Defining Software Flexibility in Space Systems
Roshanak Nilchiani, Daniel E. Hastings · Space 2004 Conference and Exhibit · 2004
*† On -board software is a vital element in the operation and functionality of a space system. The functiona l requirements of space systems can change over time, and unforeseen failures can affect systems performance, thereby necessitating modifications to the on -board software. It is thus important to know in how far the possibility of remote software upgrades can help the system to maintain its functionality in an uncertain environment, or even use the uncertainty to its advantage by adding or improving functionality. In this paper, the concept of software flexibility for space systems is defined and a measure for its evaluation is introduced. The flexibility measure is designed such that it can incorporate monetary as well as non -monetary changes in the systems performance. Subsequently, the values of software flexibility for the Deep Space One mission, and th e Galileo mission are evaluated. The case studies show how existence of this relative quantitative measure for software flexibility allows decision -makers to assess the extent of software flexibility their space systems can exhibit in the face of uncertain ty. The case studies also indicate that the flexibility of a space system depends significantly on the relative cost of substituting the entire space system versus the cost of upgrading software. Given the fact that remote software upgrades are often far l ess expensive than on -orbit servicing and upgrading of hardware components, it becomes clear that software flexibility could be used as a first choice in flexibility to the extent that hardware limitations permit. Nomenclature b a t t F � = Flexibility of the system over a time interval i R = Discounted value of monetary benefits of function i of the system over its specified lifetime i = system function i that is of importance to the stakeholders ) (t p i = Probability that a flexible change occurs to function i at time t i U = Utility of non -monetary system function i for stakeholders