## 2 Measurement Method and Experimental Setup Design
### Martian Air Sample Preparation  
Preparation of the purified Martian air sample with certain values of its pressure and temperature is necessary for correct spectroscopic measurements. Therefore, the Martian air sample preparation system has a complex of devices to form a Martian air sample with necessary characteristics. The simplified air sample preparation system diagram is shown in Figure 3. This system includes an air intake device, gas line, four vacuum electromagnetic air sample regulation (ASR) valves, fine filters cassette, a vacuum pump, an ICOS cell volume, an electrical heater, pressure and temperature sensors and MGAP interface. The air intake device consists of a telescopic aluminum tube with coarse filters for dust protection. In the transportation position, this device is folded and locked, whereas in the working position,  
Figure 3: Principal Martian air sample preparation system diagram, joint for both the M-DLS and the MGAP (Martian gas analytical package) instruments. ASR valve is air sample regulation valve. The Martian air sample is purified by complex of coarse and fine filters. ASR valves 1, 2, 3, 4 and the MGAP pump control the Martian air sample update in the integrated cavity output spectroscopy (ICOS) cell. The ICOS cell contains multiple pressure and temperature sensors and is wrapped by nichrome wire (heater) for temperature maintenance. Figure 2: **(a)** View of the Martian multichannel diode laser spectrometer (M-DLS) with external interfaces power supply, BIP (a Russian acronym for the block of interfaces and memory), JTAG (joint test action group) and representative dimension; **(b)** the M-DLS view in its operating position on the landing platform with the MGAP (Martian gas analytical package) interface. Here the air intake device is held in transportation position, after landing it is going to be deployed 15 cm long. the tube is deployed 15 cm long by a loaded spring and is fixed vertically up to 0.5 m above the landing platform. This allows us to take samples of an undisturbed air and reduce the inclusion of volatile components contaminated by the landing platform in the studied samples of air. Electromagnetic valves, as well as a four vacuum pump, are designed by IKI RAS specifically to operate at low Martian ambient pressure. They are intended for the Martian air sample direction through the air sample preparation system to the ICOS cell before spectroscopic measurements. The pump, which is a part of the MGAP, is used for providing the M-DLS with Martian air sample at different pressures in the range of 5-30 mbar. Each valve is represented by steel tube with a diameter of 3 mm, inside of which there are a magnetic core, a sealant and a limiter. The sealant and the limiter are located on opposite sides of the tube. The valve is closed when the core is on the sealant position, whereas when the core is on the limiter, the valve is open. Core movement is provided by a constant magnetic field, created by an inductor wound around the tube. Further explanation of valve switching can be found in the electronics subsection. Fine filter cassette installed into the gas line is necessary for protecting vacuum electromagnetic pumps and high reflective ICOS mirrors against the dust. Metal powder filters are used as filtering elements. These filters are the 0.5 \(\upmu\)m class solid-state disks with a diameter of 1.27 cm and a thickness of about 1 mm. The resonator of the ICOS cell is a part of the air sample preparation system and is connected to it by two stainless steel tubes. Martian air sample is sent to the resonator with the volume of V \(\approx\) 155.6 cm\({}^{3}\) for spectroscopic measurements. During measurements, the temperature of this volume is maintained at 30 \({}^{\circ}\)C by the ICOS cell heater, while the actual values of Martian air sample temperature and pressure are measured by several kinds of sensors. Two types of pressure sensors are used to measure the pressure level of the gas probe in the cuvette in different pressure ranges.