Spectrometers employing acousto-optic tunable filters (AOTFs) are rapidly gaining popularity in space, and in particular on interplanetary missions. According to a paper published by the National Center for Biotechnology Information, “they allow for reducing volume, mass, and complexity of the instrumentation and are used for analyzing ocean color, greenhouse gases, atmospheres of Mars and Venus and for lunar mineralogy. The AOTFs are used in point (pencil-beam) spectrometers for selecting echelle diffraction orders, or in hyper-spectral imagers and microscopes.”
Spectrometers use direct observation of light—visible, ultraviolet, or infrared—to form images, to analyze the composition of atmospheric gases, or to determine the composition of rocks and soils. These sophisticated devices are composed of complex electronics, firmware, software, state-of-the-art signal processing algorithms, and a wide variety of technologies.
The key element to the overall performance of an AOTF design—the RF Driver Amplifier
An AOTF is a crystal that acts as an optical filter. When the crystal is excited with a specific radio frequency signal, its response is tuned to a specific wavelength. As such, the instrument can use this excitation property to dynamically select specific wavelengths with unmatched accuracy by electrically selecting the radio frequency of the driver. The reason the RF Amplifier/RF Driver is the critical component in this part of the signal chain is the low power RF signal needs to be boosted to the few but critical watts needed by the AOTF crystal.
This is a challenge due to the special conditions of the space environment and the specificities of the signal required by the AOTF. The varying thermal, shock/vibration and gravitational conditions are critical amplifier design considerations with varying performance, cost and size/weight tradeoffs needing to be carefully analyzed. This is especially challenging in that when creating the optimum RF output power, a designer must also minimize harmonic output over a wide bandwidth and achieve the lowest possible energy consumption to allow for a long trip through space.
ERZIA Powers the NOMAD in the EXOMARS Project
Currently making incredible discoveries in Mars’ atmosphere, the NOMAD instrument, was launched in 2016 and began science operations in 2018. In 2014, ERZIA delivered RF Driver Amplifiers for the NOMAD instrument for installation on the Trace Gas Orbiter (TGO) of the ExoMars mission. This science payload is performing the most highly sensitive orbital identification of atmospheric components, concentration, temperature and cycles. It measures the sunlight reflected from the surface and atmosphere of the planet and analyses the wave lengths received to determine the components of the atmosphere.
During its first two years of operation (of an expected seven-year program), the NOMAD instrument recorded the absence of methane in the atmosphere, and confirmed the direct observation of a green oxygen glow, which was predicted by models 40 years ago, but which had not been observed until now. These findings confirm the remarkably high sensitivity of the NOMAD instrument, and the critical importance of it to the space community in better understanding Mars’ atmosphere and the processes and dynamics it holds.