Reducing the power of a command language to improve rover safety

When designing the command language for the Mars Exploration Rovers, it turned out to be important to decide what to omit. Sequences had to be flexible enough to react appropriately to contingencies, but if they became too complex, the team wouldn´t be able to validate them on the tight tactical schedule. (The rovers are commanded daily, so the uplink team has only hours to design, implement, and validate the day´s sequences, which typically run to hundreds of commands.) As a result, the rovers´ command language does not have the power of a full programming language. Many of these tradeoffs were wise, some have required workarounds, and a few lessons can be learned for future rover missions. On the whole, the MER command language is a valuable reminder that sometimes less is more: the chosen restrictions, by striking a careful balance between complexity and power, have enabled the uplink team to greatly exceed the mission´s goals.