The Mars Pathfinder spacecraft was sent aloft aboard a Delta II expendable launch vehicle on December 4,1996 to begin a seven-month journey to the Red Planet. The Pathfinder mission, one of the first of the NASA Discovery-class missions, was the first mission to land on Mars since the successful Viking spacecraft over two decades ago. After traveling over 497,418,000 km, the spacecraft impacted the Martian surface on July 4,1997 with a velocity of about 18 m/s. Upon impact the spacecraft bounced up approximately 15 meters, then continued to bounce another 15 times and rolled to a stop about 1 km from the initial impact point. The landing site is known as the Sagan Memorial Station and is located in the Ares Vallis region at 19.33 N, 33.55 W. Pathfinder deployed the first-ever autonomous rover vehicle, known as the Sojourner, to explore the landing site area. The mobile Sojourner had a mass of 10.5 kilograms and was designed to roam in a 300-m2 area for around 30 days. The 0.25-m2 solar array provided 16 watt-hours of peak power and the primary battery provided about 150 watt-hours of power. The steering control of this vehicle had to be accurate and had to limit the power consumption. Control engineers play a critical role in the success of the planetary exploration program. The role of autonomous vehicle spacecraft control systems will continue to increase as flight computer hardware and operating systems improve. In fact, Pathfinder used a commercially produced, multitasking computer operating system hosted in a 32-bit radiation-hardened workstation with 1-gigabyte storage, programmable in C. This is quite an advancement over the Apollo computers with a fixed (read-only) memory of 36,864 words (one word was 16 bits) together with an erasable memory of 2,048 words. The Apollo "programming language" was a pseudocode notation encoded and stored as a list of data words "interpreted" and translated into a sequence of subroutine links. Interesting real-world problems, such as planetary mobile rovers like Sojourner, are used as illustrative examples throughout the book. For example, a mobile rover design problem is discussed in the Design Example in Section 4.8.