Editing Launch window (section)

{{Short description|Time period during which a rocket must launch to reach its target}}
[[File:Animation of InSight trajectory.gif|280px|thumb |right |Animation of ''[[InSight]]''{{'s}} trajectory<br />{{legend2|magenta| ''InSight''}}{{·}}{{legend2| RoyalBlue |[[Earth]]}}{{·}}{{legend2| Lime |[[Mars]]}}]]
[[File:Mars distance from Earth.svg|280px|thumb|right|Mars launch windows and distance from Earth]]

In the context of [[spaceflight]], '''launch period''' is the collection of days, and '''launch window''' is the time period on a given day, during which a particular [[rocket]] must be launched in order to reach its intended target.<ref>{{cite web|last1=Walsh|first1=Kris|title=Launch Period vs. Launch Window|url=https://genesismission.jpl.nasa.gov/educate/scimodule/kriswalshsoundfiles/launch_period.html|website=Genesis Mission|publisher=NASA JPL|access-date=3 May 2018}}</ref><ref>{{cite report|last1=Sergeyevsky|first1=Andrey|title=Interplanetary Mission Design Handbook, Volume I, Part 2|publisher=NASA JPL|ref=JPL PUBLICATION 82-43|date=September 15, 1983|citeseerx=10.1.1.693.6602}}</ref> If the rocket is not launched within a given window, it has to wait for the window on the next day of the period.<ref>[https://www.nasa.gov/missions/highlights/schedule101.html What is a launch window?]</ref> Launch periods and launch windows are dependent on both the rocket's capability and the [[orbit]] to which it is going.<ref>{{cite web|title=Introduction to the GMAT Software|url=https://indico.esa.int/indico/event/111/session/2/material/0/0.pdf|publisher=NASA Goddard Space Flight Center|access-date=3 May 2018|date=Oct 29, 2014}}</ref><ref>{{cite web|title=Document Requirements Description|url=http://emits.sso.esa.int/emits-doc/ALCATEL/EXM-MS-RS-ESA-00010_ExoMarsDocumentRequirementsDiscription.pdf|website=ExoMars Project|publisher=European Space Agency|access-date=3 May 2018|date=16 July 2007}}</ref>

A launch ''period'' refers to the days that the rocket can launch to reach its intended orbit. A mission could have a period of 365 days in a year, a few weeks each month,<ref>{{cite web|title=Gravity Recovery and Interior Laboratory (GRAIL) Launch Press Kit|url=https://www.nasa.gov/pdf/582116main_GRAIL_launch_press_kit.pdf|publisher=NASA JPL|access-date=3 May 2018|date=August 2011}}</ref> a few weeks every 26 months (e.g. [[Exploration of Mars#Launch_windows|Mars launch periods]]),<ref>{{cite web|title=NASA Targets May 2018 Launch of Mars InSight Mission|url=https://www.nasa.gov/press-release/nasa-targets-may-2018-launch-of-mars-insight-mission|publisher=NASA|access-date=3 May 2018|date=March 9, 2016}}</ref> or a short period time that won't be repeated.

A launch ''window'' indicates the time frame on a given day within the launch period that the rocket can launch to reach its intended orbit.<ref>{{cite web|title=Launch Schedule 101|url=https://www.nasa.gov/missions/highlights/schedule101.html|website=Missions|publisher=NASA|access-date=3 May 2018|date=March 31, 2014}}</ref><ref>{{cite web|title=Aiming for an Open Window|url=https://www.nasa.gov/centers/kennedy/launchingrockets/launchwindows.html|website=Kennedy Space Center|publisher=NASA|access-date=3 May 2018|date=February 23, 2012}}</ref> This can be as short as a second (referred to as an [[#Instantaneous launch window|instantaneous window]]) or as long as the entire day. The launch window can straddle two calendar days (for example, starting at 11:46&nbsp;p.m. and ending at 12:14&nbsp;a.m.). Launch windows are rarely at exactly the same times each day. For operational reasons, the window almost always is limited to no more than a few hours.<ref>{{cite web|title=Dawn Launch Mission to Vesta and Ceres Press Kit|url=https://www.jpl.nasa.gov/news/press_kits/dawn-launch.pdf|publisher=NASA JPL|access-date=3 May 2018|date=September 2007}}</ref>

Launch windows and launch periods are often used interchangeably in the public sphere, even within the same organization. The definitions given here are as used by launch directors and trajectory analysts at [[NASA]] and other space agencies.<ref>{{cite web|title=Launch Vehicle Facts|url=https://mars.nasa.gov/insight/mission/launch-vehicle/|archive-url=https://web.archive.org/web/20180507232729/https://mars.nasa.gov/insight/mission/launch-vehicle/|url-status=dead|archive-date=7 May 2018|website=Mars InSight Press Kit|publisher=NASA JPL|access-date=3 May 2018}}</ref><ref>{{cite web|title=Launch Time and Window, H-IIA F37 (with upgraded function) Encapsulating SHIKISAI and TSUBAME|url=http://global.jaxa.jp/press/2017/12/20171221_h2af37.html|website=JAXA Press Releases|publisher=Japan Aerospace Exploration Agency (JAXA)|access-date=3 May 2018|date=December 21, 2017}}</ref>