Research On High-Speed Modulated Pulsed X-ray Source Technology And Application Of Mars X-ray Communication

Mars is a hot spot area for the deep space exploration.With the continuous advancement of Mars exploration,in the future Mars missions,Mars probs will face harsh conditions,such as the Mars atmospheric entry phase communication blackout and large-scale Martian dust storms.In these special Martian environments,traditional communication methods cannot work in good condition,which increases the risk of Mars missions.Therefore,it is highly necessary to find a new communication method.X-ray communication(XCOM)is an advanced space-communication technology.The high penetration of X-rays enables XCOM systems to work in harsh deep space environments.This study proposes to use XCOM technology in Mars special communication scenarios.The research on highspeed modulated pulsed X-ray source technology,Mars XCOM system construction,and Mars XCOM channel characteristics has been conducted.The main research contents and results are as follows:(1)The grid-modulated X-ray source(GMXS)was designed for the Martian blackout-area XCOM scenario.Based on CST particle studio and Monte Carlo N-particle code 5(MCNP5),the optimization on the GMXS was carried out.The optimized GMXS could achieve a modulation rate better than 1 MHz and a transmitting power better than 100 m W.By optimizing the vacuum chamber of GMXS,the modulation voltage was limited to the range of-14 V to +5 V,the electron beam size is less than 0.2 mm× 0.4 mm,and the electron pulse-broaden is less than 2.2 ns.By optimizing the X-ray conversion target of GMXS,the optimal tilt angle was determined to be 48 °,and five candidate target materials were determined.The experimental research on the pulse response characteristics of GMXS was carried out,and the result proved that the optimized GMXS could achieve a modulation rate of 1 MHz.(2)The laser modulation pulsed X-ray source(LMPXS)was designed for the Martian dust storm XCOM scenario.Based on numerical analysis method and CST particle studio,the LMPXS was optimized by considering the temporal characteristic.The optimized LMPXS could achieve a modulation rate of 1.99 GHz and a transmitting power of 4.98 m W.The temporal characteristic analysis of LMPXS showed that the pulse-broaden caused by the gradient-doped negative electron affinity Ga As photocathode and the microchannel plate is about 50 ps,while the vacuum chamber will cause the pulsebroaden of about 400 ps.The pulse conversion process in LMPXS was analyzed,and the relationship between the component parameters and the modulation rate was established.The analysis results showed that the pulse-broaden caused by the vacuum chamber and the current saturation effect of MCP are the main factors affecting the modulation rate of LMPXS.(3)Based on the GMXS and LMPXS,two XCOM system construction schemes were designed for the Martian blackout-area and Martian dust storm environment,respectively.In order to improve the XCOM link power to achieve long-range communication in the Mars mission,the array XCOM system scheme was proposed.The multichannel electronics system(MES)required by the array XCOM was developed.The MES could simultaneously transmit and receive 44 channels of synchronous data at a data rate of 125 Mbps per channel.72-hour long-term communication tests of the MES were carried out,and the result of MES’s bit error rate(BER)lower than 10-14 was obtained.These tests verified the synchronization performance and reliability of MES.(4)The XCOM channel characteristic of the Martian blackout-area was evaluated,and the results proved the feasibility of using XCOM links to eliminate the communication blackout during the Mars entry phase.Based on the FDTD and WKB methods,it had been theoretically proved that the plasma sheath has the significant attenuation effect on the radio frequency carrier,and X-ray beams could penetrate the plasma sheath without attenuation.The transmittance of the X-ray beams in the upper Martian atmosphere was evaluated based on MCNP5.The results showed that X-ray beams with energies higher than 20 ke V could realize long-range propagation.The XCOM link performance was evaluated,and the conditions for implementing XCOM in Martian blackout-area were obtained.The results showed that,the XCOM system with 35 GMXSs could be used to establish communication between the entry vehicle and orbiters with a data rate of 1 Mbps and a BER lower than 10-6.(5)The XCOM channel characteristic of Martian dust storm environment weas evaluated,and the results proved that XCOM links could achieve high-speed data transmission in the Martian dust storm environment.The transmittance of X-ray beams in dust storms and the Martian atmosphere were evaluated based on the light scattering theory and MCNP5 code.The results showed that X-ray beams with energies above 20 ke V are immune from Martian dust storm disturbance,and X-ray beams with energies above 50 ke V can realize long-range transmission in the Martian atmosphere.The XCOM link performance was evaluated,and the conditions for implementing XCOM in a Martian dust storm were obtained.The results showed that in the Martian dust storm,the XCOM system with 23 LMPXSs could be used to establish communication between Mars rovers,and the XCOM system with 30 ~ 80 LMPXSs could be used to establish communication between rovers and orbiters.In the Martian dust storm,the data rate of the XCOM link can reach 100 Mbps and the BER is lower than 10-6.This work provides important theoretical reference for the implementation of Mars XCOM and the development of high-speed modulated pulsed X-ray source.The results of this study are expected to provide communication technology support for China’s future Mars exploration project.