An Integrated Software Defined Radio Navigation

System for Space Navigation

Alison Brown and Ben Mathewswww.navsys.com

ION GNSS 2007Session C5: Software Receivers 1

September 28, 2007

Problem Statement• Existing space-qualified attitude control and

navigation solutions are not suitable for deployment on microsatellites due to size, weight, power, and cost constraints

• Small spacecraft require higher bandwidth attitude control authority due to faster response needed to counter disturbance forces

• A small, flexible, and low-cost attitude control and navigation solution is required to support future microsatellite missions and applications

Benefits of a Software Defined Radio (SDR) Navigation Approach

Flexible waveform processing

using FPGAs

Multiple Frequencies supported by

flexible RF/Digital

Transceivers

Software control of SDR configuration and operation

Easy integration of

additional sensors and components

Integrated GPS / INS / Star-Tracker

GPS Antenna

ADL855 PC-104(Windows, RTX)

PC-104 CAC Board

PC-104 GPS DAE (L1) /

DAE Passive Adptr

Parvus SpacePCPC-104+

(400 MHz Celeron)

Ethernet

RF

1 PPS

Spacecraft I/F

NAVSYS Interface ModuleSPI

Microcosm

NAVSYS

MicroMakStar Sensor

ADL PC-104Power Supply

(5V & 12V Out)

Fujitsu Hard Drive(80 GB)

Oven Controlled Crystal Oscillator

12 VDCPower

MEMS IMU

PC/104 SDR Components

DAE Adapter and GPS DAE

PC/104+ CACXilxinx 2000FPGAs

P502 PowerPCMain Board

GMS IO Board

NAVSYS CustomPC/104+ AdapterBoard

NAVSYS Oscillator Board

Mounting Plate

GPS DAE Board

CAC FPGABoard

Pentium IVSBC

CristaMEMS IMU

MicroMakStar-Tracker

Digital Antenna Element and Correlator Accelerator Card

• Digital Antenna Element• Front-end down-conversion

and digitization• Frequency/waveform agile• Beamsteering/Beamforming

• GPS Correlator Accelerator Card• Firmware-based correlations under SW control• Can support other signal processing besides GPS• Snapshot acquisition for external post-processing

Integrated Navigation Filter• Must gracefully fuse data from multiple and

disparate sensors into an integration attitude and navigation solution• GPS – Satellite pseudorange / carrier-phase

measurements• Star-Tracker – Low-rate, high precision

attitude estimates for in-orbit operations• IMU – High rate inertial information during

orbit insertion and augmentation of star-tracker during satellite in-orbit maneuvering

InterNav Modular Inertial Navigation Product

• Integrates GPS, inertial, and a variety of other sensor data• PR/DR or Pos/Vel• ∆θ, ∆V from gyros and accels

• Modular design facilitates integration of different sensors• Was modified under this effort to integrate star-

tracker data into the combined navigation solution• Performs inertial navigation functions• Uses Kalman Filter for applying GPS updates• Can be configured to optimize performance

based on sensor characteristics

Filter Implementation

v∆

θ∆

v∆

NbQ

INSX G INSX G∆

NAVSYS Advanced GPS Hybrid Simulator (AGHS)

• Simulator control provided through Matlab/Simulink interface

• Open architecture to facilitate integration with trajectory generators

• Precise digital signal generation under software control

• Multiple antenna elements for wavefront simulation (8+)

• Jammer simulation• Simulated inertial output• Simulated star-tracker output

AGHS Simulink Interface

• Provides a user-friendly interface for simulation control and analysis

• Open, flexible architecture supports easy modification for prototyping – This architecture was leveraged for rapid insertion of star-tracker simulation capability

AGHS Test Set-Up

AGHS HWIL Test Architecture

D/A

and Tune to RF

Phase-C

oherent Mixing

AG

HS

Control Logic

GPS Tracking Results

Integrated Filter Test Results

Importance of Star-Tracker Input

2000 2200 2400 2600 2800 3000 3200-8

-6

-4

-2

0

2

4

6

8

10x 105

Atti

tude

Erro

r [m

icro

-rad]

Attitude Error: InterNav GPS/INS/ST vs. INSSIM Trajectory Truth

Receiver Time Since T0 = 475269.990 (s)

ΨxΨyΨzσ-xσ-yσ-zRequired

With Star-Tracker Without Star-Tracker

Conclusions

• Prototype integrated space navigation receiver has been developed and tested

• Benefits of star-tracker integration into navigation filter have been shown

• Provides an affordable navigation option for low-cost microsatellite missions

• Future efforts are focusing on radiation hardening and incorporation of NAVSYS IMU

Questions?