New Mars Forums

The new CatGen catalyst bed technology promisses more compact and fuel efficient GT engines.
https://youtu.be/-TDoteS9QZA

I can see a number of problems with this idea in practice.

1. Whilst the catalyst allows efficient combustion in a compact volume, its presence limits combustion temperature to the melting point of the catalyst and substrate.  This places limits on cycle efficiency.
2. The catalyst bed adds weight.
3. The compressor must force air through the narrow channels of the cataylst bed, which increases pumping losses through the engine.  In a conventional GT, compression already consumes at least half of the energy produced by the turbine.
4. Although the video talks about the tolerance of the catalyst to different fuels, the reality is that fuels containing sulphur or soot will poison the catalyst.

In spite of these problems, this engine concept may offer value in burning lean fuel mixtures that would not otherwise support combustion.  In the Martian context, we know that the Martian atmosphere contains small amounts of CO and O2.  If CO2 can be seperated from the bulk air, the remaining gas mix could be preheated and passed through a catalyst bed to extract energy.  Given the small concentration of CO, this is unlikely to be a net energy producing reaction.  But assuming we are inputting energy to extract specific gases from the Martian atmosphere, this reaction would allow some portion of input energy to be recovered.  It also scrubs CO out of the N2/Ar gas mix, which is important if we are gathering life support gases.

GW,
Out of interest, what would you estimates the rate of return on your investment to be?

A man has been jailed in the UK for 'possessing rightwing music'.
https://youtu.be/kKrBDsFBlxw

TH, impressive image.

Kbd512, thanks for this.  I am going to attempt to balance the rotor on the ground before lifting it up the tower.  My rotor will work at a far lower rotational speed compared to an aircraft propeller.  But vibration could damage the cradle supports, bearings and tower over time.  So I want to balance the rotor as well as possible.  The weather has been awful here today, but looks better tomorrow, so I should be able to make progress and report on results.

It is on the to do list.  I know the rotor is out of balance because one of the blades is slightly out of alignment from when I dropped the rotor whilst trying to install it.  When it is mounted on its bearings, I will be able to trim it by adding steel strip to the blades.  I doubt that I can fix the problem entirely.

The weather is poor at present.  It is raining with a 40mph gale.  The scaffold is up, but I wont be able to install the rotor before tomorrow at the soonest.

After work today, I am going to start work on a table saw.  This will be a cubic wooden box with internal dimensions 12", sufficient for a 10" diameter circular saw blade.  I can use this to saw firewood.  The thing that is taking time is safety features.  The saw will carry the female part of the cone clutch.  The saw box will be mounted on rails and will be pushed against a spring until the two parts of the the clutch fit together.  A peg is then inserted, holding the saw box in place against the compression spring.  To seperate the two parts of the clutch, the peg can be pulled out, and the compression spring pushes the two parts of the clutch apart.  It will take me at least a few days to build this.  But it will be the first tool that I build for the machine.  It is therefore a proof of concept.

I have added four new blades to the rotor of my machine and made some improvements to the pulley.

When the paint is dry, the rotor can be installed.  I will be putting up the scaffold today.

Why British people looked older than they were in old photos.
https://youtu.be/ECfhU_I9mjQ

In short, life was tougher.  The air was polluted, food was unhealthy, almost everyone smoked.  The work environment was dangerous and polluted.

I will be resuming work on my windmill on Tuesday.  I am hoping to have it finished and up and running a week today.  Making tools will take a while longer.

The problem with building large and thin masonry domes, is not the strength of the materials, it is stability.  Prior to pressurisation, the dome will be subject to external forces from the overburden.  If these are too high, they will buckle the dome inwards, even if the crush strength of the dome is never exceeded.  The critical external pressure that could result in buckling instability for a sphere or hemisphere, is given by:

Where:
Pcr = critical external pressure for onset of buckling (Pa);
E = Young's Modulus (Pa);
v = Poisson's Ratio;
t = dome wall thickness (m);
R = Dome radius (100m).

For Class A engineering brick, Poisson's Ratio is 0.15 - 0.25.  I have taken an average value of 0.2.  I could not find a value of Young's Modulus for hard engineering bricks.  This site proposes a value of 20GPa for brick generally.
https://www.engineering.com/youngs-modu … the-brick/

We will be putting enough overburden on the dome to impart a 50KPa external pressure.  This will be sufficient to counteract internal pressure when the dome is fully pressurised.  Prior to pressurisation, during construction, there will be a net inward pressure of 50KPa acting downwards.  Maximum effective pressure will be experienced at the dome apex.  This is where buckling is most likely to occur.

Solving for the known variables, gives a minimum stable value of t of 14.56cm.  The mortar between bricks will also effect youngs modulus of the structure.  We are planning to use epoxy resin to glue the bricks together.  However, assuming that individual bricks are polished, only a very thin layer (0.1mm) of epoxy need be applied to bond them.  So the effect of the mortar in this case will be minimal.  With this in mind, for a 200m diameter dome, wall thickness should not be less than 14.56cm.  A thickness of 20cm allows for some margin of safety.

Of course, the dome presented here is not a perfect hemisphere.  It is parabolic, which allows downward compressive forces to be absorbed with reduced shearing stress within the structure.  This reduces the risk of buckling.  In addition, Martian regolith is known to possess adhesive properties due to its high iron oxide content.  Indeed, compressing regolith fines in a mold would produce a reasonably strong ceramic.  This gives reason to expect that any compacted regolith layer would tend to redistribute load around the dome, reducing the downward pressure acting on the apex.  These factors tend to suggest that the calculated value of minimum safe thickness is conservative and a 20cm dome thickness will be more than adequate to ensure structural stability.

The ratio of t/R is constant for all values of R with the same materials properties.  This means that a dome with 50m radius required a 10cm minimum brick wall thickness.  Likewise, a 500m diameter dome would require a minimum wall thickness of 50cm.

Teraforming would provide a solution here.  If Mars is warmer and has an active hydrosphere, then the fines that are currently being blown about would end up as clay minerals in sediments.  If Mars had a large sea anywhere on its surface, it would tend to eat up this dust, because dust could enter the sea, but would have no way of leaving once it did.  It would tend to settle as mud at the bottom.  But the atmosphere is too thin at present and temperatures too cold to allow a sea to form anywhere on Mars.

If the bricks are quite smooth, then a thin layer of epoxy glue could be used to bond them.  If we assume a brick height of 10cm and a 1mm layer of epoxy glue, then we would need about 50 cubic metres for the whole dome.  The glue would weigh about 50 tonnes.  There are three potential challenges that I can see:

(1) As the dome rises, the work surface curves inwards.  Beyond about 1/3rd of the way up, each new layer of bricks would need to be held in place whilst the glue sets.
(2) Mars is cold compared to most environments on Earth.  Glue would be extremely stiff at temperatures <0°C.  Setting time would be long, if indeed it sets at all.  We may need to apply resistance heaters to keep the bricks and glue warm while the glue sets.
(3) Mars has an atmosphere with non-negligible pressure, which is a strong advantages over the moon.  However, epoxy monomers are quite volatile.  Will evaporation negatively impact the glue?

Assuming we can solve these problems, epoxy glue looks like the best approach.  We could potentially produce a fine paste of epoxy glue and martian fines as a cement.  That way, we can reduce the required mass of glue still further.