Copyright © 2004 by Edward N Brown. Published by The Mars Society with permission.
SPACECRAFT COMPUTER SYSTEM DESIGN CONSIDERATIONS FOR A PILOTED MISSION TO MARS - Part 1
Edward N. Brown
Piloted deep space missions, such as a human mission to Mars, present new challenges in the design of spacecraft computer systems. Because of the human element involved, the demands of the operational mission, and the constraints imposed by weight, electrical power, reliability, environmental (especially radiation), and data processing performance considerations, general-purpose consumer or business oriented computer solutions are not acceptable . That does not imply that every circuit and every microchip for the computer system needs to be designed and constructed from scratch. Some may indeed be, but most will be developed by utilizing, modifying, or tweaking existing designs and products. But it’s not as simple as just selecting top-rated top-value components from a computer catalog or store shelf, hooking them up, and then fine-tuning the result. That system won’t do the job. The solution for this application must be engineered. What this really means is that it is not sufficient to simply state that the system must be “user-friendly, long life, low weight, low power, high reliability, robust quality, and high performance”. Like many other complex designs, “the devil is in the details”  and that is especially true in this application. While these design characteristics are valid, exactly how best to achieve them is a very difficult task. There are many questions to answer. How reliable does it need to be? How much power should it consume? How small does it need to be? How much processing throughput should it have? These are just some of the major and more obvious questions. A myriad of questions will present themselves as each area is investigated. The engineering challenge is to determine the optimal or appropriate levels and tradeoffs (quantitative where possible) among these characteristics such that all the operational, system design, and programmatic requirements (cost and schedule being just another two parametric constraints) are satisfied and the system contribution to overall mission success can be assured to a level that is acceptable to all the stakeholders. The best way to systematically go about doing this is to utilize standard Systems Engineering procedures and techniques to flush out the driving design requirements and eventually synthesize a working design . This two-part paper represents a combination of a presentation made at the 2002 Mars Society Convention (Part 1) and one made at the 2003 Mars Society Convention (Part 2)
There are no showstoppers and no technological leaps are required. The basic concepts, trade-offs, and approaches are presented in this Paper and the design process is well established in industry. We are better prepared to go to Mars today than we were to go to the Moon in 1961. Only sound engineering judgment and practical engineering planning are needed (plus the requisite funding and management direction). That, together with some old fashioned hard work, and the spacecraft computer system will be ready to support the first human mission to explore Mars.