Saturday, January 5, 2013

The Radiation environment and its effect on human spaceflight: A Lunar Mission

Relative monthly infall of galactic cosmic rays from 1958 through December 2012 shows the inverse relationship with solar activity. The highest GCR infall rate (since the beginning of the Space Age) was recorded in late 2009 (arrow), occurring at the same time was the latest and unusually lengthy solar minimum [Moscow Neutron Monitor].
João Sabino
Instituto Superior Técnico
Lisboa, Portugal

This work is an overview of the quantities and concepts common in radiation physics and describes the types of radiation important to planning crewed missions to the Moon. Radiation effects on biological tissue and the consequences to astronaut health are addressed.

The environment of a mission to the Moon was simulated based on data obtained with the CREME program along with data from Lunar Prospector neutron measurements. The virtual mission was divided into stages of a trajectory: Low Earth Orbit, traversing the Van Allen Radiation Belts (VARB), the geostationary orbit radiation environment (GEO), lunar orbit and surface radiation environments. 

Major details in the development of a software application in Geant4 (CERN) are presented. The application was used to reproduce the transport of radiation particles through matter, to simulate the physics involved and to obtain the resulting absorbed dose, equivalent dose and the spectre of secondary radiation. The quantities were evaluated for solar minimum, solar maximum, and solar conditions wre evaluated for each mission phase.

The radiation environment in the solar system presents the main constraint to human spaceflight outside Earth's protecting radiation belts.

As the human presence in space tends to increase, or the will to reach other planets grows, radiation in space becomes a more compelling obstacle that needs to be dealt with. The risks that radiation exposure presents to space missions directly effects mission planing. For this reason a good knowledge of the radiation environment in all mission phases is essential. Development of reliable prediction tools is of major importance to assist mission planing and assure minimum safety for the crew.

This work pretends to explain subjects that need to be taken into account to understand problems space radiation pose to human spaceflight, taking as an example the case of a real lunar mission scenario and also documenting the development of software simulating the radiation environment and analyzing the effects of exposure.

Robotic space exploration looks promising in the immediate future, but despite huge advantages many scientists acknowledge it is not sufficient alone, that humans are needed in space to perform more complex research tasks such as field geology and the acquisition and analysis of samples.

This is a strong incentive towards human spaceflight and also a natural drive based on curiosity and adventure the human being has shown in this kind of challenge that lead us to go farther and farther; not to mention technological and industrial advancements always associated with meeting such challenges. Nowdays, even the tourism industry has begun to recognize space as an interesting destination for the wealthy, and some companies have already flown tourists to the International Space Station.

Human space exploration beyond LEO is presumably going to reemerge very soon, especially if some of the present risk it poses are minimized.

Download or read the study (pdf), HERE.

Cosmic ray flux effects lunar ice (March 19, 2012)
a perfect storm of cosmic rays” (September 29, 2009)
Cosmic rays and manned space travel (September 16, 2009)
Cosmic ray flux highest ever recorded (September 3, 2009)
LUNAR-TEX radiation blanket: Skeptical (May 11, 2009)

Managing Space Radiation Risk in the New Era of Space Exploration (2008)
Committee on the Evaluation of Radiation Shielding for Space Exploration
National Research Council

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