How Arid Israel Became a Water Titan in the Middle East

Colonizing Callisto

Evaluating Lockheed Martin's Reusable Lunar Lander and Orbital Propellant Depot Concept

Notional  reusable lunar landing spacecraft on the lunar surface (Credit: Lockheed Martin)

by  Marcel F. Williams 

At the 69th International Astronautical Congress held in Bremen, Germany this month,  Lockheed Martin  unveiled a new reusable lunar crew lander concept.

For simplicity,  I'll designate the notional Lockheed Martin spacecraft discussed in this article as the R-LL (Reusable Lunar Lander).   According to Lockheed Martin, the R-LL will have dry weight of 22 tonnes and be capable of storing up to 40 tonnes of LOX/LH2 propellant. The R-LL will have up to 5 km/s of  delta-v capability.

Lockheed Martin argues that the R-LL should be capable of crewed round trip  missions to any area of  the lunar surface from NASA's future Deep Space Gateway (DSG) which is to be located at a Near Rectilinear Halo Orbit (NRHO).    Such round trip missions, they argue,  would also be capable of delivering up to one tone of payload to the lunar surface in addition to a crew of four individual astronauts. 



While Lockheed Martin has been rather vague about the exact dimensions of the R-LL, they have indicated that it will consist of only two cryotanks and will be derived from the Centaur upper stage family and its descendants. They also suggest that the R-LL will have a diameter close to that of  the future Orion spacecraft.

Since Lockheed Martin's Centaur V is currently in development as the future upper stage for the ULA's future 5.4 meter in diameter Vulcan rocket, one might speculate that the diameter of the R-LL cryotanks might be the same as  and  is supposed to have the same 5.4 meter diameter as the Centaur V. Such large diameter liquid hydrogen and liquid oxygen tanks should be capable of easily accommodating the 40 tonnes of propellant required for the R-LL. So deriving the lunar vehicle from the Centaur V cryotanks might be the simplest and cheapest path towards rapidly developing the R-LL.

Lockheed Martin's Notional  Reusable Crewed  Lunar Landing Vehicle

Propellant: 40 tonnes of LOX/LH2

Inert Weight: 22 tonnes

Engines: Four RL-10 derived engines

Maximum delta-v capability: 5.0 km/s

Maximum number of crew: Four

Additional cargo capability: one tonne of additional cargo
The R-LL would use four engines to provide engine out capability. This would enhance crew safety during attempted landings in case of a serious malfunction with one of its engines. So just two counter balancing engines could be used during a landing in case of single malfunction engine.     Lockheed Martin says that engines for the R-LL  would be derived from  Aerojet Rocketdyne's  RL-10 family or from Blue Origins restartable BE-3 engine. Aerojet Rocketdyne's RL-10 derived CECE engines would be  capable of at least 50 restarts with a throttling range from 104 percent to  just eight percent of thrust. 

Departing from the Deep Space Gateway, it would take approximately 12 hours for the R-LL to reach any point on the lunar surface. Another 12 hours would be required for the R-LL to return to the  gateway at NRHO.

NRHO: (Near Rectilinear Halo Orbit):

Travel time to and  from LEO:~5 days from LEO (3.95 km/s)

Station keeping: 5 m/s per year

Travel time to and from LLO:~ 12 hours to LLO (0.730 km/s)

Lockheed Martin says that their notional lunar spacecraft would be capable of accommodating  a crew of four astronauts on the lunar surface for up to two weeks. Such a lengthy stay would require at least four tonnes of additional shielding mass to protect astronauts from the inherently  deleterious heavy nuclei component of cosmic radiation and from a major solar flare. So one would assume that such enhanced radiation shielding would be part of the notional space vehicle's 22 tonnes of inert mass.

Lockheed Martin has also suggest that propellant depots could be co-orbited with the Deep Space Gateway so that the R-LL can be refueled at NRHO.

The simplest propellant depots would probably have to be utilized within a month after deployment to NRHO since approximately 3.81% of its liquid hydrogen and 0.49% of its liquid oxygen would boil off within a months time. For the 40 tonne LOX/LH2 requirement for the R-LL, such propellant depots would probably have to NRHO by the SLS or the BFR.

More sophisticated propellant depots could be equipped with cryocoolers and solar arrays capable of re-liquefying fuel boil-off.  Ullage gases from the boil-off of liquid hydrogen could be used to re-liquefy gaseous oxygen while 12 to 15 kWh of electricity would be needed to liquefy one kilogram of gaseous hydrogen. The 5.7 tonnes of liquid hydrogen required for a lunar mission would lose more than 217 kilograms of LH2 per month (7.2 kilograms per day).  But a 10 kWe solar  array deployed to NRHO capable of producing more than  240 kWh of electricity per day would be capable of re-liquefying 16 to 20 kilograms of LH2 per day.  The solar arrays for the Orion spacecraft will be capable of producing more than 11  kW of electric power. So it should be rather simple to deploy propellant depots already equipped with cryocoolers and and solar panels in order to prevent fuel boil-off. 

Solar powered depots that simply re-liquefied its ullage gases and powered pumps for storing and transferring liquid fueles would only  require the continuous delivery of liquid hydrogen and liquid oxygen.  Future Vulcan Heavy/Centaur rocket could deliver 7.3 tonnes of liquid hydrogen or oxygen to NRHO per launch. Monthly launches could deliver more than 87 tonnes of propellant to depots located at NRHO per year, more than enough for two R-LL missions to the lunar surface per year.

Notional propellant producing water depot (Credit: Lockheed Martin)

The most technologically complex propellant depots could use solar power to  actually  produce liquid hydrogen and liquid oxygen directly from water. This would require the addition of an electrolysis plant plus substantially more solar power.  A 375 KWE solar array proposed by Lockheed Martin could produce 40 tonnes of liquid hydrogen and oxygen propellant at NRHO per month. Such huge 375 KWE solar arrays would weigh  less than four tonnes. And two such arrays could be directly delivered to NRHO with a single SLS launch. But much smaller commercial launch vehicles could deploy 300 KWe arrays to LEO for later transport to NRHO by fueled upper stages deployed to LEO. 300 KWE arrays at NRHO could produce 40 tonnes of propellant in five or six weeks rather than just four weeks for the larger arrays.

Solar powered propellant producing water depots would make it much simpler and safer for commercial rockets to deliver fuel to NRHO since the payload would only be water. Propellant producing water depots at NRHO could eventually be supplied with water from the lunar poles.

Of course, water and propellant being produced on the lunar surface itself would dramatically reduce the amount of propellant required for   R-LL departures from NRHO. Reusable tanker vehicles directly derived from the R-LL could deliver more than 40 tonnes of lunar water  to propellant producing water depots at  NRHO per flight.  Just 12 round trips from the lunar surface could deliver enough water to NRHO to manufacture enough fuel for crewed missions to the orbits of Mars or Venus.

Lockheed Martin envisions that astronauts would be deployed to the NRHO gateway via the Orion and the Space Launch System. And then the would take the R-LL to the lunar surface and back to the NRHO gateway. And then they would take the Orion back to Earth.

However, propellant depots deployed at LEO  would make SLS crew launches of the Orion vehicle obsolete.  Refueling at LEO, the R-LL would have more than enough delta-v capability to transport crews from LEO to the  NRHO gateway. And refueling at NRHO, the R-LL would, of course, be capable of returning crews from NRHO back to LEO.  And even with  22 tonne of inert weight, a  5.4 meter in diameter R-LL could be launched to Leo aboard a Vulcan/Centaur launch vehicle within  a  6.4 meter in diameter payload fairing.

So for trips to the lunar surface, astronauts would simply take a Commercial Crew Launch vehicle (Falcon9/Dragon or Vulcan/Centaur/CST-100) to a commercial space habitat at LEO where a propellant depot refueled R-LL was already docked and ready to be boarded.  The R-LL would leave LEO with enough  propellant to take its crew on a 5 day journey to the NRHO gateway where another already depot fueled R-LL would already be docked.  The second R-LL  would take the crew for a round trip to the lunar surface, 12 hours to reach the surface and 12 hours to return to astronauts to the Deep Space Gateway.  The astronauts would return to the gateway with the first R-LL already fueled for their return to a commercial space station at LEO. The Crew would than take a Dragon or CST-100 Starliner back to the Earth's surface.

Such an architecture would, finally,  allow the SLS to be used--exclusively-- as a super heavy lift cargo transport. Such payloads could include: large and spacious microgravity and artificial gravity habitats derived from SLS propellant tank technology,  large water and propellant depots derived from SLS propellant tank technology, interplanetary spacecraft capable of accommodating at least 400 tonnes of propellant derived from SLS propellant tank technology for crewed missions to the orbits of Mars and Venus, 8 meter in diameter space telescopes exceeding the capability of the James Webb telescope,  and large inflatable microgravity and surface habitats that could make it a lot more spacious and comfortable for future astronauts and tourist to live under artificial gravity conditions in space or on the hypogravity surfaces of the Moon and Mars.


Links and References

Concept for a Crewed Lunar Lander Operating from the Lunar Orbiting Platform Gateway

Lockheed Martin unveils lunar lander concept

Cis-Lunar Gateways and the Advantages of Near Rectilinear Orbits

Lockheed Martin's Reusable Extraterrestrial Landing Vehicle Concept for the Moon and Mars

NASA's Lunar Resource Prospector

Resource Prospector

Pioneering and Commercial Advantages of Permanent Outpost on the Moon and Mars

Twin Regolith shielded habitats on a sintered  lunar surface area. Each habitat module is connected to each other by an inflatable pressurized  walkway. 

Permanent outposts on the surfaces of the Moon and Mars  could be the first major steps towards the expansion of human civilization into the rest  of the solar system.  Unaided traction for human walking requires a gravity that is at least 10% of the gravity at the  Earth's surface. The Moon, Mars, Mercury, and the Jovian moon, Callisto, are all worlds that have surface gravities higher than 0.1 g. So these are extraterrestrial worlds  that will probably be accessible for continuous human occupation before the end of the century. However, whether such  low gravity environments would  have significant deleterious effects on  human health and reproduction is currently unknown. But long before the permanent settlement of extraterrestrial worlds,  human outpost on the Moon and Mars, could have beneficial scientific, commercial, and even strategic benefits for those nations and businesses that dare to venture there.

Planets and Moons within the solar system that are potentially suitable for human colonization:

Moon

surface area relative to the Earth: 7.4%     

surface gravity relative to the Earth: 0.17g 

diameter relative to the Earth: 27.3%


Mars

surface area relative to the Earth: 28.4%
   
surface gravity relative to the Earth: 0.38g 

diameter relative to the Earth: 53.1%


Mercury
 
surface area relative to the Earth:  14.7%
   
surface gravity relative to the Earth: 0.38g 

diameter relative to the Earth:  38.3%


Callisto 

surface area relative to the Earth:  14.3%
   
surface gravity relative to the Earth: 0.13g 

 diameter relative to the Earth:  37.8%

Note: Land area comprises 29% of the Earth's surface with 71% covered by water

Regolith shielded habitat designed for the Moon and Mars. Mobile water tanker provides water to the habitat for drinking, washing, growing food, and for the production of air.

Internal view of a regolith shielded habitat with regolith placed within the two meter cavity within the automatically deployed walls surrounding  the 8.4 meter in diameter pressurized habitat.

Permanent outpost on the surface of the Moon could immediately exploit lunar regolith to protect humans from significant exposure to harmful levels of radiation.  Just two meters of lunar regolith dumped within the walls of a lunar regolith habitat could reduce annual cosmic radiation exposure below the maximum legal limit for radiation workers on Earth (5 Rem per year)  during the solar minimum while also protecting astronauts from radiation exposure from major solar events. Protection from micrometeorites and extreme temperature fluctuations would be an added benefit of  insulating a lunar habitat with regolith.

A single lunar habitat derived from the technology used to make the light weight 8.4 meter in diameter hydrogen fuel tanks for the SLS could provide two levels of floor space  approximately 111 square meters in area. That would be more floor space than the average home in Germany, Japan, Sweden, Italy, Spain, Russia, and in the UK. The deployment of such  habitats for the private commercial community could also be used  as lunar hotels for space tourist or to house workers for private companies involved in the export of lunar water or regolith for government and private entities.

Creating solid pavement for the deployment of  habitats and other lunar outpost components upon dust free surfaces could be created by using mobile robots to pave and sinter lunar regolith.  This could eliminate tracking in deleterious lunar dust into pressurized habitats when astronauts are working in the paved  lunar outpost area. 

Mobile water tanker for storing and transporting water and a mobile water extracting  robot that uses microwaves to extract water from regolith from the shadowed areas of the lunar poles.

In the lunar polar regions, roving microwave water extraction robots could mine ice particles from the  permanently shadowed areas for the production of water. Water, of course, can be used for drinking, washing, food preparation, and for growing food. Water can also be electrolyzed for the production of oxygen for air and for the production of hydrogen and oxygen for rocket fuel needed to return to Earth.

Human biowaste could be converted into methanol through pyrolysis. Methanol and oxygen can be used with fuel cells to produce electricity for back up energy during periods of lunar darkness. The water produced from the combustion of methanol and oxygen can be recycled. The CO2 produced from the manufacture of methanol and from the combustion of methanol in fuel cells can be used to enhance the growth of indoor lunar crops. Small portable methanol fuel cells could also be used to provide power for pressure suits during lunar excursions.

Nitrogenous biowaste, such as urine, could be used as fertilizer for lunar crops.

However,  there is some  evidence that substantial quantities of carbon and nitrogenous material may also  be a significant component of the permanently shadowed areas at the lunar poles. Astronauts stationed at  lunar outpost at the lunar poles could used to explore and to quantify the amount of volatiles located within the shadowed regions.

Buried nuclear power plant on the lunar surface (Credit: NASA)

While solar panels attached to the habitats would provide the initial power for a lunar habitat, small nuclear reactors   buried beneath the lunar regolith only a few hundred meters away could provide substantial amounts of electricity for the lunar facility, 24 hours a day.

Outposts originally designed for the lunar surface could also be utilized  on the surfaces of Mars, Mercury, and Callisto and even on the meager surfaces of large asteroids and on the moons of Mars.

Three regolith shielded habitat modules on a sintered  Martian surface area. Each habitat module is  connected to each other by two inflatable pressurized  walkways.   

Permanent outpost on the Moon and Mars and on other worlds, would allow the continuous exploration of those surfaces by both humans and robots. Unmanned solar or nuclear powered rovers on the lunar surface, operated by humans on Earth, could visit and collect samples from  practically every area on the surface of the Moon. The collected rocks and soil could then be returned to the lunar outpost for immediate study or for eventual export back to Earth.

On Mars, both robotic rovers and hydrogen blimps could be utilized to continuously explore the Martian surface. Such robots could be operated in real time by the astronauts on the Martian surface or in orbit around Mars at a  space station.  Again, the collected samples by the remote controlled robots could be returned to the Martian outpost for immediate study or for eventual export back to Earth.

A permanent US government presences on the surface of the Moon and Mars will also enhance the ability of private American companies to protect their assets from potentially hostile foreign entities that will probably also be on these new worlds by mid century.

Marcel F. Williams

© New Papyrus


Links and References

 D. Bryant Cramer.  "Physiological Considerations of Artificial Gravity."  Applications of Tethers in Space, volume 1, pages 3·95-3·107.  Edited by Alfred C. Cron.  NASA Scientific and Technical Information Branch, 1985.  Conference Publication 2364: proceedings of a workshop held in Williamsburg, Virginia, June 15-17, 1983.

Lunar Station Protection: Lunar Regolith Shielding

Wet vs Dry Moon

Utilizing the SLS to Build a Cis-Lunar Highway

Cosmic Radiation and the New Frontier

NASA Steps Closer to Nuclear Power for Moon Base

How big is a house? Average house size by country
 
Mission and Implementation of an Affordable Lunar Return (Spudis & Lavoie) 

Using the resources of the Moon to create a permanent, cislunar space faring system (Spudis & Lavoie)

The Market for Space Fuel from Asteroids

Cosmic Radiation and the New Frontier

Mars and its inner moon, Phobos

by Marcel F. Williams

The average woman on Earth is born with an approximately 38% chance of developing cancer sometime in her lifetime. And the average man  is born on our planet with about a  44% chance of developing cancer sometime in his lifetime.

Oxidative stress from the production of oxygen free radicals created during the metabolism of  proteins, carbohydrates, and fats (food) appears to be the primary cause of cancer and aging amongst humans and other animals on Earth. But ionizing radiation from space and from  the natural geology of the  Earth and in the food we eat and the water we drink can also  contribute to cancer and aging.

Ionizing radiation interacts with the tissue of humans and other animals by stripping away electrons from molecules, leaving behind  chemically active radicals that can be harmful to the cells of the human body.  As our civilization begins to expand off the Earth in the 21st century, the human species will encounter substantially higher levels of ionizing radiation from the cosmos.   Enhanced exposure to Galactic Cosmic Rays (GCR)  could significantly increase the rate of cancer and aging  and even brain damage amongst explorers and settlers in the New Frontier-- unless appropriate  means are  utilized to mitigate the potentially  deleterious effects  of cosmic radiation and major solar events.

Humanity and all other creatures on Earth live under a sea of air whose mass substantially reduces our exposure to cosmic radiation and the ionizing  effects of solar storms. The average amount of cosmic radiation exposures experienced on the surface of the Earth is approximately 0.039 Rem. Within inhabited US territorial areas, annual cosmic radiation exposure may be as high as 0.13 Rem (Wyoming)  or as low as 0.03 Rem (Puerto Rico).

The Earth's crust is also naturally radioactive thanks to uranium and thorium and a radioactive component of potassium (potassium-40) that is naturally found in our soil. Terrestrial soil contains about 6 parts per million  of thorium on average and 0.7 to 11 parts per million of uranium.  The Earth's oceans contain more than 4 billion tonnes of uranium 238 which has a radioactive half-life  of 4.47 billion years. The world's rivers dump about 32,000 tonnes of uranium annually into the world's oceans.

The human body, of course, is naturally radioactive thanks mostly to the naturally radioactive potassium in our bodies. Human body mass typically contains about 40 grams of potassium of which 1/1000 of this element is radioactive potassium-40. Humans also ingest food and water that is naturally radioactive thanks to the natural potassium, uranium and thorium contained in these foods. So internal radiation in the human body contributes about 0.04 Rem of annual radiation exposure.

However, the inhalation of  radon  222 and 220 is the predominant contributor of ionizing radiation in humans on Earth.  Radon gas is a radioactive by product from the decay of uranium or thorium and has a half-life of approximately 3.8 days. Radon exposes humans and other animals to approximately 0.23 Rem annually.

Smoking, however, can add even more radiation exposure to the human lungs than radon. The inhalation of tobacco contains  radionuclides  polonium 210 and lead 210. While a typical non-smoking American is exposed to about 0.36 Rem of radiation annually on Earth, a smoker can add an additional 0.28 Rem of radiation exposure to the human lungs.

Typical medical diagnostic procedures that use nuclear material can add 0.06 Rem of annual radiation exposure.

Ionizing Radiation on Earth

 0.039 Rem - Average annual amount of natural radiation in the human body
 0.2 Rem -  Average annual  internal radiation exposure due to the inhalation of  radon
 0.28 Rem - Annual radiation exposure for individuals who smoke cigarettes

 0.029 Rem - Average annual  exposure to terrestrial radioactive decay
 0.026 Rem - Average annual exposure to cosmic radiation in the US

0.36 Rem - Total average amount of natural and man-made ionizing radiation exposure for a person living in America

Boeing 747 (Credit: Boeing)

 The US legal limit for radiation exposure for workers is 5 Rem per year. Personal working at a nuclear facility are normally exposed to  0.115 Rems annually. However, personal aboard an airliner are typically exposed to 0.22 Rem per year.


Ionizing Radiation Exposure Limits on Earth

5 Rem - annual maximum radiation exposure allowed for radiation workers in the US

0.22 Rem - The average annual cosmic radiation dose experienced by flight personnel

0.12 Rem - Annual radiation exposure experienced by workers at a nuclear power plant

0.007 Rem - Annual radiation exposure while living in a stone, brick, or concrete building

0.003 Rem - Annual radiation exposure while living near the gate of a nuclear power plant

People who live near the gate of a nuclear power facility are normally exposed to about 0.003 Rem annually.  Living in a brick, stone, or concrete building would expose you to 0.007 Rem of annual radiation exposure. And each individual living inside of your home with you adds another 0.04 Rem of annual exposure. 

It should be noted, however, that there are places on Earth where people are exposed to substantially higher levels of ionizing radiation. A community of over 2000 people exist in Iran, that is naturally exposed to 1 to 25 Rem of radiation annually-- with no signs of any deleterious physical or reproductive effects on that population.

 In space, however,  exposure to ionizing radiation would be substantially above that typically experienced on Earth.

International Space Station (Credit: NASA)

On our planet of evolutionary origin, humans are typically exposed to 0.36 Rem annually. The annual exposure to cosmic radiation aboard the ISS (International Space Station) space station, however,  can range from 20 to 40 Rem depending on whether our solar system is experiencing solar maximum or solar minimum conditions. This is one of the reasons why astronauts typically remain aboard the ISS for only a few months. The solar maximum is a period when the sun has the most sunspot activity and the solar minimum is a period when the sun has the least sunspot activity. Solar maximum conditions can help to mitigate  the rain  of galactic cosmic radiation (GCR) within the Solar System. However, large solar flares often occur during solar maximum conditions.

Cosmic radiation levels become even worse as we leave the protective proximity of the Earth's massive globe and its surrounding magnetosphere. A space habitat located near the Moon at EML4 (Earth-Moon Lagrange point Four) for instance would be exposed to as much as 73 Rem annually  during the solar minimum. Being beyond the Earth's magnetosphere  also exposes astronauts to the heavy nuclei components of cosmic radiation.

Cosmic rays are mostly of galactic origin, resulting from super nova explosions. Approximately 85% of cosmic radiation particles are composed of hydrogen derived protons;  13%  are derived from helium atoms.   Heavy nuclei are accelerated particles  whose nuclei are derived from atoms heavier than hydrogen and helium. While heavy nuclei comprise only about 2% of cosmic radiation particles, they can do substantially more damage to biological tissue.

Astronauts in low Earth orbit, are only infrequently exposed to heavy nuclei bombardment thanks to the Earth's protective magnetosphere. Beyond the Earth's magnetosphere, however, astronauts frequently experience ' retinal flashes'. These visual flashes appear to be the result of heavy nuclei impacts upon the visual cortex of the human brain. Most cosmic ray ions pass harmlessly though the vacuous space between the atoms of the human body. But the relentless rain of cosmic radiation inevitably results in impacts upon our corporeal components. Heavy nuclei, especially the heaviest ions, can be particularly damaging to human tissue and especially to the human brain. Additionally, the particle  impacts of cosmic radiation impacts can produce significant amounts of secondary particles such as neutrons that can enhance the deleterious effects of cosmic radiation on biological tissue. 
 
Twenty seven Apollo astronauts returned to Earth after nearly two weeks beyond the Earth's magnetosphere with no significant deleterious effects to their body as the result of exposure to cosmic rays and its heavy nuclei component.  So a few days or weeks of cosmic ray exposure beyond the magnetosphere appears to have no significant impact on human health.

However, it is estimated that during a future 6 month journey to Mars, the nucleus of  one out of every three  cells in the human body would receive at least one hit from a cell damaging heavy ion. While most human tissue has the ability to repair itself, this is mostly not true for the neurons of the human central nervous system. So during a  mere six months of relentless cosmic ray exposure, heavy nuclei could potentially destroy a third of the neurons in the human brain-- without any repair or replacement. And rodents exposed to significant amounts of heavy nuclei bombardment have displayed some mental impairment.  So protecting the human brain from significant heavy nuclei exposure during multi-month or multi-year space missions should, obviously, be a priority.

Fortunately, astronauts traveling or living beyond the Earth's magnetosphere for months or for years could easily be protected from the dangers of heavy nuclei with only about 10 centimeters of lunar regolith, or an equal mass of less than 20 centimeters of water or ice.

But cosmic rays would not be the only danger astronauts could experience from ionizing radiation. A major solar storm could expose an unprotected crew to up to 1000 Rem over a short time period. Just 600 Rem of acute radiation exposure can cause radiation poisoning and even death. But 20 centimeters of water or ice would appear to be enough to reduce radiation exposure during a major solar event to well below NASA's 25 Rem per month radiation exposure limit.

Apollo 16 astronaut on the lunar surface (Credit: NASA)

Ionizing Radiation in Space

Interplanetary Space:

73 Rem - annual amount of cosmic radiation in interplanetary space during the solar minimum 

28 Rem -annual amount of cosmic radiation in interplanetary space during the solar maximum 


Surface of the Moon:

38 Rem - annual amount  of cosmic radiation on the Lunar surface during the solar minimum

11 Rem - annual amount of cosmic radiation on the Lunar surface during the solar maximum

Surface of Mars:

33 Rem - annual rate of cosmic radiation on the surface of Mars beneath 16 gm/cm2 of Martian atmosphere during the solar minimum

8 Rem - annual rate of cosmic radiation on the surface of Mars beneath 16 gm/cm2 of Martian atmosphere during the solar maximum

Martian Surface (Credit: NASA)

Ionizing Radiation Exposure Limits for NASA Astronauts for a maximum 3% lifetime excess risk of cancer mortality

25 Rem - maximum 30 day exposure limit to ionizing radiation

50 Rem - maximum annual exposure limit to ionizing radiation 

100 Rem - maximum career exposure limit to ionizing radiation for  a 25 year old woman

150 Rem - maximum career exposure limit to ionizing radiation for  a 25 year old man

175 Rem - maximum career exposure limit to ionizing radiation for  a 35 year old woman

250 Rem -maximum career exposure limit to ionizing radiation for  a 35 year old man

250 Rem -maximum career exposure limit to ionizing radiation for  a 45 year old woman

325 Rem -maximum career exposure limit to ionizing radiation for  a 45 year old man

300 Rem -maximum career exposure limit to ionizing radiation for  a 55 year old woman

400 Rem -maximum career exposure limit to ionizing radiation for  a 55 year old man

NASA's annual limit for radiation exposure is 50 Rem. But the lifetime exposure limit for a 25 year old woman is only 100 Rem. Philosophically, I don't believe  that  a single space mission should ever end the extraterrestrial  career of a young individual. So the radiation shielding levels proposed here are designed to limit total cosmic ray exposure during an entire mission to less than 50 Rem.  A rotating interplanetary habitat module exposing astronauts to less than 25 Rem per year during an interplanetary journey would require nearly 50 centimeters of water to protect against cosmic radiation and major solar events. The internal shielding requirement for the inhabited areas for two rotating SLS fuel tank derived habitat modules would require nearly 240 tonnes of water shielding. This water shielding could be provided from lunar water resources shuttled to an interplanetary space craft located at one of the Earth-Moon Lagrange points.

ETLV derived Reusable Water Tanker Lunar Shuttle

Shielding astronauts below the 5 Rem per year requirement for terrestrial radiation workers in the US would require approximately 50 centimeters of iron shielding  or at least 4.5 meters of water. A rotating space station with two SLS hydrogen fuel tank derived habitat modules would require nearly 1900 tonnes of internal iron shielding. Fortunately, there's no shortage of iron ore in the lunar regolith. So exporting regolith bags heavily enriched with iron to shield rotating space stations located at EML4 or EML5 shouldn't be too difficult-- especially with reusable transport vehicles with replaceable CECE engines.

ETLV derived Reusable Lunar Regolith Shuttle

50 centimeters of water shielding would probably make it prohibitive to launch manned interplanetary vehicles from LEO.  The delta-v requirement to travel from LEO to Mars capture orbit would be around 5.2 km/s. However, the cheapest fuel source for an interplanetary vehicle would be from the Moon's low gravity well rather than from the huge gravity well of the Earth. The delta-v to LEO from Earth is over 9.3 km/s while the delta-v from the Moon to one of the Earth-Moon Lagrange points is less than 2.6 km/s. So it would  be cheaper to fuel the interplanetary vehicle at one of the Earth-Moon Lagrange points rather than at LEO.   The delta-v budget for traveling from an Earth-Moon Lagrange point to Mars Capture Orbit would be less than 2 km/s vs the 5.2 km/s delta-v of launching an interplanetary vehicle from LEO to Mars Capture Orbit.

Lunar Regolith Habitat with automatically deployed regolith wall. A similar habitat could be used to protect astronauts from cosmic radiation on the surface of Mars.

On the surface of the Moon or Mars, humans would be exposed to only half the amount of cosmic radiation thanks to the natural mass shielding of being on a planetary surface.

Interior configuration of a Regolith Habitat for the Moon or Mars

Two meters of Lunar or Martian regolith would be enough to lower annual radiation exposure below 5 Rem. The metallic shells of the pressurized habitat and the outer regolith wall would add additional radiation protection.   However, two meters of iron enriched regolith shielding could reduce radiation exposure within the Lunar or Martian habitat to terrestrial levels, if desired.

Links and References

Lifetime Risk of Developing or Dying From Cancer

Oxidative stress

What is Oxidative Stress

Biological consequences of oxidative stress-induced DNA damage in Saccharomyces cerevisiae

Oxidative DNA damage: mechanisms, mutation, and disease

THE HIGH BACKGROUND RADIATION AREA IN RAMSAR IRAN

Natural Radiation

Fueling our Nuclear Future

Space Faring The Radiation Challenge


Cosmic Ray Interactions in Shielding Materials


Galactic Cosmic Radiation Leads to Cognitive Impairment and Increased Aβ Plaque Accumulation in a Mouse Model of Alzheimer’s Disease

Radiation Protection for Human Missions to the Moon and Mars


Radiation Hazards and the Colonization of Mars: Brain, Body, Pregnancy, In-Utero Development, Cardio, Cancer, Degeneration


Mission to Mars: Health Risk Mitigation

(Rich Williams: NASA Chief Health and Medical Officer)


Radiation Effects and Shielding Requirements in Human Missions to the Moon and Mars


Regolith Biological Shield for a Lunar Outpost from High Energy Solar Protons


Lunar Station Protection: Lunar Regolith Shielding


Radiation exposure in the moon environment


Utilizing the SLS to Build a Cis-Lunar Highway

In the Light of a Watery Moon

NASA's Future Water Prospecting Robot for the Moon

Dr. Paul Spudis Discusses Latest Lunar Discoveries