Using plasmas is interesting for ISRU because they may work at Mars ambient atmospheric conditions. I'm quite surprised that this plasma reactor approach is more energy efficient than the solid electrolysis technique used by the MOXIE experiment.
Producing materials from other materials such as extracting oxygen from various compounmds is ultimately an energy problem. Better processes might reduce the ultimate cost by reducing the capital cost or reducing the running cost. For example: we can make hydrocarbons from the atmosphere. It's just uneconomic because of the energy cost.
The energy source itself presents issues. If you need a $50 billion fusion reactor that takes 20 years to build and a thousand people to maintain then that's a problem to bootstrap on Mars.
I personally believe that on Mars, much like on Earth, the future is solar. Solar has a lot of benefits on places like Mars. It's the only form of power generation that reduces electricity directly rather than boiling water and turning a turbine.
So mars still has the two big problems it always has had:
1. It's further from the Sun so solar is less effective. This just increases the cost of energy, ultimately. Of course, there'll occassionally be a months-long dust storm that'll stop you producing any power or just a shorter one that covers all your panels in dust; and
2. What are you going to do with this oxygen? You're going to be living underground because living above ground exposes you to radiation and the Martian surface itself is toxic (eg perchlorates). If you're living underground anyway, why are you living on Mars instead of the Moon?
> The energy source itself presents issues. If you need a $50 billion fusion reactor that takes 20 years to build and a thousand people to maintain then that's a problem to bootstrap on Mars.
ITER is a research facility, not a practical reactor. We have new (relatively) high temperature superconductors that are much better than what was state of the art when ITER was originally designed, meaning we ought to be able to build much smaller and cheaper reactors going forward once the basic technology is worked out. The MIT ARC and SPARC reactors are an example.
> If you're living underground anyway, why are you living on Mars instead of the Moon?
Mars has air that be used to manufacture rocket fuel. It has closer to Earth-standard gravity. The temperature swings are less dramatic. Water is more abundant. It's closer to the asteroid belt, which means it functions as the local gas station and resupply depot for asteroid mining. It has close to an Earth-normal day/night cycle. Basically, it's a much more hospitable environment for humans than the moon. The main thing the moon has going for it is that it's far quicker and easier to get there from Earth.
Isn't there plenty of oxygen which could be much more simply burned out of mars rocks? Place is covered with fine dust that's almost entirely metal oxides. I'm thinking concentrated solar to liberate the oxygen and produce a nice metal building material that could be refined to base metals for all sorts of things.
On earth a great deal of life's variety happens at the boundaries, such as in tidal zones and estuaries. There are no oceans on Mars but there is also very little atmosphere. I suspect we will want to engineer our oxygen producing equipment to make estuaries and tidal zones for atmosphere, where there is either a steady stream of atmosphere, or daily pulses that push life to adapting to temporary deficits and surpluses of resources.
Later on that could be accomplished just by routing the exhaust down into the canyons, but early on that may have to go through greenhouses, which either vent above a certain pressure or aren't quite hermetically sealed.
I think a big difference between Earth and Mars is that, because our planet is still geologically “alive” (it has a molten core and off gassing occurs on its own, the most easily observed example are volcanoes), the planet has been off gassing the needed molecules for life for millions, if not billions of years, and because of the nature of the molten iron core of our planet, we are able to hold these chemicals within our complex atmosphere without much artificial effort.
While mars may have been geologically dynamic at one point, it either is drastically much less so now or pretty much dead. Terraforming by means of burning through the surface would have to be an ongoing thing process because not everything we’d burn would be beneficial for our understanding of life (us and the ecosystems we are used to on earth), but it would also be very hard to keep what we generate on Mars in an atmosphere. Could be wrong, though.
The binding energy of the carbon dioxide taken from the Martian atmosphere is much less than the binding energy of the metal oxides from the Martian rocks.
So the thermal decomposition of the rocks will require much more energy.
As you say, the thermal decomposition could be done directly with solar light, bypassing the conversion efficiency of the photovoltaic cells.
That brings the energy requirements to similar values. Which would be the more efficient process would depend on details, e.g. the type of photovoltaic cells, the exact composition of the rocks whose decomposition is attempted, the usefulness of the byproducts, e.g. reduced carbon or reduced metals, and so on.
When taking into account the byproducts, it is likely that both processes will be needed anyway.
That's my intuition too, though given's gene-h's citation [1] in this thread, there may be an interesting analogy between water evaporation and reverse osmosis, as the proposed tech creates a plasma and the oxygen diffuses through a membrane (like osmosis tech). We know that reverse osmosis is the more efficient tech compare to evap, so who knows.
I've always thought this was the obvious choice. I wonder what the logistical issues are. As a bonus, you get pure iron as a byproduct, which would be worth it's weight in gold as a building and additive manufacturing resource.
If you just roast common Martian soil you don't just get iron but many metals mixed together (the three mars landers tested and got pretty similar results at a high level)
Near identical axial tilt to Earth, meaning a similar seasonal cycle (none on the moon).
Day/night cycles near identical to Earth differing by less than an hour (2 week long day/nights on moon).
A land surface area near identical to Earth's land area, which means room for vast expansion. (moon is a bit more than 2x Russia)
Somewhat more tolerable gravity at 0.38g compared to .17g on the moon.
Vastly more tolerable temperature ranges. A day on the equator in summer can get up to around 70 degrees F, though nights hit -100 F. The large difference owing to no atmosphere. The moon ranges from nearly absolute zero at night, to greater than boiling during the day.
And many more. These are just a handful off the top of my head.
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And some would consider the distance to be a feature, not a bug. It creates a necessity for a large degree of self sustainability which is ultimately a prerequisite to becoming a multiplanetary species. On the Moon, self sustainability not only more challenging, but ultimately not really necessary given it's just a stone's throw away from a resupply. And necessity really is the mother of invention.
Ultimately I also don't even view Mars as a goal (though it may be able to over millennia developed into an amazing place, and I would be the first to sign on for a mission to such), so much as a stepping stone. By the time the first human settlement is established on Mars, we should be looking outward from there as well. Titan being a possible next destination.
The moon also offers a way to develop self-sustainability. When you've got "oops I forgot the ketchup" it's only 2 days away, not years. Far more people will be willing to spend a few weeks on the moon than several years to Mars.
If fuel and machinery can be made on the moon, with its lower gravity well, it becomes far more practical to build big ships to go to Mars and elsewhere.
That would all be outside. Polypropylene is proof against sulfuric acid.
But you will need that sulfuric acid for the hydrogen it carries. Carbon from CO2 for structural members, hydrocarbon for plastics and fabric for gas bags, oxygen to breathe. There is thin gaseous silicides, in case you need any silicon.
It will be hard to keep the concentration of CO2 in the breathing air thin enough not to make everyone stupid, with so much of it outside.
Sabatier reaction plus ordinary rain will solve that problem away but nothing will solve the slow rotation rate and lack of a molten core and resulting magnetosphere. Still Venus is a better candidate than Mars for terraforming.
What if we terraformed Venus by shipping the CO2 to Mars? That way we'd be terraforming both planets.
I've been wondering about the feasibility of self-replicating floating comet factories that make dry ice comets that could be launched to mars. You could even wrap them in some sort of carbon based exterior to prevent them from boiling off too much in transit.
It would be more efficient just to redirect some comets. There is more then enough of everything floating around the inner solar system, and the Oort cloud has even more.
The composition of Mars' atmosphere is less important then getting the pressure right - at 1 atmosphere, humans don't need suits just respirators, and Earth-microbes will be more then happy to normalize things to suit them (they did it here, after all).
For Venus the big problem is water: Venus is dry. The reason it's in run-away greenhouse is because all that CO2 just will not precipitate into carbonate minerals, which to do so needs water. Again: something comets have plenty of.
The difference between the two in suitability though is the tidal lock: Mars has a day-night cycle. Venus has a day-night cycle but it's 116 Earth-days long - half the planet, if you got the atmosphere under control, would be in a freezing night for 3 and half months. You could settle it, but life would only really survive at the polls. While we can process a planetary atmosphere with plausible near-future technology and local resources, there's no known way we could "spin up" Venus (ironically a fully-tidally locked planet would have much more usable surface area as an oculus-world).
The amount of water available in comets is laughably inadequate to fill Venus's shortfall. But anyway its day length would make it very close to useless to try to terraform.
Shipping in enough hydrogen from (say) Neptune might be possible in principle using billions of automated, self-reproducing nuclear powered spacecraft.
If its atmosphere could be precipitated and the carbon freed of oxygen and somehow permanently protected from runaway combustion, the planet's low (2.64°) axial tilt and solar proximity might make a polar existence possible. But the overwhelming excess of oxygen would need to be removed or bound up in water. (The carbon might then be safely kept under water. Or, be crystallized out as diamond, which is hard to ignite.)
Quadrillions of aluminum foil balloons full of nitrogen bobbing in the stratosphere might suffice to bring temperature down.
Perhaps surprisingly, the present 3.5% of its atmosphere that is nitrogen is more than Earth's total.
As noted elsewhere, Venus's magnetic field is not much like Earth's, although it stretches almost to Earth's orbit, and might have crossed it in the past. (Such events might account for Venus's baleful reputation in to the oldest myths.)
The clouds (and presumably anything floating in them) ‘orbit’ the planet much faster than the planet rotates. It only takes about 4 days for the upper cloud decks to circle the planet.
From an energy-efficiency perspective, the difference is negligible. Getting out of the gravity well is by far the biggest hurdle. From there you might as well just give it a gentle push over to mars.
Why waste precious carbon that could be turned into life, industrial equipment, and fuel when energy from the sun is plentiful and otherwise wasted as it radiates into space?
Depends how dense the oxygen is ;) It wouldn't, but there are methods to retain it. If we had the capability, which we definitely don't, currently.
On earth we have a magnetosphere that protects our atmosphere from erosion from the deluge the sun gives us (hello Auroras!) but Mars doesn't have that. It's size is an issue too plus it's distance and orbit around the sun now. It didn't used to be so barren, it had massive lakes and oceans and possibly life once upon a time. To terraform it now would take a level of engineering that we don't have, but could, if we manage to not nullify ourselves in the next 200 years.
No, particularly in combination with the lack of an active magnetic field to shield the atmosphere from the solar wind. It's thought Mars had a much thicker atmosphere in the far past, now mostly bled off into space. Though if a new atmosphere were created, it would be lost again on a very, very long time-scale -- hundreds of millions of years. It might work to just "top up" once in a while.
It's almost 10% less. It's either a really weird coincidence or it says something interesting about planet formation that Earth, Venus, Saturn, Uranus, and Neptune all have almost the same gravity at the surface. (Of those five, Neptune has the highest gravity at 1.137g and Uranus is the least at 0.886g.)
It is also unique, among those, in being wholly unable to sustain a buoyant aerial unshielded nuclear reactor.
Titan can. But its surface gravity is less than a seventh of Earth's. It seems unlikely people can live on Titan or the Moon for long without fatal loss of skeletal tone. (Mars might be possible, but why bother?)
As a tourist destination, perhaps. As a self sustaining colony absolutely not. Since you have to float in the atmosphere to survive, mass is at an enormous premium. On-world industry would be nearly impossible.
If your goal is to build an exotic resort for billionaires go to Venus. If you're trying to ensure the survival of humanity in the event of a planet-scale catastrophe go to Mars.
Going to Mars would contribute exactly nothing to the survival of humanity, because everybody on Mars would remain absolutely dependent upon frequent shipments from Earth.
Any attempted Mars colony would die out not long after the last shipment, as materials necessary to its continued survival remain unobtainable there.
Furthermore, Starship is anyway wholly inadequate to establish a continued presence on Mars. If it works fully l as well as promised, it might suffice to maintain a Lunar outpost.
Anyone who hopes to establish a sustainable presence off-Earth must look to O'Neill Cans.
That is not true. The tech required to maintain long-term living on Mars would be extremely valuable here on earth. It is directly relevant to many of our current goals for more sustainable lifestyles.
Much like the moon missions, the side-effect benefits that it encourages will likely end up making such a mission worthwhile for the tech alone.
I don't understand your criticism of starship though, would you clarify why you think it's not suitable?
Maintaining an adequate technological basis for continued survival on Mars requires, simply, many, many times more people than Mars could support. So, all the more tricky components and chemicals have to come from Earth. When those stop, the technological basis soon declines below the level that can support the population living there.
All the choices after that become very unpleasant, of questions about who gets to continue living. The supportable number declines inexorably to zero.
Yes, similarly to Mars, anyone living on the ISS would die not long after the last shipment from Earth arrives. Except for this similarity, I'm not sure what you mean.
only one small problem with that idea, the lack of a magnetic field, mars also has this problem but you atlest can bury your self in the ground to protect yourself agains the solar radiation
If you've already figured out how to live in space for the many months required to get to Mars, why would you want to abandon your (presumably shielded) ship to live underground at the bottom of a massive gravity well? Stay in orbit. The view is better and you're halfway to anywhere.
The cloud tops go around in 4-5 days, depending on latitude. That is pretty high winds already.
For solar power, you need storage for the long night. A heavy weight on a cable could be played out at night to spin a generator, and then wound back up in the daytime.
A nuke power plant, if you would rather, could be as simple as a naked pile hung inside a big fabric tube with a wind turbine at the top. No need for shielding, cooling, or containment.
> "In the future it is quite possible that an inflatable structure(s) can generate a magnetic dipole field at a level of perhaps 1 or 2 Tesla (or 10,000 to 20,000 Gauss) as an active shield against the solar wind."
The article is unclear whether this is 1 or 2 Tesla at a point, or if what's needed is a field that's 1 or 2 Tesla over a large area, which would be a lot more than "an MRI machine's worth". Interesting idea anyways.
>As a result, Mars atmosphere would naturally thicken over time, which lead to many new possibilities for human exploration and colonization. According to Green and his colleagues, these would include an average increase of about 4 °C (~7 °F), which would be enough to melt the carbon dioxide ice in the northern polar ice cap. This would trigger a greenhouse effect, warming the atmosphere further and causing the water ice in the polar caps to melt.
Also suspiciously absent is any mention of how long this kind of change would be expected to take... I would be legitimately surprised if it'd take less than 20 years though, which is somewhat implied by the paragraphs that follow:
>"A greatly enhanced Martian atmosphere, in both pressure and temperature, that would be enough to allow significant surface liquid water would also have a number of benefits for science and human exploration in the 2040s and beyond," ...
A lot of it does seem to be very carefully avoiding making any clear statements or connections between critical bits of info though. There's room for "that wasn't claimed" arguments, but it's certainly standing very close to some lines...
We are clearly talking about a planetary-sized magnetic field. But I don't think it's in the realm of impossibility. With a sun-shade like that of JWST, temperatures naturally drop to superconducting ranges and at that point a closed electric loop has effectively zero resistance. So, at least in theory, you could induce an infinite current into it, slowly gathering solar energy until you build up the required magnetic field. The limiting factor would be the physical strength of the winding.
I don't have the technical expertise to estimate if such a project would require mere billions, or planetary sized piles of money.
I don't think the carrying capacity of superconductors is infinite. If you exceed the capacity, the superconductor "quenches" and ceases to be superconducting.
I'll point out you couldn't just park it at L1. If it's deflecting the solar wind, then it's acting as a solar sail. You would need active propulsion to keep it on station.
I was thinking the same thing but you likely have an area to work with however L1 points are unstable as it is and require satellites to alter the courses every once in a while potentially if you use the magnetic field as a light sail slightly in front of the point you'd be balanced between the sun and mars with less active thrust
> I'll point out you couldn't just park it at L1. If it's deflecting the solar wind, then it's acting as a solar sail.
Assuming the solar wind is constant, you could presumably park it somewhere other than L1. That's certainly not a valid assumption, though, so propulsion is going to be necessary.
Sounds like an incredible single point of failure. You would have to keep it constantly maintained and fuelled, and maybe build ten of them for redundancy, and even then whoever controls them would be able to hold the entire planet to ransom.
Just because it works with martian atmospheric conditions doesn't mean you have to do it in open atmo. Instead you can fill a chamber at atmospheric pressure, run the device, then pump the oxygenated air into a filtration system to process from there. This is pretty similar to what the researchers did to prove the concept on earth anyways (build it in a sealed tube with mars-like atmo).
The main issue after simply having oxygen is that the martian atmosphere has so much CO2 and so little everything else. Considering that subsurface temperatures can get low enough to sublimate CO2 into dry ice, you could potentially (and I say potentially because this isn't my specialty by any means) build an air production loop that uses relatively little power other than to drive the plasma reactor itself and a thermal pump to bring cold fluid to the surface to chill the oxygenated air so that the CO2 sublimates out. Of course here you could also just use energy to chill the gas via a compression chiller or make some tradeoff between the two. This process would move you along the following steps:
Standard Atmosphere with 95% CO2, 2.5% N2, and 2.5% trace elements (mostly argon, also a very small amount of O2, and a tiny amount of CO).
After Plasma Reactor: 65% CO2, 30% O2, 2.5% N2, and 2.5% trace elements.
After Sublimation: Lower volume of gas with 85% O2, ~7% N2, 5.5% argon (from trace elements), and the rest of the trace elements. And the CO2 is now dry ice.
Then it's just a matter of diluting the "purified air" with nitrogen or other inert gasses, adjusting the pressure, and preventing buildup of any nasties in the trace elements (such as the carbon monoxide). Now you should have breathable, earth-like atmosphere for suits and cabins.
This is mainly based on my knowledge of processes we use on earth already for extracting stuff from the air so caveat that I could be missing important details.
One book I read suggested it would take about 100,000 years for the atmosphere to ablate into space. We should be on Europa and other outer moons by then.
Of course “Corey” (The Expanse) are probably right that each colony will develop her own personality, and it will be difficult to abandon any of them. The cultural trauma of such an event could be profound.
It absolutely would not be vented. It would be liquified and stored to use in rockets. They can't go home until they get enough of that and of methane. It will soon occupy all their thought, and squat their dreams. being stuck until the launch window opens up again.
To workaround this we could build a modular planet wide “city” and have everything shielded by walls. Expand it as you go along and keep everything needed inside. No need for expensive and time consuming terraforming.
That was sort of how C.S. Lewis imagined Mars in Out Of The Silent Planet, before we really had a good idea of what Mars was really like. Most of the planet was unlivable without an air supply, but the valleys trapped enough air for plant and animal life to thrive.
If one were to make a hole like the one described in the video, I wonder how much that would affect the atmospheric pressure on the rest of Mars?
Interesting idea, but wouldn't the ejecta from multiple impacts create a global cooling effect, which would be counterproductive to the intent of the project (i.e. a warm, high pressure area)?
Methods that involved splitting CO2 will always be power intensive due to physics.
What many people forget is that the martian atmosphere has massive total amounts of gaseous oxygen, even if it makes just 0.16% of a very thin atmosphere, if you could capture it and store it would be more than enough for centuries of human colonization. NASA is investigating this very scenario with some low energy adsorption methods, that promise to be very energy efficient:
https://www.reddit.com/r/spacex/comments/vhnuqa/nasa_funding...
This could enable, for example, the creation of suits that extract unlimited oxygen from the surrounding atmosphere as long as they have electric power - say a few solar panels.
> They estimate that the device could create about 14 grams of oxygen per hour: enough to support 28 minutes of breathing, the team reports today in the Journal of Applied Physics.
So the greenhouse is going to be a better option, though having backup plans is good.
If we're never going to colonize it, then it's a net-negative to resources from Earth, and therefore that money is wasted. It seems extremely unlikely that we'll make some discovery that makes this all worth it.
Needing to lift all the materials into space from Earth seems energy intensive. On the other hand, maybe we'll have fusion-based rockets in the future where the energy cost to escape Earth's gravity well isn't as important. You'll still have potentially two planets worth of needs to support. I know that the various space companies are looking at asteroid capture. I wonder if it makes sense to just smash some of those into Mars before it's inhabited. Yes it potentially destroys scientific data but that risk can be managed vs the benefit of having easily-accessible building materials on Mars to build large-scale industrial equipment / housing if we get serious about colonizing Mars.
There was a plan at one point to put solar powered gliders into the stratosphere above the ozone holes and use coronal discharge device to create ozone with the excess power. I don’t imagine for a moment you could fly a reactor especially in such a thin atmosphere. But you might be able to park one pretty high up on Olympus Mons.
And not even fun before that. People suffering from CO poisoning don't realize anything is wrong, they just die. Which is why we all have CO monitors now.
GP's comment was a pun based off Total Recall, a science fiction movie with Arnold Swarzenegger set on the red planet. Unless yours is a pun within a pun that flew over my head.
SpaceX will need to split CO2 into CO and O2, H2O into H2 and O2, combine the firsts into methanol and pour all this into the Starship tanks for the Earth bound trips. That means that they will probably bring nuclear reactor(s) there (my hope though is that Musk will decide to do to fusion that he had already done to EV, space, etc.). O2 for humans will be just a noise (also greenhouses for food production will probably generate O2 enough for humans).
> my hope though is that Musk will decide to do to fusion that he had already done to EV, space, etc.
Fusion power doesn't need the kind of incremental advances and smart marketing that Musk's companies have benefitted from, it needs huge fundamental advances in science and engineering.
That said, by the time anyone actually tries to establish any kind of base on Mars, we may well have figured fusion (my money is still on ITER's follow-ups, the DEMO plants, being the first to actually do anything, in 2050 at the earliest). Musk's "plans" for Mars are just part of his pretty smart marketing / outright lying to bolster his companies.
Although something tells me that Fusion would be a solved problem in about 18 months if we were in a wartime and have all hands on the deck. I am joking only slightly.
>Fusion power doesn't need the kind of incremental advances and smart marketing that Musk's companies have benefitted from, it needs huge fundamental advances in science and engineering.
It is systems engineering - take the available science and engineering and combine into an actually working thing. That is exactly what we need with fusion today.
> take the available science and engineering and combine into an actually working thing
This doesn’t describe the present situation. For example, high-temperature superconducting magnets open design space which simply didn’t exist a decade or two ago.
Not really. For example, no one has ever tried to extract even a milliwatt of power from a fusion reactor. We have some good ideas how to do it, but it's just never been attempted, so we might discover some fundamental challenges.
Then, even if all current plans go right, current designs have no realistic hopes of being economical. Plants will cost extreme amounts of money, as they require state of the art technology at every level, and the irradiation caused by the fusion reaction will turn all materials in close contact with the fusion core brittle (reactor vessel, support structure, possibly even magnets) in a few years, requiring a complete replacement.
Not to mention, an accident can easily be catastrophic for the entire reactor, making the whole thing an extremely risky endeavor. Even the environmental risk is large, even if not nearly as bad as fission - if such an explosion occurs, it will send radioactive materials (concrete, steel, cooling agents), plus radioactive tritium, all around the plant, requiring expensive cleanup and risking the future of the whole plant.
Nuclear has the problem that you somehow need to hoist a reactor from the Earth into space, and putting nuclear materials makes a lot of people nervous. (What happens if the rocket launch fails and scatters radioactive debris?)
An alternative is to gather the reactor fuel on Mars, but that sounds like a difficult undertaking.
I think the expectation is that the energy needed to make methane on Mars will be provided by a lot of solar panels.
(I would be curious to know how the math works out. For instance, if you send a Starship fully loaded with solar panels to Mars and spread them out on the ground, how long will it take those solar panels to gather enough energy to make enough methane to return the rocket to Earth? Is it one year? 10 years? 100 years?)
There are plenty of nuclear reactors already in space. The Voyager probes are famously powered by radioisotope thermoelectric generators, and even the Perseverance lander mentioned in the article is powered by one. Full list here: https://en.wikipedia.org/wiki/List_of_nuclear_power_systems_...
Those aren't "reactors". They're just lumps of plutonium that are decaying naturally and producing heat. A reactor has to be able to control a fission reaction; these can't.
Interestingly the biggest reactors (mostly 2kw and a few 5kw) were deployed by the Soviet Union. Presumably they just didn't care about the safety risks.
The risks weren't purely theoretical either. They had one nuclear-powered satellite that re-entered over Canada.
Couldn't we just use low enriched uranium for that? And as long as you aren't actively powering it up on takeoff, even in an accident, how radioactive would it be?
That's a good question, I don't know enough to answer.
I suppose one way to mitigate the risk is to use the same kind of "emergency escape" systems that humans use during rocket launches. I.e. if the rocket fails to achieve orbit, a capsule is ejected and floats down on parachutes. I wonder if that sort of thing is already done with RTG launches?
The amount of highly enriched U and Pu that has already been put into space is at least several hundred of kilograms across at least 10+ of launches. And reliability of SpaceX launches is highest in history of human space programs.
My bet is on nuclear vs solar as the nuclear is the next rocket engine type after chemical and will loose the dependency on launch windows and shorten the trip time.
The safety risk isn't necessarily an insurmountable obstacle; I could imagine the U.S. government being more likely to approve sending a nuclear reactor into space if it was NASA that was asking as opposed to a private company, but either way it's more of a political problem than a technical one.
Nuclear rocket engines are tricky. Nuclear reactors don't actually work very well in space because there isn't any convenient way to get rid of the excess heat. A vacuum is a very good insulator, so usually your only option is just to radiate it away as infrared light.
With a rocket there's another option which is to transfer all the heat to the reaction mass you're expelling out the back of the ship. That sounds like a hard engineering problem though.
Using a reactor on the Mars surface is a lot more straightforward because you can use the local air and ground to transfer heat. And since Mars is so cold, you might even get better steam generator efficiency there than on Earth, where the ambient temperatures are higher.
One of the hopes with fusion is that if it pans out it might be reasonable to send a fusion reactor to Mars since you wouldn't need to send radioactive fuel rods. In fact, maybe the first practical fusion reactors will be used on Mars before they're used in more than a demonstrative capacity on Earth because they fit a very specific need, there are barriers to using the alternatives, and cost per kw/h isn't the most important constraint.
The US did build a nuclear powered ramjet engine and test it. This isn't an insurmountable hurdle, it's an achieved one. The design they used of course has lots of good reasons we should not use it on Earth (namely, the reactor would activate the air, meaning it spews a plume of oxygen and nitrogen isotopes) but it does work.
You can solve the radionucleotide problem by running it off hydrogen instead, which doesn't activate in any meaningful quantity.
Basically, not only do we have the ability, we had it in 1961.
Interesting. That requires an atmosphere though; it might work for the first stage of a launch from Earth, and maybe even for Mars. Once you're out of the atmosphere you'd need some other method of propulsion.
I think nuclear space propulsion would be used as a reactor generating energy for ionic drive. That would work as a Mars-Earth shuttle while never going into atmosphere. The landing to and launching from the plane surface would be done by regular chemical rockets.
Specifically it requires propellant, which on Earth is the air intake. For space travel you have to still take a propellant, but it can be essentially any type of gaseous reaction mass - for example, water.
On mars you have a day not too different from ours and solar looks attractive. On the moon you really need nuclear because the night lasts two weeks. It is so bad people are thinking about reversing O’Neills idea and microwave beaming power from the Earth to the Moon.
Why would you need to do that? Just put solar arrays at the poles. There might be some practical limitations with power transmission to other parts of the moon, but extremely high-voltage power should be easier to do there than on Earth, since there's no oceans in the way, nor any atmosphere (so no problems with discharge from the high voltage wires).
> I would be curious to know how the math works out...how long will it take those solar panels to gather enough energy to make enough methane to return the rocket to Earth?
Somewhere around a year.
A Starship, refuelled in Earth orbit, intends to carry 100 tons to Mars [0] using 1200 tons of propellant [1] with an oxidizer/fuel ratio of 78:22 [1], so 265 tons of methane.
Spacex's numbers are likely measured from low Earth orbit to low Mars orbit and assuming aerobraking on the way down. According to [2] that takes 5.8 km/s delta-v, but it's an additional 3.8 km/s to travel from the Mars surface. That's 65% extra, meaning we will need e^0.65 as much fuel because of [3], which is 1.9x, so 500 tons of methane.
So the first answer is, it can't be done by refueling a Starship final stage alone - you'd need a booster, or (simpler) reduce payload by half. I'll assume instead we divided the load between two rockets coming back.
Methane has a specific energy of 55MJ/kg, [4] so we need 28 TJ of energy to fill the tank. That's 8 GWh.
Mars receives about 50% as much sunlight as Earth [5]
Spacefaring solar panels weigh 2kg/sqm and produce 350W/sqm in Earth orbit. [6]. Terrestrial solar panels are cheaper to produce, but heavier. That's baseplate capacity, so make it 1/3 of that to average over day and night, and halve it again for running at Mars light levels, giving 60W/sqm or 30W/kg.
100 tons of that is 3 MW.
Typical conversion efficiency for power-to-methane is 50%. [7]. This is done via hydrogen and requires carbon dioxide, which is abundant in the Mars atmosphere, and water, which is not, but is hopefully available in the quantities we require. So our solar plant produces 1.5MW of methane. I'm going to assume we get our oxygen for free as a by-product without any loss of efficiency, which seems plausible to me but not well documented.
8 GWh/1.5 MW is 5,300 hours or 225 days (either type) or about 8 earth months.
I haven't allowed for the mass cost of the infrastructure for methane refining, or degradation of solar panels in the Mars dust. So all this should be a considered a lower bound for your answer.
Future Apollo missions mitigated the danger of fires by being really careful about the materials in use, but that's not a good answer for long term missions, particularly if the astronauts are going to conduct industrial activities such as in-situ resource utilization.
If you want to make breathing gas on Mars, O2 covers 20% of it, the rest of it is going to be an inert gas like Nitrogen, Argon, Helium or SF6.
Of course every method of producing O2 in space works by separating O from something else and the "something else" is likely to be useful, such as H2, C, Al, etc.
A major contributing factor to the Apollo 1 fire was they didn't merely have a pure oxygen atmosphere, but a pressurized pure oxygen atmosphere. Pressurized above 1 atmosphere, for testing purposes. In space they would have operated with a substantially lower pressure; I believe about 1/5th of atmospheric pressure. A low pressure pure oxygen environment is still a fire hazard relative to regular air with the same partial pressure of oxygen, but it's not nearly as dangerous as a pressurized oxygen atmosphere.
Sure, the breathing gas for a crewed mission or habitat would need to include an inert gas as well as oxygen. But oxygen is consumed during respiration and the inert gas isn't, so oxygen will be needed in much larger quantities, so in-situ production is a much more pressing problem.
You are probably recycling the CO2 from the astronauts breath which is easier than cracking it from the air. Also many practical breathing systems (especially for spacesuits) leak some of the inert gas for cooling and other purposes.
The real thing you’ll need O2 for is an oxidizer for fuel but of course you need to make fuel too.
If you are interested in making anything interesting such as large plastic sails or small biospheres nitrogen is the big missing piece of the puzzle right now in the moon, mars and asteroids.
CO2 needs to be scrubbed/vented out of the breathable atmosphere. Even if there is abundant of oxygen anyway, too much CO2 will make people feel dizzy and confused, cause splitting headaches, increased heart rated, reduced senses, and eventually death. CO2 can't take the place of inert nitrogen in a breathable atmosphere, that much CO2 in the air just isn't compatible with human life.
being extremely generous, and assuming he meant "martian atmosphere" when he said "air", it _might_ be a bit more challenging (depending on your process and what you've got available) to convert the CO2 at 0.095 PSI into O2, than it would be to pull the CO2 out of ~14.7 PSI human exhalations and convert it to O2.
seems like the kind of thing where there is a bunch of engineering that could be productively done.
Using plasmas is interesting for ISRU because they may work at Mars ambient atmospheric conditions. I'm quite surprised that this plasma reactor approach is more energy efficient than the solid electrolysis technique used by the MOXIE experiment.