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See Inside August 2011

Readers Respond to "Rethinking the Dream" and Other Articles

Letters to the editor from the April 2011 issue of Scientific American


Red Planet Mars Life
Lawrence M. Krauss’s “Rethinking the Dream” [Forum] rightly points out that the benefits of flying humans in space have not been commensurate with the cost, especially when human flight is compared with advanced robotic or automatic systems that can do many of the same tasks at one tenth of the cost and with no risk to humans. I think this is a result of nasa’s focus on dramatic, exciting exploration and failure to create an economical, durable infrastructure. I disagree with Krauss only where he advocates one-way missions to Mars. I believe that keeping humans alive on the planet for more than a few weeks will be extremely costly.

The Martian atmosphere is very thin and contains essentially no oxygen. The average surface temperature is about –60 degrees Celsius. Humans must always be in a pressurized enclosure, with a suitable atmosphere and adequate temperature and humidity control. Unlike Earth, Mars does not have a protective magnetic field, and the thin atmosphere provides little shielding from cosmic rays. I suspect some rather heavy shielding will have to be included in any habitats, rovers, and so on. Living off the land is, I think, absolutely ruled out on Mars, where there is no free water and what water ice there is seems to lie below the surface. To be of use, it would have to be collected, thawed and purified.

NASA has learned that an average human will require about five kilograms of food, water and oxygen each day and will produce an equal amount of waste. Of course, water can be recycled, oxygen can be extracted from CO2 and solid waste can be treated, but all that requires power and equipment. Solar arrays on Mars must be twice the size of Earth arrays because solar radiation is weaker (the planet is farther away from the sun). And the arrays will likely require cleaning from Martian dust. For safety reasons, there must also be redundant equipment, plus tools and spare parts for repair. Solid food cannot be recycled, and growing food would require a large, totally enclosed “hothouse.”

The habitat must have air locks to enable humans and their rovers to get in and out without depressurizing the entire living environment. Surface excursions must not go so far from the habitat that participants will not be able to walk back in case their rover breaks down. Furthermore, if a sortie lasts longer than a few hours, the rover must provide food, water and toilet facilities.

Finally, there are human considerations that do not factor directly into costs but that I think make the whole idea unfeasible. Will the colonial-nauts include a doctor? Will the habitat include clinical/hospital facilities? What about recreation? What about normal family life? What happens when the colonial-nauts age and die?

Most of all, why would anyone go?
Don Peterson
Retired U.S. Air Force pilot and NASA astronaut
El Lago, Tex.

COCKTAIL PARTY CHATTER
I am deaf in one ear, and even though my hearing is much better than most, I experience the issues described in Graham P. Collins’s “Solving the Cocktail Party Problem” every day. For me, it is only when a room is very noisy and I am struggling to comprehend the conversation that I notice the process I use to solve the cocktail party problem. My technique seems to be a combination of those mentioned in the article. As in spread-spectrum signal processing, once I know what a person sounds like, I listen for the sounds he or she is making. Second, I take in the sounds and try to reconstruct the words based on the expected probability of sounds surrounding each one. Finally, I use the probability of words surrounding each one based on the context to fill in the sentence. I knit the sounds into words and the words into a sentence.

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