In the previous parts of the book we have discussed individual systems which carry out purposeful functions. In Part 4 we will consider more complex projects and programs, which involve multiple systems. Multiple systems can exist and interact at a given point in time. They can also and grow and evolve individually and together over an extended time.
An optimized design to implement a set of goals or tasks will often result in such a multiplicity of systems. There are several reasons for this, which are described in the following paragraphs. We will call a set of systems that exist together at one time under one management, and have a common goal, a Project. When the set under common management and purpose exists for a long time, and there is significant growth, evolution, and replacement of older systems with newer systems, we call it a continuing Program. Despite the complexity or duration, the principles of Systems Engineering can still be applied to optimize the design of such programs. When the time period is long relative to changes in technology, society, and the environment, the Systems Engineering task may need to done repetitively or continuously to get the most benefit.
The Need for Multiple SystemsEdit
In general, the more complex, or more extended in location, volume, traffic, or time a project is, the more likely it will result in multiple systems. Different environments and available resources will drive different local solutions. Changes in technology and economics over time will also guide changes in design. Therefore in any large project or long duration program, using a combined system approach should at least be considered to see if it gives a better result. Some specific reasons include:
- Non-Linearity - A given transportation or engineering method often has a non-linear term in it's equations - at least quadratic if not an exponential. For example drag goes as the square of velocity, and rocket fuel required goes as an exponential function of velocity. Therefore it often is more efficient to break up the total job into components because the sum of smaller non-linear terms is less than a larger value with an applied exponent.
- Complex Needs - Humans have complex needs, and projects we wish to accomplish typically have multiple goals. This drives design solutions which use multiple materials, devices, fuels, etc. Therefore no single technical solution is likely to best satisfy all the needs.
- Economics - This is another advantage of a combining several systems. An "all or nothing" type monolithic system which requires a large up-front investment often turns out to be wasteful. Aside from the non-linear effects noted above, we cannot predict future technology developments, and large projects often have long development times. If you build in smaller steps, you have the opportunity to change direction if new developments come along, or retrofit an improvement to just the part that needs it. Finally, with an incremental project, you can get use out of it sooner, which can produce a higher return in the purely economic sense.
Whether to use one system or multiple systems should not be set ahead of time or by fiat. The decision should be made by analysis of the alternatives and choosing the best one. Sometimes this may not be possible because of non-engineering reasons. As a hypothetical example, the existence of a national civilian space program in the US (NASA) would make it difficult to divide or set up separate systems, even if it turned out to make sense from an engineering standpoint. Conversely, the historical divisions of space activities between NASA, and the Defense, Commerce, and Energy departments also would be difficult to combine, even if it were economical.
Structure of Part 4:Edit
The overall intent of Part 4 is to use the methods described earlier in the book to teach by example. We will work through an extended example for the design of a future program. Unlike printed paper books, the example does not have to remain static. The completed portion will show how the calculations and decisions are made. There will be opportunities for individuals or teams to develop ideas further, and those will be added as design studies. The best ideas will get incorporated back into the main discussion of the book. It is hoped this approach is both a useful teaching method, and a way to gain real experience and make progress in space programs.
Note that as the book as a whole is about 60% complete (Sep 2012), the organization of Part 4 is somewhat fragmentary, but we hope to improve it in the near future.
Example Program for Human ExpansionEdit
Our chosen example is a program for human expansion to more difficult environments, including space. The component systems within such a complex program interact with each other and the outside world, and the whole program evolves stepwise over time. We choose this as an example for several reasons:
- As a long duration and wide ranging example it allows us to demonstrate design methods for many types of systems and subsystems.
- In the following Design Studies section (Part 5) we can show in some detail how the calculations and decisions are made to arrive at a design.
- It is intended to also be a realistic program proposal incorporating current technology and concepts.
- Finally, readers are encouraged to add to the design studies to gain individual design skills and experience, and to practice working in teams with diverse skills.
Background of ExampleEdit
This program concept is partly based on work by Dani Eder, the original author of the Canonical List from which this Wikibook originated. It also includes many new ideas not yet pursued by government programs. In its present state it is not claimed to be the best possible program concept. Rather it is intended as a starting point, using recent ideas for space development, from which an optimal design can evolve by the contributions of many other people. We will use the Systems Engineering methods described in Part 1 in developing the proposed program.
Conceptual Design is the first stage in the life cycle of a program or system. We determine needs and goals to be satisfied, what criteria to use in selecting among designs, and a design concept for the major parts of the program, including how they will be built, operated, maintained, and disposed at end of life. We compare our new program to existing programs using the same selection criteria. If the new program is "better" by these measures, we recommend going forward to the next design stage. If it is not better, then we stop and wait for circumstances or technology to change, or try to devise alternate concepts. The full details of our reasoning, calculations, and decisions are too long to include in our discussion here. We will summarize them here, and refer readers to the full Human Expansion Design Study for the details.
The general process flow in Conceptual Design starts with general description and goals, which are noted in the next section. Following that we perform an analysis step to develop these goals into more detailed and quantitative statements. At present this has been done for the program requirements and evaluation criteria. The functional analysis to define more detailed program elements has been started, and later parts of the Conceptual Design process are incomplete. Candidate designs to fulfill the program elements are collated in the remainder of Part 4. They should be considered as pieces which might fit into the overall program, but have not yet been linked, or completed individually.
Human Expansion Program GoalsEdit
The program is intended to expand human civilization to more difficult environments, including space, for a number of reasons:
- Improving Life on Earth by developing better technology for living sustainably from local resources.
- Understanding the Earth Better by observing our home planet, its environment in space, and other planets and environments.
- Reducing Hazards from Space by identifying what they are, followed by developing methods to deal with them.
- Increasing Biosphere Security by adapting to more difficult environments, including future variations in the Earth itself.
- Expanding Material and Energy Resources by access to currently difficult Earth and space locations.
- Long Term Survival by dispersal to multiple locations and acquisition of critical new resources.
- Increasing Choice and Freedom by opening unoccupied locations to habitation.
- Increasing Opportunity by access to unclaimed resources and more efficient technology.
Side benefits from such a program are low cost access to space, removing a current barrier to its use; spin-off technology from doing difficult tasks, which then have use elsewhere; and optimism for the future by demonstrating we are not in a finite, closed world. An optimistic viewpoint in turn changes how people act. The benefits of the program accrue to civilization as a whole, although the specific projects may be funded and carried out by smaller organizations.
Initial Program AnalysisEdit
The initial set of program requirements were developed by carefully looking at the program goals and benefits, general systems engineering experience, and natural and human constraints. We divided the general goals into more specific statements with measurable parameters. We also looked at our ideas for approaching the design, and the first list of elements to be included in the program, to see if they yield any requirements. We combined and formalized the resulting statements to create a first draft of the top level requirements. Some of the numerical values are arbitrary, but we need to set something as a starting point, which can be adjusted later as the design evolves.
- 1. Objectives
- 1.1 Program Goal - The program shall expand human civilization to a series of new locations with increasingly difficult environments and distance.
- 1.2 Program Scale - Expansion shall be demonstrated by permanently supporting at least 95,000 humans total among new Earth locations and at least 2,000 humans per new space location.
- 1.3 Choice - Specific locations and their internal organization, function, and operation shall be chosen by program participants and location residents within the limits of design constraints.
- 2. Performance
- 2.1 Number of Locations - The design shall maximize the number of new locations, where new is defined by at least a 10% increase in an environment parameter or distance measured in time or energy terms.
- 2.2 Growth - Each location shall increase the capacity for production, habitation, and transport in a progressive manner.
- 2.3 Improved Technology - Locations shall increase the levels of self-production, cyclic flows, and autonomy in a progressive manner.
- 2.4 Improved Quality of Life - Completed locations shall provide an improved physical and social quality of life relative to the upper 10% of Earth civilization.
- 2.5 Data - The program shall collect and disseminate [TBD] data about the Earth's environment, surrounding space, and objects therein.
- 2.6 Resources - The program shall output a life cycle surplus of at least 100% of internal material and energy resource needs.
- 3. Schedule
- 3.1 Completion Time - The expansion to a new location shall be completed before expected progress in technology indicates a re-design is required.
- 4. Cost
- 4.1 Total Development Cost - The total program development cost for new technology and hardware designs shall be less than 50 times the unit cost on Earth, and 5 times the unit cost in space of the hardware.
- 4.2 New Location Cost - The peak net project cost for a new location shall be less than 50% of the expected long term net output.
- 4.3 Earth Launch Cost - The program shall progressively lower the Earth launch cost component of total system cost, with a goal of $0.08/kg of total system mass.
- 5. Technical Risk
- 5.1 Risk Allowances - Program designs shall include allowances for uncertainties and unknowns in knowledge, performance, failure rates, and other technical parameters. New designs with higher risk can be included in program plans, but a process shall be included to resolve the risk, and an alternate design with lower risk maintained until resolved.
- 6. Safety
- 6.1 New Location Risk - New locations shall progressively lower internal risks to life and property, with a goal of significantly lower risk than the general population.
- 6.2 Population Risk - The program shall significantly reduce natural and human-made risks to the general population, including external risks created by the program.
- 7. Sustainability
- 7.1 Biosphere Security - The program shall increase biosphere security by establishing alternate biospheres and long term storage of biological materials.
- 7.2 Survivability - The program shall design for the long term survival of life and humanity from changes to the Earth which will render it uninhabitable and depletion of critical resources.
- 8. Openness
- 8.1 Open Design - Technology and design methods developed within the program shall be open for others to use. Specific instances of a design and produced items may be proprietary.
- 8.2 Access - Development of a new location shall not prevent reasonable access for transit or to unused resources.
Setting discrete program requirements like the ones listed above are unlikely to be the optimum values, and do not help in choosing among design alternatives. For those purposes we choose parameters to measure our evolving design and guide it to the preferred result. We identify these parameters by again carefully looking at all the work done so far, and selecting the ones most important at the program level. After selection, we then scale and adjust their relative importance to each other so that a score can be determined for each design option or variation. Our resulting criteria and how they are scored is as follows:
|Criterion||Weight (points)||Scoring Formula (percent)||Notes|
|1.2 Program Scale (per location)||3.0||ln(average population per location/100) x 25%||Population is final design size for location after growth|
|1.2 Program Scale (total all locations)||4.5||ln(total population all locations/5000)x25%||Population is total design size after growth|
|2.1 Number of locations (count)||3.75||actual count of locations > minimum size @ 1% each||Minimum size = final size/years to grow to final size|
|2.1 Number of locations (range)||3.75||steps in environment, time, and distance range @ 0.5% each||10 parameters and definition of steps from discussion 2.1 above|
|2.2 Growth (rate/yr)||5.0||(equivalent % annual GDP growth of all locations -2.5%) x 10||internal production valued as if sold at market rates|
|2.3 Improved Technology (local resources)||1.0||% of local resources from program locations||by kg (mass) or Joules (energy)|
|2.3 Improved Technology (self production)||1.0||% of finished products from program locations||by economic value|
|2.3 Improved Technology (cyclic flow)||1.0||% of location mass flows reused||includes propellants, but not production for growth or sale|
|2.3 Improved Technology (automation||1.0||% reduction human labor hours||relative to current technology|
|2.3 Improved Technology (autonomy)||1.0||% required labor and control from within locations||based on necessary location functions|
|2.4 Quality of Life (GDP)||5.0||(equivalent GDP - $20,000)/1600||includes value of internal production and labor|
|2.6 Resources (surplus)||5.0||ln(material & energy output/internal use)/ln(2) x 25%||over program life cycle. Clip at -100%|
|4.1 Total development cost (Earth)||14.0 - S||(avg unit cost/total development cost) x 1000||S = 14 x (space/total) development cost|
|4.1 Total development cost (Space)||S||(avg unit cost/total development cost) x 100||see above for S|
|4.2 New Location Cost (Earth)||14.0-S2||[(ln(0.25xUS capital per person/location cost))/ln(2) x 25%]+100%||includes land value for US capital. S2 see below|
|4.2 New Location Cost (Space)||S2||[(ln(0.5 US capital per person/location cost))/ln(2) x 25%]+100%||S2 = 14 x (people in space/total in program|
|4.3 Earth Launch Cost ($/kg)||7.0||log($1600/(LEO transport per total system mass)) x 20%||total mass includes local space resources|
|5.1 Technical Risk Allowance (%)||5.0||(50% - technical uncertainty allowance) x 2||includes performance and design uncertainty|
|6.1 New Location Risk (relative)||7.5||[ln(0.25x general casualty risk/location risk)/ln(2) x 25%] +100%||casualty risk includes life and property|
|6.2 Population Risk (relative)||7.5||(% reduction to general population risk) x 5||from natural and program causes. Increased risk not allowed.|
|7.1 Biosphere Security (species-locations)||5.0||[(log(species maintained outside natural range x locations)) - 1] x 20%||in vivo or stored, humans are a species|
|7.2 Survivability (relative)||5.0||(% compensation for critical risks) x 5||includes all civilization level risks|
|Total||100||Sum partial scores x weight from each line above|