Ajay Kumar: Created a new article

2023-08-07T05:20:51Z

Created a new article

New page

{{short description|Temporary orbit used during the launch of a spacecraft}}
A '''parking orbit''' is a temporary orbit used during the launch of a [[spacecraft]]. A launch vehicle boosts into the parking orbit, then coasts for a while, then fires again to enter the final desired trajectory. The alternative to a parking orbit is ''direct injection'', where the rocket fires continuously (except during staging) until its fuel is exhausted, ending with the payload on the final [[trajectory]]. The technology was first used by the Soviet [[Venera 1]] mission to Venus.

==Reasons for use==

===Geostationary spacecraft===
[[Geostationary orbit|Geostationary]] spacecraft require an orbit in the plane of the equator. Getting there requires a [[geostationary transfer orbit]] with an apogee directly above the equator. Unless the launch site itself is quite close to the equator, it requires an impractically large amount of fuel to launch a spacecraft directly into such an orbit. Instead, the craft is placed with an upper stage in an inclined parking orbit. When the craft crosses the equator, the upper stage is fired to raise the spacecraft's [[apogee]] to geostationary altitude (and often reduce the inclination of the transfer orbit, as well). Finally, a [[circular orbit|circularization]] burn is required to raise the [[perigee]] to the same altitude and remove any remaining inclination.<ref>{{cite book|author=Charles D. Brown|title=Spacecraft Mission Design|url=https://books.google.com/books?id=vpilMLP7OHQC&pg=PA83|year=1998|publisher=AIAA|isbn=978-1-60086-115-4|page=83}}</ref>

===Translunar or interplanetary spacecraft===
[[image:Ranger Parking Orbit-en.svg|thumb|Parking orbit for one of the early [[Ranger program|Ranger]] missions to the Moon. Note that the launch angle varies depending on the launch time within the launch window.]]
In order to reach the Moon or a planet at a desired time, the spacecraft must be launched within a limited range of times known as the [[launch window]]. Using a preliminary parking orbit before final injection can widen this window from seconds or minutes, to several hours.<ref name="Ranger">{{Cite tech report |last=Hall |first=R. Cargill |date=1977 |title=LUNAR IMPACT - A History of Project Ranger |work = NASA History Series |publisher=[[NASA|National Aeronautics and Space Administration]] |id=NASA SP-4210 |url=https://history.nasa.gov/SP-4210/pages/TOC.htm |access-date=2011-11-11}}</ref><ref name="Apollo">{{cite web |url=https://history.nasa.gov/SP-350/toc.html |title=Apollo Expeditions to the Moon}} [https://history.nasa.gov/SP-350/ch-3-4.html Chapter 3.4]</ref> For the [[Apollo program]]'s crewed lunar missions, a parking orbit allowed time for spacecraft checkout while still close to home, before committing to the lunar trip.<ref name="Apollo"/>

==Design challenges==
The use of a parking orbit can lead to a number of technical challenges. For example, during the development [[Centaur (rocket stage)|Centaur]] upper stage, the following problems were noted and had to be addressed:<ref>{{cite web |url=https://ntrs.nasa.gov/api/citations/20050070711/downloads/20050070711.pdf |title=Taming liquid hydrogen: the Centaur upper stage rocket 1958-2002 |publisher=NASA}}</ref>
*The injection burn occurs under [[Weightlessness|zero g]] conditions.
*If the same upper stage which performs the parking orbit injection is used for the final injection burn, a restartable [[liquid-propellant rocket]] engine is required.
*During the parking orbit coast, the propellants will drift away from the bottom of the tank and the pump inlets. This must be dealt with through the use of tank diaphragms, or [[ullage motor|ullage rockets]] to settle the propellant back to the bottom of the tank.<ref>{{cite tech report
|title=Research on Zero-Gravity Expulsion Techniques
|author=Krivetsky, A.
|author2=Bauer, W.H.
|author3=Loucks, H.L.
|author4=Padlog, J.
|author5=Robinson, J.V.
|name-list-style=amp
|date=1962
|institution=Defense Technical Information Center
|url=https://apps.dtic.mil/sti/pdfs/AD0274044.pdf|archive-url=https://web.archive.org/web/20210718042426/https://apps.dtic.mil/sti/pdfs/AD0274044.pdf|url-status=live|archive-date=July 18, 2021}}</ref>
*A [[reaction control system]] is needed to orient the stage properly for the final burn, and perhaps to establish a suitable thermal orientation during coast.
*[[cryogenics|Cryogenic]] propellants must be stored in well-insulated tanks, to prevent excessive boiloff during coast.
*Battery life and other consumables must be sufficient for the duration of the parking coast and final injection.

The Centaur and [[RM-81 Agena#Agena-D|Agena]] families of upper stages were [[Centaur (rocket stage)#Characteristics|designed for restarts]] and have [[Atlas V#Atlas V launches|often been used in missions using parking orbits]]. The last Agena flew in 1987, but Centaur is still in production. The [[Briz (rocket stage)#Briz-M|Briz-M]] is also capable of coasts and restarts, and [[Briz (rocket stage)#Launch chronology|often performs the same role]] for Russian rockets.<ref>{{cite web |url=http://www.russianspaceweb.com/briz-m.html |title=Briz-M: Russia's workhorse space tug}}</ref>

== Examples ==

*The Apollo program used parking orbits, for all the reasons mentioned above except those that pertain to geostationary orbits.<ref>{{cite web |url=https://history.nasa.gov/afj/launchwindow/lw1.html |title=Apollo lunar landing launch window: The controlling factors and constraints |publisher=NASA }}</ref><ref>{{cite web |url=https://history.nasa.gov/ap08fj/02earth_orbit_tli.htm |title=Apollo Flight Journal - Apollo 8, Day 1: Earth Orbit and Translunar Injection |publisher=NASA |url-status=dead |archive-url=https://web.archive.org/web/20080218181006/https://history.nasa.gov/ap08fj/02earth_orbit_tli.htm |archive-date=2008-02-18 }}</ref>
*When the [[Space Shuttle orbiter]] launched interplanetary probes such as [[Galileo (spacecraft)|Galileo]], it used a parking orbit to deliver the probe to the right injection spot.<ref>{{cite journal |url=https://link.springer.com/article/10.1007/BF00216849 |title=Galileo trajectory design|year=1992|doi=10.1007/BF00216849|last1=d'Amario|first1=Louisa.|last2=Bright|first2=Larrye.|last3=Wolf|first3=Arona.|journal=Space Science Reviews|volume=60|issue=1–4| page=23 | bibcode=1992SSRv...60...23D |s2cid=122388506}}</ref>
*The [[Ariane 5]] does not usually use parking orbits.<ref>{{cite web |url=https://www.nasaspaceflight.com/2020/02/ariane-5-japanese-south-korean-satellites-gto/ |title=Ariane 5 lifts Japanese, South Korean satellites to Geostationary Transfer Orbit |author=Chris Gebhardt |date=Feb 18, 2020 |publisher=NasaSpaceFlight.com}}</ref> This simplifies the launcher since multiple restart is not needed, and the penalty is small for their typical [[Geostationary transfer orbit|GTO]] mission, as their launch site is close to the equator. A less commonly used second stage, the [[Ariane 5#Second stage|Ariane-5ES]] has multiple restart capability, and has been used for missions such as the [[Automated Transfer Vehicle]] (ATV) that use parking orbits.<ref>{{cite web |url=https://space.skyrocket.de/doc_lau_det/ariane-5es.htm |title=Ariane-5ES}}</ref>
*In a literal example of a parking orbit, the ATV could park for several months in orbit while waiting to rendezvous with the [[International Space Station]]. For safety reasons, the ATV could not approach the station while a Space Shuttle was docked or when a [[Soyuz (spacecraft)|Soyuz]] or [[Progress spacecraft|Progress]] was maneuvering to dock or depart.<ref>{{cite web |url=http://www.spaceflightnow.com/news/n0802/10atv1/ |title=Maiden launch of Europe's resupply ship gets new date |author=Stephen Clark |publisher=Spaceflight Now}}</ref>

==References==
{{Reflist|30em}}

{{orbits|state=expanded}}

[[Category:Astrodynamics]]
[[Category:Spacecraft propulsion]]
[[Category:Orbits]]

Parking orbit - Revision history

Ajay Kumar: Created a new article