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#1 2016-02-22 21:04:23

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 16,516

Light weight rover for Mars

What I am working on is a mass restricted light weight design for a mars crew use in space suits.

Moon_Buggy_Ap16-KSC-71PC-777.jpg

A Point of past design would be the lunar rovers but designed to be able to take the abuse that mars can dish out.

http://www.hq.nasa.gov/alsj/lrvhand.html

https://en.wikipedia.org/wiki/Lunar_Roving_Vehicle

Powertrain
Electric motor Four 0.25-horsepower series-wound DC motors
Hybrid drivetrain Four 80:1 harmonic drives
Battery Two silver-oxide, 121 A•h
Range Greater than 35.9 km (22.3 mi)

Dimensions
Wheelbase 2.3 m (90.6 in)
Length 3.1 m (122.0 in)
Height 1.14 m (44.9 in)
Curb weight 210 kgf (463 lbf) (on Earth)
35 kgf (77 lbf) (on the Moon)

Apollo15LunarRover.jpg

http://nssdc.gsfc.nasa.gov/planetary/lu … o_lrv.html

We can also learn from the Mars rovers in the lessons of driveability that we can see by the wear of the tires being cracked and with holes in them ect....

Curiosity-Sol-494_1a_Ken-Kremer--580x463.jpg


This is a first mission type of vehicle to aid in base exploration as time away from the base will be limited for safety.

What other changes or design features should be in such a vehicle for Mars?

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#2 2016-02-22 23:57:27

kbd512
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Re: Light weight rover for Mars

Personally, I like the Ryno unicycle concept.  It keeps the astronaut close to the ground where a fall is less likely to result in serious injury or serious compromise to the suit, it's quite compact, and reasonably light.  It weighs 73kg on Earth and only 28 kg on Mars.  Range on Earth is stated as 24km per charge, although better batteries and the lighter loading should improve that on Mars.

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#3 2016-02-23 05:52:21

Antius
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Posts: 1,003

Re: Light weight rover for Mars

I think you would need to start with some sort of requirements capture.  What tasks do you want the rover to actually carry out?  What is its basic function in assisting the first mission?  Everything starts with the 'need' you are attempting to meet and the design evolves from there.

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#4 2016-02-23 11:27:58

RobertDyck
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Re: Light weight rover for Mars

If this is for Mars Direct, the primary use is emergency backup. If the hab lands more than walking distance to the ERV, the rover will be used to drive astronauts to it. So Mars Direct required a rover with 1,000km one-way range.

Another requirement is to use energy that's available. Robert Zubrin suggested a methane/LOX engine, because the ERV uses it. The ISPP device could produce a little more fuel for the rover. The lunar rover was electric, batteries. Would an electric rover have the required range? While carrying all 4 astronauts?

Different mission plans have different number of astronauts. A mission plan that doesn't have surface rendezvous may not need the range. So what's the mission architecture?

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#5 2016-02-23 17:33:19

SpaceNut
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Re: Light weight rover for Mars

oK 1,000Km one-way range if we could drive 60 mph or 97 km in an hour means that we will be driving non stop for approximate 10 hours and we must be with the ability to extend suit life support for that range. I have a feeling that if we could do 15 to 20 mph we would be doing pretty good. Then again the drain time on the batteries is quite long and would require a larger battery to be sure that it would last if there is no recharging method to help extend its time of use. Plus the only reason for surface rendezous is due tol anding inaccuracy of other units that are are a must to make use of.

The purpose is simple for base camp exploration short hall distances and later possibly longer time periods within the astronauts space suit abilities. Sure it can be use to get from lander to lander as needed but let keep it to a minimal distance between each or its just not practicle....as walking is out.....if its more than probably 3km one way from base camp.

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#6 2016-02-23 17:41:45

SpaceNut
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Re: Light weight rover for Mars

Antius wrote:

I think you would need to start with some sort of requirements capture.  What tasks do you want the rover to actually carry out?  What is its basic function in assisting the first mission?  Everything starts with the 'need' you are attempting to meet and the design evolves from there.

I am looking at leveraging a working design with slight adaptation for mars conditions, making improvements in construction plus materials used and then by considered control of design growth creap forcing a fresh design as well would use it for the same purpose as apollo did....

Sure we may want a more capable design but its for obvious reasons that we would design for those functions not self evident.....Its not about Nasa methods but that of commercial market....

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#7 2016-02-23 19:37:53

kbd512
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Re: Light weight rover for Mars

SpaceNut wrote:

oK 1,000Km one-way range if we could drive 60 mph or 97 km in an hour means that we will be driving non stop for approximate 10 hours and we must be with the ability to extend suit life support for that range. I have a feeling that if we could do 15 to 20 mph we would be doing pretty good. Then again the drain time on the batteries is quite long and would require a larger battery to be sure that it would last if there is no recharging method to help extend its time of use. Plus the only reason for surface rendezous is due tol anding inaccuracy of other units that are are a must to make use of.

If you drove that fast out in Baja with a small vehicle of the size/weight you want while wearing a space suit, you would have to have your head examined after the ride.  30 mph is much more realistic.

SpaceNut wrote:

The purpose is simple for base camp exploration short hall distances and later possibly longer time periods within the astronauts space suit abilities. Sure it can be use to get from lander to lander as needed but let keep it to a minimal distance between each or its just not practicle....as walking is out.....if its more than probably 3km one way from base camp.

You want an electric multi-person ATV with substantial range.  That's not an easy thing to design without substantial weight.  Half day EVA's are only marginally practicable.  Perhaps you would be willing to sit in a wet diaper for six hours, but I think what you're asking for is really a set of requirements for a light pressurized rover to provide.  I could be wrong, but that's what it seems like.

If it's just a base camp utility rover, that's entirely different use case and there's no reason it needs a 1000km range for that.

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#8 2016-02-24 00:13:11

RobertDyck
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Re: Light weight rover for Mars

I have suggested bringing a small dome tent. Dr. Zubrin told me at one point he designed a tent trailer that could be towed behind an open rover. That's because I questioned the weight of a pressurized rover. I'm not the first to suggest a tent, one of the Apollo astronauts who walked on the Moon said we need tents. I came up with a design for a dome tent, which doesn't require poles or ribs because pressure will hold it up. The floor built as an air mattress. And layers of aluminized polymer held with threads between the upper and lower faces of the air mattress. That's similar to multilayer insulation, but with air. And circulation channels directly from the top of the air mattress to the bottom, with a fan the size of a computer case fan. This fan would be controlled by a thermostat. and the tent itself would be aluminized polymer, reflective to keep in radiant heat at night, and keep out sunlight in day. So it doesn't get too hot or too cold. Since the tent would be laid on cold Mars ground, the thermostat would maintain relatively stable heat. Of course leave a small section of tent transparent, a window, with a reflective flap over the the window. A 7-foot diameter dome tent would allow you to stretch out. You could sleep, or do spacesuit repairs. Or remove the suit for a bowel movement. Don't forget a plastic baggie to go into.

Life support for this tent would be the spacesuit PLSS backpack itself. No need for separate life support.

Spacesuit batteries would be recharged from the rover. So the rover required enough power to do that. Apollo spacesuits used lithium hydroxide to scrub CO2, but an upgrade on ISS uses silver oxide sheet metal. The sorbent canister is baked out in a toaster oven on the station. I have mentioned a paper from the 1990s of a microwave oven to bake it out. Because it's microwave, it requires silver oxide granules instead of sheet metal. But granules have greater surface area per unit mass anyway, so the canister is lighter for a given duration. Design the suit PLSS so you can replace canisters while outside. And include a microwave unit on the rover to bake-out canisters. For long duration, the rover would carry a large bottle of oxygen, to refill suit PLSS oxygen.

This is sounding like substantial power requirements. If the rover is restricted to 25km/h due to rough terrain, then 1,000km would take 40 hours. Depends on terrain. Spirit got stuck in dunes. We would have to ensure this rover won't. Could it bomb along like a dune buggy? If it could average 50km/h, that distance could be covered in 20 hours. Still, Mars gets cold at night, so you would want a warm tent.

My mission plan included a pre-landed laboratory with pressurized rover, and recycling life support. If the hab fails completely, the rover's life support could be connected to the laboratory to form a backup hab. Normally, that rover would be used for extended duration exploration. But the hab with crew would not have enough mass for that. The hab would need a light, open rover. The hab would have life support in the hab itself, while the laboratory would have life support in the pressurized rover. The lab would be all-soft inflatable, because if everything works, you want to move it to the hab when crew arrives. Would the hab have hard walls, or also inflatable? I keep waffling. Really depends on launch mass available. But if one goal of the rover that comes with the hab is 1,000km one-way range to get to pre-landed equipment, then you need a good rover.

The lunar rover already looks like a modern dune buggy, sans roll cage. Add a second row of seats for a total of 4 astronauts. Replace the dish antenna with a Mars relay antenna, that can communicate with the Mars relay on MGS, Odyssey, MRO, and Mars Express. And WiFi range extender, with smart-phone built into the forearm of each spacesuit. Control your spacesuit? There's an app for that.

So how about a hybrid rover? Hybrid greatly extends fuel efficiency. Actually, early railroad locomotives were hybrid diesel-electric since the turn of the century, production locomotives have been hybrid diesel-electric since the 1920s. Cars are just now. So a hybrid methane/oxygen - electric Mars rover? I notice modern high capacity lithium-ion batteries can operate down to -30°C, although recommended charge temperature is 0°C to +40°C. Spirit/Opportunity used plutonium heaters for the warm electronics box, same for this rover?

Methane boiling point at 1 atmosphere (1.013 bar) is -161.48°C. Critical point is -82.59°C @ 45.99 bar, so at Mars daylight temperature if you pressurize it enough, it becomes supercritical rather than liquid. I kind-a wish we could produce propane. That's a 3 carbon alkane: C3H8. Fischer-Tropsch can convert methane to heavier hydrocarbons, including propane. It doesn't produce just one, but a mixture. Then you have to separate out what you want to keep. Perhaps too complicated. Some cars use natural gas, which is almost pure methane.

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#9 2016-02-24 09:00:44

kbd512
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Re: Light weight rover for Mars

SpaceNut,

To be quite honest, I think your range, capacity, and duration requirements are too extreme for an unpressurized rover.  The requirements place this type of vehicle solidly within the light pressurized rover category.  Rob has proposed a potential solution that solves the duration issue, but I still think you're better off with a light pressurized rover.

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#10 2016-02-24 18:26:50

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 16,516

Re: Light weight rover for Mars

Actually that was what RobertDyck suggested with the 1000km range from Mars Direct as that is the realm of a pressurized rover for sure.

What I am looking at is the general purpose utility vehicle for short range constant every day useage....as we are not going to walk to where the cargo lander is for more supplies ect....

I agree that the rover should act a power backup for the space suit with some sort of recharging port...as a safety feature to be added.

Also some sort of protective tent for dust devils would not hurt as well for the emergency area for if a suit should fail while out....

Making it with enough seats for all not bad as no one will want to stay home while the others are out taking in that sunshine and smelling the roses.....

With a hybrid engine for power backup and extension we only need to have small tanks to make it work.

Not sure about using "plutonium heaters to the warm electronics box or batteries as what would we need for shielding to make it safe.

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#11 2016-02-24 19:07:27

RobertDyck
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From: Winnipeg, Canada
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Re: Light weight rover for Mars

Mars Exploration Rovers: Batteries and Heaters

Each radioisotope heater unit produces about one watt of heat and contains about 2.7 grams (0.1 ounce) of plutonium dioxide as a pellet about the size and shape of the eraser on a standard pencil. Each pellet is encapsulated in a metal cladding of plutonium-rhodium alloy and surrounded by multiple layers of carbon-graphite composite material, making the complete unit about the size and shape of a C-cell battery. This design of multiple protective layers had been tested extensively, and the heater units are designed to contain their plutonium dioxide under a wide range of launch and orbital-reentry accident conditions. Other spacecraft, including Mars Pathfinder's Sojourner rover, have used radioisotope heater units to keep electronic systems warm and working.

Radioisotope Heater Unit (RHU) (isotope, pictures & animation)

Plutionium-238 decays by alpha emission with half-life of 87.74 years to Uranium-234
U-234 alpha 245,000 years to Th-230
Th-230 alpha 75,400 years to Ra-226
Ra-226 alpha 1,599 years to Rn-222
Rn-222 alpha 3.8235 days to Po-218
The periodic table lists the last decay mode, but does not have data for Po-218. It may be stable. But look how many years it takes to get there. And every decay mode is alpha emission.

Wikipedia: Alpha decay

Alpha decay can provide a safe power source for radioisotope thermoelectric generators used for space probes and were used for artificial heart pacemakers. Alpha decay is much more easily shielded against than other forms of radioactive decay. Plutonium-238, for example, requires only 2.5 millimetres of lead shielding to protect against unwanted radiation.

The graphite casing of a Radioisotope Heater Unit is sufficient to shield alpha radiation.

::Edit:: Found another web periodic table. Po-218 alpha decays with half-life 3.167 minutes to Pb-214.
Pb-214 beta 26.833 minutes to Bi-214
I could go on, but the chain is all alpha and beta, ending with lead Pb-206.

Last edited by RobertDyck (2016-02-25 01:08:17)

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#12 2016-02-25 03:11:53

kbd512
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Registered: 2015-01-02
Posts: 2,991

Re: Light weight rover for Mars

SpaceNut wrote:

Actually that was what RobertDyck suggested with the 1000km range from Mars Direct as that is the realm of a pressurized rover for sure.

What about a light pressurized module carrier like NASA's ATHLETE, but without multiple articulating legs or a solid wall module?

I was thinking something along the lines of NASA's Centaur 2, but without the multi-axis articulating legs (perhaps the legs would simply articulate in one or two directions for storage purposes and swing out to increase stability during use.  Each wheel arm would consist of a spar with a shock absorber attached to permit travel at greater speeds).  The batteries, ECLSS, fresh and grey water tanks (could be delivered empty and filled by the astronauts prior to an excursion and the grey water tank emptied after an excursion), and cargo compartment for consumables would reside in a heavy base unit (relative to the inflatable module strapped to the top of the vehicle) for stability.  For delivery, the inflatable would stow atop the base unit.

The seats and in-module storage racks for the MCP suits would be fabric.  The front end of the inflatable would have a large polycarbonate plate sewn into it to provide good visibility for driving.  The module would consist of two separate pressurized compartments so that the pair of astronauts who remain in the vehicle don't have to suit up while the other pair perform an EVA.  The rear end of the inflatable would have a standard port that could also attach to a habitat module to permit crew transfer without suiting up.

SpaceNut wrote:

What I am looking at is the general purpose utility vehicle for short range constant every day useage....as we are not going to walk to where the cargo lander is for more supplies ect....

I think an inflatable pressurized module would be useful for short range transport of personnel and light cargo (presumably consumables for the crew and scientific instruments for field geology).

SpaceNut wrote:

I agree that the rover should act a power backup for the space suit with some sort of recharging port...as a safety feature to be added.

Agreed.

SpaceNut wrote:

Also some sort of protective tent for dust devils would not hurt as well for the emergency area for if a suit should fail while out....

Does that mean a pressurized tent such as the one Rob suggested or something like a plastic or Gore-Tex fabric shell for the vehicle to keep dust and debris off of the crew?

SpaceNut wrote:

Making it with enough seats for all not bad as no one will want to stay home while the others are out taking in that sunshine and smelling the roses.....

Ok.

SpaceNut wrote:

With a hybrid engine for power backup and extension we only need to have small tanks to make it work.

How about a nuclear battery?

SpaceNut wrote:

Not sure about using "plutonium heaters to the warm electronics box or batteries as what would we need for shielding to make it safe

RHU's are nowhere near as dangerous to the crew as running out of power, air, or water.

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#13 2016-02-25 18:16:43

RobertDyck
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Re: Light weight rover for Mars

A couple people complained about Curiosity's wheels. This was the Moon rover tire...
news-120508c.jpg

Four major components comprised the LRV tire's design: mesh, tread, inner-frame and hub.

The mesh was woven out of piano wire to provide a soft, springy surface to contour to the ground and provide good ride quality. The tread was made from a series of metal strips intended to protect the mesh from impact while providing increased contact area for floatation in soft soil.

The inner-frame, comprised of a relatively rigid metal structure, prevented the mesh from over-deforming during impact, while the hub held the mesh and frame together as well as connected the wheel assembly to the rover.

"Before the wire mesh could be woven, 3,000 feet of wire had to be custom-crimped and cut into 800 pieces," said Laske in a statement issued this week by Goodyear.

A hand loom was designed to weave the crimped wires into a rectangle measuring approximately 100 inches long and 25 inches wide. Each end of the rectangular weave was then interlaced by hand to form a cylinder, such that it behaved similarly to a child's finger trap puzzle, lengthening and shortening with changes to its diameter.

Sides of the mesh cylinder were pulled down and clamped to a circular jig, roughly the size of a wheel hub, to give the mesh the shape of a tire. Then the jig and mesh were baked in an industrial oven to relieve residual stress from the wire.

The end result was a tire that looked like the skeleton of an Earth tire. The approach worked because each tire was only required to support about 60 pounds of weight (on the Moon, the equivalent of 360 pounds on Earth) and be used for a maximum of 75 miles.

We want a Mars rover to last more than 75 miles (120 km), and Mars has 38% gravity. How do you design a durable wheel for Mars?

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#14 2016-02-25 19:10:15

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 16,516

Re: Light weight rover for Mars

The two front and two rear wheels also have individual steering motors (1 each). This steering capability allows the vehicle to turn in place, a full 360 degrees. The 4-wheel steering also allows the rover to swerve and curve, making arching turns. The rover rocker-bogie design allows the rover to go over obstacles (such as rocks) or through holes that are more than a wheel diameter (50 centimeters or about 20 inches) in size. Each wheel also has cleats, providing grip for climbing in soft sand and scrambling over rocks. The rover has a top speed on flat hard ground of 4 centimeters per second (a little over 1.5 inches per second).

http://www.planetary.org/blogs/emily-la … amage.html

3. What is the expected lifetime of the wheels, and how does that life end?
Both of the causes of wheel damage are exacerbated by driving over hard bedrock with pointy protrusions. Erickson told me that when they tested the lifetime of the wheels over this kind of substrate, the news wasn't good. "The really bad stuff, it only takes 8 kilometers or so and you can destroy the wheel."

20140818_steffy_wheel_broken.jpg

The good news is that a better choice of terrain can substantially prolong expected wheel lifetime. Erickson told me that they tested wheels on a wide variety of terrains, and came up with the following lifetimes. Keep in mind that these are conservative estimates, because there were no rover drivers working to steer around pointy rocks -- this assumes blind driving over all the worst rocks.

•Bedrock with lots of rocks: ~8 kilometers
•Lots of rocks, not on bedrock: 13-14 kilometers
•Bedrock with few rocks (think flagstones): 30-40 kilometers or more
•Smooth or sandy, with few or no rocks: indeterminate (causes no damage)

Back to upgrades of the lunar tire and not all that surprised that Nasa did work on improving it...
NASA & goodyear: spring tire

moon2.jpg

The national aeronautics and space administration (NASA) joined forces with goodyear to develop an airless tire to be used on extra-terrestrial surfaces. the ‘spring tire’ features 800 load bearing springs and is designed to carry heavy vehicles over much greater distances than the wire mesh tire used on the apollo lunar roving vehicle.
It’s able to withstand the sharp temperature differences of outer space and will not blow out if it is punctured. should a puncture occur, it would affect only one or a few of the 800 load bearing springs. With the combined requirements of increased load and life, we needed to make a fundamental change to the original moon tire. What the goodyear-NASA team developed is an innovative, yet simple network of interwoven springs that does the job. The tire design seems almost obvious in retrospect, as most good inventions do. "Along with having this ultra-redundant characteristic, the tire has a combination of overall stiffness yet flexibility that allows off-road vehicles to travel fast over rough terrain with relatively little motion being transferred to the vehicle". – vivake asnani, NASA principal investigator.

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#15 2016-02-25 19:38:44

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 16,516

Re: Light weight rover for Mars

Here is another interesting design choice in Airless Tires

tire1.jpg

michelin has been slow to roll out the technology beyond the test phase. In light of this, a company called resilient technologies has also been working on an airless tire. The company recently announced that prototypes of their honeycomb-like tires will ship in 2011 for use in the US military

Not really sure about the wear factor....

tire4.jpg

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#16 2016-02-25 20:07:57

RobertDyck
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From: Winnipeg, Canada
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Re: Light weight rover for Mars

Sound good, but... Conditions on Mars are quite harsh. It's not just rocks. Temperatures swing terribly, the Moon worse. Mars can swing +24°C to -111°C. I get those numbers from the high I saw reported by MGS in the first year it operated, to the low recorded by the Viking 2 lander over more than a Martian year. I heard a rumour that the high can get up to +30°C, but I haven't been able to confirm that. And Curiosity recorded night time temperatures colder. What temperatures will rubber remain resilient? Remember the O-ring for Challenger didn't break, didn't embrittle, but became non-resilient so couldn't seal the joint as it flexed. Which rubber? Polybutadiene, neoprene, silicone, other?

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#17 2016-02-25 20:37:07

kbd512
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Posts: 2,991

Re: Light weight rover for Mars

This really isn't rocket science.  Just heat the tires.  Use nitrogen filled rubber tires with conductive polymer or metal woven into the belt and heat the rubber using RHU's.

Make the tire 50C warmer than the environment, or whatever it needs to be, using RHU's.  The amount of thermal output required of the RHU is an engineering question that's pretty easy to test.

If you want to make it stupid simple, use a "push-in and twist" RHU design that makes or breaks contact with plates on the aluminum hubs to transfer the heat via conduction.  Near the end of the day's last EVA, the crew would twist the RHU's to make contact with the hub to heat the tire.  If the vehicle won't be used, just turn the RHU's "on" and leave it.  Having tires heated to 85C on a non-moving vehicle is not a problem.

No goofy airless wheels or metal tires are required.  Use the same tech we use here on Earth and add a heating element to it.

NASA already has a good durable rubber compound that's highly heat, cold, chemical, and radiation resistant.  I don't know if it's suitable for tires, but it deserves a test.

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#18 2016-02-25 21:11:53

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 16,516

Re: Light weight rover for Mars

I know here on earth even with a 67 % nitrogen atmosphere inside a tire that when its heated it can explode http://arlweb.msha.gov/Accident_Prevent … eating.asp but maybe at 100% and a rubber that does not decompose into combustible gas/air mixture of any type it sounds like we need to build it and test it to find out for sure. Maybe even a Co2 inflating would be also something to try. The Rhu's in contact to the rim would sound to be the best for not having them bouncing all around lossly inside a tire. If we need more heat we could add more of them to the rim in optional already made holes for them and less when its not needed.

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#19 2016-02-25 22:13:52

RobertDyck
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Re: Light weight rover for Mars

Duh! Should have thought of that. Good idea. What did Shuttle use for its tire? Those had to survive space. Wheel wells were not pressurized. (Or whatever you call the space landing gear retracts into.)

Found something: Space Shuttle Tire Basic Facts and Figures

  • The space shuttle tires are filled with nitrogen (as are most aircraft tires) due to the shuttle's stability at different altitudes and temperatures. Due to extremely heavy loads, these bias ply tires are inflated to 340 psi (main gear) and 300 psi (nose gear).

  • Shuttle tires go from in excess of -40 degrees Fahrenheit in space to +130 degrees Fahrenheit on landing in a matter of minutes.

  • The main landing gear shuttle tires are only used one time and the nose landing gear are typically used for two landings.

  • Weight: Since weight is of extreme importance, the tires are made with a minimum amount of tread to conserve weight, allowing for larger payloads. A few pounds may not seem to make much difference, but when you add up all of the ways to decrease weight throughout the shuttle it can have a significant impact.

These are Michelin aircraft tires: Space Shuttle

You know, we may not need aircraft tires for a ground vehicle on Mars. A vehicle isn't as heavy, tires are expected to last longer, and terrain is rougher and more varied. Filling with nitrogen is good enough? Ok, we can do that. Or CO2; anything non-oxidizing.

I'm surprised at temperature rating. Spacesuits are designed to endure temperatures −156°C (−249°F) to +121°C (+250°F). Enclosing in a wheel well is good enough? Even stratosphere air gets down to -70°C (depending on altitude, latitude, and season). Weather here in Winnipeg can get down to -40°C, so car tires have to endure that. That's real temperature, not wind chill, although the last time it got that cold was January 2005. The record low for this city was -45°C during a blizzard in 1966. What do cars use in Alaska in winter? And I mean Fairbanks, not just Anchorage.

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#20 2016-02-26 00:09:04

kbd512
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Re: Light weight rover for Mars

Soucy Defense of Canada makes band tracks for M113's that are designed to operate at temperatures between -73C and 80C.

However, NASA, through small business initiatives, worked with NanoSonic to develop a variety of advanced rubber compounds with some very interesting properties.

pd101_lalli_2014_o.pdf

I see no reason why NASA couldn't develop regular rubber tires made of compounds that don't even require RHU's to heat the rubber.

Apart from operating temperature range, chemical and radiation resistance, the performance requirements are simply not that extreme.

This rover will primarily be driven during the day when temperatures are well within the operating range of typical rubber compounds.

Perhaps hand-made spring steel tires are required for lunar operations due to the high direct sunlight temperatures reached in the vacuum of space.  However, the tires for vehicles on Mars will never see temperatures that high, so there's no need for that kind of technology.

If you can't afford the weight of spare tires for the rover, then you can't afford the weight of the rover, either.  Much like vehicles on Earth, vehicles on Mars require spare parts.  Four spare tires and a spare battery pack should be mandatory items for any surface vehicle.

My light rover concept is a base unit similar to Centaur 2 (batteries, life support, water tanks, cargo compartment for food storage) with a wider wheel base (wheels on struts like a Baja racing car / truck) and inflatable module with a polycarbonate window on one end and an inflatable airlock on the other end.  It'd look similar to NASA's ATHLETE vehicle, but without multiple motors or servos and larger wheels.

Inside the inflatable, the passenger compartment would have fabric seats attached to the walls of the module using bungee cords.  The astronauts would have fabric hammocks to sleep in, which would also be attached to the walls of the module at taps and removed and stowed in a fabric pouch built into the wall after reveille.  There would also be fabric pouches to stow the MCP suits and helmets.  The rear of the vehicle would contain suit servicing utilities, an inflatable camping style toilet (hopefully there's a way to seal it off from the rest of the vehicle), and perhaps a manually operated washing machine to launder clothes and suits.  A micro galley would rehydrate rations and provide water for drinking and personal hygiene.

The heaviest items in the inflatable module would be the astronauts.  The base unit would be about the size of my pickup truck's bed, but have a much wider wheel base than my truck, and the inflatable module would overhang the front and rear of the base unit.  I'm thinking this vehicle would be in the 1.5t to 2t range.  Perhaps advanced batteries could get us to 1t.  The majority of the mass is batteries and water.

Edit:

If that resonant nuclear battery technology works, that means range unlimited vehicles that are well within the "lift and throw" capability of a Falcon Heavy.

The same Falcon Heavy could deliver miniature supply stations (MSS) near sites that look interesting.  Each MSS would store rations for the crew, spare parts for the rovers, and scientific instruments for field geology.  Alternatively, assuming minimal ISRU for oxygen and water, four rovers could carry all the consumables and spares required.  That's the entire surface exploration and habitability architecture right there, all delivered with a single rocket and four separate payload containers (presumably HIAD and forced inflation parachutes to eliminate the use of sky cranes to minimize retropropulsion requirements).

Delivery of two two person pressurized MAV's would require two Falcon Heavies.  Storable chemical propellants are more than sufficient to provide the dV required to reach orbit.  Obviously use of cryogenic propellants, especially when combined with ISRU, could dramatically decrease payload mass but this level of complexity is simply not required.

This is a lot like Mars Semi-Direct, but with unlimited surface mobility and ISRU for oxygen and water only- two things that Mars has plenty of that require little advanced technology to acquire and store.  Between CL-ECLSS, a technology similar to that used in MOXIE for oxygen generation, and regolith baking for water extraction, the delivered tonnage requirement is quite reasonable.  If ISRU for propellant production proves feasible, then only 2 Falcon Heavies are required to deliver the surface exploration architecture, although I think delivery of a backup MAV aboard another Falcon Heavy is highly desirable.

Last edited by kbd512 (2016-02-26 12:37:43)

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#22 2016-02-29 15:06:19

kbd512
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Registered: 2015-01-02
Posts: 2,991

Re: Light weight rover for Mars

Rover Crew Sustainment and Power Requirements:

MOXIE is supposed to be a 1% scale demonstrator of the device that NASA wants to use to make propellant on Mars.  The demonstrator requires roughly ~168W of power and produces 22g/hr of oxygen.  If MOXIE is scaled up 60%, it can make the maximum amount of oxygen that NASA says an astronaut would consume in a day, 35g/hr.  Alternatively, 2 units similar to the demonstrator would produce 44g/hr.  The rover would likely require six such units to provide backup oxygen generation capability in the event of failure of any two units, with four units active at any given time.  That's 672W just to produce oxygen.  The dimensions of MOXIE is 30cm x 23.5cm x 23.5cm, but I can't seem to find the mass.  Maybe we can get away with using four units or fewer with a highly efficient CL-ECLSS.

I have no idea how much power is required to bake the water out of the Martian soil, but we need to know this in order to provide for the astronauts water requirements.  I expect that the every-day EVA's will result in a loss of water as well as oxygen.

What are the power, mass, and volume requirements for two 95% efficient CL-ECLSS capable of sustaining two crew members in a 2M by 5M inflatable enclosure with a 1M x 2M inflatable airlock that the astronauts open and close at least four times per day?

For a rover with a mass of 1t carrying a payload with a mass of 1t to 1.5t, how much power is required to move at 50kph?  The rover only weighs .95t on Mars with a 1.5t payload.  So for a rover that weighs roughly three times what Curiosity weighs on Mars, how much electrical power is required to move it over relatively smooth terrain between 25kph and 50kph?

To keep things simple, let's say the rover is a 4 wheel design like a normal light vehicle and each wheel supports 237.5kg of the rover's weight.  Each wheel would have its own electric motor.  Let's say each hub motor can provide power from .5kW to 2.5kW, and is 85% efficient.  If the rover is driving over sand, how much power would the vehicle consume at a roughly constant speed of 25kph?

If no nuclear battery technology is forthcoming and we're limited to rollup solar panels and batteries, what's the mass of the battery pack required to permit 8 to 12 hours of off-road travel over soil with a consistency similar to sand?  If we had a 20kWh battery pack is this doable?  If there are 5 hour mid-day stop for recharging the batteries, is that sufficient time to recharge a 20kWh battery pack?

2 Person Rover Concept of Operations:

* 1 to 3 days of travel to site of interest

7AM to 10AM travel
10AM to 3PM stop for battery recharge
4PM to 9PM travel

* 1 to 2 days of exploration of site of interest

Astronauts deploy solar panels at 7AM during the first EVA and then repack them at 5PM when they come in from the second EVA
7AM to 11AM EVA-1
1PM to 5PM EVA-2

* 1 day of preparation for travel to next site of interest (rover maintenance, samples cataloging and cursory examination, route planning)

Astronauts deploy solar panels at 7AM during the first EVA and then repack them at 5PM when they come in from the second EVA (EVA's for solar panel deploy/stow and rover inspection and maintenance only)

Does a 20kWh battery pack provide enough power for movement and replenishment of lost oxygen in that time frame?  I was thinking that while the rover isn't moving, it would generate oxygen and water for the crew.  While on site in the exploration area, the crew would simply lay the solar panels out during the morning EVA and then pack them up after the afternoon EVA.  I have no idea how much power the ECLSS would consume or what a realistic battery discharge/depletion rate is for the type of off-road travel encountered.

I know that the flexible roll-up arrays are less efficient than the crystalline arrays, but their flexibility should mean that 1.5M square array panels can simply be laid out on the ground near the rover versus some sort of deployment mechanism that requires mechanical devices to function properly.  The astronauts would use flexible nylon pouches for solar panel storage and brushes to wipe off dust.  Each astronaut would carry his or her panels in the rolled up pouch through the airlock, deploy the panel squares, and connect detachable power cables from the panels to the rovers.

Anyway, just some thoughts about how this could work and a lot of questions.

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#23 2016-02-29 19:23:53

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 16,516

Re: Light weight rover for Mars

The Moxie demostrator is part of the 2020 rover....

http://www.newmars.com/forums/viewtopic.php?id=7014

Thinking about the life support is really part of the next size up and bigger manned rover useage design. Will add your post to the Rving topic...

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#24 2016-02-29 21:34:16

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,516

Re: Light weight rover for Mars

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#25 2016-03-01 07:16:48

kbd512
Moderator
Registered: 2015-01-02
Posts: 2,991

Re: Light weight rover for Mars

Some More Thoughts on Rover Power Requirements:

Assuming the new cobalt electrode technology for lithium ion batteries delivers the expected energy density increase to 2.5kWh/kg, then I think 2 20kWh batteries would be sufficient with 4 .5kW to 2.5kW motors that are 85% to 90% efficient.  The cobalt electrode batteries are reported to charge significantly faster than current technology, too, and resolve electrode corrosion issues.

The insanely energy dense 3D lithium ion batteries can deliver energy density greater than gasoline and stupidly fast charging times, but there's no indication that those batteries can be scaled up to the size required for an electric vehicle.  It seems that the researchers were more interested in providing substantially smaller power supplies for portable electronics than power supplies for electric vehicles.

In any event, I have a mass budget 250kg for two batteries for the rover, 60kg for four electric motors and wiring, 200kg for two CL-ECLSS, 50kg for the oxygen generation equipment, 50kg for the water generation equipment (does not include fresh or grey water storage, which is part of the CL-ECLSS), 20kg for electronics, and a further 20kg for communications equipment.

We're already up to 625kg of the rover's dry weight.  The remaining 375kg is reserved for rover structure.  Virtually everything has to be exceptionally light for this thing to come in at the target 1t dry weight, but I think it's doable.  Virtually all of the rover's structure is fabrics and composites to limit the adverse affects of GCR interactions that aluminum alloys would cause.

I'll post more as I am able to determine what the weight of individual components will be.  I'm still trying to figure out what the mass of the structure will be.

Edit:

For those wondering how the rover will robotically drive itself to the landing site when the humans land, given that the solar panels are stowed inside the vehicle and manually deployed by its occupants, three of the panels will be deployed atop the rover in the landing configuration and the inflatable module will be deflated.  No power will be consumed by the ECLSS or oxygen and water generation units.  When the humans arrive, they will remove the solar panels from the top of the vehicle, deploy all the solar panels around the vehicle, inflate the inflatable module to confirm that there are no leaks, and then wait two to three days to confirm that all vehicle systems perform as expected.

Although I expect our explorers to take care of their vehicle and power generation units (PGU's), the PGU's are stowed in the vehicle (with the astronauts in the inflatable or in the base unit) because PGU's must be protected from vehicular accidents to assure power availability.  Even if a vehicle is incapable of travel, it should still be capable of life support.

My first thought was to simply stow the PGU's atop the inflatable module in their storage sleeves using tie-downs.  If the vehicle accidentally rolls or impacts a terrain feature like a rock formation, I don't want that accident to crush the PGU's and kill the astronauts, irrespective of whether or not any other injuries were sustained in the accident.

Another weird requirement unique to this rover concept is that no sharp tools may be stowed in the inflatable.  The only tools permitted in the inflatable are blunt tipped hex drivers and blunt tipped scissors for meals.  All knives, drill bits, and shovels must have kevlar sleeves and be stowed in a tool pouch located in the base unit.

The inflatable modules are removable and secured to the base unit using kevlar or nylon tie-downs.  If a base unit from one vehicle is damaged and an inflatable unit from another vehicle is punctured, then a complete working vehicle can still be constructed using available parts.  Four two seat rovers are delivered to Mars for each mission, so absent loss on reentry like-kind spares should always be available.

Although all four vehicles are habitation capable and each loaded with one quarter of the rations required for a nominal 500 day surface stay, the intent is to store scientific instruments in two of the vehicles and have the astronauts occupy the other two vehicles.  Alternatively, each astronaut could drive his or her own vehicle.  Although I think using two crewed and two tele-robotically operated rovers is best for crew morale, maybe giving each crew member their own vehicle would work better.

Last edited by kbd512 (2016-03-01 11:05:22)

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