Nextbigfuture – Dana Andrews looks at a minimum transit speed of 2 percent of the speed of light (fifty years per light year) for an interstellar generation ship. This makes for transit times in the neighborhood of hundreds of years, depending on destination. A key requirement is the ability to decelerate and rendezvous with the destination planet using a magnetic sail (magsail) that can be built using high-temperature superconductors. Andrews also assumes 20-30 years of research and development before construction actually begins. Andrews develops an interesting take on using space-based lasers, working in combination with four-grid ion thrusters using hydrogen propellant and optimized for a boost period of thirty-two days. The specific impulse is 316,000 seconds. The lasers are mounted on a small asteroid (one or two kilometers) and take advantage of a 500-meter Fresnel lens that directs their beam to a laser reflector on the spacecraft. Let me take this directly out of the paper:
An actively steered 500 m diameter Fresnel lens (risk scale 3) directs the beam to the laser reflector on the Generation Ship Spacecraft, where it is focused onto hydrogen-cooled solar panels (risk factor 1), using a light-pressure supported ¼ wave Silicon Carbide reflector (risk factor 2.5). The light conversion panels operate at thousands of volts at multiple suns (risk factor 2) to allow direct-drive of four-grid Ion thrusters using hydrogen propellant and optimized for short life (30 days) and very low weight (risk factor 3). The four-grid thrusters provide a Specific Impulse (Isp) of 316,000 seconds operating at 50,000 volts using hydrogen. The triple point liquid hydrogen propellant is stored in the habitat torus during boost (the crew rides in the landing pods for the duration of the 32 day boost period), so there is no mass for propellant tanks. After acceleration the crew warms up the insulated torus, fills it with air, and moves in.
Nextbigfuture – Solar pumped lasers have long been a technology which are an important enabling option for space based solar power and for beam powered propulsion for interplanetary and interstellar applications. Recent work has looked at laser starways where laser power is beamed 70 Astronomical Units
There has been earth based progress towards using solar powered lasers for Magnesium production. Having a profitable industrial application to fund and drive and scale the development of solar powered lasers is good news for accelerating solar powered lasers for space applications. There was a 2012 research paper that also looked at solar powered lasers. They are scaling to 1 megawatt of solar collection and 30 watts of laser per square meter of collection area. A space based system could have 60 watts of lasers since there is no atmosphere blocking sunlight. Space based being application would then need another fresnel lens to focus the lasers for long range beaming.
Brian Wang is a Futurist Thought Leader and a popular Science blogger with 1 million readers per month. His blog Nextbigfuture.com is ranked #1 Science News Blog. It covers many disruptive technology and trends including Space, Robotics, Artificial Intelligence, Medicine, Anti-aging Biotechnology, and Nanotechnology.
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