The supersonic parachute is one of the key parts of successful soft landing of the Mars probe; however, the mainstream parachute type used in the landing mission of Mars exploration, the disk-gap-band parachute, has reached the size limit of the deceleration capacity of this type of parachute. Due to the requirement of the heavier payload of Mars exploration missions in the future, NASA has carried out special research on supersonic disksail parachutes. However, all the flying tests of disksail parachute have failed, and the reason is probably related to the air permeability of the parachute (fabric permeability and geometric porosity). In this paper, the fluid-structure interaction method is used to design different combination schemes of air permeability of the supersonic disksail parachute. The influence mechanism of different geometric porosity/fabric permeability distribution ratios on the flow field structure and aerodynamic characteristics in the process of parachute opening is analyzed under the premise of the same total porosity. In addition, a disk-gap-band parachute with the same porosity as that of the G5F5 and G7F3 disksail models are designed, and its opening characteristics are analyzed. The results show that for the supersonic disksail parachute with a total porosity of 12%, when the contribution ratio of geometric porosity/fabric permeability is 5∶5, the fluctuation amplitude of the bow shock ahead of the canopy is small, the stability performance of the parachute has obvious advantages over that of the parachute with the air permeability of other combinations, and the inflating time is the longest under the joint action of geometric porosity and fabric permeability; when the contribution ratio of geometric porosity/fabric permeability is 7∶3, the drag performance of the parachute is the best, and the drag performance of the disksail parachute shows a downward trend as the contribution of fabric permeability increases from 30% to 70%; when the contribution ratio of geometric porosity/fabric permeability is 6∶4, the parachute has the largest oscillation angle and the worst stability. By comparing the opening processes of the disksail and disk-gap-band parachutes, it is found that disk-gap-band parachutes exhibit a common “disk-style” inflation sequence, while disksail parachutes exhibit a “band style” inflation sequence, that is, the airflow first inflates from the canopy band and then gradually spreads to the entire canopy surface. The results of this study can provide a theoretical reference for the design of a new generation of Mars parachutes.

In through-the-wall detection scenarios with low signal-to-noise ratio (SNR) and strong clutter, existing target detection methods generally suffer from inaccuracies, poor real-time performance, and the limitation of detecting only moving or stationary targets. To address these challenges, this paper proposes a through-the-wall radar (TWR) target detection method based on cross-correlation adaptive robust principal component analysis (CCARPCA) capable of simultaneously detecting multiple moving and stationary targets. First, pulse compression is applied to original echo signals using the inverse fast Fourier transform, resulting in high-resolution one-dimensional range profiles. Second, the principal component analysis algorithm suppresses strong clutter interferences, thereby improving the SNR. Next, the back projection algorithm is employed for multi-channel coherent imaging, enabling the extraction of 2-dimensional information and enhancing the sparsity of cross-correlation data. Lastly, considering the drawbacks of the robust principal component analysis (RPCA), such as long detection time and poor robustness, this paper introduces the cross-correlation coefficient and proposes the CCARPCA algorithm, which completely separates the target from the background noise. The experimental results based on a series of simulated and measured data demonstrate the effectiveness of the proposed method in detecting both moving and stationary targets behind walls. Compared to generalized likelihood ratio test, constant false alarm rate, and RPCA, our method achieves a substantial improvement of over 16.4% in detection accuracy based on measured data while maintaining real-time detection capability. Additionally, its detection performance is less sensitive to changes in initial parameters, indicating its superior robustness.

The supersonic parachute plays an important role in the descent and landing of Mars missions. Next-generation supersonic parachutes, such as disksail parachutes, are alternatives to disk-gap-band (DGB) parachutes. Disksail parachutes have larger porous gaps and smaller porous seams on the canopy surface than DGB parachutes. To date, the influence mechanism of porous seams or gaps and their locations on the performance of supersonic parachute systems in Martian atmospheric conditions remains unclear. In this study, different canopy models with seams and gaps based on NASA’s supersonic disksail parachutes were designed, and the aerodynamic characteristics of such geometric porosity models were studied numerically. For seam-only models, the drag coefficient of the parachute decreases when the position of the seam is close to the middle of the canopy. When the seam is close to the mouth of the canopy, the pressure difference between the inner and outer surface of the canopy becomes small, reducing the risk of tearing the canopy. For gap-only models, the drag coefficient of the middle gap model is higher, while the lateral force stability of the top gap model is better. The results show that the addition of a seam can improve the drag performance of the top gap model and improve the lateral stability of the canopy with the middle gap. This study provides some theoretical references for designing the porosity of parachutes under different requirements for Mars exploration missions in the future.

Parachutes provide rapid vertical deceleration, but are more useful if they also provide stable, controllable lateral movement. A simple, effective method for lateral motion is to cut asymmetrical slits or holes in the canopy. This study simulated flat circular parachute designs with asymmetric holes and slits. The flow fields and the drag and lateral force coefficients of several designs were compared to determine how effectively these parachutes provide lateral motion. The parachute with a 30° annular slit starting from the bottom of the canopy provides the best drag. Further design variations shortened the length of the annular seam and gradually added radial holes. In all the designs, the U-shaped slit greatly improves both the drag and the lateral motion of the parachute and gives the best stability with changes in the angle of attack.

The supersonic flows around rigid parachute-like two-body configurations are numerically simulated at Mach number of 1.978 by solving three-dimensional compressible Navier-Stokes equations, where the two-body model consists of a capsule and a canopy, and a geometric structure (i.e., gap) is located on the canopy surface. The objective of this study is to investigate the effects of gaps with different porosities and positions on the aerodynamic performance of supersonic parachute. The complicated periodic aerodynamic interactions between the capsule wake and canopy shock occur around these two-body models. From the formation of canopy shock and drag coefficient variation, the cycled flow structures can be divided into three types:(1) narrow wake period, (2) open wake period, and (3) middle wake period. In addition, it was found that the geometric gaps have no obvious influences on the flow modes. However, compared with models with different gap positions, the two-body model with an upper gap (gap is close to the canopy vent, UG model) has a smaller drag coefficient fluctuation and better lateral stability. On the other side, the increase of porosity has a more significant impact on UG models.