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The increasing space debris poses a great threat to in-orbit spacecraft and satellites, because its hypervelocity impact can bring about fatal mechanical and electrical damage to them. This work applies pulsed digital inline holography (DIH) to measure three-dimensional (3D) positions and shapes of the debris clouds generated by the hypervelocity impact in the Whipple shield. Detailed operation procedures of synchronizing the pulse DIH system with the impact event and removing the strong plasma radiation are presented, ensuring the successful capture of the transient state of ultrafast ejecta. Experiments on a 2.25 mm aluminum sphere impacting a 0.5 mm thickness aluminum target plate with a velocity of 3.6 km/s are carried out at the Hypervelocity Impact Research Center of the China Aerodynamics Research and Development Center, and results show that the holographic fringes are clearly recorded and the debris fragments are reconstructed and located accurately, agreeing well with the results measured by laser shadowgraph. This work demonstrates the powerful capability and great potential of DIH in the diagnostics of hypervelocity impact.

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Summary Spray cooling has a wide application prospect in the heat dissipation of high‐power devices due to its excellent heat transfer performance and low demand for working medium. In this work, an experimental setup was built to investigate the heat transfer characteristics of the deionized water spray cooling in the non‐boiling zone. Copper surfaces with different roughness conditions, as well as superhydrophilic/hydrophobic surfaces, were introduced to study the influence of surface property on cooling performance. Results show that no prominent change in heat transfer coefficient occurs due to the variation of roughness in the working conditions discussed. Furthermore, the superhydrophilic/hydrophobic surfaces experience a maximum reduction of 9.6% and 9.2% in heat transfer coefficient, respectively, compared with that of a smooth surface.

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