The Problem

Somepeople would like to e xtend man’s history of exploration within the solar system to exploring and colonizing the stars. This next step is necessary for man’s future, they argue. The argument they propose is that mankind does not know how to maintain a sustainable civilization. Over the long haul, a sustainable civilization must become an equilibrium civilization (resources used equals resources generated, and population is stabilized), where mankind enters a kind of stasis. Here freedom and growth are curtailed to further the common good. These people argue that such a stasis is unattainable. It makes man lose heart. Man is a dynamic being and his civilizations must both grow and expand or they will shrink and contract and eventually die out. They note that prior civilizations (Rome or China, for example) that had reached a peak in expansion, because it’s resources and population had become stretched too thin, had tried to stabilize their borders with laws or natural boundaries or by building walls. They ended up dying out or bouncing ineffectually against the limits, instead.

In a prior set of papers (ap1 through ap6-this site-Jan,Feb) a means of obtaining a sustainable, near equilibrium civilization was explored. The key to this civilization is a vessel that harvests energy and grows food on the ocean. A prototype vessel for colonizing the earth’s oceans was constructed to confirm feasibility. An orbiting satellite system for colonization was also explored as a means of absorbing any excess population, if necessary to keep the earth in an equilibrium state. This earth bound, equilibrium civilization was found to be theoretically feasible, but this work did not answer the questions, “Can such an equilibrium be maintained, or will mankind start a downward spiral? Does mankind need to grow and expand?”

One way to answer these questions is to start a growing and expanding civilization in space and compare it with the equilibrium, earth bound civilization currently being constructed. To do this, we must see if growth and expansion is possible starting with a small, earth centered, orbiting satellite system and moving on to the exploration and colonization of the solar system and then the stars. The colonization of the stars is potentially unlimited in scope, because of the huge size of the universe. Mankind could continue to expand his boundaries indefinitely. We determined (see ap6) that the satellite-based civilization is theoretically feasible. Here we must determine if a practical starship can be made for exploration and colonization of the stars to allow for the continued growth and expansion of mankind. This task will be difficult and expensive, so it will be helpful if colonization of the stars can also be made profitable for the individual participants and mankind as a whole. The problems in achieving this goal are:

Conventional boosters needed to reach the nearest stars are enormous because they must carry their own fuel and so they would require a significant fraction of the GNP of the earth to build, so a new booster type is required.
The starship must be able to be resupplied during the trip to cover expendables, since air and water and power and other expendables are leaked or used during the trip.
A means of communication with earth is needed, so the supplies needed can be ordered, and the successes and failures monitored.
For colonization, a means of growing and recycling food and water is required as well as a means of transporting people and freight at a reasonable cost.
High travel speed is required. Unless a significant fraction of the speed of light is achieved, the travel time to the nearest stars is a large fraction of a person’s lifetime, and so people would be reluctant to attempt the trip.
It is desirable to make stellar colonization profitable for the colonizers and mankind. However, because of the difficulty and expense of transportation, stellar colonization may never be economically profitable. Thus we must ask, “Can stellar travel be made profitable, and if stellar travel cannot pay for itself in earth’s coin, is it worth doing.”

The answer to the question “Does mankind need to grow and expand?” is so important, and the possibility of value in man’s expansion toward the stars is so significant, that it behooves us to see if a practical means of accomplishing this goal is possible. This paper is intended to address this question. Here, we will address each of the above-mentioned problems associated with the question.

Is Action Required?

The short answer is “not immediately”. It seems probable, however, that eventually it will be necessary to answer this question in order to insure a future for mankind. The problem is that there will not be a clear signal that indicates the correct time to answer the question or develop a starship. Thus researching the problems associated with developing a starship now is probably the best move.

The Solution

The momentum beam as a booster and a means of supplying expendables has been explored in another paper (ap6 The Final Solution to Man’s Population Problem). Perhaps it applies here as well. Let us investigate. The characteristics of a momentum beam required for interstellar travel are as follows:

There must be an inexpensive method to put the starship pieces on orbit and a method of transferring energy and momentum to and from the earth’s surface.
There must be an inexpensive method to start the star trip by an initial boost from earth to a velocity of ~1 exp5M/S in the direction of the target star.
There must be a means for a final boost up to a significant fraction of the speed of light (~1 exp7M/S)
There must be an energy source on board the starship not tied to the sun or the earth.
There must be on-board thrusters for independent movement of the satellite away from the momentum beam.
There should be a means of communicating from the satellite to the earth during the trip.
There must be a means of supplying expendables and parts to the starship during the trip.
There must be a means of sending follow-up expeditions at a reasonable cost if the first finds the conditions suitable for colonization.
A means of making interstellar colonization profitable to earth people should be explored.

Let us investigate these requirements for a momentum beam starship and see what can be achieved for a 1000KG star probe for exploring a promising stellar system. A 1000KG star ship is chosen because such a ship is big enough to carry the surveillance equipment needed to investigate a planet in an adjacent star system that is promising for colonization. A larger ship (~10,000KG) would be needed for colonists.

A Cheap Method of Putting the Starship Pieces on Orbit and a Method of Transferring Momentum and Energy to and from the Earth’s Surface.

A pellet type momentum beam such as that described in ap6 “The Final Solution to Man’s Population Problem” is well suited to putting the starship pieces on orbit. This system will put the starship pieces into a synchronous equatorial orbit. Aquater2050 vessels can serve as launch pads. The pieces can then be connected in orbit.

A Cheap Method of Boosting the Starship to ~1 exp5M/S

If a similar passive pellet type momentum beam is used as a booster in the sun’s gravitational field starting from an earth synchronous orbit, the starship can achieve ~1 exp5M/S speed (actually the sun’s escape velocity provides the limit speed in this method) toward the chosen star. The booster does not then have to carry its fuel, and the pellets and part of the pellet energy can be recovered as the pellets are drawn back to the launch point by the sun’s gravitational field. Such a system can be used to transfer energy and momentum from earth to orbit, and the orbiting satellites can transfer energy and momentum to the starship. A constellation of orbiting satellites (orbiting both the earth and the sun) will be needed to complete this task, because orbiting satellites will rotate in and out of position for accelerating the starship, so the momentum beam must be passed from one satellite to another during the boost phase. Also, a set of SEMAN platforms will be needed for each group of launch satellites, to provide energy and momentum as needed. This system can push a 1000KG (or more) satellite to as high a speed as the pellets can be pushed, (but less than the sun’s escape velocity) and still return the pellets to the launch satellites to conserve mass and energy. In addition, the momentum beam can re-supply the starship during the boost phase using the hollow pellet method. However, using an electro-magnetic drive for the pellet, there is a limit to the final travel speed achievable because of the maximum capacity obtainable in the power supply for one stage and the maximum number of stages of boost that are practical. This limit is not near the speed of light, so a modification to this method is necessary to achieve higher speeds. Nonetheless, for the first stage of the trip (say up to ~1 (exp5)M/S), the starship should be boosted with pellets driven by the electro-magnetic drive while the satellite is in the sun’s gravitational field and the pellets can be recovered. The modification needed for higher speeds will be discussed below.

The previously described booster system that can put satellites into synchronous equatorial earth orbit is under development, and so will be assumed to exist for putting the starship pieces into orbit. From this orbit, the starship pieces will be assembled and sent on its way toward a star. A speed of ~1 exp5M/S toward the star appears feasible with a satellite based electromagnetic drive. It would be essentially the same as the earth orbit electromagnetic drive and achieve roughly the same speed. The only difference would be that the pellet would have a ~5KG mass. Initial estimates of the cost of this drive show that it could be constructed for roughly $200,000/satellite. The complete constellation would cost ~$1,000,000. Capital costs would then be roughly $50,000/YR. Assuming four launches per year, the cost per launch would be ~$12,500/launch.

If the starship weighed 1000 KG, and were lifted vertically into orbit with perfect efficiency, an energy of 1.8 exp4 KWH would be necessary. Another 1.0 exp5KWH would be required to launch it toward the target star. If the cost of the energy is assumed to be $0.08/kwh, and the actual efficiency is roughly 50% (see below), the cost of the energy would be roughly $70,000/launch.

A Cheap Method of Boosting the Starship to Near Light Speed (~1 exp7M/S)

To get the next 2 orders of magnitude, it will be necessary to use active pellets with a high efficiency (specific impulse of at least ~5,000-10,000S) drive on-board the pellet. A SNAP on board power supply of 30 watts exists and can supply the power for the drive. Each pellet must have a high temperature radiator to get rid of the excess energy from the power supply. The power supply would weigh~0.08KG. An ion bombardment drive exists and can deliver a specific impulse of 5000-10,000S. Thus about 100KG of Xenon fuel plus thruster would be required to get ~1 exp7KM/S for a 5KG pellet. This fuel mass is high, and Xenon is rare, so a lighter, more common material would be more useful, since a lighter material would be cheaper, and could give a higher specific impulse and thus require less fuel. Carbon is common and easy to store and may be a good material for fuel for an electromagnetic thruster. The 5KG of pellet mass is for the pellet structure, thruster, radiator, guidance and payload. The radiator can provide a signal for guidance of the pellet behind it. The first pellet can guide on the starship radiator. The thruster can also slow the pellet during the deceleration phase of the trip, so the pellet velocity is correct to decelerate the starship when it catches up, exchanges momentum and then sends the pellet on toward the star. Note that the active pellets cannot be recovered because they are out of the sun’s gravitational field and are traveling too fast away from the launch point. Also, they can be used with an electromagnetic accelerator on the starship to increase or decrease the starship’s velocity as is required. This is a serious cost consideration. Using more fuel to actively return the pellets to the launch point can eliminate this loss of pellets. On the other hand, the pellet structure can be made in a cheap, throwaway form from injection molded plastic. The thruster, radiator, guidance and payload can be made in modules to add to the structure. An optimization would be necessary to determine if any savings in pellet cost can be achieved with a pellet that is more complex and carries more fuel and is thus returnable to the launch point for reuse as opposed to a cheap pellet. Another improvement in cost would result if the specific impulse can be increased to 100,000S or more. Such an increase appears feasible with low mass fuel (such as carbon) but difficult.

About 3 exp7 pellets would be required for the acceleration and deceleration phases. At $10/KG, if mass-produced, (excluding the Plutonium fuel), the 5KG pellets would cost ~$2 exp9, and the interest cost at 5%/YR would be ~$1 exp8/yr. If four exploration or colonization trips are made per year, the cost would be ~$2 exp7/trip. Loss of the active satellites would increase the pellet cost to $1 exp9/trip. Fixed and satellite costs would be expected to add $1 exp8 to this cost, so the cost/trip would be $1.1 billion, and the cost per KG would be $1.1 million. The energy and electromagnetic drive costs are negligible compared to this cost. These numbers are very rough, and a detailed design and optimization has not been accomplished, so the numbers only show that the exploration and colonization appears feasible, and the cost is not ridiculous. It is about the same as a modern warship in the US navy.

An On-Board Energy Source for the Starship

Two power sources seem practical for the starship. A pebble bed reactor seems ideally suited for a high power (1000 to 10,000KW), on-board energy source because it has several fail safe features, it is independent of solar distance and it can be resupplied with fuel by putting pebbles in the pellets in the momentum beam used for driving the starship. SNAP reactors are practical for low power (5 to 50 W) applications. The pebble bed reactor has been tested, but not for satellite applications. Some work is needed. The SNAP reactors are well tested for satellite operations.

An On-Board Thruster for the Satellite

There should be two types of on-board thrusters. One should be an efficient (high specific impulse) engine that operates at low thrust. Ion electrostatic thrusters are suitable for this application. Electromagnetic thrusters such as rail guns could also be used. The second should be a high thrust engine such as a hydrazine engine. Both are available and well tested.

A Means of Communication

The pellets in the starship drive can be used for communication, but this method is very slow. Initial calculations indicate that communications with microwaves at 1 light year or greater would require too much power and aperture to be practical. The wavelength of the radiation is too long. However, laser communications from up to 4 light years appears feasible if a digital laser system with a large power and aperture and a large number of signal repetitions are used. Note, however, that stellar distances ensure that messages will be drastically delayed (~years after being sent)

Supplying Expendables and Parts

Expendables can be carried on the pellets as shown above (Each pellet has 2.9KG payload). Gasses and water can be carried easily in a sealed compartment. Seeds and small parts can be put into containers, and into a pellet hold. Large assemblies will need a separate momentum beam to send to the starship.

Other Expeditions

New expeditions can be sent using the same momentum beam and same pellets (except for the active pellets) used to send the first expedition.

Can Stellar Colonization Pay for Itself in Earth Coin

For the first time in this sequence of papers, there is a question about whether an expansive step in human civilization can pay for itself in the area from which the expansion originated. An expansive step is much easier to justify and initiate if there is a chance of paying for the cost in profit or living area. In the distant past, colonization was profitable because valuable minerals, such as gold, were found, or grazing or farmland was available which could be sold or the land had such strategic importance that it was valuable on that basis alone. Recently, colonizing the ocean was found to be profitable because it addressed the problems of dwindling supplies of fresh water, land for food, jobs, energy and places to sequester carbon dioxide. Colonizing near space was found to be profitable as a place to absorb any excess population if necessary to keep the earth in an equilibrium state, and to provide products manufacturable only in zero gravity. With stellar colonization, however, the strategic value is nil, the land is so distant, and the transportation costs so high, that normal profit making techniques may not apply. As an example, if the transport costs were roughly as estimated above, 1000KG would require at least $1.1 exp9 to move to a nearby star, or $1.1 exp6/kg. Assuming this cost estimate is roughly correct, each person would need >$1 exp8 to emigrate. Also, the transportation cost of valuable materials would be $1.1 exp6/KG. Thus, trade would be limited to materials that are worth considerably more than $1.1 exp6/KG, and farmland on the new planet would have to be worth considerably more than the $1 to $10 million per farm common on earth. Note that immigrants cannot pay off investors on earth, because the high cost of transporting the goods grown or obtained would require that these goods be used on the new planet. On the other hand, some would consider any price they could manage as acceptable, because they want to be the first orbiting a new star, but they would be relatively few-not enough to justify the trip.

Normal exploration and colonization starts with an explorer who assesses the potential of the land, and reports on the reasons to exploit or colonize it. As an example, America was explored by many explorers and reports brought back to Spain, England and France before colonies were established. The first colonies from Spain were established primarily to bring back gold and silver, which were high value and small and light compared to the shipping cost and hauling capacity of a ship at that time. Expeditions from England to North America were intended to establish farming communities that could ship back high value crops such as indigo, tobacco and rum, that again were high in value and low in volume compared to the shipping cost and hauling capacity of a ship at that time. Note that the backers could easily profit from the venture while living in the mother country. Note also that one set of expeditions (to New England) came for religious reasons and paid their own way. None of this economic logic applies to stellar colonization, however.

Expeditions to stellar systems with the expectation of bringing back high value materials will not be looking for gold or silver, because the transportation cost is greater than the value of the gold or silver. Higher value materials such as enriched uranium or trans-uranic elements are a possibility, but their value is not high enough to justify an exploration and colonization program. It appears that exploration and colonization may depend on people who can pay their own way in advance. These are likely to be people who feel out of place in the existing society, or adventurers who wish to carve out an empire in the wilderness. There are many examples of such people in the history of the New World. However, the number of such people is relatively small, so a stampede to a new world is not expected.

There is one way to pay for the stellar expedition in earth’s coin, elimination of troublesome materials from earth. Two of the most troublesome materials on earth are carbon and radioactive materials. The pellets in the momentum beam carry significant amounts of both, and are lost in space. Furthermore, many disposable pellets are required. The injection molded plastic and the carbon fuel can be primarily carbon. The power supply is radioactive material. Thus a large amount of both can be gotten rid of. Also, the transport to space is done in small amounts over the ocean, so if an accident occurs in this process, the materials will end up at the bottom of the ocean, rather than in populated areas. If the transport to space is successful, these materials will finally end up in deep space where they can do no harm. Earth may be willing to pay a fee to get rid of these materials.

Perhaps the most exciting reason for exploring other stellar systems is to discover new life and civilizations. The information obtained from such a contact could be of incalculable value to civilization on earth. Unfortunately, this value cannot be determined in advance, so the value of exploration and colonization in earth’s coin is literally incalculable.

It is expected that the first step in the process of colonization will be a survey of nearby stars that will produce a catalogue of stars with planets. This is being done with Doppler and occultation measurements of the known nearby stars. These planets will then be tested for an atmosphere with the new high-resolution telescopes currently being developed for orbit. The planets with an atmosphere will then be visited with an unmanned starship and explored to see if there is a reason to visit it with a manned flight. After the manned flight visit is made, a decision will be made over whether to colonize it or not. Colonization appears to be the primary option. Sending back valuable materials or products for sale on earth appears to be a non-starter. However, getting rid of carbon and radioactive materials from earth may be a profitable enterprise. And, of course the search for new civilizations provides an important underlying motive.

Summary and Conclusions

Some people would like to continue man’s history of exploration and colonization beyond this solar system by exploring and colonizing the stars. This next step is necessary for man’s good, they argue. The argument they propose is that man does not know how to maintain equilibrium. Mankind must both grow and expand or he will shrink and die

An initial investigation of the feasibility of colonizing the stars indicates that it may be feasible with momentum beam methods and actively powered pellets to achieve near light speeds, but it would be expensive (~$1.1 billion/trip or $1.1million /KG).

An initial study of the potential profitability of such a trip indicates that it would not be profitable using normal methods. However, it may be profitable as a means of getting rid of troublesome materials such as carbon and radioactive materials. It is, of course, profitable if a sufficient number of people who are rich enough and are motivated enough, are willing to pay. Also, the search for new life and civilizations provides an important underlying motivation. And finally, it may be important as a means of continuing growth and expansion for mankind, thus avoiding possible stagnation and eventual death.

Note

The preliminary design work is done. The physical prototype has not yet been started.
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