Solar-thermal rockets are ideally suited for "living off the land'' in space. With sunlight as their source of energy and abundant hydrogen or methane as their fuel, they can operate anywhere within the orbit of Mars with relatively high thrust and high efficiency—a compromise between the best (and worst) of both chemical and electric propulsion systems. Departing the Earth with cargo, or returning to it with raw materials, solar-thermal-propelled spacecraft can carry large payloads fairly quickly and efficiently.
They can be refueled at comets, whose abundant water can be cracked into hydrogen and oxygen by passing through the water an electrical current and collecting the liberated gases in a process known as "hydrolysis." This might also be implemented at the Moon where water ice is thought to exist in forever-shadowed craters near the poles.
As well as its potential utilization as a space drive to shunt freight around the solar system, solar-thermal technology may be of use to future space-mining processes and industrialization enterprises.
The solar concentrators for a solar-thermal interorbit tug capable of ferrying large payloads will themselves be large. In one design described by Robert Salkeld and his collaborators, a 100-meter collector diameter is proposed. So a solar-thermal solar concentrator will have to be a low-mass item, with its thickness measured in microns. In order to heat the working fluid to the requisite high temperatures, the concentrator must also be precisely machined and capable ofwithstanding the space environment for long time periods. Near-term small satellite missions using solar-thermal propulsion would not have to be nearly as ambitious. Concentrators a few meters across are sufficient to produce thrust for missions in this class.
These large-scale concentrator requirements will be of great interest to those who would mine small solar-system bodies for water, other volatile substances, and higher melting point compounds or elements. A space miner might simply use the solar-thermal concentrator to focus sunlight on his or her asteroid and collect pure materials as they boil off.
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