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#76 2006-03-14 04:36:27

Dook
Banned
From: USA
Registered: 2004-01-09
Posts: 1,409

Re: Simple Mars Vehicle Part 1

I would definately rather have two full sets of lithium-ion batteries because it would make the vehicle much more capable but it's weight would be 6,387 lbs.  I think that's just too heavy.

Maximum current draw would be for the one hour that the vehicle is operated each day.  At full charge the batteries provide 6.8kw.  During vehicle operation the electric motors will draw 10.8 kw.  Remember the fuel cell provides an additional 12kw for a total of 22.8 kw available not counting solar panels.

In my range estimate I included fifteen minutes of fuel cell operation to recharge the batteries just before night fall but once the crew notices a loss of power they could stop for the night and allow the fuel cells to recharge the batteries for 15 minutes before shutting down.  This should keep the batteries from completely draining.

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#77 2006-03-14 07:33:08

GCNRevenger
Member
From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Simple Mars Vehicle Part 1

First off, planning for the rover to only operate one hour per day is pretty silly, it should be able to operate much longer, perhaps not at such a high speed. Mars has no roads, and a good fraction of its surface is terribly rough terrain (the more interesting parts), so only one hour winding through ravines or something is just impractical. You will literally never get anywhere this way.

Also, if there is a reason that you need to turn around and come back quickly, an injured astronaut or a faulty LSS system or something, relying on the solar pannels to extend your range is a dangerous proposition, you may not have enough power to come back quickly.

Just driving an hour probobly wouldn't solve the heating problems either, and it definatly wouldn't after several hours of driving. The carbon composite on the MERs isn't external either I don't think.

This whole business about using fuel cells or other power sources to recharge a battery for use as primary power makes no sense, why bother with using one storage device to refill another storage device before you use that power? The battery should only be big enough to make the vehicle a "hybrid," and solar power should be used directly for main power most of the time as a suppliment to the fuel cell/generator/etc. That will save mass and increase reliability.

Speaking of which, however, any business about the rover weighing much less then 10,000kg is just silly, lets not even go there. Bob Zubrin simply set the bar too low, and thats that.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#78 2006-03-14 10:05:16

Dook
Banned
From: USA
Registered: 2004-01-09
Posts: 1,409

Re: Simple Mars Vehicle Part 1

Silly.  Should.  Yeah, I guess some things are silly and some things should be this or that.  Do you ever wonder why the media never invents, fixes, or builds anything?  Because they make their living off of criticizing.  Just like you.

I didn't intend for the vehicle to operate only one hour per day but that makes the most of the free energy available, solar.  There is enough hydrogen/oxygen to power one fuel cell for 36 hours.  The 12 kw from the single fuel cell might get the vehicle 360 miles, that's 190 miles out then turn around whereas with solar you can go 351 out.  The crew could drive 100 miles or so out from the base then travel a circular course around the base, to examine mars.  Depending on how much fuel they've used they could head for base in a hurry, stopping once or twice for the night.     

The idea for exploring mars should be to actually explore it, not drive a long ways, take a single sample, then turn around and head back like there's only a single place to see.  Each day the vehicle spends idle would give the crew time to examine rocks and dig core samples.

I estimate the vehicles top speed to be 20 mph.  The crew would likely use slower speeds when necessary.  Did this really need to be said? 

The fuel cells power the electric motors and are only used when the vehicle is in motion unless the crew needs to recharge the batteries so there is power to operate vehicle systems (oxygen pressurization/CO2 removal/Lights/Heat lamps) at night. 

The solar panel is large, 167 cm by 83 cm but it only provides about a max of 3kw at noon (6kw to 10kw total a day) which would be used to power vehicle systems and charge the batteries while it is stopped.  There is an emergency foldable solar panel that the crew can lay out on the surface of mars to supplement (maybe an additional 4-6kw a day?) the battery charging.  This could become a standard use rather than pure emergency use. 

Also I think we are all waiting for your much much better design to show up in any of the forums.  Where is this great turbine powered mars exploration vehicle?   

I know this isn't perfect, something you can't seem to accept from others.

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#79 2006-03-14 19:51:24

GCNRevenger
Member
From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Simple Mars Vehicle Part 1

I like being a critic, I enjoy it. The real question is, why do you post your ideas if you are not looking for critical analysis? Knowing something will not work or is a bad idea is as important as good ideas or solutions.

The "arcing path" plan has two obvious flaws, first that it imposes an artifical limitation on where you can go and what you can do, particularly if you find something along the way and want to go off course. Second, there is the possibility that the direct return route will be un-traversable (or may not even exsist), the only route that should be banked on is back the way you came.

And how far from the landing site is far enough, anyway? The range from base must be balenced against the fact that you will not be stopping every few hundred feet every day, and you will probobly want to skip a large portion of terrain to get to more interesting features. Much like the MERs are doing right now.

Stopping after only twenty miles every day at useless places with a vehicle capable of much more with some extra fuel is what I think is silly. Mars is a big place, and a great deal of it isn't worth spending the limited, precious time parked at, and you can always return to the landing site to refuel. If your point of interest is 700mi away by an arcing path, then its lots less by a direct route too.

Don't think big long slow sorjuns, turning over every stone useless or not, because thats a terrible way to explore. Mars is too big to explore that way, a long-range 700mi trip at 20mi a day will chew up at least a month of time, while a more direct run straight to a site of interest will take only a few days. Time is an important factor and not just distance, you've only got ~400 days of useful exploring time on the surface.

I don't have a "design" persay, only a list of technologies that could be better and a better idea of how big the thing should be. Small turbines, like those used in light helecopters or jet liner APUs or even smaller, linked to a generator to power six in-wheel motors on "active" suspension mounts. Solar/battery as a "hybrid" function to improve fuel efficiency, with water being condensed from exhaust gasses and stored for later conversion back to fuel.

A turbine would not be quite as efficient as a fuel cell setup, but it would very likly be lighter per-kilowatt. They would be small, probobly about the size of a pressureized soda fountain syrup tank including generator at most, and light enough that you could afford to carry a pair for redundancy and burst power perhaps.

Another possibility that NASA has had is to use next-generator dynamic RTGs, which while heavy would provide continous power indefinatly with very high reliability, perhaps charging batteries at night to increase speed in the day. The RTG generator set could also be used as backup power for the HAB if something went wrong with the reactors.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#80 2006-03-14 20:49:41

Dook
Banned
From: USA
Registered: 2004-01-09
Posts: 1,409

Re: Simple Mars Vehicle Part 1

We know you like being a critic.  We're overwhelmed with it.  You're like Roger Ebert without his candy fix. 

With a 3D map of mars the crew will have already used virtual reality to travel the planned route on mars.  At any time they can pull up a visual and overhead map on their laptop computers to see what the terrain is like if they wish to change course.   

I guess I thought that maybe since so many people spend so much time here that we could all join together and maybe come up with one small piece of a mission to mars plan.  But then nothing is ever invented, discovered, or created with a critic in the room. 

The idea is to explore mars, not go in one direction as far as possible then turn around and traverse the same territory but if they wish to do just that they can.  It will simply take a few weeks to get there.  Every option has it's own set of risks. 

Opportunity and Spirit are slowly examining the surface of mars and finding some interesting things.  Your jet afterburner powered vehicle would pass right over the blueberries.

You think a helicopter turbine will work on a mars vehicle?  Yeah right.  No way you can possibly carry enough oxygen to run it for even a minute.  You obviously haven't looked at this idea with your own serious critical analysis.

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#81 2006-03-14 21:37:27

GCNRevenger
Member
From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Simple Mars Vehicle Part 1

"we could all join together and maybe come up with one small piece of a mission to mars plan"

Something like that, but nobody has all the answers, and all ideas should be tested. I like to critique because thats half of what I do for a living, and I enjoy what I do, especially since it takes the engineers' tendency to wander and hopefully steers it closer to reality. It has been my experience that the phrase "join together" usually preceeds an unsaid herding of discourse to the views of a single person however.

"With a 3D map of mars the crew will have already used virtual reality to travel the planned route on mars. At any time they can pull up a visual and overhead map on their laptop computers to see what the terrain is like if they wish to change course."

A picture is not a conclusive indication of the terrain; an image might not be able to distinguish rock from dust, and if the image is not quite new then dust dunes may have moved too. Fields of intermediate sized rocks that would making driving difficult may also not be visible from satelite imagery. Modest differences in topography can make a big difference in fuel consumption. This isn't a fullproof solution by any means I don't think.

"The idea is to explore mars, not go in one direction as far as possible then turn around and traverse the same territory but if they wish to do just that they can. It will simply take a few weeks to get there. Every option has it's own set of risks."

With, lets say, a 150mi range one-way (or 125mi "as the crow flies" for arguments sake) range from the landing site, you are able to cover a region of about Fifty-Thousand Square Miles. There is no way in heck that you are going to cover a useful fraction of this if you are moving only 20mi a day! Even a conservative ~10mph for 8hrs a day would let you get to the edge of this radius in just two days, not eight, or just one day at 20mph. 12-14 days of each "sortie" would be burned up not spending time at the site of interest.

What you CAN do is using satelite or other imagery find out the interesting places you want to go (or, more importantly, where the science teams on Earth want you to go), and then go there directly without delay. Maybe spend a few days or a week, then return to the landing site, refuel, and repeat. If you find something interesting along the way worth stopping for, by all means, but just randomly putzing around the surface, taking your time, is not an effective way to go about exploring.

"Opportunity and Spirit are slowly examining the surface of mars and finding some interesting things. Your jet afterburner powered vehicle would pass right over the blueberries."

You must not be paying attention to what the MERs have been doing: they have been driving from location to location - as designated by mission control from satelite imagery - as fast as their whimpy motors can carry them. Huge swathes of Mars are totally unworthy of wasting precious time studying, and the MERs are driving right past them as quick as they can. They are doing this so they can get to the really interesting features, and spend what limited time (or life support...) they have there, which is exactly what a manned rover team should do too.

"You think a helicopter turbine will work on a mars vehicle? Yeah right. No way you can possibly carry enough oxygen to run it for even a minute. You obviously haven't looked at this idea with your own serious critical analysis."

We have been over this before, even in this very thread catagory! But for those who might read this but not the earlier posts, the turbine only burns a small fraction of the oxygen injected into it, where the rest in the exhaust would be cooled and fed right back into the intake after CO2/H2O scrubbing. I noted a helecopter turbine simply as a reference point for a relativly compact, high-power, light-weight, and fairly mature (and potentially cheaper) way of running a rover. A helecopter turbine is probobly too big actually, but turbines as small as a few inches in diameter are easy to make too.

(Edited for niceness)


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#82 2006-03-14 22:27:37

GCNRevenger
Member
From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Simple Mars Vehicle Part 1

It may well be that the debate between fuel cells or combustion is already moot...

I have done a little poking around about Dynamic-type RTGs (radioisotope thermoelectrice generators, "nuclear batteries"), which use moving generators rather then inefficient thermocouples to convert decay heat to electricity.

Various NASA articles claim that such a device in the 10kWe range would weigh around 3MT... And thats for unlimited continuous power. Suppliment this with solar and batteries for hybrid/burst power, and the only thing limiting rover endurance will be stored supplies and crew fatigue... or perhaps rover wear or sample storage capacity.

Edit: That 3MT probobly doesn't include the radiators however, nor the structure for holding the device and any nessesarry radiation shielding. Pu-238 is an alpha  source if memory serves and shouldn't be hard to shield.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#83 2008-03-29 09:40:55

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,310

Re: Simple Mars Vehicle Part 1

Some great graphics on the Explore Mars site and an interesting approach to LEO assembly which I have always thought coudl be helpful.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#84 2019-11-21 18:52:25

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,333

Re: Simple Mars Vehicle Part 1

Bumping topic to fix

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