IEEE Geoscience and Remote Sensing Magazine - June 2013 - 57

direct signals can be used to feed the
navigation data sense, and assist the
synchronization. The sampled data
is multiplied by a replica carrier and
fed into a matrix that performs an
FFT on a row-by-row basis to form
the DDM, to achieve in effect a 7000
channel correlator, integrating over 1
millisecond. Each point is then accumulated incoherently over hundreds
of milliseconds to bring the weak signals out of the noise.
This processing is performed in
real-time on-board the satellite, which
greatly reduces the quantity of data
required to be stored and for the satellite's downlink. CYGNSS plans to use
the SGR-ReSI primarily in an autonomous manner generating DDMs at a
low data rate continuously, which will
provide gap-free measurements of the
ocean roughness throughout the tropical oceans.

Dual Freq Antennas
LNAs
RF F/E
L1
Program
SRAM
(1MB TMR)

FLASH
(16MB)

RF F/E
L1

RF F/E
L1/L2

GNSS Receiver
Core

Interlink

Flash FPGA
Soft Core Processor
and GNSS Correlators

Interfaces:
RS422/LVDS/
CAN

16.367
MHz

Power Supply

RF F/E
L1/L2

Reflectometry
Processing Unit
Reprogrammable
Co-Processor
SRAM DSP FPGA

DDR2 RAM
Data Recorder

16-40V

fIGure 6. GNSS reflectometry instrument configuration.

material stress levels with a first mode natural frequency of
211 Hz in the launch configuration, avoiding harmonic cou3.5. MicrosaTelliTe sTrucTure
pling with the LV natural frequency of 75 Hz during launch.
The microsat structure requirements are driven by physical accommodation of the DDMI antennas, the S/As,
3.6. MicrosaTelliTe MechanisMs
and launch configuration constraints. Our design uses
Observatory mechanisms are limited to heritage S/A
the same principles as our heritage avionics chassis,
deployment devices. The four "z-fold" S/A panels perform
using milled Al piece parts bolted together to provide an
a one-time deployment into a permanently locked position
integrated, mass efficient solution for CYGNSS. Close
planar with the fixed center panels. The S/As are held in
tolerance pins/holes ensure repeatability of structural
place for launch using a cup/cone interface and deployed by
alignment. The microsat's shape is specifically configa combination of flight-proven TiNi Aerospace Frangibolt
ured to allow clear nadir and zenith FOV for the DDMI
actuators and Sierra Nevada Corp. S/A single-axis, locking,
antennas, while its structure integrates the microsat and
spring-loaded hinges.
instrument electronic boards directly by creating avionics and Delay Mapping Receiver (DMR) "bays." The avi3.7. MicrosaTelliTe TherMal
onics and DMR bays form the core of the microsat; all
The CYGNSS Observatory thermal design meets requireother components are mounted to this backbone with
ments to maintain all components within their temperastructural extensions included to accommodate the Al
ture limits during all operational modes by using Southwest
honeycomb-based S/As and DDMI nadir antenna assemblies. The structural configuration
allows easy access to all Observatory
components when the nadir DDMI
Extract
Zenith Antenna
Direct Signal
antenna panel assemblies and microEphemerides
Raw Samples
Acquisition
sat endplates are removed for Observatory AI&T.
Direct Signal
Navigation
The microsat primary structure's
Tracking
Solution
nadir baseplate is the DM mechaniReflection
cal interface for launch. Primary shear
Reflection
Geometry
Tracking
and axial loads are carried by the
Calculation
microsat primary structure, providNadir Antenna
Delay Doppler
ing full compliance with the dynamic
Raw Samples
Map
launch vehicle envelope. Preliminary
FEA of the Observatory results predict
launch loads are well within allowable fIGure 7. GNSS reflectometry dataflow.
JUNE 2013

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