In response to Bob Bates’ letter, “The Solution,” I need take issue on a few points. With regard to the sustainability of current solar cell technology, I assume the consumption being referred to is the energy cost of manufacturing vs. the output energy of the cells and is not referring to a cell’s efficiency (which is mostly irrelevant since the sun is an unlimited source of power). Solar cells do not decay with use or time so their total output power is determined only by how long they are in service whereas the energy cost is a fixed amount. In other words, they can be sustainable if they are used for a long enough time.
More striking in Bob’s letter, however, is his blatant omission of alternate technologies available for converting sunlight into electricity. Solar Tres in Spain is one of dozens of examples of a successful and fully sustainable method of converting sunlight into electricity without the use of solar cells.
Finally electricity can be used to run bulldozers, elevators, etc. and is limited only by funding and innovation. To put this into perspective, the main engines on the space shuttle are powered indirectly by electricity. These engines operate exclusively by the ignition of hydrogen and oxygen, both of which are manufactured by electrolysis, i.e. electricity, from water. Converting electricity into more convenient forms of liquid fuel is probably in the minds of many scientists as I write this. Surely if the shuttle can be powered by electricity, the sky is the limit.
Ken Czepelka
This article appears in Jan 29 – Feb 4, 2009.
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For launch the STS uses 2 systems: the main engines in the orbiter that burn hydrogen and oxygen from the external tank (the great big orange cylinder that the orbiter is attached to for launch); and the SRBs (Solid
Rocket Boosters) that burn a solid rocket propellant that is a mixture of powdered aluminum and ammonium perchlorate. These are used only for launch.
The orbiter (what most people think of as “the Space Shuttle”) has two propulsion systems: OMS (Orbital Maneuvering System) used to change orbit and to return to earth, and the RCS (Reaction Control System) used for station-keeping and attitude control. Both systems burn hydrazine with oxygen. Hydrazine is a chemical compound with the formula N2H4. It is a colourless liquid with an ammonia-like odor and is derived from the same industrial chemistry processes that manufacture ammonia. All is not sunshine.