 | |
| Names | Explorer-73 SMEX-4 TRACE |
|---|---|
| Mission type | Heliophysics |
| Operator | NASA / GSFC |
| COSPAR ID | 1998-020A |
| SATCATno. | 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 | 220watts |
| Start of mission | |
| Launch date | 2 April 1998, 02:42:39UTC |
| 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[citation needed] |
| 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 ← Fast Auroral Snapshot Explorer (Explorer 70) (SMEX-2) Submillimeter Wave Astronomy Satellite (Explorer 74) (SMEX-3) → ← Student Nitric Oxide Explorer (Explorer 72) Submillimeter Wave Astronomy Satellite (Explorer 74) → | |
Transition Region and Coronal Explorer (TRACE, orExplorer 73,SMEX-4) was aNASAheliophysics andsolar 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 thesolarphotosphere, the transition region, and thesolar corona. A main focus of the TRACE instrument was the fine structure ofcoronal loops low in the solar atmosphere. TRACE was the third spacecraft in theSmall Explorer program, launched on 2 April 1998, and obtained its last science image on 21 June 2010, at 23:56UTC.[4] Itreentered the atmosphere 600 km south ofPerth,Australia on 18 July 2025, at 11:37UTC.[2]
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]
The satellite was built by NASA'sGoddard Space Flight Center. Its telescope was constructed by a consortium led byLockheed Martin's Advanced Technology Center. The optics were designed and built to astate of the art surface finish by theSmithsonian Astrophysical Observatory (SAO). The telescope had a 30 cm (12 in) aperture and 1024 × 1024charge-coupled device (CCD) detector giving an 8.5arcminutefield of view (FoV). The telescope was designed to takecorrelated images in a range of wavelengths fromvisible light through theLyman alpha line to farultraviolet. The different wavelengthpassbands corresponded toplasma emission temperatures from 4,000 to 4,000,000K. The optics used a special multilayer technique to focus the difficult-to-reflectextreme ultraviolet (EUV) light; the technique was first used for solar imaging in the late 1980s and 1990s, notably by theMSSTA andNIXTsounding rocket payloads.
TRACE was a single-instrument, three-axis stabilized spacecraft. The spacecraftattitude 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 5arcseconds. Power was provided to the spacecraft through the use of four panels ofgallium arsenide (GaAs)solar cells with a total area of 2 m2 (22 sq ft). The solar array actually produced power of around 220watts, 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 9A-hournickel–cadmium battery (NiCd) provided energy during time when the spacecraft was in the Earth's shadow. Communications were provided via a 5 WS-bandtransponder, providing up to 2.25Mbit/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 300MB. The command and data handling system used a 32-bit80386/80387processor.[5]
The telescope was ofCassegrain 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 8.5arcminutes 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 specificiron 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 inSWATH, a small explorer developed for theU.S. Air Force, andNIXT, 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 onSolar and Heliospheric Observatory (SoHO) was also used.
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Media related toTRACE at Wikimedia Commons
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