). Measurement errors for O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O are 7%–22% and 14%–25% with 8–17- and 5–10-km vertical resolution in the vertical ranges 0–55 and 0–25 km, respectively. TEREX-1 is also capable to measure minor species, O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , with a precision better than 30% within two independent layers. We used the integration time of 1 h for all simulations. Our theoretical simulation showed the instrument characteristics of the TEREX-1 sensor are able to observe vertical profiles of O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O abundances with the same level of the large class missions.
Highlights
The Vertical profiles of molecular oxygen (O2) and water vapor (H2O) have important roles to understand the oxygen and water cycle on Mars [e.g. 1, 2, 3, 4]
Studies suggested that the vertical profiles of O2 and H2O at lower altitude is influenced by surface processes on Mars
Further information related to Terahertz Explore (TEREX)-1 instrument such as an optical system including calibration loads and spectrometer can be found in Nakagawa et al [24, 25]
Summary
The Vertical profiles of molecular oxygen (O2) and water vapor (H2O) have important roles to understand the oxygen and water cycle on Mars [e.g. 1, 2, 3, 4]. Space-born THz limb sounders orbiting Mars are under study to measure global vertical profiles of parameters such as water vapor, oxygen molecules, carbon monoxide, trace gasses (e.g. O3 and H2O2), their isotopologues, winds, and temperature [18, 19, 20, 21]. These projects have not been realized yet. The lander is designed such that it can be constructed and operated by organizations with limited resources and technology such as universities or emerging countries Such observations will be complementary to those performed by Mars orbiters by providing continuous measurements over the same position.
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