The Value of the Moon by Paul D. Spudis

Author:Paul D. Spudis [Spudis, Paul D.]
Language: eng
Format: epub
ISBN: 978-1-58834-504-2
Publisher: Smithsonian
Published: 2016-04-18T16:00:00+00:00

Why Not Mars?

Virtually the entire space community, from those inside the agency to others working on spacecraft, missions or data analysis, presume that Mars is the “ultimate goal” for human spaceflight.9 In 1965, the imaginative pull that decades of science fiction and speculation about Mars as an Earthlike planet had dealt us were dashed when we found by direct investigation that the real Mars is a distant, cold, dry desert, with virtually no atmosphere. Subsequent missions over the years have shown that it may have been warmer and wetter in the past, which led to the idea that microbial life might have originated there. This single idea is largely responsible for the subsequent fixation on Mars as the “next destination” for humans in space. The obsession with “searching for life elsewhere” has hijacked our thinking about the future of people in space. It is virtually impossible to advance an idea or concept involving people at some space destination other than Mars, without proving that it “feeds forward” to our “ultimate destination.”

We do not know how to send people to Mars at this time. The difficulties with a human mission to Mars fall into several categories: technical, programmatic, and fiscal. The manned space program has conducted long-duration spaceflight, built a heavy-lift launch vehicle, and conducted landings on the Moon. But for a variety of reasons, getting humans to Mars is much more difficult. Mars is much farther away from Earth, varying between 140 to 1,000 times (55 to 400 million km) the distance of Earth to the Moon (400,000 km). No known trajectory can shorten the months of transit; most robotic missions take nine months. Although issues of crew deconditioning caused by microgravity appear to be mostly resolved from flight experience on the ISS, months of exposure to hard cosmic radiation and the occasional possible solar particle event, requires some type of shielding. People need to breathe, eat, and drink, so those consumables must be carried with them. Mars is bigger than the Moon (its gravity is about 3/8 that of the Earth, compared to the 1/6 g of the Moon); thus, it requires more energy to descend and land on the surface of Mars. This applies to the return trip as well. The larger gravity well of Mars means that bigger landers and more fuel are needed. Although there is an atmosphere on Mars, it is more than one hundred times thinner than Earth’s, so we cannot rely solely on aerothermal entry to slow down the spacecraft; a significant propulsive maneuver is required. This issue, the EDL (entry, descent, landing) problem,10 is one for which we have no solution at present.

The composition of the martian atmosphere is virtually pure carbon dioxide (CO2) and thus, not breathable; the thinness of the atmosphere requires people to wear pressure suits. The surface is not completely shielded from cosmic rays and solar UV radiation; Mars does not have a magnetosphere like the Earth, which means that it is a hard radiation environment, limiting the permissible time for surface exploration.

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