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4 Extravehicular Activity, Robotics, and Supporting Technologies EXTRAVEHICULAR MOBILITY UNIT AND EXTRAVEHICULAR ACTIVITY TOOLS The extravehicular mobility unit (EMU) is an anthropo- morphic crew enclosure made up of two major subassem- blies: the space suit assembly (SSA) and the life support system (LSS). The SSA consists largely of soft goods, with one major exception, the hard upper torso (HUT), a vest-like fiberglass structure that forms the central part of the SSA. The arms, helmet, lower torso, and LSS are mounted on the HUT. The LSS contains a primary life support subsystem (PLSS) and a backup purge flow system, the secondary oxygen package. The EMU allows the EVA crew member to work outside the ISS free of umbilicals to the spacecraft. It is pressurized to 29.6 kPa (4.3 psia), supplies oxygen, removes carbon dioxide, rejects metabolic and environmental heat, and removes moisture from perspiration and exhaled breath. The EMU, which has been called a one-person space- craft, is made up of more than 100 major components. In addition to NASA's EMU, the Russian "Orlan" space suit will also be used on the ISS (Poulos, 1999~. Although this will provide redundancy, the complexity of maintaining and operating two separate systems that provide essentially the same basic EVA capability will double the requirements for resources and funding. The current Russian space suit used for EVAs on the Mir is a derivative of the semirigid suit used during the Salyut- Soyuz program. This suit, the "Orlan-DMA," is the fourth generation model of the space suit. The Orlan DMA and the American EMU are similar in many ways. The Orlan-DMA space suit has an integrated life support system to enable EVA operations. The suit can be adjusted for size and has a metal upper torso and fabric arms and legs. The metal ball bearings and sizing adjustments are notable features. The Orlan-DMA has redundant, self-contained, integrated, pres- surization and oxygen supply systems in a backpack-type PLSS that can be maintained on orbit. The oxygen supply system includes reserve oxygen storage and equipment for 18 controlling and maintaining the pressure. The ventilation system and environmental gas composition-control system include removal units for carbon dioxide and contaminants, as well as gas circulation-control equipment. The space suit has no umbilical lines. Oxygen, water supplies, pumps, and blowers are located inside the rear hatch. Unlike the EMU, which is a waist entry suit, the Orlan-DMA is donned through a rear hatch. Unassisted entry requires only two to three minutes. Most of the tools in the large inventory of ISS EVA tools were designed to meet the needs of crew members perform- ing specific tasks. Tools are reused for other tasks only if mission similarity allows and if crew safety and productivity are not compromised. The current inventory includes 200 different part numbers and more than 4,000 parts stored in four separate storage areas. NASA is planning to store all of the tools for the ISS in a centralized, ground-based stor- age area under the control of United Space Alliance. Efforts are also under way by EVA planners to develop standard- ized tools to reduce training time as ISS EVA training evolves from task-specific training (the mode of operation dunned ISS assembly) to skills-based training (the mode of operation after ISS Assembly Complete) (Harbaugh and Poulos, 1999~. During the assembly phase of the ISS, unprecedented demands are being placed on both NASA and contractor per- sonnel and facilities. For example, during the four years of ISS assembly, 1,600 hours of EVA are planned. Compare this to the 543 hours (90 EVAs) during the first 15 years of the Space Shuttle program. This three-fold increase is known as "the wall" of EVA (Figure 4-1~. The ISS assembly demands will place significant stress on personnel and processing/training facilities, and the potential burnout of skilled people and shortage of facilities represent increased risks to the program (Poulos, 1999~. During the ISS opera- tional phase, NASA projects that there will be 20 EVAs (i.e., 120 EVA hours or 240 crew hours) per year. Training for ISS assembly and training for ISS operations
EXTRAVEHICULAR ACTIVITY, ROBOTICS, AND SUPPORTING TECHNOLOGIES are fundamentally different. Because components are added to the ISS in a rigorously planned assembly sequence, an assembly task is a choreographed event that requires task- based training. The motions of the astronauts, the robots, and the assembly pieces are not only thoroughly planned, they are also exhaustively rehearsed. The vast majority of training takes place in the Neutral Buoyancy Laboratory at the Johnson Space Center, and the environment in which the EVA task is performed is controlled and well understood. Extensive underwater EVA training is well accepted by the crews as a prerequisite for safe EVA. A maintenance or repair task during the operational phase of ISS is much more likely to be a skill-based task than a preplanned, rehearsed task. Although an astronaut could be trained for a "standard" ORU changeout, he or she cannot be trained in anticipation of all possible failures. Even if an astronaut were trained for a specific maintenance scenario, the training would not remain current indefinitely. Unlike Shuttle EVA crew members, the ISS crew may have to use procedures long after the training period, relying on memory. Therefore, there will probably be some loss in proficiency, especially for repairs late in a flight increment. Unsched- uled repairs will necessarily be performed on structures that are already assembled, when access to a damaged compo- nent may be much more difficult than during assembly. Therefore, astronauts performing EVA repair tasks will nec- essarily rely heavily on their skill-based EVA training and standardized tools. On-orbit training could be an effective way to meet the needs of astronauts who must rely on skill-based EVA train- ing to perform unpredictable maintenance and repair tasks. On-orbit training would be based on real-time communica- tions between support personnel on the ground and the EVA crew on orbit to walk them through and discuss potential EVA tasks. Real-time communications would require high bandwidth communications systems. On-orbit training could also be accomplished asynchro- nously, with the EVA crew relying on appropriate training materials and equipment on board, rather than on the ground (i.e., on-orbit CD-ROMs, videos, models and mock-ups) augmented by suggestions from mission control. With task- specific on-orbit training, the crew could be trained for a specific takes) immediately before an EVA (a practice that was used onboard Mir). On-orbit training would require meticulous planning to ensure that all of the necessary equip- ment and capabilities were aboard the ISS including: adequate computer simulation; high bandwidth communica- tions; and accurate physical or digital models that can be reconfigured and updated as the ISS evolves. Virtual-reality training, a comprehensive form of asyn- chronous training, has proved to be a useful complement to underwater training and has the potential to enable more extensive on-orbit training protocols in the absence of the neutral buoyancy facility. The training ratio for Shuttle EVAs has historically been in the range of 10:1 (i.e., 10 hours 19 of neutral buoyancy training for each hour of actual EVA). Training for maintenance EVAs after Assembly Complete is expected to be in the range of 3:1 for neutral buoyancy train- ing when augmented with virtual-reality training (Harbaugh and Poulos, 1999~. Recommendation. The National Aeronautics and Space Administration (NASA) should implement a plan to shift from current training procedures to a combination of skill- based training on the ground and task-specific training on orbit. NASA should plan for and develop an extensive on-orbit training program for rehearsing, simulating, and creating optimal extravehicular activity performance and timelines. The materials and equipment associated with on-orbit asynchronous training should be integral elements of the ground-training program so the crew can become familiar with the CD-ROM and video approaches to training before being required to use them on orbit. PREBREATHE PROCEDURES The purpose of prebreathe procedures is to decrease the potential for decompression sickness (bends) incidents asso- ciated with EVA. The current procedures are based on those used to prepare for Space Shuttle EVAs. The Shuttle depres- surizes the cabin pressure from 101.3 kPa to 70.3 kPa (14.7 to 10.2 psia) for 24 hours prior to a scheduled EVA, and the EVA crew prebreathes pure oxygen for two hours prior to Repressurizing the EMU to 29.6 kPa (4.3 psia). Unlike the Shuttle, the entire ISS cannot be Repressurized. Therefore, the EVA crew is placed in the airlock, which is depressur- ized to 70.3 kPa (10.2 psia) overnight, the so-called "camp- out" procedure. The crew then prebreathes pure oxygen for four hours prior to Repressurizing the EMU to 29.6 kPa (4.3 psia) at the start of the EVA. This entire procedure is time consuming and severely restricts the EVA crew's activities during the period. NASA has been studying methods of shortening the prebreathing period. For example, current test results sug- gest that exercise during the pure oxygen prebreathe period can reduce the prebreathing time without increasing inci- dents of decompression sickness. The target prebreathe period is one to two hours (Poulos, 1999~. Recommendation. The National Aeronautics and Space Administration (NASA) should continue its ground-based development program to reduce the risk of bends incidents in extravehicluar activities (EVA). NASA should also develop and fly instrumentation that will aid in the early detection of the onset of bends incidents (e.g., an improved in-suit Doppler, a system to acoustically measure the presence of gases in the bloodstream). NASA should continue its efforts to reduce the time required for prebreathing so that the procedure can be accomplished during the period of several hours required for other EVA preparation and checkout activities.
20 SPACE SUIT UPGRADES U.S. System The EMU was designed and certified to meet the needs of the Space Shuttle crew and has been used since 1983. For the extended on-orbit operational life required for the ISS, the robustness and durability of the EMU have been im- proved by a comprehensive enhancement program con- ducted during the l990s resulting in the recertification of the EMU for use on the ISS. All indications are that the current Shuttle/ISS EMU can meet the requirements of the ISS operational phase (Poulos, 1999~. Nevertheless, although the electronic components of the EMU have proven to be reliable and durable, they were designed between 1979 and the mid-1980s, and many of the electronic parts have become obsolete and are no longer in production. Because vendors no longer manufacture these parts, NASA's contractor has had to search for the limited quantity of parts that remain in distributor inventories and secure funding from NASA to procure them to reduce near-term risks (Francis, 1999~. The contractor has proposed redesigning the EMU electronics using components based on current technology that would be usable for both the Space Shuttle and the ISS until the end of the program in 2020. Recommendation. The National Aeronautics and Space Administration should continue to search for and acquire electronic parts to support the current extravehicular mobility unit (EMU) to reduce near-term risk and should redesign the EMU electronic components using current technology to satisfy the long-term EVA needs of the International Space Station. Logistics and Resupply NASA and the EMU contractor continue to monitor EMU supply and the demand created by the combined Space Shuttle and ISS programs. The goal is to meet a probability of sufficiency of 90 percent for the LSS and 80 percent for the SSA. Because of projected shortages of the LSS, NASA is considering procuring one additional PLSS and one addi- tional secondary oxygen package. In addition, the PLSS certification test hardware is being considered for upgrade to full flight status by NASA (Crew and Thermal Systems Division, Johnson Space Center). The SSA has significantly shorter lead-time than the LSS and therefore can be dealt with in a shorter turnaround time. However, the SSA components must be available in a variety of sizes to fit a variety of crew members.Therefore, an inventory of SSA components will be required. An analysis of LSS and SSA supply and demand reveals that shortages could prevent the program from meeting the goals of probability of sufficiency of 90 percent for the LSS ENGINEERING CHALLENGES TO THE LONG-TERM OPERATION OF THE INTERNATIONAL SPACE STATION and 80 percent for the SSA. The projected shortages, com- bined with the need to support unplanned contingencies, are likely to cause launch delays during ISS assembly, as well as delays in EVAs during the ISS operational phase. Recommendation. The National Aeronautics and Space Administration should procure additional Life Support System hardware, and/or upgrade the Crew and Thermal Systems Division's Life Support System certification hard- ware and should procure additional hard upper torsos and space suit assembly hardware and soft goods. Russian System Russian research and development is focused on improv- ing suit performance (specifically mobility), decreasing the payload weight required to replenish space suit consumables, extending operating life, and using microprocessors to con- trol and monitor space suit systems. Payload weight required to replenish consumables might be reduced by regeneration of carbon dioxide absorbers, removing heat without evapo- rative water loss, decreasing oxygen leaks, and using advanced oxygen supplies. RELIABILITY OF THE SIMPLIFIED AID FOR EXTRAVEHICULAR ACTIVITY RESCUE (SAFER) The simplified aid for EVA rescue (SAFER) was designed as the last line of defense for an EVA crew member who has become detached from the ISS. Crew members are normally attached to the ISS by a series of redundant tethers. The SAFER, which is attached to the EMU LSS, is an emer- gency return system that provides a fly-back capability in the event that the tether system fails. SAFER uses a stored gaseous nitrogen propulsion system that expels gas through 24 thrusters. SAFER operation is initiated by activating a pyrotechnic valve to initiate the flow of nitrogen through a regulator to the thruster nozzles. Gas flow is controlled to provide a velocity of up to 3.05 m/s (10 fps). The Space Shuttle has the capability of maneuvering to retrieve a detached EVA crew member, but the ISS does not. Because the ISS will be operating for more than a decade, and because hundreds of EVAs will be conducted over its lifetime, the SAFER must be absolutely reliable. Early operational evaluations of the system, however, have revealed failure modes that could compromise crew safety. The SAFER is not a "single-fault-tolerant" system, and cer- tain failures render it inoperative. Recommendation. The National Aeronautics and Space Administration should ensure that the simplified aid for EVA rescue (SAFER) is a completely reliable, single-fault- tolerant system.
EXTRAVEHICULAR ACTIVITY, ROBOTICS, AND SUPPORTING TECHNOLOGIES ROBOTIC SYSTEMS The complement of robotic devices on the ISS will include the mobile servicing system, with the SSRMS (ISS remote manipulator system) and the special purpose dexter- ous manipulator (SPDM), the European robotics arm (ERA), and the Japanese experiment module (JEM) robotics system. The SSRMS and SPDM are the primary devices that will be used for both assembly and maintenance of the station. The ERA will be used during assembly of the Russian science power platform; the Japanese robotics system will be used to service external payloads on the JEM exposed facility. The SSRMS is a large arm capable of maneuvering and berthing major components of the ISS. It also provides a platform from which an astronaut can perform EVA tasks or be transported to other EVA work sites. The SSRMS can also transport the SPDM, a dual-arm robot designed to per- form ORU changeout. Approximately 200 (out of a total of 600) ORUs on the ISS have been designed to be compatible with the SPDM. The three interfaces for handling ORUs are: a microconical fixture; a microfixture; and an H-fixture. The SPDM can also be used to perform a few tasks that do not involve specialized fixtures (e.g., opening doors that cover ORUs). The primary mode of operation of the SSRMS and SPDM is joint-controlled teleoperation. In this mode, an astronaut controls each joint of each arm directly, issuing joint motion commands based on what the astronaut observes by looking at the arm. This is an effective but limited control technique that requires great skill and extensive training. NASA has a well developed plan for assembly of the ISS based on the capabilities of the existing suite of robotic sys- tems (SSRMS and SPDM) and the skills of the EVA astro- naut. Although new robotic technologies could increase the safety and/or productivity of the astronaut-robot team, new technology will not be necessary for the completion of ISS assembly. Therefore, the NASA team has adopted an approach based largely on well proven, existing technology that mitigates much of the risk and expense of developing and applying new technology. NASA's plan for using robotic devices for the mainte- nance and servicing of the ISS after Assembly Complete is not as well developed. In fact, a compelling case can be made for incorporating new robotic technology in this phase of the program. Many maintenance and repair tasks will be fundamentally different from assembly tasks, and prepara- tion for these tasks will require skill-based training rather than task-specific training. During ISS assembly, astronauts receive training and practice robotic arm tasks just prior to each mission. There- fore, the training and practice are recent and fresh when the task is undertaken on orbit. After Assembly Complete, how- ever, significant time may elapse between training on the ground and the actual execution of robotic arm operations. 21 Thus, an astronaut's proficiency with the SSRMS/SPDM after Assembly Complete is likely to deteriorate with time. After ISS Assembly Complete, the crew may also be called upon to perform tasks that they have not specifically practiced. Improvements to the systems used to control the SSRMS/ SPDM would be very beneficial after Assembly Complete, and some technologies that could be incorporated on the SSRMS/SPDM already exist. For example, "end point" con- trol allows the astronaut to command the motion of the end point of the manipulator rather than the individual joint angles. This mode of operation (so-called "flying the end point") could simplify control of the arms, which in turn would reduce the requirements for training. If the time lag between input commands and system response does not cause errors (i.e., variations in signal travel time and signal processing time that are dependent on the communications path used in any specific instance) the SSRMS could be commanded from the ground to accom- plish portions of a task. For example, a ground-based opera- tor could control the transit of a component from one point on the ISS to another, leaving only the high-precision end task to the intravehicular activity (IVA) astronaut operating from inside the ISS. Routine maintenance tasks that do not require the resourcefulness of an onboard astronaut could also be transferred to ground operators. NASA's current plans for operating the SSRMS/SPDM are conservative but adequate for the assembly phase of the ISS. However, improved operating modes would yield sub- stantial benefits during the post Assembly Complete phase. Current plans do not include use of the SPDM to support EVAs or control of either the SPDM or the SSRMS from the ground. Recommendation. The National Aeronautics and Space Administration and its international partners should develop a plan to incorporate improved control modes for the baseline robotic systems on the International Space Station (i.e., the space station remote manipulator system and the special pur- pose dexterous manipulator) that would simplify their operation and reduce astronaut training time (e.g., "flying the end point". The plan should address cost and safety considerations as well as teleoperation by ground-based operators. VISUAL INSPECTION AIDS Additions to robotic systems on the ISS that could relieve astronaut EVA requirements would also yield substantial benefits after Assembly Complete. One of the most signifi- cant robotic capabilities currently under development is an enhanced visual inspection system. Current plans involve using the SSRMS for payload checkout before an SSRMS or
22 ENGINEERING CHALLENGES TO THE LONG-TERM OPERATION OF THE INTERNATIONAL SPACE STATION EVA task, for closeout photography, and for problem reso- lution. The SSRMS is a large, slow manipulator system that will not provide camera coverage of all parts of the ISS post Assembly Complete and cannot be operated without disturb- ing the microgravity environment. The impact of having limited visual inspection canabilitv has already been demonstrated. During STS-88, the first ISS assembly flight, repair of the undeployed antenna on the Zarya module was very difficult because of the lack of visual images. On this occasion, the EVA astronaut spent nearly an hour of EVA time trying to describe the nature of the problem to mission control. Nearly all of this time could have been saved if he had been able to provide mission con- trol with a visual image (Ross, 1999~. In this case, a camera on the EMU would have sufficed because the astronaut was already at the EVA work site. In other cases, when an astro- naut is not at the EVA work site, an autonomous maneuver- able camera could provide the critical visual inspection capability. A visual inspection system called AERCam has been developed at the Johnson Space Center and has been flown on the Space Shuttle. AERCam is a small, free-flying, remotely controlled robotic platform that can carry a camera (or two cameras when stereoscopic images are warranted) and other sensors to any part of the ISS. AERCam can per- form the following tasks: · visual inspection . pre-EVA reconnaissance · closeout video documentation · supplemental video coverage for other robotic operations positioning of cameras and lights for EVA crew nonvisual sensing (e.g., presence of ammonia, infra- red camera, measurement of structural vibration) The AERCam can be operated easily by an IVA astronaut and can be deployed without disturbing the microgravity environment of the ISS. AERCam has already proven its practicality. On the STS-87 mission, AERCam was oper- ated in a teleoperation mode in close proximity to the Space Shuttle orbiter and within the operator's line of sight. Cur- rent procedures for inspecting the station exterior to assess damage cause major disruptions to the ISS microgravity environment. Although the AERCam system could satisfy the needs of the ISS, it is not currently on the manifest for the ISS. Recommendation. Development and test of the AERCam system should be continued so that it can be included in the baseline International Space Station (ISS) equipment mani- fest for support of extravehicular activities. ADVANCED ROBOTIC TECHNOLOGIES In addition to improvements in visual inspection capa- bilities, improvements could be made in robotic systems to optimize the capabilities of the human-robot teams aboard the ISS and on the ground. Significant progress in robotics research promises to enhance the performance of robotic ser- vicing systems through improved teleoperation modes and supervised-autonomous modes of operation for all of the planned or proposed robotic systems for the ISS. Two research and development programs, the Ranger Project and the Robonaut Project being developed by NASA Johnson Space Center, are sufficiently well developed and have a high enough probability of yielding significant improvements to the operation of the ISS post Assembly Complete to warrant serious consideration. Both programs are focused on enhancing robotic servicer technologies. The focus of the Ranger Project is on advanced telepresence control concepts. The goal is to develop tech- niques that will permit a remote human user (either IVA or on the ground) to operate the system easily to perform com- plex tasks. The current system, a mobile servicer with a main body and four arms, is controlled using stereo video displays, simulated graphics, dual three-axis hand control- lers, and dual six-axis hand trackers. A robotic system with Ranger's capabilities could access objects in the tight con- fines of the assembled ISS structure that would not be acces- sible with the robotic systems now planned for the ISS (i.e., the SSRMS and SPDM). A Ranger vehicle would also be able to service the ISS without disturbing the microgravity environment. The utility and value of the Ranger vehicle has already been demonstrated in tests at the Neutral Buoyancy Labora- tory in which the vehicle functioned as an aid to astronauts performing ORU changeouts. The potential for incorpora- tion of any of these capabilities into the ISS program is remote, however, until they have been demonstrated in flight. The Ranger vehicle is fully funded for a flight test demon- stration (outside of the ISS program) but has not yet been manifested for a flight on the Shuttle. A second robotic servicer program with great potential for the ISS is the Robonaut Project also being developed at the NASA Johnson Space Center. The Robonaut is an anthropomorphic robotic servicer comprised of two seven- degree-of-freedom manipulators attached to a torso with a stereo vision head. The robot is designed to match a suited EVA crew member in both size and dexterity. Because of its small size, the robot has a variety of mounting and mobility options. A unique aspect of the Robonaut is that it has a single end effecter that can use the same tools and equip- ment interfaces as an EVA crew member. This end effecter has four fingers and an opposing thumb and resembles a human hand.
EXTRAVEHICULAR ACTIVITY, ROBOTICS, AND SUPPORTING TECHNOLOGIES 23 The Robonaut concept is different from all other servicers NASA intends the ISS to be "an important test bed for that use multiple changeout tools (such as the Ranger). With solar system exploration" (Nicogossian, 1999~. Therefore, the Robonaut servicer, EVA tasks currently designated "for the development of robotic technologies for servicing in EVA crew members only," including tasks within tight cor- space will be important for more than the ISS. Future HEDS riders and tasks that require simultaneous dual-arm opera- (Human Exploration and Development of Space) initiatives, lion, could be performed robotically. The Robonaut could and solar system exploration missions, will also benefit from be operated either by an IVA crew member or, potentially, remotely operated robotic systems that can perform external from the ground. inspections, servicing, maintenance, and repair. For un Both the Ranger and the Robonaut technologies are avail- manned missions, robotic servicing will be the only option. able and could significantly improve the efficiency and safety of both EVA and IVA tasks. However, neither is currently planned to be incorporated or tested on the ISS. Recommendation. The National Aeronautics and Space Administration should continue to explore advanced robotic technologies that have the potential to increase the efficiency of human-robot teams onboard the Internationaol Space Station. This should include space flight testing of the Ranger vehicle as a proof of concept. Recommendation. The National Aeronautics and Space Administration should assess the potential improvements in extravehicular activities from the introduction of new robotic technology into human-robot systems. This assessment should include a comparison of the cost for development and implementation and the potential cost savings and risk reduction associated with the use of these systems. EXTRAVEHICULAR ACTIVITY AND ROBOTICS The current ISS robotic teleoperators require a significant investment of crew time for extensive training in operations that require great skill and attention to detail. The current ISS robotics are based on the successful history of the Space Shuttle remote manipulator system and do not represent a significant advancement in technology. The ISS will provide a unique opportunity to establish synergistic activities by suited crew members and robotic systems. Highly mobile, reduced size and weight space suits and autonomous robotic systems with a high degree of dexterity are critical areas of research and development for which the ISS could serve as an engineering test bed. For example, a small HUT space suit, which is being considered for use on the ISS after Assembly Complete, could be used as a test bed for advanced technologies (i.e., automatic ther mal control, advanced LSS, performance and physiological measures, actively controlled materials and structures, and biological technologies). In addition, two new prototype space suits have been delivered to NASA that could to be evaluated with robotic assistants (Hatfield et al., 1999~. Recommendation. The National Aeronautics and Space Administration should use the International Space Station (ISS) as a technology test bed for advanced extravehicular activity (EVA) systems, including robotic systems to sup- port long-term ISS operations and future space missions. Rather than introducing only incremental changes, revolu- tionary approaches should be pursued to developing new materials, achieving greater mobility, and incorporating new technologies for both EVA suits and robotics systems in sup- port of future exploration initiatives. REFERENCES Francis, E. 1999. Space Suit and Life Support System Technology. Presen- tation by E. Francis, Vice President, Programs, Hamilton Standard Space Systems International, to the Committee on the Engineering Challenges to the Long-Term Operation of the International Space Station, Hamilton Standard Space Systems International, Windsor Locks, Connecticut, April 9, 1999. Harbaugh, G., and S. Poulos. 1999. EVA Status. Presentation by G. Harbaugh, Manager, EVA Projects Office, and S. Poulos, Deputy Man- ager, EVA Project Office, to D. Newman, member of the Committee on the Engineering Challenges to the Long-Term Operation of the Inter- national Space Station, NASA Johnson Space Center, Houston, Texas, February 21, 1999. Hatfield, C.A., E. Taylor, and P. Callen. 1999. Advanced Robotic Capabili- ties for ISS. Presentation by C.A. Hatfield, Mission Integration Office, International Space Station Program, to the Committee on the Engineer- ing Challenges to the Long-Term Operation of the International Space Station, NASA Johnson Space Center, Houston, Texas, March 25, 1999. Nicogossian, A.E. 1999. Conducting Research on an Orbiting Platform. Presentation by A.E. Nicogossian, Associate Administrator for Life and Microgravity Sciences and Applications, National Aeronautics and Space Administration. American Association for the Advancement of Science, 1999 Annual Meeting and Science Innovation Exposition, Anaheim, California, January 23, 1999. Poulos, S. 1999. EVA Requirements. Presentation by S. Poulos, Deputy Manager, EVA Project Office, to the Committee on the Engineering Challenges to the Long-Term Operation of the International Space Station, NASA Johnson Space Center, Houston, Texas, March 25, 1999. Ross, J. 1999. EVA Astronaut Experience. Presentation by J. Ross, Astro- naut Office, to the Committee on the Engineering Challenges to the Long-Term Operation of the International Space Station, NASA Johnson Space Center, Houston, Texas, March 24, 1999.