Tailored Force Fields
In the vacuum of Space, weak forces acting over long periods can achieve large results. Familiar examples are microthrusters and solar sails for deep space craft. Two examples used here are:
1.Quasi-steady magnetic fields
2.Radiation Force due to
unsteady interactions between beamed energy and matter.
The relevance of these observations is that automatic construction of large/complex objects from random-shaped material is feasible.
Such force fields can be described and predicted quite accurately.
Many people feel that the Space programs of nations today are stuck at the bottom of the cost-well of Earth's gravity - and getting pulled ever deeper. Economic development, though spectacular and highly publicized, has been very slow - and the Space part of most "Space Business" seems to run more on faith and enthusiasm than on real profits. Grand projects such as the Space Station and the Human Mission to Mars, all seem to grow more distant every day in a fog of funding uncertainties, delays, cost overruns, and general disappointment. This is very frustrating to the generations which extrapolated from the heady days of Apollo and science fiction to hope that they too could share in the great exploration beyond Earth.
There are many excellent concepts for various types of engineering marvels in Space and on different planets. Concepts abound for Space Elevators which would zoom us to Space in comfort, tethers which would swing us to and from the Moon - or even to Mars, huge ships which would keep running a Mars-Earth shipping route, factories which would automatically mine for Helium-3 - or oxygen and iron - on the Moon. Concepts to "terraform" parts of Mars into hospitable vacation resorts, large hotels in orbit with a grand view of Earth. Concepts to land a team of bright engineers on asteroids heading for Earth - so that they would work hard and guide it away from Earth (this was proposed in jest!!). All of these are basically stuck because no one can find the economic imperatives to set their projects moving. Worse still, the climate of declining public interest and funding forces enthusiasts of each these concepts into a survival mode of having to argue against other concepts in order to push their own concept higher in the priority ladder! The result is that the possible risks and downsides of each concept are publicized far more than the possibilities inherent in their success.
The development of a comprehensive Space-based economy is being recognized as the best way to achieve the goals of human exploration and development of Space - beyond Earth. In such an economy, humans would gradually find ever more reasons to invest in Space-based business- and eventually to live and work in Space for long periods, interacting for the most part with other humans located in other Space habitats. As Gerard O'Neill argued in the 1970s, the natural place for human habitats away from Earth is not at the bottom of the gravity well of any planet, or on an unpredictable asteroid, but in artificial, orbital settlements with controlled atmospheres, sunlight and gravity. Such settlements must be far larger than present-day Space Stations - an optimal first settlement was estimated as one which could support 10,000 humans. A fundamental obstacle to building human settlements in Space is the construction of the massive outer radiation shield. Human labor in Space is prohibitively dangerous and costly for this mission. Such a project is unthinkable to most Space engineers of today, who are trained to think "faster, lighter, smaller" if not "cheaper and better" for anything related to Space. Here we explore this neglected area of Space research from a new perspective.
Potential fields can be used to assemble and construct solid structures over a wide range of size scales. A unique set of experiments by our team had shown that by tailoring potential fields, large numbers of objects can be moved into desired positions and desired shapes can be constructed in reduced-gravity environments. This project has started planning for using such force fields to build large, massive structures in Space using extraterrestrial materials. The promise of this idea is being investigated for several types of force fields suitable for automated construction at levels ranging from micrometer-scale discs and fibers, to kilometer-scale habitats.
The force which drives objects towards specified locations in an unsteady wave field is called "Radiation Force". Although early researchers such as Lord Rayleigh recognized that the forces in acoustic fields must be similar in those in electromagnetic fields, theoretical descriptions of radiation force have been developed independently in different fields, driven by the domain of application. In this project, the theory for radiation force was generalized and applied to acoustic, optical and other electromagnetic fields. A sample case using silicon dioxide particles of various sizes was used to develop a direct comparison of the accelerations obtainable using different wavelengths of radiation.
Feasibility of building objects at the 0.1 m scale using acoustic fields had already been proven through reduced-gravity flight experiments. This was carried forward with experiments being developed for space-flight proof on the STS. A concept for a space-based experiment using microwaves was explored as a suitable intermediate-scale demonstration to be conducted from the STS in low-earth orbit.
A concept for kilometer-scale construction sites using radio waves holds promise at the 50-year horizon. This was explored, and the preliminary calculations showed that with developments in large solar collector arrays, and substantial increase in extraterrestrial infrastructure, offer strong potential as a construction technique for the future. Thus the primary obstacle to all of the ideas here is the development of an economic basis for extraterrestrial infrastructure.
A sample project was undertaken to investigate the possibilities for bootstrapping
a Space-Based Economy - the driver for the infrastructure needed to make large
projects possible. Calculations show that in the 15-30 yr time frame, a 2km
diameter radiation shield can be built at the Earth-Moon L-2 Lagrangian point
using lunar materials. The project architecture is aligned with proposals for
various other elements of a Space-Based Economy, bringing project cost well
within reason. The project detailed the process of building a 1km-radius cylinder
- and enabled the study of various ways of estimating cost and scenarios for