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Unformatted text preview: Flexibility 1. Introduction and Definition 2. Taxonomy of flexibility 3. Real Options & Other Financial Tools Introduction and Definition We have introduced the notion of the tradespace and the use of it to find Pareto optimal solutions. The idea of uncertainty was introduced as a different way of organizing the tradespace. It has also been found necessary to expand the tradespace to include other attributes: for example, flexibility, robustness etc. While many space systems have proven to be very successful, as measured by meeting technical requirements, it is often the case that they have outlived their nominal design lives. For example, the DMSP satellites have lived many more years than they were designed for. The GPS satellites have an average life of over ten years even though they were designed for seven years. Part of the reason for this is that if a satellite makes it past its infant mortality stage, the redundancy that is part of the design process combined with the design and operational workarounds for the space environment tend to be successful. Thus some satellite systems have ended up being used well beyond their design lives and in particular, have been used for missions somewhat different from what they were envisioned for. A good example is the DSP satellites. They were designed for the strategic mission of warning of attack from intercontinental ballistic missiles. They have actually been used in several conflicts for the detection of tactical missiles. This use required a substantially different architecture for use of the DSP results from that envisioned when it was designed. As another example, many commercial communication satellites routinely live 15 or more years. Indeed the limiting factor tends to be fuel on board the system for precision station-keeping. Even when this runs out and the satellite starts to drift (at geosynchronous orbit), it can be still be used for a while as long one has a tracking antenna in the ground architecture. As another consideration, the rate of change of digital technology is much shorter than the lifetime of many modern satellite systems. Note that this was not true in the early days of spaceflight when satellite lifetimes was measured in weeks. Given this, the satellite has to be designed to be using parts which will be generations out of date at the end of its life. These examples suggest that for long lived systems, the considerations of flexibility should be included in the architectural design. That is, given that the space system architecture may end up being used in different ways than originally envisioned, can the flexibility to do this be embedded in the design. We start with a formal definition of flexibility. Flexibility is defined as the property of a system to respond to changes in initial requirements and objectives, after it has been fielded, in a timely and cost effective way i . This definition places the emphasis on change after the system has been fielded. Presumably change before the system is fielded wouldafter the system has been fielded....
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- Fall '03