It is argued using a conservative approach to interstellar travel that intelligent extraterrestrials (ET’s) may be present in our solar system, living in world ships that have colonized cometary or asteroidal objects during the last billion years. The originating star systems for these advanced beings could be solar-type stars that fortuitously approach our Sun within a light year or so at intervals of about a million years or nearby stars that have left the main sequence, prompting interstellar migration. If we are indeed within such a “Dyson Sphere” of artificial worldlets, we could detect their presence through astronomical means since a space habitat will emit more infrared radiation than a like-sized comet or asteroid. Interestingly, several Kuiper-Belt objects have recently been found to have an unexpected and substantial red excess. It is argued that, in opposition to the assumptions of current SETI searches, the very advanced occupants of this possible local Dyson Sphere may have as little interest in beaming radio signals in our direction as we do in communicating with termites. A research program is proposed whereby large and small college observatories would routinely monitor the spectral irradiances of Near Earth and Kuiper Belt objects while a concurrent theoretical effort models the spectral characteristics of various proposed space habitats. Much of the observational work, at least, could be dovetailed with projects designed to detect Near-Earth Objects (NEO’s) that might impact Earth in the future. Possible strategies and protocols for direct contact, requiring humans to be the active contactees are presented to be considered for use if such intelligent ET’s are discovered within our solar system.
Interstellar Travel - 1. Bussard Ramjet
The Bussard Ramjet (Figure 1) works by using a magnetic scoop (or ramscoop) to ingest interstellar protons over a large area. The fuel passes through a fusion reactor capable of converting hydrogen directly into helium plus energy, as does the Sun and other main sequence stars. The released energy is used to accelerate the helium nuclei exhaust out the rear of the spacecraft. Although recent research indicates that a suitable ramscoop may be feasible, there seems to be no way to create a proton fusion reactor. Many less capable ramjet variants have been proposed, the most feasible is the use of a solenoidal field ramscoop to reflect oncoming interstellar ions and thereby decelerate a speeding starship.
2. Antimatter rockets
Technology and physics do not provide substantial barriers, on the other hand, for the Antimatter Rocket. Nuclear fission and fusion, those nuclear reactions currently in use by humans are relatively inefficient in that only a small percentage of the reactant mass is converted to energy. A fuel mix consisting of antiprotons (which can be produced in nuclear accelerators) and protons is the most volatile substance in the universe, on the other hand, since essentially all the reactant mass is converted into energy. Antiprotons can now be produced in small quantities and stored for long periods in “Penning Traps”. Although antimatter rocketry (Figure 2) is certainly feasible technologically, there is one “small” problem. The cost of antimatter production must fall by many orders of magnitude before the antimatter rocket can be considered economically feasible.
3. Laser Sail
For decades or century duration interstellar voyages at speeds as high as 10% of the speed of light (0.1c), a favored propulsion system is the laser light sail. A solar-pumped laser power station is constructed in space and maneuvered into position between the Sun and the destination star. A laser beam from the power station impinges against the light sail of the starship – a highly reflective metal sheet with a thickness of nanometers or microns (Figure 3). The pressure of the laser photons accelerates the spacecraft in the direction of the destination target star.
4. Nuclear pulse propulsion
5. The Hyper-thin Solar Sail
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