A greener way of conquering space?
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In the 1960s outer space
was the place to go. It still has an enduring fascination for all generations,
as witnessed by the phenomenal success of films like Star Wars.
Suppose human space
travel really takes off. It might then create a rather more pressing problem
back here on earth. Scientists tell us that a significant contributor to global
warming in coming years may come from jet engine exhausts. Won't the hugely
larger exhaust plumes of current rocket designs only exacerbate this problem?
The Nematrian website
describes a possible, if somewhat speculative, solution to this problem. This
involves increased use of solar power for space vehicle propulsion
purposes. The ideas are explored further in Kemp (2005),
(for references see Solar Powered
Space Flight References). An updated version of this paper is available via
the following hyperlink: Solar Powered
Space Flight.
Solar-powered space flight
The basic idea is that
solar-powered space flight, even prior to reaching orbit, is less
implausible than you might first think. The trick is to use a carefully
designed solar power concentrator. Even with today's technology, it ought in
principle to be possible to use solar power to lift a vehicle plus payload all
the way into orbit, as long as atmospheric drag is limited by having the
vehicle lifted in the earliest stages of its flight by more conventional
chemical rocketry.
If such a vehicle
could reach earth orbit then only relatively modest further improvements would
be needed to take the vehicle all the way to the Moon or Mars and back, or
beyond!
A killer app for graphene?
A possible material to
use to make the substrate for such a concentrator is graphene, given its high
tensile strength and its ultra-low mass per unit area. Peplow (2015)
notes that the many possible industrial uses currently being developed for
graphene has already sparked a graphene-making frenzy. This frenzy could become
much bigger still if very large concentrators made partly out of graphene could
be successfully developed for into orbit solar powered space flight.
Nice idea?
That's the theory! In
practice there are several significant engineering challenges to solve on the
way. One key requirement is to solve the problem of how to keep a large
ultra-low mass optical concentrator arrangement sufficiently accurately
positioned in different parts of such a trajectory. Here the point perhaps is
not to think too small-scale. The ideal size for an ultra-low mass optical
concentrator for use in space seems to be significantly larger than the
relatively small (rigid) concentrators that are sometimes used at present. However,
there appears to be a big disparity between currently available component
performance and what ought theoretically to be achievable using e.g. graphene
based structures.
Still, even if the ideas
set out in Solar
Powered Space Flight are ahead of their time and do not immediately lead to
the development of a solar powered space vehicle, they will hopefully stimulate
others to bring theory and practice closer together in this area. You read
about it here first!