## 1 Introduction  
Hypervelocity impact craters are ubiquitous in many areas, including asteroid collisions, meteorite impact on Earth-like planets, artificial space debris, or micrometeoroid impact on spacecraft. Consequently, the crater phenomenon has been of great concern and continuously studied by researchers from the fields of astrophysics, geophysics, and aerospace engineering [1, 2]. The experimental method is a vital means of studying the hypervelocity impact crater phenomena [3, 4]. The most common launching technique in impact experiments is the two-stage light-gas gun [5, 6, 7]. A large number of hypervelocity impact experiments have been widely used to study hypervelocity impact crater characteristics over the past six decades. Diverse influencing factors on the crater morphology have been studied, such as the impact velocity [8, 9, 10, 11], the impact angle [12, 13, 14, 15, 16], the material characteristic of the collision object [17; 18; 19; 20; 21; 22; 23], and the projectile shape [24; 25; 26; 27]. Based on dimensional analysis, several equations were proposed to represent the relationship between the crater parameters and the impact condition parameters [28; 29; 30; 31].  
The material properties of the targets made of geological materials are more complex than those of metals, leading to a complicated effect on hypervelocity impact craters. It has been found that the properties of geological materials, such as the pores, porosity saturation, and moisture content, can influence crater morphology [32]. In addition, the influence of \(\rho_{\rm p}/\rho_{\rm t}\) on hypervelocity impact craters cannot be neglected. [PERSON] et al. [33] conducted hypervelocity impact experiments using aluminum and steel spherical projectiles and diorite targets. The study showed that increasing \(\rho_{\rm p}/\rho_{\rm t}\) leads to higher \(H/D\) of the impact crater. [PERSON] et al. [34] conducted hypervelocity impact experiments using aluminum, steel, and iron meteorite spherical projectiles and sandstone targets, and the relationship between \(\rho_{\rm p}/\rho_{\rm t}\) and \(H/D\) was also found to be significantly positively correlated. However, [PERSON] and [PERSON] [35] conducted a series of hypervelocity impact experiments on small icy bodies by using spherical projectiles of various density, in which a vague correlation between \(H/D\) and \(\rho_{\rm p}/\rho_{\rm t}\) was observed. Therefore, to understand the detailed effect of \(\rho_{\rm p}/\rho_{\rm t}\) on the crater characteristics, experimental studies on hypervelocity impact cratering remain necessary. Hypervelocity impact experiments of non-spherical projectiles on the geological material targets are still scarce in the literature. There are few data available for non-spherical projectile hypervelocity impact experiments using rocks.  
The main purpose of this study was to investigate the hypervelocity impact craters of granite targets under non-spherical projectiles and the influence of \(\rho_{\rm p}/\rho_{\rm t}\) on the crater morphology. By using hemispherical-nosed cylindrical projectiles, 15 shots of hypervelocity impact cratering into granite targets were conducted at the impact velocities distributed from 1.91 to 3.99 km/s. These projectiles were made of different metals including titanium alloy, alloy steel, and tungsten alloy. The mass of each projectile was about 40 g, and the length-diameter ratio was 2. The effects of \(\rho_{\rm p}/\rho_{\rm t}\) and the impact velocity on the crater characteristics of the targets were evaluated. Then, the crater parameters were expressed as power law relations of the impact parameters through the scaling law analysis. The research results can provide some insight for damage analysis and protection of rocks under meteorite impact or kinetic energy weapon attack.