Beautiful Data

Introduction

When designing and programming an embedded system, one is faced with a variety of constraints. These include processor speed, execution deadlines, allowable interrupt latency, and memory constraints, among others. With a space mission, the constraints can be severe. Typically the computer onboard a space vehicle will have only enough expensive radiation-hardened memory to fulfill the mission objectives. Its central processing unit (CPU) will typically be a custom-made device designed to withstand the damaging effects of high-energy cosmic rays. By commercial standards, the CPU isn't fast, which is typical of radiation-hardened electronics. The trade-off here is speed versus the ability to take a direct hit from an interstellar particle and keep on running. The dual-core CPU in a typical PC, for example, wouldn't last long in space (nor would much of the rest of the PC's electronics, for that matter).

Then there are the science objectives, which in turn drive the software requirements for functionality and performance. All must be reconciled within the confines of the spacecraft's computing environment, and after numerous trade-off decisions, the final product must be able to operate without fatal errors for the duration of the mission. In the case of a robotic spacecraft, any fault may be the end of the mission, so there are requirements for getting things right before the rockets light up and everything heads off into the wild blue yonder.

On May 25, 2008, the Phoenix ...