1 Performance Analysis of the NGST “Yardstick” Concept via Integrated Modeling Gary Mosier, Keith Parrish, Michael Femiano NASA Goddard Space Flight Center David Redding, Andrew Kissil, Miltiadis Papalexandris Jet Propulsion Laboratory Larry Craig, Tim Page, Richard Shunk NASA Marshall Space Flight Center August 2000
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Performance Analysis of the NGST “Yardstick” Concept Performance Analysis of the NGST “Yardstick” Concept via Integrated Modeling ... solutions for active damping and vibration
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1
Performance Analysis of the NGST “Yardstick”Concept via Integrated Modeling
Gary Mosier, Keith Parrish, Michael FemianoNASA Goddard Space Flight Center
David Redding, Andrew Kissil, Miltiadis PapalexandrisJet Propulsion Laboratory
Larry Craig, Tim Page, Richard ShunkNASA Marshall Space Flight Center
August 2000
2
NGST “Yardstick” Concept
“Open” telescope (no external baffling) allows passive cooling to 50K
Deployable secondarymirror
Berylliumprimary mirror
Space support module (attitude control, communications, power, data handling) is on warm side
ScienceInstruments
Large (200m2) deployable sunshield protects from sun, earth and moon
Isolation truss
3
X
Y Z
sunshield long booms
sunshield short booms
Integrated Science Instrument Module
spacecraft module
isolation truss
OTA
Observatory FEM
Model contains ~5400 DOF
4
IMOS Environment
DESIGNPARAMETERS
MODELINGTOOLS
SYSTEM MODEL
THERMALDISTURBANCES
MECHANICALDISTURBANCES
ControlDesign
StructureDesign
OpticsDesign
MATLABIMOS FEMNASTRAN
STRUCTURE
CONTROLS
OPTICS
SCIENCEMETRICS
TRASYS /SINDA
SYSTEM PERFORMANCE
MATLAB
ENVIRONMENT
OPTICALERRORS
∫
MACOS
Integrated model was applied to investigate three “focus” problems during concept development phase:
• thermal-elastic deformation of OTA
• line-of-sight stability (jitter)
• wavefront sensing and control (not really addressed here)
5
System Error Budget Overview
System imaging performance
Straylight
Wide-anglescatter
Detectioneffects
Jitter
Post-WFS&Coptical aberrations
OTA figure& alignment
IM figure& alignment
OTA actuatorperformance
Imagingperformance
OTA structure OTA optics IM structure IM opticsOTA mechanical
Encircled Energy
WF error
WFS&C
WF C subsystemWFE budget
SystemEE , SR budget
Non-WF C subsystem s WFE budget s
6
Thermal-Elastic Analysis
• Linear Systems Model
• Optics Model
• Thermal Model
• OTA FEM
• Results for launch-to-orbit cooldown
• Results for transient (attitude re-orientation)
• Results for transient with active thermal control
7
Linear Error Model for Thermal Analysis
Linear optical model
w0 = Cx x + Cu u0
WF sensing
west = w0 + dwest
Control
u1 = -G west + du
G = Cu+ = [Cu
TCu] -1 Cu
w
xrb
xfig
udm
useg x =
xsegrot
xsegtrans
xIMrot
xIMtrans
xfig
u =
usegrot
usegtrans
uSM
udm
w =
w1
w2
wN
Alignment and figure states
Wavefront sampled atN discrete points in theexit pupil
Optical controls
8
MACOS Ray Trace Model
9
MACOS Spot Diagram
10
Wavefront Error – Design Residual
11
Wavefront Error – Segment Tilt
12
Wavefront Error – FEM Node Translation
13
X
Y
Z
OTA FEM
• 2.00mm thick face sheet by 4cm deep core orthogridberyllium mirror shell
•cells are 14.5 cm on a side equilateral triangles,cell wall are 1.00 mm thick
• RBE2s used to attach SIkinematically to center main ring instead of CELAS
• Three OTA to S/C I/F points instead of four
•The petal reaction structure is a beryllium frame-work of I-beams
• The center segment reaction structure is a flat Beryllium frame with a 1.3M dia inner ring. The frame is composed of a 152 mm deep I-beam inner ring and 152mm by 100mm wide box section outer ring and spokes.
• recover 1044 DOFs (344 nodes on PM, translation only, plus SM and SI)
Mapping made possible by one-to-one nodalization !!!
16
Computing the Transformation from Nodal Temperatures to Displacements
λ Net Force Balance: {rnet} = 0 = -Ku + {rTemp}
Where {rTemp} = ∫ BT E {ε 0} dV = Ku
B = standard strain-displacement matrix{ε0}= temperature induced strain vector, f (α,temp)
λ We can factor out nodal temperatures, generating a temp to load transformation matrix
– {rTemp} = {rg} = [Agg] {tg}
Where {tg} = nodal temperature (and/or gradient) vector (g-size)
{rg} = nodal force (and/or moment) vector (g-size)λ Reduce [Agg] to f-set size and transform to Local (NASTRAN global) system
– [Afg] = [Tfg] [Agg]
λ Premultipy by the flexibility matrix [Kff]-1 to get the temperature to displacement transformation matrix G
– [Gfg] = [Kff]-1 [Afg]
λ Expand to g-set, and transform back to the basic coordinate system
– [Ggg] = [Tfg]T [Gfg] or
– [Ggg] = [Tfg]T [Kff]-1 [Tfg] [Agg]
λ So we have the temperature to displacement transformation matrix
– {ug} = [Ggg] {tg}
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Steady State Wavefront Error with Control
On-Orbit Thermal
Wav
efro
nt
WFE=4.6271e-0520 40 60 80 100
20
40
60
80
100
Ima
ge
Strehl=0.006111120 40 60 80 100 120
20
40
60
80
100
120
After Segment Control
WFE=2.3886e-0720 40 60 80 100
20
40
60
80
100
Strehl=0.6055520 40 60 80 100 120
20
40
60
80
100
120
After DM Control
WFE=2.4702e-0820 40 60 80 100
20
40
60
80
100
Strehl=1.011720 40 60 80 100 120
20
40
60
80
100
120
Limited DM Control
WFE=7.7059e-0820 40 60 80 100
20
40
60
80
100
Strehl=0.9647220 40 60 80 100 120
20
40
60
80
100
120
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Thermal Transient following 22.5 degree slew
4 8 . 8
4 9 . 0
4 9 . 2
4 9 . 4
4 9 . 6
4 9 . 8
5 0 . 0
5 0 . 2
0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0
D u r a t i o n ( h r s )
Tem
pera
ture
(K
)
2 9 . 5
2 9 . 6
2 9 . 7
2 9 . 8
2 9 . 9
3 0 . 0
3 0 . 1
3 0 . 2
3 0 . 3
0 2 0 40 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0
D u r a t i o n ( h r s )
Tem
pera
ture
(K)
Cold Petal(space-side)
Hot Petal(sun-side)
∆T = -0.8 K
∆T = -1.3 K
• Initial attitude has sun normal to sunshield• Final attitude is 22.5 degree pitch away from sun• Thermal equilibrium takes DAYS to reach
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Thermal Transient Wavefront Error – no Control
0 5 10 15 20 25 300
1
2
3
4x 10
-7 Wavefront Error vs. Time
Time (hr)
WF
E R
MS
(m
)
0 5 10 15 20 25 300.7
0.8
0.9
1Strehl Ratio vs. Time
Time (hr)
Str
eh
l
20
Thermal Transient Wavefront Error with Control
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Jitter Analysis
• Pointing Control Architecture
• Linear Systems Model
• Disturbance Model
• Compensation Model
• Results for parametric studies
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The CSI Challenge for NGST
frequency
ACS 0.025 Hz BW
Disturbances >400 Hz
FSM 2 Hz BW
Structure
sunshieldmodes
isolation truss andSM support modes
higher ordermodes
• Lightweight, flexible structure with very low damping limits ACS bandwidth• FSM bandwidth limited due to guiding sensor noise• Thermal environment presents challenges to “smart structures” solutions for active damping and vibration suppression
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System Level Block Diagram
Optics
Wavefront
LOS Control
ExternalTorque
Dynamics
Centroid
ACSCommands
ACS
6 4
3
74
74
2
72
72
72
6
6
3
3
2
VibrationIsolation
ACS uses wheels,gyros & trackers
ImageStabilizationloop usesNIR & FSM
Vibration Isolationhas not beendesigned in detail;model is a LP filterapproximation
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State-Space Model
111
11111
XCY
UBXAX
=
+=&
222
22222
XCY
UBXAX
=
+=&
333
33333
XCY
UBXAX
=
+=&
444
44444
XCY
UBXAX
=
+=&
1U
KFη++
+
GSη
RWℑ
W
C
2U
3U
4U2Y
1Y
3Y
4Y
+
+
4K
11K
12K
22K
21K
3K
+
+
+
++
CXYBUAXX
=+=&
ℑ
=
RW
KF
GS
U ηη
=
4
3
2
1
X
XX
X
X
=
CW
Y
+
=
4000000
00
34
3143
222221212
411
ACBACKB
CKBACKBCBA
A
=
4
3
2
0000
00000
BB
BB
=
0000
222121
212111
CKCKCKCK
C
rays
T
W NWW
=σ CCTC =σ
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Dynamics Model Sensor & Actuator Locations
ACS (10291)
ISIM (825)
SM (829)
PM (900-908)
These grid points are locatedat the center of the primary andin a circle with radius 2.8 meters,connected to mirror grid pointsby RBE2 elements
ST, IRU, RWAare co-located
FSM, DM, otheroptics are co-located
Model size is~ 5400 DOF;only 71 DOFare requiredfor jitter model