View source for Hypervelocity

{{short description|Very high velocity}}
{{Citations needed|date=November 2021}}
[[File:Hypervelocity Impact Demonstration.jpg|thumb|The "energy flash" of a hypervelocity impact during a laboratory simulation of what happens when a piece of [[orbital debris]] hits a spacecraft in orbit]]
[[File:Hypervelocity Impact.png|thumb|The aftermath of a hypervelocity impact, with a projectile the same size as the one that impacted for scale]]

'''Hypervelocity''' is very high [[velocity]], approximately over 3,000 [[metre per second|meters per second]] (11,000&nbsp;km/h, 6,700&nbsp;mph, 10,000&nbsp;ft/s, or [[Mach number|Mach]] 8.8). In particular, hypervelocity is velocity so high that the strength of materials upon impact is very small compared to [[inertia]]l stresses.<ref Name="AIAA">{{cite book
|title= Critical technologies for national defense
|author= Air Force Institute of Technology
|year= 1991
|publisher= AIAA
|location= 
|isbn= 1-56347-009-8
|page= 287
|url= https://books.google.com/books?id=HsEorBWNGWwC&dq=Hypervelocity+3%2C000&pg=PA287}}</ref> Thus, [[metal]]s and [[fluid]]s behave alike under hypervelocity impact. An impact under extreme hypervelocity results in [[vaporize|vaporization]] of the [[impact force|impactor]] and target. For structural metals, hypervelocity is generally considered to be over 2,500&nbsp;m/s (5,600&nbsp;mph, 9,000&nbsp;km/h, 8,200&nbsp;ft/s, or Mach 7.3).  [[Meteorite]] [[impact crater|craters]] are also examples of hypervelocity impacts.

== Overview ==
The term "hypervelocity" refers to velocities in the range from a few kilometers per [[second]] to some tens of kilometers per second. This is especially relevant in the field of [[space exploration]] and military use of space, where 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. The impactor, as well as the surface it hits, can undergo temporary [[liquefaction]]. The impact process can generate [[plasma (physics)|plasma]] discharges, which can interfere with spacecraft electronics.

Hypervelocity usually occurs during [[meteor shower]]s and deep space reentries, as carried out during the [[Zond program|Zond]], [[Project Apollo|Apollo]] and [[Luna programme|Luna]] programs. Given the intrinsic unpredictability of the timing and trajectories of meteors, space capsules are prime data gathering opportunities for the study of thermal protection materials at hypervelocity (in this context, hypervelocity is defined as greater than [[escape velocity]]). Given the rarity of such observation opportunities since the 1970s, the [[Genesis (spacecraft)|Genesis]] and [[Stardust (spacecraft)|Stardust]] Sample Return Capsule (SRC) reentries as well as the recent [[Hayabusa]] SRC reentry have spawned observation campaigns, most notably at NASA's [[Ames Research Center]].

Hypervelocity [[collision]]s can be studied by examining the results of naturally occurring collisions (between [[micrometeoroid|micrometeorites]] and [[spacecraft]], or between meteorites and planetary bodies), or they may be performed in laboratories. Currently, the primary tool for laboratory experiments is a [[light-gas gun]], but some experiments have used [[linear motor]]s to accelerate projectiles to hypervelocity. The properties of metals under hypervelocity have been integrated with weapons, such as [[explosively formed penetrator]]. The vaporization upon impact and liquification of surfaces allow metal projectiles formed under hypervelocity forces to penetrate vehicle armor better than conventional bullets.

[[NASA]] studies the effects of simulated orbital debris at the [[White Sands Test Facility]] Remote Hypervelocity Test Laboratory (RHTL).<ref Name="RHTL">{{cite web
 |title       = Remote Hypervelocity Test Laboratory
 |url         = http://www.nasa.gov/centers/wstf/laboratories/hypervelocity/index.html
 |url-status     = dead
 |archiveurl  = https://web.archive.org/web/20120404154535/http://www.nasa.gov/centers/wstf/laboratories/hypervelocity/index.html
 |archivedate = 2012-04-04
}}</ref> Objects smaller than a [[softball#Ball|softball]] cannot be detected on radar. This has prompted spacecraft designers to develop shields to protect spacecraft from unavoidable collisions. At RHTL, [[micrometeoroid]] and [[orbital debris]] (MMOD) impacts are simulated on spacecraft components and shields allowing designers to test threats posed by the growing orbital debris environment and evolve shield technology to stay one step ahead. At RHTL, four two-stage light-gas guns propel 0.05&nbsp;mm to 22.2&nbsp;mm diameter projectiles to velocities as fast as 8.5&nbsp;km/s.

== Hypervelocity reentry events ==
{| class="wikitable"
! Date !! Event !! Speed (km/s) !! Notes
|-
| 8 September 2004 || [[Genesis (spacecraft)|Genesis]] [[Sample return capsule|SRC]] || 11.04 || Crashed (drogue chute failure)
|-
| 15 January 2006 || [[Stardust (spacecraft)|Stardust]] SRC || 12.79 || Fastest man-made reentry on record (successful landing)
|-
| 13 June 2010 || [[Hayabusa]] SRC || 12.2 || Leading main [[Hayabusa]] spacecraft by 6,500 feet (2 000&nbsp;m) (destructive reentry)<ref Name="SPACE_COM">{{cite web
|title= Space.com
|website= [[Space.com]] |date= 10 June 2010 |url= http://www.space.com/missionlaunches/nasa-aircraft-observes-asteroid-probe-landing-100610.html }}</ref>
|}

== Other definitions of hypervelocity ==
According to the [[United States Army]], ''hypervelocity'' can also refer to the [[muzzle velocity]] of a weapon system, with the exact definition dependent upon the weapon in question.  When discussing [[small arms]] a muzzle velocity of 5,000&nbsp;ft/s (1524&nbsp;m/s) or greater is considered hypervelocity, while for [[tank]] [[cannons]] the muzzle velocity must meet or exceed 3,350&nbsp;ft/s (1021.08&nbsp;m/s) to be considered hypervelocity, and the threshold for [[artillery]] cannons is 3,500&nbsp;ft/s (1066.8&nbsp;m/s).<ref Name="DA">{{cite web
|title= Dictionary of United States Army Terms
|url= http://www.fas.org/irp/doddir/army/ar310-25.pdf
|publisher= Federation of American Scientists
}}</ref>

== See also ==
*[[2009 satellite collision]]
*[[Hypervelocity star]]
*[[Kinetic energy penetrator]]
*[[Terminal velocity]]
*[[Hypersonic]]
*[[Impact depth#Newton's approximation for the impact depth]]

== References ==
{{reflist}}

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[[Category:Physical quantities]]
[[Category:Velocity]]
[[Category:Spaceflight concepts]]
[[Category:Space hazards]]
[[Category:Materials science]]
[[Category:Collision]]