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.
SPACE SERVICING: PAST, PRESENT AND FUTURE
Dan King
MacDonald Dettwiler Space and Advanced Robotics, 9445 Airport Road, Brampton (On) L6S 4J3, Canada [email protected]
where the translational and rotational hand controllers ABSTRACT direct the movement of the arm. Although less utilised, the Canadarm can also be operated automatically using This paper examines the past achievements and current pre-programmed trajectories to complete specific developments in space servicing, with a focus on manoeuvres for the arm. The key parameters of the enabling space robotics systems. As well, an attempt is Canadarm is summarised in Table 1. made to predict future space servicing missions and applications that may help set the path for space Over the past two decades, the Canadarm has enabled robotic technologies development. space servicing missions such as payload/satellite deployment, manoeuvering, servicing and retrieval, 1 INTRODUCTION EVA astronaut assist, shuttle inspection and servicing, ORU manipulation, as well as on-orbit construction Ever since the dawn of the Space Programs, Space and assembly. Some of the more notable missions Servicing (also known as "On-Orbit Servicing") has include the rescue of Westar and Palapa satellites, motivated and captured the imagination of space Hubble Servicing Missions and the current enthusiasts and engineers alike for over four decades. International Space Station (ISS) assembly missions. As a general broad definition, Space Servicing Unplanned exercises for the Canadarm have included encompasses such on-orbit activities as spacecraft-to- knocking a block of ice from a clogged waste-water spacecraft rendezvous, inspection and docking, payload vent that might have endangered the shuttle upon re- and satellite deployment, manipulation, retrieval, re- entry, pushing a faulty antenna into place, and supply and repair; as well as satellite re-orbiting and successfully activating a satellite (using a swatter made de-orbiting. for briefing covers) that failed to go into proper orbit. To-date, the Canadarm has performed flawlessly on all Many of the above space servicing tasks have already its missions. been performed by various automation and robotics systems, or by astronauts and cosmonauts. New All four Canadarms in active duty have recently been robotics systems are currently being deployed that will upgraded in anticipation of the more challenging ISS further demonstrate those capabilities. All these will assembly and operations missions. For example, all help support new opportunities and applications that the Canadarm joints have been modified to enhance the are emerging in the horizon. payload handling capability to 100,000 kg, which gives the Canadarm the ability to berth the Shuttle itself to 2 PAST DEVELOPMENT the ISS. The Canadarm is key to almost all ISS assembly missions and will remain an integral part of Many countries around the world has endeavoured in the U.S. shuttle fleet for many years to come. space robotics development, notably Japan, United States, Europe, Russia and Canada. Canada in particular has chosen space robotics as one of its strategic development areas and continues to make significant technology investments on such.
2.1 Shuttle Remote Manipulator System
Perhaps the most well known robotics system that has ever flown is the Shuttle Remote Manipulator System ("SRMS"), also known as the "Canadarm". Since its debut in 1981, The Canadarm has successfully flown more than 50 missions on the U.S. fleet of five Space Shuttles (including Challenger). The Canadarm is a six (6) degrees of freedom remote manipulator comprising of an upper and lower arm boom, an end effector, and a control workstation at the aft flight deck of the shuttle Figure 1: "Canadarm" Shuttle Remote Manipulator System on Hubble Servicing Mission
Table 1: Canadarm Technical Details by an astronaut or the SPDM. Canadarm2 also has the additional features of four TV cameras that feed wide Canadarm Key Parameters and close-up views to the operators, force moment Length: 15.2m sensing and control to enhance smooth robotics Mass: 410 kg operations, collision-avoidance to ensure operational Speed of Movement: Unloaded 60 cm/sec safety, and an advanced vision systems to track Loaded 6 cm/sec payloads. The key Canadarm2 paramaters is Wrist Joint: Pitch/Yaw/Roll summarised in Table 2 Elbow Joint: Pitch Shoulder Joint: Pitch/Yaw Upper & Lower Arm Boom: Composite Material Rotational Hand Controller: Pitch/Yaw/Roll Translational Hand Controller: Left/Right/Up/Down/ Forward/Backward Control/Sensing Astronaut/Automatic
2.2 Space Station Remote Manipulator System
Perhaps the most sophisticated space robotics system ever flown, the Space Station Remote Manipulator System ("SSRMS") was successfully launched, installed and checked-out on the recent STS-100 Mission in April 2001. Also known as "Canadarm2", Figure 2: "Canadarm2" International Space the SSRMS is a seven (7) degrees of freedom metre Station Remote Manipulator System long arm capable of handling large payloads of up to 100,000 kg mass, including the Shuttle itself. The 7 The Canadarm2 was successfully installed on the ISS DOF configuration gives it a greater ability to bend, by Canadian astronaut Chris Hatfield and his fellow rotate and maneuver itself into difficult spots. Since astronaut Scott Parazynski on April 22nd, 2001 and Canadarm2 can almost fully rotate all of its joints, it is within days, broke some new ground for Space more agile than a human arm and provides a critical Servicing. The first "inchworm" manoeuvre was capability for the complex ISS operational successfully executed when Canadarm2 grasped a environment. Unlike the Shuttle Canadarm, the ISS PDGF on the U.S. "Destiny" lab module and step out Canadarm2 is not permanently anchored at the of its launch pallet transferring its anchor point from shoulder joint but is equipped on either side with the one hand to the other - taking its first maiden step on same Latching End Effector (LEE) that can be used as ISS. As well, near the end of the STS-100 mission, anchor point while the opposite one performs various Canadarm2 picked up its launch pallet still attached to robotics tasks, including grabbing another connecting ISS and passed it back to the Shuttle's Canadarm, point on the ISS. This gives the Canadarm2 a unique thereby completing the first robotics "handshake" in capability to move around the ISS like an "inchworm", space (Figure 2). Canadarm2 is now fully operational flipping end-over-end among Power Data Grapple on the ISS to fulfil its critical mission of ISS assembly Fixtures (PDGFs) located on the ISS. As well, the ISS and operations. will later be equipped with the Mobile Based System (MBS), which services as a storage location and work platform for astronauts; and the Mobile Transporter (MT), which can transport both Canadarm2 and the MBS from one end of the ISS main truss to another. This provides a second mode of mobility for Canadarm2.
Also unlike the Shuttle Canadarm, the ISS Canadarm2 is designed to stay in space for more than 15 years. This requirement necessitates an innovative design feature which allows astronauts or other robotics systems (such as the Special Purpose Dexterous Maniplator or "SPDM" that will be described in a later section) to repair Canadarm2 on-orbit. Canadarm2 is build in sections called Orbital Replaceable Units Figure 3. First robotics "handshake" in space (ORU's) which are easily removed and then replaced between Canadarm and Canadarm2
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Table 2: Canadarm2 Technical Details The ETS-VII experiments along with NASDA's earlier Manipulator Flight Demonstration (MFD) on STS-85 Canadarm2 Key Parameters not only helped validate some of the specific Japanese Length: 17.6m space robotics technologies, but also provided the Mass: 1641 kg world space robotics community at large valuable Average Power: 1360W insights into the challenges and solutions for space Peak Power: 2000W servicing in general. Speed of Movement: Unloaded 37 cm/sec Loaded 2-15 cm/sec Stopping Distance: 0.6 m Wrist Joint: Pitch/Yaw/Roll Elbow Joint: Pitch Shoulder Joint: Pitch/Yaw/Roll Joint Movements: 540 degrees Upper & Lower Arm Boom: Composite Material (19 plies) Boom Diameter: 35 cm Cameras: Four (4) Rotational Hand Controller: Pitch/Yaw/Roll Translational Hand Controller: Left/Right/Up/Down/ Forward/Backward Control/Sensing Astronaut/Automatic Force/Moment Control Collision Avoidance Figure 4: ETS-VII launch configuration Other features Identical on both ends Built-in-redundancy Repairable in space (built in ORU sections)
2.3 ETS-VII Unlike the Canadarm or Canadarm2 which were built for servicing new infrastructures in space (i.e. Shuttle and ISS), the ETS-VII mission (Ref.1) was flown by NASDA as a testing ground for robotics and space servicing technologies. The ETS-VII satellite was launched on November 28th, 1997 and successfully conducted a series of rendezvous, docking and space robotic technology experiments. Some of the key Figure 5: ETS-VII On-Orbit Experiments experiments executed by the ETS-VII mission include: q Visual inspection of on-board equipment by robotic vision system q Handling of orbital replacement unit (ORU) and fuel (simulated) supply experiment 3 PRESENT DEVELOPMENT q Handling of small equipment by ETS-VII small robot arm including the use of a taskboard handling tool The next few years will promise to be very exciting for the space servicing community at large, with several q Handling of truss structure new robotics systems currently under final q Antenna assembly experiment development and scheduled to be flown. This includes q Ground teleoperation of ETS-VII robot the European Robotics Arm (ERA), the Japanese q Handling and berthing of the 410kg ETS-VII target satellite with ETS-VII robot on chaser Experiment Module Remote Manipulator System satellite (JEMRMS), the U.S. Ranger Telerobotic Shuttle Experiment and the Canadian Special Purpose q Rendezvous and docking by the ETS-VII chaser satellite with the ETS-VII target satellite Dexterous Manipulator System (SPDM).
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3.1 European Robotics Arm (ERA) JEM. A dexterous tool called the JEM Small Fine Arm (SFA) is also under development, which could be The European Robotics Arm (ERA) (Ref.2) is being picked up by the JEM RMS to perform finer ORU built for use on the Russian Segment of the servicing and maintenance. Table 4 summarises some International Space Station. It consists of an 11 meter, of the key JEMRMS parameters: six (6) degrees of freedom arm, an EVA Man Machine interface, an IVA Man Machine interface, a Refresher Table 4: JEMRMS Technical Details Trainer (RTR) and a Mission Preparation and Training Equipment (MPTE). Like Canadarm2, the ERA has a relocating capability by "hopping" from one power and JEMRMS Key Parameters communication interface basepoint to another on the Length: 9.9m Russian ISS segment. Table 3 summarises some of the Mass Handling: 7000kg key ERA parameters: Positioning Accuracy: +/- 50mm Translat. +/- 1 deg Rotational Table 3: ERA Technical Details Speed: 20-60mm/s Maximum Tip Force: > 30N Wrist Joint: Pitch/Yaw/Roll ERA Key Parameters Elbow Joint: Pitch Length: 11.3m Shoulder Joint: Pitch/Yaw Mass: 630kg Rotational Hand Controller: Pitch/Yaw/Roll Speed of Movement: 0.2m/s maximum Translational Hand Controller: Left/Right/Up/Down/ Stopping Distance: 0.15 m Forward/Backward Wrist Joint: Pitch/Yaw/Roll Control/Sensing Astronaut/Automatic Elbow Joint: Pitch Shoulder Joint: Pitch/Yaw Control/Sensing Astronaut/Automatic
Figure 7: Japanese Experiment Module Remote Manipulator System ("JEMRMS") Figure 6: European Robotic Arm ("ERA")
3.3 RANGER Telerobotic Shuttle Experiment (RTSX) 3.2 Japanese Experiment Module Remote Manipulator System (JEMRMS) The Ranger Telerobotic Shuttle Experiment (RTSX) (Ref.4) is a 48 hour Space Shuttle-based flight experiment to demonstrate key telerobotic technologies The Japanese Experiment Module Remote Manipulator for servicing assets in Earth orbit. Ranger is a four System (JEMRMS) (Ref.3) is being built for use on the manipulator telerobot with one permanently attached to JEM Exposed Facility of the International Space a Spacelab pallet. The manipulators perform dexterous Station. It consists of a 10 meter, six (6) degrees of manipulation, body repositioning, and stereo video freedom arm and a robotics control workstation within viewing The flight system will be teleoperated from
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onboard the Space Shuttle and from a ground control maintenance or upgrade. Alternatively the SPDM can station at the NASA Johnson Space Center. The robot, be picked up by the free end of Canadarm2 and along with supporting equipment and tasks elements, maneuvered into position next to the payload to be will be attached to a spacelab pallet carrier within the serviced. Table 6 summarises some of the key SPDM Shuttle payload bay. parameters:
Table 5 summarises some of the key ERA parameters: Table 6: SPDM Technical Details
Table 5: RTSX Technical Details SPDM Key Parameters Length: 3.5m (each arm) RTSX Key Parameters Mass: 1662 kg Overall Size (stowed): 40" X 30" X 96" Average Power: 600W Total Mass: 1500 lb Peak Power: 2000W Two (2) 8 DOF Arms Stopping Distance: 0.15 m Length: 63" each Wrist Joint (each arm): Pitch/Yaw/Roll Wrist Video Camera Elbow Joint (each arm): Pitch One (1) 6 DOF Positioning Leg Shoulder Joint (each arm): Pitch/Yaw/Roll Length: 75" Body Joint: Roll One (1) 7 DOF video arm Cameras: Three (3) Working Envelope: 55" radius Control/Sensing Astronaut/Automatic Stereo cameras and LED lights Force/Moment Control Collision Avoidance Other features Built-in-redundancy Repairable in space (built in ORU sections)
Figure 8: Ranger Telerobotic Shuttle Experiment (RTSX)
3.4 Special Purpose Dexterous Manipulator ("SPDM")
The Special Purpose Dexterous Manipulator ("SPDM") is being built for carrying delicate maintenance and servicing tasks on the International Space Station. Its fifteen (15) degrees of freedom dual-arm configuration Figure 9: Special Purpose Dexterous Manipulator makes it highly dexterous and can undertake tasks such System ("SPDM") as installing, removing and servicing small payloads and ORUs. The SPDM is also equipped with lights, video equipment, a tool platform and four tool holders. The SPDM will normally sit on the Mobile Base System (MBS) and the ISS Canadarm2 will manipulate a payload to within the range of the SPDM for repair,
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4 FUTURE MISSIONS would government or industry finance such clean-up missions. As has been described in previous sections of this Fortunately there are recent indications that we may be paper, a tremendous amount of experience and heritage turning the corner for other emerging markets for space has been acquired by the space servicing community at servicing. large with robotics missions on the Shuttle, ISS and experimental satellites. The logical question that For the first time in space history, the U.S. comes to everyone's mind is: What Next? Underwriters Associations, a consortium of insurance underwriters, issued a RFP in 1999 for the rescue of the Indeed, the space servicing robotics community may ORION 3 commercial communications satellite. have reached a crossroad: the transition from ORION 3 was stranded in an elliptical low earth orbit government dominated space servicing missions to in April 1999 when a Delta III upper stage commercial ones. Just as when Arthur C. Clarke malfunctioned and failed to inject it into the Geo conceived the idea of Geostationary Satellite Transfer Orbit. Although there has yet been a "rescue" Communications over half a century ago, it was deal signed for the mission to-date, it marks the probably hard for him then to imagine the bustling beginning of a demand for commercial satellite rescue commercial satellite communications markets that exist services. Boeing Satellite Systems (formerly part of today: a multi-billion a year market that includes Hughes) is already embarking on a growing business of Direct-To-Home broadcasting to millions of viewers taking damaged satellites abandoned by their owners throughout the world, Global Personal and turning them into money makers starting with Communications, Live Messaging and Broadband AsiaSat3 in 1998 and recently with PanAmSat’s Internet Access. Similarly, it was hard to imagine a Galaxy 4 satellite. Meanwhile, you and I can now decade or two ago how remote sensing data from book a seat with Space Adventures Inc. (SAI) as a satellites could impact each of our daily lives. From space tourist (for about US$100,000 per person) to commercial fishing to agriculture to navigation to experience a few minutes of microgravity at about 100- property assessment, such are the commercial 150 km altitude. Accordingly to SAI there are already applications that continues to transform the remote in excess of a hundred people who has registered for sensing sector from government to commercial such an experience, which is expected to begin service applications. a few years from now. Indeed, Mr. Dennis Tito became the world's first space tourist in April 2001 when he paid US$20M to fly on board a Russian Soyuz Similarly, those of us who have been associated with and spent a week on the Russian segment of the space robotics projects have for years dreamt of the International Space Station (Figure 11). emergence of a viable market for commercial on-orbit servicing. Much as the pioneers of the satellite communications and remote sensing enthusiasts have experienced in the past, we have "toyed" with and struggled through studies, demonstrations and ideas for potential commercial concepts such as satellite servicing (Figure 10) and space debris clean-up. The former concept remains commercially challenging as both servicing vehicles and target satellites to be serviced have equal access to advancement in launch and satellite technologies. Fundamentally if the cost of embarking on a servicing mission and an orbital asset replacement mission is equivalent then the value of the servicing mission becomes questionable. Only in cases where the relative cost of the servicing mission is much lower than that of the "serviced" asset (eg. ISS re- supply and servicing) will the mission become economically attractive.
The commercial challenges associated with orbital debris removal, on the other hand, faces the same issue that has plagued environment remediation on Earth. The fundamental question to be addressed is - who Figure 9: Satellite Servicing pays? Only until such time when there is a true financial or safety penalty caused by space debris
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trains, planes and automobiles have created new economical opportunities for many parts of the world in the 19th and 20th centuries, space transportation development promises to create a similar outcome. To that end, NASA has just initiated a US$4.5B Space Launch Initiative (SLI) that promises to lower the cost of space access by an Order of Magnitude from what they are today. The start of SLI is synonymous to NASA initiating the Saturn Rocket Development Program in 1958 and the Shuttle Development Program in 1972, which underlines NASA’s resolve to lower the cost of access to space for all and to help create a viable commercial space market. Apart from NASA’s efforts, the private industry is also playing its role by creating the US$10M X-Prize which will be awarded Figure 10: Denis Tito - World's First Space Tourist to the first private team that can build and fly a reusable spaceship capable of carrying three individuals on a sub-orbital flight. The idea for the X- Targeting a similar market, major corporations such as Prize is similar to the one won by Charles Lindberg at Hilton and Shimizu have already derived plans and the beginning of the 20th century which had been blue prints for building orbiting space hotels (Figure followed by a century of rapidly growing commercial 12). Accordingly to a recent NASA study, the Space activities in the civil aviation industry. Similarly, it is Travel and Entertainment Market alone can easily hoped that the X-Prize will help promote a new civil develop into a multi-billion dollar per year industry. space industry in the 21st century. Other new commercial space industries that have been identified by NASA for the next millennium include Space Based Solar Power (Figure 13), Space “FedEx” Service, Space Based Manufacturing and Space Resources Mining (Ref.5).
Figure 11: Concept for Space "Hilton" Figure 12: Space Based Solar Power
So what is required to help open up such commercial markets that will involve space servicing? Well you might have guessed it - one of the key secret ingredients is “Low Cost Access to Space”. Much as
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5 CONCLUSIONS
As has been demonstrated by the Canadarm and other space servicing systems and experiments in the past two decades, the complex on-orbit tasks that could be performed by automation and robotics technologies is tremendous. Given the general desire to pursue commercial applications for future Space Servicing missions, it is anticipated that the next generation space servicing systems will require higher operational efficiency in an increasingly unstructured work environment. This will demand technologies that support autonomous and semi-autonomous operations with as little human-in- the-loop intervention as possible. Adaptive robotics interfaces to handle non-cooperative and uncooperative payloads, as well as intelligent vision and control systems, will be required to support such challenging space servicing tasks. All these development will be geared towards lowering the cost and increasing reliability of any space servicing mission.
Given my personal optimism for the future in space servicing, I would like to make a humble suggestion to space robotics enthusiasts around the world: keep up the good work, have faith and be creative because the best opportunities have yet to come.
6 REFERENCES
[1] Yoshiaki OHKAMI, Mitsushige ODA, "NASDA's activities in space robotics", 5th ISAIRAS (ESA SP- 440). Also NASDA official ETS-VII website.
[2] Phillippe Schoonegans, Marc Oort "ERA, the Flexible Robot Arm", 5th ISAIRAS (ESA SP-440). Also ESA official ISS website.
[3] NASDA official JEM website
[4] Joseph Parrish, "The Ranger Telerobotic Shuttle Experiment: An On-Orbit Satellite Servicer", 5th ISAIRAS (ESA SP-440). Also University of Maryland "Ranger" official website.
[5] D.V. Smitherman, "New Space Industries for the Next Millennium", NASA/CP-1998-209006
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