Editing Launch window (section)

==Launch window==
The launch window is defined by the first launch point and ending launch point. It may be continuous (i.e. able to launch every second in the launch window) or may be a collection of discrete instantaneous points between the open and close.<ref>{{cite web|title=Detailed Launch Window|url=https://marsmobile.jpl.nasa.gov/mer/mission/timeline/launch/launch-window/|website=Mars Exploration Rovers Press Kit|publisher=NASA JPL|access-date=3 May 2018}}</ref> Launch windows and days are usually calculated in UTC and then converted to the local time of where the rocket and spacecraft operators are located (frequently multiple time zones for USA launches).<ref>{{cite web|title=Launch Windows|url=https://mars.nasa.gov/insight/mission/timeline/launch/launch-windows/|website=Mars InSight Press Kit|publisher=NASA JPL|access-date=3 May 2018}}</ref>

For trips into largely arbitrary [[Geocentric orbit|Earth orbit]]s, no specific launch time is required. But if the spacecraft intends to [[space rendezvous|rendezvous]] with an object already in orbit, the launch must be carefully timed to occur around the times that the target vehicle's [[orbital plane (astronomy)|orbital plane]] intersects the launch site.<ref>{{cite web|title=GETTING READY FOR LAUNCH|url=https://www.esa.int/Our_Activities/Space_Science/Getting_ready_for_launch/(print)|publisher=European Space Agency|access-date=3 May 2018}}</ref>

[[Earth observation satellite]]s are often launched into [[sun-synchronous orbit]]s which are [[Polar orbit|near-polar]]. For these orbits, the launch window occurs at the time of day when the launch site location is aligned with the plane of the required orbit. To launch at another time would require an orbital plane change [[Orbital maneuver|maneuver]] which would require a large amount of propellant.

For launches above [[low Earth orbit]] (LEO), the actual launch time can be somewhat flexible if a [[parking orbit]] is used, because the inclination and time the spacecraft initially spends in the parking orbit can be varied. See the launch window used by the ''[[Mars Global Surveyor]]'' spacecraft to the planet [[Mars]] at [http://mars.jpl.nasa.gov/mgs/overvu/delta/window/window.html].