TRACE

Transition Region and Coronal Explorer

Names| Explorer-73
SMEX-4
TRACE
Mission type| Heliophysics
Operator| NASA / GSFC
COSPAR ID| 1998-020A
SATCAT no.| 25280
Website| TRACE
Mission duration| 1 year (planned)
12 years, 2 months and 19 days (achieved)[1]
Spacecraft properties
Spacecraft| Explorer LXXIII
Spacecraft type| Transition Region and Coronal Explorer
Bus| TRACE
Manufacturer| Goddard Space Flight Center
Launch mass| 250 kg (550 lb)
Dimensions| 1.9 × 1.1 m (6 ft 3 in × 3 ft 7 in)
Power| 220 watts
Start of mission
Launch date| 2 April 1998, 02:42:39 UTC
Rocket| Pegasus XL (F21)
Launch site| Vandenberg, Stargazer
Contractor| Orbital Sciences Corporation
Entered service| 20 April 1998
End of mission
Deactivated| 21 June 2010, 23:56 UTC
Decay date| 18 July 2025, 11:37 UTC[2]
Orbital parameters
Reference system| Geocentric orbit[3]
Regime| Sun-synchronous orbit
Perigee altitude| 520.0 km (323.1 mi)
Apogee altitude| 547.2 km (340.0 mi)
Inclination| 97.84°
Period| 95.48 minutes
Instruments
TRACE Imaging Telescope

TRACE mission patch

SMEX program

<- Fast Auroral Snapshot Explorer (Explorer 70) (SMEX-2)

Submillimeter Wave Astronomy Satellite (Explorer 74) (SMEX-3) ->

Explorer program

<- Student Nitric Oxide Explorer (Explorer 72)

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 solar photosphere, the transition region, and the solar corona. A main focus of the TRACE instrument was the fine structure of coronal loops low in the solar atmosphere. TRACE was 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 UTC.[4] It reentered the atmosphere 600 km south of Perth, Australia on 18 July 2025, at 11:37 UTC.[2]

## Contents

* 1 Mission
* 2 Spacecraft
* 3 Experiment
* 3.1 TRACE Imaging Telescope
* 4 Image gallery
* 5 See also
* 6 References
* 7 External links

## Mission

The Transition Region and Coronal Explorer (TRACE) was 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 were 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.[5]

## Spacecraft

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 had a 30 cm (12 in) aperture and 1024 × 1024 charge-coupled device (CCD) detector giving an 8.5 arcminute field of view (FoV). The telescope was designed to take correlated images in a range of wavelengths from visible light through the Lyman alpha line to far ultraviolet. The different wavelength passbands corresponded to plasma emission temperatures from 4,000 to 4,000,000 K. The optics used 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.

TRACE was a single-instrument, three-axis stabilized spacecraft. The spacecraft attitude control system (ACS) utilized 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 used an instrument-provided guide telescope as a fine guidance sensor to provide a pointing accuracy of less than 5 arcseconds. Power was provided to the spacecraft through the use of four panels of gallium arsenide (GaAs) solar cells with a total area of 2 m2 (22 sq ft). The solar array actually produced power of around 220 watts, 85 W of which was used each orbit by the spacecraft and 35 W of which was used by the instrument each orbit. The remaining power was used for operational and decontamination heating of the spacecraft and telescope. A 9 A-hour nickel–cadmium battery (NiCd) provided energy during time when the spacecraft was in the Earth's shadow. Communications were provided via a 5 W S-band transponder, providing up to 2.25 Mbit/s downlink data transmission and 2 kbit/s uplink. Data were transmitted up to six times daily. Data were stored onboard using a solid-state recorder capable of holding up to 300 MB. The command and data handling system used a 32-bit 80386/80387 processor.[5]

## Experiment

### TRACE Imaging Telescope

The telescope was of Cassegrain design, 1.6 m (5 ft 3 in) long with an aperture of 30 cm (12 in). The focal length was 8.66 m (28.4 ft). The field of view of the telescope was 8.5 x 8.5 arcminutes with a spatial resolution of one arcsecond. The light was focused on a 1024 x 1024 element CCD detector (0.5 arcseconds/pixel). The temporal resolution of the instrument was less than 1 second, although the nominal temporal resolution was 5 seconds. Exposure times for observations ranged between 2 ms and 260 seconds. The primary and secondary mirrors had normal-incidence coatings specially designed for EUV and UV observations which divide the mirrors into quadrants. These segmented coatings were designed to provide identically sized and perfectly coaligned images. Which mirror quadrant was used for an observation was determined by the position of a quadrant selector shutter mechanism, positioned behind the entrance aperture. Three of the mirror coatings provided 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 allowed broadband observations in the ultraviolet (centered on 500 nm). Further selection of observations in the UV could be made through the use of a filter wheel, mounted in front of the CCD. The filter wheel permitted 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 was based on primary mirror support assemblies used in SWATH, a small explorer developed for the 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

* TRACE image of some typical million Kelvin loops

* Image of a sunspot taken by TRACE

* TRACE mosaic of the full-disk Sun

## See also

* Explorer program

## References

1. ↑ "TRACE science mission terminated". Lockheed Martin Solar and Astrophysics Lab. June 21, 2010. http://trace.lmsal.com/POD/TRACEpod.html.
2. ↑ 2.0 2.1 McDowell, Jonathan (18 July 2025). "NASA's TRACE solar observatory, which operated from 1998 to 2010, reentered over the ocean 600 km south of Perth, W Australia at 1137 UTC Jul 18.". https://x.com/planet4589/status/1946352736775135363.
3. ↑ "Trajectory: TRACE (1998-020A)". NASA. 28 October 2021. https://nssdc.gsfc.nasa.gov/nmc/spacecraft/displayTrajectory.action?id=1998-020A. This article incorporates text from this source, which is in the public domain.
4. ↑ "Transition Region and Coronal Explorer". Lockheed Martin Solar and Astrophysics Lab. https://sdowww.lmsal.com/TRACE/.
5. ↑ 5.0 5.1 "Display: TRACE (1998-020A)". NASA. 28 October 2021. https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1998-020A. This article incorporates text from this source, which is in the public domain.

## External links

* TRACE website by Lockheed Martin
* TRACE Data Center by Lockheed Martin
* TRACE website (archived) by NASA's Goddard Space Flight Center
* TRACE movies archive by Lockheed Martin

* v
* t
* e

Space observatories

Operating|

* AGILE (since 2007)
* AMS-02 (since 2011)
* Aoi (since 2018)
* ASTERIA (since 2017)
* Astrosat (since 2015)
* BRITE constellation (since 2013)
* CALET (since 2015)
* Chandra (AXAF) (since 1999)
* DAMPE (since 2015)
* Fermi (since 2008)
* Gaia (since 2013)
* HXMT (Insight) (since 2017)
* Hinode (Solar-B) (since 2006)
* HiRISE (since 2005)
* Hisaki (SPRINT-A) (since 2013)
* Hubble (since 1990)
* INTEGRAL (since 2002)
* IBEX (since 2008)
* IRIS (since 2013)
* ISS-CREAM (since 2017)
* MAXI (since 2009)
* Mikhailo Lomonosov (since 2016)
* Mini-EUSO (since 2019)
* NCLE (since 2018)
* NEOSSat (since 2013)
* NICER (since 2017)
* NuSTAR (since 2012)
* Odin (since 2001)
* SDO (since 2010)
* SOHO (since 1995)
* SOLAR (since 2008)
* Spektr-RG (since 2019)
* Spitzer (since 2003)
* STEREO (since 2006)
* Swift (since 2004)
* TESS (since 2018)
* WISE (since 2009)
* XMM-Newton (since 1999)

Planned|

* CHEOPS (2019)
* iWF-MAXI (2019)
* Astro-1 Telescope (2020)
* ILO-1 (2020)
* LUCI (2020)
* Nano-JASMINE (2020)
* ORBIS (2020)
* Solar Orbiter (SolO) (2020)
* IXPE (2021)
* James Webb (JWST) (2021)
* LORD (2021)
* SVOM (2021)
* XPoSat (2021)
* Euclid (2022)
* Space Solar Telescope (2022)
* XRISM (2022)
* Xuntian (2022)
* K-EUSO (2023)
* Solar-C (2023)
* SPHEREx (2023)
* Small-JASMINE (2024)
* Near-Earth Object Surveillance Mission (2025+)
* Spektr-UV (2025)
* WFIRST (2025+)
* PLATO (2026)
* LiteBIRD (2027)
* ARIEL (2028)
* Spektr-M (2030+)
* ATHENA (2031)
* LISA (2034)

Proposed|

* Arcus
* AstroSat-2
* EXCEDE
* Fresnel Imager
* FOCAL
* HabEx
* Hibari
* Hypertelescope
* JEM-EUSO
* LUVOIR
* ATLAST
* HDST
* Lynx
* Nautilus Deep Space Observatory
* New Worlds Mission
* NRO donation to NASA
* OST
* PhoENiX
* Solar-D
* SPICA
* THEIA
* THESEUS

Retired|

* Akari (Astro-F) (2006–2011)
* ALEXIS (1993–2005)
* Alouette 1 (1962–1972)
* Ariel 1 (1962, 1964)
* Ariel 2 (1964)
* Ariel 3 (1967–1969)
* Ariel 4 (1971–1972)
* Ariel 5 (1974–1980)
* Ariel 6 (1979–1982)
* ATM (1973–1974)
* ASCA (Astro-D) (1993–2000)
* Astro-1 (1990)
* BBXRT
* HUT
* Astro-2 (HUT) (1995)
* Astron (1983–1989)
* ANS (1974–1976)
* BeppoSAX (1996–2003)
* CHIPSat (2003–2008)
* Compton (CGRO) (1991–2000)
* CoRoT (2006–2013)
* Cos-B (1975–1982)
* COBE (1989–1993)
* DXS (1993)
* EPOCh (2008)
* EPOXI (2010)
* Explorer 11 (1961)
* EXOSAT (1983–1986)
* EUVE (1992–2001)
* FUSE (1999–2007)
* Kvant-1 (1987–2001)
* GALEX (2003–2013)
* Gamma (1990–1992)
* Ginga (Astro-C) (1987–1991)
* Granat (1989–1998)
* Hakucho (CORSA-b) (1979–1985)
* HALCA (MUSES-B) (1997–2005)
* HEAO-1 (1977–1979)
* Herschel (2009–2013)
* Hinotori (Astro-A) (1981–1991)
* HEAO-2 (Einstein Obs.) (1978–1982)
* HEAO-3 (1979–1981)
* HETE-2 (2000–2008)
* Hipparcos (1989–1993)
* IUE (1978–1996)
* IRAS (1983)
* IRTS (1995–1996)
* ISO (1996–1998)
* IXAE (1996–2004)
* Kepler (2009–2018)
* Kristall (1990–2001)
* LEGRI (1997–2002)
* LISA Pathfinder (2015–2017)
* MOST (2003–2019)
* MSX (1996–1997)
* OAO-2 (1968–1973)
* OAO-3 (Copernicus) (1972–1981)
* Orbiting Solar Observatory
* OSO 1
* OSO 2/OSO B
* OSO 3
* OSO 4
* OSO 5
* OSO 6
* OSO 7
* OSO 8
* Orion 1 (1971)
* Orion 2 (1973)
* PAMELA (2006–2016)
* PicSat (2018)
* Planck (2009–2013)
* RELIKT-1 (1983–1984)
* R/HESSI (2002–2018)
* ROSAT (1990–1999)
* RXTE (1995–2012)
* SAMPEX (1992–2004)
* SAS-B (1972–1973)
* SAS-C (1975–1979)
* Solwind (1979–1985)
* Spektr-R (2011–2019)
* Suzaku (Astro-EII) (2005–2015)
* Taiyo (SRATS) (1975–1980)
* Tenma (Astro-B) (1983–1985)
* Uhuru (1970–1973)
* Vanguard 3 (1959)
* WMAP (2001–2010)
* Yokoh (Solar-A) (1991–2001)

Hibernating
(Mission completed)|

* SWAS (1998–2005)
* TRACE (1998–2010)

Lost|

* OAO-1 (1966)
* OAO-B (1970)
* CORSA (1976)
* OSO C (1965)
* ABRIXAS (1999)
* HETE-1 (1996)
* WIRE (1999)
* Astro-E (2000)
* Tsubame (2014–2015)
* Hitomi (Astro-H) (2016)

Cancelled|

* AOSO
* Astro-G
* Constellation-X
* Darwin
* Destiny
* EChO
* Eddington
* FAME
* FINESSE
* GEMS
* HOP
* IXO
* JDEM
* LOFT
* OSO J
* OSO K
* Sentinel
* SIM & SIMlite
* SNAP
* SPOrt
* TAUVEX
* TPF
* XEUS
* XIPE

See also|

* Great Observatories program
* List of space telescopes
* List of proposed space observatories
* List of X-ray space telescopes

* Category

* v
* t
* e

Solar space missions

Current|

* ACE
* DSCOVR
* Hinode (Solar-B)
* IRIS
* MinXSS2
* Parker Solar Probe
* SOHO
* SDO
* SOLAR
* STEREO
* Wind

Past|

* Apollo Telescope Mount
* Coronas F (Koronas F)
* EURECA
* ESRO 2B
* Genesis
* GOES 13
* Helios
* Hinotori (Astro-A)
* IMP-8
* Intercosmos 26 (Koronas I)
* ISEE-1
* ISEE-2
* ICE / ISEE-3
* Koronas-Foton
* MinXSS1
* Orbiting Solar Observatory
* OSO 1
* OSO 2/OSO B
* OSO 3
* OSO 4
* OSO 5
* OSO 6
* OSO 7
* OSO 8
* Solwind
* PICARD
* Pioneer 5
* Pioneer 6, 7, 8 and 9
* PROBA-2
* Prognoz 6
* RHESSI
* SolarMax
* Spartan 201
* Taiyo (SRATS)
* TRACE
* Ulysses
* Yohkoh (Solar-A)

Planned|

* Solar Orbiter (2020)
* Aditya-L1 (2020)
* PROBA-3 (2021)
* PUNCH (2023)
* TRACERS (2023)
* SWFO-L1 (2024)

Proposed|

* ADAHELI
* EUVST
* Lagrange
* Solar-C
* SETH
* Solar Cruiser
* Sundiver

Cancelled (C) and lost (L)|

* AOSO (C)
* Pioneer E (L)
* Pioneer H (C)
* OSO C (L)
* OSO J (C)
* OSO K (C)
* Solar Sentinels (C)

Sun-Earth|

* SORCE
* SXI
* ACRIMSAT

List of heliophysics missions

* v
* t
* e

Explorers Program

List of Explorers Program missions

Missions|

| 1958–1992|

* Explorer 1
* 2†
* 3
* 4
* 5†
* S-1†
* 6 (S-2)
* 7 (S-1A)
* S-46A†
* 8
* S-56†
* 9 (S-56A)
* S-45†
* 10
* 11 (S-15)
* S-45A†
* S-55†
* 12 (EPE-A)
* 13 (S-55A)
* 14 (EPE-B)
* 15 (EPE-C)
* 16 (S-55B)
* 17 (AE-A)
* 18 (IMP-A)
* 19 (AD-A)
* S-66A (BE-A)†
* 20 (IE-A)
* 21 (IMP-B)
* 22 (BE-B)
* 23 (S-55C)
* 24 (AD-B)
* 25 (Injun 4, IE-B)
* 26 (EPE-D)
* 27 (BE-C)
* 28 (IMP-C)
* 29 (GEOS-A)
* 30 (Solrad 8)
* 31 (DME-A)
* 32 (AE-B)
* 33 (IMP-D)
* 34 (IMP-F)
* 35 (IMP-E)
* 36 (GEOS-B)
* 37 (Solrad 9)
* 38 (RAE-A)
* 39 (AD-C)
* 40 (Injun 5)
* 41 (IMP-G)
* 42 (Uhuru, SAS-A)
* 43 (IMP-H)
* 44 (Solrad 10)
* 45 (SSS-A)
* 46 (MTS)
* 47 (IMP-I)
* 48 (SAS-B)
* 49 (RAE-B)
* 50 (IMP-J)
* 51 (AE-C)
* 52 (Hawkeye 1)
* 53 (SAS-C)
* 54 (AE-D)
* 55 (AE-E)
* DADE-A†
* DADE-B†
* 56 (ISEE-1)
* 57 (IUE)
* 58 (HCMM)
* 59 (ICE)
* 60 (SAGE)
* 61 (Magsat)
* 62 (DE-1)
* 63 (DE-2)
* 64 (SME)
* 65 (CCE)
* 66 (COBE)
* 67 (EUVE)

|

MIDEX|

* 69 (RXTE)
* 71 (ACE)
* 77 (FUSE)
* 78 (IMAGE)
* 80 (WMAP)
* FAME
* 84 (Swift)
* 85–89 (THEMIS)
* 92 (WISE)
* 95 (TESS)
* 96 (ICON)
* SPHEREx

SMEX|

* 68 (SAMPEX)
* 70 (FAST)
* 73 (TRACE)
* 74 (SWAS)
* 75 (WIRE)†
* 81 (RHESSI)
* 83 (GALEX)
* 90 (AIM)
* 91 (IBEX)
* 93 (NuSTAR)
* 94 (IRIS)
* GEMS
* IXPE
* PUNCH
* TRACERS

UNEX/MO/I|

* HETE-1†
* 72 (SNOE)
* 76 (TERRIERS)†
* 79 (HETE-2)
* INTEGRAL
* 82 (CHIPSat)
* CINDI
* Suzaku
* TWINS
* Hitomi†
* NICER
* GOLD
* XRISM
* GUSTO
* CASE

Proposals|

| Proposals|

* FINESSE
* Arcus
* OHMIC
* ASTRE
* EXCEDE

|

* Green titles indicates active current missions
* Grey titles indicates cancelled missions
* Italics indicate missions yet to launch
* Symbol † indicates failure en route or before intended mission data returned

* v
* t
* e

Orbital launches in 1998

Lunar Prospector | Skynet 4D | Ofek-4 | STS-89 | Soyuz TM-27 | USA-137 | Brasilsat B3 * Inmarsat-3 F5 | Orbcomm FM3 * Orbcomm FM4 * GFO * Ad Astra | Globalstar 1 * Globalstar 2 * Globalstar 3 * Globalstar 4 | Kosmos 2349 | Iridium 50 * Iridium 52 * Iridium 53 * Iridium 54 * Iridium 56 | Kakehashi | SNOE * Teledesic 1 | Hot Bird 4 | Intelsat 806 | Progress M-38 (VDU-2) | USA-138 | SPOT 4 | Iridium 51 * Iridium 61 | Iridium 55 * Iridium 57 * Iridium 58 * Iridium 59 * Iridium 60 | TRACE | Iridium 62 * Iridium 63 * Iridium 64 * Iridium 65 * Iridium 66 * Iridium 67 * Iridium 68 | STS-90 | Globalstar 6 * Globalstar 8 * Globalstar 14 * Globalstar 15 | Nilesat 101 * BSat-1B | Kosmos 2350 | Iridium 69 * Iridium 71 | Kosmos 2351 | EchoStar IV | USA-139 | NOAA-15 | Progress M-39 | Iridium 70 * Iridium 72 * Iridium 73 * Iridium 74 * Iridium 75 | Zhongwei 1 | STS-91 | Thor 3 | Kosmos 2352 * Kosmos 2353 * Kosmos 2354 * Kosmos 2355 * Kosmos 2356 * Kosmos 2357 | Intelsat 805 | Kosmos 2358 | Kosmos 2359 | Molniya 3-49 | Nozomi | Shtil-1 * Tubsat-N * Tubsat-N1 | Resurs-O1 #4 * Fasat-Bravo * TMSAT * Gurwin Techsat 1B * WESTPAC * SAFIR-2 | Sinosat-1 | Kosmos 2360 | Orbcomm FM13 * Orbcomm FM14 * Orbcomm FM15 * Orbcomm FM16 * Orbcomm FM17 * Orbcomm FM18 * Orbcomm FM19 * Orbcomm FM20 | Mercury 3 | Soyuz TM-28 | Iridium 3 * Iridium 76 | ST-1 | Galaxy 10 | Astra 2A | Kwangmyŏngsŏng-1 | Iridium 77 * Iridium 79 * Iridium 80 * Iridium 81 * Iridium 82 | Globalstar 5 * Globalstar 7 * Globalstar 9 * Globalstar 10 * Globalstar 11 * Globalstar 12 * Globalstar 13 * Globalstar 16 * Globalstar 17 * Globalstar 18 * Globalstar 20 * Globalstar 21 | PAS-7 | Orbcomm FM21 * Orbcomm FM22 * Orbcomm FM23 * Orbcomm FM24 * Orbcomm FM25 * Orbcomm FM26 * Orbcomm FM27 * Orbcomm FM28 | Molniya-1T #99 | STEX (USA-141) | Eutelsat W2 * Sirius 3 | Hot Bird 5 | USA-140 | Maqsat 3 | Deep Space 1 * SEDSAT-1 | Progress M-40 (Sputnik 41) | AfriStar * GE-5 | STS-95 (SPARTAN-201 * PANSAT) | PAS-8 | Iridium 2 * Iridium 83 * Iridium 84 * Iridium 85 * Iridium 86 | Zarya / ISS | Bonum 1 | STS-88 (Unity * PMA-1 * PMA-2 * SAC-A * MightySat-1 | Satmex 5 | SWAS | Nadezhda 5 * Astrid 2 | Mars Climate Orbiter | Iridium 11 * Iridium 20 | PAS-6B | Kosmos 2361 | Kosmos 2362 * Kosmos 2363 * Kosmos 2364

Payloads are separated by bullets ( * ), launches by pipes ( | ). Crewed flights are indicated in bold text. Uncatalogued launch failures are listed in italics. Payloads deployed from other spacecraft are denoted in brackets.

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