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NEXUS Spacecraft Integrated Modeling and Simulation
NEXUS Spacecraft Integrated Modeling and Simulation
Background and Motivation
Background and Motivation
Nexus Case Study
Nexus Case Study
Nexus Integrated Model
Nexus Integrated Model
Nexus Block Diagram
Nexus Block Diagram
Initial Performance Assessment Jz(po)
Initial Performance Assessment Jz(po)
Nexus Sensitivity Analysis
Nexus Sensitivity Analysis
2D-Isoperformance Analysis
2D-Isoperformance Analysis
Multiobjective Design Optimization
Multiobjective Design Optimization
Nexus Multivariable Isoperformance np=10
Nexus Multivariable Isoperformance np=10
Nexus Error Budgeting
Nexus Error Budgeting
Nexus Initial po vs
Nexus Initial po vs

Презентация на тему: «NEXUS Spacecraft Integrated Modeling and Simulation». Автор: Olivier Ladislas de Weck. Файл: «NEXUS Spacecraft Integrated Modeling and Simulation.ppt». Размер zip-архива: 772 КБ.

NEXUS Spacecraft Integrated Modeling and Simulation

содержание презентации «NEXUS Spacecraft Integrated Modeling and Simulation.ppt»
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1 NEXUS Spacecraft Integrated Modeling and Simulation

NEXUS Spacecraft Integrated Modeling and Simulation

Olivier L. de Weck July 2001

Sponsor: Gary E. Mosier, NASA GSFC

2 Background and Motivation

Background and Motivation

Subsystem Requirements

Science Requirements

Functional Requirements

HST - 1990

Requirements Flowdown Process

5 year wide-angle astro- metric accuracy of 4 masec for 20th Magnitude stars

Science Interferometer OPD < 10 nm RMS

Fringe Visibility > 0.8 for astrometry

Space-Based Observatory Multipurpose UV/Visual/IR Imaging and Spectroscopy

“Performance”

NGST-2008

SIM-2006

NEXUS-2004

TPF-2011

Deployable Cold Optics NGST Precursor Mission

Faint Star Interferometer Precision Astrometry

Nulling Interferometer Planet Detection

Lightweight 8m-Optics IR Deep Field Observations

Achieve stringent requirements in a cost-effective manner with predictable risk level.

3 Nexus Case Study

Nexus Case Study

Nexus Spacecraft Concept

Demonstrate the usefulness of Isoperformance on a realistic conceptual design model of a high-performance spacecraft

Integrated Modeling Nexus Block Diagram Baseline Performance Assessment Sensitivity Analysis Isoperformance Analysis (2) Multiobjective Optimization Error Budgeting

Purpose of this case study:

on-orbit configuration

launch configuration

The following results are shown:

NGST Precursor Mission 2.8 m diameter aperture Mass: 752.5 kg Cost: 105.88 M$ (FY00) Target Orbit: L2 Sun/Earth Projected Launch: 2004

Details are contained in CH7

OTA

Sunshield

Instrument Module

Deployable PM petal

Delta II Fairing

Pro/E models © NASA GSFC

4 Nexus Integrated Model

Nexus Integrated Model

Legend:

Spacecraft bus (84)

Design Parameters

8 m2 solar panel

m_bus

(I/O Nodes)

RWA and hex isolator (79-83)

sunshield

I_ss

K_rISO

2 fixed PM petals

Instrument

(149,169)

(207)

K_yPM

Cassegrain Telescope: PM (2.8 m) PM f/# 1.25 SM (0.27 m) f/24 OTA

SM spider

t_sp

deployable PM petal (129)

SM (202)

K_zpet

m_SM

Structural Model (FEM) (Nastran, IMOS)

5 Nexus Block Diagram

Nexus Block Diagram

Number of performances: nz=2 Number of design parameters: np=25

Number of states ns= 320 Number of disturbance sources: nd=4

6 Initial Performance Assessment Jz(po)

Initial Performance Assessment Jz(po)

23.1 Hz

Critical Mode

Time [sec]

7 Nexus Sensitivity Analysis

Nexus Sensitivity Analysis

Graphical Representation of Jacobian evaluated at design po, normalized for comparison.

RMMS WFE most sensitive to: Ru - upper op wheel speed [RPM] Sst - star track noise 1s [asec] K_rISO - isolator joint stiffness [Nm/rad] K_zpet - deploy petal stiffness [N/m]

RSS LOS most sensitive to: Ud - dynamic wheel imbalance [gcm2] K_rISO - isolator joint stiffness [Nm/rad] zeta - proportional damping ratio [-] Mgs - guide star magnitude [mag] Kcf - FSM controller gain [-]

8 2D-Isoperformance Analysis

2D-Isoperformance Analysis

joint

isolator strut

CAD Model

E-wheel

K_rISO [Nm/rad]

Ud=mrd [gcm2]

9 Multiobjective Design Optimization

Multiobjective Design Optimization

Performance Jz(piso) =Jz,req

Cost Objectives Jc

Risk Objectives Jr

Control effort Implementation Cost (mid-bound) System Mass Dissipated Power Closeness to “cheap” bound

Stability Margins (SISO) max SV of sensitivity function / mvar Nyquist Sensitivity of performance to parameter variations Knowledge Error

Since solutions piso in the isoperformance set I do not distinguish them- selves via their performance, we may satisfy additional objectives:

Can scalarize NLP problem with preference order (weightings) h,Qcc,Qrr as shown on the left or can look for efficient set E of pareto-optimal solutions, piso*.

10 Nexus Multivariable Isoperformance np=10

Nexus Multivariable Isoperformance np=10

Design A

Design B

Design C

Performance

Cost and Risk Objectives

Pareto-Optimal Designs p*iso

Best “mid-range” compromise

Smallest FSM control gain

Smallest performance uncertainty

Jz,1 Jz,2 Jc,1 Jc,2 Jr,1

Design A 20.0000 5.2013 0.6324 0.4668 +/- 14.3218 % Design B 20.0012 5.0253 0.8960 0.0017 +/- 8.7883 % Design C 20.0001 4.8559 1.5627 1.0000 +/- 5.3067 %

11 Nexus Error Budgeting

Nexus Error Budgeting

LTI System , Jz,req, p_bounds, p_nom

(Design A)

Isoperformance Toolbox

C

A

Error Source Contributions

Plot Error Contribution Sphere

Budget

B

Allocated Budget

piso

Capability Budget

Note: ACS sensor noise contributions not shown

var_contr

0.8

0.6

FGS

0.4

0.2

0

0

0.2

0.2

0.4

0.4

0.6

0.6

0.8

0.8

RWA

Cryo

LOS Budget

Capability

12 Nexus Initial po vs

Nexus Initial po vs

Final Design p**iso

Initial

Parameters

Final

Ru 3000 3845 [RPM] Us 1.8 1.45 [gcm] Ud 60 47.2 [gcm2] Qc 0.005 0.014 [-] Tgs 0.040 0.196 [sec] KrISO 3000 2546 [Nm/rad] Kzpet 0.9E+8 8.9E+8 [N/m] tsp 0.003 0.003 [m] Mgs 15 18.6 [Mag] Kcf 2E+3 4.7E+5 [-]

Improvements are achieved by a well balanced mix of changes in the disturbance parameters, structural redesign and increase in control gain of the FSM fine pointing loop.

secondary hub

tsp

SM

Dsp

Deployable segment

Kzpet

+Y

SM Spider Support

+Z

+X

Spider wall thickness

50

Centroid Jitter on Focal Plane [RSS LOS]

40

T=5 sec

30

20

10

Initial: 14.97

0

m

m

m

m

Centroid Y

Final: 5.155

-10

-20

-30

-40

-50

Centroid X

-50

0

50

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