New Mars Forums

When someone fights for your country, they deserve your respect.  If they choose to apply for citizenship, military service should be taken into account in reaching a decision.  Should it provide an automatic pass?  Absolutely not.  When you make someone a citizen, you are permanently inviting them and their descendants into the extended family of your nation.  That is not a decision to reach lightly.  This man committed a serious felony.  His military service and injuries should have been taken into account when deciding his sentence.  Presumably, they were.  But expecting to enter the American extended family having committed attempted murder on American soil would be unreasonable.

The attached image shows a possible plan view of the town built beneath the proposed 200m diameter brick dome on Mars.

The red lines indicate the walls of individual buildings.  The black shaded areas are roads, squares and the agora (in the centre).  All roads are entirely pedestrian spaces.  The two ring roads have a width of 2m for pedestrian traffic.  The two straight roads that cross the agora have a minimum width of 3m.  The streets widen at intersections.  These are natural meeting places and will likely be the location of cafes, with extra seating spilling out onto the street.

The agora is a circular paved area some 50m in diameter at the centre of the town.  Most days this will contain overspill outside seating from restaurants and bars.  It will also host open air markets, Christmas events, theatre performances and is large enough to accomdate the entire population for town meetings.

All buildings are coloured green.  This denotes the presence of roof gardens.  Every building will host roof garden space.  This will all be connected to form a continuous landscape, with foot bridges connecting all blocks above street level.  This is important, because the street level of the town is extremely confined, with almost all of space taken up by buildings.  The roof garden landscape provides an open green space that is open to all by ascending a spiral staircase from the street or from within buildings.  These garden spaces will be places for recreation.  This limits the stress of living within an otherwise crowded environment.

The buildings at the outer edge of the dome are large structures.  They will include such things as sports facilities, gymnasium, schools, cinema, university departments, hotels, government buildings, public bathhouses and overspill accomodation.  These will be constructed right up against the edge of the brick dome.  The inner districts consist of smaller buildings.  These will include terrace houses, as well as shops, bars, cafes and restaurants.

The whole town will be very densely inhabitated, due to the cost of constructing the dome.  Houses will be small in footprint, but also tall.  Flats may also be located above commercial premisses.  How many people could live in this town?  The medina in Fez, Morroco is a pedestrian city with a floor area ratio of about 1.5.  It's population density is about 550/hectare.  Our Martian town will have structures constructed on about 80% of internal land area, to a height of 5 floors.  So floor area ratio is about 4.  I will therefore conservatively assume about double the population density of the Fez medina.  The area under the dome is 3.14 hectares, suggesting a population limit of some 3,500 people.  The inclusion of underground spaces in addition to the roof garden, allows these people to spread out some more.  It might be tolerable for some people to live in underground apartments, if they can climb a set of stairs into the town when they need open space.

Basalt fiber has a tensile strength ranging from 2.8 to 3.1 GPa.  This beats most maraging steels, for a material with only about 1/3rd the density!  For larger castings, the strength is a lot less.  This is likely because cooling introduces stress fractures into the material, which is quite brittle.  Tensile stress must be kept sufficiently low to ensure that any stress fractures remain smaller than critical crack length.  This allowable stress will be much lower than the UTS of the material.  Still, the compressive strength of 300-500MPa is impressive.

I wonder if we could make rails out of this stuff?  They would need a steel strip upper surface to interface with the wheels.  But the compressive strength is plenty for a railway line.  Food for thought.  If this material cannot cope with thermal transients, then that would be its undoing on Mars.  High manganese steel should retain ductility even at Martian nighttime temperatures.  But the energy cost is much higher.  Steel making on Mars will be much easier if we find fossil methane or hydrogen in traps beneath its surface.  There are hints that that may be the case.  But the presence of large deposits is speculative at this point,

The image below shows how I think we will build brick domes on Mars.

The inner black lining is a parabolic dome that would be constructed from Class A engineering bricks.  Regolith covers the dome and forms a spiral Ziggurat.  This allows a spiral road to wind around the structure until it reaches the top.
https://en.wikipedia.org/wiki/Ziggurat

The stepped structure shown in my sketch is exagerated.  Likely, the retaining wall behind the road will be no more than 1m high, so each spiral layer as shown in the drawing would be 1m high.  This avoids any significant load concentrations that could result in buckling instability.  The road will wrap around the structure over 100 times before reaching the top.  We would build the berm incrementally around the parabolic dome as it is assembled towards its apex.  This allows assembly robots easy access to the work surface by running up the spiral road.  It also avoids the need for formwork inside the dome, as robots can climb up the regolith berm to get to the work surface.  With each new metre added to the dome, regolith would be piled around it and the spiral road will be extended once around the structure.  In this way, the only materials needed are brick, stone, graded regolith and a binding cement for the bricks.

The dome shown here has a diameter of 200m (650').  This gives an internal land area of 3.14 hectares.  The dome itself can be quite thin, as it is really acting as a retaining wall to prevent compacted regolith from crumbling inward.  We would need a minimum of 400,000 tonnes of graded regolith to build the berm.  This is the amount needed to balance an internal pressure of 50KPa under Martian gravity over an area of 3.14 hectares.  Moving and compacting this much regolith is no small task.  If we processed 1100 tonnes per day, it would take about 1 year to build the structure.  Assuming a dome thickness of 7.5cm (standard width engineering brick) we would need ~15,000 tonnes of engineering bricks.  That is 41 tonnes per day × 1 year.  That is about 12 cubic metres of bricks per day.  I think we could do that in a modest sized brick oven.

I anticipate that the dome would contain an extremely dense urban district.  This will consist of very narrow pedestrian streets lined with terrace houses and shops.  Rather like the Fez medina.  To get the most use out of our dome, I anticipate that the internal town will be built on three levels.  The lowest level will consist of a network of subsurface tunnels and chambers.  This would contain functional infrastructure (water delivery, sewage removal and treatment, electric power delivery), as well as small scale industry, inventory storage and any other functions that don't need to take place in the buildings above.  Next will be town itself, a dense network of terrace buildings designed to resemble a mediaeval town.  These would be limited to 5 floors high, to preserve the human scale of the city.  Finally, the top level will be the flat roofs of the buildings, which will be landscaped as a continuoys greenspace, with footbridges running over streets.

How many people would live in the dome?

TH, see images below.

In this example, cables support a steel frame ceiling.  The frame is covered first with a layer of coarse rocks and then a layer of compacted regolith fines.  Finally, bulk regolith is heaped ontop to a depth of about 5m.  The weight of the regolith and frame is transfered to the cables prior to pressurisation.  The cables transfer load to the cast basalt ring on top of the stone retaining wall.  Circumferential compressive forces balance the tensile forces in thebasalt fibre cables.

Once pressurised, the internal pressure would largely cancel out the downward weight of the frame and regolith overburden.  At this point, tensile stresses in the cables and shearing stresses in the frame, are largely cancelled out.  This removes any longterm fatigue problems.

The LED screen (or blue transluscent sheet?) would hang from the underside of the steel frame.  This would presumably be a lightweight structure.

I'm not quite sure why we would build a roof this way, rather than as an entirely compressive shell structure.  Can you think of advantages that a cable supported structure would have over a parabolic compressive shell?

This tool allows individually designed buildings to be uploaded and rendered into an AI generated cityscape.  Very impressive.
https://www.d5render.com/

Using tools like this, we could design a Martian city right here on Earth and have all of the design elements worked out.

The New Urbanism movement was founded in the United States in the 1990s, by people who had grown tired of the car-centric lifestyle that exists everywhere in America.  The arrival of the car utterly ruined American cities.  They became places that everyone wanted to get away from.  Europe was spared the worst of this vandalism by a mixture of historical asset inertia and lack of space to build very spread out cities.
http://www.newurbanism.org/newurbanism.html

Whoever wrote the New Urbanism website dragged a lot of their personal politics into it, which I think is a shame.  None the less, the value of compact, carfree towns and cities, is amply demonstrated by the site.

Another excellent web resource is Carfree Cities by Crawford.
https://www.carfree.com/fes/index.html

Crawford develops a city architecture that achieves pedestrianisation within districts, with rail travel working between districts.  In the referenced section, he talks about the grand medina in Fes.  This is the largest intact medieval city in North Africa.  It is entirely carfree.  The streets are too narrow to allow even bycycles.  Approximately 150,000 people live in the medina, which has an area of 300 hectares, or only slightly over one square mile in area.  That is about 20 square metres land area per inhabitant.  This is very dense and is made to feel even more cramped by the low rise buildings of the medina.

Back in the UK now.  I took this batch of pictures in Hoorn in North-Holland.

Utrecht (4)

Utrecht (2)

It may have been written in Dutch, I don't.  Whilst the IR telescopes would be valuable for Earth defence, they are equally valuable for resource prospecting.  IR emission spectra should also tell us a lot about the minerology of each asteroid.  Starship has already reached a sufficient level of technological development to do this right now, if it were used in expendible mode.  Reusability is proving to be difficult because of the sheer trauma of atmospheric entry on the ship.  But in expendible mode, the ship would appear to be fully operational.

I like the idea of kinetic impactors.  At a 30km/s relative velocity, an impactor will carry 500MJ/kg of specific energy.  That is about 100x of the explosive energy density of TNT.  It may be that we don't need nukes to deflect asteroids, just a lump of iron hitting them at high relative velocity.  But provided there is sufficient time to impact, we could make the most dangerous asteroids our first priority for mining.  By the time the impact date arrives, the asteroid would have been processed into solar power satellites, space stations and propellant.