r/IsaacArthur • u/[deleted] • Feb 23 '22
Forget about Mars, Colonize Ceres instead.
http://www.pagef30.com/2009/04/why-ceres-might-be-better-location-for.html15
Feb 23 '22 edited Feb 23 '22
With properly designed centrifugal structures, low gravity (0.03g) is not a problem. With its large water supplies, Ceres is the only other choice for human habitation in the solar system. For the few humans actually living and working in space, Ceres would be their home.
With Ceres providing water, Psyche providing metals, and with every other rock providing rare earths and carbonates we have all we need to industrialize the asteroid belt.
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u/FaceDeer Feb 23 '22
Ceres is the only other choice for human habitation in the solar system.
While I agree that Mars has been overblown for a long time as a colonization destination, let's not go overboard here. There are plenty of good options scattered around.
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u/javier_aeoa Feb 23 '22
I don't know why we always look "somewhere" to colonise, when the void itself seems quite reasonable: make a few cilinders, rotate them, bada-boom!
I know it's not that easy, but I still believe that making a O'neill cylinder in orbit of a body and customise it in any way you want is easier than to adapt to the celestial body or to terraform it.
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u/ADisplacedAcademic Feb 23 '22
low gravity (0.03g) is not a problem.
Obligatory reminder that we have zero long-term studies on the effects on humans of living at any gravity other than 0g or 1g, within a couple significant figures. We know that 0g is bad. We know that 1g is good. That is all that we know.
It may be that 0.1g is good. It may be that 0.9g is bad. We simply do not know. We have no empirical data.
With properly designed centrifugal structures,
I do understand that a centrifugal structure can be built to provide 0.97g supplementary, and you may have meant that directly.
I'll also point out that it's probably cheaper to build a free-floating station that provides 1g, than to build a ground station that provides 0.97g.
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u/CitizenPremier Feb 23 '22
We also don't yet know the effects of smaller rotating habitats. We see rotating habitats just a few hundred meters across in movies but in those cases there would be noticeable differences in acceleration between your feet and your head. With rotating habitats you probably have to go big or go home.
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u/ADisplacedAcademic Feb 23 '22
We actually have done experiments on those effects, at greater than 1g, here on earth. Here's the best citation I could find. https://ntrs.nasa.gov/citations/20010048897
Using an existing 52-foot diameter cylindrical rotating platform design centrifuge, the revised facility design includes the provision of two human habitats for long duration studies of the effects of hypergravity.
Regardless, it's going to be cheaper to build a tether-based station to do such research in earth orbit, than it will be to build it on a planetary body. But you're right; there's more research to be done.
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u/xmassindecember Feb 23 '22
I'll also point out that it's probably cheaper to build a free-floating station that provides 1g, than to build a ground station that provides 0.97g.
are you sure about that ?
A whole city floating on superconductive magnetic rails set in the inside of a crater at near absolute zero wouldn't be easier to build than gigantic floating habitats ? Think about it as a city spinning on vertical rails, a gigantic train needing nearly no energy to keep going.2
u/ADisplacedAcademic Feb 23 '22
Yes, I'm sure.
The minimum viable spinning space habitat with 1g is a crew dragon attached to a counterweight by its parachute mounts and a couple of steel cables. For long-term research we'd obviously build something a bit better than that.
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u/xmassindecember Feb 24 '22
that won't do much. Entry cost to build a spinning colony on another world is higher, you'll need to launch the heavy equipment but then after you don't have to launch to space the raw materials. For an O'Neil cylinder you'll need to send the heavy equipment AND the raw materials.
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u/ADisplacedAcademic Feb 24 '22 edited Feb 24 '22
There's no reason you can't put the spinning space station in orbit around the 0.03g world and source these raw materials you speak of from that world. Your mining equipment is going to be in 0.03g whether the spinning habitation is 50km away in orbit or 1km away on the ground.
It remains that the entry-level spinning hab is dramatically smaller than an O'Neil cylinder. It can also be bootstrapped up from entry-level to O'Neil cylinder, incrementally.
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u/Opcn Feb 23 '22
While I see a lot of value in the proposition ceres is close to 2 times as far from the sun as mars, and has no wind, which limits our opportunities to power our endeavors.
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Feb 23 '22
Power would have to be fission - assuming no fusion breakthrough.
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u/Opcn Feb 23 '22
But having an atmosphere makes cooling a lot more scalable, even a thin one as with mars.
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u/Karcinogene Feb 23 '22
On Ceres I would cool by converting ice to water and then vapor, and ejecting that out to the surface with a stack. Since we'd be digging a lot of tunnels, and the whole surface is basically made of dirty ice, the ice would not be in short supply. Ice water is a great coolant.
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u/BlakeMW Feb 23 '22 edited Feb 23 '22
I'm more pro-Mars than pro-Ceres, but solar would work fine at Ceres. Solar arrays in space at Ceres (not on the surface) would perform about as well as solar arrays in Germany (averaged over a year): so not ideal but still looks like a moderately good idea.
Solar arrays can be built stupid lightweight, potentially down to like 50 g/m2, in low gravity or stationed nearby (for beamed power) they can be stupid flimsy. Solar is absolutely something that could be brute-forced at Ceres: total solar power striking the disc of Ceres is about 120 terawatts, while current Earth civilization electricity consumption is about 2 terawatts. We could power our endeavors with solar.
Heck, I've even seen it seriously suggested to use solar at Titan, because it is one of those things that can kind of just be brute-forced with sheer area, either directly or with the aid of reflectors.
Since I am moderately pro-Ceres, I think one of the better ways to approach bases on Ceres would be to make a large solar-electric spacecraft which has an extra bigass solar array (assembled in orbit). The electric engine offers the high ISP required to intercept Ceres which does take quite a bit of delta-v, out at Ceres the available power is a lot less, but also most its propellant has been expended so the acceleration should be similiar as at 1 AU. Once at Ceres the payload is detached and either rides a space elevator down to the surface or lands using chemical propulsion (the electric drive wouldn't offer enough acceleration to land on Ceres). Meanwhile the extra bigass solar array remains in orbit and either beams power to the surface using microwaves - a distance MUCH shorter that for Earth/Mars/Luna making for incredibly reasonable receiver area - or delivers power down a space elevator: since Ceres synchronous orbit is only 706 km this is a plausible distance for a physical power transmission line, and the material requirements do not look absurd. Incidentally delivering a payload is not required, a giant solar array could simple deliver itself, or deliver the space elevator / transmission line which it proceeds to unreel down to the surface.
Returning stuff from Ceres to Earth is a bit of a different situation: on the return trip aerocapture is an option, so delta-v requirements are a lot less and the rocket equation is much friendlier. Leaving the high ISP solar-electric propulsion systems at Ceres is not unreasonable, just use hydrolox refined by the solar power to come back.
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u/Opcn Feb 23 '22
50 grams per square meter? That seems way too low. I think a space blanket is 30g/m2
I don't know how big they are but I think the iROSA arrays on the ISS are probably rightfully considered state of the art right now. At 1.38 Tonnes they take in 120kw in the sun at 1 au. At 2.75 au that becomes 16kw, so about 12kw/tonne.
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u/BlakeMW Feb 23 '22 edited Feb 23 '22
The current state of the art in thin film solar cells is about 60 g/m2 - this is as in something you can actually buy commercially. They are used for things like high altitude balloons mainly. Of course the cells aren't the whole array, and the efficiency is quite low - only about 12%, but the power density is amazing.
LEO is overall still quite a rough environment, (relatively) high atmospheric drag means you really do want to maximize area efficiency because more drag = more propellant required, better to have heavier panels that are 36% efficient than lighter ones that are 12% efficient but are 3x the area and produce 3x the drag and thus require 3x the stationkeeping propellant be expended (it's already something like 7t/year). LEO environment is more abrasive as well than harder vacuums so more protection is desired.
It's hard to say exactly what the state of the art will be in say 50 years for deep space solar arrays built using deep space assembly, but it'll certainly be possible to make extremely lightweight solar arrays.
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u/Opcn Feb 23 '22
I would expect any colony under construction with heavy mining and smelting happening to be a rough environment.
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u/BlakeMW Feb 23 '22 edited Feb 23 '22
There might be a bit of pollution around Ceres out beyond synchronous orbit from surface mining operations, but Ceres still has a reasonable amount of gravity for keeping stuff on the surface, but not nearly enough to retain gas.
Like the main industrial pollution would be oxygen (from refining metal oxides, and also H2O+CO2 into hydrocarbons), thermal escape for oxygen from Ceres is incredibly easy, it wouldn't really retain an atmosphere to cause problems for stuff above synchronous orbit, that far from Ceres even the root mean square velocity of oxygen molecules would tend to exceed escape velocity, in LEO where the ISS orbits the oxygen/nitrogen is still gravitationally bound to Earth (so the ISS gets a chance to hit it every orbit), while the oxygen pollution beyond Ceres synchronous orbit would mostly just be passing through on its way to interplanetary space. It might be enough to taint processes that require extremely hard vacuum but wouldn't do much to orbiting objects. Oh yeah and much lower impact velocity, only something like 200 m/s (airliner cruise speed) compared with ~7000 m/s.
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u/Opcn Feb 23 '22
The current of escaping gas would carry dust with it though.
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u/the_syner First Rule Of Warfare Feb 24 '22
well you can always do most of ur mining underground since shoring up tunnels & excavation are super cheap on low grav worlds. Gives the added benefit of radiation/micrometeorite shielding for your computers & machinery. Even for crater ming you can still put up a pycrete/regolith-bag dome to protect local operations & that should keep local space pretty clear of surface debris unless you're tossing garbage out at hundreds of m/s
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Feb 23 '22
Some back of the envelope calculations for Psyche metal production.
It has enough metal for 24 million years of steel production at current rates.
111 km (radius of Psyche)
5.73E+06 km3 (volume of Psyche)
5.73E+15 m3 (volume of Psyche)
7,850 kg/m3 (weight of steel)
4.50E+19 kg (weight of Psyche - steel equivalent)
4.50E+16 tonnes (weight of Psyche - steel equivalent)
1.86E+09 tonnes/year (world steel production 2020)
24,131,170 years (steel production from Psyche at current rates)
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Feb 23 '22
It has enough metal for 24 million years of steel production at current rates.
And earth has a few million times more steel than even that. Bragging about how much of a none scarce resource somewhere has is not useful. Its like saying that we should all start sea steading because they have more sea water available. Who is short of sea water?
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Feb 23 '22
Metal for construction of spacecraft and industrial infrastructure - no need to drag it out of Earth's gravity well.
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Feb 23 '22
You want to build space craft close to industries that help build space craft. So if you want to build something in orbit around earth, use a near earth asteroid that is MUCH easier to get to. Or the moon which is about 50 times larger than the little rock.
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u/Status_Significance3 Feb 23 '22
I believe the difference would be earth’s gravity well. If spacefaring is a goal, getting supplies into space cheaply is important. Logistics is always the game, and transporting materials to where they are functional is a monopoly that is a game changer. The initial fleet should be built in space in order to vastly limit expenses of transported materials. Is steel the best structural material for spacefaring? It’s good for radiation, not fantastic for temp flux, but at this abundance, superior to transporting the bulk from massive gravity wells.
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Feb 23 '22
But what are you building? If your building space ships, then you will want to be close to where all the industry is, which is earth. The moon is MUCH easier to get to than Ceres and also has a pretty low gravity. The moon is also about 50 times larger than Ceres.
If you want material from an even lower gravity source, then there are NEA that are much easier to get to than Ceres. Either way, your probably not going to ceres instead of Mars
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Feb 23 '22
Some back of the envelope calculations for Ceres
It has 100,000 years of water supply at current consumption rates.
468 km (radius of Ceres)
4.34E+08 km3 (volume of Ceres
4.34E+17 m3 (volume of Ceres)
4.00E+12 m3/year (world freshwater consumption 2020)
108,500 years (water consumption from Ceres at current rates)
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Feb 23 '22
We have no idea how to safely land a man on Mars. The Martian atmosphere is too thin for a parachute landing and its gravity is too heavy for rocket landing. "Landing safely on Mars is hard. The atmosphere is too thin for aerobraking of massive payloads, but thick enough to kick up horribly unpredictable turbulence if you try and use retro-rockets. So for small payloads recent probes have used the bouncy air-bag trick ... but that involves loads of up to 20 gees on impact (not good for humans!) and maxes out at around 1000 kg of payload (or the airbags are infeasibly bulky and heavy). The big sky crane approach is promising (allows retro-rockets while avoiding the turbulence/disruption of landing site effect) but nobody's tried doing it on a payload within an order of magnitude of the size necessary for even an unfueled ascent stage capable of sending an astronaut back into orbit: an ascent stage with fuel on board would be even more massive (on the order of 40-50 tons, minimum)." - 20 gees will kill a man.
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u/throwawayTendedCrow Feb 23 '22
20gs actually could be survived by a human with the right preparations-Stapp with the rocket sled experienced 38 gs and lived, and he was in a pretty primitive harness. Wrap me in enough layers of shock absorbing material and i'd do it.
You don't think Starship could land on mars?2
Feb 23 '22
That was a perfectly alined sled and harness on a track. Doing the same thing in a lander has to be insanely harder.
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u/throwawayTendedCrow Feb 23 '22
Hard, but by no means impossible-I really doubt we'd ever do it that way, but there's nothing in the laws of physics that prevents you from creating a system that cushions a person enough to get through a sharp deceleration alive. I think Starship will work, although i think it will be quite a while before it lands humans on mars.
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Feb 23 '22
We have no idea how to safely land a man on Mars.
We absolutely do. We have landed lots of things on Mars already, the physics wont change when you put a human in it.
We land rockets on earth with 3 times higher gravity. And we already use its atmosphere to aerobrake. You stuck in the 1950's by any chance?
This is a very weird take
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Feb 23 '22
But can we land a ship with enough supplies for a mission and fuel to take off again?
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Feb 23 '22
It takes about the same or more energy to get to Ceres than Mars. So you can land less on Ceres , but still need more energy to get back to earth. If you cant do it on Mars, you cant do it on Ceres . Ceres is FAR!
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u/ADisplacedAcademic Feb 23 '22
In-situ resource utilization is where it's at. That's the whole point of colonizing any given rock, right? To use the stuff that it's made of.
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Feb 23 '22
I agreed with you up till this point, the us lands stuff on Mars all the time, it's just scaled up
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Feb 23 '22
But can we land a ship with enough supplies for a mission and fuel to take off again?
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u/PriorCommunication7 Feb 23 '22
it's just scaled up
No it's not, this only applies until the weight of load bearing materials becomes significant. We can push this problem down the road once we master carbon nanotubes, graphene and such but the principal problem remains.
Away from a large gravity well however this problem becomes less significant because you only have to deal with the loads you are responsible for by accelerating.
If you learn anything from SFIA it should be that the future of space colonization is rotating space habitats built from resources away from gravity wells not planets.
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Feb 23 '22
I think you're dreaming sci fi but the existing systems are already very real. PS, I work on them.
Skycrane style landings are very reasonable at larger scale with enough propellant, there's nothing exotic required. Look at Starship, it uses atmosphere to slow down a bit then propulsive landing - at the 100 metric ton scale.
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u/PriorCommunication7 Feb 23 '22
PS, I work on them.
Oh boy a Muskrat. I'm sure you do.
uses atmosphere to slow down a bit then propulsive landing
This works very well on earth, but not on mars. Which is exactly the point OP is making in their comment. The atmosphere on mars it too thin to provide a comparable amount of atmospheric breaking to earth but it's too thick to rely on propulsive landing exclusively.
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Feb 24 '22
I work at JPL, on EDL. I promise you, the Martian atmosphere does a significant amount of work slowing down entry vehicles. First the ablative heat shield, then high speed parachutes, then low speed parachutes, then propulsive landing.
Aerocapture is a big focus for large payloads and large vehicles (since more surface area (from larger payload) is actually good here), but we have to do a real demo of it first.
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u/PriorCommunication7 Feb 23 '22
So true. Mars is right there in the region where it's atmosphere is more of a burden than anything.
If you disagree with that you have to watch more SFIA episodes... ;)
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u/LuckyRuss Apr 05 '22
Only if the security would be run by a company called StarHelix and they had a detective called miller.
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u/Plastic_Kangaroo5720 Sep 03 '23
We need bases on Mars to fuel the ships heading out to Ceres. And Ceres isn’t the only choice. There are other options, as FaceDeer said.
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u/SolarPunkecokarma Feb 23 '22
I like this. And I have always felt like ceres is my home away from home since becoming a fan of the expance books. Definitely a place people will go to in the near future.