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The Mars Ion and Neutral Particle Analyzer (MINPA) is one of the three scientific instruments onboard the Tianwen-1 orbiter to investigate the Martian space environment. During Tianwen-1’s transfer orbit to Mars, the MINPA was switched on to measure the solar wind ions. Here, we present the first results of the MINPA observations in the solar wind. During cruise, nearly half of the MINPA ion field-of-view (FOV) was blocked by the lander capsule; thus only the solar-wind ions with azimuthal speeds pointing towards the unblocked FOV sectors could be detected. We perform a detailed comparison of the MINPA’s solar wind observations with data from Earth-based missions when MINPA reached its count-rate peak, finding a general consistency of the ion moments between them. The blocking effect due to the lander is evaluated quantitatively under varying solar-wind velocity conditions. Despite the blocking effect, the MINPA’s solar wind measurements during the transfer orbit suggest a good performance.

A lot of electromagnetic anomalies observed by satellites before earthquakes indicate that there is interrelation between earthquake and ionosphere.China seismo-electromagnetic satellite (CSES) is the first Chinese space-based platform of three-dimensional earthquake monitoring system.The scientific payload of plasma analyzing package (PAP) aboard CSES is designed to study the possible influence of the seismic activity on the ionospheric plasma and thereby to monitor the earthquakes from space.The PAP is made up of three sensors,retarding potential analyzer (RPA),ion drift meter (IDM),and ion capture meter (ICM).The main objective of IDM is to detect the ion bulk velocity from-3 to 3 km/s with a precision better than 20 m/s,perpendicular to the sensor-look direction. The IDM sensor consists of six-layer grids and a collector.The grid is made of beryllium copper,plated with gold.Polyimide is used to achieve electrical insulation between grids.The grid transmission rate of signal layer is designed to be 82.64%,and total transmission rate of six layers is 31.85%.To ensure the performance of IDM,the side length of the square aperture and the depth of the sensor are designed to be 40 and 20 mm,respectively.The radius of segmented planar collector is 50 mm.The arrival angle of the ions is determined by measuring the ratio between the currents from the different electrically isolated collector segments.Accordingly,velocity perpendicular to the sensor-look direction is calculated,based on arrival angle and ion velocity parallel to the sensor-look direction which is measured by the RPA. In addition,a wide-range and high-precision current measurement circuit is designed to measure the current of IDM.The preamplifier circuit has three measurement ranges,providing different amplification factors.The right measurement range is chosen automatically by the field programmable gate array (FPGA).The test results show that the circuit provides a total measuring dynamic range from 20 pA to 6A with an accuracy better than 0.4%. Finally,the method of testing in the plasma environment and the measurement results are discussed.The plasma environment test of the IDM flight model is carried out in the Institute for Space Astrophysics and Planetology,National Institute of Astrophysics (INAF-IAPS).Since the plasma source is fixed to a large volume vacuum tank,the arrival angle of the plasma with respect to the sensor-look direction is changed by horizontally or vertically mounted IDM on the rotating platform in the vacuum tank.As the platform rotates,the performance of IDM is proved by testing different ion arrival angles in vacuum tank.The ion velocities along the Y and Z axes of the spacecraft are validated by testing the horizontal arrival angle and the vertical arrival angle respectively.The IDM test data are consistent with those obtained under the setting angle of the rotating platform.The experimental results show that the detector has good performance and will fulfill the mission goal of monitoring the bulk velocity of ion,perpendicular to the sensor-look direction.

China seismoelectromagnetic satellite (CSES) is the first space-based platform of three-dimensional earthquake monitoring system in china. Plasma analyzing package (PAP) is one of scientific payloads aboard on CSES, which is the first application to the field of Chinese satellite. The main scientific objective of PAP is to measure ion density, ion temperature, ion composition and ion drift velocities (parallel and perpendicular to the direction of the satellite flight on orbit), and ion density fluctuation in the ionosphere. The PAP payload is composed of four parts, including retarding potential analyzer (RPA), ion drift meter, ion capture meter, and metal plate. The RPA is used to test ion density, ion temperature, ion composition and ion drift velocity (parallel to the direction of the satellite flight on orbit). The detailed design process of the sensor of RPA is described in this paper. The grid of RPA sensor is made of Beryllium copper, plated with gold to ensure uniform surface work function, and to prevent space atomic oxygen from eroding. The design value of the transmission rate of grid is 82.64%1.4%, with taking into account the Debye length on the orbit of satellite. And the total transmission rate of multilayer grid for RPA is verified by SIMON simulation experiment. To ensure the accuracy of RPA, the radii of sensor window and sensor collector are designed to be 20 mm and 50 mm respectively, and the height of sensor is 20 mm. The sweeping voltage ranges from -2 V to 20 V. And the step of sweeping voltage is adjustable between 0.056 and. 179 V. In this paper electronic design of RPA is also discussed. The electronic box is composed of preamplifier circuit, digital logical circuit, satellite interface circuit, etc. The sweeping voltage and the signal acquisition are controlled by field-programmable gate array. The design of three measurement ranges in digital logical circuit improves RPA measurement accuracy, which is better than 1.3% in the full range. In addition, the method of testing the plasma environment and the testing results are introduced. The plasma environment test of the RPA payload is carried out in INAF-IAPS. The performance of ion density measurement is validated by testing different ion densities in a vacuum tank, through changing three different distances between RPA and the plasma source. And the ion drift velocity measurement is verified by testing three different ion energies of the plasma source. Furthermore, the RPA test data are consistent with the test data from the INAF-IAPS reference RPA. The experimental results show that the detector has good performances and will contribute much to monitoring the space plasma parameters.