New post up at Air & Space discusses events at the recent annual meeting of the Lunar Exploration Analysis Group (LEAG), including a report on Congressman Jim Bridenstine’s great speech to the attendees (which I urge you to read in its entirety). Comment here, if desired.
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These are obviously the days to get busy, and I hope you are prepared for it, Dr. Spudis! The sentiment, at least from the outside far far away, is that this is it: If the new administration doesn’t prioritize the Moon, it will be delayed by another decade. Again.
In addition to the relatively near-term economic returns from Lunar development, by benefiting what is today already profitable in Earth’s orbit, and the value of cis-Lunar development for national security in competition with China, I suggest you also consider using language he as a construction businessman recognizes. Such as the Moon being the last frontier free real estate up for grabs in competition with the Chinese. Maybe referring to private space Bigelow style “Hotels” in cis-Lunar space and constructing bases on the Moon. Founding and constructing a new space infrastructure. He’s spoken out strongly for nuclear power, so it’s benefits for spaceflight might appeal. Bringing the rationale of space policy down to his worldview and language.
I sense that there’s a new opening here to accomplish something other than a new crazy won’t-happen asteroid boulder retrieval thingy that wastes another 8 years. The president presumably doesn’t know or care much about space, it is up to the lobbyists to define the new space policy. You, Dr. Spudis, should have the weight to get a personal talk with the next president to persuade the master persuader about how to win that space thing. You should be one of his official space policy advisers.
Fluff,
Thank you for your comments. Indeed, I think that we do have a glimmer of hope, but right now, it is only a glimmer. I am contacting people and spreading the gospel of the Moon as best I can. I urge you and other readers who are likewise inclined to write their Congressmen, Senators and even the President-Elect and advocate the re-insertion of the Moon as the near-term goal beyond LEO.
Couldn’t hurt.
Hopeful news.
As far as it being a slim hope, that coincides with dialog from a movie I watched over the weekend.
Two characters are talking about a project. One says there is only a slim of hope for success.
The other replies – “Every time I have met Hope, it has been on a diet.”
Congressman Bridenstine’s talk was indeed impressive. While there have always been members of congress who supported space development he is the first (at least in a long time) who seems to understand the basic technical issues involved. Interestingly the “scuttlebutt” says he has term limited himself and this will be his last term in the House, but that he is actively campaigning to get the job as NASA Administrator.
Do not know if he has the administrative skills or would have the political connections with the incoming administration to make a successful NASA Administrator but at least “his heart is in the right place”.
Also NASA apparently announced at a recent meeting of the Human Exploration and Operations Committee of the NASA Advisory Council that they have not costed the Mission to Mars past the Cis-Lunar Space Phase. That cannot be helpful to the Mars first and only crowd either.
One other point, the Chinese are not the only players in the Lunar game. In spite of their current economic difficulties, the Russians are continuing to press forward with development of infrastructure to support Cis-Lunar development.
http://www.russianspaceweb.com/imp-shm.html
The decisive argument might be:
“- It’s a great tower you have created here in Manhattan! The only thing above it beyond the sky is indeed the Moon. But what if Jeff Bezos of the NY Times built a hotel on the Moon, blinking down at you. Would you enjoy the view from this roof top as much then?”
😉
And he could easily beat your golf records there too. On yuge golf courses with lots of bunkers.
Now, do you, Mr POTUS, realize how space flight is important?
We currently live in a rather turbulent political environment where there are deep divisions between the left and the right in this country. But there has been strong bipartisan support for NASA over the last few decades by both of the major political parties. And America could certainly use a powerful symbol of bipartisanship right now!
Our stagnating human space program could easily be fixed by simply focusing on a near term goal that could capture the public’s imagination while also aiding us in our long term pioneering and private commercial exploitation of the solar system. Returning to the surface of the Moon to exploit the polar water ice and other regolith resources is obviously the most logical near term goal!
The biggest flaw with the old Apollo program, IMO, is that it was never set up to be a pioneering program. It was an effort designed to explore a few areas on the lunar surface but not to establish a permanent human presence on the lunar surface. There were a few proposals to do such a thing but it never received very much support from Congress and the Executive branch.
A permanent American presence on the surface of the Moon could have assured America’s absolute technological and economic dominance within cis-lunar space and beyond. And America would probably be a substantially wealthier and more technologically advanced nation today– if we had.
Returning to the Moon has to be more than just an expensive stunt! It has be be coupled with the exploitation of lunar ice resources and the production of propellant and the deployment of propellant depots within cis-lunar space for reusable extraterrestrial vehicles.
I also believe that the exploitation of lunar resources has to be an integral part of any sustainable architecture designed to send human crews safely to Mars and beyond.
Marcel
If Mars could be finally and forever exposed for the red herring it is in any dialogue about space exploration it would be a huge step forward. I find it ever more difficult to accurately express my complete disgust and disdain for anything having to do with that rock.
I’m not sure that Lunar resources will be useful for Mars exploration. A fuel factory on the Moon represents quite a big overhead upfront investment and risk. Reusable launchers directly from Earth is a formidable competitor. You need a very ambitious Mars program in order to make Lunar resources helpful. Today one can lift fuel from Earth to LEO for about $3,000 per kg, with costs certainly going lower. And that is highly purified super cooled fuel in tanks and with rocket engines ready to go interplanetarily. So 100 tons costs about $0.3bn, about one tenth the budget of the Curiosity rover. What does a Lunar fuel factory cost until it delivers that to a rendezvous with a mission to Mars? Even if one screws this by a factor of two or four, I still wouldn’t buy that stock expecting a profit in my lifetime. I doubt the Moon will play a role in Mars exploration during the next several decades.
And for servicing old satellites in Earth’s orbit, I think it is only viable for uniquely valuable assets like the Hubble Space Telescope or a crewed space station. Simply because the technological development makes the economic lifetime of communication and Earth observing satellites too short to motivate (risky) refueling instead of simply paying the $3,000 extra per kg of fuel at the launch to begin with. A ten year old satellite isn’t worth much any longer compared to launching a new one. The economies of scale and time speak against using the Moon as a cis-Lunar gas station. It also has to compete against stuff like Solar sails and SEP for station keeping.
I think that Lunar resources will be used for Lunar development, and that this is the best way to argue for a Lunar space program. The Moon for the sake of the Moon and Earth. A glance at the sky, day or night, reveals that there’s something up there, looking like a half eaten rice biscuit. And it ain’t Mars. But it’s got something intimately to do with us. Even a (new) politician should be able to follow this line of reasoning. They too know about PMS.
Fluff,
Two comments in regard to your points 1 and 2.
The idea of using lunar propellant for a human Mars mission is not to enable a single mission — it is to enable continuing, ongoing access to Mars (and any other destination that intrigues us). I do not believe any cost/benefit analysis is valid, simply because we don’t know these numbers very well. But the real goal of going to the Moon in the first place is to create new spacefaring capabilities and producing propellant for use on deep space missions is one of our objectives.
In regard to “satellite servicing”, you’re right that the current crop of satellites are not amenable to servicing, but future ones — large, distributed systems in cislunar — could be. It’s not a question of technological obsolescence; it’s the idea that we cannot launch from Earth satellites large enough and capable enough to meet all future needs. We need to be able to assemble large comsats and other facilities in deep space using people and machines. The construction of ISS shows the new paradigm.
If I can be allowed to make a couple of additional points on those subjects.
(1) Launch of cryogenic propellants from Earth.
“And that is highly purified super cooled fuel in tanks and with rocket engines ready to go interplanetarily.”
On of the problems for the (much derided by new space advocates) launch and a half architecture selected for the Constellation Systems Lunar Program was the need to oversize the Earth Departure Stage (EDS) tankage to allow for boil off while awaiting crew launch. This caused the stage to need to be much heavier than other wise required.
For a Mars Mission the problem becomes even more of a problem. Unless the Earth launches can take in a very short period of time the first deliveries will be significantly dissipated by the time the last fuel loads are delivered.
Adding in extra requirements for the fuel to be “super cooled” by which I assume Fluff to mean SpaceX’s “super cooled” Methane/LOX proposal further complicates the issue.
Remember in reality SpaceX can only claim (with some difficulty) to keep the LOX “super cooled” for about 30 minutes on the ground.
(2) Satellite Servicing.
There is an additional issue to increased capability. Using expendable payloads that are then abandoned and replaced is already causing a “space junk” problem. Eventually that issue in addition to the need for increased capability is going to need to be addressed. Both of those issues will drive towards large/centralized/assembled in orbit applications platforms that would benefit greatly from use of Lunar ISRU.
I agree and somewhat understand that Lunar resources would transform the “ecosystem”, so to speak, of space flight economics in unforeseen ways. In combination with miniaturization of satellites and Solar sails and inflatables who knows what’s next. Those are developments that seem to conspire to give cis-Lunar space development even better competitive advantages than interplanetary exploration. Today’s cost structures will certainly not be applicable for long term space flight. But I doubt this will change substantially before the first crewed mission directly from Earth and LEO to Mars in the 2030s. And after that first experience it might be concluded that Mars isn’t a good place to “sustainably colonize” this century after all. I wouldn’t like to see the ambitions for the Moon lose interest because of that learning process. The Moon is (literally) about Earth, not about Mars.
One of the few things in all of this that certainly will remain for ever, is the vicinity of the Moon. As it gets integrated with our Earthly economy, it’s basically just about real estate. And real estate is said to be about three things: Location, location, location. Well, the shipping business is also only about three things: Relocation, relocation, relocation. The Moon wins however one turns it.
“I wouldn’t like to see the ambitions for the Moon lose interest because of that learning process. The Moon is (literally) about Earth, not about Mars.”
I do not think we really need to be debating that point.
I am not trying to speak for him, but I believe if you look through Dr. Spudis’s writing, you will note he advocates the development of Cis-Lunar Space as a goal with many purposes the first of which is development of large assembled/maintainable applications platforms for direct benefit to Earth.
Then later developing interplanetary capabilities for anywhere in the Solar System (including but not limited to Mars).
I know that is what I favor.
In order to have a sustainable outpost on the Moon, you’re already going to need a propellant factory (electrolysis plant plus cryocooler) on the lunar surface and probably at EML1 to fuel reusable extraterrestrial landing vehicles operating between EML1 and the lunar surface.
A sustainable Mars architecture would probably require propellant manufacturing water depots located at EML1 and High Mars Orbit, plus on the surface of Mars.
You really don’t need to use methane in order reduce propellant boil-off for a long interplanetary journey since NASA has already invented cryocoolers that can utilize electric power from solar panels to re-liquify ullage gasses.
You can also substantially reduce propellant requirements for entering Mars orbit by dumping the space habitats massive water shielding just before the final trajectory burns. Water for the habitat can then be replenished by the orbiting water/propellant depot once the interplanetary spacecraft is in orbit.
So water and propellant for the return trip from Mars to cis-lunar space will probably also come from the Moon.
Mining water from the lunar regolith at the poles and on most regions on the martian surface may only require the flip of a switch from mobile microwave robotic vehicles that capture the vaporized water from the regolith, depositing the vapor in cold traps that convert it back into water ice for later liquefaction and utilization.
Marcel
Marcel, you seem to be trying to inextricably link the Moon and Mars when the two have nothing to do with each other.
“You really don’t need to use methane-”
Nothing can push the required kiloton range cosmic ray water shields Beyond Earth and Lunar Orbit (BELO) except nuclear energy and only one form of nuclear propulsion will work- and that form is not the pathetically inefficient Nuclear Thermal Rocket. Even if chemical propulsion could do the job (it absolutely cannot without a Battlestar Galacta full of propellant) it is a fundamentally bad idea to expect “solar powered cryocoolers” to successfully maintain several thousand tons of liquid hydrogen propellant for month after month.
Mars is a dead end anyway. No reason to go there. This fantasy that Mars will be some kind of utopian second home for humankind is bizarre in the extreme.
There’s no doubt that the Moon is going to be the economic juggernaut of the solar system in the 21st century.
But lunar resources are also the key to sustainable human space travel beyond cis-lunar space, IMO.
Lunar water and propellant derived from lunar water for reusable LOX/LH2 spacecraft could allow humans to travel to the orbits of Mars, Venus, and even Jupiter.
There’s no logical reason to confine long term human expansion into space– solely to the Moon.
Marcel
I wish you argued for going to the Moon instead of arguing against going to Mars. “Dead end, no reason to go there” is as applicable to the Moon as to Mars.
“The in-orbit maintenance, servicing, and refueling market, already being planned, could be greatly enhanced by an architecture that includes staging nodes, fuel depots, transit spacecraft and lunar landers. – To be clear, satellite servicing and assembly requires a lunar program that is permanent to include long term human habitation, machines, rovers, and resource production.”
In my view, this is re-arranging the deck chairs on the Titanic. I am not saying Bridenstine has it all wrong, I am saying the ship he is trying to launch is doomed to start with. The satellite infrastructure is the problem. Replacing this mess with a few dozen large shielded human-crewed space stations in GEO is the solution. Human technicians can constantly maintain, repair, and upgrade the equipment on these space stations and provide an order of magnitude improvement in both connectivity and reliability.
The critical lunar resource that enables this critical human resource is water shielding to protect the humans (and the telecom systems) from radiation. The ice on the Moon is the key to not only a greatly expanded human presence Beyond Low Earth Orbit (BLEO) in GEO but also the construction of true spaceships capable of multi-year missions to the outer solar system.
“The U.S. government must work to retire risk, make the operations routine, and once again empower commercial companies. This has already worked to an extent in low Earth orbit, and now we should apply this model to cis-lunar space. This is not only appropriate for economic development and to improve the human condition on Earth, but to provide for national security, which is now entirely dependent on space-based capabilities. Every domain of warfare today depends on space.”
I would argue NewSpace has NOT worked to a great enough extant in LEO to be considered feasible. In fact, it has failed by almost every measure to deliver the promised miracle. Improving the human condition on Earth is going to be a state-run public works project on the scale of the Panama Canal and Hoover dam. That project being Space Solar Power as envisaged by Gerard K. O’Neill and requiring Super Heavy Lift Vehicles and lunar resources. The SLS is the only such vehicle actually being constructed at this time.
The preeminent domain of warfare is nuclear. War as it was known from the beginning of civilization ended in 1945 and the struggle for global domination took a new form that has spared humankind from a third world war for over half a century. “Warfare” today is not war- it is….”vastly restrained regional proxy conflict” for want of a better description. National security would be best served by moving the nuclear arsenal onto spaceships (also propelled by nuclear devices) months away from Earth. The only place to assemble, test, and launch these true spaceships is the Moon.
LEO is the worst place to do it.
“It must be stated that constitutionally, the U.S. government is required to provide for the common defense. This includes defending American military assets in space AND commercial assets in space, many of which have and will have a dual role of providing commercial and military capabilities.”
Nuclear energy is the final arbiter in all such contests. A “Nuclear Moon” is inevitable. It must be stated that transporting fissionable material Beyond Earth Orbit should be the main goal of space legislation.
Defending planet Earth from Comet and Asteroid impacts, as well as deescalating the present hair-trigger-launch-on-warning-situation is the over-riding benefit to transforming the U.S. space program and pointing the space agency back at the Moon and building true spaceships.
“Water ice not only represents a critical in situ resource for life support (air and water); it can be cracked into its components, hydrogen and oxygen, to create the same chemical propellant that powered the Space Shuttle.”
What is “critical” is placing humans in space again and for all time (LEO is not really space). The only path to a sustained human presence Beyond Low Earth Orbit (BLEO) are massive water shields derived from lunar ice. Hydrogen is probably not the cislunar propellant of choice due to the difficulty in storing and transferring it in space: the volatiles likely trapped in lunar ice will make the production of methane a better choice.
“From the discovery of water ice on the moon until this day, the American objective should have been a permanent outpost of rovers and machines at the poles with occasional manned missions for science and maintenance.”
Truer words were never spoken! Semi-expendable robot lunar landers that can harvest ice, produce their own propellants, and shuttle water shielding from the surface to wet workshops is the way to quickly establish a long-term human presence in cislunar space. Spinning such water-filled stages with tethers would create Earth gravity and sea level radiation habitats. Mating nuclear propulsion systems with these habitats would create spaceships capable of multi-year deep space journeys.
Very encouraging news. I especially liked Brudenstine saying that, the moment we confirmed lunar polar ice, we should have moved ahead to develop it for a cis-lunar transportation system. Totally agree. Like they say, better late than never.
A focus on the Moon is something that just makes sense. The only thing that really worries me, is
talk from Trump’s space advisors suggesting that duplicate efforts to build launch vehicles should be scrapped, possibly aiming at SLS. Discarding it at this point would really be a huge mistake for many reasons. SLS was never meant to compete with launchers built by private firms. And contrary to popular belief, there isn’t any alternative launcher out there to fill the void if SLS is scrapped (Falcon Heavy included).
Dr. Spudis, do you have any insight about Trump’s advisors views on the subject?
I do not. However, given the strong Congressional support for SLS, I think it unlikely to be terminated.
“The only thing that really worries me, is talk from Trump’s space advisors suggesting …”
Actually, we do not know who Trump’s “space advisors” are (or will be).
The things you are talking about are generally attributed to former Congressman Robert Walker, who has been a Trump supporter and assumed to be on the Trump transition team.
Scuttlebutt as of this morning is that Walker is saying he is not on the transition team.
If true one reason might be that Vice President Elect Mike Pence is now running the overall team and does not want any lobbyist on it. Walker has been a lobbyist, working in the past for (among other entities) SpaceX.
That’s really encouraging to know Joe, thanks for the info. Yes, you’re right, I was referring to comments made by Walker, who according to several space news sites, was advising Trump on space policy during the last leg of his campaign.
The last thing NASA needs right now is another ‘reset’ moment, development-wise.
What NASA needs more than anything else is to “reset.”
The space station to nowhere and its commercial cargo and crew albatross’, the Absurd Retrieval Mission, and the J2M all need to be unceremoniously dumped in the trashcan.
The SLS core production at Michoud needs to be expanded to support a minimum of 6 missions a year while 8 to 10 would be much better and just as easy to accomplish.
The NewSpace “entrepreneurs” who are currently the worst thing to ever happen to space exploration can turn their attention to robot lunar landers and actually do good instead of harm.
Before the upper stage wet workshops and tethers there is that most critical missing piece of hardware to invest in: the pressure fed booster originally specified for the shuttle.
Abandon the dead ends of LEO and Mars and point the agency toward the ice on the Moon.
Effective protection from high energy and high mass Galactic Cosmic Rays (GCR) traveling at significant fractions of the speed of light remains a critical issue for humans doing long missions in Lunar surface exploration vehicles and spacecraft in Deep Space.
To critically understand the relevant issues we should mathematically compare water, aluminum, and iron GCR shields that offer comparable densities of shielding per surface area for the interior of the habitat.
Volume of a sphere = 4/3 x 3.1415 x r x r x r Where r = radius
Assume a spacecraft with a 6 meter diameter spherical habitat that will be shielded by adding a layer of H2O or Al or Fe to provide an effective shielding mass of about 1000 grams per square centimeter of area.
The volume enclosed by such a spherical habitat is:
V = 4/3 x 3.1415 x 3 x 3 x 3 = 113 cubic meters Volume
with 3 = radius of the habitat in meters
If we use a 10 meter layer of water shielding (with a mass of 1,000 kg/m3) around that 6 meter diameter spherical habitat with a 113 cubic meter volume, we get a volume of the shielding material of:
V = (4/3 x 3.1415 x 13 x 13 x 13) – 113 = 9,202 – 113 = 9,089 cubic meters of H2O weighing about 9,089 tones or 9,089,000 kilograms of mass.
If we use Al (aluminum) (with a mass of 2,700 kg/m3) for a layer about 3.704 meter thick of shielding, the Al shielding volume will be:
V = (4/3 x 3.1415 x 6.704 x 6.704 x 6.704 x 6.704) – 113 = 1,262 – 113 = 1149 cubic meters of Al weighing about 3,102 tones or 3,102,000 kilograms of mass.
If we use Fe (iron) (with 7,840 kg/m3) for a layer about 1.27 meters thick of Fe of shielding, the Fe shielding volume will be:
V = (4/3 x 3.1415 x 4.27 x 4.27 x 4.27) – 113 = 326 – 113 = 213 cu meters of Fe weighing about 1,670 tones or 1,670,000 kilograms of mass.
Obviously it is raising the radius to the third power in the volume of a sphere equation that causes the dramatic rise in the volume (and thus also mass) that occurs with the layers of the not so dense GCR shielding materials.
A not so dense material such as H2O must be much better on a mass per square centimeter basis in order for it to overcome its obvious flaw of not being dense. Spaceship and Lunar surface vehicle design engineers will be mostly concerned about the total mass of an effective GCR shield for a habitat.
And, since protons produced in the thick GCR shield and spaceship, or surface vehicle, are the most essential risk issue for astronaut health, it is worth noting again:
“For a given thickness, iron outperforms lead by a factor of 5 and hydrogenous materials on average by a factor of 20, making it the shielding material of choice for neutrons above 20 MeV.”
From: Page 76 of ‘Cosmic Ray Interactions in Shielding Materials PNNL-20693 Prepared for the U.S. Department of Energy under Contract DE-AC05-76RL01830’ By E Aguayo, RT Kouzes, AS Ankney, JL Orrell, TJ Berguson, and MD Troy July 2011
At: http://www.pnnl.gov/main/publications/external/technical_reports/PNNL-20693.pdf
Note:
“CR secondary particle shower species, especially neutrons, dominate effects on electronic systems and human health at high shielding mass”
From: ‘Practical Applications of Cosmic Ray Science: Spacecraft, Aircraft, Ground Based Computation and Control Systems and Human Health and Safety’
By Steve Koontz – NASA, Johnson Space Center, Houston, Texas Spring 2015
Graded-Z shielding is also an option worth considering.
I do make lots of errors. Corrections to my logic, science, and math would be appreciated.
Eugene N. Parker is the world’s leading expert on interplanetary gas and magnetic fields. His 2006 Scientific American article drives most space enthusiasts into a state of outraged denial. It is, however, so far the best explanation of the radiation problem and the solution. As he relates, the heavier elements make poor shielding because they generate so much secondary radiation (“shrapnel”) while hydrogen-rich lighter compounds and distance efficiently break down the heavy nuclei fragments.
“The relatively few heavier nuclei among the cosmic rays do as much or more damage than the protons because their ability to break bonds is proportional to the square
of their electric charge. An iron nucleus, for example, does 676 times more damage than a proton does.
To match the protection offered by Earth’s atmosphere takes the same one kilogram of shielding material per square centimeter, although astronauts could comfortably make do with 500 grams, which is equivalent to the air mass above an altitude of 5,500 meters. Any less would begin to be counterproductive, because the shielding material would fail
to absorb the shrapnel. If the material is water, it has to be five meters deep. So a spherical water tank encasing a small capsule would have a mass of about 500 tons. Larger, more comfortable living quarters would require even more.Water is commonly proposed because astronauts would need it anyway and because it is rich in hydrogen. Heavier elements make less effective shields because the extra protons and neutrons in their nuclei fall in one another’s shadows, limiting their ability to interact with an incoming cosmic ray. To increase the hydrogen content, engineers could use ethylene (C2H4), which has the further advantage that it can be poly merized to polyethylene, a solid, thereby avoiding the necessity for a tank to contain it. Even so, the required mass would be at least 400 tons-
Pure hydrogen would be lighter but would require a heavy pressurized vessel.”
Yikes!
“And, since protons produced in the thick GCR shield and spaceship, or surface vehicle, are the most essential risk issue for astronaut health, it is worth noting again:”
That should have been written as:
“And, since neutrons produced in the thick GCR shield and spaceship, or surface vehicle, are the most essential risk issue for astronaut health, it is worth noting again:”
The “protons” should have been “neutrons”. Sorry about my confusing writing mistake!
The large cascade of neutrons is apparently the main issue with using thick shielding.
A meter, or more, thick layer of Iron is a good shield against the cascade of high energy neutrons caused by the heavy nuclei among the cosmic rays hitting into thick shielding.
Due to its density and because it is the “shielding material of choice for neutrons above 20 MeV” Lunar iron might become quite useful as shielding on the Moon and as an export to Cislunar Space because of its ability to shield against GCR while using much less mass than H2O.
Lunar iron might be layered with another material on the inside and nearest to the habitat to stop neutrons below “20 MeV”.
More research seems to be needed.
Or, instead of acting stupid in order to make up arguments against space flight, one designs the spacecraft such that the astronauts spend half their time in a highly shielded radiation bunker made out of useful payload and the rest of the time next to it. Radiation shielding does not require new physics, and it doesn’t require 500 tons as you here just make up in order to try to convince politicians to never invest in any kind of space flight.
No astronaut has ever been hurt by either radiation or microgravity. Those are red herrings for the space hypochondriacs. Astronauts die because their spacecraft explodes. There are test pilots who don’t care about the theoretical 3% probability of getting cancer sometime later in life for going to Mars, if they do it completely unshielded. They don’t need a nanny to “protect” them from doing what humans do when at good spirits. Your argument is not relevant. It’s just a bad excuse for not going to school today.
Fortunately, there’s no shortage of regolith on the lunar surface for shielding habitats from excessive amounts of cosmic radiation. A couple of meters of lunar regolith should be more than enough to reduce radiation levels inside of a habitat below the legal limit for radiation workers on Earth.
Permanent space stations in orbit around Mars or Venus will have to be equally radiation shielded, from all directions. Because of its high density, lunar iron or iron extracted from asteroids may be the most convenient way to internally shield permanent habitats in space– especially rotating habitats.
Assuming that interplanetary journeys are going to take less than 1.5 years to reach their destinations within the solar system, 30 centimeters of water should be more than enough to protect astronauts from heavy ions and major solar events while also keeping their general radiation exposure well within NASA short term and long term exposure limits.
Marcel