Transition Region and Coronal Explorer

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INSTRUMENT Telescope: 30 cm diameter x 160 cm length, 8.66 m focal length Cassegrain Detector: 1024 x 1024 Lumigen coated, front illuminated, three-phase CCD Optics: Super-polished mirrors individually coated in four quadrants. Active secondary with image motion compensation Thermal: Detectors passively cooled to -65�C SCIENCE OBJECTIVES To follow the evolution of magnetic field structures from the solar interior to the corona. To investigate the mechanisms of the heating of the outer solar atmosphere. To investigate the triggers and onset of solar flares and mass ejections. KEY SCIENCE PARAMETERS Wavelength: 171� FelX, 195� FeXII, 284� FeXV, 1216� HI, 1550� CIV, 1600� continuum Spatial Resolution: 1 arcsecond; 0.5 arcsecond pixels Temporal Resolution: <1 s; 5 s nominal Exposure Time: 2 ms - 260 s Field of View: 8.5 x 8.5 arcminute MISSION FACTS Mission Duration: 1 year requirement/multi-year goal Orbit: 600 x 650 km Sun synchronous Mass/Power: 250 kg/200W Launch Vehicle: Pegasus XL Launch Site: Western Range/Vandenberg AFB Launch Date: 4th quarter calendar year 1997 SPACECRAFT SMEX Computer System: 80386/80387 Processor, 300 Mbps Solid State Recorder, 1553 Data Bus Communication System: S-band transponder, 2 Kbps uplink, 2.25 Mbps downlink Attitude Control System: Analog acquisition using an 8085 processor, Science mode uses instrument provided guide telescope as fine error sensor for spacecraft and image motion compensation, pointing accuracy < 5 arc seconds SMEX Power Electronics: Direct energy transfer, partial array shunting with no shunt resistors Mechanical Structure: Semi monocogue, thrust tube design using riveted Aluminum Battery: 9 Ah "Super" Nickel Cadmium Solar Arrays: Gallium Arsenide Solar Cells, some multi-junction test cells Actuators: Four reaction wheels, three magnetic torque rods Sensors: Three two-axis gyros, one digital Sun sensor, six coarse Sun sensors, one three-axis magnetometer, instrument guide telescope

TRACE data at Lockheed Martin Launch Information Integration and Test Activities Mission Operations The Science TRACE will explore the three-dimensional magnetic structures that emerge through the visible surface of the Sun - the Photosphere - and define both the geometry and dynamics of the upper solar atmosphere: the Transition Region and Corona. The magnetic field geometry can be seen in images of solar plasma taken in wavelengths emitted or absorbed by atoms and ions formed in different temperature ranges. The transition from the 6000 K Photosphere, where magnetic fields and plasma are in rough equipartition (low beta), to the multi-million degree Corona, where the magnetic fields dominate (high beta), is extremely difficult to model. Many of the physical processes that occur here - plasma confinement, reconnection, wave propagation and plasma heating - arise throughout space physics and astrophysics. TRACE will nearly simultaneously capture high spatial and temporal resolution images of the transition region. The TRACE data will provide quantitative observational constraints on the models and thus stimulate real advances in our understanding of the transition region. The solar atmosphere is constantly evolving because the magnetic fields that dominate the Corona are continuously displaced by the convective motions in the outer layers of the Sun just below the Photosphere. A major objective of the TRACE investigation is to explore the relation between diffusion of the surface magnetic fields and the changes in heating and structure throughout the Transition Region and Corona. The simultaneous movies of the 6,000 to 10,000,000 K volume of the solar atmosphere will allow us to determine the rate of change of the magnetic topology and the nature of the local restructuring and reconnection processes. TRACE, a three-axis stabilized spacecraft, uses an instrument provided guide telescope as the fine Sun sensor. The spacecraft must null the peak error to the guide telescope to within 20 arcseconds. The TRACE telescope has an image motion compensation mechanism which can attenuate jitter to about 0.1 arcseconds resolution. The Attitude Control System (ACS) uses three magnetic-torquer coils, one digital Sun sensor, six coarse Sun sensors, four reaction wheels, one three-axis magnetometer, and three two-axis inertial gyros. The ACS uses the spacecraft computer to perform closed loop attitude determination and control. Power is provided from four deployed panels of gallium arsenide solar cells totalling 2.0 m2. The array produces >222 W. The spacecraft can use 85 W and the instrument 35 W orbit average. The remaining power is used for spacecraft and telescope operational and decontamination heating. A 28 volt unregulated bus distributes the power and a 9 Ah battery provides energy storage. The command and data handling system includes a 32-bit processor and 300 Mbytes of science usable bulk memory. A MIL-STD-1553 data bus is used to connect all subsystems and the instrument. Science data is passed over the RS-422 interface at rates up to 900 Kbps. A 5 W S-Band transponder is used to downlink 2.25 Mbps of data up to six times a day. Commands are uplinked at 2 Kbps. Author: Jim Watzin (jim.watzin@gsfc.nasa.gov) Web Design provided by Swales Aerospace The last time this page was updated was 11/21/97.