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CaseStudy_SpaceArm - Case Study MDA Canadian Space Arm View...

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Case Study: Space Station Robot Embeds Ada Despite rumors of its demise, Adas is at the heart of the International Space Station’s in-orbit Canadarm 2 where it assures software safety and reliability. View COTS W hile safety-critical characteristics have been introduced into the design of many programming languages, Ada is the language specifically targeted at “life-critical” systems. Developed between 1975 and 1984 by the US Department of Defense (DoD), Ada has been classically targeted for use in mission-critical embedded systems that emphasize safety, low cost, and a near-perfect degree of reliability. The most important safety features that make Ada ideal for development of fail-safe software include its information-hiding capability, its ability to provide re-useable code and its “strong typing”, which helps detect and solve many types of coding errors at compile time, very early in the development cycle. Despite the perception by some that Ada is a dying language, the fact is that Ada’s use is on the rise and it’s being adopted for some of the most rigorous and critical embedded applications under development today. Under contract to the Canadian Space Agency (CSA), MacDonald Dettwiler (MDA) chose open-source GNAT Ada 95 from Ada Core Technologies to develop control software for the Mobile Servicing System (MSS), an essential com- ponent of the International Space Station (ISS). The MSS is a complex robotic manipulator system that plays a key role in space station assembly and maintenance. It helps move equipment and supplies around the station, supports astronauts working in space, and services instruments and other payloads attached to the space station (Figure 1). Space-Based Robotic Arm Ideal for a program like the MSS, Ada has clearly carved itself a comfortable and sustainable niche in large, complex high-reli- ability systems, including safety-critical systems where human life might be at stake. This language, which has little visibility compared with its cousins C and C++, continues be very effective in developing systems that absolutely must be reliable. So it is no surprise to find Ada in space—a harsh, unyielding environment where the slightest malfunction can lead to death. The ISS-based, next-generation Canadarm 2, the key element of the MSS, is a bigger, better, smarter version of Canadarm, the robotic arm that operates from the cargo bay of the Space Shuttle. This arm is capable of handling large payloads and assisting with docking the space shuttle to the space station. The new arm, built specifically for the space station, is 17.6 meters (57.7 feet) long when fully extended and has seven motorized joints, each of which operates as a complex real-time embedded control system. Canadarm 2 is “self-relocatable” and can move around the sta- tion’s exterior like an inchworm. Each end of the arm is equipped with a specialized mechanism called a Latching End Effector that can lock its free end on one of many special fixtures, called Power
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