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Readers Respond to "The Low-Cost Ticket to Space"

Letters to the editor from the April 2013 issue of Scientific American.


PRIVATIZATION'S PERIL

While S. Alan Stern rightly identifies “the advent of new, reusable suborbital vehicles” and technologies designed “with an eye to simplicity” as keys to cheaper spaceflight in “The Low-Cost Ticket to Space,” he fails to explain why the same revolutions in technology could not be incorporated into traditional, governmental space programs. He ignores the fact that the leaps made by private space companies are largely attributable to inordinate investment by their starry-eyed and deep-pocketed backers. For the most part, they have not proved their financial sustainability.

Also, despite Stern's enthusiasm, space researchers should be wary of relinquishing control of technological developments. Privatizing spaceflight means the market will shape the field's evolution. And market forces are likely to pull spaceflight toward manned missions, which are more profitable but limited in scientific value.

Zachary Miller
Fleetwood, Pa.

ENERGY COSTS OF FUELS

“The True Cost of Fossil Fuels,” by Mason Inman, gives measurements of the energy return on investment (EROI)—a calculation of energy provided per unit of energy spent—for fossil fuels and renewables.

It appears to me that issues with renewables that were not quantified are significant. For example: the need for storage or backup capabilities for wind and solar; the need for new transmissions systems to handle the typically remote locations for large-scale solar or wind projects; or the impact of battery production for electric vehicles. I wonder how the charts would look if they had been so modified.

Peter Gartman
Media, Pa.

Unlike the entry for corn, the calculation of the EROI for biodiesel from soy does not appear to include fertilizer as energy consumed during production. I raise soybeans on my farm, and although soy requires little or no nitrogen, full amounts of phosphorus and potassium are needed for reasonable yields, which would lower soy's EROI. Also, the production biodiesel from canola is worthy of much greater consideration. Canola produces about the same average yield per acre as soy, but whereas soy contains about 16 percent oil, canola contains about 44 percent.

David C. Brown
Shoemakersville, Pa.

NEUTRINO MASS

“Ghostly Beacons of New Physics,” by Martin Hirsch, Heinrich Päs and Werner Porod, describes the search for the fundamental neutrino particle.

One of the difficulties in further characterizing the elusive neutrino is the question of its mass. As the article shows, observed beta decay results in emission of a single electron and antineutrino (or two when two decays occur simultaneously).

This, combined with the difficulty in obtaining an accurate measurement of the mass of the particles involved, leads me to wonder how accurate current measurements of the masses of the neutron, proton and electron are. If the mass measurements of these particles were accurate enough, a simple equation would result in the mass of the antineutrino.

If the current mass measurements of these basic particles are not sufficiently accurate, can a more accurate measurement be made with today's equipment?

Carl Gruel
Kilmarnock, Va.

PÄS REPLIES: Indeed, nuclear beta decay is being used to search for the neutrino mass. According to special relativity, though, energy and mass are equivalent. So the mass of the emitted antineutrino is not simply given by the neutron mass minus the proton and the electron mass; in addition, the kinetic energies of the emitted antineutrino and the electron enter the equation. What experimentalists do, then, is look at the maximum possible energy of the electron and check whether it can carry away all the missing energy in the budget above. If it doesn't, the difference corresponds to the neutrino mass.

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