Response to New Scientist Article - Space elevators: 'First floor, deadly radiation!'

The recent New Scientist article with the ominous title 'First floor, deadly radiation!’ has been floating around the net and causing some discussions. I have been asked by a couple people for my take on it.

This is an old issue, nothing new. Anders, I and others have been discussing it for a few years and there are some very critical aspects of this that the article neglected to mention. The new report referred to in the article by Anders and Blaise is about a year old and the issue has been reported several times over the last couple years. Anders himself was surprised by the negativity of the article and how dramatic they made the entire issue.

First, let’s start this discussion with a little perspective. Space is dangerous. It is a vacuum with radiation, meteors, and extreme temperature swings. If you go to space without protection the lack of air will kill you, thermal differences will kill you and, yes, as the article states – without shielding radiation will kill you. The limits set for radiation exposure for astronauts is 50 rems. Below this level there is no expected radiation sickness but you do run a slight chance of getting cancer later in life. No astronauts have been exposed to this but in one case a near miss of a solar storm almost gave a set of Apollo astronauts a much higher and deadlier dose.

The radiation belts are deadly, no question. Apollo astronauts went through the belts but went through quickly. The elevator goes more slowly so that is why this discussion is being had. There are two ways to reduce radiation exposure in this case: reduce the time in the radiation belts and/or shield the radiation. We must also understand the radiation. It is composed of high-energy electrons and protons with energies that range from keV to hundreds of MeV. The low energy particles are the most abundant and easiest to stop whereas the high energy ones have the lowest flux but are much more difficult to stop. A very large fraction of the radiation will be stopped by the hull of any transport vehicle proposed that can hold in the required atmosphere and the associated hardware of a climber. Anders points out that 10g/cm^2 of material will essentially stop almost all of the radiation. On a climber the structure of a climber, floors, air, chairs, water, food, luggage, other people,… all that act as radiation shielding. For a climber carrying people, perhaps 100 tons, this intrinsic shielding will reduce the radiation load by more than 75% before we do anything. Even the first climbers may have this intrinsic shielding but we should make it clear the first elevators have been designed for cargo. The intrinsic shielding will limit travelers radiation exposure to perhaps 20 rads of primarily protons. This level of radiation is less than the limits set for astronauts and would cause no radiation sickness except in rare cases. It is not near a fatal dose. Also, people will not want to take 7 days to travel to geosynchronous for their vacation or whatever. We have been planning that the trip would be done by a high-speed climber. A speed of 500km/hr may be much more reasonable and though this will take development it is possible. We are now looking at a radiation load that is down by a factor of six from the radiation limits set for short-term exposure of astronauts. These are general numbers but also show roughly where we are before we even start working on this issue.

Anders and I are planning to write up a more detailed analysis and that should give a good basis for people to work with.

Everyone must also remember, whether someone travels to space by rocket or by elevator the primary radiation dose and hazard will be during your stay in space not during the trip there.

The New Scientist title was clearly to attract readers and had little to do with reality. The article itself appears to have been intentionally slanted to make it more exciting and ignore some very basic facts and information provided by Anders.

One other comment I just have to toss in… New Scientist needs to check the credits on their images. The image in the article was done for NASA long before Liftport existed.

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