Research On Ground Simulation Experiment Of Micrometeoroid High-speed Impaction On Spacecraft Shield

With the increase of human space activities, the space environment isdeteriorating, and the high-speed impaction of space debris and micrometeoroidthreaten orbiting spacecrafts at any time. Therefore, it is very urgent to carry outthe impact characteristics study on spacecraft shield structure against space debrisand micrometeoroid. People tend to use aluminum spherical projectile to simulatespace debris ground high-speed impact experiments. Due to the complexity ofmicrometeoroid physical properties, its impact properties are difficult to grasp.Generally damage characteristic data of aluminum alloy projectile simulating spacedebris impacting on shield structure are used to carry out micrometeoroid impactrisk assessment and shield structure design, which may lead to design too much orbe lack of design. With the development of manned space flight, and especiallydeep space exploration, micrometeoroid has become an important risk factor forspace activities, which can not be ignored. So it is urgent to study damage effectsof typical micrometeoroid high-speed impaction on spacecraft shield structures.Based on the above background, some exploratory research has done in thispaper about the damage effects of micrometeoroid high-speed impaction onspacecraft shield. The principle of micrometeoroid simulation materials selection,production technology of the projectile, projectile high-speed impact experimenttechniques, simulation and others have mainly been studies systematically. Sometypical materials with high brittleness and high melting point, high brittleness andlow melting point, and porous brittle were selected and producted to do someresearch on micrometeoroid high-speed impact characteristic on shield structure.Some basic data were obtained, which could provide technical support for thestructure design and risk assessment of spacecraft shield. The main contents wereas follows:Firstly，based on the analysis of micrometeoroid physical characteristics,material selection principle and production methods of projectile which were usedto simulate micrometeoroid were proposed. According to existing research resultsof the micrometeoroid chemical composition and physical mechanical properties,three typical physical properties of micrometeoroid have been studied includingthe micrometeoroid with high brittleness and high melting point, high brittlenessand low melting point, and porous brittle. And diamond material projectile wasused to simulate micrometeoroid with high brittleness and high melting point, volcanic rocks or silicate material were used to simulate porous brittlemicrometeoroid, and icy material was used to simulate micrometeoroid with lowmelting point and high brittleness. The projectile production method has also beenstudies.Due to micrometeoroid characteristics such as irregular in shape, brokeneasily, melting easily and so on, projectile launch technology of high-speed impactexperiments of the different characteristics projectile have been studied includingthe sabot design, gasket selection, refrigeration equipment and others. Themicrometeoroid projectile with high brittleness and high melting point was hardand was difficult to be polished. Its shape was often irregular. To ensure thesuccess of micrometeoroid projectile with high brittleness and high melting pointimpact experiments, the sabot was been designed to be inner horn-like sabot.Porous brittle micrometeoroid projectile was easily to be broken when it withstandthe shock waves generated by the emission process. The study found that it couldensure that projectiles would not be fractured in advance during launch and alsoensure their integrity before landing on the plate through adding EVA rubberimpedance gasket between projectile and sabot.Th micrometeoroid projectile with high brittleness and low melting point wasproduced by mold injection. Because of its melting characteristics at roomtemperature, special refrigeration equipments were installed to ensure the successof low melting point icy projectiles launch. The ground high-speed impactexperiments showed that three technologies of high-speed impact experimentswere feasible and effective.The damage effects of micrometeoroid with high brittleness and highmelting point impact on spacecraft shield structure have been studies and analyzed,which were compared with space debris high-speed impact damage effects. Themicrometeoroid projectiles produced by diamond particles were selected to carryout9times ground simulation experiments.4series of typical data were analyzed.And the damage effects of micrometeoroid with high brittleness and high meltingpoint impact on the Whipple shield structure were abtained. The design focus ofshield structure impacted by such micrometeoroid was revealed at low speed andhigh speed because the projectile speed would produce the phenomenon ofgraphitization. The results showed that high temperature and high pressure effectsof the rear plate was greater, which led to diamond projectile transform from a fulldiamond to the mixed composition of diamond and graphite, and then the fullgraphite composition with increasing of impact velocity. And the main reason thatdistinguished damage effects of micrometeoroids with high brittleness and high melting point from that of space debris was micrometeoroid’s graphitizationphenomenon. If the same quality and size of the aluminum projectile was used todo risk assessment on micrometeoroid with high brittleness and high melting point,the shield structure was thought to be lack of design according to obtained damageeffects.The damage effects of porous brittle micrometeoroid high-speed impact onspacecraft Whipple shield structure were studied through ground experiments andsimulation studies according to the micrometeoroid characteristics with differentminerals composition. The natural volcanic rocks and artificial silicate projectilewere adopted, and7times and11times high-speed impact experiments werecarried out respectively. The5and6set of typical experiment results were selectedand analyzed, and the damage effects of porous brittle micrometeoroid impact onshield structures were obtained at defferent speed. The paper come to a conclusionby simulation analysis that impact damage effects by porous brittle micrometeoroidis smaller than that of space debris with the same speed and quality. The resultsalso showed that the projectile was broken much and the debris cloud wasdispersed after impacting on the front plate, which weakened the damage effect onthe rear plate because of the porous brittle characteristics, and then cause lessimpact damage than the same quality aluminum projectile. And analysis showedthat the shield structure is designed too much if the same diameter aluminumprojectile was adopted to conduct risk assessment on the porous brittlemicrometeoroid.Last，there has lots of ice in comets which produced micrometeoroids, so thepaper studies the impact damage characteristics on spacecraft shield structure by iceprojectile with high brittleness and low melting point. The experiments adopted theice projectiles produced in low-temperature environment to simulate micrometeoroidwith high brittleness and low melting point, and twelve high-speed impactexperiments were carried out. Five typical results were selected and analyzed, whichabtained much impact damage characteristics such as big deformation, perforationcrack, tear damage and so on. The paper also simulates impaction damagecharacteristics by ice projectile, and obtained the ballistic limit curve which has beencompared with limit curve got by aluminum projectile. The results show that thedamage mode of ice projectile impaction on the front plate is petal-type tear, and withthe increasing of the ice projectile’s velocity, the debris cloud’s velocity also increasedwhich lead to more serious damage to the rear plate. By compared the impact limitcurve which is got from the simulation of ice projectile with that of aluminum’s, theresult can be obtained that shield structure is thought to be over designed if it conduct risk assessment by the same size aluminum projectile.In summary, the disciplines and data from the ground impact experiments andsimulation can be useful to the design and risk assessment of spacecraft’s shieldstructure. The results also have important value for long-term, reliable, safe operationof in-orbit spacecraft. Especially the choice of projectile’s material and experimentmethods, as well as the impact damage characteristics obtained by three typicalmicrometeoroids which have properties as high brittleness and high melting point,high brittleness and low melting point, and porous brittle, are of great significancefor the establishment of micrometeoroid protection design system.