Proceeding of the 6th International Symposium on Artificial Intelligence and Robotics & Automation in Space: i-SAIRAS 2001, Canadian Space Agency, St-Hubert, Quebec, Canada, June 18-22, 2001. CANADARM: 20 YEARS OF MISSION SUCCESS THROUGH ADAPTATION Michael Hiltz, Craig Rice, Keith Boyle and Ronald Allison MacDonald Dettwiler Space and Advanced Robotics Ltd. 9445 Airport Road Brampton ON L6S 4J3 & National Aeronautics and Space Administration Lyndon B. Johnson Space Center Houston, Texas, 77058 [email protected] [email protected] [email protected] & [email protected] Keywords: RMS, Space Shuttle, Space Station, 3.) Improving the arm’s ability to meet the flight operations, support, Canadarm, Shuttle Remote manifest (supportability). Manipulator Systems, SRMS, shuttle robotics, payload deployment and retrieval system, PDRS. The purpose of this paper is to examine how the SRMS has been improved to address lessons Abstract learned from the prolonged use of robotics in space. This paper will also discuss trends in the As part of the National Aeronautics and Space operational use of the arm and how they relate to Administration’s Space Shuttle Transportation past, current and future upgrade activities. System, the Shuttle Remote Manipulator System has played a vital role in the success of over 60 2 Canadarm Adaptations to Expand space missions. This paper examines the Operational Capability enhancements made to the arm to improve its operational capabilities, reduce risk and extend its 2.1 Original Operational Requirements: life. This paper concludes that the robustness and Payload Deployment and Retrieval success of the Canadarm over its 20 year life can be attributed to the adaptations that have been made to The original arm was designed primarily for the it to meet the increasing demands that have been deployment and retrieval of payloads and is part of placed on the system. Potential future the Shuttle’s Payload Deployment and Retrieval enhancements based on operational trends are also System (PDRS). It was designed to capture “free- discussed. flying” payloads fitted with a grapple fixture and manoeuvre them for both berthing (in the cargo 1 Introduction bay) and deploying. The arm was originally designed to manoeuvre with unloaded tip speeds of 2 ft/sec and 2 deg/sec yet be able to precisely The Shuttle Remote Manipulator System (SRMS, control payloads up to 65,000 lbm. a.k.a the Canadarm) flew its inaugural flight onboard the Space Shuttle Columbia (STS-2) in 2.2 Operational Evolution of Canadarm: November of 1981. The four arms that are in Common Uses service today as part of NASA’s Space Shuttle fleet have enjoyed 20 years of successful use over 60 Although originally designed for payload missions. Although it shares common mechanical deployment and retrieval, over the years the SRMS elements with its original design, the SRMS is has proven very useful for a wide variety of other significantly different than it was 20 years ago. mission critical tasks. In addition to deployment Mission success over its operational life has been and retrieval of payloads current use of the arm achieved by making constant adaptations to the regularly includes such vital tasks as: Canadarm. These changes have been based on the experience of the hardware performance in the a) Assembling Space Stations: The arm was used environment of space as well as addressing new to help install a docking module on the Russian operational requirements. Since 1981 the arms have MIR space station in November of 1995. The undergone numerous hardware changes, arm has become essential in the assembly of improvements in manufacturing processes and over the International Space Station (ISS) having 39 changes to the control software. assembled approximately 100 tons of ISS hardware to date. In making adaptations to the arm, three key items have been, and continue to be, addressed: b) Workhorse for Spacewalks: Using different 1.) Expanding the system’s capabilities. types of foot restraints attached to the end of 2.) Reducing risk through improvements in safety. the arm, the arm has provided a mobile and stable work platform for Extra Vehicular c) Use of the arm’s end effector as a sunshade for Activities (EVA). This allows the astronomy observations (STS-85; Southwest spacewalking astronauts to accomplish a Ultraviolet Imaging System). greater variety of tasks in a shorter period time. In conjunction with the EVA crew, relatively d) “Pushing” on jammed antenna: The arm was large payloads can be moved about the cargo used to assist stowing of the stuck SIR-B bay for repair and assembly operations. antenna on STS-41G. c) Flying “eye-in-the-sky” for visual inspection of e) Experimental platform for Orbiter plume the Orbiter and payloads: The arm elbow characterisation tests. (SPIFEX). camera with a pan and tilt unit and an arm tip camera mounted on the wrist roll joint have f) Contingency operations in support of payload been instrumental in troubleshooting many on materials experiments; The Wake Shield orbit anomalies. Facility (WSF) experimental platform was designed to generate an ultra-vacuum The arm and its cameras are commonly used to environment to support Molecular Beam observe the functions of other Orbiter Epitaxy (MBE) growth of semi-conductor subsystems and troubleshoot Orbiter thermal films. On its inaugural flight an anomaly with protection system deterioration. The arm has Wakeshield’s attitude control systems occurred also been used to view cargo bay debris jarred that prevented its release. The arm was used to loose from launch, jammed EVA hatch doors hold WSF away from the Orbiter cargo bay to and view ice that has frozen to the Orbiter. avoid debris and allow completion of mission d) Portable light source: Lighting mounted on the objectives. end of the arm is used to provide extra illumination for both direct window viewing and camera inspection and grapple tasks. 2.4 Canadarm Operational Trends e) Use for Public Relations activities: In addition As the importance and versatility of the Canadarm to providing vital video cues to the crew for became more evident over the life of the Orbiter, an performing operational tasks, cameras on the increased engineering emphasis on expanding and arm and mounted in payloads attached to the improving existing capabilities emerged. New arm (such as IMAX cameras) have been used operational requirements, driven in large part by to bring the experience of space to the general ISS assembly tasks, requires the arm to perform public. more challenging tasks that had not been envisioned when it was originally designed. ISS f) Experimental platform for Materials: To study assembly tasks involve connecting large mass the effect of micrometeorite debris on various payloads with a variety of interface attachment materials the arm has been fitted numerous systems. The interfaces between ISS elements are times with a witness plate near the wrist joint. designed by a diverse assortment of subcontractors (including several international partners) and are significantly different than the those used in the shuttle’s cargo bay which were designed for regular 2.3 Operational Evolution of Canadarm: payload deployment and retrieval. Unique Tasks As a result of past and planned ISS assembly tasks In addition to the now common tasks, the arm has there has been an explicit focus on the following also been used for a variety of unique tasks. capabilities and features of the arm: Examples of these include: a) Ability to manoeuvre larger mass payloads a) “Fly-swatter / lacrosse stick” to activate a with large centre of mass offsets satellite's separation switch; After the Syncom (including a fully assembled Space failure on STS-51D, a "flyswatter/ lacrosse Station), stick” (fashioned from the binder of an b) Accurate trajectory control, operations checklist) was attached to the end of c) Precise (finer) control at low rates, the arm and used to activate Syncom’s d) Positioning accuracy, separation switch. e) Force capabilities, f) Ability to backdrive arm, b) Ice-pick to knock ice off the Orbiter to prevent g) Displaying more data to the operator, damage during re-entry of the shuttle (on STS- h) More flexibility in command and display 41D). capabilities Page 2 2.5 Expanding Canadarm System Capabilities corresponded with low joint and tip rates) a non- linearity existed in the output of the Motor Drive While some of the Canadarm tasks have been Amplifier (MDA) in the SPA (see Figure 1). This within the inherent capabilities of the original resulted in less precise control of payloads at very design, many new tasks have been accomplished low rates. This is a particular concern when through modifications to the arm. The following is manoeuvring large mass payloads such as the ISS. a list of adaptations made to the arm to address With the design of the digital SPA this non- operational trends (discussed in 2.4) that have linearity has been eliminated resulting in consistent either provided new functionality or improved servo performance throughout the operational range existing capabilities. These enhancements to the of the MDA. arm capabilities now allow these new tasks to be Non-Linearity of Analog SPA MDA Output routinely performed. 2.5 2.0 2.5.1 Joint Controller Upgrades 1.5 One of the biggest challenges of the original 1.0 Canadarm servo design was the requirement to 0.5 manoeuvre a wide range of payload masses over a 0.0 considerable range of rates. The ability to quickly move the tip of an unloaded arm at 2 ft/sec and 2 -0.5 deg/sec and yet still be able to manoeuvre a 65,000 MDA Voltage Drop (Volts) -1.0 lbm payload was accomplished in the original -1.5 design using only one set of servo control -2.0 parameters in the joint’s analog Servo Power -2.5 Amplifiers (SPAs).