Shock Waves (2008) 18:169–183 DOI 10.1007/s00193-008-0156-8 ORIGINAL ARTICLE Experimental study of hypervelocity impacts at low temperatures D. Numata · K. Ohtani · M. Anyoji · K. Takayama · M. Sun Received: 20 October 2007 / Revised: 21 April 2008 / Accepted: 18 June 2008 / Published online: 29 July 2008 © Springer-Verlag 2008 Abstract This paper reports the results of hypervelocity impact (HVI) experiments on cryogenic aluminum alloys at 122K. Target plates were impinged by room temperature aluminum spheres at speeds ranging from 1 to 3.7 km/s in air at 10 Pa. The results were compared with HVI results at room temperature. We visualized the HVI processes by sha- dowgraph and recorded them with a digital high-speed video camera. We showed temperature effects of target plate phy- sical properties on the formation of debris clouds and impact craters and hence the shielding efficiency of aluminum alloys at low temperature. Keywords Hypervelocity impact (HVI) · Low temperature · Ballistic range · Space debris bumper shield PACS 81.70.Bt · 07.20.Mc Communicated by F. Lu. D. Numata (B ) · M. Anyoji Graduate School of Engineering, Tohoku University, 2-1-1, Katahira, Aoba, Sendai 980-8577, Japan e-mail: numata@rainbow.ifs.tohoku.ac.jp K. Ohtani Interdisciplinary Shock Wave Research Laboratory, Institute of Fluid Science, Tohoku University, 2-1-1, Katahira, Aoba, Sendai 980-8577, Japan K. Takayama Biomedical Engineering Research Organization, Tohoku University, 2-1-1, Katahira, Aoba, Sendai 980-8577, Japan M. Sun Center for Interdisciplinary Research, Tohoku University, 6-3, Aramaki, Aoba, Sendai 980-8578, Japan 1 Introduction Space debris impacts against space structures and space vehicles are serious hazards in space explorations [1]. Space debris in low earth–orbit of over 100mm in diameter are monitored and catalogued by the Space Surveillance Net- work. Space debris of diameters between 10 and 100 mm are hard to monitor and move at 10 km/s on average but some- times the speed can be as high as 14 km/s [2]. Their kinetic energy is enormous and, if impinged, would create a catas- trophe. There were around 8,000 large objects monitored so far, and were an estimated 110,000 pieces of debris between 10 and 100 mm diameter, whereas small debris were estimated to be over 35 million pieces and composed over 99% of the total debris numbers. The protection of space structures from small debris impacts is an urgent task to solve. Various protection tech- niques were proposed and laboratory scale experiments have been intensively performed. The design of space debris bum- per shields is one of the solutions [2–5]. Among ground test facilities, two-stage light gas guns [4–8] and shaped charge induced high-speed jets [9] are commonly used for small debris impingements. Plasma accelerators and rail guns are also possible sources of high velocity particles. However, these ground test facilities can simulate only a limited combination of parameters of real impact events [10]. Hence, the development of hypervelocity ground test facili- ties, their diagnostic methods, and numerical simulations are one of the most important research topics of not only space technology but also high-speed gas dynamics. Whipple [3] conceived the use of metal plate armor outside main walls for protection from space debris. His shielding was improved and today is known as the Whipple bumper shield. More advanced armor shields are proposed [2, 4, 5] 123