Презентация на тему «NEXUS Spacecraft Integrated Modeling and Simulation»

NEXUS Spacecraft Integrated Modeling and Simulation

Olivier L. de Weck July 2001

Sponsor: Gary E. Mosier, NASA GSFC

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.

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

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)

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

Initial Performance Assessment Jz(po)

23.1 Hz

Critical Mode

Time [sec]

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 [-]

2D-Isoperformance Analysis

joint

isolator strut

CAD Model

E-wheel

K_rISO [Nm/rad]

Ud=mrd [gcm2]

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*.

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 %

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

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