That can only be done with either staying close to a planet with a strong magnetic field like Earth, or putting more mass between the Sun and the astronaut. On an orbital station you need to bring your mass shielding with you, which thanks to the tyranny of the rocket equation quickly adds to the fuel requirements. On Mars' surface the atmosphere will do a lot of the work. An ideal scenario also involves prefab storm shelters that sit on the surface of Mars and onto which dirt is piled. They don't need to be complicated structures either.
One of my favourite ideas is to adapt the Bigelow expandable habitat design technology currently being used on the ISS for this. These types of modules take up relatively little size and mass when shipped, but expand to a large size. It's sometimes called "inflatable" but that's not quite accurate. It's a rigid structure when deployed. The BEAM module was originally attached to the ISS for a planned 2-year test but it's been so reliable and successful that it's been kept attached permanently. Bigelow is pretty much out of business, but they transferred ownership of BEAM to NASA, and NASA contracts with the original engineering subcontractors that designed and built it. By space engineering standards it would be straightforward to adapt it into a Mars surface solar-storm shelter.
A surface base on Mars also has other major benefits, like being able to cool equipment by atmospheric convection. The only way to cool a spacecraft while not on the surface of a planet with an atmosphere is with radiators, which are big and heavy. The ISS has to have massive radiators, the big white panels that are perpendicular to the solar panels in this photo. And again, big and heavy radiator equipment means less cargo space/mass available for other supplies.
Synthesizing oxygen and methane using the Sabatier process for breathing and for refuelling a ship can't be done from orbit.
Isn't this done on the ISS already (for oxygen recovery)?
Not exactly. The ISS replenishes oxygen three ways. First is with a small-scale Sabatier system, but this is a fairly recent addition and can't do the job on its own. It's basically a small scale experiment to see if it can be done at all with relatively low power requirements and applied to future space stations. The test hardware on Perseverance is part of that research as well. The ISS mostly replenishes oxygen from gas canisters shipped from Earth on cargo supply ships. There's also an electrolysis unit in the Zvezda service module that cracks water into oxygen and hydrogen using power from the main solar panels. But that electrolysis unit requires water as an input and the hydrogen is just vented into space. It's as much about humidity control as it is about supplying oxygen. There's also emergency oxygen candles available if all other supplies fail. All these systems just reduce the need for resupply, they don't allow for long term self-sufficiency.
And if you're doing long duration missions, crew comfort matters as well. Astronauts charitably describe the ISS as smelling like an old locker room. A Mars ground station running a larger-scale Sabatier process using atmospheric CO₂ could easily swap out the whole station atmosphere on a regular basis with no Earth resupply needed.
It also functions as an emergency oxygen backup. The average ISS astronaut needs only about 800 to 900 grams of of oxygen in a day and most Mars mission profiles estimate the same amount needed. The main oxygen tank in the current Starship design holds about 900 metric tonnes. Even if there's no holding tanks for the Sabatier factory and all the oxygen and methane is pumped straight into a crewed landed Starship, when topped-up it would have enough oxygen for a dozen astronauts to breathe in comfort for roughly 240 years (give or take a few decades). The first Sabatier factory on Mars is probably going to be a customized Starship that has all the Sabatier equipment onboard, using its own tanks as holding tanks. With an orbital station, you'd need to figure out regular replenishment flights from the surface which adds wear-and-tear on equipment.
1/3 G is a total unknown
Low enough it won't be great. Agreed that artificial gravity needs to be tested.
I've heard rumours that the CNSA is planning small-scale experimental centrifuges for their current station and future stations, like the planned but cancelled ISS Centrifuge Accommodations Module. Hopefully that engineering expertise will eventually translate into large-scale centrifuges like on the fictional Discovery One from 2001. I think that's decades off at best though.
I wish the CNSA wasn't so tight-lipped about civilian space technologies. They're great for announcing scientific findings but frustratingly secretive about the engineering needed to make them. Even height-of-cold-war space-race NASA was better at public outreach.
Starship is actually the least-crazy way to get people and bulk cargo to Mars
Have they even built the variant that is planned to take 100 tons to the moon?
Not until they finalize the basic Starship design. They can't do that until they nail down rapid reusability which will probably take another year or two of prototype flights. The good news on that front is that the Raptor engine is quickly becoming simpler and cheaper to manufacture, while also increasing thrust performance and reliability. They may be able to do a lot more than 100 tonnes lunar-landed mass at this R&D pace. The first few Starship/Super Heavy test flights had many problems with the old Raptor v1 engine, but the latest flight had had all but one of the v2 engines firing reliably for the full mission duration. The v3 engines are starting to get mass-produced and installed in prototype ships and boosters. The original Artemis III crewed landing timeframe of 2026 is pure fantasy, it ain't gonna happen. But all the basic technologies needed to accomplish it are finally coming together. Assuming civilization doesn't collapse I'd bet on 2026 for uncrewed landing tests, and maybe 2028 or so for a crewed flight to the Moon.
You'll have to address it with shielding anyway
Isn't this done on the ISS already (for oxygen recovery)?
Low enough it won't be great. Agreed that artificial gravity needs to be tested.
Have they even built the variant that is planned to take 100 tons to the moon?
Crewed missions to Mars are putting the cart before the horse - moon first, then decide how much you really want to go down another gravity well.
Radiation is a known quantity. You just store your water in your walls to shield against radiation
That can only be done with either staying close to a planet with a strong magnetic field like Earth, or putting more mass between the Sun and the astronaut. On an orbital station you need to bring your mass shielding with you, which thanks to the tyranny of the rocket equation quickly adds to the fuel requirements. On Mars' surface the atmosphere will do a lot of the work. An ideal scenario also involves prefab storm shelters that sit on the surface of Mars and onto which dirt is piled. They don't need to be complicated structures either.
One of my favourite ideas is to adapt the Bigelow expandable habitat design technology currently being used on the ISS for this. These types of modules take up relatively little size and mass when shipped, but expand to a large size. It's sometimes called "inflatable" but that's not quite accurate. It's a rigid structure when deployed. The BEAM module was originally attached to the ISS for a planned 2-year test but it's been so reliable and successful that it's been kept attached permanently. Bigelow is pretty much out of business, but they transferred ownership of BEAM to NASA, and NASA contracts with the original engineering subcontractors that designed and built it. By space engineering standards it would be straightforward to adapt it into a Mars surface solar-storm shelter.
A surface base on Mars also has other major benefits, like being able to cool equipment by atmospheric convection. The only way to cool a spacecraft while not on the surface of a planet with an atmosphere is with radiators, which are big and heavy. The ISS has to have massive radiators, the big white panels that are perpendicular to the solar panels in this photo. And again, big and heavy radiator equipment means less cargo space/mass available for other supplies.
Not exactly. The ISS replenishes oxygen three ways. First is with a small-scale Sabatier system, but this is a fairly recent addition and can't do the job on its own. It's basically a small scale experiment to see if it can be done at all with relatively low power requirements and applied to future space stations. The test hardware on Perseverance is part of that research as well. The ISS mostly replenishes oxygen from gas canisters shipped from Earth on cargo supply ships. There's also an electrolysis unit in the Zvezda service module that cracks water into oxygen and hydrogen using power from the main solar panels. But that electrolysis unit requires water as an input and the hydrogen is just vented into space. It's as much about humidity control as it is about supplying oxygen. There's also emergency oxygen candles available if all other supplies fail. All these systems just reduce the need for resupply, they don't allow for long term self-sufficiency.
And if you're doing long duration missions, crew comfort matters as well. Astronauts charitably describe the ISS as smelling like an old locker room. A Mars ground station running a larger-scale Sabatier process using atmospheric CO₂ could easily swap out the whole station atmosphere on a regular basis with no Earth resupply needed.
It also functions as an emergency oxygen backup. The average ISS astronaut needs only about 800 to 900 grams of of oxygen in a day and most Mars mission profiles estimate the same amount needed. The main oxygen tank in the current Starship design holds about 900 metric tonnes. Even if there's no holding tanks for the Sabatier factory and all the oxygen and methane is pumped straight into a crewed landed Starship, when topped-up it would have enough oxygen for a dozen astronauts to breathe in comfort for roughly 240 years (give or take a few decades). The first Sabatier factory on Mars is probably going to be a customized Starship that has all the Sabatier equipment onboard, using its own tanks as holding tanks. With an orbital station, you'd need to figure out regular replenishment flights from the surface which adds wear-and-tear on equipment.
I've heard rumours that the CNSA is planning small-scale experimental centrifuges for their current station and future stations, like the planned but cancelled ISS Centrifuge Accommodations Module. Hopefully that engineering expertise will eventually translate into large-scale centrifuges like on the fictional Discovery One from 2001. I think that's decades off at best though.
I wish the CNSA wasn't so tight-lipped about civilian space technologies. They're great for announcing scientific findings but frustratingly secretive about the engineering needed to make them. Even height-of-cold-war space-race NASA was better at public outreach.
Not until they finalize the basic Starship design. They can't do that until they nail down rapid reusability which will probably take another year or two of prototype flights. The good news on that front is that the Raptor engine is quickly becoming simpler and cheaper to manufacture, while also increasing thrust performance and reliability. They may be able to do a lot more than 100 tonnes lunar-landed mass at this R&D pace. The first few Starship/Super Heavy test flights had many problems with the old Raptor v1 engine, but the latest flight had had all but one of the v2 engines firing reliably for the full mission duration. The v3 engines are starting to get mass-produced and installed in prototype ships and boosters. The original Artemis III crewed landing timeframe of 2026 is pure fantasy, it ain't gonna happen. But all the basic technologies needed to accomplish it are finally coming together. Assuming civilization doesn't collapse I'd bet on 2026 for uncrewed landing tests, and maybe 2028 or so for a crewed flight to the Moon.