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Would you believe there are speeds so great that they can make metal behave like a liquid upon impact? Or some so great that they cause both the impacting object and its target to vaporize on collision? It’s called Hypervelocity, and believe it or not, it happens a lot more often than you’d think. The most common occurrence comes in the form of meteor showers, and where human agency is involved, when deep-space vehicles are making reentry. And when it happens, it leaves its mark! On look at the moon or any other stellar body that has absorbed a meteoric impact leaves little doubt as to the kind of force involved. As a result, understanding hypervelocity is of considerable importance when studying astrophysics, stellar objects, stress testing for aerospace vehicles, and even disaster relief.
By definition, hypervelocity refers to speeds in excess of 2,500 – 3,000 meters per second (9,000 – 11,000 km/h, or Mach 7.3 – 8.8). In particular, it refers to velocities so high that the strength of materials upon impact is very small compared to inertial stresses. It is therefore dependent on the materials involved, but in general tends to refer to velocities in the range of a few kilometers per second to some tens of kilometers per second. As a concept, it is especially relevant to the field of space exploration and the military use of space, the latter of which is likely to have real-world applications very soon. In either case, hypervelocity impacts (e.g. by space debris or an attacking projectile) can result in anything from minor component degradation to the complete destruction of a spacecraft or missile, with both the impactor and the ship being liquefied in the process. In addition, the impact process can also generate plasma discharges which can interfere with spacecraft electronics.
In terms of astrophysics, hypervelocity has been observed in the behavior of certain types of stars. These “exiled” stars, are essentially stars with velocities that are so great that they are able to escape the gravitational pull of a galaxy. Ordinary stars in a galaxy have velocities on the order of 100 km/s, while hypervelocity stars (especially those near the center of the galaxy, which is where most are thought to be “produced”), have velocities on the order of 1000 km/s. Meanwhile, here on earth, hypervelocity remains an area of interest for those interested in developing hypersonic aircraft, kinetic energy weapons (such as those used by modern tanks), and spacecraft capable of atmospheric take off and reentry without the need for booster rockets.
We have written many articles about hypervelocity for Universe Today. Here’s an article about space landing, and here’s an article about shooting stars.
We’ve also recorded an episode of Astronomy Cast about the space shuttle. Listen here, Episode 127: The US Space Shuttle.