Directed Energy for Relativistic Propulsion and Interstellar Communications

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P. Lubin et al. (2015), JBIS, 68, pp.172-182

Refcode: 2015.68.172
Keywords: relativistic propulsion, interstellar communications

Abstract:
An orbital planetary defense system that is also capable of beamed power propulsion allows mildly relativistic spacecraft speeds using existing technologies. While designed to heat the surface of potentially hazardous objects to the evaporation point to mitigate asteroid threats the system is inherently multi-functional with one mode being relativistic beamed spacecraft propulsion. The system is called DE-STAR for Directed Energy Solar Targeting of Asteroids and exploRation. DE-STAR is a proposed orbital platform that is a modular phased array of lasers, powered by the sun. Modular design allows for incremental development, test and initial deployment, lowering cost, minimizing risk and allowing for technological co-development, leading eventually to an orbiting structure that could be erected in stages. The main objective of DE-STAR would be to use the focused directed energy to raise the surface spot temperature of an asteroid to ~3,000 K, allowing direct evaporation of all known substances. The same system is also capable of propelling spacecraft to relativistic speeds, allowing rapid interplanetary travel and relativistic interstellar probes. Our baseline system is a DE-STAR 4, which is a 10 km square array that is capable of producing a 30 m diameter spot at a distance of 1 AU from the array. Such a system allows for engaging an asteroid that is beyond 1 AU from the DE-STAR 4. When used in its "photon rail gun mode", a DE-STAR 4 would be capable of propelling a 1, 10, 102, 103, 104 kg spacecraft that is equipped with a 30 m diameter reflector to 1 AU in approximately 0.3, 1, 3, 10, 30 days, respectively, with speeds of about 4%, 1.2%, 0.4%, 0.15%, 0.05% the speed of light at 1 AU. With continued illumination to 3 AU the spacecraft, with a 30 m diameter reflector, would reach speeds 2 faster. A DE-STAR 4 could propel a 102 kg probe with 900 m diameter reflector to 2% the speed of light with continued illumination out to 30 AU, and ultimately to 3% the speed of light after which the spacecraft will coast. Such speeds far exceed the galactic escape velocity. Smaller systems are also extremely useful and can be built now. For example, a DE-STAR 1 (10 m size array) would be capable of evaporating space debris at 104 km (~diam. of Earth) while a DE-STAR 2 could divert volatile-laden asteroids 100 m in diameter by initiating engagement at ~0.01-0.5 AU. All sized systems can be used to propel varying sized systems for both testing and for interplanetary use. An extreme case is a wafe scale spacecraft (WaferSat) with a 1 m reflector that can achieve >25%c in about 15 minutes. The phased array configuration is capable of creating multiple beams, so a single DE-STAR of sufficient size could engage several threats simultaneously or propelling several spacecraft. A DE-STAR could also provide power to ion propulsion systems, providing both a means of acceleration on the outbound leg, and deceleration for orbit insertion by rotating the spacecraft "ping-ponging" between two systems in either a photon rail gun mode or power ion engines. There are a number of other applications as well including SPS for down linking power to the Earth via millimeter or microwave. A larger system such as a DE-STAR 6 system could propel a 104 kg spacecraft to near the speed of light allowing for true interstellar travel. The same technology can also be used for extremely long range communications with continuous communication between Earth and the interstellar spacecraft. This technology also has direct implications for interstellar and intergalactic beaming allowing for SETI across the universe for civilizations that have mastered this technology. There are a number of other applications for the system. While decidedly futuristic in its outlook many of the core technologies now exist and small systems can be built to test the basic concepts as the technology improves. While there are enormous challenges to fully implementing this technology the opportunities enabled are truly revolutionary.

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