Comments on: Delusions of a Mars Colonist

By: Joe

Joe — Thu, 23 Jun 2016 17:33:53 +0000

Eighty Six information dense pages. Always interested in a “little lite reading”. 🙂

Thanks for the link.

By: Marcel F. Williams

Marcel F. Williams — Thu, 23 Jun 2016 15:57:10 +0000

Those of you who are interested in more details about the relative effectiveness of various types of cosmic radiation shielding materials (including secondary radiation) should read the 2011 US Department of Energy Study which can be found at:

http://www.pnnl.gov/main/publications/external/technical_reports/PNNL-20693.pdf

By: Joe

Joe — Thu, 23 Jun 2016 12:04:15 +0000

“We do know what level of Rem is “acceptable” and what level of gravity and the rotation rates.”

No we do not.

To pick just one example, several years ago I had the good fortune (at a human factors conference) to meet and have an extended conversation with Dr. Joseph Kerwin (medical doctor Skylab Astronaut).

The current rotation rate conventional wisdom (essentially a maximum of 1 to 2 RPM) is based on ground based tests run in the 1960’s. Kerwin said based on testing run on Skylab he believed the actual maximum to be 5 RPM. Since the centripetal force increases with the square of the RPM that would reduce the required spin diameter for any desired gravity level by a factor of 6.25 even if you use the previous maximum 2 RPM as a base (by 25 if you use 1 RPM).

You seem to want all issues to be completely settled and they are not. In fact many issues may well be resolved in a positive way for any one truly interested in space development.

By: Paul Spudis

Paul Spudis — Thu, 23 Jun 2016 12:02:10 +0000

The advantage of water over regolith for radiation shielding is that for comparable levels of protection, you need less water than you do using regolith. When high-energy gamma- and cosmic rays interact with regolith, they induce reactions in the heavy atoms, which can cascade and shower down as secondary radiation. This problem is lessened with water because, as mentioned above in the comment by Marcel, it has fewer neutrons on a mass per mass basis. However, it was assumed in early lunar base studies that there was no water to be had on the Moon, thus those scenarios showed using regolith exclusively as regolith shielding. It will work, but you need several meters of it to absorb the secondary radiation.

By: billgamesh

billgamesh — Thu, 23 Jun 2016 11:26:47 +0000

I stand corrected.

By: Paul Spudis

Paul Spudis — Thu, 23 Jun 2016 07:06:45 +0000

Sorry, Bill — regolith (unpacked – 1400-1800 kg/m^3) IS denser than water (1000 kg/m^3).

By: Paul Spudis

Paul Spudis — Thu, 23 Jun 2016 07:03:39 +0000

The post generated 95 comments.

Yeah — nothing like internet wisdom to solve technical problems.

By: billgamesh

billgamesh — Thu, 23 Jun 2016 03:05:15 +0000

“-it will then be time to move out into the rest of the Solar System (including, but not limited to, Mars).”

We do know what level of Rem is “acceptable” and what level of gravity and the rotation rates.

If you mean to settle colonies on other natural bodies when you write “move out” then I have to disagree.

Much of what is being discussed here are just the dead ends explored and left behind by the early 1970’s work of Gerard K. O’Neill and his students at Princeton. Nothing less or more than Earth radiation and gravity is acceptable. Mega-structures created with lunar material make rotation rates a non-issue.

By: Shannon

Shannon — Thu, 23 Jun 2016 00:48:44 +0000

Structures, use of glass on Mars’ surface: My query in the Mars Society’s Facebook Group on 18 March 2016 reads: “According to this site (http://marshield.com/medical-shielding/lead-glass/), lead glass ‘2.0 mm Pb offers the same protective effect as a 2 mm thick lead wall.’ So, since Curiosity rover detected surface radiation to be 300 mSv, roughly 24 CAT scans …. What thickness of glass would be necessary to provide adequate radiation shielding on the surface of Mars?” The post generated 95 comments. It turns, “glass has a density of 2.7, so 10 g/cm2 = 3.7 cm, 20 g/cm2 = 5.4 cm, 10 g/cm2 =8.1 cm” thick. This suggestion was the best alternative: “Polycarbonates like lexan have densities of about 1.2, so 10 provide 10 g/cm2 shielding you would need 0.83 cm of lexan.”–both were provided by Johnathan Clarke.

Plants and soil: see article, “Farming on Mars: How Could Martian Soil be Cultivated?” aka “Evolution of Soil on Mars” (Astronomy & Geophysics academic journal) –
http://astrogeo.oxfordjournals.org/content/57/2/2.18.full?keytype=ref&ijkey=NWL0rzGK5CzJJOM

By: billgamesh

billgamesh — Thu, 23 Jun 2016 00:07:38 +0000

“-future colonies on Mars-”

There are not going to be any colonies. The most glaringly obvious fact you are completely ignoring is the one that was the genesis of the space colonization movement of the 70’s: there are not natural bodies besides Earth suitable for human colonization.

Humans evolved in a 1 gravity environment and that is what is required. Mars is a scam.