Bug severity is an important factor in prioritizing which bugs to fix first. The process of triaging bug reports and assigning a severity requires developer expertise and knowledge of the underlying software. Methods to automate the assignment of bug severity have been developed to reduce the developer cost, however, many of these methods require 70-90% of the project’s bug reports as training data and delay their use until later in the development process. Not being able to automatically predict a bug report’s severity early in a project can greatly reduce the benefits of automation. We have developed a new bug report severity prediction method that leverages how bug reports are written rather than what the bug reports contain. Our method allows for the prediction of bug severity at the beginning of the project by using an organization’s historical data, in the form of bug reports from past projects, to train the prediction classifier. In validating our approach, we conducted over 1000 experiments on a dataset of five NASA robotic missions software projects. Our results demonstrate that our method was not able to predict the severity of bugs earlier in development, but it was also able to outperform an existing keyword-based classifier for a majority of the NASA projects.