Nextbigfuture commenter, Goatguy, did interplanetary travel calculations to check the numbers that I had cited. I had estimated that 1 meter of water surrounding astronauts would be enough to protect them from space radiation. Definitely, 5 meters of water would be enough.
Mass production of SpaceX Starships is likely by 2030. There is a Raptor engine factory that will make 4000 engines per year. Each Super Heavy Starship stack would use about 40 engines. Full production is 100 Super Heavy Starships per year.
Each SpaceX Starship has 1000 cubic meters of volume. One hundred of them would have 100,000 cubic meters of volume. Ocean going cruise ships are measured in terms of gross tonnage (GT), which is a measurement of the internal volume of a ship. The average cruise ship has a gross tonnage of 120,000 GT.
300 meters by 30 meters by 11 meters would be 99000 cubic meters. The picture above is of Space Shuttle External fuel tanks arranged into a rotating space station configuration. There are about 24 tanks. Space Shuttle fuel tanks were similar in size to the SpaceX starship. There are about 20 tanks going around the outside ring and about 4 bundled in the center. If there were 100 Starships, then there could be a triple ring going around the outside and bundles of 25 in the interior. Three stack of eight bundled together. There could be Super Heavy Boosters or other engines in the central part.
If we wanted to reduce the surface area, then a 50-meter-tall cylinder with 50 meters of diameter would be almost 97000 cubic meters. The outer one meter would be about 12000 cubic meters. If we wanted to reduce weight, then we could move the water shield from the outer wall to an inner set of walls or around “safe-room” living areas.
Each SpaceX Starship is 50 meters tall and 9 meters in diameter. The least surface area for 100 would be to pack them in a single-layer bundle.
There could be more of the Starships stack end to end in the central area. It depends how one would want the weight distributed around propulsion or for a rotating system for centrifugal force in place of gravity.
There are some other configurations where one could imagine using Starship modules to form a larger structure.
If mass production is further scaled then 1000 Super Heavy Starships per year could be made. There could be a stream of say forty-two Mars Cyclers in constant cycling orbits of Mars and Earth. Mars cyclers would travel from Earth to Mars in 146 days (4.8 months) and spend the next 16 months beyond the orbit of Mars. This would be almost 21-month cycle. 42 cyclers would mean they would be two weeks apart. There would be nine or ten between Earth and Mars and 32 beyond the orbit of Mars.
Detailed Calculations of Space Radiation and Shielding
Earth’s atmosphere, with a ground-level pressure of about 100,000 pascals (N/m²) corresponds to (÷ 9.81) = 10,200 kg or 10.2 tons of atmosphere ‘above our heads’ per m².
Placing 1 ton of water between the inside and outside of the proposed radiation-proofed capsule is ¹⁄₁₀th that radiation protection. Space radiation consists largely of 4 components: solar protons, neutrons, gamma/x-rays and so-called cosmic rays.
Is a particularly good estimator of actual space radiation in inter-planetary space. Apologies for being highly technical, but ‘the answers and concerns’ are well laid out. In a nutshell, 50 cSv (or 50 RAD, which are dose-by-absorption-energy adjusted) per year is probable during Solar Minimum.
And what does 1.0 m of H₂O shielding do? It definitely quenches the lowest energy GCRs (galactic cosmic rays) as well as ALL protons. Many neutrons succumb too. Around 90% of them. From another source
Beating 1 Sievert: Optimal Radiation Shielding of Astronauts on a Mission to Mars
Key Points on Optimal Shielding
* Space missions to Mars should be scheduled to be launched during solar max
* Optimal spacecraft shielding is ~30 g/cm2, which allows long-duration flights of ~4 years
* Increase of shielding thickness beyond ~30 g/cm2 results in dose increase
* The best time for launching a human space flight to Mars is during the solar maximum, as it is possible to shield from SEP particles. Our simulations show that an increase in shielding creates an increase in secondary radiation produced by the most energetic GCR, which results in a higher dose, introducing a limit to a mission duration. We estimate that a potential mission to Mars should not exceed approximately 4 years
Continuing Goatguy Calculations
We get a pretty good summary of the effectiveness expected of shielding. Essentially, it cites that too much shielding is counterproductive, since the incoming GCRs spall off all sorts of secondary particles, radiation in their own right. In any case, compared to Earth’s atmosphere, shielding walls (however you want to look at them) are far inferior to air itself.
50 cSv/year. That’s the shielding take-away, with perhaps 50% less having water shielding over aluminum. Hydrogen is a good thing. 1 m/m² thickness corresponds to 1,000,000 g ÷ 100² cm = 100 g/cm², which is arguably adequate.
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Léts see if the cylindrical figure is right. Volume of cylinder is ¼π𝒅²𝒍 where 𝒅 = 3.5 meters, and 𝒍 = 20 meters. So, the area of a pair of cylinders subtracted (smaller from larger) gives the total water. 1 meter thickness, uniformly spread out.
Vol₁ = ¼π⋅3.5²⋅20
Vol₁ = 192 m³
Vol₂ = ¼π⋅(3.5 ⊕ 2)²⋅(20 ⊕ 2)
Vol₂ = 522 m³
ΔVol = 330 m³ = 330 tons.
Excellent! The math works.
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I think underestimating the transit cost of all that shielding is the real problem to solve. If we recall Tsiolkovsky’s Rocket equation
ΔV = Isp • G₀ • ln( M₀ / M₁ )
Where M₁ is the end-of-acceleration total ship+fuel+etc mass, and the M₀ is the beginning … and if one considers that some 70% of the mass needs to drop on the outbound acceleration leg, leaving 22% left for deceleration, and until we come up with more energetic propulsion means, that Isp’s greater than 2,000 (ions) with nuclear power are optimal, then:
ΔV = 2,500 × 9.81 • ln( 100% / ( 100% – 70% ) )
ΔV ≈ 30 km/s
Sounds good, right? It is. But getting to Mars is a long way to go … something on the order of 100,000,000 km. Just a linear fit to that is 100×10⁶ ÷ 30 = 3.3×10⁶ seconds (40 days) But … there’s Sol’s gravity well to overcome. Sling-shots around Luna might help some, but sling-shots around Venus wouldn’t really save a whole lot of time, and exacerbate the approach problem (deceleration). Turns out more like a 200 day trip.
And there’s the problem of creating enough nuclear power, safely enough, to accelerate 70% of the rest-mass of the whole shebang, quickly enough, to not ruin the time-savings in so doing. 200 to 300 days. A year.
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In that year the cosmonauts would almost irreducibly absorb some 50 cSv, which is about ⅓ of the NASA and ESA recommended lifetime exposure limit. Depending as the article said on ‘age and physical condition’.
Goatguy agrees with Brian Wang: the possibility of making the trip in a reasonable amount of time, with a reasonable exposure to GCR and ESR (solar) has been well worked out. The real gotcha is coming up with the energy-production plan and engineering the system.
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And what would be the energy production needed? Let’s say that 5,000 ton interplanetary cruiser. It needs to accelerate 70% of its rest mass (70% × 5,000,000 kg = 3,500,000 kg) to accelerate. At an Isp of 2,500 (equiv to 25,000 m/s) at maybe 70% electrical-to-ion efficiency (VASIMR), then you have
2 × ½ • mv² = mv² = 3,500,000 kg × 25,000² → 2×10¹⁵ joules or 600,000 megawatt-hours
of electrical input energy. Nuclear power. If its to be produced over 4 months (⅓ the trip), continuously, then thats 600,000 MWh / (4 × 30 × 24) = 200 MW of specific output energy. That’s a pretty potent nuclear reactor, but not ridiculous.
Feels do-able, to this old physics goat. The actual acceleration would be 30,000 m/s / (4 × 30 × 24 × 60 × 60) = 0.0029 m/s² or about 0.30 milli-G
Imperceptable. Stately. But effective over months. Never stops, basically.
Brian Wang is a Futurist Thought Leader and a popular Science blogger with 1 million readers per month. His blog Nextbigfuture.com is ranked #1 Science News Blog. It covers many disruptive technology and trends including Space, Robotics, Artificial Intelligence, Medicine, Anti-aging Biotechnology, and Nanotechnology.
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So Starship isn’t the vessel that can bring large number of colonists to Mars, regardless of what Elon Musk said and what Brain repeated.
However it can bring first explorers and maintain a small almost constant presence there.
There is no need for 100 passengers per Starship. If you send just 6 explorers and the leaving area will be a disc with 6m diameter and 2m height, you need just 90 m^3 of water for 1m thick water protection shield.
Also the explorers ship needs to carry only supplies for the 6 explorers for the duration of the trip. All supplies for the time on Mars and for the return trip, will be delivered by unmanned cargo ships.
Before first human are sent there, SpaceX need to prove several things:
1. They can land cargo ships there
2. They can use robots to generate fuel, air and water from Mars soil.
3. They need to send at least one Starship in Human Passenger configuration, with life support systems, solar power and everything needed to get the first explorers in good shape there and back, only without any real passengers only dummies representing them.
4. They need to send the human Starship back to earth.
5. They need to show that proper conditions for life support (including low radiation) where maintained for all the trip 3 stages (there, on Mars and return).
Maybe if everything goes OK, they can send the first cargo ships on Q4 2026 window, and unmanned Human carrier at end of 2028, and first explorers at Q1 2031.
You shouldnt go there to occupy it, mine it for resources or negatively impact it in any way. Only rejeuvenate it for its own health. ROBOTS will understand that. People will not.
You shouldnt go there to occupy it, mine it for resources or negatively impact it in any way. Only rejeuvenate it for its own health. ROBOTS will understand that. People will not.
Not so sciency information here but when i was a kid i had a very real dream about mars as if i was in its orbit. I knew exactly what it was and never knew anything about science or space. It was precious and alien like another mans testical or something. You shouldnt go there to occupy it, mine it for resources or negatively impact it in any way. Only rejeuvenate it for its own health. ROBOTS will understand that. People will not.
What are delightful discussion!
Regarding the radiation protection issue, I favor of an army of robots to the moon first, and then to Mars, to build all the facilities necessary to support human colonization. Humans to follow.
However, my main reason for responding is to put forth an idea that, while not pointedly about radiation protection, would inevitably impact the issue.
First, it seems inescapable to logic that a moon base should be built first to facilitate the project to colonize Mars. Launching from the moon is substantially easier then from the Earth. The moon has no atmosphere and the gravity is 1/6 that of Earth. Additionally, there is a matter little discussed regarding the advantages of launching from the moon: The moon is tide-locked to the Earth, which keeps all locations on the moon in a static position relative to the Earth-Moon Lagrange points. This means that an appropriately sited, permanent launch facility on the lunar surface — electromagnetic linear induction or sling launch — can be built that will always be in the correct position for a launch to the L1 Lagrange point. That would allow the transport of substantial quantities of building materials from the lunar surface to the L1 point for the construction of a transit station for Mars colonization and further solar system exploration.
This concept is nothing new, and I expect extensive work has already been done to develop the concept. I mention it here to lay the groundwork for what comes next.
There’s an extensive body of work regarding innovative methods for space propulsion: solar sails, ground-based laser-powered propulsion, others (?). I’d like to offer one of my own, which I have not heard or read of elsewhere. (I’d like to believe this is original with me, but since I haven’t read everything ever written about space propulsion, I prefer to be a bit humble.)
I came up with this idea and then shared it with my friend Doug (aka “Spike”) Jones, legacy member of the Extropians list and Lockheed Martin rocket scientist. We played with it for a while before returning to real life.
I call it the Davis-Jones Tether and here’s the basic idea:
First, it dispenses entirely with conventional reaction mass expulsion as the mechanism by which to propel the spacecraft. Instead, the spacecraft is attached by a tether to a counterweight, this system is then spun up at the launch site until the spacecraft achieves the necessary tangential velocity to take it to its destination, at which point the tether is disconnected and the spacecraft is “launched”. Solar energy for “propulsion” — ie spinup — is provided in place at the L1 (or L2) launch site. This substantially reduces the need for — and the cost and mass of — onboard fuel and propulsion systems (with the exception of mid-course correction capability). This mass saving makes room for more cargo mass, or for more adequate radiation shielding for human transit.
There are a raft of details which, for the sake of brevity I’m skipping over here, such as the need for a counter-rotating system at the “launch” site to zero out the angular momentum of the system, and the variability of tether length and counterweight mass to perhaps find some practical use/destination for the “counterweight”. And a bunch more.
Human beings of necessity come from the good Old Terra Firma. Everything else can come from the moon. And as others have noted, robots don’t need no shielding except perhaps around their electronics.
I’m interested to see what you guys have to say.
Ad astra.
I had an alternative possibility, but ChatGPT doesn’t think it’s practical. Agree or disagree?
could an artificial magnetosphere be created for a spaceship traveling to Mars to protect the passengers from cosmic rays?
ChatGPT
Creating an artificial magnetosphere to protect a spaceship traveling to Mars from cosmic rays is a fascinating concept, but currently, it poses significant technological challenges.
A magnetosphere is a region around a celestial body, such as Earth, that is influenced by its magnetic field. Earth’s magnetosphere acts as a shield, deflecting and trapping charged particles from the solar wind, including cosmic rays, away from the planet’s surface. However, replicating this protective mechanism for a spaceship is highly complex.
One potential approach for creating an artificial magnetosphere involves generating a magnetic field around the spaceship. This could be achieved using superconducting magnets or electromagnetic coils. However, there are several challenges to consider:
Power requirements: Generating a magnetic field strong enough to deflect cosmic rays would require a significant amount of energy. The power source would need to be robust and efficient to sustain the magnetic field for extended periods.
Size and weight constraints: Installing the necessary equipment to generate a magnetic field would add considerable weight and size to the spacecraft, impacting its overall design, launch feasibility, and payload capacity.
Technical feasibility: Developing superconducting magnets or electromagnetic coils that are both powerful and durable enough to withstand the harsh conditions of space travel is a significant technological hurdle.
Magnetic field shape and direction: Cosmic rays come from various directions in space, so designing a magnetosphere that can effectively shield the spacecraft from all angles is challenging. The shape and orientation of the magnetic field would need to be carefully engineered.
While the concept of an artificial magnetosphere for spacecraft is intriguing, current technology and our understanding of magnetic fields are not yet advanced enough to create a fully functional and practical magnetosphere for protecting astronauts on a journey to Mars. However, ongoing research and advancements in materials science, energy generation, and magnetic field technologies may contribute to future possibilities in this area.
The real issue here is that idea of inflating the field using plasma.
In theory it would work in a complete vacuum, or one where the background plasma/gas was at rest relative to the shield. But in the presence of the solar wind, I suspect that beyond a certain point you’re just blowing plasma bubbles that get blown away in the wind.
The idea needs some real world testing outside Earth’s magnetosphere before being taken seriously.
So you are basically here to post ChatGPT responses?
Assuming that the people are living in the Starship for the trip, and the cycler only provides shielding… The fuel tanks on the Starship provide adequate shielding on that end.
The payload bay is 17M long by 8m diameter, this is the volume we actually need to shield.
For one Starship, the can shield design with one open end has a volume of 559 cubic meters. If you hexagonal dense pack 7 Starships, though, that drops to 272 cubic meters per Starship. Continuing to stack more next to each other provides diminishing returns.
So your cycler would probably consist of honeycombs of shielding that you slide the starships into, payload bay first, leaving the tankage end exposed. Ideally opposing pairs of these, connected by tethers, permitting rotation for gravity. Put the reactor, radiator, course correction engines, on the central shaft, and have pairs of these spinning in opposite directions for conservation of angular momentum. All that stuff would be dwarfed by the mass of the shielding. All told, I think you’re looking at two launches worth of payload per Starship docking bay to construct this thing.
It would probably actually save on total mass to orbit, though, because the cycler would be on a low energy trajectory, not having the same need to minimize trip time/exposure.
The downside of the cycler approach is that all the Starships that use it have to launch in a narrow launch window as it goes by. Gonna get pretty hectic about the time it comes by, up there.
The system detected the duplicate comment and warned me but it managed to post it again anyway.
Yes.water is a great radiation shield,it is the H atoms, but that is not the way to go to Mars, nuclear thermal propulsion, NTP , gets you there in 5 months. Plastic also has H atoms.
So,NASA knows this and already has companies with contracts doing research. We can use TRISO fuel, with H2 as propellant.
Starship can ship cargo if it turns out cheaper. With a hybrid system we can also use an ion system, for constant thrust.
We’re trying, Edwin. We’re trying very hard.
All this effort and extra engineering needed to move some meat-sacks to mars. If you just send an army of robots, all these problems go away.
But…. WE want to go to Mars. Robots are already there, and they don’t care if they are on Mars, the Moon or even the Earth.
Agreed. But if you could send a dozen teslabots, or one human plus food supply, water, living space, radiation shielding etc… I don’t know where the cost/benefit equation balances out.
What I want to see on Mars is robots that are capable of building and staffing the physiotherapy clinch that humans will need to recover from the trip.
Well we aren’t trying to ensure the continuity of robots.
What I want to see on Mars is robots that are capable of building and staffing the physiotherapy clinch that humans will need to recover from the trip.