## 2 Measurement Method and Experimental Setup Design
### Control Electronics System  
The electrical part of the device is represented by several boards, connections and separate modules shown in Figure 6. Two main boards named the atmospheric measurements unit (AMU) and the service system unit (SSU) are responsible for handling an experiment and basic functionality of the M-DLS. The AMU performs driving of diode lasers (DLs) and acquisition of photodiode (PD) signal, thus carrying the main role in experiment conduction. A laser driver circuit is based on a single transistor scheme and provides currents of up to 200 mA. One 16-bit aerospace DAC is used for the current setting with the sampling frequency of 87 kHz. Every DL is equipped with the TEC for the temperature setting, which is controlled by similar DAC with the sampling frequency of 70 Hz. For the temperature control, there are thermistors inside and outside the DL case. A simple differential amplifier is used for the temperature conversion within 20 to 45 \({}^{\circ}\)C with a multichannel 12-bit analog-to-digital converter (ADC) built in the microcontroller in oversampling mode. Temperature readings are then proceeded to the digital proportional-integral (PI) controller to maintain a selected constant laser temperature with an error less than 5 mK. As for the photodiode, its operation requires analog signal digitalization and temperature control by the AMU. Preamplified PD signal is digitized by a 16-bit industrial ADC on the AMU with the sampling frequency coinciding with the DACs frequency of 87 kHz. For the PD to function in regime with the highest SNR and sensitivity it is necessary to cool it down to the temperatures around -31 \({}^{\circ}\)C using the inbuilt TEC. Since the temperature of PD is not obligated to be retained precisely, a simple circuit with an analog PI controller was selected. The core of the AMU is represented by the radiation and heat resistant Milandr 1986 BEST Cortex-M4 microcontroller (\"PKK Milandr\" joint-stock company, Zelenograd, Russia) running at 40 MHz with \"write once read many\" memory type. Its performance was enough for simple real-time operations with collected spectral data. The SSU is the second main board in M-DLS, responsible for the M-DLS communication with the BIP, for relaying data from BIP to AMU, and for the operation of all auxiliary systems. Being responsible for the control of auxiliary systems, the SSU converts data from all pressure and temperature sensors. To get the pressure sensors readings a Wheatstone bridge arrangement was used, the output signal is fed to a differential amplifier and digitized by a 12-bit ADC. The SSU also controls the sample  
Figure 6: Block diagram of electric circuits of the M-DLS. There are four main blocks: the atmospheric measurements unit (AMU) for experiment handling; the service system unit (SSU) for auxiliary systems operation and data transfer to the landing platform; the air sample preparation unit and the ICOS cell for spectroscopic measurements. preparation electronic board. The core of the board is a heat resistant Milandr 1986 BE94T Cortex-M3 microcontroller running at 24 MHz. As for the serial interfaces, all input packets from BIP are received by SSU from full-duplex RS-485 with a second reserve line. These input packets are either intended for the SSU or relayed to the AMU by CAN bus between the SSU and AMU. The ICOS cell, which is highlighted as separate section in Figure 6, from the electronics point of view consists of several components: the PD, two DLs, the cuvette heater, and temperature/pressure sensors. Photocurrent from the PD is converted into a voltage by a transimpedance amplifier (TIA). A bootstrapping amplifier is set along TIA to lower PD capacity and increase its bandwidth. Then the PD signal passes through a low-pass filter of 200 kHz with a variable gain of 1 or 2 and a single-to-differential converter at the end.