multi-attribute tradespace exploration for survivability

Multi-Attribute Tradespace Exploration for Survivability: Application to Satellite Radar

Matthew G. Richards, Ph.D.Matthew G. Richards, Ph.D.Doctoral Research Assistant, Engineering Systems Division

Massachusetts Institute of Technology

David B. SteinDavid B. SteinUndergraduate Research Assistant, SEAri


AIAA Space 2009AIAA Space 2009

Adam M. Ross, Ph.D.Adam M. Ross, Ph.D.Research Scientist, Engineering Systems Division


Daniel E. Hastings, Ph.D.Daniel E. Hastings, Ph.D.Professor, Aeronautics and Astronautics & Engineering Systems


seari.mit.edu © 2008 Massachusetts Institute of Technology 2

Agenda

• Problem Statement• Research Questions• Methodology Overview• Case Application: Satellite Radar• Discussion• Future Work


Temporal system properties known as “ilities” (e.g., flexibility) are a critical design challenge for engineering systems

– Survivability is a critical challenge for aerospace system architecture

Given limitations of survivability engineering for aerospace systems,* need design methodology that:

1. incorporates survivability as an active trade throughout design process2. reflects dynamics of operational environments over entire lifecycle3. captures path dependencies of system vulnerability and resilience4. extends in scope to architecture-level survivability assessments5. takes a value-centric perspective

Opportunity to build on recent research on dynamic tradespace exploration (Ross 2006)

Application of survivability methodology may address critical issue for military space

– Satellite radar architecture development

Problem Statement

*Richards, M., Hastings, D., Rhodes, D., and Weigel, A., “Systems Architecting for Survivability: Limitations of Existing Methods for Aerospace Systems,” 6th Conference on Systems Engineering Research, Los Angeles, CA, April 2008.


Research Questions

1. What is a dynamic, operational, and value-centric definition of survivability for engineering systems?

2. What design principles enable survivability?

3. How can survivability be quantified and used as a decision metric in exploring tradespaces during conceptual design of aerospace systems?

4. For a given space mission, how to evaluate the survivability of alternative system architectures in dynamic disturbance environments?


Definition of SurvivabilityAbility of a system to minimize the impact of finite-duration disturbances on value delivery

through (I) the reduction of the likelihood or magnitude of a disturbance, (II) the satisfaction of a minimally acceptable level of value delivery during and after a disturbance, and/or (III) a timely recovery

time

value

Epoch 1a Epoch 2

original state

disturbance

recov

ery

Epoch: Time period with a fixed context; characterized by static constraints, design concepts, available technologies, and articulated attributes (Ross 2006)

emergency value threshold

required value threshold

permitted recovery time

VxVe

Tr

Epoch 1b

V(t)

disturbance duration

Td

Type I

Type II

degradation

Epoch 3

Type III


Survivability MetricsNeed to evaluate ability of system to (1) minimize utility losses and (2) meet critical value thresholds before, during, and after environmental disturbances

time-weighted utility loss• Difference between design utility,

Uo, and time-weighted average utility

• Internalizes lifecycle degradation• Inspired by Quality Adjusted Life

Years in health economics*

dttUT

UUdl

L )(10

threshold availability• Ratio of time above critical value

thresholds (Vx during baseline Epoch, Ve during disturbance and recovery Epochs) to design life

• Accommodates changing expectations across contexts

dlT T

TATA

desirable attributes: value-based, dynamic, continuous

*Pliskin, J., D. Shepard and M. Weinstein (1980). "Utility Functions for Life Years and Health Status." Operations Research, 28(1): 206-224.

TAT = time above thresholdsTdl = time of design life


Legend

Multi-Attribute Tradespace Exploration (MATE) for Survivability

Define Mission

Enumerate Disturbances

Apply Design Principles

Elicit Attributes

Calculate Utility

Specify Design Vector

Explore Tradespace

Estimate Cost

Model Baseline Performance

Calculate Survivability

Model Lifecycle Performance

Monte Carlo analysis

Evolved

MATE

New


Phases of MATE for Survivability

1. Elicit Value Proposition – Identify mission statement and quantify decision-maker needs during nominal and emergency states.

2. Generate Concepts – Formulate concepts that address decision-maker needs.

3. Characterize Disturbance Environment – Develop concept-neutral models of disturbances in operational environment of proposed systems.

4. Apply Survivability Principles – Incorporate susceptibility reduction, vulnerability reduction, and resilience enhancement strategies into design vector.

5. Model Baseline System Performance – Model and simulate cost and performance of design alternatives to gain an understanding of how decision-maker needs are met in a nominal operational environment.

6. Model Impact of Disturbances on Lifecycle Performance – Model and simulate performance of design alternatives across a representative sample of disturbance encounters to gain an understanding of how decision-maker needs are met in perturbed environments.

7. Apply Survivability Metrics – Compute time-weighted utility loss and threshold availability for each design alternative as summary statistics for system performance across representative operational lives.

8. Explore Tradespace – Perform integrated cost, utility, and survivability trades across design space to identify promising alternatives for more detailed analysis.


Case Application: Satellite Radar

Critical issue in national security space– Unique all-weather surveillance capability– Opportunity for impact given ongoing studies– Rich multi-dimensional tradespace

Unit-of-analysis: SR architecture– Radar payload– Constellation of satellites– Communications network

Availability of data– Systems Engineering Advancement

Research Initiative (SEAri)

To assess potential satellite radar architectures for providing the United States Military a global, all-weather, on-demand capability to track moving ground targets; supporting tactical military operations; maximizing cost-

effectiveness; and surviving disturbances in the natural space environment.

Case Application Goal (CBO 2007)


Phase 1: Elicit Value Proposition

0

0.2

0.4

0.6

0.8

1

0 2 4 6 8

number of target boxes

0

0.2

0.4

0.6

0.8

1

0 20 40 60

minimum detectable velocity (m/s)

0

0.2

0.4

0.6

0.8

1

0 500 1000 1500

minimum radar cross section (dB)

0

0.2

0.4

0.6

0.8

1

0 100 200 300 400

target acquisition time (min)

0

0.2

0.4

0.6

0.8

1

0 20 40 60 80

track life (min)

0

0.2

0.4

0.6

0.8

1

0 100 200 300

tracking latency (min)

ki=3/18

ki=1/18 ki=1/18

ki=1/18

ki=3/18

ki=9/18

Util

ity

1

Attribute value

0

Excluded Attribute Values

Excess Attribute Values (typically assigned Utility = 1)

single-attribute utility curve

Util

ity

1

Attribute value

0

Excluded Attribute Values

Excess Attribute Values (typically assigned Utility = 1)

single-attribute utility curveAttributes: concept-neutral evaluation criteria specified

by a decision maker

sate

llite

rada

r attr

ibut

es

number of target boxes minimum radar cross section (m2) minimum detectable velocity (m/s)

tracking latency (min)track life (min)target acquisition time (min)


Phase 2: Generate Concepts

Peak Transmit Power 1.5 10 20 [KW] 9 9 9 3 1 1 9 9 9 0 1 9 9 9 9 96Radar Bandwidth .5 1 2 [GHz] 9 9 3 3 1 1 9 9 9 0 1 3 3 3 3 66Radar Frequency X UHF 9 9 3 3 1 1 9 9 9 0 1 3 3 3 3 66Physical Antenna Area 10 40 100 200 [m^2] 9 9 9 3 1 1 9 9 9 1 1 9 9 9 9 97Receiver Sats per Tx Sat 0 1 2 3 4 5 9 9 3 3 1 1 9 3 3 1 1 9 9 9 9 79Antenna Type Mechanical vs. AESA 9 9 9 3 3 1 9 9 9 1 1 9 9 9 9 99Satellite Altitude 800 1200 1500 [km] 9 9 3 9 9 3 9 9 9 9 3 1 1 1 1 85Constellation Type 8 Walker IDs 0 0 1 9 9 3 0 0 3 9 3 9 9 9 9 73Comm. Downlink Relay vs. Downlink 0 0 0 0 0 9 0 0 0 0 9 9 9 3 9 48Tactical Downlink Yes vs. No 0 0 0 0 3 9 0 0 0 0 9 9 9 3 9 51Processing Space vs. Ground 0 0 0 1 0 3 1 0 0 0 3 9 9 9 9 44Maneuver Package 1x, 2x, 4x 1 1 1 1 1 0 1 1 1 1 0 9 3 3 3 27Tugable Yes vs. No 1 1 1 1 1 0 1 1 1 1 0 9 9 9 9 45Constellation Option none, long-lead, spare 0 0 0 0 0 0 0 0 0 0 0 9 9 9 9 36Total 65 64 42 39 30 33 66 58 62 23 33 106 100 88 100

Bas

elin

e Cost

Act

ual

Cost

s (E

ra)

Imag

ing L

aten

cy

Res

olu

tion (

Pro

xy)

Tar

get

s per

Pas

s

Fiel

d o

f Reg

ard

Rev

isit F

requen

cy

Definition RangeVariable Name Min

imum

Tar

get

RC

S

DES

IGN

VA

RIA

BLES

MissionATTRIBUTES

ScheduleProgrammaticsCost

Bas

elin

e Sch

edule

Act

ual

Sch

edule

(Era

)

To

tal Im

pact

Tracking Imaging

Min

. D

etec

table

Vel

oci

ty

Num

ber

of

Tar

get

Box

es

Tar

get

Acq

uis

itio

n T

ime

Tar

get

Tra

ck L

ife

Tra

ckin

g L

aten

cy

Design Value Mapping Matrix establishes

traceability between value-space and design-space


Phase 3: Characterize Disturbance Environment

Enumerate disturbances– Orbital debris– Signal attenuation

Gather data on disturbance magnitude and occurrence– NASA ORDEM2000 debris model

• Space Surveillance Network• Haystack and Haystack radar data• Goldstone radar data• Long-Duration Exposure Facility • Hubble Telescope array impact data• Space Shuttle impact data• Mir impact data

Develop system-independent models of disturbance environment

6.5

7

7.5

8

8.5

9

9.5

150 300 450 600 750 900 1050 1200 1350 1500 1650 1800 1950

km/s

Average Orbital Velocity

Spatial Density

10-3

10-2

10-1

100

101

102

10-10

10-8

10-6

10-4

10-2

100

102

debris size (cm)

spat

ial d

ensi

ty (

obje

cts/

km3 )

Debris Spatial Density (800 km circular, i=42.6º)

ORDEM2000 spatial density estimates

fit (piecewise cubic hermite interpolating polynomial)

>10um>100um>1mm>1cm >10cm>1m

altitude (km)

Phase 4: Apply Survivability Principles

design principles concept enhancements design variables (units) atm

osph

eric

dra

g flu

ctua

tions

arc

disc

harg

ing

high

-flux

radi

atio

n

mic

rom

eteo

rites

/ de

bris

sign

al a

ttenu

atio

n

chan

ge in

targ

et c

hara

cter

istic

s

failu

re o

f rel

ay b

ackb

one

loss

of t

actic

al g

roun

d no

de

prevention reduce exposed s/c area antenna area (m^2) 9 0 3 9 0 0 0 0mobilityconcealmentdeterrencepreemption

∆V (m/s) 9 0 3 1 0 0 0 0s/c servicing interface 9 0 1 1 0 0 0 0

ground receiver maneuverability mobile receiver 0 0 0 0 3 0 0 3radiation-hardened electronics hardening (cal/cm^2) 0 3 9 1 0 0 0 0bumper shielding shield thickness (mm) 0 0 0 9 0 0 0 0duplicate critical s/c functions bus redundancy 0 1 9 3 0 0 0 0on-orbit satellite spares extra s/c per orbital plan 0 1 3 3 0 3 0 0multiple ground receivers ground infrastructure level 0 0 0 0 3 0 0 9over-design power generation peak transmit power (kW) 0 0 0 3 9 9 0 0over-design link budget assumed signal loss (dB) 0 0 0 0 9 0 0 0over-design propulsion system ∆V (m/s) 3 0 3 0 3 9 0 0excess on-board data storage s/c data capacity (gbits) 0 0 0 0 0 0 3 3excess constellation capacity number of satellites 0 1 3 9 0 0 0 0interface with airborne assets tactical downlink 3 3 3 3 3 3 3 3

communications downlink 0 0 1 1 9 0 9 3tactical downlink 0 0 1 1 9 0 9 3

spatial separation of spacecraft orbital altitude (km) 1 1 3 3 0 9 0 0spatial separation of s/c orbits number of planes 0 0 3 9 0 1 0 1

failure mode reduction reduce s/c complexity bus redundancy 0 0 9 0 0 0 0 0fail-safe autonomous operations autonomous control 0 0 0 0 3 0 3 3

antenna type 0 0 0 0 3 9 0 0radar bandwidth (GHz) 0 0 0 0 9 3 0 0

retraction of s/c appendages reconfigurable 0 0 9 3 0 0 0 0containment s/c fault monitoring and response autonomous control 0 1 3 1 0 0 0 0replacement rapid reconstitution constellation spares 0 1 3 9 0 0 0 0repair on-orbit-servicing s/c servicing interface 9 1 3 3 0 3 0 0T

III

disturbances

Type

IITy

pe I

s/c maneuveringavoidance

hardness

margin

heterogeneity multiple communication paths

redundancy

flexible sensing operationsevolution

distribution

13

Survivability Variable Mapping Matrix establishes traceability between environment and design-space

Orbit Altitude (km)8001500

Peak Transmit Power (kW)1.51020

Walker ID5/5/19/3/227/3/166/6/5

Radar Bandwidth (MHz)50010002000

Antenna Area (m^2)1040100

Comm. ArchitectureDirect Downlink Only

Relay Backbone

Constellation Spares012

Shield Thickness (mm)1510

finalized design vector (n=3888)

surv

ivab

ility

varia

bles


Phase 5: Model Baseline System Performance

desi

gn

0 20 40 60 80 100 1200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

lifecycle cost ($B)

utili

ty (

dim

ensi

onle

ss)

p y p ( )

012

22 23 24 25 26 27

0.5

0.51

0.52

y(

Baseline tradespace only internalizes costs of survivability features

Satellite Radar Tradespace by Constellation Spares (n=2268)

number of spares

Phase 6: Model Impact of Disturbances on Lifecycle Performance

Tt AU ,

DesignVector

designs

Static SR Model

debris impactscross-sectional area

debris flux (>1mm)

utilityreplace

t

attenuationloss

loss

500 Monte Carlo runs per constellation

UtilityCost

Survivability

Tear Tradespace

1

7

6

5

4

3

2 shieldingdownlink(s)

signal attenuation

t t

Susceptibility

Vulnerability

spare satellites

Resilience

kinetic energy

Pk

0%

5

0%

1

00%

threshold availability (1stpercentile)

10 15 20 25 300.1

0.15

0.2

0.25

0.3

0.35

0.4

lifecycle cost ($B)

utili

ty (

dim

ensi

onle

ss)

Survivability Tradespace - No Filtering

0.9

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1

time-weighted utility loss (99th percentile)threshold availability (1st percentile)

dttUT

UUdl

L )(10

dlT T

MTATA

15


0 20 40 60 80 100 1200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

lifecycle cost ($B)

desi

gn u

tility

(di

men

sion

less

)

Tear Tradespace - all designs (n=2268)

0.9

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1


Phase 7: Apply Survivability Metrics


0.35 0.36 0.37 0.38 0.39 0.4 0.410

50

100

150

200

250

300

350Time-Weighted Average Utility - Design 3109 (n=500)

num

ber

of r

uns

0.95 utility loss


0 20 40 60 80 100 1200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

lifecycle cost ($B)

desi

gn u

tility

(di

men

sion

less

)

Tear Tradespace - all designs (n=2268)

0.9

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1


Phase 8: Explore Tradespacethreshold availability (1

stpercentile)


Magnify Tear Tradespacethreshold availability (1

stpercentile)

20 25 30 35 40 45 50 55 60 650.2

0.3

0.4

0.5

0.6

0.7

0.8

lifecycle cost ($B)

desi

gn u

tility

(di

men

sion

less

)

Tear Tradespace (magnified)

0.9

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1



20 25 30 35 40 45 50 55 60 650.2

0.3

0.4

0.5

0.6

0.7

0.8

lifecycle cost ($B)

desi

gn u

tility

(di

men

sion

less

)

Pareto Efficient Set for Cost, Utility, Utility Loss, and Threshold Availability (magnified)

0.9

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1


Identify Pareto-Efficient Surface of Cost, Utility, and Survivability

2908 2901

3718 3711



20 25 30 35 40 45 50 55 60 650.2

0.3

0.4

0.5

0.6

0.7

0.8

lifecycle cost ($B)

desi

gn u

tility

(di

men

sion

less

)

Pareto Efficient Set for Cost, Utility, Utility Loss, and Threshold Availability (magnified)

0.9

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1


Select Interesting Point Designs

3231

risk averse decision maker

2908 2901

3718 3711




20 25 30 35 40 45 50 55 60 650.2

0.3

0.4

0.5

0.6

0.7

0.8

lifecycle cost ($B)

utili

ty (

dim

ensi

onle

ss)

Filtered by Cost, Utility, Utility Loss, and Threshold Availability

0.9

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1


desi

gn

2908

Extract Survivability Insights from Selected Point Designs

• Survivability insights from selected point designs– Relay backbone critical for achieving continuous threshold availability– Investing in spare satellite(s) minimizes utility losses– Satellite shielding has limited impact in nominal debris environment– Distributed constellation mitigates worst-case risks

Design Vector ID 2908 2901 3231 3718 3711 orbit altitude (km) Walker constellation 9/3/2 9/3/2 27/3/1 66/6/5 66/6/5 transmit frequency (GHz) antenna area (m^2) 100 100 40 antenna type radar bandwidth (MHz) peak transmit power (kW) tugable comm. architecture direct relay relay direct relay tactical link shield thickness (mm) 1 1 10satellite spares 0 2 2 0 2 lifecycle cost ($B) 22.3 25.8 31.2 54.8 57.4 utility 0.51 0.51 0.47 0.74 0.74 utility loss (95th) 0.09 0.01 0.00 0.06 0.00 utility loss (99th) 0.12 0.02 0.00 0.07 0.01threshold availability (1st) 0.95 1.00 1.00 0.95 1.00

1

20 20

yes yes

no no

40AESA AESA2000 2000

1500 1500

10 10


1500 1500

10 1040

AESA AESA2000 2000

1

20 20

yes yes

no no


1

no no20 20

yes yes


1500 1500

10 10

2901

3231

3718 3711



20 25 30 35 40 45 50 55 60 650.2

0.3

0.4

0.5

0.6

0.7

0.8

lifecycle cost ($B)

utili

ty (

dim

ensi

onle

ss)


0.9

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1


desi

gn

2908




1

20 20

yes yes

no no


1500 1500

10 10


1500 1500

10 1040

AESA AESA2000 2000

1

20 20

yes yes

no no2901

3231

3718 3711



20 25 30 35 40 45 50 55 60 650.2

0.3

0.4

0.5

0.6

0.7

0.8

lifecycle cost ($B)

utili

ty (

dim

ensi

onle

ss)


0.9

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1


desi

gn

2908




1

20 20

yes yes

no no


1500 1500

10 10

2901

3231

3718 3711


Methodological Insights

MATE for Survivability incorporates survivability as a decision metric into conceptual design – Design principles reveal latent survivability trades and inform selection

of survivability design variables– Survivability metrics enable discrimination among thousands of design

alternatives

Implementation considerations– Subject percentile reporting levels to sensitivity analysis– Balance broad exploration with selected of individual point designs

MATE for Survivability improves on existing tradespace approaches– Pareto front in traditional MATE study excludes most survivable designs– Evaluates survivability implications for selection of baseline architecture


Future Work

• Methodological improvements– Parameterize concept-of-operations in design vector

– Extend scope for systems-of-systems (SoS) engineering

• Apply MATE for Survivability to additional systems for prescriptive insights

water distributionpower distribution transportation communications

Questions?


Limitations of Existing Metrics

• Construct validity• Binary assessment criteria

Inherent Availability

• Survivability preferences confounded with availability and capability

Mission Effectiveness

• Construct validity• Binary assessment criteria• Time to failure assumed as exponential density function

Reliability Function

(aka Survival Function)

• Binary assessment criteria• Assumes independence among shot and mission outcomes

Campaign Survivability

• Binary assessment criteria fails to internalize graceful degradation

Engagement Survivability

MTBFtetFtR /)(1)(

HKHKS PPPP 11

(Ball 2003; Blanchard and Fabrycky 2006)

MTTRMTBFMTBFAi

NK

NS PPCS )1(

t = operating time

MTBF = mean time between failure

MTTR = mean time to repair

S = survive, K = kill, H = hit

N = number of engagements

CapabilityPAMoME Si


Need Measures of Central Tendency Across Runs

0 2 4 6 8 100

0.05

0.1

0.15

0.2

0.25

time (years)

utili

ty (

dim

ensi

onle

ss)

DV(19) - Run(2/500)

V(t)

Threshold

0 2 4 6 8 100

0.05

0.1

0.15

0.2

0.25

time (years)

utili

ty (

dim

ensi

onle

ss)

DV(19) - Run(1/500)

V(t)

Threshold

0 2 4 6 8 100

0.05

0.1

0.15

0.2

0.25

time (years)

utili

ty (

dim

ensi

onle

ss)

DV(19) - Run(89/500)

V(t)

Threshold

0 2 4 6 8 100

0.05

0.1

0.15

0.2

0.25

time (years)

utili

ty (

dim

ensi

onle

ss)

DV(1137) - Run(3/500)

V(t)

Threshold

0 2 4 6 8 100

0.05

0.1

0.15

0.2

0.25

time (years)

utili

ty (

dim

ensi

onle

ss)

DV(1137) - Run(20/500)

V(t)

Threshold

0 2 4 6 8 100

0.05

0.1

0.15

0.2

0.25

time (years)ut

ility

(di

men

sion

less

)

DV(1137) - Run(426/500)

V(t)

Threshold


General Conclusions

• Definition of baseline system architecture should include survivability considerations for efficient mitigation of disturbances

• Uniting tradespace exploration with survivability analysisgenerates knowledge that may ultimately lead to better design decisions

• Importance of survivability will grow as critical infrastructures become increasingly large-scale, long-lived, and interdependent

• Conceptualization of survivability for engineering systems is a solution-generating and decision-making framework, enabling discovery of systems robust to finite-duration disturbances

multi-attribute tradespace exploration for survivability

Documents