R&D project planning with multiple trials in uncertain environments

We study project scheduling when individual activities carry a risk of failure, and where an activity's failure may lead to the project's overall failure. In the project planning and scheduling literature, this technological uncertainty has typically been ignored and project plans are developed only for scenarios in which the project succeeds. To mitigate the risk that an activity's failure jeopardizes the entire project, more than one alternative may exist for obtaining certain results, and these alternatives can be implemented either in parallel or sequentially, allowing to model the pursuit of alternative technologies.