Research On Velocity And Range Measurement Method Of FMCW Radar For Planetary Exploration Lander

With the development of technology and economy,deep space exploration has become a hotspot of the space plans around the world,in recent years,planetary exploration has become the focus of all the countries.During the planetary exploration,in order to capture valuable science data,the lander needs to land on the surface of the planet and make use of the auxiliary equipments to sample and analyze.Therefore,the lander could land on the predetermined surface area safely and accurately is the key to the success of the detection.During the landing,in order to improve landing accuracy and amend the motion state of the lander,the landing system needs the distance and velocity measurement sensor to provide the distance information from the lander to the planet's surface and the lander's velocity information.In order to reduce the launch costs,the planetary exploration lander has strict requirement on the volume and weight,therefore,the radar system with simultaneous velocity and distance measuring capaility has great research significance and application prospect.In this thesis,the FMCW radar is used to measure the lander's distance and velocity,the main work is making a deep research on the distance and velocity measuring method of the FMCW radar in the planetary exploration lander.Firstly,the landing trajectory model of the lander is studied according to the principle of the rectangular coordinate transform.On this basis,the echo calculation model is studied and the radar echo analogy procedure of the planet's surface is introduced which provides data support for echo processing.Then,it is difficult to estimate the distance and velocity of the beam center because the spectrum of the beat signal under the area target is broadened.So,several key technologies in the radar echo processing flow of the FMCW radar in the planetary exploration lander are studied and solved.Use the center of gravity estimation algorithm to estimate the beam center of FMCW radar area target echo,so that the velocity and distance measurement accuracy of the area target is improved.Use the ratio of beat signal spectrum width to the frequency of the beam center distance to estimate the radar beam incidence angle on the planet's surface.Get the correction factor for the gravity center correction of echo envelope through the incidence angle,so that the corrected distance and velocity estimations can be obtained.The distance and velocity measurement processing flow with gravity correction of the FMCW radar modulated by the saw tooth wave and the triangular wave are given respectively.Finally,aiming at the infulence of the lander's acceleration,the acceleration estimating method which combines the discrete polynomial-phase transform with the center of gravity estimation algorithm is proposed.By means of compensating the error caused by acceleration after getting the lander's acceleration estimated value,the velocity measurement accuracy is improved.According to the simulation experiment of the radar echo processing,the feasibility of the distance and velocity measurement method of the FMCW radar in the planetary exploration lander is verified.The high distance and velocity measurement accuracy at each stage of landing by using the radar echo processing flow and the modulation selection scheme proposed in this thesis is confirmed.The landing system could measure the lander's distance and velocity at the same time using a radar system,the research provides important technical support to complete the planetary exploration landing task precisely.