Space Station Design Workshop 2006 - IRS

Transcrição

Institut für
Raumfahrtsysteme
Space Station Design Workshop 2006
International and Interdisciplinary
Student Education at the IRS
Institute of Space Systems (IRS)
Universität Stuttgart, Germany
© Oktober 2006
SSDW 2006 PEOPLE
Staff
Prof. Dr. Ernst Messerschmid
Jürgen Schlutz
Florian Renk
Britta Ganzer
Marcel Düring
Ilse Müllner-Korell
Jochen Noll
Kornelia Stubicar
Invited Guests
Dr. Rudolf Benz (EADS Astrium)
Dr. Reinhold Bertrand (ESA/ESOC)
Jason Held (ACFR, University of Sydney)
Prof. Dr. Gerhard Krülle (IRS, Universität Stuttgart)
Philippe Schoonejans (ESA/ESTEC)
Dr. Ulrich Schöttle (IRS, Universität Stuttgart)
Prof. Dr. Werner Sobek (ILEK, Universität Stuttgart)
Participants
Team Green
Laura Anselmi (ITA)
Christian Eger (GER)
Thalia Flessa (GRE)
Olivier Helbig (GER)
Nico Hübel (GER)
Matthias Lau (GER)
Nicholas Lawrance (AUS)
Christian Messe (GER)
Bastian Olberts (GER)
Lucas Rye (AUS)
Fabian Schmid (GER)
Tony Schönherr (GER)
Ilya Sentchenkov (RUS)
Antoine Triboulet (FRA)
Team Blue
Matthäus Alberding (GER)
Philipp Altenhöfer (GER)
Stefan Belz (GER)
Coralie Buccianti (ITA)
Stefanie Fingerloos (GER)
Ebrahim Haririan (IRA)
Kai Hoffmann (GER)
Calvin Hung (NZ)
Jan Lehmann (GER)
Campbell Pegg (AUS)
Thibault Sandre (FRA)
Marcus Schwab (GER)
Sascha Tietz (GER)
Supporters
Institute of Space Systems (IRS), Universitaet Stuttgart
Institute of Lightweight Structures (ILEK), Universitaet Stuttgart
Institute of Aerodynamics and Gasdynamics (IAG), Universitaet Stuttgart
Landeshauptstadt Stuttgart & Planetarium Stuttgart
Maxon Computer GmbH
SMART Technologies (Germany) GmbH
Stiftung Landesbank Baden-Württemberg
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Institute of Space Systems, Universitaet Stuttgart
FOREWORD
Future space programmes involving astronauts and targeting destinations
beyond the International Space Station require new technologies and new
approaches in coping with the requirements given by the space agencies.
The various groups of people involved for such endeavours formulate these
requirements often in the form of rather vague scientific, economic or political
objectives which enter normally into a programme or mission statement.
The systems architect or systems engineer tasked with a conceptual design
of the spaceflight mission has to translate such a mission statement into
objectives by defining technological requirements together with the nontechnical constraints of an international and multidisciplinary programme.
This requires well-trained systems engineers who are familiar with modern
tools and methodologies and have gained sufficient hands-on experience at
the universities or in their first years of professional preoccupation.
Since many years lectures on space stations and its utilisation have been
given at the Institute of Space Systems at the Universitaet Stuttgart. This was
done long before the International Space Station become an international
project with European countries involved. When it became clear in 1995
that many European countries would join such a project, the space station
lectures were extended and supplemented by the so-called Space Station
Design Workshop or “SSDW”. Here students learn, as part of their regular
studies, in a hands-on, interactive, team-centred environment to perform
conceptual design studies of a complex human spaceflight system. They
are supported by a concise methodology and by customised software tools
that were developed and are constantly improved at the IRS in the frame
of research projects mainly carried out by PhD students. By doing so, we
also react on the recent plans and concepts towards sustainable human
exploration beyond low Earth orbit.
Normally many disciplines other than engineering are to be involved in SSDW
activities. It involves students from partner universities and consequently
is conducted with English as the working language. In many instances, the
SSDW was also held at the partner universities’ sites, e.g. in Toulouse, at
the International Space University and at ESTEC in the Netherlands.
Now, the latest SSDW 2006 was hosted again as an international,
interdisciplinary and intense one week event at the Institute of Space Systems.
It was a pleasure for me to see the fresh design ideas, the enthusiasm
emerging from working together with student teams and supported by
equally motivated university staff. I wish to take this opportunity to thank
all of the participants, including the students and the instructors for their
contributions to making this Space Station Design Workshop 2006 such a
valuable experience for all of us.
October 2006
Ernst Messerschmid
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WHEN DID YOU DESIGN YOUR LAST SPACE STATION?
Team Red
IRS 1998
“The opportunity to meet and work
with students from all over Europe and
beyond was invaluable ...”
Team Green
IRS 2005
Team Blue
IRS 1997
Team Yellow
ISU 2003
Team Blue
IRS 2001
“A fantastic experience:
well organized and well supervised.”
Team Blue
ESTEC 2002
“The best chance to get really involved in
space station topics I have ever had.”
Team Blue
IRS 2005
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Team Green
IRS 2001
Team Green
ISU 2001
TABLE OF CONTENTS
1
Introduction .............................................................................. 6
2
Space Station Design Workshop ................................................ 7
2.1
The Conceptual Design Problem ............................................ 7
2.2
SSDW Methodology ............................................................. 8
2.3
2.2.1 Design Team Composition and Collaboration .................. 9
2.2.2 Principles of the Design Process ................................... 9
2.2.3 Principles of the Design ............................................... 10
2.2.4 Integrating the Knowledge: Heuristics of Human Aspects . 10
SSDW Tools ........................................................................ 11
2.4
2.3.1 Software Tools ........................................................... 11
2.3.2 COMET – Space Station Configuration Modelling Software 12
2.3.4 IRIS++ – Spaceflight Simulation Software ..................... 13
2.3.4 ELISSA – Subsystem Simulation Software ...................... 14
2.3.5 Supporting Software ................................................... 15
International Design Workshops ............................................ 15
2.4.1 Approach and Objectives ............................................. 16
2.4.2 Design Team Composition and Room Set-up ................... 17
3
4
SSDW 2006 at the IRS ............................................................... 18
3.1
Organisation ....................................................................... 18
3.2
Mission Statement ............................................................... 19
3.3
3.2.1 Situation ................................................................... 19
3.2.2 Task Description ......................................................... 20
3.2.3 Background Information on Libration Points ................... 20
Design Results .................................................................... 21
3.4
3.3.1 Team Blue ................................................................. 22
3.3.2 Team Green ............................................................... 24
Design Evaluation ................................................................ 27
3.5
3.4.1 Evaluation Task .......................................................... 27
3.4.2 Evaluation Findings .................................................... 27
Feedback ........................................................................... 30
Conclusions ............................................................................... 31
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1
INTRODUCTION
The conceptual design of a manned space system is one of the most challenging
tasks in aerospace engineering. The history of space station Mir and the still
ongoing assembly and redesign of the International Space Station demonstrate
that even within the assembly phase quick solutions have to be found to cope with
budget and technical problems or changing objectives. However, with appropriate
methodology and tools, a space station can be conceptualised within a timeframe as
short as one week, and by a design team consisting of no more than 15 dedicated
engineers, architects and scientists.
Since 1996 the “Space Station Design Workshop” took place as an international
student challenge annually at various locations in Europe. It proved that designing
a space station is a formidable educational activity and can be done in a truly
international, multidisciplinary environment with small design teams: Two to four
competing design teams composed of highly qualified graduate students, selected
by local and SSDW staff from a large applicant pool, can be tasked with challenging
design problems within realistic boundary conditions in order to achieve overall
design goals such as science return maximisation and lowering cost.
The latest design workshop SSDW 2006 was hosted from 23 July to 29 July 2006 at
the Institute of Space Systems (Institut für Raumfahrtsysteme, IRS), Universitaet
Stuttgart, Germany. It demonstrated once again the potential of such a design
workshop within student education. The participants worked for one intensive
week in a hands-on, interactive, team-centred environment and were tasked to
design a manned transfer and exploration vehicle for missions in cis- and translunar
space. It focused on satellite and telescope servicing and rescue missions in a
programmatic context of space exploration beyond low Earth orbit (LEO). The teams
were supported by a concise, yet flexible methodology incorporating elements
from systems engineering as well as from other disciplines, and by customised,
intuitive, rapid-turnaround software tools enabling them to successfully tackle the
complex problem of conceptual design of crewed space systems. Due to the design
task, a strong emphasis was put on the mission analysis and vehicle configuration,
as they are the major contributors to mission success.
This report will first document the methodology and tools that together make up
the Space Station Design Workshop (SSDW) approach and then describe in detail
how this approach was implemented during the SSDW 2006. The design results
produced by both teams are presented as well as the feedback gathered from
the participants after the workshop. The conclusion summarises the findings and
lessons learned of this unique opportunity for the students and points out future
SSDW activities.
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2
SPACE STATION DESIGN WORKSHOP A CONCEPTUAL DESIGN ENVIRONMENT
2.1
The Conceptual Design Problem
In the beginning of designing a space mission or system stands a mission statement
describing the objectives of the customer. Customers like politicians, economists or
scientists have their specific needs and expectations in formulating these objectives
that have to be understood and verified for project success. Therefore, from the
engineering point of view, the given mission and system requirements are rather
vague and have to be translated into primary and secondary objectives, defining
technological requirements and technological as well as political and economical
constraints. This early phase of a space project is referred to as the conceptual
design phase.
Figure 2.1: Mission and system element interactions
As illustrated in Figure 2.1 all mission and system elements are strongly
interdependent. Changes to one element impose direct or indirect changes to
largely every other element with more or less significant consequences to the
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whole system. Within this early project phase of conceptual design, every one of
its elements must be considered simultaneously while major decisions have to
be made in terms of project complexity, applied technologies and cost elements.
Conflicting requirements must be dispelled and fundamental mission and system
parameters have to be concretised, optimised and fixed in a baseline concept
following an iterative process.
The designers of complex space systems are faced with a set of challenges
stemming in part from the general “wickedness” of the design problem, which
make it impossible to apply linear, “scientific” approaches to their solution, and in
part from the special environment of space and the boundary conditions which it
imposes. These include:
• Fuzzy problem formulation: Objectives and boundary conditions are initially
vague. The mission and the space system must be developed together.
• Strong interdependencies between system elements: A methodological
approach is required that enables the designers to deal with the space system
as a whole due to the complex network of links among its elements.
• Adverse relationship between available information and consequences of
conceptual design decisions: System elements are defined and central
decisions about mission performance, system architecture, technical risk,
developmental effort, cost, and organisational structure are made, usually
despite the availability of sufficient information. Subsequent design phases
provide more information, but the new decisions have to stay within the
envelope defined during the conceptual phase and are thus limited in their
mitigative potential.
• Extreme boundary conditions: Compared to other systems of comparable
technological complexity, space systems are subject to much tighter
boundary conditions due to the harsh space environment (temperature,
vacuum, radiation, µ-gravity, debris), the high g-loads during launch,
lightweight design and maintainability under difficult access conditions.
Designing a crewed space station adds the complications of life support requirements,
increases demands on safety and reliability, crew integration, as well as the degree
of public scrutiny, and all this in a highly politicised design environment.
2.2
SSDW Methodology
In order to tackle the conceptual design challenges, an interdisciplinary methodology
for the conceptual design of inhabited space systems has been developed and
extended to mission design beyond LEO at the Institute of Space Systems of the
Universitaet Stuttgart. It emphasizes the most efficient integration of the crew into
a space system as one solution to this conceptual design problem, given that,
“the main system driver is human presence itself since it largely determines
overall design and cost by technical and safety requirements.”
Thus, the space engineers shall not treat human-rated space structures as
“machinery-with-attached-crew”, but primarily as habitats. The approach is
based on space systems engineering methodology with elements from terrestrial
architectural practice. It also integrates specially developed software tools for the
modelling, assessment and dynamic simulation of the space system configuration,
for the analysis of life support systems, and for the assessment of other key
subsystems during the early phase of conceptual design.
Systems engineering is referring to the complete space system design process as
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part of the space mission – not only in the conceptual design phase. It includes the
science, technical and business issues involved within the task to be performed.
These issues range from creating a system architecture and coming-up with creative
solutions to the use of mathematics, constructing physical models and simulating
systems and subsystems to evaluate their properties, performance, mission utility
and cost.
2.2.1 Design Team Composition and Collaboration
The design teams often consist of people of different cultural backgrounds and
various disciplines, mirroring the heterogeneous environment of space business.
The first central element is the composition of the design teams and their mode
of collaboration. The following ground rules should be adhered to as much as
possible:
• All members of the design team see themselves as cooperation-oriented
experts in their respective fields, not as isolated subsystem specialists.
• Design team members come from different fields and backgrounds but
develop a common language. This suggests that they share joint experience
in designing gained through participation in previous design projects, or in
hands-on training workshops such as SSDWs.
• Design team members look for solutions based on their disciplinary
experience, but their ideas are triggered by interdisciplinary face-to-face
interaction and by the unexpected brought out by it.
• Designers are aware of the design process also being a two-tiered learning
process: the process allows them to learn about the problem itself and also
to increase their own knowledge from the design experience.
• Design team leaders, by personality, are eager for face-to-face
communication and learning experiences, and can deal with and accept
imperfections during the search for solutions (but not in the final result).
They integrate team members’ contributions and have the strength to push
logically-derived solutions to group acceptance.
• Designers are on the lookout for the usual hazards of requirements creep,
fuzziness, disciplinary infighting, and marginal performers.
From the perspective of participants, the workshop is goal-oriented to maximise
output with a focus on a proper and feasible manned space system design concept,
but it is also highly process-oriented. Team building, getting acquainted with the
problem, identifying the team members’ know-how and coordinating process flow
and last but not least reviewing the design during evaluation are the processes to
be coped with.
2.2.2 Principles of the Design Process
The interdisciplinary design process is outlined in Table 2.1. Design team preparation
and background research prior to launching the design itself, as well as thorough
documentation afterwards, are emphasized due to their importance for a quality
design.
The workflow is further guided by the following design process principles:
• The early phase of the design effort is crucial and should therefore extend
far into the design process. This is aided by the use of accumulated, easily
accessible knowledge in the form of design heuristics.
• Alternatives not selected are not discarded, but kept for future reference
as sources of ideas or as fallback options.
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• Important details (e.g. staging locations, crew size) are identified and
developed as soon as the task is properly understood and the relevant
boundary conditions have sufficiently evolved. From the beginning, they
help to provide focus and continuity for the designers’ intent.
Task
Step Details
0. Design work preparation
and monitoring
• assemble team, allocate responsibilities
• verify consistency throughout the team
• perform information retrieval & analysis
A. Objectives definition
• review mission statement
• identify objectives, requirements & constraints
B. Mission and system
characterisation
• develop alternative concepts and architectures
• characterise elements
• identify design drivers & technical requirements
C. Concepts assessment
• prepare & evaluate system & subsystem budgets
• select baseline scenario
D. Requirements verification • review concept & refine mission & elements
• allocate requirements on system & subsystem level
E. Results documentation
• conserve baseline concept and rationales
• conserve alternatives for later reference
Table 2.1: SSDW process of conceptual design
2.2.3 Principles of the Design
The addressing of human-specific aspects by the design team is emphasized. For
each step of the design process, the designers are encouraged to adhere to the
following conventions:
• The “human element”, i.e. the crew, is not treated as a subsystem among
many, but is emphasized as the overall design driver; the design objective
is the creation of a habitat that optimises crew efficiency.
• Human possibilities and limitations determine the types of modules to be
used and their internal layout, as well as the dynamic linking of these
modules within the overall habitat.
• The influence of the human presence on all sub-systems, ranging from
maintenance options to ECLSS demands to zero-g disturbances, is taken
into account.
On a cautionary note, however, the design team should realise that this humancentred paradigm of inhabited space systems conceptual design must be seen
in the context of overall design limitations. While the methodology emphasizes
optimisation with respect to habitability (and thus crew efficiency), history shows
that expedition participants have frequently been able to withstand extreme levels
of discomfort, although this significantly reduced their operational efficiency.
Exaggerated fear of the “Human Factors Dragon” carries the risk of jeopardising
overall mission feasibility.
2.2.4 Integrating the Knowledge: Heuristics of Human Aspects
The vast body of knowledge related to optimising human integration and human
performance that has been assembled during the past decades represents a crucial
resource to the designers of inhabited space systems and must be reviewed in
depth during the background research phase of the design process. This adds
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important information to the engineering knowledge already provided by the
traditional design approach. However, these insights are usually spread out over a
large number of publications.
In order to efficiently support the design team with more of the information it needs,
an additional collection of the most significant findings and rules for manned space
systems design is provided as part of the SSDW methodology. The form chosen
for this compilation is that of tables of design heuristics. Heuristics (comparable to
“rules of thumb”) are an important element of the conceptual designer’s tool kit.
They are especially suited for subjects which cannot be expressed or optimised
using only equations and numerical simulation, and are thus ideal for addressing
most human-related aspects of spaceflight during the conceptual design phase.
2.3
SSDW Tools
To make the conceptual design of a complex technical system feasible, tools
supporting design and analysis are crucial. Table 2.2 gives an overview of different
types of tools principally used within conceptual design. Often these tools combine
implementations in software, manual form or other.
Tool Type
Tool Details
Formal tools
• management & documentation tools
• creativity & communication tools
Field
S/M
Procedural tools
• recipes (step-by-step procedures, approximations)
• interference matrix, parameter tables
S/M
S
Analytical tools
• mission design calculation schemes
• budgeting and parametric system engineering tools
M
S
Numerical tools
• Modelling & dynamic simulation software
• trajectory generation & optimisation
• data analysis & visualisation software
S/M
M
S/M
Table 2.2: Types of tools for conceptual design (S,M: system/mission design)
2.3.1 Software Tools
Software programmes are indispensable for a rapid and efficient conceptual design
process, especially if several iteration loops – and thus repetitive execution of
numerical analysis tasks – are required. Besides the modelling and simulations,
visualisation of data and design concepts are important tasks. Because the SSDW
is so design-intensive and because of the short timeframe, the tools to be used
during the workshop must meet certain prerequisites:
• Easy to learn and intuitive user interface
• User friendly and reliable operation
• Fast calculation and appropriated output for analysis and visualisation
• Configurable to adapt to various design problems
• Compatibility with a common operating system
• Modular software design to ensure easy further development and software
maintenance
The package of software tools currently in use consists of custom-developed
software dedicated specifically to the conceptual design of space stations as well
as commercially available general-purpose software. Figure 2.2 gives an overview
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of the design tools and illustrates how these tools are embedded in the design
process. The major software programmes developed at IRS are COMET, ELISSA
and IRIS++. This exclusive software package is described in more detail in the
following sections.
Figure 2.2: SSDW tools within the conceptual design process
2.3.2 COMET – Space Station Configuration Modelling Software
COMET stands for „Configuration Modelling and Editing Tool“. It is a proprietary
add-on to the commercially available 3D graphics software Cinema4D and it was
developed to model and edit space station modules and configurations. It provides
an intuitive graphical user interface for generating and managing space station
objects and a convenient output filter to export space station configurations as
IRIS++ compatible model files for orbit simulations and analysis. This enables
quick-turnaround space station design iterations.
Figure 2.3: Main user interface of the COMET software
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COMET is object-oriented software using three hierarchically ordered types of object
classes (“Spacecraft”, “Module” and “Primitive”): Primitives make up modules, and
modules make up a spacecraft or station. Every object can be saved separately to an
object library, in which predefined modules and other elements of the International
Space Station (ISS) are also readily accessible. Figure 2.3 gives an impression of
the COMET user interface. In addition to the principal user interface provided by
Cinema4D, the modelling software COMET extends the software with its following
components:
• COMET object class structure
• Object generator for creating various space station elements
• Docking assistant for convenient object positioning and alignment
• Object library containing main elements of the ISS and transfer vehicles
• Output filter to export space station configurations as IRIS++ model files
• Data container for geometric, mass and functional properties
• Event-triggered update functions for convenient user-object interaction
• Tracking preview and verification routine
2.3.4 IRIS++ – Spaceflight Simulation Software
IRIS++ is the spacecraft simulation programme developed for the analysis of
dynamic space systems. Inputs are the geometry and mass distribution of a space
station or platform (provided by COMET), and the simulation commands defining
the simulated mission specification. Figure 2.4 illustrates the workflow when
using IRIS++. Outputs are stored in data files for post-processing in spreadsheet
applications and 3D visualisation.
Because IRIS++ is used for educational purposes (i.e. SSDW) and space systems
research, it emphasizes generic applicability to a wide range of spaceflight missions.
Although emphasis lies on space station applications, IRIS++ provides a generic
multi-spacecraft and multi-mission simulation environment. Today simulation
scenarios dealt with include Earth, Moon and Mars orbital missions and cis-lunar
as well as interplanetary transfer missions.
Figure 2.4: IRIS++ program flow and features
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The following features are currently provided:
• Command interface to specify mission, attitude control and orbital
operations
• Attitude dynamics (6D-Euler equations of motion) and attitude control
• Orbital dynamics (cartesian and equinoctial parameters) and orbit control
• Various numerical integration methods
• Perturbations (gravity field, atmosphere, third-body forces, solar radiation
pressure, user-defined forces)
• Dynamic motion model of the solar system
• 3D surface model and shadowing algorithm
• Simulation of structural dynamics (i.e. tracking of panels)
• Top-level simulation of the AOCS, EPS and TCS subsystems
• Virtual Reality Modelling Language (VRML) output file
In addition to the state variables, perturbations and model information, specific
output data include:
• Microgravity levels at user-specified locations within the spacecraft
• Shadowed ratio of solar/radiator panel active areas
• Accumulated momentum stored in momentum wheels
• Propellant consumption due to attitude or orbit control thruster
operations
2.3.4 ELISSA – Subsystem Simulation Software
ELISSA stands for „Environment for Life-Support Systems Simulation and Analysis“.
It is a support tool for the design of subsystems. A powerful, intuitive graphical
user interface provides convenient simulation features and easy customisation
and extension. The environment is based on the commercially available software
„LabVIEW“, providing the graphical programming language „G“.
Predefined component libraries exist for the life support system as well as for
the power supply and attitude/orbit control subsystems. Using drag-and-drop
techniques, the user models the subsystem to be analysed before starting simulation
runs, as depicted below. Interactive simulation control allows analysis of dynamic
problems.
Figure 2.5: ELISSA user interface
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2.3.5 Supporting Software
The Microsoft Office package and other software is used within the SSDW
methodology in various fields to support the overall design process:
• Spreadsheet application for quick budgeting, estimations, accounting,
generation of system balances and graphing of simulation results,
• Presentation software to support lectures, communication within the design
teams and presentation of design results,
• Text editor for reports, handouts and other workshop documents,
• VRML software for visualisation and verification of the configuration.
Figure 2.6: Examples of supporting software application within the SSDW
2.4
International Design Workshops
The methodology and tools described above have been and are continuously used
in a complete design environment for annual student workshops on human space
mission design. These workshops have been established at various European
locations, each time focusing on a challenging space station scenario, namely at:
• the “Ecole Nationale Supérieure d‘Aéronautique et de l‘Espace“ (SUPAERO)
in Toulouse, France, in 1996,
• the International Space University (ISU) in Strasbourg, France, annually
between 1997 and 2001 and in 2003,
• the Institute of Space Systems (IRS) of the Universität Stuttgart, Germany,
annually between 1997 and 2001, 2005 and 2006,
• ESA’s European Space Research and Technology Centre (ESTEC) in
Noordwijk, The Netherlands, in 2002.
The primary objective of the workshops is to give students the opportunity to learn
and practice systems engineering on a space-related subject, to provide hands-on
experience on the application of knowledge acquired during academic lectures,
and to participate in a competitive, international, multidisciplinary team-based
design project. At the same time, the workshops help to test and validate the
developed methodology and tools, and allow the collection of direct feedback from
the participants regarding functionality and usability improvements.
The participants come from a variety of fields and backgrounds, but all share a
common interest and knowledge about space stations or related topics. They are
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expected to fully commit themselves to their task throughout the workshop in order
to play a valuable role in their respective design teams, and to be open-minded
towards other cultures and personalities, as social skills become as important as
knowledge of technical issues.
2.4.1 Approach and Objectives
Within the short timeframe of a SSDW, the participants are confronted with
the challenge of space systems engineering, team building and customer
presentations. The workshops are usually carried out in the form of an intensive
one week programme to enable and facilitate international participation. They
generally comprise two parts, focusing on the system design followed by a system
evaluation.
To ensure a comparable level of background information and familiarisation with
methodology, technology and terminology, the SSDW begins with lectures on
relevant system and subsystem topics, partly given by selected experts from
agencies and industry. The hands-on design teamwork is started as early as possible
in the timeline and continues to grow in importance throughout the workshop.
The workshop task of the design part is formulated as a Mission Statement
including general objectives of the projected human space mission. It can refer to
different space station scenarios, e.g. current problems of ISS or other stations
in LEO, or future human spaceflight missions beyond Earth orbit such as outposts
and infrastructure for Moon and Mars. A virtual customer presents the Mission
Statement to the participants that play the role of competing industries in terms
of two or more design teams. Subsequent to this kick-off meeting, the workshop
follows a typical early project development timeline with its different phases and
milestones (Figure 2.7).
Preliminary Requirements Review (PRR)
Initial Systems Engineering (II)
Develop alternatives & the baseline concept incl. budgets
System Concept Review (SCR)
Systems & Subsystems Engineering (III)
Simulations & analysis of the selected concept(s)
Preliminary Design Review (PDR)
Design Evaluation (IV)
SYSTEM DESIGN
EVALUATION
Final Design Presentation
Requirements Engineering (I)
Identify project objectives, requirements & constraints
Reflect, compare & analyse the differences of the designs
Figure 2.7: General SSDW process breakdown
The design team members are guided through the steps of the design process
by means of handouts with step-by-step instructions and recommendations, socalled “Recipes”. These handouts include information about process milestones
and associated deadlines, but they also cover various aspects of space systems
development, background information and software tools. Experienced student
assistants and the workshop organisers are always on call in case of questions, and
proactively observe the design teams to ensure a smooth process flow.
The second part of the workshop is the design evaluation of the teams’ findings. The
previous design teams are broken up and the participants form several evaluation
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committees, mostly related to sub-systems design. From the educational point
of view this part of the workshop emphasizes reviewing the design work and all
the decisions made on the way to the final design by reflecting, comparing and
analysing the differences of the design results based on the presentation and
documentation of all previous work. Hence the students have to develop and to
apply special evaluation criteria which allow for a comparison of different design
proposal with respect to the initial Mission Statement.
From the participants’ perspective the workshop is both goal-oriented and highly
process-oriented. The exceptional team challenge includes familiarisation with the
problem and the fellow team members, coordination of the process flow, as well
as technical design work for a true hands-on systems engineering experience. The
evaluation ensures that the students are reflecting their approach and solutions.
Task
Step Details
Management, cost
• cost analysis and management
• utilisation and future potential
Configuration
• overall system architecture
• assembly strategy and planning
AOCS
• mission analysis
• attitude and orbit control strategy
EPS & TCS
• electrical power system
• thermal control system
ECLSS
• life support system
• synergy analysis
Human Factors
• habitability and ergonomics
PR, marketing
• marketing strategy and outreach
• documentation and presentation
Robotics
• robotics design and autonomy
Table 2.3: SSDW subteams at the SSDW 2006
2.4.2 Design Team Composition and Room Set-up
A typical number of team members in each design team is ten to fifteen, but
well-elaborated design results have been achieved with a group size as low as
five to eight participants. The various backgrounds, cultural environments and
specialisation fields of the team members reflect the multidisciplinary tasks to be
solved during the workshop. The team itself nominates a team leader and forms
several sub-teams according to specific mission tasks as indicated in Table 2.3. The
team leader takes responsibility for proper communication and information flow,
organisation of regular team meetings, and the time- and goal-oriented design
progress.
Analogue to the sub-teams the team’s design room set-up should reflect the
particular tasks. This means that similar to ESA’s Concurrent Design Facility (CDF),
the room includes networked PC workstations with general and sub-team specific
software as well as general presentation, discussion and meeting hardware. Thus,
the design teams shall be provided with individual workstations for the sub-teams
while at the same time fostering the multidisciplinary direct team interaction which
is vitally important for the conceptual design approach.
17
3
SSDW 2006 AT THE IRS
Prompted by the success of previous Space Station Design Workshops, the Institute
of Space Systems (IRS) of the Universitaet Stuttgart decided to host another
workshop within its local facilities in summer 2006. In line with current exploration
strategies, the SSDW 2006 tasked with a human mission beyond low Earth orbit in
preparation of a sustainable architecture and permanent human presence in cisand translunar space.
3.1
Organisation
The SSDW 2006 continued the history of truly international, interdisciplinary and
intense workshops. It was hosted and organised by the staff from the IRS with the
support of other university institutes and external sponsors.
Participants for this workshop were selected after call for applications at the SSDW
website, direct mailings to European partner universities and local announcements.
28 participants were chosen from the pool of applicants based on such criteria as
educational background, professional experience, English skills and motivation. The
team members thus originated from nine different countries, including Australia,
France, Germany, Greece, Iran, Italy, New Zealand, Russia and the USA, with
backgrounds in aerospace engineering, mechanical engineering, physics, technical
cybernetics, architecture and information science. They were assigned to two
competing design teams, tagged “Blue” and “Green”, with 14 members each.
Each team had a fully equipped design room, including seven laptop computers,
a beamer, an interactive pen-display and whiteboard, and a group meeting table.
The PCs were set up with general software as well as SSDW specific tools and
connected via a local area network and with a printer for each team.
Figure 3.1 gives an impression of the intense one-week program of the SSDW
2006. The workshop started Sunday with introductory lectures by SSDW staff and
invited guests to ensure a common basic knowledge of systems engineering and
space systems design for all participants. On Monday morning, Prof. Messerschmid
presented the “Mission Statement” to the students. While the rest of Monday morning
and Tuesday morning saw further preparatory lectures, the afternoons were already
dedicated to the actual design work, concluding with the requirements review and
the system concept review at the end of the respective days. The participants also
visited the Institute of Lightweight Construction and Conceptual Design (ILEK) to
get some additional inspiration from advanced architecture approaches.
The following two days were fully devoted to design team work, where the participants
followed the handout guidelines and extensively used the SSDW software tools to
detail and analyse their system and subsystem design. The Preliminary Design
Review (PDR) on Thursday night concluded the team design phase of the workshop,
with the teams finishing their documentation throughout the night.
On Friday morning the participants were assigned to evaluation commitees to
reflect and analyse the two designs. The day and the workshop culminated in the
public presentation of the workshop design and evaluation results to an audience
of SSDW and university staff and students. On this occasion, each participant was
also awarded a certificate documenting the successful participation in the SSDW
2006. A reception followed and provided possibility for technical and personal
18
conversation among participants, staff and visitors.
The last day was then used for a short workshop wrap-up and feedback.
Time
Sun, 23.07.
Mon, 24.07.
Topic
Introduction and
Lectures
Lectures and
Requirements Eng.
08:30
Mission Statement
08:45
and Task Intro
09:00
09:15
09:30
09:45
10:00
10:15
10:30
Lecture 4:
B. Ganzer (IRS)
10:45
F. Renk (IRS)
ECLSS
Lecture 5:
AOCS
11:00
11:15
11:30
Coffee Break
Tue, 25.07.
Lectures and
Systems Engineering
Lecture 7:
EPS & TCS
J. Schlutz (IRS)
Lecture 8:
Human Factors
Wed, 26.07.
Thu, 27.07.
Systems and
Subsystems Eng.
Subsystems Eng.,
Documentation
Workshop
Workshop
Session III:
Session III (cont.):
Systems and
Systems and
Subsystems
Subsystems
Engineering
Engineering
Coffee Break
Coffee Break
Messerschmid (IRS)
Coffee Break
Fri, 28.07.
Evaluation and
Sat, 29.07.
Workshop
Final Presentation
Introduction to
Wrap-Up
Session IV:
Finalisation of
Design Results
Documentation
Evaluation
(if necessary)
Coffee Break
Coffee Break
PRR: Lessons Learned
Visit of
Workshop
Workshop
Workshop
Robotics
Session III (cont.)
Session III (cont.)
Session IV (cont.)
12:00
Schoonejans (ESA)
ILEK
Lecture 10:
(V27.01)
Teamwork
Lightweight
12:30
12:45
Initiation
W. Sobek (ILEK)
13:00
13:15
13:30
13:45
IRS Presentation
14:00
Schlutz (IRS)
14:15
14:30
14:45
15:00
15:15
Lecture 1:
15:30
15:45
16:00
16:15
16:30
16:45
17:00
Snack / Coffee
Workshop Wrap-Up
Messerschmid (IRS)
12:15
Lunch
12:45
Lunch
13:00
13:15
13:30
13:45
Lunch
Session III (cont.):
Session I:
Systems and
Engineering
SSDW Introduction
Workshop
Subsystems
Session II:
Engineering
Initial Systems
Renk (IRS)
Lecture 2:
Coffee Break
Engineering
14:00
Design Results
14:15
14:30
14:45
15:00
15:15
Evaluation (cont.)
Documentation and
Preparation of
Design Team
Presentations
Coffee Break
and
Preparation of
Evaluation Team
15:30
Presentations
15:45
16:00
16:15
Systems
Engineering
R. Benz (EADS)
Coffee Break
Lecture 3:
Workshop
Session I (cont.)
17:15
Configuration
Team Blue
17:30
and SSDW Process
System Concept Rev.
17:45
R. Bertrand (ESA)
Team Green
18:00
Preliminary Require-
18:30
ments Review (PRR)
16:30
Workshop
Coffee Break
System Concept Rev.
Introduction to
SSDW Tools
19:00
19:30
20:00
20:30
21:00
21:30
Sofie’s Brauhaus
Social Event
(Welcome Dinner)
Beergarden
...
Stuttgart
Stuttgart
11:45
12:00
12:30
Lunch
Workshop
Requirements
10:45
11:00
11:15
11:30
and
Workshop
History, ISS & Plans
09:00
09:15
09:30
09:45
10:00
10:15
10:30
Feedback
Structures
Welcome
Lunch
08:45
Workshop
Lecture 6:
12:15
08:30
Evaluation
11:45
Time
Topic
Session III (cont.)
Coffee Break
16:45
17:00
Public Presentations
and Graduation
Preliminary Design
17:15
(V27.02)
17:30
Review (PDR)
17:45
18:00
Social Event
Planetarium
Stuttgart
Reception
18:30
(V27.02 Foyer)
19:00
19:30
Social Event
Lectures
Locations
Groupwork
Main Room
Team Design Rooms
Other
Figure 3.1: Timeline of SSDW 2006 at IRS
3.2
Mission Statement
3.2.1 Situation
July 2008. The assembly of the International Space Station (ISS) is well underway
to its planned completion. International exploration plans for the post-ISS assembly
era, under the leadership of NASA, call for concepts for the next steps of space
exploration, including astronaut-piloted missions to destinations in cis- and translunar space. A European-Russian lead project to install a Lunar Space Station
(LSS) at the Earth-Moon libration point 1 (EML1) has been studied and ratified by
the international partners; and the design and construction of its elements has
begun. This space station will be assembled in the timeframe 2015-2018 and in
the following serve as a gateway to and from the surface of the Moon and other
destinations in near-interplanetary space.
ESA and Roskosmos reached an agreement to undertake a demonstration and
validation project of the LSS infrastructure in which a new transportation vehicle
dubbed Geospace Exploration Vehicle (GEV) is studied which reaches – from low
Earth orbit (e.g. assembly at ISS) – not only the LSS station but also destinations
such as Sun-Earth libration points (SEL1 & SEL2) and Near Earth Objects (NEOs),
with a high degree of re-usability.
19
You are a group of space architects and design engineers in the virtual “European
Manned Spaceflight Industries (EMSI)”. ESA and Roskosmos jointly invite you
to tender for a design study on a human-tended Geospace Exploration Vehicle
focusing on maintenance and repair of the LSS and space telescopes stationed on
(Halo) orbits around the Sun-Earth libration points. After completion of the design
study, ESA will review the competing proposals.
3.2.2 Task Description
The primary objective of the conceptual study is to define a transportation vehicle
named Geospace Exploration Vehicle, capable of shuttling from LEO to cis- and
trans-lunar destinations and back. In particular, the GEV shall:
• accommodate a permanent crew of 3 astronauts for servicing missions of
satellites at the Sun-Earth libration points of duration of up to 50 days,
or 6 astronauts (in “taxi” or rescue mode) for missions of up to 20 days
duration;
• support mission to the LSS stationed at the Earth-Moon libration point 1 and
missions to low Lunar orbit (LLO) to assist in lunar exploration projects;
• return the astronauts back to Earth in a re-entry vehicle;
• allow for repair, maintenance and other life extension actions of telescopes
and infrastructures in trans-lunar space; and
• support long-term preparations for mankind’s next steps in space, human
expeditions to the Moon and Mars
The GEV shall be available at “LSS core complete” which is expected for year
2017.
3.2.3 Background Information on Libration Points
The libration points, often also referred to as Lagrange Points, mentioned in the
mission statement exist in every system of two bodies orbiting each other. They
are five points, where the gravitational and the rotational forces on a third mass,
which has to be negligible compared to the two other bodies, are balanced. Three
of the points are on the axis connecting the two central bodies and the other two
points form an equilateral triangle with these bodies. An example for the libration
points of the Earth-Moon system is given in Figure 3.2. Theoretically, L4 and L5 are
stable, but with perturbations of the real space environment being present, all five
points are unstable. However, orbits about the libration
points exist, that require almost no station keeping
effort. The collinear points L1 and L2 of the EarthMoon system provide a good staging location on the
way to and from the Moon and they also provide good
access to the Sun-Earth libration points, which are on
almost the same energetic level. The environment of
the Sun-Earth libration points is very benign for large
space observatories. Dependant on the orbit there are
no eclipses or years between two eclipses, providing
a stable thermal environment and constant power
supply. Furthermore, astronomical observations can
be performed uninterrupted from SEL2, since Sun, Figure 3.2: Libration points
in the Earth-Moon system
Earth and Moon remain close together.
20
3.3
Design Results
The difficulty of the above task was to design a human-tended Geospace Exploration
Vehicle (GEV) capable of performing two different missions: while for the repair
mission to SEL2 a huge payload capability and a robotic arm are required, the
rescue and support missions need a life support system suitable for up to six
astronauts. Both teams suceeded in fulfilling the requirements given in the mission
statement and came up with elaborated GEV designs using the SSDW methodology
and software tools as well as the support of the staff from the IRS. This section
provides a closer look at the design and simulation results of both teams.
Since the GEV development shall be inline and also support the Lunar Space Station
(LSS), both teams utilise similar transportation hardware developments such as
modified Soyuz crew transfer vehicles, reconfigured ATV elements and modules
with ISS heritage. Considering also the political constraints, implicitly given in the
mission statement, only the future European Ariane 5-27 and the Russian Soyuz
and Angara launchers were used.
It is remarkable that, starting from the same mission statement, the two teams
developed very different approaches in terms of mission analysis and architecture.
Each of these designs shows specific advantages and constraints, providing a
perfect starting point for extended design work by merging the strengths of the
two concepts.
Mission
Staging
SEL2 mission
LLO mission
Crew (nominal)
Technical data
In-orbit mass
Departure mass
Propulsion
EPS (solar)
TCS
Robotics
Team Blue
Team Green
GEV in LEO (ISS ?)
GEV in EML1 (LSS ?)
∆V = 4000 m/s, 76 days
∆V = 4980 m/s, 20 days
3 (4-6 for short duration)
∆V = 1000 m/s, 64 days
∆V = 1400 m/s, 6 days
3 (4-6 for short duration)
25.4 t
95 – 100 t
LH2/LOX, MMH/N2O4; Aerobraking
20 kWel (BOL), 12 kWel (EOL)
24.5 kWth (body-mounted)
1 advanced SRMS, Eurobot
21.0 t
26 – 34 t
CH4, LOX
10 kWel (BOL), 8 kWel (EOL)
15 kWth (deployable)
1-2 advanced ERA, Eurobot
Logistics
Assembly
2 Ariane 5 (EOR)
Mission/Resupply 2 Ariane 5, 1 Angara (1 Soyuz)
3 Ariane 5 (EOR)
3 Ariane 5, 1 Soyuz (-2 Ariane 5)
Table 3.1: Overview and comparison of the SSDW 2006 design results
Figure 3.3: Mission analysis and ∆V requirements for SSDW 2006 designs
21
3.3.1 Team Blue
Due to the different mission scenarios, the GEV design of team blue is planned to
be very modular.
Configuration and Assembly
Basically, the Geospace Exploration Vehicle consists of two different parts: the
reusable part with the crew and service modules and the non-reusable part including
both crew transport vehicles and the propulsion modules.
The reusable part of the GEV contains several modules for the different aspects of
the mission:
• The Crew and Command Module (CCM, mass 12t, cylindrical 6m x Ø4.5m,
based on European COF) includes living quarters, part of the life support
system, the control unit for the spacecraft, two large solar panels and
body-mounted radiators. The interior is designed with respect to the latest
recommendations regarding human factors for long term space missions,
i.e. seperated areas for work, living and recreation, private areas for crew,
inner dimensions, colouring, etc.
• The Service Module (SM, mass 5.45t, cylindrical 4m x Ø4.5m) houses
the rest of the life support system, the thermal control system, the main
computers, the batteries and the fuel tanks of the attitude control system.
It is not pressurized.
• The Maintenance and Repair Module (MRM, mass 5.45t, cylindrical 4m
x Ø4.5m) is especially designed for the servicing mission to SEL2 and
includes all the subsystems required to repair the telescopes: airlock with
suits for EVAs, a robotic arm and the Eurobot. There is a payload capacity
of approximately 2 tons for spare parts.
• The Docking Node System (DNS, mass 3t, spherical Ø3m) is the central
connecting element between the modules of the GEV.
The complete reusable core structure of
the GEV stays in orbit once assembled
using two Ariane 5 launches from Kourou,
with the CCM and the SM in the first and
the DNS, MRM and ATV-Logistic in the
second launch. The ATV-Logistic is used
for the reorganisation and assembly of the
modules after launch. The total in-orbit
mass is about 25.4t after both launches.
The non-reusable part has to be replaced
for each mission. For these high ∆Vs, a
Figure 3.4: GEV configuration at LEO
staged propulsion system has to be used
departure to SEL2, Team Blue
to minimize the required propellant. The
non-reusable section comprises:
• The modified Russian Soyuz vehicle with an improved heat shield for direct
reentry from the moon or SEL2.
• The ATV Heavy Duty (ATV-HD) as the main booster from LEO to the
transfer trajectories. It has a cryogenic VINCI engine (180kN, Isp 467s)
and contains around 22t of LH2/LOX, resulting in the total mass of 27t
(maximum payload capacity of enhanced Ariane 5-27).
• The Large External Tank Module (LETM, based on ATV) extends the tank for
LH2/LOX by about 24t.
22
• The ATV Low Duty (ATV-LD) uses the RD-72 engine (55.4kN, Isp 340s) with
storable propellants (MMH/N2O4) and performs minor orbit manoeuvres.
With this modular configuration as shown in Figure 3.4, the GEV is able to perform
both missions, which will be described in more detail in the next section.
Mission Design and Orbit Control
The major design drivers for the mission design were identified to be safety and
effectiveness in terms of propellant consumption and ∆V requirements. To fulfil all
safety requirements LEO was chosen as the staging location due to its closeness
and the possibility to use the ISS as a safe haven.
For a SEL2 repair mission the existing reusable part of the GEV is extended with
the propulsion elements which are launched with an Ariane 5 each. The crew
launches with a Soyuz spacecraft and docks to the GEV in LEO. After checkouts the
ATV-HD provides the neccessary ∆V of 3200m/s for the transfer injection to SEL2,
followed by jettison of the now empty ATV-HD and LETM. The transfer time to SEL2
strongly depends on that first ∆V, with 3200m/s the transfer time is around 34 days.
The ATV-LD is used for orbit insertion (340m/s) into the Halo orbit about SEL2,
rendezvous with the target for a staytime of about 8 days, and transfer injection
to Earth (340m/s). While the Soyuz with the astronauts separates from the main
vehicle for a direct reentry, the GEV uses a complicated aerobraking manoeuvre
to reach LEO again. All this results in a large total ∆V of about 4000m/s, where a
higher ∆V capability could reduce the mission time to 48 days instead of 76.
The general setup for a LLO rescue mission is the same, with the MRM being
left behind in LEO (possibly at the ISS). Then the ATV-HD provides the transfer
injection with a ∆V of 3150m/s (5 days transfer time). The ATV-LD can provide
the ∆V for LLO insertion, rendezvous and docking, and trans-lunar injection. Again
the Soyuz returns directly to Earth and the GEV uses aerobraking. The total ∆V is
4980m/s for this mission. A major disadvantage of the design is that the timing is
very important because the transfer to the moon is only possible once about every
11 days.
Keeping the idea of a Russian-European cooperation in mind, both Russian and
European launchers are used. While the Ariane 5 launches only from Kourou, the
Soyuz and Angara rockets are launched from Baikonur. Naturally the support of the
International Space Station (ISS) and Lunar Space Station (LSS) is also possible
using these launch sites.
The most interesting part of the mission
design is the aerobraking manoeuvre
for LEO recapture. Using only small ∆Vs
from the ATV-LD for orbit corrections,
the GEV reaches its final circular orbit
after about 95 to 100 days and enters
the atmosphere repeatedly down to 105110km (Figure 3.5). This aerobraking
manoeuvre reduces the total ∆V for both
missions significantly, while still allowing
up to two missions per year.
The
Figure 3.5: Altitude developing during
aerobraking as well as the orbit control
aerobraking, Team Blue
requirements in the parking orbit were
calculated using the IRIS++ software provided by the SSDW.
23
Subsystems
Most of the subsystems are based on current systems and technologies. The attitude
control system uses bipropellant hydrazine thrusters. The electrical power system
consists of two solar panels with an overall surface area of 100m² providing up
to 20kW (BOL) in travel-mode. The energy is stored using four battery sets with
Li-Ion cells. Around 75m² of radiator surface are body mounted on the modules,
which can also be used as shield against micro-meteroids and debris.
A robotic arm, based on the Shuttle Remote Manipulator System (SRMS) and
capable of lifting up to 30t, is mounted to the MRM. Additionaly one Eurobot, also
stored in the MRM, can be used to support the astronauts during EVAs.
The life support system ensures a habitable environment and consists of the
following subsystems: atmosphere management, water management, food
management, waste management, and radiation protection. For the atmosphere
management and the water recycling a (semi-)regenerative system is provided,
while food, waste and water pollutants are stored (Figure 3.6).
Figure 3.6: Sketch of the GEV-ECLSS, Team Blue
3.3.2 Team Green
The GEV designed by Team Green is based on a linear and modular structure. As
shown in Figure 3.7 large free space is provided for maintenance activities. The
main difference of this GEV approach is its localisation at the Lunar Space Station
(LSS) in the Earth-Moon libration point 1 (EML1). This significantly reduces vehicle
mass and ∆V requirements, however, it comes with a more complicated logistics
need.
Assembly and Configuration
The reusable GEV itself comprises three modules:
• The Habitation Module (HM, mass 12t, cylindrical 8m x Ø4.15m) offers the
complete life support system with radiation shielding, habitation volume,
and the thermal control system. Extensive work has been done concerning
the human aspects and particularly the interior design of this module. It
24
is divided into three parts, dedicated to private and common activities and
the operation interface respectively.
• The Mission Module (MM, mass 2.5-5t, cylindrical 2.5m x Ø4.5m) has three
docking ports and one airlock. Two lightweight truss elements on both
sides are used to store the maintenance payload and robotics.
• The Service and Propulsion Module (SPM, mass 21t, cylindrical 9m x Ø4.5m)
contains the fuel tanks, the fuel cells for the ECLSS, the solar arrays as
well as thrusters and gyros for attitude control. Its CH4/LOX main engine
(30kN, Isp 360s) boosts the spacecraft during the mission.
The GEV is assembled in LEO within one year and transferred to EML1 using the
ATV-HD transfer vehicle with two additional external tanks. This mission scenario
requires only a single boost to EML1, where the GEV is docked to the LSS. It results
in a total, reusable in-orbit dry mass of about 21t.
Basically the already developed transport
elements for the LSS are used to provide
crew exchange and resupply flights for
GEV mission preparation. A Soyuz Crew
Transfer Vehicle (S-CTV) brings the
astronauts to EML1, while an ATV-derived
cargo vehicle carries fuel, pressurized
and unpressurized cargo. Each of them
needs an ATV-HD kick stage for transfer
injection, resulting in two launches each
for crew and supply flights. Due to the
large size of the SPM, two missions can
be flown with one tank refill from Earth,
possibly reducing the necessary number
of launches for GEV operations.
Figure 3.7: The reusable GEV
configuration, Team Green
Mission Design
The GEV is stationed in EML1 where the crew and the supply modules joining
it for a mission. These modules are left behind while the GEV (HM, MM, SPM)
travels to SEL2 or LLO. Due to the staging in EML1, the ∆V for the actual missions
is drastically reduced, being about 1000m/s as a very conservative round-trip
estimate to SEL2 and about 1400m/s for the round-trip to LLO. This can easily be
handled by the SPM without any need for further propulsion modules. After the
mission the GEV returns to the LSS and the astronauts use the S-CTV for the flight
back to Earth. This configuration allows transferring only the required mass from
and back to Earth. Also it makes complicated and costly manoeuvres for Earth
recapture unneccessary since only the crew vehicle returns using a direct reentry.
Docked to the LSS the GEV can stay in standby mode or be used as temporary
extension of the station capabilities.
Subsystems and Simulation Results
Some new technologies have been used like ultra-thin GaAs solar cells (46m2, 4kg/
kW) and advanced carbon-carbon heatpipe radiators (15.6m2, 2.11kg/m2).
For the repair mission a single manipulator arm derived from the European ERA
(DS-ERA) and a compact multi arm robot (Eurorobot) are used. If necessary, the
LSS robotic arm could be taken for further support to astronauts and maintenance
tasks.
25
The life support system is based on a partially regenerative physiochemical system
optimized for serving three astronauts for about 70 days with a margin of 14 days.
It supports long standby periods and easy starts. Water and oxygen cycles (Figure
3.8) have been designed as regenerative systems while food shall be supplied and
solid waste will be discarded. Based on an Electrochemical Depolarized Concentrator
(EDC) for CO2 removal, a Sabatier reactor (SR, H20 recovery), a Vapour Phase
Catalytic Ammonia Removal (VPCAR, H20 processing) and Multifiltration units
(waste water processing) the ECLSS ensures redundancy. A synergy with the
radiation protection is identified since the water tanks protect the crew. For safety
reasons, the control devices are disposed all along the Habitation Module and
each compartment is autonomous in terms of atmosphere management. A Salad
Machine is used for experimentation with respect to future exploration.
Figure 3.8: Air (left) and water (right) management in the ECLSS, Team Green
Several system failures such as damaged CO2 filtration, oxygen tank leakage
and complete system failure have been simulated using the ELISSA software and
showed sufficient safety factors for the crew. In case of a complete failure of the
atmosphere management, a number of non-renewable elements such as oxygen
candles and CO2 absorption pads can be used. Table 3.2 exemplarily presents the
survival time in case of oxygen tank damage, which shows to be long enough for a
three astronaut crew to return from SEL2 to the LSS if half of the oxygen is lost.
The cost of development and 10 missions operations has been estimated at about
8.5 billion €. As future options some alternative launchers could be used and
inflatable structures could improve usable volume. Since the GEV is a modular
structure it is easily upgraded and new missions could become possible by variation
of the configuration and modules.
Crew
Loss of 1/2 O2 tanks
Total loss of O2 tanks
3
32.00 days
13.03 days
6
16.00 days
6.65 days
Table 3.2: Survival days (non-toxic) with oxygen tank loss, simulated by Team Green
26
3.4
Design Evaluation
3.4.1 Evaluation Task
After the designs of the space stations were completed and the results presented,
the teams were disbanded. With respect to their task during the conceptual design
phase the former team members were now reassigned to one of seven evaluation
committees (see below). Each committee focuses on different evaluation criteria
regarding the accomplishment of the objectives, the requirements and the
constraints specified in the mission statement:
• Committee 1 : Utilization and Programmatics
a) Utilization potential according to customer’s demands
b) International cooperation
c) Costs
• Committee 2 : Overall Configuration
a) Minimum configuration and growth scenarios
b) Overall mass and size comparison
c) Pressurized module and external facility configuration
d) Rendezvous and docking
• Committee 3 : Mission Design
a) Mission/Systems hardware concept
b) Assembly strategy
c) Operations strategy
• Committee 4 : Attitude and Orbit Control Issues
a) Orbit control and trajectories
b) Attitude stability and controllability
• Committee 5 : Subsystem Issues
a) Power generation
b) Thermal Control
c) Propulsion
d) Synergetic Issues
• Committee 6 : Human Aspects
a) Environmental Control and Life Support System
b) Radiation protection
c) Human Factors
• Committee 7 : Operations and Servicing
a) Operations
b) Robotics
c) Extravehicular activities
3.4.2 Evaluation Findings
Each committee examined and analysed the designs of Team Blue and Team Green
in detail. This section summarises the results of three exemplary committees –
Committee 2, Committee 5, and Committee 6 – and shows how the members of
both teams reflected their own designs and evaluated the different solutions.
27
Committee 2: Overall Configuration
To evaluate the space station configuration the committee compared general
configuration issues like mass, hardware concept, and crew safety. Both teams
presented a successful configuration without any major flaws or conceptual
mistakes.
a) Minimum configuration and growth scenarios
Both GEVs are quite well balanced. Team Blue offers better expansion capabilities
by two free docking ports and four reusable modules whereas Team Green provides
one docking port and three reusable modules. Team Blue has to consider the
balance issue when docking only one additional module at the DNS.
b) Overall mass and size comparison
Parking the space station at the LSS, size and weight of the GEV of Team Green
are smaller than for the vehicle of Team Blue parking the GEV in LEO: Team
Green installs a total mass of 37t in space in contrast to 100t of Team Blue. But
consequently the re-supply mass of Team Green is much higher. Comparing the
power budgets Team Blue demands 50% more power than Team Green, resulting
in a bigger EPS.
c) Pressurized module and external facility configuration
None of both teams appoints a defined crew orientation. Both teams provide
redundant access and no dual egress. Team Blue permanently offers the Soyuz
vehicle as escape vehicle while Team Green’s escape vehicle is left at the LSS.
d) Rendezvous and docking
For rendezvous and docking manoeuvres Team Blue provides better redundancy
than Team Green. There is no special flight mode needed in both vehicle designs.
Committee 5: Subsystem Issues
The task of Committee 5 was the analysis of the design strategy. The type, the
technology and the amount of subsystem elements and their synergetic relations
are compared.
a) Power generation
Both teams provide a combination of solar arrays for power generation and lithiumion batteries for energy storage, thus no future technologies like solar dynamic
generators or regenerative fuel cells are considered. Team Green calculated a
maximum of 8kW based on calculations of each subsystem whereas Team Blue
assumed a maximum power of 12kW by an extrapolation of existing space stations.
Team Green installed solar arrays of ultra-thin-film GaAs cells, a future technology
available at 2015 with higher efficiency. The area of the panels is calculated to
46m². Team Blue resorted to conventional GaAs cells with an area for the panels
of 100m². The Li-Ion batteries of Team Blue are a new generation and supply
8.8kWh fully charged and are used for shadow phases, Team Green installed a
battery supply of 35.6kWh absorbing power peaks or emergencies of the system
and forfeits the mass advantage by the solar panels.
b) Thermal Control
The thermal control system of Team Green consists of a 33kg light carbon-carbon
heat pipe radiator rejecting a heat of 12kW. It outmatches the conventional bodymounted radiator with a mass of 750kg at 23kW used by Team Blue.
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c) Propulsion
Both teams developed propulsion systems for the main propulsion and the AOCS.
Team Blue elaborated a more detailed concept for the main propulsion system
consisting of an ATV-HD equipped with a VINCI engine using LH2/LOX as propellant,
an ATV-LD equipped with a RS 72 engine using MMH/N2O4 as propellant and a
Large External Tank Module (LETM) carrying 17.8 t of propellant for the ATV-HD.
The maximum propellant mass is 20 t. The AOCS provides two sets of 16 thrusters:
one set for AOCS during assembly and assisting the GEV, another set is scattered
over the complete GEV structure. Team Green uses 40 thrusters and four CMG
systems with three CMGs per system. They are placed on the SPM, HM, and MM.
The main propulsion is a 30 kN engine running on CH4/LOX as propellant but not
specified in detail. The maximum propellant mass is 25 t. Differences to Team Blue
result from the different mission concept.
d) Synergetic Issues
Both teams integrate synergetic effects. Docking the GEV to the LSS, Team Green
identified synergisms like additional living room capacity, robotic support and
AOCS capability. 1.5 t of re-supply mass can be provided for the LSS. The GEV can
be used as a rescue module for the LSS crew in case of emergency. Solar arrays
and radiator panels support the AOCS. Team Blue combined the solar arrays with
aero braking manoeuvres and calculated the saved propellant. The body mounted
radiators also serve as a protection shield against debris and meteoroid impacts.
Committee 6: Human Aspects
Committee 6 analyzed the elements and the performance of the ECLSS. The
criteria base on rateable facts written in the final report and the final presentation
of each team. The radiation protection is evaluated by comparison of mass and
GEV position. Evaluating the Human Factors the committee refers to detailed ideas
of each team.
a) Environmental Control and Life Support System
The ECLSS of both teams differ scarcely. The main difference occurs at the failure
management in the atmosphere system. Team Green uses oxygen candles and CO2
absorption pads whereas Team Blue provides redundant second devices. Considering
gas losses through leakage both teams designed a widely closed atmosphere
system consisting of an EDC, Sabatier Reactor, SWFE, TCCS, and CHX. The water
system is half-closed and arranged by multifiltration and urine filtration. Open
loops are applied for food (re-supply) and waste (return) management. Studies
at biological systems for closing the carbon loop are offered by a photobioreactor
(Team Blue) and a salad machine (Team Green). The ECLSS of Team Green is
capable of performing a mission of 70 days with three persons, Team Blue regarded
a mission of 80 days with three persons and a mission of 30 days with six persons.
Team Blue calculated a higher total mass for its ECLSS than Team Green.
b) Radiation protection
Radiation protection against solar flares, the most minatory radiation source in
terms of the mission statement, is adequately considered by both teams. The
equivalent masses for both shelters result from a combined structure of the water
tank and an aluminium structure. The shelters have to be positioned perpendicularly
to the Sun during relevant solar activities.
c) Human Factors
Human Factors contain many different aspects like zoning, interior design,
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ergonomics, scheduling, operation responsibilities, social organisation, and
psychological support. Team Green designed a very detailed concept of the interior
design of the HM incorporating many human factors aspects. Three zones are
created for privacy, working and social activities with appropriate lighting, colours
and window locations. A detailed division for the crew and the ground support were
elaborated depending on the mission mode. The daily schedule was composed
in terms of a regular operation mode. Team Blue provides also three zones, a
schedule, and a social structure but not in the same detail as Team Green.
3.5
Feedback
To provide feedback the participants were ask to fill in questionnaires concerning
the tools, methodology and the SSDW in general. Many participants returned the
completed forms with valuable information to improve the workshop. The outcome
is very encouraging as indicated in the figures below. The diagrams show the most
relevant results, based on 18 questionnaires. The participants regarded the task as
very challenging. Yet they greatly enjoyed and appreciated the workshop, as also
reflected by the quotes and comments below.
“... good opportunity to train team working
and also project management ...”
“The workshop made clear that we need more of these to
prepare students for their life after university ...”
“... it was nice to meet so many people from many
different countries, exchange ideas, design together ...”
“Experience, knowledge, fun and friends
- what do you want more?”
“Excellent, well worth the effort to come. The task was very interesting and I learned a lot
new things. The atmosphere was very good and the organizers were helpful and friendly ...”
“Great social events...“
“I was expecting to put the theoretical work we
learn in university into practical use, and it turned
out pretty well. ... It is a really valuable experience
that I can recommend to other people.”
“It was a really good experience. It enabled me to learn
a lot about project designing, space engineering and
team working. I want to thank all persons who worked
out to make this great event happen and also all the
participants for having such a good time together.”
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4
CONCLUSIONS
The Space Station Design Workshop 2006 at the Institute of Space Systems in
Stuttgart was yet another very successful and intensive event. With 27 truly
motivated participants from all over the world, it demonstrated the demand and
the potential of such interdisciplinary workshopon human space missions and
systems engineering in general.
Reacting to the current and future human exploration strategies to Moon and
Mars, the SSDW environment has been extended within the last years and the
students were tasked with a transportation scenario within the framework of a
sustainable exploration architecture. The Geospace Exploration Vehicle (GEV) is a
versatile space systems, capable of travelling to numerous destinations in cis- and
translunar space. Its primary task are servicing missions to multi-billion-dollar
hardware installed at SEL2, but it can also support lunar exploration as a transfer
or rescue vehicle.
Supported by a concise, yet flexible methodology, by customised, intuitive, rapidturnaround software tools and by experienced scientific staff the students and
young professionals successfully tackled this complex design problem. Both
designs, although very different in their implementation, show a high level of detail
and fulfil the objectives and requirements of the Mission Statement.
Therefore, the SSDW 2006 once again tested and verified its developing
methodology and tools. Future workshops will benefit from its findings, seeing
also further expansion of the tool capabilities to speed up the design process
through integration of analysis and simulation tools with various levels of detail.
More exploration mission scenarios towards Moon, Mars, and other interplanetary
destinations within our solar system will provide a great range of Mission Statements
for upcoming workshops, creating a design environment and educating capable
system engineers for our future in space.
We want to thank all guests, supporters and participants for their commitment and
contributions that made this SSDW such a success and valuable experience for all
of us.
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Contact Information
Space Station Design Workshop (SSDW) Team
Institute of Space Systems (Institut für Raumfahrtsysteme, IRS)
Universität Stuttgart
Pfaffenwaldring 31
70569 Stuttgart
Germany
Phone: +49 - 711 - 685 62375
Fax: +49 - 711 - 685 63596
Mail: [email protected]
http://www.irs.uni-stuttgart.de/SSDW

Space Station Design Workshop 2006 - IRS

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