Battery power construction equipment

SeaDragon · 2020-07-27 05:29:47

kbd512,

Hrm. Sorry about that, upon closer inspection there was a problem with my reasoning:

In “The Case for Mars” 2011 edition by Dr Zubrin (my freaking hero), pp 158, there’s a table that states that H2/CO2 can give an energy density of 25,833 W-hr per kg of H2. Comparing enthalpies of formation on either side of the Sabatier reaction I assume this is talking about:

4H2 + CO2 -> CH4 + 2H2O

Gives something closer to 5,700 W-hr/kg H2, which isn’t much better than just bringing your own oxygen with you and burning H2/O2 instead (3,750 Whr/kg, same source as above, confirmed by my calculations also).
Given that the latter reaction is way more compact (most of the mass is in dense liquid O2 not H2) and the operating temperature must be lower for the Sabatier process to stop the competing (and very annoying) endothermic reaction:

2CO2 + 5H2 -> C2H2 + 4H2O

That H2/CO2 propellant combination now just looks pretty terrible.
If I’ve gotten something wrong and someone can see how H2/CO2 can give the quoted 25,833 W-hrs per kg please let me know, obviously my default is that I’ve done something wrong somewhere and that the text is correct but I can’t currently see how.

Anyway, even using something like CH4/O2 as a propellant combination and accepting your very reasonable counter-points to powered flight I still think our flight capability with a powered heavier-than-air vehicle is far improved over blimps.

My major qualms with them are:
1)You have to move with the wind and at or below the wind’s speed when using a blimp, greatly limiting choice of destination and speed
2)They can’t lift very much without either unrealistically thin skin or being colossal in size
3) As in my previous post I suspect they aren't flying for free (barring colossal size): like a helium filled party balloon on Earth I suspect (though I can't find the damn figures for leak rates of H2 through anything anywhere online) with many hundreds of thousands of square metres of blimp surface area that hydrogen leaks through any practical skin at an appreciable rate and must be replaced, made worse by long flight times limited by wind speeds. If you have to make more fuel anyway every time you fly my feeling is that you might as well make a conventional airplane and be done with it.

Of course, this thread is only tangentially about air travel (sorry ><) so I’ll make a new topic, justify my case in detail and hope that either I’ve got a much better way to get across Mars and get us properly industrialised or else my approach can be demonstrated as a dead end/blimps can win out and effort (mine included!) can be redirected to something else.

EDIT: There's already a plane thread, will post to there instead of making a new one

Last edited by SeaDragon (2020-07-27 05:34:32)

kbd512 · 2020-07-27 09:37:19

SeaDragon,

My thought process on this was that the blimp wouldn't lift the mass of anything except its own structure, a relatively short power cable, and a large thin film solar array. The solar array was intended to be a mobile power station that the vehicle it's powering would not have to bear the weight of, in addition to any other cargo it's carrying. The reason for doing this to begin with is the weight and balance and obstacle clearance issues associated with directly attaching an array of sufficient size to the vehicle. This design negates most of those issues and I can also tether it off to a heavy stationary piece of equipment to provide power to LCO2 accumulators / compressors (to power air tools), LOX/LCH4 plants (getting home), banks of batteries (life support), scientific instruments (understanding the local environment to determine the feasibility of habitation), etc. I could also feasibly carry aloft one astronaut in a harness for an unobstructed view of upcoming terrain as well to communicate a driving plan to the heavy vehicle operator to prevent driving off cliffs, driving through impassable debris fields, or driving over partially exposed lava tubes. It's a multi-purpose piece of equipment, even though its primary function is to provide mobile power.

For a heavy cargo vehicle, or any heavy off-road vehicle for that matter, I figure the max practical off-road speed is in the 20kph to 40kph range. Going much faster than that starts to destroy suspension components. Even main battle tanks use governors on their engines that limit top speed to prevent the vehicle from shedding a track or destroying the suspension. Anyway, at those speeds the combination of the blimp's size and the local atmospheric pressure won't generate sufficient dynamic pressure on the blimp to significantly affect the operation of the blimp or the heavy cargo vehicle it's tethered to. This wouldn't work on Earth due to the atmosphere / wind's dynamic pressure on the blimp, but it can work on Mars.

If the array was directly attached to the vehicle, then the weight of the array and all support structure are bearing down on the vehicle at all times, they're subject to high dynamic loads and vibrations generated by the vehicle bouncing over rough terrain, and if the vehicle's attitude changes from one side going over a large rock or uneven terrain, for example, then the entire structure must clear any ground obstructions, probably with an active attitude control system, else it will be destroyed. There's no vegetation for the array to catch on, but there are numerous fields containing very large rocks, sand hills, and craters that will cause drastic attitude changes. If the vehicle is forced to navigate a debris field filled with large rocks, then I don't want its power array striking a large rock and being sheared off the vehicle. The reason you see cages around rock crawlers has nothing to do with vegetation, it's to prevent damage and protect occupants when the vehicle strikes the terrain the operator is trying to navigate. If we rigidly mounted a gigantic solar array to a vehicle, then somebody would simply sheer it off trying to navigate terrain or get stuck somewhere and then require towing assistance and back-tracking to leave the area. We don't go off-roading here on Earth with objects the length of telephone poles or main sailing masts attached to the tops of our vehicles and it's highly unlikely that we'd fare any better if we tried to do that on Mars, either. Even with only 38% of Earth's gravity, gravity is still not on your side, and center-of-gravity is still just as important as it is on Earth for the vehicle to remain upright when navigating rough terrain.

Using a tethered floating array, I can provide a nearly arbitrary level of power output, easily up to several hundred kilowatts or so, if that's what the vehicle requires. I don't need large and heavy batteries to provide prime power if the vehicle limits movement to daylight hours. I can provide motive power during daylight hours using the solar array and use a comparatively smaller battery to sustain the vehicle's life support systems through the night. The curved surface of the blimp and flexible surface of the solar array also promotes shedding of atmospheric dust to reduce power losses associated with dust plate-out of static inflexible arrays, which is what killed Spirit and Opportunity, along with being, say, 25m to 50m from the surface (the source of the dust), which also limits dust accumulation. The array is inherently self-leveling and does not affect the vehicle's CG, no matter what the vehicle its tethered to does with respect to attitude changes from rough terrain.

If H2 is too difficult to come by or is too much of a pain to store, although I would argue that it's not if we must make hundreds of tons of the stuff from local water supplies, then I simply use heated CO2 as my working gas. This would undoubtedly increase the size of the blimp, but there are other working gas options available if all accumulated H2 has to be devoted to rocket propulsion to leave and come home.

The technological challenges to overcome are the durability of the membrane material of the blimp with H2 workin gas, cleaning the solar array, and adjusting the buoyancy of the blimp to correct for atmospheric density changes caused by temperature and elevation changes. That said, there are no fundamental physics problems, like drastic vehicle CG changes from a rigidly attached array, that we're fighting against using this solution. Additional working gas can be stored onboard the vehicle in cylinders and fed to the blimp using hoses and pressure regulators. A tether reel can adjust the operating height of the tethered blimp, as required, for the terrain being navigated. We're purely trying to support the mass of the blimp itself, the thin film array laminated to the pressure membrane, the power takeoff cabling (we're going to use CNT fiber like that sold by DexMat for both power transmission and for its incredible strength as a tether or rope), and the working gas.

The alternative solutions would be much heavier and would materially affect the CG of the vehicle, thus its utility as a heavy off-road vehicle.

A liquid hydrocarbon engine would be great, except that you have to carry both the fuel and oxidizer with you, unlike here on Earth. The LOX tank will dwarf the LCH4 tank. Even with exhaust gas recirculation and other tricks to improve the thermodynamic efficiency of the engine itself, it remains a very heavy and bulky solution. A high temperature fuel cell would roughly double the efficiency over something like a diesel engine with all the tricks in our engineering toolbox, but you're still talking about very large tanks for several hundred miles of driving range and that combination has to be continuously supplied using local infrastructure. In other words, not very practical in a power-limited environment.

We previously discussed the potential to use a very small nuclear reactor and while it could technically work, there are no-go zones around the vehicle from limitations to shielding mass unless we resort to exotic and expensive fissionable materials like Am242m to reduce the core diameter to the point where adequate 360 degree shielding mass becomes practical (and even then there are still limitations, like you can only stand directly in front of the vehicle for 30 minutes or so because the bulk of the shielding mass was devoted to protecting the crew compartment, which is literally feet away from an operating nuclear reactor). If the reactor was placed in its own vehicle, then you have to power two vehicles and now we're right back to having to supply or store more power using more mass.

A radioisotope thermoelectric generator could feasibly power a super capacitor bank and battery combination that supply prime power for a small tracked rover, but the tethered solar array is the only practical solution that can supply prime power in the range normally generated by tank engines here on Earth, if total system mass and usability for the intended use case are any considerations, and I would argue that they are. If we had an O2 atmosphere, liquid water, and plentiful power to work with, then we'd send diesel tank engines or fuel cells and call it a day. Since we don't, we felt the need to "get creative" with our mobile power solutions.

tahanson43206 · 2020-07-27 12:22:27

For kbd512 re #27 to SeaDragon ...

Your explanation of the value of a balloon mounted solar panel for exploration of Mars sure makes sense to me, but then, I'm already sold on the idea << grin >>

However, your suggestion of using the already well developed practice of heating the local atmosphere inside a lift envelope to provide the lift for the blimp caught my attention, because there ** is ** a connection (in my mind at least) to the well pounded topics elsewhere in the forum, where nuclear power is offered as a solution to various on site problems.

In this case, since the ** only ** output of a nuclear fission reactor (that I know of) is simple heat, it follows that it would be 100% efficient if it were given the task of heating local CO2 for the purpose of providing lift along the lines you have described.

It should be possible for a forum member with a well oiled calculator, or spreadsheet for the ambitious, to calculate the design requirements for a fission reactor able to provide heat lift for a vehicle of various sizes.

Edit#1: I recognize that some might quibble that radiation itself is a useful output of a fission reactor, but ** that ** output would have no use in a Mars blimp, and in fact it would have to be planned for and adjusted to.

(th)

Last edited by tahanson43206 (2020-07-27 12:24:21)

SpaceNut · 2020-07-27 17:16:57

An RTG unit similar to the rovers would supply a continuous heat and power even during the mars night.

SeaDragon · 2020-07-27 17:31:23

kbd512,

I see, I think I get the intentions of your design now, that's intruiging!

In which case, bearing in mind tahanson43206's request for number crunching, I have the following thoughts to contribute:

In the northern side of the dichotomy, say Acidalia Planitia, you might have an altitude at the surface of 6,000 m below "sea level" (at which the pressure is 610 Pa). With a scale height of 11.1 km the pressure near the surface roving across Acidalia Planitia is thus something like 610*e^(6/11.1) ~ 1 KPa. During the day (when you need it up most to catch sunlight) this corresponds to a density of some 20 grams per m^3. A hundred metre wide sphere thus holds ~(100^3)/2 ~ 500,000 m^3, with a mass of some 10 tonnes atmosphere - if you had H2 instead it's about 22 times lighter at the same temp and pressure so even ramping up the pressure to keep it rigid H2 lifting gas still should mass less than a tonne. The skin has to cover 30,000 m^2 so if you want to lift any solar cells etc. it can't mass more than about 6 tonnes, giving 200 grams per metre. That's about enough to buy you 100 microns PET coated with 20 microns Aluminium film to hold in the H2. With an internal pressure of 1,500 Pa the internal stress trying to push the sphere apart is the cross sectional area exposed by cutting it in half times the pressure: some 7,500 m^2 * 1,500 N/m^2 ~ 11,000,000 N. This must be held by the skin exposed across the circumference of the cut, which is ~300 m. At 100 um thick (0.1 mm) the load-bearing PET surface across the circumference is ~0.3 m^2, meaning it’s loaded at some 33 MPa. That’s within PET’s 50-ish MPa tensile strength but I wouldn’t push it when winds and local stresses from cables etc are included so a little Keflar or carbon fibre (or basalt fibre, much cheaper and almost as good) are probably needed in practice but that’s well within what’s possible. A quick perusal of Wikipedia ( https://en.wikipedia.org/wiki/Power-to- … tovoltaics ) gives ~70 W/kg for solar cells in Earth orbit (where it’s much brighter than Mars) so even at 40 W/kg that 2 tonnes or so left over (with 1 tonne’s weight on Mars lifting force for margin of error) hefts a good 80 KW of photovoltaics.

So: a 100 metre wide balloon with 6 tonnes reinforced aluminised plastic skin, around 0.7 tonnes H2 and a capacity for lifting an additional 3 tonnes on top of this and still floating, of which it’s practical to get something like 100 KW photovoltaics up. What about wind?
I can’t find good data on the wind speed at moderate altitude on Mars but on Earth the no-slip condition makes it much slower on the surface than even a few tens of metres up (hence chimneys). Taking it as 10 m/s provincially, since this has been reported sometimes at the surface and you could always take it down if you had serious winds developing that day:

Reynolds # ~ (0.02*100*10)/(10*10^-6) ~ 2,000,000 -> the flow is pretty turbulent!

Turbulent flow around a sphere gives a drag coefficient of around 0.15, so the drag force for 10 m/s wind is something like:

F ~ (0.15*0.02*7,500*10^2)/2 ~ 1,000 N

This is around the magnitude of the net upward force I’d let the balloon have in order to keep the tow cable tight and it very definitely floating rather than falling so no problems - provided it’s reliable at this altitude you can even afford to carry more stuff with it by using it as a kite. The problem is if you’re driving against the wind.

At your top design speed of 40 km/h (about 11 m/s) and assuming relatively gentle 10 m/s wind again the analysis gives something closer to 4,000 N which is getting pretty dangerous (that’s around the weight of a tonnes on Mars). Since the force goes as the square of relative wind speed this can get progressively worse if wind speed is above 10 m/s in practice - at 20 m/s + 10 m/s driving speed it’s closing in on 10,000 N. Besides the obvious danger of high stresses on the tow cable and rover etc, aeroelastic flutter might put undue stresses on the balloon also.

Provided it’s relatively peaceful at our altitudes it’s surely possible to just bring it down for a while if the wind picks up too much. A winch firmly attached to the rover can reel the balloon down to accomplish this but decompression is much more difficult, requiring pumps and a thicker storage balloon etc. (turning H2 into a liquid is a very difficult proposition for a machine that must fit casually on the back of your rover!). I guess with accurate weather reporting giving you a few hours warning you could tie it down though, hammering in tent pegs and hooking on trailing ropes etc.

How much do you/others here know about the wind speeds at altitudes a few tens to hundreds of metres up from the surface on Mars? I can’t find much information, assumed it just isn’t possible to get with modern equipment presently on the planet. Under the right conditions a kite/dirigible hybrid could serve at least the observation post or communications purposes of the previous (I wouldn’t put delicate equipment like thin film solar cells on a kite of course) for much lower mass, cost and complexity.

SpaceNut · 2020-07-27 19:47:00

A bidirectional hose from a temp tank and compressor pump from the balloon to the rover seems to fit the deflation and inflation for the balloon under windy conditions.
Thanks for the post.

tahanson43206 · 2020-07-27 20:06:26

For SpaceNut re #31 and this topic...

It seems the topic has become focused on using balloons to secure power for a rover.

Do you already have a topic where this line of discussion would be a better fit?

I think it is worth developing further, but I'm not convinced the title of the topic matches this new direction.

(th)

kbd512 · 2020-07-28 16:17:00

tahanson43206,

To the extent that we can, we should at least attempt to reduce our dependency on batteries and battery powered tools for long term sustainability. A properly maintained air tool should last a lifetime. I suppose battery powered tools could also be made similarly reliable, but they would be costly to make and definitely not something you'd pick up from a Lowes or Home Depot. There are still good reasons to have both. Compressed CO2 powered tools are fundamentally simpler and easier to maintain in a dusty field environment than dozens of electrically powered tools. Any electrical tool would require adequate thermal sink mass to shed heat from prolonged operation. In any event, I'll try to get back on topic here.

I actually think that some kind of standardized battery should be mandated so that all electrical power tools can be plugged into a luggable / backpack battery, the same way that Husqvarna and GreenWorks or eGo (can't recall ATM) have a battery backpack for their line of battery powered landscaping and construction tools. A singular interface or connector for the battery is required, with double-ended detachable cords of varying lengths (possibly some variant of Apple's "MagSafe" connector since the dust and salts might abrade (most probable failure scenario) or corrode (if the tools are taken inside a humidified environment like a habitat after use) anything that wasn't very well protected and sealed. Anyway, battery powered tools can be comparable in weight and power output to equivalent air tools by mounting a much more powerful battery on a vehicle or pack frame or work stand.

So, should we implement standards for interoperability or is it "anything goes", so long as it works?

Maybe it's just me, but I think leaving the "correct type" of battery at home is just a silly problem to have. If there are corded interfaces for battery powered tools and task lights, the batteries all supply the same voltage, and all of the tools accept the same connector interface to connect them to the battery, then we can have varying length cords for different jobs and you just have to remember to take the correct tools and enough extension cords with you. It seems as if that'd be simpler, but maybe not. There's also the possibility of connecting multiple low current draw tools around a work site to a singular battery or multi-headed power cable. If I had 10 guys with either battery backpacks or a vehicle battery bank, then everyone at that work site simply brings their cords and tools. There's less of a baggage train and fewer pieces of specialized equipment that way.

tahanson43206 · 2020-07-28 17:35:23

For kbd512 re #33

Your concept of a solar powered balloon towing rover deserves development so I'm hoping you (or someone) will start a topic dedicated to that idea. It should be possible to work out many of the details over the course of a few months.

Meanwhile, your suggestion for a uniform electrical system for Mars makes a lot of sense. Now is the time to ** try ** to find consensus on that point, before the Chinese, Indians, Russians, Europeans, UAE/Japanese and (perhaps even) the US try to set up their own unique systems.

You've made the point before that pneumatic tools are a good fit for a difficult environment such as Mars will be, and I'm glad to see you bring it back in the context of SpaceNut's topic here.

It might even be worth setting up pneumatic tools as a specialty within My Hacienda.

(th)

SpaceNut · 2020-07-28 19:10:25

Dry ice pneumatic tool

The power blimp also Nicely fits with the nomadic exploration as well in the "My Hacienda.".

I believe we have more of it in another topic as well.

tahanson43206 · 2020-07-29 08:41:13

This is for kbd512, in support of the idea of (trying to) arrive at a consensus for power distribution and generation on Mars.

For close-in power distribution, Edison showed the way a century ago (give or take). DC power is still widely used in many situations.

Here is an offer of a white paper on finding ground faults in DC systems. The problem of faulty ground is in my mind due to learning recently that the Robonaut sent to the ISS was unsuccessful because of a poor ground somewhere in the system that caused flakey behavior.

If anyone is interested in the source just let me know. As usual I don't publish source data for this sort of item if it comes in an ad.

Finding that elusive ground fault on your DC system
This whitepaper explains how to avoid costly system disruption, equipment damage and safety risks by easily identifying DC ground faults.

(th)

kbd512 · 2020-07-29 09:50:00

tahanson43206,

All I know is that if our electrical wiring looks the way some of those power poles in India look, then we're going to have serious problems. A standards based approach ensures that everyone's equipment is interoperable and less likely to fail if design specifications take the Martian environment into account. There are arguments for (established tech) and against (potentially materially better tech), but I think our battery and connector technologies are mature enough at this point to specify standards to adhere to. I think high voltage and low amperage will work best, given the great difficulty of dissipating heat in that near vacuum of an atmosphere that Mars has. I would specify a 240V for tools and individual battery packs (remember that these batteries are also intended to be used in electric vehicles and for prime power storage). A power divider / control box can regulate current flow to individual tools and deal with electrical shorts to preserve the life of the batteries the tools are connected to.

SpaceNut · 2020-07-29 15:50:38

A DC-to-DC power supply converts a direct current (DC) input supply to a DC output supply typically at a different voltage level. Many types of DC-to-DC converters are available and are grouped into three categories: linear, switching, and switching flyback.
https://en.wikipedia.org/wiki/DC-to-DC_converter

AC to DC Switching Power Supplies. Switching power supplies, sometimes referred to as SMPS power supplies, switchers, or switch mode power supplies, regulate the output voltage using a complex high frequency switching technique that employs pulse width modulation and feedback.

So, an inverter circuit is employed for converting the DC to AC converter. The converter is a power electronic device, used to convert DC to AC. These devices use switching devices. The DC to AC conversion can be done among 12V, 24V, 48V to 110V, 120V, 220V, 230V, 240V with supply.

”Switching power supply” is a generic term that describes a power source with a circuit to convert dc to ac voltages that can be further processed into another dc voltage. Switching power supply can be categorized as ac-dc power supplies (ac input) or dc-dc converters (dc input) since both incorporate dc to ac conversion for voltage change.

tahanson43206 · 2020-07-31 05:20:27

For kbd512 (#37) and SpaceNut (#38)

As we are discussing the risk of incompatible electrical systems on Mars, here is a report of a shakeout underway in the automotive industry on Earth:

https://www.yahoo.com/tech/m/98c8906e-8 … ar-of.html

The VHS-Betamax war of electric cars is about to be decided
Electric vehicles still have the chance to avoid a frustrating mess of incompatible pins, prongs, and plugs.

Michael J. Coren
July 31, 2020 4:00 AM

(th)

Calliban · 2020-07-31 15:45:30

Two interesting articles from Kris DeDecker's Low Tech Magazine.
https://www.lowtechmagazine.com/2016/04 … power.html
https://www.notechmagazine.com/2019/07/ … -farm.html

If we intend to run a Martian settlement on solar power, it may make sense to use low voltage DC networks, in which electrical equipment draws power directly from solar panels as direct current. Also, instead of attempting to store power in batteries, direct balance of load to supply might make more sense. This would mean running heavy loads during daylight hours when insolation levels are high and switching them off when power levels are lower. Most equipment would be powered down at night.

Balancing load to supply makes sense in terms of efficiently utilising energy and reducing the embodied energy of the energy supply system. Unfortunately, it is not the optimum strategy for efficient utilisation of other equipment. But it may turn out to be the cost optimum approach given the very significant embodied energy and energy losses in batteries.

Last edited by Calliban (2020-07-31 15:49:32)

SpaceNut · 2020-07-31 16:59:01

Lower voltage mean high current and large guage wire to limit power drop across the conductor.

tahanson43206 · 2020-07-31 17:36:44

For Calliban re #40

It is an impression, from reading about setting up solar power systems, that it is better to feed the output of solar panels into batteries using a regulator to protect the solar panels, and to draw power from the batteries separately. I bought a kit but never set it up. It's just one of many started but not finished projects around here << sigh >>.

I'd be interested in further comments to this topic, if anyone in the membership has experience with such systems.

This topic of SpaceNut's ** could ** turn into something helpful, if we can find knowledgeable and ** very ** patient people to nudge the learning process along.

(th)

kbd512 · 2020-07-31 18:08:40

Calliban,

If we could feasibly make that work, then that's an even better solution. Either way, you'll almost certainly be setting up solar panels and dealing with cords, no matter what solution is used. The batteries are merely a way to make power a little more portable. My plan wasn't to use individual batteries for individual pieces of equipment, rather to power that equipment using vehicles or structures that already use battery power. To be clear, we'd plug all of our tools into power distribution boxes that protect the tools and batteries or solar panels. If you can only work during certain hours of the day, that tends to make the work schedule very inflexible. It may not be possible to complete certain jobs if solar alone is all that's available.

SpaceNut · 2020-08-29 18:35:38

Yes this was from the venus topic but we can alter it for Mars....

I reminded of this topic: so copying your post to here,,,

Tom Kalbfus wrote:

Also remember half of the Sun's disk would be below the horizon at all times as the disk of the Sun slowly moves eastward along the horizon, it might even be cooler at the 55 km altitude at 1 atmosphere of pressure. I think the Sun would appear rather red as it does along our horizon. If the balloon is not tethered, it could use propellers to move away from the Sun, and thus make it appear to set, so there could be night, then it would turn around and head back towards the Sun for a Sunrise, that way we could have a normal 24-hour diurnal cycle. Maybe that's worth considering.

Doesn't say how fast these things move. I wonder how fast this airship would have to move to get the entire disk of the Sun below the horizon?

These folks may have to be couch potatoes. I wonder if they could have exercise equipment behind those chairs. I think a treadmill would be nice, they'd need a lavatory, and maybe a small kitchen in the back. Also when they flushed the toilet, where do you suppose the water would go? Probably get recycled I imagine, if the equipment to do that wasn't too heavy. The engines that propel the airship would be electrical, they would probably hear a whirr sort of like a giant fan. Do you think there would be handholds along the sides of the airships so astronauts can climb to the top of the gas bag in protective suits? If the airship climbs high enough, they can get a good view of the stars at night, as there never is a Moon to drown them out. Maybe they can set up a telescope on the top and look at the Earth.

SpaceNut · 2020-09-05 19:59:03

kbd512 wrote:

SpaceNut,
Current batteries are absurdly impractical for anything other than light duty passenger vehicles. Sandy Munro, one of his people, actually, gave a good little run down on current and projected battery technology. If you don't already know who that is, type his name into YouTube to see what comes up.
For various reasons, current Lithium-ion battery energy density is about as good as it gets unless and until someone comes up with a solid state battery. Sandy said a few dozen people have come to Tesla claiming to have solid state battery technology, but none of their products functioned well enough, or at all in most cases, to even consider further EMD funding. Translation: All of the "better batteries" are, to the best of his knowledge, vaporware. Matter of fact, I think he actually used that term. If anyone had a functioning prototype, then Tesla would cash them out on the spot. He says Tesla has the best control electronics designs and systems integration by far, but their cells are just ordinary commercial Lithium-ion technology that any car maker can purchase. The ability to very precisely control the cell voltages of the hundreds or thousands of cells in the battery packs is what sets them apart. The more Sandy talked about the design of their pickup, the more I came to love the design for its functionality, even if it looks like the Halo video game truck.
Every day there's at least one new claim about a revolutionary new battery technology that's just two years to five years away. That's been going on for at least two decades. Our battery technologists are either more interested in satisfying their intellectual curiosity or reinventing the proverbial wheel, as NASA so frequently does, than they are in devising a more energy dense cell chemistry / configuration or they have nothing with better energy density to offer.
If you give a battery powered semi truck equivalent range to a diesel powered semi truck with the same GVWR, then the battery powered truck has to give up half of its payload to stay under 80,000 pounds. That means you have to double the number of trucks on the road or increase the rolling resistance by adding more axles and more batteries to produce more power to overcome the increased rolling resistance. That's just how this "orders of magnitude problem" works. You either use appropriate technology to work around the problem, or you don't, and then you're stuck with whatever you have that actually works.
Is continuing on with combustion engines looking like a better option than fuel cells and electric motors?

SpaceNut · 2020-09-06 11:12:40

tahanson43206 wrote:

For SpaceNut ... this item would fit in a number of topics that have balloons as a theme...
https://www.yahoo.com/news/french-compa … 00900.html
This is a French company building a dirigible (from the description) for a number of potential customer applications. It was originally designed to move logs for environmentally friendly forest operations, but the team has expanded its vision as well as its staff.
(th)

It sure does...

SpaceNut · 2020-11-29 10:18:02

This is the power creation platform for mars:
This was made under the gravity power storage topic

tahanson43206 wrote:

For SpaceNut re topic and post #40
Thanks for the research you have done, and for the image of a home-sized water wheel power generator.
I was inspired to ask Google what (if anything) has happened in the gravity storage field since the last time I looked.
To my complete surprise, ** this ** showed up at the top of the results ...
http://www.stratosolar.com/gravity-energy-storage.html
The author claims 85% efficiency grid to grid
The kicker is the use of a balloon platform to hold the weights.
Someone was ** really ** thinking outside the box !!!
Because the atmosphere of Earth is constantly moving, a platform of that size could hold wind turbines to augment the supply coming from the grid.
Balloon suspended wind turbines is not a new idea, and "flying/kite" systems would fall into the same category.
** This ** is the first time I've seen balloons suggested to hold dead weight.
Oh ... looking more closely ... the entire surface of the balloon platform is covered in PV panels. That ** is ** more elegant than wind turbines, but of course it only works during the day.
I'll be interested in any comments that might come in from our registered members.
(th)

Nice image of the design of a more rigid platform to mount other items on....

SpaceNut · 2020-12-17 19:45:14

A different style of construction equipment is needed inside a greenhouse

with this one fitting nicely in the Grass topic as who wants a putting green that is more like a rough...

kbd512 · 2020-12-18 19:04:21

This was originally a response to something written about batteries vs internal combustion engine powered construction equipment in another thread:

tahanson43206,

I'm not sure what you really mean here. If you mean driving a bulldozer's loading bucket into Martian regolith, that's going to take considerable traction and torque to push the vehicle's dozer blade into the regolith. If you mean lifting 1t of excavated material 1m into the air to remove it and cart it off, the way a typical bulldozer or backhoe does, then that's merely 1,000kg * 3.711m/s (Martian gravity constant) * 1m in height, which equates to just 3,711 Joules of energy. If you want to accomplish that task in 1 second, same as a real diesel / hydraulic powered bulldozer does here on Earth, that requires an instantaneous power of 3,711 Joules per second. Joules/sec is the same thing as Watts, so 3.711kW. If it has to do that continuously for 1 hour, which is clearly something that only a conveyor system at an open pit mining operation would do, then that's 3.711kWh to continuously lift 1t of material. If you presume the force transfer system is 90% efficient by using electric motors, then you need about 1.11 times that amount of continuously supplied power, so 4.12kWh/hr. That equates to 13.73kg worth of batteries for each hour of operation using Tesla's new 4680 cells, as Sandy Munro stated that Tesla told him that they're achieving a pack-level energy density with the new larger 4680 batteries of 300Wh/kg. We seem to be missing something, though. Oh yes, how could I forget, we haven't accounted for lifting the weight of that massive steel bucket. We have to lift that thing as well. Caterpillar's 2m^3 capacity extreme duty bucket weighs 403kg, so that raises our energy requirement to 5.78kWh/hr. Now we need something to attach that bucket to, and I'm guessing that those movable struts will add another 500kg or so (I'm presuming a jointed tubular steel mechanism, since nothing made from lighter alloys would be as durable), now we're at 7.84kWh/hr. Martian basaltic sands, some of the heaviest overburden we'd have to remove, weigh roughly 2,330kg/m^3, so 4,660kg for our 2m^3 capacity bucket, which means we're at 27kWh/hr for a realistic light duty bulldozer with a durable bucket. That means we need a 216kWh battery pack to operate the bucket for 8 hours straight to lift 4.66t / 4,660kg of overburden at a rate of 2m^3 per second, which doesn't include doing anything else with it, such as transporting it away. However, we're clearly not using energy at a constant rate. The battery pack to do that (lift 2m^3 to 1m in 1 second, continuously, with 90% efficient electric motors, for 8hrs straight) would only weigh 720kg.

That doesn't seem that bad, but we haven't accounted for any vehicle movements or the energy to push the shovel into the overburden, just the act of lifting our loaded regolith scoop to a height of 1m with 2m^3 of the heaviest regolith we're likely to encounter, which is pretty much what an actual bulldozer would do while removing overburden. Plowing or piling the overburden, such as burying habitat modules for radiation protection, would require more energy. BTW, we're using electric motors and latches or brakes to hold our scoop in the elevated position, instead of hydraulics, because hydraulic fluid freezes at Martian night temperatures, constant power is required to pressurize the system, and hydraulic systems would require maintenance schedules we probably don't have the luxury of maintaining. Basically, this machine needs to be minimum maintenance and minimum constant power.

The most realistic power plant for this bulldozer would still be a small combustion engine. The latest hybrid gasoline engines from Mercedes, that they developed for their F1 racing program, are more than 50% efficient, somewhere between 55% and 60%, IIRC. That means at least 50% of the energy content of the gasoline was converted into mechanical work. Methane provides 13.9kWh/kg, or 6.95kWh/kg. If a 70% efficient simple cycle SOXE fuel cell is used, then 9.73kWh/kg. Sandy Munro stated that the latest Tesla 4680 batteries and structural battery pack achieves a pack-level energy density of 300Wh/kg, so 23 to 32 times more battery weight would have to be allocated. That may not be an actual problem for a bulldozer and might be a benefit since we need a seriously heavy machine to push the bucket into the regolith.

Presume the SOXE fuel cell scenario since we're already developing SOXE fuel cells for use on Mars. At 3kW/kg, a 27kW SOXE fuel cell would weigh 9kg. At 70% simple cycle efficiency, 1.45kW of input power from the CH4 produces 1kW of power and at least 450W of waste heat we have to reject or otherwise use to keep the fuel cell hot. I'm presuming it has to be rejected with a Copper radiator. I need to find the equation for calculating the mass of the radiator. It'll be relatively small since SOXE fuel cells operate at very high temperatures. NASA has a formula for calculating radiator mass for a given temperature range. We do need 310kWh (22.3kg of CNG / CH4) using the less efficient fuel cell, to supply the same 216kWh as the battery pack supplied. At 10,000 psi storage pressure using a steel CNG / CH4 tank, that equates to a tank mass of 187.4kg. So... We're at 263.2kg for the SOXE fuel cell, 23.2kg of CNG / CH4, 205kg for steel high pressure CNG tanks with 26kg of CNG storage capacity, and 21kg for the tank mounting brackets. We need to store roughly double that weight in terms of compressed O2. The molecular weight of O2 is roughly double that of CH4, so another 105kg for the O2 tank, another 21kg for the brackets, and 44.6kg of O2. We'll have to compute our radiator mass, but let's say it's 75kg for sake of argument. Final mass, with radiator, is 508.8kg.

That doesn't seem all that great compared to batteries, does it? Well, that's for 13kg capacity Type I steel CNG tanks. The same Type I tank with 185kg CH4 capacity would weigh 1,110kg, or 2,385kg for the complete storage system (oxidizer and fuel). A type IV Carbon Fiber Overwrap system would weigh less than half of that, but this is Mars and we're going with cold hard steel. That provides 2,571.5kWh of power, of which our fuel cells provides 70% of that, so 1,800kWh. An equivalent battery system would weigh 6,000kg. The mass not included with the battery or fuel cells is the source power supply system to furnish 1.8MWh worth of power to store in the form of chemical reactants or electrochemical potential.

Maybe the extra weight of the batteries is a good thing for a low-speed bulldozer to have, especially for plowing, but it's pretty clear that the structural support mass for the battery powered vehicle would have to double to provide equivalent durability, unless there's a clever way to combine the battery pack with the vehicle chassis, which may or may not be possible. I just don't know. My gut says there's a way to do it, but my brain says that's not going to be easy and the batteries really should be shock isolated from the chassis if ultimate durability is desired. The batteries would also require a fairly large Aluminum radiator assembly to remove waste heat, but again, it could be a structural chassis component. I feel as though an Aluminum chassis would simply fatigue and crack over time. There's an engineering reason that steel is used in virtually all construction equipment here on Earth.

SpaceNut · 2020-12-18 20:14:46

Thank you, Its important that we do focus rather than miss the chance to develop a useable product from the many discussions that are parts to success or failure and while some will be the primary mode of use the alternative will be just as important for the reasons of backup and for not duplicating what we bring but make it different on purpose.
If nothing else bust the alternative down and use what you can to build what you need....

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