Space architects and experts on intergalactic exploration, Neil Leach and Madhu Thangavelu, are joined by ChatGPT to discuss how close humans are to space travel. What is their prediction on when the first humans could inhabit the moon, or even Mars?
Neil has worked on two robotic space missions. Madhu teaches advanced Space Engineering at USC.
I disagree with Neil about the issue of radiation on human crews in space over the long term.
Many people talk about the technical problem of too much radiation for missions to Mars or long-term operations in space beyond the protection of Earth’s magnetic field. The problem comes from the assumption that we fly in Apollo mission like tin-cans. We can build cruise ships in space with the SpaceX Starship so all of the radiation problems of tiny life rafts go away.
Europe’s space agency talked about the radiation show stoppers for Mars Exploration. Astronauts are exposed to 200 times more radiation on the International Space Station than an airline pilot or a radiology nurse. A human on a Mars mission where the mission did not have radiation shielding would get radiation doses up to 700 times higher than on Earth. Data from ExoMars Trace Gas Orbiter showed that on a six-month journey to the Red Planet an astronaut could be exposed to at least 60% of the total radiation dose limit recommended for their entire career.
The survivability problems for Tom Hanks in the Castaway movie raft are a lot different than a cruise ship with an all you can eat buffet.
A 5-meter thick shield of water around a capsule would weigh about 500 tons. So if we have large reusable SpaceX Super Heavy Starship then the costs of each launch could drop to $3 million. Rapid complete reuse could make daily flights a reasonable possibility.
Radiation on a trip to Mars is about 90,000 R/yr or about 10 R/hour. Reducing that to lower than Earth background radiation would only require a layer of water around 1 meter thick. A Mars vehicle cylinder that is 3.5 meter by 20 meters with 1 meter of water shielding would weigh 330 tons.
Twenty flights to orbit could affordably build a 1000-ton mission to Mars. An even larger Mars cycling space station could be built and re-used. A 5,000 ton Earth-Mars cycler would have plenty of mass for radiation protection. It would be like a cruise ship on Earth.
If those who planned the Dieppe raid kept trying to figure out how to make a 237 ship, 6500 person assault work for D-day they would have failed. Even if they started thinking about fancier, lighter technology. This is what I find annoying when Astronaut Chris Hadfield and others talk about how it will take many decades before we can safely send people to Mars. D-day would be in 2050 or never if we had to figure out how to create a beachhead with 6500 people. It is like trying to solve the large wave problem on the ocean with a Castaway sized raft or vehicle. Just make it cheap to go big and heavy and then problems of being light and small go away.
When we will go out of the solar system in meaningful ways with people? After we have colonized and developed the entire solar system.
We can also use the large plasma structures of the solar system as a means to use the solar wind to bootstrap to 24% of the speed of light. I have that described. I have many other articles on getting nuclear fusion or nuclear fission that uses 100 times less volume. Dense power sources are better for space. Advanced molten salt nuclear reactors could be 50 times more energy dense than current nuclear reactors in submarines.
I have various videos describing how Space development can be vastly different.
Money, profits and scale are keys to when and how things happen.
Human civilization needs to get millions and billions of times more economically powerful to launch meaningful interstellar missions. One possible path is described in this video. Conquering the solar system completely is needed to enable the resources to send out fleets of large colonization ships.
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.
Known for identifying cutting edge technologies, he is currently a Co-Founder of a startup and fundraiser for high potential early-stage companies. He is the Head of Research for Allocations for deep technology investments and an Angel Investor at Space Angels.
A frequent speaker at corporations, he has been a TEDx speaker, a Singularity University speaker and guest at numerous interviews for radio and podcasts. He is open to public speaking and advising engagements.
“They’re demanding that the existing environmental approvals be thrown out and redone, potentially delaying future SpaceX launches for years.”
Sorry for the “downer” post ladies and gents…personally I don’t think it will work out that way. Firstly they will try to frame it as earthly environment vs “crazy” rich man’s (Musk) “mad dream” of colonizing Mars; missing a key element. The key element is Space Force/DOD/SDI; the super heavy wedded to the Starship can deliver 100MT to orbit and will be reusable. Larger sats/stations/structures in orbit would be possible assembled from multiple launches. This would be of enormous value to the Pentagon as far as launching larger, more powerful spy sats; to say nothing of space-borne components of SDI. Just the thing for counteracting Russian/Chinese next generation hypersonic missiles. Large powerful lasers/particle beams /kinetic kill weapons in orbit at last rendered practical/feasible. These things would likely happen concurrent to if not before any significant action colonizing Mars. Taking on Musk is one thing, getting in the way of DOD’s ambitions is quite another; the Pentagon has lots of clout (some would say too much but still).
Most humans only have a few hours of activity per day. The rest they spend seated at desks etc or sleeping. Small spaces inside thick shielding with good VR would mean 90% of time could be spent in well shielded space without too much mass. The obvious solution is using onboard cryogenic tanks and put a small insulated chamber inside them.
Magnetic shielding is another interesting option. There is potentially nice synergy with some fusions rockets – magnetic shielding can be used to enable whole ship to be used as a Giga Volt capacitor to store energy up for fusion ignition schemes – as in F. Winterbergs Deuterium fuelled concept
Good news!!..looks like the problem of humans long term exposure to radiation in space has been solved:
“Environmentalist Lawsuit Could Delay SpaceX’s Starship Launches for Years”
“In the wake of another SpaceX rocket explosion, a coalition of environmental groups and nonprofits have filed a lawsuit against the Federal Aviation Administration (FAA) claiming that the agency failed to perform adequate environmental analysis of private space company SpaceX’s operations at its Boca Chica, Texas, launch site.
They’re demanding that the existing environmental approvals be thrown out and redone, potentially delaying future SpaceX launches for years.
“Federal officials should defend vulnerable wildlife and frontline communities, not give a pass to corporate interests that want to use treasured coastal landscapes as a dumping ground for space waste,” said Jared Margolis, a senior attorney at the Center for Biological Diversity, one the plaintiffs, in a press release.”
https://reason.com/2023/05/03/environmentalist-lawsuit-could-delay-spacexs-starship-launches-for-years/
“The real concern here isn’t the background level of ionizing radiation. It’s high energy cosmic rays, which kill whole columns of cells on their passage through the body…”
In addition to the proposed “water shield” a final layer of perhaps Tungsten lining around the part of the large ship designed for continuous habitability? Also during a long trip you could deploy a protective “umbrella” of super conductive wiring around the continuously inhabited part of the ship. It could be deployed say 100 meters or so from the vessel like a umbrella; the strong current setting up a very strong magnetic field to deflect the charged particle cosmic rays (especially heavy primaries like Fe) away from the ship. It (said magnetic shield) wouldn’t have to be an impenetrable “deflector shield”; just strong enough to deflect the incoming cosmic ray path(s) sufficiently to avoid the parts of the ship designed for continuous human presence.
Hmmm… many things, and probably limit-of-comment-length issues.
Anwyay
SHIELDING — Léts not forget that 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.
https:\\izw1.caltech.edu\ACE\ASC\DATA\bibliography\ICRC2005\usa-mewaldt-RA-abs1-sh35-oral.pdf (repl \ with slash)
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
https:\\agupubs.onlinelibrary.wiley.com\doi\full\10.1029\2021SW002749 (repl \ with slash)
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’.
Basically I agree 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.
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So there Brian is your napkin calculations. Just got to cobble together the nuclear reactors (plural), the water, the whole contraption, get it bolted together, load it with tasty foods and pleasant beverages, and light the fuse.
Right?
⋅-=≡ GoatGuy ✓ ≡=-⋅
Basically, that’s why you have two options:
1) Minimize cosmic ray primaries by making the transit quick, and mostly not making round trips. Minimize secondaries by keeping most of the shielding light. Have a “storm cellar” for solar flares. This is the avenue SpaceX is pursuing.
2) Minimize everything BUT trip time, by having a heavily shielded cycler. Once you have it up to speed, the delta v for each trip is very low, basically just course corrections. The downside is that it’s only useable at best half the time. And you have a narrow launch window for the “taxi”, which has to meet up with it fairly quickly.
3) Magnetic shielding, which is still just theoretical, which is why I said two options.
We have been waiting for VASIMIR to work for years, it is not even on the space stone ,is it? Have to go with NTP and maybe hybrid with ion added on.
space station
and of course for ships built on the moon – there is all the steel & titanium you can ever want
And O2, from refining.
It wont be without risks. Explorers through history took much larger risks. If they had not taken them, we would still be in caves.
Some people are willing to take risks, let them go to Mars if they want to be pioneers. It is their choice.
Multiple Starships in a cluster solve the ambient radiation issue.
Put simply if you were the center core of falcon heavy with 3 strapped together you’d only have exposure from front and back. If you go to a cluster of 5 starships for the trip, you get shielding for the center. where sleeping or activities could take place with freight / fuel on the outer layer ships. Scale this up to 32 ships etc and you get better ratios of shielded to shield.
Massive nuclear orbiter trains Earth-Mars orbit that never stop just slow at each point for pickup drop off then can use gravity to assist back to speed is the future but first is what Elon is doing the ground work of foundation to justify the cost of most efficient long term back forth travel.
“Reducing that to lower than Earth background radiation would only require a layer of water around 1 meter thick.”
Why would we set that as a goal, if we were being rational, rather than just phobic about radiation? Background radiation levels vary wildly from place to place on Earth. Average is 3mSv. There are substantial populations in India living at radiation levels of about 15 mSv per year. In Ramsar Iran, 132mSv!
People are not dropping in the streets in these places. If anything, there’s some evidence of net hormesis! (Remember, Earthly life evolved in a higher radiation environment than we experience today, due to decay of radioactive isotopes gradually lowering radiation levels over geologic time.) Low level ionizing radiation isn’t a world ending threat for space colonization. It’s just another risk for people who have already chosen a very risky venture.
The real concern here isn’t the background level of ionizing radiation. It’s high energy cosmic rays, which kill whole columns of cells on their passage through the body, (But likely don’t cause cancer, because they outright kill cells.) and solar storms, which can deliver a deadly acute dose of radiation.
Both are issues for the trip, but much less so once you’re actually on Mars.