Editing Ballistic missile (section)

== Flight ==

In order to cover large distances, ballistic missiles are usually launched into a high [[sub-orbital spaceflight]]; for intercontinental missiles, the highest altitude ([[apogee]]) reached during free-flight is about {{convert|4500|km|mi|sp=us}}.<ref>{{Cite news |last1= |first1= |last2= |first2= |last3= |first3= |date=28 November 2017 |title=North Korea launches 'highest ever' ballistic missile |url=https://www.bbc.com/news/world-asia-42160227 |access-date= |work=[[BBC]]}}</ref> A ballistic missile's [[trajectory]] consists of three parts or [[Ballistic missile flight phases|phases]]: the boost phase, the mid-course phase and the terminal phase. Special systems and capabilities are required to facilitate the successful passage from one phase to the other.<ref name=":4">{{Cite book |last=Chun |first=Clayton K. S. |title=Thunder over the horizon: from V-2 rockets to ballistic missiles |date=2006 |publisher=Praeger Security International |isbn=978-0-275-98577-6 |series=War, technology, and history |location=Westport, CN. |page=2}}</ref> 

The boost phase is the [[powered flight]] portion, beginning with the ignition of the engines and concluding with the end of powered flight. The powered flight portion can last from a few tenths of seconds to several minutes and can consist of multiple [[rocket]] stages.<ref name=":1" /> Internal computers keep the missile aligned on a preprogrammed trajectory.<ref name=":4" /> On [[Multistage rocket|multi-stage missiles]], stage separation (excluding any post-boost vehicles or [[Multiple independently targetable reentry vehicle|MIRV]] bus) occurs primarily during the boost phase.   

The mid-course phase is the longest in the missile's trajectory, beginning with the conclusion of powered flight. When the fuel is exhausted, no more [[thrust]] is provided and the missile enters free flight. During this phase the missile, now largely consisting of a [[warhead]] or payload and possibly defensive countermeasures and small propulsion systems for further alignment toward its target, will reach its [[Apogee|highest altitude]] and may travel in space for thousands of kilometres (or even indefinitely, in the case of some [[Fractional Orbital Bombardment System|fractional-orbital]] capable systems) at speeds of up to {{convert|7.5|to|10|km/s|nmi/s|0|abbr=off}}.<ref name=":5">{{Cite book |last=Chun |first=Clayton K. S. |title=Thunder over the horizon: from V-2 rockets to ballistic missiles |date=2006 |publisher=Praeger Security International |isbn=978-0-275-98577-6 |series=War, technology, and history |location=Westport, Conn. |pages=4}}</ref>

The last phase in the missile's trajectory is the terminal or re-entry phase, beginning with the [[Atmospheric reentry|re-entry of the missile into the Earth's atmosphere]] (if [[exoatmospheric]])<ref name=":1">{{Cite web |last=McFadden |first=Christopher |title=What is an intercontinental ballistic missile and how does it work? |date=4 December 2017 |url=https://interestingengineering.com/what-is-an-intercontinental-ballistic-missile-and-how-does-it-work}}</ref><ref name=":5" /> where atmospheric [[Drag (physics)|drag]] plays a significant part in missile trajectory, and lasts until missile [[Impact force|impact]].<ref name=":1" /> Re-entry vehicles re-enter the Earth's atmosphere at very high velocities, on the order of {{convert|6-8|km/s|km/h mph|sp=us}} at ICBM ranges.<ref name=":0">{{Cite web |date=June 2017 |title=Ballistic and Cruise Missile Threat |url=https://www.nasic.af.mil/LinkClick.aspx?fileticket=F2VLcKSmCTE%3d&portalid=19 |publisher=Defense Intelligence Ballistic Missile Analysis Committee}}</ref> During the beginning of this phase, the missile's trajectory is still relatively well defined, though as the missile reaches the heavier layers of atmosphere it is increasingly influenced by gravity and aerodynamic drag, which can affect its landing.<ref name=":5" />