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INSTRUMENT
  • 24 Hour Autonomous Operation
  • Independent Safehold
  • Onboard Attitude Determination
  • Onboard Orbit Propagation
  • Onboard Maneuver Calculation
  • Onboard Data Compression
  • Bulk Data EDAC- Pyro Firing Circuitry
  • Standard 1553 Data Bus
  • High Speed Serial Data Ingest Port
  • Instrument Overcurrent Protection
  • Transportable Ground Station
  • 3 arcsecond attitude knowledge on all axes
  • 5 arcsecond pointing accuracy on all axes
  • More than 1 degree/sec average for large angle slews
SPACECRAFT
Structure: One-piece cast aluminum main structure
Battery: D size packs provide 12 Ah with multiple attach points
RF Transmitters: 4 Mbps X-Band downlink, QPSK, 3.5 W RF power, 95% spherical coverage
RF Receivers: 4 Kbps S-Band uplink, BPSK modulated directly on the S-Band carrier with Bi-phase L capability, 95% spherical coverage
Processor: Loral RAD-6000 32-bit RISC processor with 4 Mbytes of SRAM and PCI local bus. 25 MIPS processing capability, 1 MB EEPROM for program storage, 200 Mbytes DRAM with EDAC
Solar Arrays: Two double-fold deployable array panels provide 12.5 W each
Sensors:
Coarse Sun sensors: 2° accuracy with a ±85° field of view
Fine Sun sensors: 0.5° accuracy with a ±64° field of view
Star Tracker: 5.5 arcsecond (1 sigma) accuracy/star with an 8 x 8 degree field of view
Magnetometer: Three-axis flux gate with 0.342 milligauss resolution and ± 700 milligauss range
Gyroscope: Three two-axis gyros in a single package with 1.2433 x 10-6 resolution; 1.5 arc-sec/sec (1 sigma) noise and 0.6°/hour drift
Actuators:
Magnetic Torquers: 30-140 Am2 torquer bar
Reaction Wheels: Low-noise design provides 14 N-m-s (maximum) momentum storage

MISSION FACTS
Mission Duration: 1 year minimum operational lifetime
Orbit:  
Spacecraft Weight: 75 Kg (baseline configuration), 56 Kg for the avionics alone
Instrument Weight: 150-400 W for the instrument (baseline configuration)
Power: Radiation
Radiation Tolerance: 30 K Rads total dose
Launch Vehicle:  
Launch Site: Western Range/Vandenberg AFB
Launch Date:  

The Science

The SMEX-Lite spacecraft concept is innovative for its end-to-end consideration of all elements that contribute to mission costs. The SMEX-Lite team developed a spacecraft that not only reduces design and test engineering, development team size, flight hardware costs, and the cost of flight operations, but also maintains mission reliability and improves performance over previous SMEX missions.

SMEX-Lite is instrument friendly. Its design provides experimenters with flexibility and a growth path for future enhancements by accommodating the expansion or deletion of capabilities. Experimenters can take advantage of mission configurable spacecraft services while utilizing a common, flight proven, SMEX structure.

The SMEX-Lite has "plug-and-play" architecture that allows components to be added or deleted from the system with virtually no redesign and without disturbing other subsystems. Functions are segregated into "slices" that are independent at the subsystem level. The "plug-and-play" concept was extended to the electronics, sensors, actuators, software, solar arrays, the mechanical system, and the ground support (integration and test and operations) system.

Onboard the spacecraft, a radiation hard, 32-bit computer ties all the functions together. The flexibility inherent in the SMEX-Lite design is made possible by a heavy reliance on software. In the software, "plug-and-play" is made possible by an applications layer that contains independent modules that support a variety of sensors and actuators. Several functions traditionally performed by dedicated hardware (such as the safehold and the battery charge integrator) were moved to software. Where software development is needed, software modules are coded using the C/C++language. To maintain integrity of the mission, hardware watchdogs supervise the operation of the software and will reset the computer should software failures occur.

Communication between subsystems flows via MIL-STD-1553 interfaces. The instrument and subsystems communicate with the computer using this bus. For instruments that produce high data rates, there are four EIA RS422 Direct Memory Access (DMA) interfaces to the computer memory. In addition, the on-board computer uses the Peripheral Connection Interface (PCI) backplane commonly found in IBM-compatible PC's. The industry standard PCI backplane allows development of custom interfaces that provide DMA to instruments with unique interfacing requirements.

The flight software enjoys a significant degree of heritage from previous SMEX missions. Its architecture utilizes modular design techniques that maximize software reuse. This approach provides flexibility for tailoring the system to unique mission requirements and improves the overall reliability of the flight code.

OTHER MISSION INFORMATION:

More mission info.
EnviroNET Radiation Survey of the SAMPEX mission.

Back to the SMEX project home page or the GSFC home page.

Author: Jim Watzin (jim.watzin@gsfc.nasa.gov)
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The last time this page was updated was 06/17/97.