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Simulation, Test and Verification of SHEFEX-2 Hybrid Navigation System

Dr. Stephan Theil (DLR Institute of Space Systems, Bremen, Germany)Dr. Andreas Himmler (dSPACE GmbH Paderborn, Germany)Stephen Steffes, Malak Samaan and Michael Conradt(DLR Institute of Space Systems, Bremen)

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SHEFEX2

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HNS Motivation

Some passenger experiments require attitude accuracy of 0.17° at entryOnboard navigation system

Equipped with decoupled GPS and IMUIMU (ISI DMARS-R) can achieve 0.3° alignment accuracyHigh vibrations cause the INS to drift 3° before entry

Hybrid navigation system is developed to meet the needs of the passenger experiments by fusing GPS, IMU and Star Tracker measurements

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Flight Profile

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Sensors

Inertial Measurement Unit (IMU)iIMU-FCAI-MDS3 fiber optical gyros and 3 servo-accelerometersGyro: 1°/hr bias, 0.03°/√hrAccel: 2mg bias, 50μg/√Hz

GPS ReceiverPhoenix-HD receiverPVT Accuracy: 2-50m, 0.05m/s

Star Tracker (STR)Developed by DLR Bremen3-axis attitude accuracy: 0.1°

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Hybrid Navigation System Concept

STR

GPS

IMUState

Integration

KF Update

KF Propagate

Internal Clock

Acquisition Aiding

Attitude @2Hz

Trigger @2Hz

Trigger @500Hz

PPS

ΔV, Δθ @500Hz

Pos, Vel, Time @1Hz

Pos, Vel @1Hz

Δt @500HzGPS, STR Times

Error estimates

Nav solution

Δt, ΔV, Δθ

Pos, Vel, Att

Navigation Filter

Navigation Computer

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Software Simulation

Purpose: test functionality, measure system performance, stress the system, debugMATLAB®/Simulink® is an excellent simulation tool and provides good visibility of models and flight code

Simulation SetupUsing nominal flight dynamics from rocket developerContains high fidelity models of IMU, GPS and Star Tracker

Generic models of IMU and Star Tracker with instrument specific parametersGPS model specifically designed to model Phoenix-HD

Flight software embedded with s-function

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Hardware-In-the-Loop Testing

Purpose: test interfaces, test unmodeled instrument details, use real time, debugdSPACE allows model development using Simulink, provides hardware API, range of hardware interfacesControlDesk provides visibility of dSPACE simulation

Hardware-In-the-Loop SetupSpirent GSS7700 simulates analog GPS antenna input3-axis rotation table simulates flight rotations for IMUJenoptik Optical Sky Stimulator provides images for star tracker camera

Hardware testing is done in 4 phasesProgressively swapping software model for flight hardware

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dSPACE

HNS hardware-in-the-loop setup:Main processor board (DS1006)

Controls mission and instrument simulationsSynchronizes to external trigger

Digital interface board (DS2202)Interface to external TTL signals

Serial interface board (DS4201)Serial interface for all sensor models

Ethernet interface board (DS4504)Remote trajectory to Spirent GPS simulator

Scramnet interface board (DS4503)Rotation table control

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Benefits of Using dSPACE

Modular system for all sizes of hardware-in-the-loop systemsProduct range: from component test systems up to turn-key integration test systemsBased on full range of product-level componentsAny customer-specific solutions, if requiredEasy to configure, upgrade and adaptWorldwide support by local engineers in major countries

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Working with dSPACEReal-Time Interface – RTI

Automatic implementation of MATLAB®/Simulink®/Stateflow®

models on dSPACE hardwareGraphical configuration of all I/O interfaces in the Simulink® block diagramAutomatic real-time code generation from the block diagram and download to the dSPACE prototyping hardwareEasy and safe to use due to automatic consistency checks

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Working with dSPACE: ControlDeskManaging and Instrumenting Experiments

Creation of virtual instrument panels by drag & dropReal-time data capture and online parameter tuningGraphical experiment and hardware managementEasy access to all model variables

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Software Simulation Results

Quick simulation development due to Matlab/Simulink heritageModels were kept modular to easily reuse in dSPACE simulationNavigation flight code wrapped in s-function and seamlessly integrated

On-going development and testing

Initial software performance results:

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Hardware-In-the-Loop Development

Quick dSPACE simulation development due to model reuseMinor problems synchronizing dSPACE with SpirentCustom software needed for Optical Sky Simulator to remotely control image in real timeRotation table control not yet implemented

HNS hardware interface software still under development

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Conclusions & Outlook

Status:On-going H/W integration and testingH/W delivery in June 2010Launch expected in winter 2011

Expected results:Confirmation of predicted performanceRecorded flight data for further development

Goal:Develop autonomous Hybrid Navigation System for sounding rockets, hypersonic flight and space transportation systems