|
Richard Jernigan -> RE: Space-X Falcon Heavy Launch (Feb. 19 2018 0:36:45)
|
Shielding the Mars pioneers from ionizing radiation is necessary because it disrupts synapses, and indeed entire cells in the brain. Large enough doses lead to cognitive decline. The effects are noticeable in some people who receive radiation treatments for brain cancer. Animal experiments indicate that high enough levels of damage can be long lasting, if not permanent.
Our magnetosphere shelters us from the full force of the solar wind, but a few particles leak through. We have evolved to survive the lifetime dose, pretty well. Shielding alternatives that I know of cost weight, the main nemesis of the rocket designer. Each ounce of payload weight is multiplied by the weight of the required additional structure, and a very heavy penalty in required fuel, fuel tankage, etc.
The Apollo astronauts survived the Van Allen belt and translunar space without visible long term effects. I recollect reports of occasional visual light flashes, tentatively attributed to ionizing radiation. However, the possibility of a large solar flare was a worrying prospect. Radiation exposure was monitored by instrumentation on the spacecraft, but above a certain threshold the medical officer (often my brother) was to be notified. I never asked him what, if anything, they might have done.
I seriously doubt that a practical threshold of safe radiation exposure is known. There are legal guidelines in the USA, generally considered to be very conservative. For example, people who work near high power radar transmitters are required to wear X-ray badges. If their exposure exceeds a certain threshold, they are removed from the environment for a period of time, and management are required to make engineering changes to lower the radiation level.
Space travel introduces two more variables: how much risk are you willing to take to save weight? and how do you quantify the risk relative to the level of exposure to high energy particles? The first question is an ethical one, the second scientific.
I am reminded of a conversation I had with my brother. While we were visiting them he came home one day saying he had been battling with the engineers. They were specifying the backup life support system for the Apollo spacecraft. The engineers were badgering him with the question, "What is the minimum amount of oxygen required to sustain human life?"
My brother responded that the answer was unknown to medical science.
"Well, can't medical science find out?"
"No," he replied.
"Why not?"
"We take an oath not to intentionally kill anybody."
Of course the oath reads, "First, do no harm." How you quantify the risk of radiation damage without doing harm to anybody is a vexed question. Animal studies are a fairly blunt instrument if you're trying to quantify the effects on human cognition.
RNJ
|
|
|
|
