New Mars Forums

Official discussion forum of The Mars Society and MarsNews.com

You are not logged in.

Announcement

Announcement: We've recently made changes to our user database and have removed inactive and spam users. If you can not login, please re-register.

#151 2018-11-13 14:49:25

kbd512
Moderator
Registered: 2015-01-02
Posts: 2,959

Re: Mars Cart

In order to prepare the propellant to come home in 24 months, that means 1.178t of LOX production per day for two years since BFS requires 860t of LOX.  That's just over 49.08kg per hour.  That means MOXIE needs 294.5kWe to produce enough LOX to fill BFS's LOX tank, assuming zero losses, which would never happen in real life.  That's a lot of power just to get the O2.  That doesn't include the power to run the Sabatier reactor or the cryocooler to keep the propellant cold.  The people at SpaceX and NASA certainly have their work cut out for themselves.

I recall reading somewhere that we've been researching using vacuum ultraviolet lasers to drastically reduce the amount of power required to split CO2 and produce C and O2, rather than CO and O, but I've no clue how that effort is going.

Offline

#152 2018-11-13 14:57:07

JoshNH4H
Moderator
From: Pullman, WA
Registered: 2007-07-15
Posts: 2,513
Website

Re: Mars Cart

Seeing as the efficiency of lasers is generally on the order of 10% it's hard for me to imagine that it's going very well


-Josh

Offline

#153 2018-11-13 19:10:02

kbd512
Moderator
Registered: 2015-01-02
Posts: 2,959

Re: Mars Cart

Josh,

Some of the newer GaAs-diode lasers have achieved greater than 75%+ electrical-to-optical efficiency.  A very interesting new fiber-based high-power laser that Lockheed-Martin is working on is in excess of that, but optical-to-optical efficiency limits electrical-to-optical efficiency to between 25% and 35%.  The best commercial diodes that you can buy are only have an electrical-to-optical efficiency of 50%.  Alas, UV lasers are some of the worst when it comes to efficiency, although the new solid state models could help change that and reduce the requirement to continually replace the gas every couple weeks or so.

In this application we definitely need beam shaping, which further hurts our efficiency.  We'll need an UV transparent quartz tube to lase through.  Gas pressure will push the Carbon residue through the tube, so an electrostatic Carbon separator downstream of the laser aperture is required, else the CO2 and O2 will be contaminated with Carbon fouling.  We also need a method to separate the CO2 from the O2 to recirculate the CO2 back through the system until we have acceptably pure O2.  That means we also need a molecular sieve.

It looks interesting to me.

Offline

#154 2019-02-24 22:05:04

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,150

Re: Mars Cart

From page 5 with design notes continuing to make a means to move and to haul cargo as needed but to know how to fix what breaks is a key element to being able to sustain man while he is there.
https://ecomodder.com/wiki/Open_ReVolt
We can make motors insitu, batteries but when it comes to controllers and devices to send the power from the battey in measured amounts to produce movement makes for either learning how to recycle the parts for the cargo ship or learning how to build lower tech controllers.
Relays and switches are low tech....

https://www.brighthubengineering.com/di … r-circuit/

https://makezine.com/2018/03/19/control … ic-relays/

https://www.homepower.com/

https://www.hindawi.com/journals/mpe/2010/627836/

https://www.engineersgarage.com/contrib … ay-at-home

https://www.anaheimautomation.com/manua … -guide.php

http://ddmotorsystems.com/ElectricVehicles.php

https://www.electricmotorsport.com/e-bikes

http://www.ebikeschool.com/how-to-build … 650-cells/

http://ev-bg.com/wordpress1/wp-content/ … ehicle.pdf

Offline

#155 2019-02-25 03:39:15

elderflower
Member
Registered: 2016-06-19
Posts: 1,115

Re: Mars Cart

It takes a lot less energy to split the first O from CO2, making CO, than to split the second O to make Carbon. In addition the resulting C will be deposited all over your equipment and catalysts. Also heat recovery from a CO stream is a lot easier than trying to cool the solid carbon. On the downside, CO is not so easy to separate from your O2 product.

Offline

#156 2019-02-25 17:52:47

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 5,790
Website

Re: Mars Cart

elderflower wrote:

On the downside, CO is not so easy to separate from your O2 product.

Direct CO2 electrolysis is done across a thin ceramic wall. With high temperature (900°C+) and electric potential. O2 passes through, CO and CO2 do not. Inside the tube starts with pure CO2, ends with 80% CO, 20% CO2 by volume. Outside the tube is pure O2. That's was the Mars ISPP Precursor ("MIP") on Mars Surveyor 2001 Lander mission. MOXIE on Mars 2020:

MOXIE collects CO2 from the Martian atmosphere, then electrochemically splits the CO2 molecules into O2 and CO. A solid oxide electrolysis cell works on the principle that, at elevated temperatures, certain ceramic oxides, such as yttria-stabilized zirconia (YSZ) and doped ceria, become oxide ion (O2–) conductors. A thin nonporous disk of YSZ (solid electrolyte) is sandwiched between two porous electrodes. For oxygen generation from carbon dioxide, CO2 diffuses through the porous electrode (cathode) and reaches the vicinity of the electrode-electrolyte boundary. Through a combination of thermal dissociation and electrocatalysis, an oxygen atom is liberated from the CO2 molecule and picks up two electrons from the cathode to become an oxide ion (O2–). Via oxygen ion vacancies in the crystal lattice of the electrolyte, the oxygen ion is transported to the electrolyte-anode interface due to the applied DC potential. At this interface the oxygen ion transfers its charge to the anode, combines with another oxygen atom to form oxygen (O2), and diffuses out of the anode.

The net reaction is thus 2CO2 ⟶ 2CO + O2

Offline

#157 2019-02-26 14:22:28

elderflower
Member
Registered: 2016-06-19
Posts: 1,115

Re: Mars Cart

That is a very energy hungry process, Robert. It might be more economic if you can find a use for the CO byproduct.

Offline

#158 2019-02-26 14:58:07

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 5,790
Website

Re: Mars Cart

elderflower wrote:

That is a very energy hungry process, Robert. It might be more economic if you can find a use for the CO byproduct.

It takes about 3 times as much energy vs water electrolysis to produce a certain mass of O2. On ISS, it would require power from solar panels. Obviously this wouldn't be primary oxygen generation, rather it would replenish recycling losses. You want to recycle wash water, and recover moisture from feces. All this to close the loop sufficient for a life support system for transit to Mars.

As for using CO, on the surface of Mars you can use CO to smelt iron. Or to make plastic: 2 CO + 4 H2 to make ethylene + water, or CO + Cl to make phosgene (an ingredient for polycarbonate), or 4 H2 + 8 CO over a catalyst to make butadiene and CO2 (first step for polybutadiene rubber), or ammonia + CO to make hydrogen cyanide + water (first step to make nylon). You obviously want to be very careful with phosgene (World War 1 poison gas) or hydrogen cyanide gas.

Offline

#159 2019-02-26 17:57:12

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,150

Re: Mars Cart

INTEGRATED MARS IN-SITU PROPELLANT PRODUCTION SYSTEM

3CO2 + 6H2 > CH4 + 2CO + 4H2O

Mars In Situ Resource Utilization and the Importance of Water Resources

http://www.geoffreylandis.com/propellant.html

Sabatier reaction (which requires hydrogen as well as carbon dioxide):

4H2 + CO2 --> CH4 + 2H2O

electrolyzing CO2 into carbon monoxide (CO) and Oxygen, using a zirconia electrolysis 2 CO2 --> 2CO + O2

MARS IN SITU PROPELLANT PRODUCTION UTILIZING THE REVERSE WATER GAS SHIFT

Of course we could make a hybrid solid booster on mars as well.

BREAKTHROUGH CONCEPTS FOR MARS EXPLORATION WITH IN-SITU PROPELLANTS

Hybrid Rocket Propulsion and In-Situ Propellant Production for Future Mars Missions

Offline

#160 2019-02-27 04:03:39

elderflower
Member
Registered: 2016-06-19
Posts: 1,115

Re: Mars Cart

I'm thinking of early days on Mars, not of the time when we have large settlements and industrial activity. CO/LOX could be used as vehicle fuel for hoppers and rovers and as an emergency fuel store for thermal electric generators, I suppose. But methane or methanol would be much better for these purposes. Hydrogen is the key so we must find useable water.

Offline

#161 2019-03-26 21:02:36

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,150

Re: Mars Cart

An important part to power is saving it and converting it back out for use. The trick is to match the abilities for each to the batteries that are used.
https://www.brighthubengineering.com/di … -inverter/

Of course a cart needs a strong motor
https://www.goldenmotor.com/frame-bldcmotor.htm

matching all of this with the controller
http://cdn.intechopen.com/pdfs/9563/InT … ollers.pdf

Offline

#162 2019-08-10 15:48:24

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,150

Re: Mars Cart

I see that we talked about battery to supply power and one key lelement is what we consider a dead battery versus a fully charged ready to use for the number ampere hour ratings that the battery can suppy for a 12v battery (lead scid or alykeline) that dead voltage is roughly 9 volts and if your item requires constant current the battery will have gotten quite hot by that point causing it to become degraded once recharged.
Each battery chemistry will have different cell dead or what is considered a voltage to low to operate with.

Offline

#163 2019-08-16 20:34:48

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,150

Offline

Board footer

Powered by FluxBB