Relationship between Ballistic Coefficient and Static Mechanical Properties for Armor Materials

The relationship between the ballistic coefficient and the static mechanical properties of armor materials was studied. The results show that the ballistic coefficient is determined by the strength, hardness and the toughness of materials. According to the Martel rule, the equation of the relationship between ballistic coefficient and static mechanical properties satisfies the following formula: W-s=M(1+NK1C/rho )Hr. From the mixture law of composite, the prerequisite, for which ballistic coefficient has maximum to reinforcement volume fraction, is obtained by the following equation: dWs/Df=b(K(1)rho (0)-K(0)rho (1))H/rho (2)+(a+bK/rho)(H-1-H-0).

Estimation of ballistic coefficients of space debris using the ratios between different objects

This paper proposes a new method to estimate the ballistic coefficient（BC） of low earth orbit space debris.The data sources are the historical two-line elements（TLEs）.Since the secular variation of semi-major axes is mainly caused by the drag perturbation for space objects with perigee altitude below 600 km,the ballistic coefficients are estimated based on variation of the mean semi-major axes derived from the TLEs.However,the approximate parameters used in the calculation have error,especially when the upper atmosphere densities are difficult to obtain and always estimated by empirical model.The proportional errors of the approximate parameters are cancelled out in the form of ratios,greatly mitigating the effects of model error.This method has been also been validated for space objects with perigee altitude higher than 600 km.The relative errors of estimated BC values from the new method are significantly smaller than those from the direct estimation methods used in numerical experiments.The estimated BC values are used for the prediction of the semi-major axes,and good performance is obtained.This process is also a feasible method for prediction over a long period of time without an orbital propagator model.

Aerodynamics of ducted re-entry vehicles

Ballistic parameter plays a major role in determining the re-entry trajectory.Lower ballistic coefficient offers an optimal re-entry,wherein the vehicle decelerates higher up in the atmosphere thereby decreasing the imposed aerothermal loads.The current computational study proposes an add-on,to the existing Orion-based re-entry vehicle:a duct circumventing the capsule from the shoulder to the base,to improve the aerocapture ability of the re-entry vehicle.The design cases are categorised based on a non-dimensional parameter termed the Annular Area Ratio(AAR).Dragand ballistic coefficient of the Ducted Re-entry Vehicles(DRVs)at various Mach numbers are evaluated and compared with those of the baseline model.The results show that the proposed design increases the drag for all the AARs considered in the subsonic regime.In the supersonic regime,ducted models of higher AAR are more promising with the increase in Mach number.DRVs also exhibit lower ballistic coefficients than their baseline counterparts.