Editing Advanced Composition Explorer (section)

{{Short description|NASA satellite of the Explorer program, at SE-L1 from 1997}}
{{Use American English|date=January 2014}}
{{Use dmy dates|date=October 2021}}
{{Infobox spaceflight
| name              = Advanced Composition Explorer
| names_list        = Explorer 71<br/>ACE
| image             = Advanced Composition Explorer.jpg
| image_caption     = An artist's concept of ACE
| image_size        = 

| mission_type      = [[Solar wind|Solar research]]
| operator          = [[NASA]]
| COSPAR_ID         = 1997-045A
| SATCAT            = 24912
| website           = {{URL|http://www.srl.caltech.edu/ACE/}}
| mission_duration  = 5 years (planned)<br/>{{time interval|25 August 1997|show=ymd}}<br/>''(in progress)''

| spacecraft        = Explorer LXXI
| spacecraft_type   = Advanced Composition Explorer
| spacecraft_bus    = ACE
| manufacturer      = [[Applied Physics Laboratory|Johns Hopkins Applied Physics Laboratory]]
| launch_mass       = {{cvt|757|kg}}
| dry_mass          = {{cvt|562|kg}}
| dimensions        = {{cvt|2|m}} in diameter<br/>{{cvt|1.9|m}} in length<br/>wingspan of {{cvt|8.3|m}}
| power             = 444 [[watt]]s

| launch_date       = 25 August 1997, 14:39:00 [[Coordinated Universal Time|UTC]]
| launch_rocket     = [[Delta II|Delta II 7920-8]]<br>D-247
| launch_site       = [[Cape Canaveral]], [[Cape Canaveral Space Launch Complex 17|LC-17A]]
| launch_contractor = [[McDonnell Douglas]]

| entered_service   = 12 December 1997
| last_contact      = 
| deactivated       = 
| decay_date        =

| orbit_reference   = [[Heliocentric orbit]]
| orbit_regime      = [[Lissajous orbit]]
| orbit_periapsis   = {{cvt|145700000|km}}
| orbit_apoapsis    = {{cvt|150550000|km}}
| orbit_inclination = ~0°
| orbit_period      = 1 year
| apsis             = gee

| instruments       = Cosmic-Ray Isotope Spectrometer (CRIS)<br/>Electron, Proton, and Alpha-particle Monitor (EPAM)<br/>Magnetometer (MAG)<br/>Real-Time Solar Wind (RTSW)<br/>Solar Energetic Particle Ionic Charge Analyzer (SEPICA)<br/>Solar Wind Electron, Proton and Alpha Monitor (SWEPAM)<br/>Solar Isotope Spectrometer (SIS)<br/>Solar Wind Ion Composition Spectrometer (SWICS) and Solar Wind Ion Mass Spectrometer (SWIMS)<br/>Ultra-Low-Energy Isotope Spectrometer (ULEIS)

| insignia          = ACE mission logo.png
| insignia_caption  = ACE mission patch
| insignia_size     = 200px

| programme2        = '''[[Explorer program]]'''
| previous_mission2 = [[Fast Auroral SnapshoT Explorer]] (Explorer 70)
| next_mission2     = [[Student Nitric Oxide Explorer]] (Explorer 72)
}}

[[File:Animation of Advanced Composition Explorer's orbit viewed from the Sun.gif|thumb|Animation of Advanced Composition Explorer's orbit viewed from the Sun<br>{{legend2| RoyalBlue|Earth}}{{·}}{{legend2|Magenta|Advanced Composition Explorer}}]]
[[File:Advanced Composition Explorer in space.jpg|thumb|upright=1.0|right|ACE in orbit around the Sun–Earth L<sub>1</sub> point.]]

'''Advanced Composition Explorer''' ('''ACE''' or '''Explorer 71''') is a [[NASA]] [[Explorer program]] satellite and [[space exploration]] mission to study [[matter]] comprising energetic particles from the [[solar wind]], the [[interplanetary medium]], and other sources.

Real-time data from ACE are used by the [[National Oceanic and Atmospheric Administration]] (NOAA) [[Space Weather Prediction Center]] (SWPC) to improve forecasts and warnings of [[solar storm]]s.<ref>{{cite news |url=http://onlinestore.usatoday.com/06241999-issue-of-usa-today-p6651.aspx |archive-url=https://web.archive.org/web/20091018171022/https://www.usatoday.com/weather/solar/wswx198.htm |archive-date=October 18, 2009 |url-status=dead |title=Satellite to aid space weather forecasting |date=June 24, 1999 |access-date=October 24, 2008 |newspaper=USA Today}}</ref> The ACE [[robotic spacecraft]] was launched on 25 August 1997, and entered a [[Lissajous orbit]] close to the {{L1}} [[Lagrange point]] (which lies between the [[Sun]] and the [[Earth]] at a distance of some {{cvt|1500000|km}} from the latter) on 12 December 1997.<ref>{{cite web |url=http://www.srl.caltech.edu/ACE/ASC/DATA/ace_dly_reprts/HTML/December_text_1997.html#97346 |title=Operations Day -- 346/1997 (12 December 1997) |website=srl.caltech.edu |date=31 December 1997 |access-date=28 October 2021}}</ref> The spacecraft is currently operating at that orbit. Because ACE is in a non-[[Keplerian orbit]], and has regular station-keeping maneuvers, the orbital parameters in the adjacent information box are only approximate.

{{as of|2023}},<ref name="ESA1">{{cite web |url=https://directory.eoportal.org/web/eoportal/satellite-missions/a/ace |title=ACE (Advanced Composition Explorer) - Mission Status |publisher=ESA eoPortal Directory |date=15 June 2021 |access-date=29 October 2021}}</ref> the spacecraft is still in generally good condition.<ref name="ACE Home Page">{{cite web |url=http://www.srl.caltech.edu/ACE/ace_mission.html |title=Advanced Composition Explorer (ACE) Mission Overview |publisher=California Institute of Technology |date=February 10, 2017 |first1=Eric R. |last1=Christian |first2=Andrew J. |last2=Davis |access-date=December 14, 2017}}</ref> NASA [[Goddard Space Flight Center]] managed the development and integration of the ACE spacecraft.<ref name="Display">{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1997-045A |title=Display: Advanced Composition Explorer (1997-045A) |publisher=NASA |date=28 October 2021 |access-date=28 November 2021}} {{PD-notice}}</ref>