From SEDSWiki

Contents 1 SEDSat-2 - An international 'open design' collaboration of students constructing a Cubesat 1.1 Abstract 1.2 Introduction 1.3 The Project and the Team 1.3.1 Systems Engineering 1.3.2 Structure 1.3.3 Payload 1.3.4 Ground control 1.3.5 Communications 1.3.6 Attitude Determination and Control 1.3.7 Command and Data Handling 1.3.8 Power 1.3.9 Marketing and PR 1.4 Decision making and design process 1.5 Technical Specifications 1.6 Conclusion 1.7 References

SEDSat-2 - An international 'open design' collaboration of students constructing a Cubesat

Abstract

SEDSat-2 is an international collaboration of students around the world planning, designing, constructing and running an open design remote sensing satellite that will be launched in 2008. The primary payload will consist of a digital imaging device, however the main focus of the project is of educational nature and wants to prove that it is possible to work together on a common goal and include modern virtual tools for online collaboration and decision making in a complex technical project. The project wishes to demonstrate how virtual collaboration happens and strives to become a test-bed for similar future projects. The project has two portals to the outside world, a blog (http://blogs.seds.org/sedsat2) and a website (http://sedsat2.seds.org/) where current activities, decisions and outcomes can be pursued by public.

Introduction

Ever since 1983 Theodor Levitt wrote his well-known article on globalization, many things have changed, globalization has moved on into other areas of human activity than only the markets and changed people's lives to an unanticipated extent. Nevertheless, the average university-level students' learning experience once revolved around their local geographic vicinity. This is partly a consequence of the fact that these students face challenges, including homework, curriculum-based projects, examinations, thesis, the need for networking, etc. Students who plan to forge a career path in the space industry have to work even harder, as this pioneering field needs individuals of the highest caliber in every respect. Many fields in the space industry are still in their early stages and have need of young visionary entrepreneurs who harness every resource available to them to break barriers and bring these activities to a new level. This is precisely the point of SEDSat-2, a project undertaken by the Students for the Exploration and Development of Space (SEDS). Students from Austria, Bulgaria, Canada, Germany, India, Italy, Kuwait, Nigeria, Norway, Philippines, Russia, Spain, United Kingdom, and United States have come together with a common vision to build a pico-satellite, overcoming geographical, financial, personal and other obstacles, not only to prepare themselves for the competitive and challenging world of the space industry, but also to do their part in serving the education of students globally.

With the diverse backgrounds of all the participants in the project, it was understood from the beginning that there would be unique obstacles and limitations. These include the limitations that are inherent in communicating almost exclusively via the Internet, the limitations of the tools that are available for networking over the Internet, the challenges in forming a working organizational structure, and a work flow process, and finally, the challenges in finding funding for the project. All these obstacles are present as well when an entire team is situated in one place; there is an inherent sense of cohesiveness, which helps in overcoming said obstacles. They are, however, magnified when one considers that most of the team members have, at this point, not even met each other, and that scheduling meetings are difficult when the sun rises at different times for many of the people involved.

It is these challenges we intend to provide first-hand insight to in this paper, as well as providing such solutions as our experience has brought to us, in order that similar projects in the future might benefit from them. We also hope to, in this paper, underscore the fact that the novel paradigm of collaboration among geographically distributed students (with varied backgrounds) in building a picosatellite may be emulated by future student picosatellite teams – benefits are derivable from the tools and methods employed whilst collaborating on the SEDSat-2 project. Future cubesat project teams may also benefit by learning lessons from studying how our kind of collaboration impacts a cubesat project; this in turn enables them to adopt best-case experiences while avoiding drawbacks.

The Project and the Team

The SEDSat-2 project aims to build a picosatellite, strictly adhering to the specifications of the California Polytechnic Institute's CubeSat program(CubeSat Design Specifications, 2004). It will have a mass of not more than 1000 gramms and have dimensions of ten centimeters by ten centimeters by ten centimeters. The primary payload is proposed to be an Earth imaging payload, specifically an imager doing visible wavelength remote sensing. All systems onboard will be build with commercial off-the-shelf (COTS) components in order to minimize the time required to finish the project and to ensure that the main focus of the team remains unchanged, i.e., to study ways of integrating subsystems that have been designed and built in different parts of the world, with the limitations that the vast distances bring.

As mentioned, the team includes members from thirteen countries. These participants have been grouped into different sub-teams, most of them corresponding to the different subsystems in the satellite. Each subsystem has a leader, who not only coordinates the decision making process within their own subsystem, but also acts as a liaison with the other sub-teams. Thus, the team leaders effectively form a committee, which is headed by a body called the Core Committee, composed of three of its members. This core committee was introduced with the purpose of accelerating and centralizing decision taking processes by effectively having a steering team, and was influenced by the proved concept of project management in larger free and open source software projects. (Mockus et al. 2000, Raymond 1999, Sanders 1998)

Systems Engineering

The systems team works to maintain relationships between the distributed SEDSat-2 teams and individual team members while analyzing the technical feasibility of integrating all satellite components. This is particularly challenging as worldwide dispersion of collaborators requires increased communication among different teams to ensure mutually balanced information levels. For this, a matrix of team representation has been set up, ie each member of this team is responsible for communication with a certain other subsystem. The systems team is responsible for testing the final satellite and ensuring overall program and mission success. The team manages the system budgets in coordination with other subsystems. It takes care of requirement management on Protoforge and ensures the traceability of those. At the same time, the interface definition for all technical subsystems is being guided with the establishment of interface tables for documentation. Also, the team will take care of the planning of validation and verification of the CubeSat.

This team is particularly heterogeneous in terms of internationality and university backgrounds. We have members from Austria, Bolivia, India, Russia and Spain who are studying thermodynamics, international business, mechanical engineering and astrodynamics. Our external advisor, Reinhard Pruegl, is assistant at the department of Entrepreneurship and Innovation Management at Vienna University of Economics and Business Administration providing us valuable feedback based on his professional background in technology management and science. Internal advisors are Aaron Schultz and Kirk Kittell, professionals in the aerospace industry and SEDS alumni who are enourmously helpful with advises in this specific area and provide the project with valuable contacts in the industry. Also, Aaron Schultz is the programmer of our online open design collaboration tool Protoforge that enables us to manage our requirements.

Structure

The Structure Sub-system is responsible for the design of inner and outer structure of SEDSat2. and design of the thermal control system. The sub-system also ensures that dimensional and mass criteria specified in the CubeSat Design Specifications are met by all sub-systems.

Design of a cubesat without an idea of the mass and dimensional specifications of all sub-system is meaningless. Towards this end we fixed the mass budget for each sub-system and requested for inputs via the Interface Tables. The Interface Tables would serve as a one point reference to the data required by all/whichever sub-system.

Thus far, the Structure sub-system has been accumulating data using the Interface Tables and have been looking into requirements and implementation of the thermal control sub-system. We are sure that as soon as all the data input is provided, we can begin the design and testing phase of SEDSat2.

Payload

The Payload team of SEDSat2 consist of physics and computer science students at the university of Wales, Aberystwyth. In the concept design phase of the project, the payload team suggested and evaluated different payload proposals as well as receiving payload proposals from other subsystems. Each concept was thoroughly examined by criteria such as risk, technical complexity and educational potential.

The goal of this procedure was the payload selection process, which was carried out after the various payload concepts were properly researched. For the actual selection the payload team produced a report to the rest of the project participants, presenting its evaluations of each concept as well as recommending several concepts for a project-wide vote.

Ground control

The responsibility of the ground control subsystem is to facilitate communication between the satellite and the earth. This shall be accomplished by one or more ground stations using amateur radio frequencies and open, unencrypted data. Ground control will have to coordinate their efforts with the communications and command and data handling subsystem to agree on a command set for satellite command operations and data downlink.

In more detail the task of the ground control subsystem will be to create at least one automatically tracking ground station unit. Downlink capacity can be further increased by using more than one ground station at a different geographic location, thereby providing us with access to additional satellite passses. Cooperation with existing ground station networks such as GENSO will be considered.

Communications

The Communications team consists of two members, both living in Manila, Philippines; one is a mechanical engineering student and the other is an electronics and communications engineering student. The team's advisor is also in the Philippines. The responsibilities of the team include the design and selection of the components that will make up the satellite's communication system, i.e., the system that will facilitate the communication of the satellite with the ground.

Attitude Determination and Control

It is understood that given that SEDSat2 will include an imager doing visible wavelength remote sensing, that it will require an Attitude Determination and Control System. It is further understood that given the complexity of such systems in general, and the limited experience of the students involved, the simplest, most reliable system possible should be chosen. For this purpose census of previous CubeSat missions was conducted to determine what kinds of systems exist, and which ones are most frequently used.

A candidate ADCS System fitting the simplicity and reliability requirements mentioned above was found. It is one that uses an on-board system of magnetometers to determine the local magnetic field, and then compares the result with that contained in an on-board map of the earth's magnetic field. For the purposes of obtaining a result from the on-board map, a model of the satellites predicted orbit is also included on-board. With the satellites attitude and the local magnetic field known, magnetic torquers are then used to leverage this magnetic field to achieve the desired attitude. This system satisfies the simplicity and reliability requirements because it involves the fewest number of components, and has been tried, tested, and documented by two previous missions: Aausat and NCUBE.

Command and Data Handling

The command and data handling subsystem team is composed of members from Canada, Nigeria, Norway and the United States. The command and data handling subsystem is responsible for directing and managing the flow of information between satellite subsystems. This will involve both control and data transfer operations between satellite subsystems and the CDH main computer as well as transfer to and from ground via the communications subsystem.

Responsibilities of the CDH subsystem team also include the designing of the onboard serial control interface that will link various subsystems together in a network with the command and data handling subsystem as the controlling node. In addition, it involves the programming and design of the SEDSat2 main computer system that will link up with the rest of the satellite via the aforementioned serial control bus.

Due to design constraints such as very limited power supply, radiation and extreme temperatures the command and data handling subsystem will have to be designed in a manner that ensures both robustness and redundancy.

Power

The power team consists of members from Norway, the United States and Africa. Communication between the power team is mostly on e-mail and instant messengers. Meetings are scheduled between the members through e-mail first, in order to verify a day and time, then put into Protoforge to alert members of other teams to the meetings. Participation of members from teams other than power is encouraged because they have much insight into how to make the power system function efficiently with their respective systems.

The power system will consist of space-grade solar panels on all sides of the satellite. Solar panels will be used because solar energy is abundant and reusable. If a satellite power system were to only use batteries or some other form of energy besides solar power, the power capacity would eventually run out without some kind of recharge. The reason all sides of the satellite will be covered with the solar panels is so that whatever side is facing the sun, the various systems will be able to receive solar power.

The solar panels will be connected by wires to a circuit board, which will distribute the power received from the solar panels to the various satellite systems.

Lithium-ion batteries will be used to power the satellite during dark hours and eclipses. The batteries will be charged by the solar panels while exposed to sunlight. They will also be connected to the circuit board for distribution of the power to the various systems.

Marketing and PR

Recently a need for a specialized team working on Marketing and PR has been detected. We have recruited a team of highly ambitious business students who have been working on a strategic plan for raising the funds necessary to run the CubeSat project, create a brand including corporate design and identity, establish a decent web appearance and manage relationships with our corporate sponsors.

Recently a need for a specialized team working on Marketing and PR has been detected. We have recruited a team of highly ambitious business students who have been working on a strategic plan for raising the funds necessary to run the CubeSat project, creating a brand including corporate design and identity, establish a decent web appearance and manage relationships with our corporate sponsors. The team focuses on three strategies. Research and development: Our subsystems use products, manufactured by our R&D partners. Image marketing: Internationally operating partners are given the opportunity to show themselves supportive of an enthusiastic, young and motivated generation; this certainly creates a positive image. Active marketing: We give organizations the chance and a platform to present themselves effectively in the aerospace industry sector.

Decision making and design process

Designing a satellite that's about one kilogram heavy and is a cube with ten centimetres to a side may not seem challenging to most of the readers of this paper. What needs to be be stressed is that the satellite provides an object for the team members. The real novelty of this project is the effective virtual collaboration and integration of a project not designed in one geographic locale. In essence, the real result of this project would not be a space-worthy satellite (although, that is certainly the mark of a successful project) but a finely tuned and efficient decision making and design system that will enable students in this increasingly global world to be a part of similarly challenging projects, and not be limited by time or distance.

Team Communication

Central to the decision making process is effective communication between team members. The Internet provides valuable, affordable and efficient tools. The project makes use of instant messaging clients, voice-over-IP clients, email lists, the Wiki and an internet software application developed by one of the project's advisors, called Protoforge. So far our blog (blogs.seds.org/sedsat2) is the portal for the world to gain insight into our project status, in addition a representative webpage is about to be set up at the time of writing. Meetings are held via e-conference functionalities in instant messengers, and transcripts and minutes provided records for the rest of the team to see. We have found that instant messaging has its limitations. Such a conference ideally accommodates only a few participants in order to facilitate an effective conversation flow. The medium requires strong discipline as otherwise sub-topics emerge and reduce overall efficiency and productivity of a meeting. Despite its limitations, decisions can be made in a comparatively shore time. In contrast, while email lists allow for a more structured and detailed discussion, it may take days before the conclusion to a discussion is reached.

The Wiki and Protoforge serve as tools for documenting and formalizing team decisions, which is a very important part of team communication. This paper was written using the Wiki with a number of geographically dispersed co-authors adding to it and editing it as needed. Protoforge is a requirements management tool that is similar to the Wiki in function with the additional feature of being able to vote on individual requirements in order to make them static. Requirements that are baselined by a team vote cannot be changed unless there is another team vote. This has proven to be useful for official, formalized decision making in the form of baselined system requirements that all team members can respect and abide by regardless of personal relations or geographic location.

To facilitate the need for decision making and for a central repository of well organized information the SEDSat-2 project adopted a wiki like, web based tool called Protoforge (http://protoforge.org/). This tool provides our team with a mechanism for individual team members to express ideas for what the satellite should be. After discussing, editing and voting on those ideas as a group the definition of our satellite is expressed as a baselined set of system requirements that can only be changed again through another vote. Having an organized set of system requirements allows us to organize our information as to facilitate trade studies during the early design phase, change impact analysis during the mature design phase, and will support system verification efforts by managing information associated with tests, analysis, and inspections.

Our decision making process was then structured to take advantage of the tools at our disposal, and minimize the effect of the disadvantages. Meetings within each subsystem were solely in the domain of the subsystem leaders, and took place according to their discretion. Since each subsystem had a small number of members, this allowed decisions on the most basic level, i.e. decisions pertaining to the respective subsystems, to be made quickly. Regular weekly meetings are held with the team leaders and these decisions are then communicated to the others. This allowed an efficient and productive discussion about the design of the overall satellite, as well as communicated important design considerations in each subsystem, which would undoubtedly affect other subsystems. The Core Committee acts as both a guide and a check, making sure that no decision would be reached that would compromise the integrity, scope and timeline of the project.

Decisions that have undergone discussion and are considered as necessary parameters for the satellite were then proposed as requirements on Protoforge, where it would undergo a voting process before being baselined.

Technical Specifications

Preliminary Mass Budget

Subsystem	Mass
Structure	300g
Payload	200g
Attitude Control	100g
Power	250g
Communications	100g
Margin	50g
Total	1000g

Preliminary Power Budget

Subsystem	Power
ADCS	250mW
Communications	320mW
Payload	300mW
CDH	80mW

Conclusion

The SEDSat-2 project has the unique challenge of connecting many students who are geographically distributed across the globe. Making decisions in such an environment can be very hard using classical approaches, and so minds must reach out and every available resource harnessed to create new approaches. Decision making and the design process must not only reflect an awareness of the limitations that the project faces, but must also turn these into an advantage. In the case of SEDSat-2, the limitation provided by geographical separation turned into an advantage in several ways. First and most important, expertise that was the result of different systems of education melded together to provide all participants with a unique learning experience that far outstripped that of their respective classrooms. Second, the team was made to come up with a structure that suited all participants regardless of cultural, academic or professional background. This resulted in an effective and productive design and decision making process that allowed the full participation of all the team members to their fullest capacity.

Further, a project of this scope and magnitude brings a lot to its participants despite the inherent setbacks. It connects like-minded individuals across the world and unites them with a common vision and goal, thereby securing a link between the future professionals of the fledgling space industry. This project also provides its participants with the training and experience in structured decision making for technical projects, which is necessary for their future careers.

References

CubeSat Design Specifications, Revision 9 (June 2004), downloadable at http://cubesat.atl.calpoly.edu/media/Documents/Developers/CDS%20R9.pdf

CubeSat Community website: http://www.cubesat.org (rem: do we need this?!?!)

Requirements for using Amateur Frequencies (2003) International Amateur Radio Union, downloadable at http://iaru.org/satellite/IARUSATSPECREV14A.pdf

Shisko, R.: "Systems Engineering Fundamentals", Defense Acquisition University, downloadable at http://www.dau.mil/pubs/gdbks/sys_eng_fund.asp

Riis, Ole: "Spacecraft Structures" (YEAR) Terma Industries Greena

Hansen, Flemming: [http://www.dsri.dk/roemer/pub/Cubesat "DTU Satellite Systems and Design Course Space Environment"] , Danish Space Research Institute

Levitt, T.: "Globalization of markets", Harvard business review (1983) vol:61:3 p92

A. Mockus, Roy T. Fielding, J. Herbsleb: "A Case Study of Open Source Software Development: The Apache Server"; 2000;

Raymond, E. S. : The Cathedral & the Bazaar (1999) Sebastopol;

Sanders, J.: "Linux, Open Source, and Software's Future"; 1998.

SEDSat1 Project: http://www.seds.org/sedsat

NASA Systems Engineering Handbook, SP-6105, pp. 50-51, (1995) http://ocw.mit.edu/NR/rdonlyres/Aeronautics-and-Astronautics/16-892JFall-2004/9722DD5E-CDBB-4B0F-8F5E-791CFF5FD359/0/nasasysenghbook.pdf