Engineering Research and Technology Development on the Space Station (1996)

The committee reviewed nine technical fields in which engineering research or technology development activities on the ISS might be appropriate: electric power, robotics, propulsion, thermal control, life-support systems, space environment and effects, structures, communications, and autonomous systems. With respect to each, the committee examined (1) the scientific or technical value of the research to the station itself, to other space activities, or to uses on Earth, (2) the advantages and disadvantages of performing the work on the ISS rather than on the Earth or on an uncrewed spacecraft, (3) the demands that the activities would put on ISS resources, and (4) whether additions of generic instrumentation or modifications of station hardware would be needed to carry out such activities.

This chapter is not intended to be a complete survey of all the fields of engineering research and technology development that might benefit from work on the ISS. For example, it does not address ERTD on fluid handling or tethers. Rather, the chapter explores a few areas that seem to have particular promise and appear well-suited to space station experimentation. Other groups have highlighted other promising areas for ERTD on the ISS, including electronic performance, fluid behavior, information systems, and microgravity measurement (SSTAC, 1987; NASA, 1987).

The ISS could be the site of (1) extensive research on the long-term effects of the LEO environment on electric power generation systems, components, and subsystems, and (2) in-space testing of new electric power technologies, such as solar dynamic systems, tethered satellite systems, advanced photovoltaic power

generation systems, and energy storage devices (including batteries, flywheels, and solid state thermal storage).

Lessons learned from power systems ERTD could be used to improve the ISS power system, reduce maintenance costs, and provide additional power for ISS operations and experiments. The station's initial power system will be very costly to operate and maintain. The large solar arrays, for example, will create a major fraction of the drag on the station and will make it necessary to ship large amounts of propellant from Earth to maintain the station's orbit. In addition, the space environment will be harsh on the solar panels. Micrometeoroids, radiation, orbital debris, and atomic oxygen will significantly degrade solar array performance. For this reason, the panels will initially be “over-designed,” which will increase their size and weight. They will also require significant maintenance over the life of the station.

More advanced systems derived from electric power technology development and testing on the ISS could result in smaller power generating systems (either advanced photovoltaic or solar dynamic), which would reduce the amount of drag and therefore the amount of propellant needed to maintain the station's orbit. The results of electric power system ERTD may also make it possible to develop power systems that are more durable and require less maintenance. Similarly, work done at the station could lead to the creation of energy storage devices that are lighter and safer than the ISS's original batteries.

Tests of some new power systems also could be used to provide additional power to ISS experiments and housekeeping functions. Electric power is likely to be a major limiting factor in space station utilization, and any additional power would be useful for other station users.

Much of the power system research conducted on the ISS would probably be relevant to other space systems, potentially significantly reducing their costs and extending their lifetimes. Power generation technologies developed or initially tested on the space station, for example, could be used in other spacecraft, although some (such as solar dynamic systems) may be appropriate only for high-powered spacecraft. Information gathered on the ISS about the long-term degradation of electric power systems in space may be particularly useful for the increasing numbers of spacecraft that will have long functional lifetimes.

The results of electric power system ERTD on the ISS could potentially be applied to uses on Earth. ERTD on advanced solar cells, batteries, and flywheels, for example, may help in the development of electric-powered automobiles.

The solar, vacuum, radiation, contamination, and micrometeoroid environments that will be experienced by power systems in space are very difficult to simulate on the Earth. The microgravity environment is also very hard to simulate, and the combined effects of these environments on electric power systems are even more difficult to simulate. Ground testing is even less feasible for research on the long-term effects of the space environment on space power systems.

The presence of a crew will allow electric power experiments to be monitored and reconfigured in response to observations by the crew. Astronauts could periodically inspect experiments involving the long-term effects of the space environment on photovoltaic systems, for example, to determine the extent of contamination or the sources of degradation over the life of the system. This would be a more effective means of assessing the factors that cause the degradation of electric power systems than the current method, which takes the form of Earth-based monitoring of the voltage output of components in space.

Another advantage is that it will be possible to return experiments to Earth for further tests and evaluation. Energy storage devices like batteries and phase change materials, for example, could be tested in the microgravity environment to provide data on depth of discharge and subsequently returned to Earth for the thorough examinations needed to determine failure modes and effects. This could result in better solutions to the problem of extending the life of energy storage devices.

Finally, the engineering needed to allow an experiment to fly on the ISS would make it easier to incorporate the technology into upgrades or modifications of the station's power system.

Some of the environmental information gathered by the ISS will not be applicable to the power systems of spacecraft in higher orbits. Many of the long-term environmental effects that will be experienced by the station (such as the atomic oxygen environment, moderate radiation flux, thermal cycling, and eclipse duration) are different in low Earth orbit than in other orbits. Moreover, rocket plumes, outgassing, venting, and other activities associated with ISS operations may contaminate the local environment, and the effects of such local contaminants would have to be factored into the analyses.

Another disadvantage is that extensive analyses, tests, inspection, and documentation would have to be performed to meet the ISS's stringent safety requirements. High energy density storage devices, such as batteries and flywheels,

would be a particular concern on a crewed spacecraft. It will also be necessary to minimize interference with other ISS experiments. Tests of flywheels for energy storage, for example, might have to be coordinated with the station's attitude control system. Careful experiment design, however, could minimize interference.

The electric power requirements for power component testing on the ISS should be relatively small. Complete systems normally generate their own electricity, and component testing typically requires very small power levels to check out individual components.

Crew involvement (including human or robotic EVAs) will probably be necessary to erect large power subsystems, such as solar arrays or solar dynamic power systems. Some crew time will be required to monitor power system experiments, and additional crew time—including EVAs—may be needed to retrieve samples or components for analysis on Earth. Much of the setup and recovery of the experiments could potentially be performed by robotic systems.

No significant communications or data processing would be required for electric power systems tests on the ISS. Transfer of data at low rates over the duration of the testing will be sufficient for most experiments.

Some electric power experiments may require the transport of potentially large and heavy batteries and solar arrays. Others, such as experiments testing the effects of the space environment on power system components, could be small but would eventually have to be returned to Earth. Solar power generation systems would have to be attached to the outside of the station.

Studies of the effects of the space environment on power systems over the long term should cost less than a million dollars, but full-scale tests of advanced power systems, such as a solar dynamic system, could cost tens or even hundreds of millions of dollars.

Tests of advanced solar power generation systems would require a radiator as well as a point and track platform to follow the Sun. A safe testing area outside the pressurized volume of the ISS would be needed to reduce the hazard of corrosive spills during battery tests. The same area could prove useful for tests of other potentially hazardous items. Tests of environmental effects would require a facility where sample materials could be exposed to space in a controlled manner. This facility should be able to expose materials in the ram (in the direction of travel) and wake (away from the direction of travel) orientations, as well as toward and away from the Sun.

An external port that would permit power from experiments to be used to augment the main station power system (through a fault protection system) would increase the benefits of tests of new power systems. Provision for attaching a large additional solar power generation device to the station also would be desirable.

The ISS could function as a site for testing and improving the ability of humans and robotic systems to work cooperatively in space. Research would focus primarily on (1) developing robots that would function as capable, reliable, and intelligent agents that would respond to higher-level commands from humans and (2) verifying the performance of robots under space conditions.

Robotic systems have tremendous potential for supporting both EVA and intravehicular activities (IVA) on the station. Robotics could be used in conjunction with or instead of astronauts to perform a wide variety of tasks, including inspecting, servicing, and repairing the station; manipulating and placing large objects outside the ISS; and servicing scientific experiments.

The current state of the art in controlling robotic manipulators (e.g., the Shuttle Remote Manipulator System) is extremely limited. The primary mode of operation is a “tele-operator mode,” in which an astronaut directly controls the individual motors at the joints of the manipulators. This has the advantage of giving the crew member full control of the robot's actions, but it also has several disadvantages. One is greatly limited performance. The system bandwidth is necessarily low to avoid excitation of dynamic modes (which are very difficult for human operators to control) within the manipulator. A second disadvantage of this mode of operation is that it mandates a high workload for the operator.

The astronaut must control not only the task being performed but also the performance of the robot. Because of this, one of the major benefits of a robotic system is lost (i.e., reducing or eliminating the need for astronaut involvement in a task).

Other disadvantages include restricted performance because of slow astronaut response times (as compared with a computer), and limited possibilities of control from Earth because of the lag in communications time (approximately 2.5 seconds) between Earth and the station. This time delay is sufficiently large compared to the dynamics associated with robot motion to make remote control from Earth of current space robots impractical.

If robots on the space station were able to respond to high-level task directives from either the ground or the station, the human operator would be able to focus on the tasks themselves instead of on low-level control of the robot. (Low-level control of the robot —including control of its dynamic response—would be the responsibility of the robot's internal systems.) The operator would simply issue commands (such as “pick that up” or “move that over there”) and monitor the robot's actions to ensure safe operation. In this type of system, the speed of response of the robot can be increased dramatically, the robot can be commanded from a remote site (e.g., the ground), and the human operator's workload is greatly reduced. This capability is applicable to (semi-) fixed-base systems (e.g., the Shuttle Remote Manipulator System) as well as to mobile systems.

Much of the robotic technology developed for the ISS could be relevant to other crewed space platforms. Improved ground-based control of remote robotic systems would also enable “manipulation” of equipment on uncrewed space platforms. Advances in remote control of robotic systems would also be applicable to planetary exploration. As distance increases, so do communication times, which makes high-level control of robots of even greater importance.

The Fisher-Price report (Fisher and Price, 1990) stated that rigorous verification of both hardware and software will be required for robotic space systems. As noted below, ground-based testing would not provide sufficient verification and validation (V&V). An operational environment is required. The testing and use of robots in and around the ISS could go a long way toward providing the V&V required (particularly since V&V standards in the vicinity of a crewed platform would be very stringent).

Much of the technology required for a remotely operated robotic system in space is identical to that required for terrestrial applications. Human/robot teams are used (or have been proposed) for exploration of the ocean depths, for hazardous waste cleanup, and for other activities in environments that are hazardous to

humans. Consequently, there should be good opportunities for applying new robotic technology developed in space to terrestrial systems.

Although ground-based testing of robotics systems will be adequate in many cases, many aspects of space robotics cannot be fully tested on the ground. For example, it is difficult to test on Earth a robot designed for microgravity. Verification and validation of robotic system capabilities are best performed in an operational environment, particularly since a robot's motion involves the dynamic response of the system, and there is no means of replicating the exact dynamic behavior of a space robotic system on Earth.

Because one of the primary goals of robotics work on the ISS would be to develop human/robot teams (both local and remote), human presence will be a prerequisite. The presence of the crew would also allow experiments to be monitored and reconfigured if necessary. Testing on the ISS would have an additional advantage in that the ISS itself would probably be the first customer for the robotic technologies that are developed. Consequently, if a robotic capability could be demonstrated in a controlled environment on board the ISS, an implementation path with a large payoff would become apparent.

The fact that robots move and contain energy storage devices could make them a danger to both astronauts and nearby equipment. The potential risks would have to be minimized, and analyses, tests, inspections, and documentation would have to be performed to meet the ISS's stringent safety requirements. In addition, robotic experiments must be designed so that the movement of the robots does not corrupt the low-vibration environment of the station.

Fixed-base robotic manipulators will need a moderate amount of power drawn directly from the station's power supply. Mobile robots will generate and/or store their own power, but may have to be recharged from the station's power source.

A significant amount of crew time would be required to carry out basic robotics tests on the ISS. Semi-operational robotic systems, however, might reduce overall demands on crew time.

High data rate, bi-directional, intra-station communications networks that can accommodate the mobility of the robots would be required. Ground-controlled remote operation activities could also stretch communications capabilities. Devising a protocol for these activities which minimizes path delay and compression/decompression delay will be a challenge. Also, significant amounts of video and other sensor data would have to be downlinked as part of dynamic robotics experiments.

The robots (and support equipment) will have to be transported to the station. EVA or IVA activity will be required to support robotic experiments, but the robots will require less supervision as their capabilities are developed and verified.

The cost of basic robotics tests on the ISS would be moderate, but the use of larger and more capable robots could be very costly.

Robotics ERTD on the ISS would require power sources, laboratory space, attachment structures, and computers. Specific requirements would vary widely, depending on the robotic application. For free-flying robotics applications, a local Global Positioning System (GPS) grid for navigation would be desirable, and a communications network would be a necessity. Attached applications, such as the use of specialized end-effectors on the space station remote manipulator system, would make use of power, attachment, and computer capabilities that are already part of the design.

Special tracks or support structures would be required to allow robots to move around both inside and outside the station.

The ISS could serve as a testbed for advanced space propulsion systems, particularly low-thrust systems. These could include electric propulsion, chemical propulsion, hybrid propulsion, and waste gas propulsion systems. These systems

could be tested on either a dedicated testbed or on self-contained deployable/retrievable test units.

Under the current design, over 120,000 kg of propellant will be needed to keep the ISS in orbit through the year 2012. Reducing the required amount of propellant by developing and employing a more efficient propulsion system would reduce the number of required logistics flights or allow them to be used for other purposes. Using waste gases from the station as propellant also would reduce the amount of additional propellant required and could also reduce the local contamination caused by waste gas dumping.

Some tests of low-thrust propulsion systems could be used to help counter drag on the station. This would reduce propellant requirements and might improve the microgravity environment. Such tests could also provide redundancy or backup for the ISS's primary propulsion system.

Low-thrust technology developed and tested on the ISS would be widely applicable both to orbital transfer stages and to other spacecraft. Advanced propulsion systems would make it possible to use smaller and cheaper transfer stages and could greatly improve spacecraft reliability and lifetime. Advanced propulsion systems developed on the ISS also might lower the costs of future interplanetary missions.

There are a number of advantages in testing propulsion systems in space rather than on Earth. First, experimenters would be able to evaluate the effects of the space environment on components of the systems. Second, the low gravity field of the ISS would make it much easier to measure long-term degradation in the functioning of low-thrust engines. Third, space provides a high-level vacuum that is difficult and expensive to replicate on Earth. (Maintaining a vacuum on Earth while a rocket is firing can be a very difficult, albeit not insurmountable, problem.) Finally, it would be possible to measure engine contamination effects in space accurately by setting up measurement devices in the vicinity of the engine. On Earth, the presence of the vacuum tank and the 1-g environment distorts the pattern of contamination from an engine.

Experiments could be returned to Earth for further evaluation, which would be particularly useful if the cause of an engine failure had to be determined.

There would also be frequent opportunities to bring up new experiment components from Earth. Also, incorporation of low-thrust rockets into ISS upgrades or modifications would be facilitated if the rockets had already been tested on the ISS.

The pressurized propellant tanks used in some propulsion systems, the propellants themselves, and the exhaust emissions would all present hazards to the crew. These hazards will be hard to minimize, and significant testing procedures and design constraints, which will add to the cost of experiments, would be needed to ensure crew safety. Since the ISS will already be using hazardous propellants, however, the problems arising in the testing of new propulsion systems may not impose a large additional burden.

In addition, tests of propulsion systems carried out on the ISS would have to be designed to minimize disturbances to other experiments that require high levels of microgravity. This would not be a problem in tests using deployable/retrievable propulsion units.

Some propulsion systems will require little power, but others (including some electric power thrusters) may have power requirements in the kilowatt range.

Tests of propulsion systems would require crew involvement (including EVAs) for initial set-up, in the event of an anomaly, and on a regular basis to perform inspection and periodic changes of components. Robots might eventually be used to perform some of these tasks.

Nominal communications and data processing capabilities would be sufficient to take measurements and command propulsion system experiments.

Experimental propulsion systems would have to be transported to the station (and sometimes back to Earth for inspection). It would also be necessary to transport propellants. Some propellants would be hazardous, requiring special containers as well as costly and time-consuming handling procedures. Since the ISS design is capable of handling hazardous propellants, however, these added burdens might be small.

The cost of creating a propulsion test facility on the ISS might be large. Various safety procedures and design constraints would be needed to ensure the safety of both the crew and the station itself. Any facility for engine testing would therefore have to be well thought out, and procedures and components would have to be designed for different users whenever possible. Propellant resupply would also incur significant costs, not only for transporting supplies to orbit but also because transporting and transferring certain propellants to the test systems would require additional steps to ensure safety. The cost of individual deployable/retrievable test units would not be as high as the cost of a dedicated testbed, but the former would not produce as much data as the latter.

Optimally, a propulsion testbed would be equipped with video cameras, infrared sensors, contamination sensors, thrust measurement devices, flow meters, electric field measurement devices, pressure transducers, temperature monitors, flow meters, and strain gauges. Standard equipment for handling hazardous propellants, including equipment for managing spills and cleanup, would also be required.

A propulsion test bed would require an external mounting. Attaching this test bed so that the experimental systems operated in the same direction as the thrust required to maintain the orbit of the space station would be desirable. Attachments in other directions, however, could be helpful in controlling the ISS's attitude. The test bed also would need an area for storing propellants and a system for supplying propellant to the engine. A high-voltage power source would be required for some experiments. Deployable/retrievable test units might also require a capability to store propellants but would not require unique accommodations.

The ISS could serve as a site for the testing and evaluation of thermal control components, such as transport, storage, and refrigeration devices (including heat pipes, phase change materials, thermal electric devices, and cryogenic coolers), radiators, and insulation. Observations of the long-term effects of the space environment on thermal control components could also be made on the ISS. Finally, the ISS could function as a research laboratory for basic engineering research on fluid flow in microgravity aimed at improving the performance of space thermal control devices (such as heat pipes).

The space station's thermal control subsystem could require costly maintenance over the station's lifetime. The external thermal control components of the ISS, such as blankets and radiators, will be exposed to damage from atomic oxygen degradation, micrometeoroids, radiation, and contamination, all of which will affect the thermal stability of the station. Research that produced a better understanding of the causes and rates of degradation of thermal control components could result in lower operation and maintenance costs for the ISS. In addition, research and development activities devoted to advanced thermal control materials and components could further reduce ISS operation and maintenance costs and improve thermal performance.

Research on the ISS into the long-duration effects of the space environment on thermal control subsystems would only be applicable to space systems that fly in a similar orbit. However, research in such areas as the lifetime of coolers and the performance of fluid systems in zero gravity would be widely applicable and could enhance the performance, reduce the costs, and extend the lives of other spacecraft.

Advances in thermal control technology in space have already been adapted for use in cooling devices on Earth (e.g., heat pipes, phase change radiators). It is possible that further research might lead to the development of new technologies usable on Earth.

The factors that limit the life of some thermal systems in space cannot be duplicated on Earth for long periods of time, and the combined long-term effects of the space environment as a function of time are not yet well enough known to be accurately modeled. In addition, many thermal control devices cannot be accurately tested on the ground because they use fluids as their basic transport mechanism. These fluids are acted upon by capillary action and liquid vapor interfaces, which behave in a different manner in space than on the ground.

The presence of a crew would allow for periodic inspection and assessment of the performance of thermal control components without requiring large

amounts of additional instrumentation and could help provide insight into the use and design requirements of these systems for serviceability as well as for improved performance and longer life. In addition, experiments could be returned to Earth for further tests and evaluation.

Some of the information on environmental effects gathered in the ISS's low Earth orbit would not be applicable to spacecraft in higher orbits. In addition, potential risks to the station and crew would have to be minimized, meaning that additional analyses, tests, inspection, and documentation would have to be performed to meet safety requirements.

Thermal components and subsystems generally require little power, and the ISS's power system should have little trouble meeting the demand.

Members of the crew would have to configure thermal experiments, monitor performance, and evaluate and resolve anomalies, but these tasks would be neither time-consuming nor time-critical. System level and external component testing would require EVA activities to connect and inspect the systems, but the amount of EVA required would probably vary significantly from system to system.

Nominal communications and data processing would be required to take measurements and command the experiments. No exceptional needs are foreseen.

Component testing would require transport to orbit, set-up (sometimes externally), and occasional monitoring. None of the components would necessarily be particularly large.

Some of the thermal control research (e.g., into the effects of the space environment) would involve the station's original thermal materials and would be inexpensive. Other experiments in this area are also not likely to be costly.

Storage areas might be required for the hazardous chemicals used in some thermal devices. Standard sensors for monitoring temperature, and voltage controls for heaters, valves, and pumps would also be needed.

To carry out experiments in this area, the ISS would have to be equipped with attach points that would allow components to be tested in extreme environmental conditions (e.g., ram and wake directions, sun pointing and shadowed). Tests involving radiators, for example, would need attach points with an unobstructed view of space.

The ISS could function as a laboratory in which controlled environmental life support systems (CELSS) would be tested and improved. The technologies involved could include atmosphere revitalization systems, water purification and recovery systems, and biological systems. This research could include work on plants, which can be used to remove CO₂, generate O₂, recycle “gray water,” and provide nourishment (as well as psychological comfort) to the crew, and on the interactions between living systems (humans, animals, and plants) in a closed environment.

CELSS experiments could be used to improve the crew's environment and to reduce logistics requirements for consumables. Under current plans, thousands of kilograms of consumables (including oxygen, water, and food) will be moved from the Earth to the ISS each year. CELSS experiments could allow increasing amounts of these consumables to be recycled instead of transported from Earth.

Any future long-duration crewed space missions (including future space stations and missions beyond Earth orbit) would benefit from reductions in resupply requirements achieved with the help of CELSS experiments. The need for advanced CELSS is particularly great for missions beyond Earth orbit, for which resupply of consumables will be extremely costly.

Advances in water treatment and purification systems achieved by experiments on the ISS could potentially be used in remote and underdeveloped areas of

the world. Basic research into plant physiology (growth cycles, reproduction, multi-generation viability, etc.) in microgravity might also be of direct benefit on Earth. Space research on plants in CELSS, for example, could potentially lead to increased knowledge of plant growth and even to increased yields and greater survivability.

Some CELSS systems, such as gas/water separation systems, perform differently in 1-g and microgravity environments. If CELSS research is to be successful, it would have to be carried out in an environment where it was possible to study the continuous operation in microgravity of pumps, filters, fluid lines, and connectors, as well as multi-generation plant growth.

Most CELSS research must be performed on a crewed vehicle. For example, the balancing of human CO₂ production with plant activity (CO₂ removal and O₂ production) clearly requires a human presence. Long-term work with plants is also likely to require crew time for harvesting and for specimen preparation and analysis. In addition, the operation of the ISS life support systems will be an experiment in itself in which unexpected problems and solutions are likely to arise.

Potential risks must be minimized, and additional analyses, tests, inspection, and documentation would have to be performed to meet the ISS's stringent safety requirements.

Life support research is scaleable, making resource demands flexible. Some amount of power would be required to operate pumps and monitoring and measuring equipment. Additional power might be required to provide illumination for plants.

Crew time would be needed for monitoring and reconfiguring experiments, for intermittent plant harvesting, and for specimen preparation and analysis. For large-scale operational plant growth systems, additional crew time would be needed for harvesting and food preparation.

Nominal communications and data processing capabilities would be required to take measurements and command the experiments. No special communications or data processing needs are foreseen.

Initially, developmental and then operational hardware for life support experiments would have to be delivered to the ISS. Because of the scaleable nature of the hardware, the logistics requirements could vary from transporting a single experiment rack to launching a complete logistics module. After life support systems became operational, however, enormous benefits would be gained because of significantly reduced logistics requirements.

Individual CELSS experiments would not be costly, but large-scale experiments and facilities could cost tens or hundreds of millions of dollars.

Experiments in life support systems would require such items as temperature (air and water) and humidity monitors, PCO₂, PO₂, and trace gas (e.g., ethylene) monitors, flow meters, water quality measuring devices, pressure gauges, electronic instrumentation, and vibration measuring devices.

Experiments on mechanical components of life-support systems and the initial experiments on plant systems could be performed in standard racks. Modifications of the station's original subsystems could be made in a building block manner as CELSS subsystems became operational. Since many life-support components would require periodic maintenance and replacement, this should be feasible on a selective basis.

The ISS could be used to verify models of the space environment, including space debris and micrometeoroid models, and models of the thermal, radiation, atomic oxygen, plasma, and ultraviolet environments in LEO. Models of the contamination caused by technological operations in space also could be verified. The ISS could also be used to determine the effects of the space environment on

materials, including coatings, photovoltaic cells, thin films, composites, and electronic materials.

Both active and passive experiments could be conducted. Passive experiments involve exposing samples to the space environment and sending them to a laboratory for analysis. Active experiments typically involve storing and transmitting data collected by sensors.

Studies of the effects of the space environment on materials might help engineers develop more durable or more effective space station components. Such research also might provide better indications of when exposed surfaces or components should be replaced. A better understanding of the contamination caused by the ISS would help to guide future selection of ISS materials and experiments and perhaps lead to improved docking and venting procedures to reduce contamination.

Improvements in environmental models would directly benefit the designers and operators of spacecraft in orbits similar to the station's orbit by giving them more accurate information on their spacecraft's environment. Very few spacecraft operate in the ISS's planned orbital regime, however, so this data would be of direct interest to only a few other systems. Research on the effects of the space environment on materials would also be particularly helpful to the designers and operators of spacecraft in similar low orbits, but would in many cases also be applicable to spacecraft in other orbits.

Experiments designed to explore the environment of space and to verify models of the space environment must, by definition, be performed in space. The long-term combined effects of the solar, radiation, atomic oxygen, and thermal environments on materials must also be performed in space because they cannot be simulated accurately on Earth.

The large size, unusual configuration, and long functional lifetime of the ISS would allow the collection of sets of data that could not be gathered on most uncrewed vehicles. Sensor inputs on the ISS could also be supplemented with crew observations. Astronauts would be able to notice areas where materials appear to be showing signs of wear or where other changes (e.g., arcing) were

occurring. Observation opportunities might be limited, of course, by the external location of an experiment unless EVAs were used, but robotics might be able to improve the situation. Regular crew rotations would also make it possible to return experimental materials to Earth for further testing and evaluation.

Much of the information gathered by the ISS about the environment in its low Earth orbit would not be applicable to spacecraft in other orbits. Furthermore, some measurements will be skewed because the ISS will be surrounded by its own atmosphere. Careful placement of experiments could ameliorate this problem to some degree.

Many experiments in this area would have no power requirements. Some debris/meteoroid sensors would have small power requirements. Tests to simulate arcing and other plasma effects might have higher power requirements.

Crew duties might include occasional assessments of environmental effects. EVA might be required for initial deployment of samples as well as to retrieve samples.

Communications and processing requirements would vary, depending on the experiment. Some meteoroid/debris sensors might have significant communications and data processing requirements.

Samples of materials would have to be transported to the ISS, attached externally, and eventually returned to Earth.

Most materials exposure experiments would be inexpensive. Space environmental sensors could be more expensive. The prices of powerful meteoroid/debris sensors might range in the tens of millions of dollars.

Studies of the environment would require a facility exposed to space in various directions that would be the site of a variety of sensors or material samples.

Sensors located at various points around the station would be needed to measure contamination from ISS operations.

No modifications of hardware would be required.

The ISS could be used as a laboratory for many areas of structures research, including erectable structures (integrated with the development of EVA and IVA robotics and automation), and effects of jet plume impingement on structures and materials. Research could also be performed on “smart” structures, including (1) controlled dynamic smart structures, (2) actively and passively damped structures, and (3) structural fault detection and correction. Deployable structures, including inflatable, foam and other rigidized, gossamer, and tethered structures, also could be investigated. The station itself could be used by researchers to verify structural dynamics models and as a test bed for investigating controls/structures interaction (CSI).

Smart structures research could enhance the ISS's controllability and stability, thereby improving its performance as a platform for observations of Earth and space. Research of this kind could also improve the station's ability to maneuver to avoid orbital debris and provide a means for structural maintenance and repair over the space station's long functional lifetime. Better CSI prediction would lead to improved control laws and algorithms, which might also be applied to enhance the station's stability and maneuverability.

Research on deployable and erectable structures could lead to improvements in lightweight solar collectors, antennas, reflectors, and other structural elements that might eventually be added to the ISS. In conjunction with improved automation and robotics, research on erectable structures could also contribute to automated logistical techniques for ISS resupply.

Research on smart structures could improve the precision and reduce the weight of communications antennas and do the same for reflectors and instruments with active shape correction used in space astronomy and astrophysics. Research on deployable structures could lead to improved lightweight solar collectors, antennas, and reflectors for low-cost robotic spacecraft. Research on deployable structures could also reveal additional design options for ultralight

spacecraft. Verification of structural dynamics models could have wide applicability, especially for other large and complex space structures.

Deployable and erectable structures might have specialized applications in remote locations, in difficult terrain, or underwater. Improved structural dynamics modeling could possibly have applications for designing structures on Earth.

The interactions between structural dynamics and the controls of smart space structures can only be accurately demonstrated in space. Research on some erectable and deployable structures can also only be performed effectively in space because these structures are unable to function on Earth. Finally, verification of the results of ground testing and verification of structural dynamics models would, of course, have to be performed in space.

The ISS's exceptional size, configuration, and long functional lifetime would make it possible to gather unique sets of data. The crew of the ISS would be in a position to monitor and reconfigure experiments in response to observed behavior. For verification of structural dynamics models, data from sensors could be supplemented by observations by the crew, and the crew could halt the tests if unsafe responses became evident. The crew would also be able to assess control/dynamics interactions, as well as the effectiveness of fault detection and repair. The crew might also be able to take corrective action if a test structure did not deploy properly. Finally, regular shuttle visits would permit some test structures to be returned to Earth for examination.

Potential risks must be minimized, and additional analyses, tests, inspection, and documentation would have to be performed to make sure tests met ISS safety requirements. In addition, because the ISS is a very complex structure, the verification of structural dynamics models would require careful analysis of the data gathered.

The amount of power needed for smart structure testing would be small for sensors and moderate to high for vibration inducers. The sensors used in tests of

erectable and deployable structures would have small power requirements, while power requirements during deployment or erection tests would be moderate. The sensors used in structural dynamics tests would have small power requirements, but the demand for power would extend over long periods of time.

Some crew time would be required to carry out structural experiments. Interactive experiments might require intensive attention from the crew. EVA or robotic operations might be needed for setup, for erection or deployment, and for resolving problems with deployable and erectable structures.

The communications and data processing needs of structural experiments would vary from experiment to experiment but would generally be moderate.

The only notable effect of structural experiments on logistics would be the need to deliver (and possibly return to Earth) large deployable or erectable structures. By their nature, however, these need not be particularly large when launched.

Smart structure research and verification of structural dynamics models would be relatively cheap if sensors were integrated in the ISS before launch. Research on expendable and deployable structures should not be particularly expensive either, although the robotics development that would go hand-in-hand with erectable structure development could be costly.

Strain gauges, acoustic sensors, vibration inducers and pickups, thermocouples, laser targets and length measurement devices, accelerometers, video cameras, radar equipment, capacitance sensors, and other items, would all be needed for ERTD in this area. In addition, a common hard mount interface (“backstop”) would be needed for research on erectable and deployable structures. This item would optimally be equipped with a high-precision, documented, standardized metrology system using noncontact imaging and laser doppler as well as point and base excitation input systems and a thermal imaging system. The backstop should also be compatible with EVA robots and would need a means for safing (and perhaps disposing of) test articles.

Sensors installed at various points in the station's structure would be required for smart structure research and structural dynamics model verification. In addition, structural attachment pads for vibration inducers would be needed on the station truss. A site for attaching a “backstop” would also be needed.

The ISS could serve as a test bed for technology development issues of importance to commercial communications satellites, including phased array antenna deployment and testing, on-orbit radio frequency environment characterization for electromagnetic interference, high-data-rate communications, complex on-board processors for asynchronous transfer mode signal processing, optical communications, and deployable (including inflatable) antenna structures.

Communications is a primary enabling technology for ISS experiments, both inside and outside the station. Using the station as a communications testbed might in some cases allow experimenters on the ISS to make use of the additional communications capability. In addition, some of the advances in communications technology obtained with the help of the ISS might be applicable to upgrades of the station's own communications system.

Communications technology tested on the ISS could be used in commercial spacecraft, improving their performance (in terms of data rate, on-board processing capability, etc.) and giving the companies that use them a competitive advantage in a multi-billion dollar business. Technologies like optical communications could also have significant impact on deep-space communications applications.

Optical high-data-rate communications networks (which tend to optimize power efficiency and minimize power consumption) tested on the ISS might be applicable to power-limited networks (e.g., underwater networks).

Demonstrations of the performance of new space communications technologies must, by definition, be performed in space. Tests of the inflatable and gossamer

antenna structures needed by some light-weight spacecraft also are very difficult to conduct on Earth.

The presence of the crew would allow experiments to be monitored and reconfigured in response to observed behavior and returned to Earth for further testing and evaluation. The ISS also will offer frequent opportunities to bring up new experimental components from Earth, and incorporation of the technologies into ISS upgrades or modifications would be facilitated.

Some of the information gathered in communications experiments in the ISS's low Earth orbit would not be applicable to spacecraft in higher orbits. In addition, potential risks to the station and crew would have to be minimized, meaning that additional analyses, tests, inspection, and documentation would have to be performed to meet safety requirements.

Communications experiments should have no unique power requirements. Proper design of the power system would minimize any concerns about electromagnetic interference affecting the transmission bit error rates.

Crew time would be needed for installation, setup, and operation of test bed experiments. If high-data-rate fiber networks were not included as part of the initial design, the stringing of these networks would require significant crew time.

Although many of these experiments would be provided with data handling and uplink/downlink capabilities via ISPR racks or other interfaces with the ISS, some experiments—such as those requiring real-time video links—would need additional bandwidth beyond that provided by the ISPR.

Logistics requirements would consist chiefly of the delivery and return of components for insertion into the communications test bed.

The costs of communications experiments could vary widely, ranging from well under a million to tens of millions of dollars.

A secondary high-data-rate communications system that would utilize commercial satellite-based communications networks to transmit messages to Earth would be needed on the ISS, as would a secondary computer network capable of rapidly assimilating state-of-the-art hardware and software. Instrumentation for measuring experimental communication system performance, such as antenna gain, receiver performance, and bit error rates, would be needed for some research, as would transmit/receive hand-off hardware to tie into either commercial satellite links or other high data rate satellite links (e.g., Ka-band, Ku-band, 60 GHz, optical communications). Some experiments would need radio receivers (e.g., Ka-band) to characterize the on-orbit noise spectrum at proposed commercial frequencies.

Fiber-optics data buses would have to be installed (preferably) before launch, as would external mounts for communications antennas.

The ISS could serve as an operational testbed for the development of autonomous space systems. Such systems could play a crucial role in future space operations. Autonomy includes such areas of technology as artificial intelligence (software), information and communications, advanced sensor and actuator technology, and human/machine interfaces. The goal of research in this area would be to reduce dependence on “external” monitoring and control by either the ISS crew or monitors on Earth.

Increasing the autonomy of space station operations could generate rewards in many areas. Reducing reliance on ground control could greatly reduce the standing army of people working on the ground as well as in the Earth-to-space infrastructure. On-orbit crew time (and training) for systems monitoring, control, reconfiguration, and other tasks could be reduced with advanced autonomous systems, and on-orbit safety and reliability could be enhanced through the use of an automated FDIR system. Crew operations could be simplified by the use of “top-level” commands or status messages for system control.

Greater autonomy would reduce the amount of tele-operation required in future planetary exploration. This is especially important, considering the long communications delays. In addition, self-contained FDIR systems would increase the flexibility and reliability of robotic spacecraft. Through the application of intelligent control strategies, the spacecraft would be able to “learn” and thus modify its actions.

The applicability of advanced autonomous systems to Earth-based uses could extend from control of remote installations (such as oil pipeline stations) to control of nuclear power plants. Other systems whose failure could cause catastrophic results also are candidates for autonomous control. Although reducing human intervention is the major driver, the major benefits of autonomous systems would be increased safety and reliability.

The major reason for developing and testing autonomous control systems on the ISS is that the station would benefit greatly from them through the reduction in the amount of expensive monitoring and support needed from both the crew and ground control. Although there would be no particular advantage in testing autonomous technologies in space, the space station could act as a “driver” in the quest for more autonomous operations.

The presence of a crew would allow experiments in autonomy to be monitored and reconfigured in response to observed behavior. Since the ISS will not initially be operated in an autonomous mode, the crew (both in space and on the Earth) will be trained to assure the integrity and safety of the station. Autonomous capabilities would be added gradually and be overseen by space and ground-based personnel, ensuring that the ISS is not dependent on untried technology. Even in the advanced stages of autonomy, the crew would be able to intervene in case of an inappropriate autonomous action.

The potential risks of autonomous operation must be minimized, meaning that additional analyses, tests, inspection, and documentation would have to be performed to make sure that ISS safety requirements were met.

Very powerful computing systems would be needed to implement autonomous control of the ISS, as would additional sensors, actuators and control paths. Additional power would be needed, but since computing capabilities per watt continue to increase, the extra power demands should be low.

During the development, testing, and verification phases, the workload of the crew would be somewhat greater than normal. Once the system was verified, however, crew and ground monitoring could be significantly reduced.

Additional downlinking of data might be required during the testing stages so that ground systems could monitor the operation of the autonomous systems. Once the systems were proven, these requirements would decrease. Also, the ISS would need increased computational power to handle autonomous controls. More sensors might be required, but these would be low power, low-volume “smart sensors” that might be integrated into the systems (pumps, etc.) they are designed to monitor.

After the initial deployment of advanced computers and “smart” sensors and wiring, it should be possible to reduce logistics resupply of station systems equipment because of increased system reliability and better predictions of hardware lifetimes.

Developing autonomous controls on the ISS would require substantial investments in hardware (smart sensors, upgraded computers, etc.) but would have the potential to significantly lower costs in the long run due to greater on-board safety and reliability as well as a significant reduction in ground support personnel.

Testing of autonomous systems would require high bandwidth communications equipment (e.g., a fiber-optic local area network). Advanced computers would be needed for many experiments.

Hardware modifications could probably be achieved during component replacement and thus would not affect initial space station design and development. Autonomous systems might require new hardware that would have “smart sensors” incorporated in them. For example, a pump might have built-in electrical, thermal, vibration, and leakage sensors to notify the central control system of problems. The ISS computers would have to be upgraded to more advanced commercially available chips.

Fisher, William F., and Charles R. Price. 1990. Final Report. Space Station Freedom External Maintenance Task Team. Houston: NASA Johnson Space Center.

NASA/OAST. 1987. Space Station—Phase I In-Space Technology Experiments Model Source Book. NASW-4138. Washington, D.C.: National Aeronautics and Space Administration.

Space Systems and Technology Advisory Committee. 1987. Report of the Ad Hoc Committee on the Use of the Space Station for In-Space Engineering Research and Technology. Washington, D.C.: National Aeronautics and Space Administration.