Over the last decade and continuing into the foreseeable future, a trend has developed in the spacecraft industry of both number of missions and the amount of data taken by each mission increasing faster than bandwidth capabilities to send these data to Earth. The result of this trend is a bottleneck between data gathering (on-board) and data analysis (on the ground). This bottleneck can be overcome by performing data analysis on-board and only transferring the results of this analysis to the ground, rather than the raw data. One attempt to do this is being made by the NASA HPCC Remote Exploration and Experimentation (REE) Project, which is developing spaceborne embedded clusters. Spaceborne embedded clusters share many characteristics of traditional, ground-based clusters such as POSIX-compliant operating systems and message-passing applications, but also have significant differences, including packaging and the need for fault-tolerance and real-time scheduling in software. This paper discusses these similarities and differences, and how they impact application development.