Robots vs. Humans: Who Should Explore Space?
Paul D. Spudis
Criticism of human spaceflight comes from many quarters. Some critics point to the high cost of manned missions. They contend that the National Aeronautics and Space Administration has a full slate of tasks to accomplish and that human spaceflight is draining funds from more important missions. Other critics question the scientific value of sending people into space. Their argument is that human spaceflight is an expensive "stunt" and that scientific goals can be more easily and satisfactorily accomplished by robotic spacecraft.
But the actual experience of astronauts and cosmonauts over the past 38 years has decisively shown the merits of people as explorers of space. Human capability is required in space to install and maintain complex scientific instruments and to conduct field exploration. These tasks take advantage of human flexibility, experience and judgment. They demand skills that are unlikely to be automated within the foreseeable future. A program of purely robotic exploration is inadequate in addressing important scientific issues in space.
Many of the scientific instruments sent into space require careful emplacement and alignment to work properly. Astronauts have successfully deployed instruments in Earth orbit — for example, the Hubble Space Telescope — and on the surface of Earth's moon. In the case of the space telescope, the repair of the originally flawed instrument and its continued maintenance have been ably accomplished by space shuttle crews on servicing missions. From 1969 to 1972 the Apollo astronauts carefully set up and aligned a variety of experiments on the lunar surface, which provided scientists with a detailed picture of the moon's interior by measuring seismic activity and heat flow. These experiments operated flawlessly for eight years until shut down in 1977 for fiscal rather than technical reasons.
Elaborate robotic techniques have been envisioned to allow the remote emplacement of instruments on planets or moons. For example, surface rovers could conceivably install a network of seismic monitors. But these techniques have yet to be demonstrated in actual space operations. Very sensitive instruments cannot tolerate the rough handling of robotic deployment. Thus, the auto-deployed versions of such networks would very likely have lower sensitivity and capability than their human-deployed counterparts do.
The value of humans in space becomes even more apparent when complex equipment breaks down. On several occasions astronauts have been able to repair hardware in space, saving missions and the precious scientific data that they produce. When Skylab was launched in 1973, the lab's thermal heat shield was torn off and one of its solar panels was lost. The other solar panel, bound to the lab by restraining ties, would not release. But the first Skylab crew — astronauts Pete Conrad, Joe Kerwin and Paul Weitz — installed a new thermal shield and deployed the pinned solar panel. Their heroic efforts saved not only their mission but also the entire Skylab program.
Of course, some failures are too severe to be repaired in space, such as the damage caused by the explosion of an oxygen tank on the Apollo 13 spacecraft in 1970. But in most cases when spacecraft equipment malfunctions, astronauts are able to analyze the problem, make on-the-spot judgments and come up with innovative solutions. Machines are capable of limited self-repair, usually by switching to redundant systems that can perform the same tasks as the damaged equipment, but they do not possess as much flexibility as people. Machines can be designed to fix expected problems, but so far only people have shown the ability to handle unforeseen difficulties.
Astronauts as Field Scientists
Exploration has two stages: reconnaissance and field study. The goal of reconnaissance is to acquire a broad overview of the compositions, processes and history of a given region or planet. Questions asked during the reconnaissance phase tend to be general — for instance, What's there? Examples of geologic reconnaissance are an orbiting spacecraft mapping the surface of a planet, and an automated lander measuring the chemical composition of the planet's soil.
The goals of field study are more ambitious. The object is to understand planetary processes and histories in detail. This requires observation in the field, the creation of a conceptual model, and the formulation and testing of hypotheses. Repeated visits must be made to the same geographic location. Field study is an open-ended, ongoing activity; some field sites on Earth have been studied continuously for more than 100 years and still provide scientists with important new insights. Field study is not a simple matter of collecting data: it requires the guiding presence of human intelligence. People are needed in the field to analyze the overabundant data and determine what should be collected and what should be ignored.
The transition from reconnaissance to field study is fuzzy. In any exploration, reconnaissance dominates the earliest phases. Because it is based on broad questions and simple, focused tasks, reconnaissance is the type of exploration best suited to robots. Unmanned orbiters can provide general information about the atmosphere, surface features and magnetic fields of a planet. Rovers can traverse the planet's surface, testing the physical and chemical properties of the soil and collecting samples for return to Earth.
But field study is complicated, interpretive and protracted. The method of solving the scientific puzzle is often not apparent immediately but must be formulated, applied and modified during the course of the study. Most important, fieldwork nearly always involves uncovering the unexpected. A surprising discovery may lead scientists to adopt new exploration methods or to make different observations. But an unmanned probe on a distant planet cannot be redesigned to observe unexpected phenomena. Although robots can gather significant amounts of data, conducting science in space requires scientists.
It is true that robotic missions are much less costly than human missions; I contend that they are also much less capable. The unmanned Luna 16, 20 and 24 spacecraft launched by the Soviet Union in the 1970s are often praised for returning soil samples from the moon at little cost. But the results from those missions are virtually incomprehensible without the paradigm provided by the results from the manned Apollo program. During the Apollo missions, the geologically trained astronauts were able to select the most representative samples of a given locality and recognize interesting or exotic rocks and act on such discoveries. In contrast, the Luna samples were scooped up indiscriminately by the robotic probes. We understand the geologic makeup and structure of each Apollo site in much greater detail than those of the Luna sites.
For a more recent example, consider the Mars Pathfinder mission, which was widely touted as a major success. Although Pathfinder discovered an unusual, silica-rich type of rock, because of the probe's limitations we do not know whether this composition represents an igneous rock, an impact breccia or a sedimentary rock. Each mode of origin would have a widely different implication about the history of Mars. Because the geologic context of the sample is unknown, the discovery has negligible scientific value. A trained geologist could have made a field identification of the rock in a few minutes, giving context to the subsequent chemical analyses and making the scientific return substantially greater.
The Melding of Mind and Machine
Human dexterity and intelligence are the prime requirements of field study. But is the physical presence of people really required? Telepresence — the remote projection of human abilities into a machine — may permit field study on other planets without the danger and logistical problems associated with human spaceflight. In telepresence the movements of a human operator on Earth are electronically transmitted to a robot that can reproduce the movements on another planet's surface. Visual and tactile information from the robot's sensors give the human operator the sensation of being present on the planet's surface, "inside" the robot. As a bonus, the robot surrogate can be given enhanced strength, endurance and sensory capabilities.
If telepresence is such a great idea, why do we need humans in space? For one, the technology is not yet available. Vision is the most important sense used in field study, and no real-time imaging system developed to date can match human vision, which provides 20 times more resolution than a video screen. But the most serious obstacle for telepresent systems is not technological but psychological. The process that scientists use to conduct exploration in the field is poorly understood, and one cannot simulate what is not understood. Finally, there is the critical problem of time delay. Ideally, telepresence requires minimal delays between the operator's command to the robot, the execution of the command and the observation of the effect. The distances in space are so vast that instantaneous response is impossible. A signal would take 2.6 seconds to make a round-trip between Earth and its moon. The round-trip delay between Earth and Mars can be as long as 40 minutes, making true telepresence impossible. Robotic Mars probes must rely on a cumbersome interface, which forces the operator to be more preoccupied with physical manipulation than with exploration.
Robots and Humans as Partners
Currently NASA is focusing on the construction of the International Space Station. The station is not a destination, however; it is a place to learn how to roam farther afield. Although some scientific research will be done there, the station's real value will be to teach astronauts how to live and work in space. Astronauts must master the process of in-orbit assembly so they can build the complex vehicles needed for interplanetary missions. In the coming decades, the moon will also prove useful as a laboratory and test bed. Astronauts at a lunar base could operate observatories and study the local geology for clues to the history of the solar system. They could also use telepresence to explore the moon's inhospitable environment and learn how to mix human and robotic activities to meet their scientific goals.
The motives for exploration are both emotional and logical. The desire to probe new territory, to see what's over the hill, is a natural human impulse. This impulse also has a rational basis: by broadening the imagination and skills of the human species, exploration improves the chances of our long-term survival. Judicious use of robots and unmanned spacecraft can reduce the risk and increase the effectiveness of planetary exploration. But robots will never be replacements for people. Some scientists believe that artificial-intelligence software may enhance the capabilities of unmanned probes, but so far those capabilities fall far short of what is required for even the most rudimentary forms of field study.
To answer the question "Humans or robots?" one must first define the task. If space exploration is about going to new worlds and understanding the universe in ever increasing detail, then both robots and humans will be needed. The strengths of each partner make up for the other's weaknesses. To use only one technique is to deprive ourselves of the best of both worlds: the intelligence and flexibility of human participation and the beneficial use of robotic assistance.