Mars Direct Rethought - Fixing the potholes in Zubrin's plan

RobertDyck · 2002-09-24 01:37:46

I checked photovoltaic panels. Space rated improved tripple junction photovoltaic panels from one supplier mass 2.06 kg/m^2 with 3 mil ceria doped coverslide. The coverslide is a thin glass coating. The ceria dopant will conduct static electricity away. The cell itself is 7.5 mil thick. This has a 26.5% conversion efficiency at load voltage, beginning-of-life, to produce 330W/m^2 for panels greater than 2.5m^2. That is in sunlight intensity at Earth orbit. Mars will have 43.075% the light intensity, so 142W/m^2 BOL. Radiation will degrade the panels. It has 22.3% at load voltage end-of-life. Designing for end-of-life, then 6kW on Mars would require 50.16m^2 area, and mass 103.3kg or 0.1033t. That mass doesn't include substrate: a backing on which to mount the cells. Light-weight aircraft wings are made from carbon fiber / epoxy composite. Two layers of 3K graphite fiber fabric mass 0.3865 kg/m^2. Add 50% mass for the epoxy and spars, so about 29kg for the support petals, or 132kg total mass. A "hollow wing" design support structure is overdesign for space, but provides additional structural support for atmospheric entry and landing.

That means 6kW solar panels only mass 0.132 tonne, not 1 tonne.

Pioneer Astronautics made a presentation about ISPP on August 28, 2002. They have come up with a MetaMars ractor that converts methane into benzene: 6 CH4 -> C6H6 + 9 H2. Together a Sabatier reactor, electrolysis, and MetaMars reactor convert 1 tonne of hydrogen into 45 tonnes of benzene / oxygen fuel. The presentation detailed several catalysts for the reaction, but didn't give total reactor mass or power requirement.

Bill White · 2002-09-24 08:52:42

Robert, the depth of your investigation into technical issues is most impressive. Now, a question.

Have you looked into the photocatalytic production of free hydrogen from water? DOE link I am rather obsessed with this idea but if someone explains why it is impractical, I will let it go.

The idea is to fill a large glass jar with water and photocatalysts and set in Martian sunshine, siphoning off H2 and O2 as the reactions progress. Burn the H2 for fuel (whether by combustion or fuel cell) and return the resulting water back into the jar.

The Japanese apparently are working on this idea quite vigorously, in order to produce free hydrogen for fuel cell automobiles here on Earth.

RobertDyck · 2002-09-24 10:27:17

Hydrogen/oxygen generation this way is an interesting idea. In fact, the oxygen generating side has the same net effect as photosystem II from the light reaction of photosynthesis in plants.

Photosystem II uses 2 molecules of pheophytin to split water into oxygen, positive hydrogen ions, and electrons. Each pheophytin molecule splits one water molecule releasing one oxygen atom. The two oxygen atoms combine to form molecular oxygen (O2). Splitting two water molecules at a time so oxygen can directly recombine into O2 is more energy efficient than producing mono-atomic oxygen. Photosystem II has 50 molecules of chlorophyll "a" and a half dozen carotenoid molecules (such as beta-carotene), all of which act as antennas to convert light to electric charge. The carotenoids have a different absorption spectrum than chlorophyll, so that increases light collection efficiency. Electrons are then passed to the electron transport chain which uses a series of redox reactions.

In plants, all of this is embedded in a bilipid membrane. The Florida Solar Energy Center is attempting to this in a tank. An enzyme to do the same thing as photosystem II must hold itself together while floating free in water. In plants, the H+ ions are released on one side of the bilipid membrane, which forms a sealed bag. The first step of the electron transport chain pumps more H+ ions into the bag. Outflow of H+ ions drives production of ATP, the chemical "food" of cellular metabolism. These guys aren't producing a highly structured nano-machine; they are attempting to produce a simple pair of tanks. Producing oxygen in one tank and hydrogen in the other using two pairs of catalytic reactions sounds like an ingenious solution.

The only question now is how much water and enzymes this needs, and what is the total mass? Since this discussion is about rethinking Mars Direct, I assume you are proposing this as a replacement for the electrolysis tank for ISPP. If so, we have to compare its total mass against an electrolysis tank and the photovoltaic panels required to power it.

RobS · 2002-09-24 14:30:11

I'm glad to see so much discussion of some of these very intersting technical details and problems. I've been preparing another very long posting, but it isn't ready yet; lots of things to check.

The question about photolytic cracking of water is interesting and I have enjoyed your postings about them, Bill White. I didn't not figure it in because it is still very experimental. What works in the laboratory on Earth will take a lot of research to make it work on Mars, where the temperature is about 50 below zero Centigrade. I suspect it can be made to work, but who knows how many hundreds of millions of dollars must be invested. I was trying to stick to known technology. So I didn't rule it out, and please keep up apprised of future developments.

Thank you, Robert, for more details about the solar panels. There are so many different "facts" available it is mind-numbing. Mars Direct says somewhere that a 100- kilowatt solar array would weigh 27 tonnes. Zubrin says he was assuming 15% efficiency. The new gallium-arsenide solar cells have achieved 32% efficiency in the lab. I assumed 30% efficiency because that seems achievable in 10-15 years, and because we know there will be a lot of commercial investment in the technology.

I think I gave some of these details already, but I refined my design a bit since: if you assume a six-meter in diameter lander and the cargo floor (once the cargo is removed) is covered with solar panels, the floor has a 28 square meter area. The circumference is 18 meters (yes, I know, it's a little bit more). Four petals would be 18/4 = 4.5 meters wide at the base. I assumed that the cargo lander was covered by petals up five meters (beyond that would be a nosecone) and at the top the petals are 3.1 meters wide. Thus each petal has an area of 19 square meters. I then assumed that each petal was hinged at the end and that a second panel rested on top of the first one that could be folded out, making the panels a total of ten meters long. The extension petal would probably be cut in half down the middle so that each half could fold out separately; that descreases the mass and makes it easier for a rover, controled telerobotically from Earth, to lift and swing the extension petal. Airbags could probably do a lot of the work of unfolding the petals, but maybe rovers would have to finish the job.

Each petal and each extension petal has an area of 19 square meters. Thus 19 x 8 = 152 square meters. Add the 28 square meters of the floor of the cargo hold and you have 180 square meters. I calculated the power output based on 500 watts per square meter (Mars insolation) x 0.3 efficiency x 0.3 (because the sun is up half the time and not overhead; basically, the inverse of pi) which gives a power output of 45 watts per square meter. You need 21 square meters to make a kilowatt of power (on a continuous basis; when the sun is overhead, the same area makes 3 kilowatts). Thus 180 square meters makes 8 kilowatts.

Since I have seen masses for solar panels range as high as 10 kg per square meter and much lower, I figures on about 5 kg per square meter to be on the safe side, and threw in another 500 kg for electric cables (to connect to the next nearest lander), voltage conversion, and maybe a fuel cell system. So I came up with 1.5 tonnes and 180 square meters to produce 8 kilowatts.

Yes, there are a lot of other ways to figure the problem. Right now, I'm trying to figure out a way to make a bigger array easily, because if you need about 1 kilowatt of power output to make 1 tonne of fuel a year, and you need to run a base as well, you really need 80-100 kilowatts of power output. I can see landing 5 or 6 of these small landers and connecting them together, but the more landers, the more complicated this scheme gets. Once people land, they can pick up panels, walk around with them, deploy them, and wire them together, but with robots that's tricky (especially with a 5-45 minute time delay!). It seems to me the best one can do before people arrive, realistically, is wire together a 40-50 kilowatt array, and even that may be unrealistic. That doesn't produce all the fuel the crew needs to take off before they land, which is one of the Mars Direct criteria.

Anyway, more later.

-- RobS

P.S.: One more tricky problem to this design; the rovers have to drive down a petal (which would serve as a ramp) to get off the lander. So at least two of them would have to be reinforced. With the "extension petal" design, the extension petal is folded up on top of the inner petal, so the solar arrays themselves would be enclosed and not driven on directly. Presumably one petal has to be deployed in order to let the rover out; it then can bulldoze rocks out of the way so that the others can be deployed safely. The entire procedure would take months.

RobertDyck · 2002-09-25 01:48:00

I know, a mass of 3.2195 kg per square meter and 26.5% conversion rate may seem radical, but that is based on figures available now. The same manufacturer states the maximum conversion rate for those panels is 26.8%, but that is without anything using that power. They also make photovoltaic panels designed for use on Earth that have 30% conversion, but the ones for space have to be radiation resistant and designed for the light spectrum in space (more intense UV, etc). I even have a price quote for the space rated panels. The power figures I calculated are exact, but don't include the fact that the sun is only up half the time on Mars. Dividing by pi may be a good idea.

I can suggest how to make a bigger array. I notice you are following the design of Mars Pathfinder: opening petals covered by photovoltaic panels on the inside. However, satellites have used an accordion deployment mechanism for years. This permits stacked panels to become long wings. On Mars, to avoid the problem of the wing supporting its weight in gravity just "unroll" the wing onto the ground. Deployment could be by placing a floppy hose along the side of the panels, and inflating it. As the hose pressurizes it will become stiff and straight. This will push out the photovoltaic panels attached to it.

Here is another figure for you. SEO142 cable will remain flexible to -50?C and resists oil, acids, chemicals, solvents. It can carry 18 amps at 600 volts for 10.8kW along 2 conductor cable. It masses 224.7kg per km. Other gauges are available from 10 to 30 amp (6kW to 18kW), or 45 amp for 4 conductor cable (effectively 54kW). That last cable masses 977.7kg per km.

RobS · 2002-09-26 00:19:12

Thank you for the additional information about solar panels. I like the idea of unrolling them! That is immensely simple and straightforward, if they roll up alright. I hesitated to use an accordion design because the lander platform is elevated, so the panels have to expand to the ground, then roll along it. Not only are there stresses in the panels, but there may be surface irregularities even if one tries to clear the ground of rocks beforehand, and the panels could get stuck on the bumps.

But unrolling is very clever. Thanks for the cabling information as well.

Our calculations for total power output per square meter come out to be about the same. Your figure is what I think the panels make at high noon, when the sun is overhead.

I already have a detailed and lengthy "article" to post that uses 1.5 tonnes for 256 square meter, triple-folded petals making 11.5 kilowatts. I think I'll leave that for now. I did not include the weight of cables or transformers and figured those items have to be included in the 1.5 tonnes. And I need to build a little spare into the calculations anyway!

Someone asked about a radiometer for making power. I have no idea how much you can make that way. I suspect it is not very efficient, but maybe it could be improved.

-- RobS

RobS · 2002-09-26 00:35:02

Here is an expanded proposal for reorganizing Mars Direct. I am still revising it, but the moving target is not moving as fast, now, so here it is. As it was originally composed in Word, importing it onto this Bulletin Board messed up some formatting. I welcome your comments.

-- RobS

The Mars-24 Plan, version 2.0

The plan derives its name from the idea that Mars can be explored by human beings using the Space Shuttle or large commercial rockets capable of launching about 24 tonnes to low earth orbit. It derives its ideas from various authors. One feature is the reusability of the principal transportation elements.

EQUIPMENT

1. SOLAR-ELECTRIC VEHICLE (SEV)
High-efficiency solar panels (900 square meters, 300 kw), ion engine (Isp, 3,000 seconds), avionics, etc.

SpaceNut · 2017-05-21 10:43:30

I just happened on the old topic, have not had the chance to read through the discusion but it still hold true even today as we are trying to come up with a plan that not only works but is fundable and sustainable for the future of being able to colonize mars....

tahanson43206 · 2021-12-18 11:43:48

For SpaceNut ... I just deleted a post that somehow ended up in this topic with my name on it. Just FYI (th)

SpaceNut · 2021-12-18 14:13:46

With all that Zubrin has done and written we should have already been to mars but the main issue has to due with funding for the ride so that it could be done. Even the moon plan using the Space X Falcon 9 Heavy was a do able mission to push for as it would prove Zubrin right...

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#126 2002-09-24 01:37:46

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#127 2002-09-24 08:52:42

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#128 2002-09-24 10:27:17

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#129 2002-09-24 14:30:11

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#130 2002-09-25 01:48:00

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#131 2002-09-26 00:19:12

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#132 2002-09-26 00:35:02

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#133 2017-05-21 10:43:30

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#134 2021-12-18 11:43:48

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#135 2021-12-18 14:13:46

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

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