with your host…
Dr. Hyland
489, Lecture 2 - Questions Addressed
What are the life-cycle phases of a space mission and which phase and
point of view will we consider?
What are some systematic approaches to space system design and
analysis?
What approach will we take and what are the steps involved?
How will the class be organized to carry out these steps and what is
the schedule of events?
Suggested reading:
L&W, Chapter 1 (and Chaps. 2 and 3 for more detail)
The Space Mission Life Cycle - Four Phases
Concept exploration: The initial study phase that results in a broad
definition of the mission and its components
Detailed development: The formal design phase which results in a
detailed definition of the system components and, in larger programs,
development of test hardware or software.
Production and deployment: The construction of the ground and
flight hardware and launch of the first full constellation of satellites.
Operations and support: The day-to-day operation of the space
system, its maintenance and support, and finally its de-orbit or
recovery at the end of the mission life.
Various parties & constituencies:
Sponsor: The group that provides and controls the program budget
Operators: The group (typically an applied engineering organization) that
controls and maintains the space and ground assets
End users: Groups who receive and use the products and capability of the
space mission
Developer: The procuring agent, e.g. DOD, NASA or a commercial enterprise
In this class, we concentrate on the Concept Exploration Phase from the
point of view of the Contractor - Developer
Space Mission Analysis and Design Process
- The Eightfold Path Typical
Flow
Phase
Define
Objectives
Step
A. Define broad objectives and
constraints.
B. Estimate quantitative needs
and requirements.
Characterize
the Mission
C. Define alternative mission
concepts.
D. Identify system drivers for
each.
E. Characterize mission
concepts.
Evaluate the
Mission
F. Identify driving
requirements.
G. Evaluate mission utility
H. Define mission concept
(baseline)
Step A: Define Broad Objectives and Constraints
• Define what the mission needs to achieve. What are our
qualitative goals and why?
• The qualitative goals are summarized in the Mission
Statement - a 3 to 4 sentence, crisp and cogent statement
of overall goals.
• This is the all-important starting point. We need to
repeatedly refer back to the Mission Statement to ensure
we remain "on track".
• Usually, missions have several objectives. Besides the
primary objectives, there may be secondary objectives
that can be met by the defined set of equipment, or
additional objectives that may demand more equipment.
•Almost always, missions have a hidden agenda - which consists of secondary
non-technical, objective, frequently of a political, social or cultural nature.
Example:
We will harness the best of current technology to establish a permanent human
presence on the Moon. This paves the way to the human colonization of Mars
and beyond, opening new vistas for science and new resources for the benefit
of humankind.
(Some hidden agendas: Boost space activity, encourage public interest and
support for space exploration, imply economic benefits, etc.)
Step B: Estimate Quantitative Mission Needs and Requirements
•In contrast to Step A, this quantifies how well we wish to achieve the
broad objectives, given our needs, applicable technology and cost
constraints.
•These quantitative requirements should be subject to trade as we go
along. In the early stages of design, it is very important not to set
these requirements "in concrete".
•To transform mission objectives into requirements, look at three broad
areas:
oFunctional requirements, which define how well the system
must perform to meet its objectives.
oOperational requirements, which determine how the system operates and how
users interact with it to achieve its broad objectives.
oConstraints, which limit cost, schedule and implementation techniques
available to the system designer.
•Establishing top-level mission requirements is extremely difficult. Therefore,
we should be prepared to iterate the numerical requirements many times in the
design process.
•The first estimate of requirements should come from the goals and objectives
combined with some view of what is feasible. Then be prepared to iterate.
•Also, look at the "hidden agenda", which contains the implicit goals and
constraints.
Quantitative requirements – Lunar Base Example:
Number of crew that can be sustained on the base = ?
Amount of electrical power required = ?
Fraction of food grown in-situ versus stored supplies =
?
Water supplies required = ?
Surface transportation system required = ?
Maintenance facilities, in-situ resource extraction, etc.
=?
Step C: Define Alternative Mission Concepts
As used here (as distinct from the usage in Larson and Wertz) a mission concept or
architecture is a broad sketch of how the mission will work plus a definition of each
of the principal components of a space mission:
Subject: The thing that interacts with or is sensed by the space payload.
Spacecraft or Space Segment: The self-contained portion that resides in space to carry out
the mission long-term, comprising:
Payload: The hardware and software that sense or interact with the subject.
Spacecraft Bus: Subsystems that support the payload by providing orbit and
attitude maintenance, power, command, telemetry and data handling, structure
and rigidity and temperature control.
Launch System: Includes the launch facility, launch vehicle and any upper stage
required to put the s/c in orbit as well as interfaces payload fairing and ground
support.
Orbit: The spacecraft's trajectory or path. Usually, there is an initial parking orbit, a
transfer orbit and final mission orbit.
Communications Architecture: The arrangement of components that satisfy the
mission's command, control and communication (C3) requirements.
Ground System: Fixed or mobile ground stations used to command and track the
s/c, receive and process data and distribute the information to operators and users.
Mission Operations and Timeline: The overall strategy and schedule for planning,
building, deployment, operations, replacement and end-of-life.
Process for Identifying Alternative Mission Concepts
Five Steps:
1. Identify the mission elements subject to trade
2. Identify the main options for each tradeable element
3. Construct a trade tree of available options.
4. Prune the trade tree by eliminating unrealistic combinations.
5. Look for other alternatives that could substantially influence how
we do the mission
Trade Tree – Basic Concept
Mission Phase
Alternatives for each mission phase
Wheeled
ground
vehicle
Base-tolander
traverse
Cargo
offloading
system
Landerto-base
traverse
Crane+
fork-lift
Wheeled
vehicle
Manipulator arms
Hovercraft
Hover-craft
vehicle
Crane
&
Fork-lift
Ballistic
transfer
Manip.
arms
Crane
&
Fork-lift
Ballistic
transfer
Etc. …
Each line connecting one
“node” at each level marks
out a distinct design
Manip.
arms
Trip Time
Transport
System Mass
Wheeled
vehicle
Hover
-craft
Ballistic
transfer
Tradeoffs – Choosing one branch of the tree (Lander-to-base traverse)
The above diagrams showed fully branched trade trees – i.e., where each option at a given
level branches to all the possible options at the next level. In practice, only the distinct
alternatives at each level are shown. Using this convention, previous diagrams look like:
Alternatives for each mission phase
Mission Phase
Base-tolander
traverse
Cargo
offloading
system
Landerto-base
traverse
Wheeled
ground
vehicle
Crane+
fork-lift
Wheeled
ground
vehicle
Hover-craft
vehicle
Ballistic
transfer
Manipulator
arms
Hover-craft
vehicle
A line connecting one option
at each level marks out a
distinct design
Ballistic
transfer
TRADES LIST
System Element
Trade Options
Base Location on the
Moon
• North pole
• South pole
• Somewhere in between
• In a Mare
• In a crater … etc.
Base topographical
position
• Metal habitats on the surface
• Within a lava tube
• Built into a cave
• Excavated into the side of a
rim-wall crater
Base power system
• Nuclear
• Solar arrays
• Seleno-thermal
TRADES LIST
System Element
Trade Options
Hypogravity
prophylaxis
• Exercise machines
• Pharmacological
• Vibration devices
• Crew rotation to an orbiting
centrifuge
Radiation protection
• Shielding material built into the
habitat walls
• Layer of regolith enclosing the
surface habitats
• Built into a cave
• Excavated into the side of a
rim-wall crater
Water supply
• Collected from surface
deposits at the poles
• Imported
TRADES LIST
System Element
Trade Options
Toxic dust
• Ultra-fine particulate scrubbers
protection/management • Cleansing apparatus adjoining
airlocks
• Improved airlock, spacesuit
seals
Food production
• Hydroponics
• Aeroponics
• Partial reliance on stored food
Base construction
• Pre-fab components from
Earth
• Pre-fab cartons filled with
regolith
• 3-D printing via sintering
regolith
Step D. Identify System Drivers for Each Mission Concept
1. In any real system, overall cost and performance or the design
of detailed components are mainly influenced by a relatively small
number of key parameters or components (which the user or
designer can control) - called drivers
2. In this step, we identify the cost and performance drivers for
each alternative system concept.
3. For most missions, system drivers include the number of satellites,
altitude, power, instrument size and weight
4. In identifying the drivers, we must clearly determine whether we
are looking for drivers of performance, cost, schedule or risk.
5. The results of this step tell us where to put most of our effort
when we do detailed performance estimation for each mission
concept in the next step.
More on “Drivers”
There are two qualitatively distinct Characterizations of a system design:
Quality or Performance: Measures of how well the system performs its mission. “How good it
is going to be”. For the Lunar Base, one such measure could be the amount of in-situ
resources processed per year.
Burden or Penalty: Usually summarized in the cost. Also: Schedule, risk. This is what we have
to pay in order to get the performance offered by the design.
In addition, both of these types of measurements have uncertainty attached to them. The
decision-maker needs to know: How good is it going to be; what’s the price, and how sure
are you of both?
Distinct from Quality and Burden (or Performance and cost) are design parameters – e.g.
maximum range from base, maximum size/weight of cargo per trip, handling parameters,
etc. Performance and cost describe the utility of the design and are functions of the design
parameters.
Design Drivers are those design parameters that most sensitively affect Performance or Cost
(or other selected measures of quality and burden). One says: “This parameter is a cost
driver” or “This is a performance driver”. Not: “Cost is a design driver”, etc.
Step E : Characterize Mission Concepts
1. This step defines in detail what the system is and does. We determine the power, weight
and pointing budgets and decide what to process on the ground or in space.
2. The objective here is to define the mission concepts in enough detail to allow
meaningful evaluations of effectiveness and the relative merits of the various concepts
and architectures.
Process for characterization: There are a variety of processes used - see Larson and
Wertz, Section 2.4 -- but, in the case of LBSS, we suggest you follow the outline provided
by the TECHNICAL APPROACH STUDY PRODUCTS LIST
TECHNICAL APPROACH STUDY PRODUCTS LIST (Exhibit IV)
1. Lunar Base System Description (including at least
the following)
1.1 Lunar Base Introduction
1.2 Overview of all system elements
1.3 Mass lists and power requirements,
including at least current best estimate and
identification of mass and power growth
rationale for margin levels, power budgets
should identify power utilization and margins
1.4 Functionality
1.5 Block diagrams for system and critical
subsystems
(where appropriate)
1.6 Computing needs and margins
1.7 Degree of autonomy
1.8 Identification of all relevant margins, including
mass margin above expected mass including growth
contingency
1.9 Heritage assumptions
1.10 Critical interface properties
1.11 Robustness to off-nominal conditions
1.12 Redundancy, treatment of single point failures
2. Required Infrastructure
2.1 Deep Space Network tracking requirements
2.2 Requirements at the Moon (telecom network is
one example)
3. Operations
3.1 Operations concept
3.2 Operations development
3.3 Command & control team composition and
responsibilities
3.4 Operations margins (for example, up and
downlinks system buffers and required data
download intervals)
3.5 Operations phase flow diagram showing data
and command flow to and from system and
including all Lunar-based elements and
operations teams
4. Technology
4.1 Assumed performance for advanced
technology elements and basis of assumptions
4.2 Fallback options if technology performance
is not achieved and impact
4.3 Required technology demonstrations
5. Cost and Schedule
5.1 Overall mission schedule including
development, integration and test, and
operations
5.2 Overall development cost, and cost
profile per development phase and per NASA
fiscal year
5.3 Assumptions regarding benefits from
duplicating systems flown in technology
demonstrations
5.4 Cost and schedule risk, cost
uncertainty
5.5 Basis of cost (nominal and
uncertainty) and cost estimating
methodology (analogy, parametric,
grass-roots are some examples)
5.6 Identify schedule and cost reserves
5.7 Cost elements (estimates not
required) for technology development and
demonstration and for mission operations
Step F: Identify Driving Requirements
 Having defined and characterized the alternative mission concepts, we return in this step
to our initial quantitative requirements and identify the driving requirements.
 These are the key requirements principally responsible for determining the cost and
complexity of the system.
Some driving requirements might be: Mass of supplies delivered per year, number of crew,
etc.
 This step forces us to get a deep understanding of the relationships between the system
design drivers and the driving requirements. These are the all-important "pressure points" in
the design.
We can use this understanding to see how to improve chances of success by:
Striking a compromise in the initial requirements.
Finding potential technology advances in subsystems areas that relieve the system
drivers.
Identify new approaches that circumvent the drivers.
The end result of this step is to revisit the requirements in the light of the drivers and
revise as necessary.
Step G: Evaluate Mission Utility
In this step and in the light of updated requirements, we quantify how well we are meeting both
the requirements and the broad objectives as a function of cost or key system design choices.
The ideal goal is to provide the decision maker a single chart of potential performance versus
cost __ although in practice we must settle for a good deal less.
A key component of mission analysis is documentation, which provides the organizational
memory of both the results and the reasons for the results. It is critical to understand fully the
choices made, even those that are neither technical nor optimal.
The Mission Analysis Hierarchy
Analysis Type
Goal
Depth
Feasibility
Assessment
To establish whether an objective is achievable and its approximate
degree of complexity
Quick,
limited detail
Sizing Estimate
To estimate basic parameters such as size, weight, power or cost
Point Design
To demonstrate feasibility and establish a baseline for comparison
of alternatives
Trade Study
To establish the relative advantages of alternative approaches or
options
Performance
Assessment
To quantify performance parameters for a given system
Utility Assessment
To quantify how well the system can meet overall mission objectives
More
detailed,
complex
trades
Mission Utility (continued)
For Lunar Base design, we are interested (among other things) in maximizing
autonomy – or minimizing the mass of imported supplies
MC  Mass of Imported cargo needed by the Base per year
to sustain the specified number of crew
So, one desirable (and perhaps an ideal decision-makers chart) characterization of mission
utility might look like:
“Knee of the curve”
MC
Performance
Uncertainty
Cost
Uncertainty
Expenditure for closedsystems technology
MC = Minimum possible mass
of imported cargo
Step H: Define Mission Concept (Baseline)
Having evaluated alternative designs and done a preliminary assessment of mission utility for each, we
select one or more system designs.
A baseline design is a consistent definition of the system that meets most or all of the mission objectives.
A consistent system definition is a single set of values for all of the system parameters that fit with each other
In designing a space system, many parameters are being defined and changed simultaneously.
The baseline provides a temporary milestone against which to measure progress.
It also allows us to limit the number of options that must be evaluated. Rather than looking at
all possible combinations and variations of parameters, it is much more feasible to look at the
impact of varying several of the more important parameters relative to one or two baseline designs.
As the system design matures, the baseline becomes firmer and eventually becomes the system
design.
Example of Mission Baseline Concept:
Design Process and Class Teaming Arrangements
Phase
Define Objectives
Step
A. Define broad objectives
and constraints.
B. Estimate quantitative
needs and requirements.
Characterize the
Mission
C. Define alternative mission
concepts.
D. Identify system drivers for
each.
E. Characterize mission
concepts.
Evaluate the Mission
Class org./Activity
Up through midterm
Steps A and B primarily
determined by Contract
Exhibits.
Class forms Contractor Teams
(CT’s)
Up to midterm, each CT
defines one mission
concept and carries out
steps C through G.
Midterm to FR
PM and APM elected, Mission
Scientist selected,
Technical Groups formed
Refined execution of steps
E, F, G. and H
F. Identify driving
requirements.
G. Evaluate mission utility
Baseline (point) Design
Roadmap of Technology devel
H. Define mission concept
(baseline)
PTAR – Design Concept
Downselect
(choice of baseline concept)
THE END