This article shows how exploring potential conflicts between requirements can anticipate development complexity. It showcases with the differences between the initial concept for the Space Shuttle, what the Space Shuttle had to become to guarantee its funding, and the Soyuz spacecraft. DOI: http://dx.doi.org/10.2514/6.2013-5357

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©2013 Stevens Institute of Technology
Date: 10th of September of 2013
By: Alejandro Salado and Roshanak Nilchiani
Using Requirements-Induced Complexity to Anticipate
Development and Integration Problems: Analysis of
Past Missions
AIAA SPACE 2013 Conference &Exposition
San Diego, CA (USA)

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Was Apollo a failure?

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Is Huble Telescope a failure?

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Was Mars Orbiter a failure?

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Was Space Shuttle a failure?

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What is a failure?
“Lack of success”

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Performance target
Economic budget Time to market

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Schedule
Cost
Performance
Not compliantCompliant
TARGETS
Delay
Overrun
Degraded performance
SUCCESS FAILURE
CANCEL
CANCEL
LOSS

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Lack of funding
Naive estimations
Inexistent technologies
Many customers
Lack of experience
Emergent behavior
Many contractors
Many parts
Impossible testing
Unexpected
dependencies

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Complexity

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𝐻 = −
𝑖=1
𝑛
𝑝𝑖 ∙ 𝑙𝑜𝑔2 𝑝𝑖 𝐻 = −𝐾 ∙
𝑖=1
𝑛
𝑝𝑖 ∙ 𝑙𝑜𝑔𝑗 𝑝𝑖
𝐶 = 𝐶1 + 𝐶2 ∙ 𝐶3
Level of disorder within the system
A measure of the constituent parts and
their interactions

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Structural complexity
Functional
complexity
Organizational
complexity

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Category Indices
Architecture Science payload, complexity, operations complexity, redundancy,
ADCS type, payload instruments, number of thrusters, thermal type,
modularity, design standards.
Contractual Launch approval, type of customer, multiple sponsors, multiple
partners, poor allocation of key functions, lack of well-defines lines of
authority, lack of experience.
Technology Main stage, orbiter, Earth return vehicle, science payload, space
system technology, in situ and sample return technology, sensors and
instruments technology, autonomy technology, heritage, BOL/EOL
power, solar array area, solar array type, battery type, battery
capacity, structures material, ADCS type, solid state memory.
Requirements Cruise stage, entry or aeroassist system, descent and landing,
rendevouz capture, Earth return vehicle, planetary protection,
descent and landing, planetary mobility, ascent vehicle to orbit,
ascent vehicle to upper atmosphere, science payload, complexity,
lifetime, temperature, pressure, radiation, other environment,
spacecraft cost, development time, satellite dry mass, orbit, pointing
accuracy, pointing knowledge, uplink band, downlink rate, conflicts,
incomplete science requirements, multiple launchers.

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We can measure the
complexity of…
Functional architecture
Physical architecture
Project organization
…but we cannot ANTICIPATE the complexity
of the PROBLEM!

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Overall
complexity
Problem
complexity
Organiz.
complexity
Functional
complexity
Structural
complexity
𝐶 𝐶 𝑝, 𝐶𝑓, 𝐶𝑠, 𝐶 𝑜 = −
𝑐 𝑝 𝑐 𝑓 𝑐 𝑠 𝑐 𝑜
𝑃 𝑐 𝑝, 𝑐𝑓, 𝑐 𝑠, 𝑐 𝑜 ∙ 𝑙𝑜𝑔𝑗 𝑃 𝑐 𝑝, 𝑐𝑓, 𝑐 𝑠, 𝑐 𝑜

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Value level
Functions
(Do)
Performance
(Being)
Resources
(Have)
Interaction
(Interact)
Break-event Req. 1
Req. 2
Req. 3
Req. 4 Req. 5
Req. 6
Req. 7
Goal Req. 8 Req. 9
Wish Req. 10 Req. 11
Req. 12
Functional requirements (Do)
What the system does in essence, which includes what it accepts and what it delivers
Performance requirements (Being):
How well the system does it, which includes performance related to functions the
system performs or characteristics of the system on its own, such as –ilities
Resource requirements (Have):
What the system uses to transform what it accepts in what it delivers
Interaction requirements (Interact):
Where the system does it, which includes any type of operation during its life-cycle.
Source: A. Slado, R. Nilchiani. (2014), A Categorization Model of Requirements Based on
Max-Neef’s Model of Human Needs, Syst. Eng., 17: 348-360.

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…two or more requirements compete for the same
resource.
…two or more requirements inject opposing directions in
laws of physics.
...two or more requirements inject opposing directions in
laws of society.
…two or more requirements oblige the system to operate
in two or more phases of matter.
A conflict may exist when…

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𝐶 𝑝 =
𝑖=1
𝑛
𝑝𝑟𝑖 𝑅𝑅, 𝐼𝑅 +
𝑖=1
𝑚
𝑓𝑟𝑖 𝑅𝑅, 𝐼𝑅 ∙ 𝑚𝑒 𝑎 ∙ 𝑟𝑐 𝑏 ∙ 𝑙𝑝 𝑐 ∙ 𝑙𝑠 𝑑
Performance & Functional
Multi-environment
Competition for resources
Conflicting laws of physics
Conflicting laws of society

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GAO reports are too general
Detailed data is confidential
Some data is even classified
Calibration is needed, but…

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Publicly known case-study
VS
Source: Wikipedia

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The spacecraft was a partially reusable human
spaceflight vehicle for Low Earth Orbit, which
resulted from joint NASA and US Air Force
efforts after Apollo. “The vehicle consisted of a
spaceplane for orbit and re-entry, fueled by an
expendable liquid hydrogen/liquid oxygen
tank, with reusable strap-on solid booster
rockets. […] A total of five operational orbiters
were built, and of these, two were destroyed
in accidents.”
“Soyuz is a series of spacecraft initially
designed for the Soviet space programme
and still in service today. […] The Soyuz
was originally built as part of the Soviet
Manned Lunar programme. […] The Soyuz
spacecraft is launched by the Soyuz rocket,
the most frequently used and most reliable
Russian launch vehicle to date.”
Source: Wikipedia

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Human (cheap?) access to LEO
Fast, frequent, cheap, and safe human access to LEO
Fast and frequent access for military satellites
Specific military aerodynamic requirements
Competitive access for communication satellites
Source: Wikipedia

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Spacecraft Fast Frequent Cheap Safe
Military
P/L
Telecom
P/L
Military
aerod.
Space
Shuttle
No No No No Partially Partially Yes
Soyuz
Spacecraft
Unknown No Yes* Yes N/A N/A N/A

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Artificial calibration
Simplified requirement set
Combined funct./perf. requirements
Limitations on the
case study
Subjective assessment
𝐶 𝑝
=
𝑖=1
7
𝑝𝑟/𝑓𝑟𝑖 𝑅𝑅, 𝐼𝑅 ∙ (1 + 𝑒𝑛𝑣𝑖𝑟𝑜𝑛𝑚𝑒𝑛𝑡𝑠)2∙ (1 + 𝑝ℎ𝑦𝑠𝑖𝑐𝑎𝑙 𝑝𝑎𝑟𝑎𝑚)1.3

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ID Element pr/fr(RR,IR) Environments Physical param.
R1 Fast access 3 Space Low prep. time
R2 Frequent
access
3 Space
R3 Cheap access 2 Space Low mass
Low volume
Low prep. time
R4 Safe access 6 Space High mass
High prep. time
R5 Military P/L 6 Space High mass
High volume
R6 Telecom P/L 6 Space High mass
High volume
R7 Military
aerodyn.
4 Atmosphere
Total amount of conflicts 1 3
𝐶 𝑝
=
𝑖=1
7
𝑝𝑟/𝑓𝑟𝑖 𝑅𝑅, 𝐼𝑅 ∙ (1 + 𝑒𝑛𝑣𝑖𝑟𝑜𝑛𝑚𝑒𝑛𝑡𝑠)2
∙ (1 + 𝑝ℎ𝑦𝑠𝑖𝑐𝑎𝑙 𝑝𝑎𝑟𝑎𝑚)1.3

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Alternative R1 R2 R3 R4 R5 R6 R7 Note
A1 X X X X X X X Actual Space Shuttle
A2 X
A3 X X Soyuz Spacecraft
A4 X X X X Initial Space Shuttle
Concept
A5 X X X X X
A6 X X X
A7 X X X X
A8 X X X X X
A9 X X X X X
A10 X X X X X X
𝐶 𝑝
=
𝑖=1
7
𝑝𝑟/𝑓𝑟𝑖 𝑅𝑅, 𝐼𝑅 ∙ (1 + 𝑒𝑛𝑣𝑖𝑟𝑜𝑛𝑚𝑒𝑛𝑡𝑠)2∙ (1 + 𝑝ℎ𝑦𝑠𝑖𝑐𝑎𝑙 𝑝𝑎𝑟𝑎𝑚)1.3

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Actual
Space
Shuttle
Actual
Soyuz
Spacecraft
Initial
Shuttle
Design
0
100
200
300
400
500
600
700
800
A1 A2 A3 A4 A5 A6 A7 A8 A9 A10
ProblemComplexity
Alternatives

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Wrap-up
10/15/201528 ©2011 Stevens Institute of Technology
Failure is multi-dimensional
Conflicting requirements lead to difficulty
Anticipate problem complexity

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Disclaimer:
The views and opinions expressed during this presentation are
those of the authors and do not necessarily reflect the official
position of the Stevens Institute of Technology or any of its
schools.

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©2013 Stevens Institute of Technology
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