IEEE Geoscience and Remote Sensing Magazine - June 2013 - 60

WISE, and DoD flight missions. The board receives +28
Vdc from the PPT and regulates low voltages, including
+/-12 Vdc, +5 Vdc, and +3.3 Vdc, for use by the Centaur, FCP, and PPT control circuitry. Further, the board
includes low voltage switches (+5 Vdc) to power ADCS
components, including the magnetometer, momentum
wheel, and horizon sensor.
4.2. coMMunicaTions and daTa subsysTeM
Most of the hardware to implement the CDS resides within
the CYGNSS avionics bay, with the exceptions of the S-band
antennas, diplexer, and hybrid.
centaur
All on-board microsat processing is performed on SwRI's
Centaur board. The Centaur consists of our space-qualified
heritage Atmel SPARC8 processor with heritage CCSDS
compliant command and telemetry interface, instrument
data interface, and ADCS interface designs. The board
architecture is based on the Juno JADE IPB (launched Aug
2011) and extensively reuses the command and telemetry
circuitry from Deep Impact, Orbital Express, Kepler, and
WISE only requiring a board relay out for CYGNSS. This
board was designed to be a very low power embedded
microcontroller and was also designed with multiple mission requirements in mind. The CYGNSS version of the
board will be tailored to a LEO radiation environment, providing a dense non-volatile memory, and ample interfaces
to ADCS, CDS, DDMI, and thermal components throughout the observatory.
The Centaur provides the following functionality:
◗ Processor: The LEON3 ASIC is the spacecraft computer,
which provides all resources for on-board microsat
flight soft-ware processing. The LEON3 dual-core processor, successor to the LEON2 core, utilizes a 7-stage
pipeline, 8 register windows, a 4#4 kBytei-cache and
d-cache, branch prediction, hardware multiply/divide,
and hardware watchdogs. It interfaces to EDAC-protected memories, including MRAM, SDRAM, and Flash.
External interfaces include multiple SpaceWire, 1553,
CAN, Ethernet, and UART ports.
◗ Processor Support Circuitry: The processor requires
additional parts, including memories, clock, reset, and
power management, and interface drivers. Memories
include MRAM for code storage, SDRAM for code execution, and Flash memory for data storage. The radiation
tested Flash parts are being used on MMS.
◗ CCSDS Command and Telemetry Core (CTC) (Heritage HDL in FPGA): Resident in the Centaur FPGA,
the CTC autonomously receives and routes ground
commands from the transceiver, assembles and packetizes science data, and autonomously collects and
formats housekeeping telemetry for transmission to
the transceiver, significantly reducing flight software
processing loads. The telemetry algorithms to perform
the CCSDS packetization are identical to those used
60

on the WISE Mission Unique Board, which produced
CCSDS Telemetry TM Source Packets and Transfer
Frames with Reed-Solomon Codeblocks (E-16, I=5).
The command algorithms are identical to those used
on Deep Impact, Orbital Express, Kepler, and WISE,
which produce CCSDS TC Transfer Frames with Viterbi (rate 1=2) encoding. The CCSDS File Delivery
Proocol (CFDP) File Protocol for hardware acceleration of CFDP Protocol Data Units (PDUs) is used,
leveraging designs from MMS. Further, Level 0 telemetry and commanded resets are generated by the CTC
without required intervention from the processor. In
this manner, the ground station can reset the spacecraft even with the processor in a non-responsive state.
◗ CCSDS Command and Telemetry Circuitry: The
CCSDS command and telemetry circuitry includes
ADCs (Analog to Digital Converters), RS422 command
interfaces, and power switches, controlled by the
Centaur but housed on the Peak Power Tracker. All
components utilize the same circuitry as the Command
and Telemetry Boards on Deep Impact, Orbital Express,
Kepler, and WISE.
◗ General Purpose Interfaces: The Centaur design includes
LVDS, RS422, analog, and discrete (low-level) interfaces. The CYGNSS ADCS and DDMI are compatible
with these interfaces and do not require Centaur modification to accommodate.
4.3. cds flighT sofTWare
The simple operational nature of the DDMI and science
profile allows the CDS flight software to be designed for
autonomous control during all normal science and communication operation using only on-board Level 0 command
capabilities of the Centaur, stored command sequences,
and CCSDS File Delivery Protocol (CFDP) processes. CDS
flight software refers specifically to the portion of software
dealing with data upload and downlink, including command upload, parsing, telemetry generation, and transmission. Engineering operations require standard command
services provided by our hardware-based heritage designs
located on the Centaur. Command services include COP-0
uplink command processing with BCH error detect and
correction. The Centaur also provides FSW-independent
execution of a Level-0 command set used for ground-based
fault management. All other commands are passed to the
FSW Command Manager for execution or to the Stored
Command Sequence Manager as onboard absolute and
relative time sequences.
The FSW Telemetry Manager provides collection and
high-level formatting of housekeeping data. These data
are either downlinked in real-time or passed to the FSW
Storage Manager to be stored for later downlink. The Storage Manager software controls data acquisition, recording, and playback of housekeeping and science data
using the 4 GB on-board memory for data storage. The
heritage 4 GB Flash memory data store allows for >10
ieee Geoscience and remote sensing magazine

JUNE 2013

Table of Contents for the Digital Edition of IEEE Geoscience and Remote Sensing Magazine - June 2013