OPTICAL DESIGN AND BREADBOARD OF THE RAMAN SPECTROMETER FOR MMX

This paper reports the laboratory confirmation of an optical design for a 0.2 numerical aperture confocal miniaturized, ruggedized Raman visible light spectroscope (RAX) to be borne by an autonomous rover landed on the martian moon, Phobos

High étendue Fourier transform spectroscopy by quadratic off-axis path difference error cancellation

Instrumentation design for Fourier transform spectroscopy has until now been hindered by a seemingly fundamental tradeoff between the étendue of the analyzed light source on one hand and the spectral resolution on the other. For example, if a freespace scanning Michelson interferometer is to achieve a spectral resolution of 4 per centimeter, it can have a maximum angular field of view of roughly 1 degree for wavelengths in the neighborhood of 800 nm, where the general tradeoff for this instrument is that the quotient \theta_m^2 / \Delta k of the square of the angular field of view \theta_m and the minimum resolvable wavenumber difference \Delta k is a constant. This paper demonstrates a method to increase the angular field of view allowable for a given resolution by a full order of magnitude, and thus to increasethe étendue and, with it, the potential power gathered from an extended source and potential measurement signalto-noise ratio, by two orders of magnitude relative to the performance of a freespace Michelson interferometer. Generalizing this example, we argue that there may be no fundamental thermodynamic grounds for the tradeoff and that a scanning Fourier transform spectrometer can accept an arbitrarily high étendue field and still, in theory, achieve an arbitrarily narrowspectral resolution

RAX: The Raman Spectrometer for the MMX Phobos Rover

We present the Raman Spectrometer onboard JAXA’s Martian Moons Exploration (MMX) mission. As part of the MMX Rover, the RAX instrument is built to measure and identify the surface mineralogy of Phobos. This is realized by acquiring Raman spectra in-situ, surveying the geology beneath the Rover body. The RAX data supports the MMX top-level science by providing ground truth information of Phobos, complementary to the samples returned to Earth by the MMX spacecraft. RAX is a very lightweight and highly compact Raman spectrometer with a mass of 1.5 kg and a volume of only approximately 1 dm³. The spectrometer is equipped with a miniaturized and highly sensitive optical assembly, that allows for measuring rather weak Raman signals and enables the identification of water-bearing minerals. The Raman excitation (λ = 532 nm) is realized via a separate laser module based on the Raman Laser Spectrometer (RLS) laser developed for the ExoMars2022 mission. In order to focus the laser onto the Phobos ground below the Rover, the spectrometer includes an autofocus mechanism. The RAX instrument covers a spectral range of 535 to 680 nm, corresponding to a Raman shift of approximately 90 to 4000 cm−1. The spectral resolution over the whole spectral range is about 10 cm−1. This paper presents the design and development of the RAX instrument. The optical performance of the spectrometer is demonstrated using Raman spectra recorded on the physical hardware models. The RAX flight model has been delivered to the MMX Phobos Rover in August 2022. The MMX mission is to be launched in 2024. First RAX data obtained from Phobos are expected in 2027. The RAX instrument is a joint contribution by the German Aerospace Center (DLR), Instituto Nacional de Técnica Aerospacial (INTA) and JAXA