Pioneering the Space Frontier – Part I

Our drive to explore comes first from our human curiosity, a central attribute of intelligence. Closely following that urge to know, to understand, to see and touch with our own senses, there comes the practical desire to make use of what we learn.

Exploration, settlement, and enterprise are closely connected actions. Throughout the history of all three activities on Earth, we have explored both to search for scientific truth and to find valuable resources. We settled new territories not just to “be there,” but to extend our presence on a permanent basis, generally to work at productive enterprises. In exploring and settling the inner Solar System, we expect the same close connections to prevail, because they make as much sense in space as they continue to do on Earth.

In the next section, Space Enterprise, we discuss commercial activities in space and the productive benefits of using the energy and material resources of space. This section focuses on discovery and exploration. We must keep in mind that space resources are already benefiting exploration and will do so even more in the future. Solar energy is a full-time resource everywhere in space except in the shadows of planets. Supplemented by nuclear generators when necessary, it powers the sensors, the computers, and the radio transmitters of the robotic spacecraft that we have sent ahead of us as our scouts to examine the planets and moons of our Solar System. Future research outposts, like today’s major observatories in remote regions of Earth, will use local resources wherever possible to minimize costs. Once again by analogy to Earth’s history, most of the people who pioneer the inner Solar System in the 21st century will do so to work at jobs based on the resources of space.

We must therefore transform the way that we operate in space both for science and for industry. The few short forays of humans beyond low Earth orbit repeated in method and spirit the early polar expeditions. Each was a quick dash, lasting only a few days, supported entirely by stores of food, water, air, and fuel lifted from the home base. As we move out farther, stay longer, and establish first outposts, then bases, then long—term settlements, some for scientific goals and others for production based upon space resources, we must “live off the land” for both energy and materials in order to reduce our costs of operation. In testimony before the Commission, there was remarkable unanimity on the need to develop indigenous resources to sustain the flow of settlement and enterprise stemming from initial periods of exploration. As phrased in one presentation to the Commission:

The umbilical to Earth must be severed, or at least severely nicked. . . . This is best accomplished by the [on-site] utilization of extraterrestrial resources…. [We must] plot a future space strategy that “bootstraps” itself through the Solar System by the utilization of the resources found along the way.

For exploration and settlement, cutting the apron string to Mother Earth is necessary because we must otherwise support operations at the end of an increasingly long supply line. The logistics problem in space has its analog in the challenge of climbing Earth’s highest mountains. Here on Earth, we five at the bottom of one of the deepest gravitational wells of the inner Solar System. Everything we hoist into space from Earth must be lifted out of a gravitational well 4,000 miles deep. By contrast, lifting materials from the Moon requires climbing a well only 180 miles deep. In recent years asteroids have been discovered which can be reached with even less cost in energy than traveling to the Moon. Finding them confirmed that the inner Solar System is a treasure trove of materials, available to support pioneers on the space frontier, Lunar, asteroidal, and planetary materials are valuable where they are found, and valuable also in “free space” which is the modem analog to the high seas (See sidebar Earth’s Gravity Well).

Exploration and settlement have an additional close connection because the distances we must traverse to reach all objects in space beyond our Moon are so great, and the times required to reach them are so long, that humans can best travel to them in ships that are much like movable settlements. What we learn about long—term fife support in space will therefore be of value to us not only to support our exploration of the Solar System, but also for building the settlements necessary to support the space industrial activities of the 21st century.

Explorers throughout Earth’s history could see only short distances ahead. The unknown, and with it often unknown dangers, lay just beyond the next headland or over the next mountain range. For that reason the charts of our nearly spherical Earth were built up only slowly and painfully over centuries, until flight wits achieved. In space exploration we are already past that stage, because we can look outward in any direction through the transparent medium of space itself. There will be many surprises in detail, but we know in general which bodies are of potential interest. From the smallest to the largest, with some overlap of size, they are cornets, asteroids, moons, and planets.

The Exploration of the Moon

To obtain a great value in knowledge from a small investment, we should send robotic explorer probes to the Moon equipped with sophisticated sensors. It is a first priority to search the permanently shadowed craters near the lunar poles, where ices containing carbon, nitrogen, and hydrogen may be found. We therefore recommend: A robotic lunar polar prospector to examine the entire surface of the Moon from low orbit. The prospector spacecraft should be equipped with remote sensors to examine the polar craters. We also recommend: Probe missions to drive penetrators into the lunar surface, for on-site analysis at particularly interesting or valuable locales and missions to return samples for analysis from regions selected from prospector and probe date. It win then be time for people to return.

Only 24 individuals have traveled as far from Earth as our nearest neighbor in space, and only 12 have landed upon it; The total time spent by humans on the lunar surface was less than two weeks, all of it in the Apollo years from 1969 to 1972. In those brief journeys a remarkable amount was learned: more than 800 pounds of soil and rock were returned to be analyzed on Earth; equipment was set up to measure heat flow from the Moon’s interior, and to report Moonquakes, and meteorite impacts. Laser reflectors were set up, which have allowed us to measure changes in the Earth-Moon distance to a few inches. Metal foils were stretched like sails to catch the wind of protons and heavier elements streaming from the Sun. And with electric roving vehicles, astronauts explored outward from their landing sites. But the 12 men who trod the lunar surface in the course of six Apollo missions could not venture more than five miles from their landed spacecraft. Quite literally, they could do no more than scratch the surface of the Moon. We therefore recommend that: We return to the Moon, not only for brief expeditions, but for longer, systematic explorations; eventually, we should come to stay.

As in the exploration of Earth, our exploration of the Moon can best proceed by a combination of visits to specific points, and the establishment of permanent outposts at locations of continuing interest. Separation of sites by purpose is more likely than the concentration of all activities at one “lunar base.” Seismologists will need locations remote from mining, to achieve seismic quiet. Prospectors will need to make a series of land traverses, as is customary in resource exploration, and the promise of the lunar poles may draw prospectors at an early stage of lunar exploration. The first expeditions will make use of transfer vehicles as temporary camps on the Moon, just as the shuttle serves on each flight as a temporary space station. As more is learned and we find reasons to zero in on specific points, the temporary camps will be enlarged. Caches of food, fuel, water, and oxygen will be left there between visits and, finally, explorers will “overnight” at outposts through the lunar darkness that lasts 15 Earth days. We will return to the Moon for diverse reasons. As the first stage of the return to the Moon, we recommend: Establishing human-tended lunar surface outposts, primarily for a variety of scientific studies.

As revisits to the Moon become more frequent, the need will certainly grow for larger permanent “base camps,” to serve as supply centers, local research laboratories, and medical centers for explorers taken ill or injured. One important facility will be located in lunar polar orbit. This will give excellent access to operations, particularly near the lunar poles or on the far side of the Moon, and good access to solar energy. Both before and after such facilities are established, we will have reason to visit specific points on the Moon for their scientific or resource interest. Volcanic features have been observed from Earth, and may yield vital information on the Moon’s interior. The far side of the Moon offers locations for radio astronomy, shielded from the noise of earthly radio interference by 2,000 miles of rock.

In the development of technology for more distant travels, the Moon will serve as a laboratory. Because of its very slow rotation and consequent long nighttime, nuclear plants are likely to be necessary for power to provide life support on the lunar surface. They will be tested there before similar plants are sent as far as Mars. The movable space settlements which are likely to be used for journeys to Mars and the asteroids will be put through their proving voyages by trips around the Moon. All that we learn about long-term life support and medical service to astronauts in the relatively nearby environments of lunar orbit and the lunar surface will be put to good use when we venture farther into space.

Readily-accessible Asteroids

A special group of asteroids, almost unknown until the past decade, is particularly promising for exploration and resource utilization: the “Earth-crossing” group, whose orbits bring them closer to the Sun than Earth itself. About 40 such asteroids are now known, and we propose an intensive search for more members of what is believed to be a large family of these potentially valuable celestial bodies. The Earth-crossers are of more than academic interest—about five miles across, may have been responsible for our existence. About 65 million years ago that body, traveling perhaps 20 times faster than a bullet, is believed to have drilled through Earth’s atmosphere and buried itself deep in Earth’s surface. The resulting splash of material spread throughout the atmosphere in the form of finely powdered dust, cutting off sunlight to such a degree that, it is thought, plants died and the dominant fauna, the dinosaurs, were wiped out by starvation. That astronomical event allowed a tiny creature, the ancestral mammal, to grow, differentiate, and fill vacated ecological niches, giving rise eventually to homo sapiens.

A small number of the Earth-crossing asteroids have orbits that so nearly match Earth’s that they can be reached more easily, in energy terms, than the lunar surface. Others are of interest for enterprise and settlement because they appear to contain the life-giving elements carbon, nitrogen, and hydrogen.

We have seen and tracked some of the Earth-crossers, but another group of asteroids, whose existence is still unproven, could be of even greater importance. Orbital theory suggests that asteroids may be trapped at other locations in Earth’s own orbit, 600 million miles in circumference, around the Sun. Because of the unfavorable viewing angles from Earth, these “Earth-Trojan” asteroids are exceedingly difficult to spot. None has been seen. If they exist, material from them could be returned to the Earth-Moon system with almost no expenditure of energy. We therefore recommend: Expanded Earth-based and space-based searches for readily accessible asteroids; continued telescopic characterization of their surfaces; and robotic prospector missions to particularly promising asteroids.

The Exploration of Mars and Its Moons

After the accessible asteroids, the next easiest objects to reach in our Solar System are our neighboring planets Venus and Mars. Several decades of science fiction picturing Venus as a wet, steamy jungle planet were laid to rest when astronomical observations and Pioneer, Mariner, and Soviet Venera spacecraft confirmed that Venus has a poisonous atmosphere, a crushing pressure at the surface, and a temperature hot enough to melt lead. It is no place for humans. But Mars, our other nearest neighbor, is far more hospitable. Even more celebrated in science fiction than Venus, Mars turns out to be rich in surprises, mysteries, and promise.

The distance from Earth to Mars, averaging about 1,000 times as far as to our Moon, is great enough that we are more likely to visit the planet for exploration than for enterprise. The exploration of Mars therefore offers an excellent potential for cooperation between nations. Discussions have occurred looking toward cooperative U.S. soviet mars missions. In voyages to Mars orbit and to Mars itself, we can make good use of two techniques already proven in both piloted and unpiloted space travel: gravitational assists and aerobraking. A simple form of aerobraking was used for the safe return of Apollo astronauts, and the technique is also applied to reduce the orbital speed of shuttles before landing. Gravitational assists, in which the dose passages of spacecraft around planets provide a “slingshot” effect to change directions and speeds, were used in the Apollo journeys and have been essential in the Voyager encounters with the outer planets. Mars has sufficient atmosphere to provide aerobraking, and the red planet is massive enough to provide useful gravitational assists.

Comparisons of the energy required to reach the Martian moons with that required to reach the surface suggest that Phobos and Deimos, the moons of Mars, should be investigated and some of their materials used before crews descend to the planetary surface. The Soviet Union plans to launch an international robotic prospector mission to Phobos and Deimos in 1988. Phobos, the larger moon, circles Mars at a distance of only 6,000 miles, closer than New York is to Australia. The period of time taken for one orbit of Mars by Phobos is correspondingly short, less than eight hours. Deimos orbits about three times as far away, with a period of 30 hours. Phobos is so dose that it can become a natural space station, a potential location for an early base camp. Its color is very dark, suggesting that it may be a captured asteroid rich in carbon. Similar meteoritic material indicates that nitrogen and hydrogen are found with the carbon. If that is true in the case of Phobos, it could become an ideal refueling depot for descents to the planetary surface and for the return of spacecraft to the Earth-Moon system. Both moons are tiny, just 12.5 and 7 miles across; their gravities are weak and their shapes are lumpy and irregular. By contrast, Earth’s Moon is about 250 times bigger than Phobos, with more than 15 million times its mass. A weak gravity can be an advantage: one need not “land” on Phobos or Deimos, but rather “dock” with them, as with an asteroid.

Mars has remarkable similarities to Earth, but in other respects is more like our Moon or Mercury. The Martian day is just over 24 hours long. Mars has polar caps of carbon dioxide (dry ice) and water ice which advance and retreat with the seasons, and its gravity is about one-third of Earth’s, intermediate between our own and our Moon’s. The U. S. Viking landers that set down on Mars in 1976 transmitted television images showing a pinkish sky, rolling hills covered by a reddish-gray soil, and a foreground scattered with numerous rocks. One could find in desert regions of the American Southwest, Australia, or North Africa, landscapes reminiscent of Mars.

The red planet retains a thin atmosphere with less than one percent of the density at Earth’s surface. The atmosphere is mainly carbon dioxide, with traces of argon and nitrogen. Thin as it is, the Martian atmosphere supports winds powerful enough to carry dust and sand, and there are years when dust storms persist for months over much of the planet. Clouds, fog, and frost have been seen, and wisps of clouds frequently trail from the top of the highest Martian peak, giant Olympus Mons. Surface temperatures on the planet range from + 68 degrees Fahrenheit in winter at the poles, to a summer record high of + 68 degrees in an oasis” near the equator, but at most places Martian temperatures are perpetually far below freezing.

Mars has impact craters, but it is also a world of immense canyons, volcanoes, sand dunes, and polar caps of water ice and dry ice. Television images from robot spacecraft orbiting Mars found vast erosional features, quite possibly formed by the swift flow of liquid water. If so, Mars must once have been far warmer and wetter than it is now. Its carbon dioxide atmosphere may have been much thicker in its early history, trapping the Sun’s heat by “the greenhouse effect.” There is evidence for the existence of. permafrost and of liquid water about a mile below the surface at high latitudes, and water ice appears to underlie the northern dry ice polar cap.

The two Viking landers carried out chemical and biological experiments which detected no organic compounds. Although this tended to deny that life as we know it exists at those landing sites, the chemical reactions of the Martian soils resembled those which, it is now believed, may have been the precursors to life on Earth. As we learn more about Mars, we are likely to gain further insights to an important question: Is the origin of life commonplace in the Universe, and does it occur under a wide range of conditions? Or is it an extraordinarily rare event, which takes place only when everything about a planet is just right for it?

The distance of Mars, its gravity and atmosphere, and its tiny moons suggest a relatively complex Plan for its exploration. The beginnings of that program have already been carried out by spacecraft in the 1960s and 1970s. A major step forward wi1l be taken in 1989 when the Soviet space probe approaches Phobos and Deimos, firing laser beams at them to blast off tiny Puffs of vapor for chemical analyses. Someday in the future, a new generation of robotic spacecraft, aerobraking in the Martian atmosphere to circularize their orbits, can return to Earth extremely detailed television images of the surface. Later, robotic hard landers can be targeted to potential Mars landing sites to carry out more detailed analyses of surface and subsurface soils in a search for water and other materials to support human habitation. It will be necessary to follow up these remote sensing missions by returning samples from Mars and its moons.

One of the most revealing exploration opportunities on Mars would be a journey by an automated rover vehicle down the length of one of the sinuous, water-carved channels that abound on the planet. Visual examination of the strata on the channel walls, or, even better, chemical examination, would yield information of a richness and complexity paralleling the data from an oil well drill core or the record of tree rings on Earth. This would be a Particularly rich area in which to renew the search for evidence of life on Mars.

Sometime in the early decades of the 21st century we will establish permanent base camps either on the Martian surface or in orbit, possibly on Phobos. Exploratory journeys from Earth will then become routine, and will involve a series of cargo and crew transfers between vehicles considerably more complex than the maneuvers carried out for each Apollo mission. The people chosen for a mission will ride to an Earth-orbiting space station. From the space station they will move to a Libration Point Spaceport and then into a transfer vehicle capable of matching orbits with a cycling spaceship, repeatedly shuttling between the Earth and Mars systems. On the “cycler” they will experience a rotational gravity somewhere between that of Earth and Mars, possibly starting at an Earth-normal gravity and shifting to that of Mars in the List weeks before the cycler reaches its dose encounter with the red planet.

Nearing Mars after a half-year voyage, the expedition will move into another transfer vehicle to make the transition to an orbiting spaceport or a base camp. There, after meeting and exchanging information with a crew that can provide current advice on Martian conditions, the expedition will transfer to a lander. The short trip to the surface will have as its destination either a major base camp or an outpost with a cache of supplies and equipment. Once on the surface, the expedition members may separate to carry out individual missions: geological, with instruments newly brought from Earth; exploratory, using roving vehicles permanently left on Mars; or atmospheric and geographical, using remotely piloted or passenger-carrying aircraft capable of much closer passes over the terrain than would be prudent for machines guided only by computers.

Nearly all of the spacecraft and habitation modules needed for Martian expeditions and for eventual permanent human settlements on Mars will have been proven out in the much closer environment of the Earth-Moon system. Enclosures containing an atmosphere like Earth’s and covered over by soil as protection against solar flares, will satisfy the same needs on Mars as on the Moon (See sidebar on Biospherics). Greenhouse biospheres for growing food will have been tested on the Moon or in Earth orbit, where a failure will mean only the call for a resupply mission, taking just a few days. Nuclear reactors, which are appropriate sources of energy during planetary nighttimes, will have been checked out both on the Moon and in orbit. Transfer vehicles are likely to be identical at both ends of the Earth-Mars transportation link, and even landers for the Moon and for Mars may differ only in minor details.

Mars has been for centuries a magnet to our curiosity and our imagination. Within the next few decades it will become a relatively familiar outpost of human civilization, comparable perhaps to the Antarctic settlements now maintained permanently by several countries. The permanent settlement of Mars, even if by a relatively small number of people, win be a later milestone, though not the last, in the human settlement of the inner Solar System. In that sense it will be, in Winston Churchill’s phrase, “the End of the Beginning.”

Settlement in Space

In the early years of pioneering the space frontier, people will go to specific sites of action for specific assignments. The choice of carrying out assignments by tele-operation, by autonomous robots, or by human crew members is likely to be governed both by economics and by subjective and national pressures, as in the past. By the terms of treaties which the United States has signed, no claims of national sovereignty are to be made on the planets, moons, or asteroids, so “Planting the flag” does not have the same symbolism in space as on Earth.

When the enabling technologies are in place for the private sector to begin substantial operations in space, political motives for the choices among piloted, robotic, or remotely controlled methods of carrying out operations are likely to become less important, and economy and efficiency are likely to dictate to a greater degree how things are done.

For survival and good health, humans who must work in space or on planetary surfaces for long periods of time will have five material requirements: air, water, food, gravity, and protection from cosmic and solar radiation. The water cycle has been partially closed already on Soviet space stations, and they have made progress toward recycling air. For long-duration voyages of at least several months, it will be economic to grow rather than carry food.

The equivalent of Earth gravity, in which our bodies have evolved and probably work best, can be provided relatively easily in free space, but not on the surfaces of any of the moons or planets accessible to humans in the inner Solar System. In space, gravity’s equivalent can be provided by connecting a spacecraft or habitat to a tether cable and counterweight, and rotating one about the other (See sidebar Tethers in Space). Once set rotating, the dual-mass system requires no further energy to maintain its rotation. We recommend that: Relatively simple experiments in space be performed soon to find the effects of various rotation rates and levels of artificial gravity on people so we can establish practical design parameters.

The fifth and last requirement for human survival and safety is protection from damaging radiation. Large amounts of shielding are needed to reduce radiation to the levels common on Earth. Fortunately, any material whatever is suitable as a shield. The surface material from any moon, asteroid, or planet will do. The slag from industrial processing activities is equally usable. For the short trip to the Moon, it was common practice in the Apollo years, and will be again, to rely on solar flare forecasting rather than shielding. For the half-year voyages to Mars or the asteroids, astronauts will retreat to shielded “storm shelters” in their spacecraft when solar flares occur. The need for heavy shielding on long voyages is one of the reasons for using “cycling spaceships” on what may come to be called the “Mars Run.”

On or near an asteroid, and on the surfaces of the Moon and Mars, there should be no difficulty in providing ample shielding using the local surface material. In orbital space, the same level of shielding can be provided economically when material transporters with very low operating costs and high capacities are available. The electromagnetic “mass-driver,” described in sidebar Electromagnetic Accelerators, is one candidate for that service. It seems likely that settlements in space itself, built to house the workforce needed to control industrial activities, will be shielded by the slag from industrial operations. With such shielding orbital settlements can be made as safe from cosmic and solar radiation as the surface of Earth.

There will be a need for long-term human settlements in orbit and, at some point, on the surfaces of the Moon and Mars. The five requirements for human health can be provided at any of those locations, with the one caveat that Earth-normal gravity can be provided easily in space, but not on the Moon or Mars.

We have focused on the “mechanistic” questions of air, water, food, gravity, and protection from radiation. For the space frontier to become attractive to human pioneers it will be necessary to bad settlements with additional Earth-like characteristics: Normal intensities of sunshine and gravity, a normal day/night cycle, the same area and volume per Person that are normal in comfortable urban environments, and plenty of area and volume for growing flowers, grass, and trees. Conceptual engineering studies confirm that attractive settlements of this kind can be built in orbital space, where full-time solar energy is available for power and where the day/night cycle of sunshine can be provided by shading incoming sunlight on a regular schedule. Settlements in orbit will not be locked into planetary rotations, and will therefore be able to “point” toward the Sun at all times. When all the questions of health, safety, economy, and comfort are considered, the optimal shape for settlements in orbit appears to be spherical, with a pressure shell rotating within a non-contacting outer spherical shell of shielding. Such habitats could accommodate thousands of people.

As we look forward to pioneering the space frontier, we can speculate on the far-reaching human consequences, which many people see as loftier than the economic and scientific Payback from all space missions. This is the extension of life itself beyond the precious and fragile planet where it was born, to the far reaches of the inner Solar System. As in all previous pioneering, only the adventurous will choose to leave the familiar territory of home and strike out for the frontier. Historians have written that many of the characteristics we are proudest to call “American” were shaped by the frontier environment of our ancestors. Many children and young people today expect and anticipate that they will five and work in space. We can be confident that they will be fully as capable of taming that new frontier environment as were our ancestors who built America.