Editing TRACE

{{Short description|NASA satellite of the Explorer program}}
{{other uses|Trace (disambiguation){{!}}Trace}}
{{Use American English|date=November 2021}}
{{Use dmy dates|date=November 2021}}
{{Infobox spaceflight
| name              = Transition Region and Coronal Explorer
| names_list        = Explorer-73<br/>SMEX-4<br/>TRACE
| image             = 506998main TRACE artist rendition.jpg
| image_caption     = 
| image_size        = 

| mission_type      = [[Heliophysics]]
| operator          = [[NASA]]{{\}}[[Goddard Space Flight Center|GSFC]]
| COSPAR_ID         = 1998-020A
| SATCAT            = 25280
| website           = [https://sdowww.lmsal.com/TRACE/ TRACE]
| mission_duration  = 1 year (planned)<br/>{{Age in years, months and days|1998|04|02|2010|06|21}} (achieved)<ref name="lmsal-final">{{cite web |url=http://trace.lmsal.com/POD/TRACEpod.html |title=TRACE science mission terminated |publisher=Lockheed Martin Solar and Astrophysics Lab |date=June 21, 2010 |access-date=September 13, 2015 |archive-date=7 February 2016 |archive-url=https://web.archive.org/web/20160207100712/http://trace.lmsal.com/POD/TRACEpod.html |url-status=dead}}</ref>

| spacecraft        = Explorer LXXIII
| spacecraft_type   = Transition Region and Coronal Explorer
| spacecraft_bus    = TRACE
| manufacturer      = [[Goddard Space Flight Center]]
| launch_mass       = {{cvt|250|kg}}
| dimensions        = {{cvt|1.9|xx|1.1|m}}
| power             = 220 [[watt]]s

| launch_date       = 2 April 1998, 02:42:39 [[Coordinated Universal Time|UTC]]
| launch_rocket     = [[Pegasus (rocket)|Pegasus XL]] (F21)
| launch_site       = [[Vandenberg Space Force Base|Vandenberg]], ''[[Stargazer (aircraft)|Stargazer]]''
| launch_contractor = [[Orbital Sciences Corporation]]

| entered_service   = 20 April 1998
| deactivated       = 21 June 2010, 23:56 UTC
| last_contact      = 21 June 2010
| decay_date        =

| orbit_reference   = [[Geocentric orbit]]<ref name="Trajectory">{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/displayTrajectory.action?id=1998-020A |title=Trajectory: TRACE (1998-020A) 
|publisher=NASA |date=28 October 2021 |access-date=29 November 2021}} {{PD-notice}}</ref>
| orbit_regime      = [[Sun-synchronous orbit]]
| orbit_periapsis   = {{cvt|520.0|km}}
| orbit_apoapsis    = {{cvt|547.2|km}}
| orbit_inclination = 97.84°
| orbit_period      = 95.48 minutes
| apsis             = gee

| instruments       = TRACE Imaging Telescope

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

| programme         = '''[[Explorers Program|SMEX program]]'''
| previous_mission  = [[Fast Auroral Snapshot Explorer]] (Explorer 70) (SMEX-2)
| next_mission      = [[Submillimeter Wave Astronomy Satellite]] (Explorer 74) (SMEX-3)

| programme2        = '''[[Explorer program]]'''
| previous_mission2 = [[Student Nitric Oxide Explorer]] (Explorer 72)
| next_mission2     = [[Submillimeter Wave Astronomy Satellite]] (Explorer 74)
}}

'''Transition Region and Coronal Explorer''' ('''TRACE''', or '''Explorer 73''', '''SMEX-4''') was a [[NASA]] [[heliophysics]] and [[solar observatory]] designed to investigate the connections between fine-scale magnetic fields and the associated plasma structures on the Sun by providing high-resolution images and observation of the [[Sun|solar]] [[photosphere]], the transition region, and the [[solar corona]]. A main focus of the TRACE instrument is the fine structure of [[coronal loop]]s low in the solar atmosphere. TRACE is the third spacecraft in the [[Small Explorer program]], launched on 2 April 1998, and obtained its last science image on 21 June 2010, at 23:56 [[Coordinated Universal Time|UTC]].<ref>{{cite web |url=http://trace.lmsal.com/ |title=Transition Region and Coronal Explorer |publisher=Lockheed Martin Solar and Astrophysics Lab}}</ref>

== Mission ==
The Transition Region and Coronal Explorer (TRACE) is a NASA small explorer mission designed to examine the three-dimensional magnetic structures which emerge through the Sun's photosphere (the visible surface of the Sun) and define both the geometry and dynamics of the upper solar atmosphere (the transition region and corona). Its primary science objectives are to: (1) follow the evolution of magnetic field structures from the solar interior to the corona; (2) investigate the mechanisms of the heating of the outer solar atmosphere; and, (3) determine the triggers and onset of solar flares and mass ejections. TRACE is a single-instrument, three-axis stabilized spacecraft. The spacecraft [[Spacecraft attitude control|attitude control]] system (ACS) utilizes three magnetic-torquer coils, a digital Sun sensor, six coarse Sun sensors, a three-axis magnetometer, four reaction wheels, and three two-axis inertial gyros to maintain pointing. In science mode, the spacecraft uses an instrument-provided guide telescope as a fine guidance sensor to provide a pointing accuracy of less than 5 [[Minute and second of arc|arcseconds]]. Power is provided to the spacecraft through the use of four panels of [[gallium arsenide]] (GaAs) [[solar cell]]s with a total area of {{cvt|2|m2}}. The solar array actually produces power of around 220 [[watt]]s, 85 W of which is used each orbit by the spacecraft and 35 W of which is used by the instrument each orbit. The remaining power is used for operational and decontamination heating of the spacecraft and telescope. A 9 [[Ampere|A]]-hour [[nickel–cadmium battery]] (NiCd) provides energy during time when the spacecraft is in the Earth's shadow. Communications are provided via a 5 W [[S band|S-band]] [[Transponder (satellite communications)|transponder]], providing up to 2.25 [[Data-rate units|Mbit/s]] downlink data transmission and 2&nbsp;kbit/s uplink. Data are transmitted up to six times daily. Data are stored onboard using a solid-state recorder capable of holding up to 300 [[Megabit|MB]]. The command and data handling system uses a 32-bit [[I386|80386/80387]] [[Processor (computing)|processor]].<ref name="Display">{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1998-020A |title=Display: TRACE (1998-020A) |publisher=NASA |date=28 October 2021 |access-date=29 November 2021}} {{PD-notice}}</ref>

== Spacecraft ==
[[File:TRACE in cleanroom during assembly.jpg|thumb|TRACE in cleanroom during assembly]]
The satellite was built by NASA's [[Goddard Space Flight Center]]. Its telescope was constructed by a consortium led by [[Lockheed Martin]]'s Advanced Technology Center. The optics were designed and built to a [[State of the art]] surface finish by the [[Smithsonian Astrophysical Observatory]] (SAO). The telescope has a {{cvt|30|cm}} aperture and 1024 × 1024 [[charge-coupled device]] (CCD) detector giving an 8.5 [[Minute and second of arc|arcminute]] [[field of view]] (FoV). The telescope is designed to take [[correlated]] images in a range of wavelengths from [[visible light]] through the [[Lyman alpha line]] to far [[ultraviolet]]. The different wavelength [[passband]]s correspond to [[Plasma (physics)|plasma]] emission temperatures from 4,000 to 4,000,000 [[Kelvin|K]]. The optics use a special multilayer technique to focus the difficult-to-reflect [[extreme ultraviolet]] (EUV) light; the technique was first used for solar imaging in the late 1980s and 1990s, notably by the [[MSSTA]] and [[NIXT]] [[sounding rocket]] payloads.

== Experiment ==
=== TRACE Imaging Telescope ===
The telescope is of [[Cassegrain reflector|Cassegrain design]], {{cvt|1.6|m}} long with an aperture of {{cvt|30|cm}}. The focal length is {{cvt|8.66|m}}. The field of view of the telescope is 8.5 x 8.5 [[Minute and second of arc|arcminutes]] with a spatial resolution of one arcsecond. The light is focused on a 1024 x 1024 element CCD detector (0.5 arcseconds/[[pixel]]). The temporal resolution of the instrument is less than 1 second, although the nominal temporal resolution is 5 seconds. Exposure times for observations range between 2 ms and 260 seconds. The primary and secondary mirrors have normal-incidence coatings specially designed for EUV and UV observations which divide the mirrors into quadrants. These segmented coatings are designed to provide identically sized and perfectly coaligned images. Which mirror quadrant is used for an observation is determined by the position of a quadrant selector shutter mechanism, positioned behind the entrance aperture. Three of the mirror coatings provide for observations in specific [[iron]] emission bands: Fe IX (central wavelength/bandwidth: 17.3 nm/0.64 nm); Fe XII (19.5 nm/0.65 nm); and Fe XV (28.4 nm/1.07 nm). The final mirror coating allows broadband observations in the ultraviolet (centered on 500 nm). Further selection of observations in the UV can be made through the use of a filter wheel, mounted in front of the CCD. The filter wheel permits continuum observations (170 nm/20 nm) as well as observations in emission bands for C (carbon) I and Fe II (160 nm/27.5 nm), C IV (155 nm/2 nm), and H (Hydrogen) I (Lyman-alpha) (121.6 nm/8.4 nm). The TRACE primary mirror assembly is based on primary mirror support assemblies used in [[SWATH]], a small explorer developed for the [[United States Air Force|U.S. Air Force]], and [[NIXT]], a set of rocket flights flown by the Smithsonian Astrophysical Observatory (SAO) five times between 1983 and 1993. Many of the designs and some of the space flight hardware from the MDI instrument on [[Solar and Heliospheric Observatory]] (SoHO) was also used.

== Image gallery ==
<gallery>
File:Traceimage.jpg|TRACE image of some typical million Kelvin loops
File:Sunspot TRACE.jpeg|Image of a [[sunspot]] taken by TRACE
File:Tracemosaic.jpg|TRACE mosaic of the full-disk Sun
</gallery>

== See also ==
{{Portal|Spaceflight}}
* [[Explorer program]]

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

== External links ==
{{commons category-inline|TRACE}}
* [https://sdowww.lmsal.com/TRACE/ TRACE website] by Lockheed Martin
* [http://trace.lmsal.com/trace_cat.html TRACE Data Center] by Lockheed Martin
* [https://web.archive.org/web/20120726082944/http://sunland.gsfc.nasa.gov/smex/trace/ TRACE website] (archived) by NASA's Goddard Space Flight Center
* [https://sdowww.lmsal.com/TRACE/POD/TRACEpod.html#movielist TRACE movies archive by Lockheed Martin]

{{Space observatories}}
{{Sun spacecraft}}
{{Explorers program}}
{{Orbital launches in 1998}}
{{Authority control}}

[[Category:Spacecraft launched in 1998]]
[[Category:Explorers Program]]
[[Category:Missions to the Sun]]
[[Category:Solar telescopes]]
[[Category:Ultraviolet telescopes]]
[[Category:Solar space observatories]]
[[Category:Spacecraft launched by Pegasus rockets]]