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#1 2003-11-01 01:09:31

Hazer
Member
From: Texas/Oklahoma
Registered: 2003-10-26
Posts: 173

Re: RTGs - And Rovers

[color=#000000:post_uid0]Hey does anyone have any information on the RTG that powered Galileo?  I was wondering if you could power a remotely-controlled rover with one.[/color:post_uid0]


In the interests of my species
I am a firm supporter of stepping out into this great universe both armed and dangerous.

Bootprints in red dust, or bust!

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#2 2003-11-01 12:07:14

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

Re: RTGs - And Rovers

[color=#000000:post_uid0]Hmmm that isn't a great deal of power for a large rover, but it might be if it were used in a sneaky way: Use the RTG to charge up a light-weight-as-possible battery and use that to drive the motors or high power science equipment for short periods in the day and recharge at night.[/color:post_uid0]


"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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#3 2003-11-01 12:18:58

RobS
Member
From: South Bend, IN
Registered: 2002-01-15
Posts: 1,695
Website

Re: RTGs - And Rovers

[color=#000000:post_uid0]RTGs are only 5% efficient converting heat to electricity. But a Stirling cycle engine could probably manage 20%, so that would help a lot.

The Martian atmosphere is probably thick enough to allow small, light-weight heat exchangers like car radiators, which would help maintain the delta-t (change of temperature) you need for stirling or other engines. They haven't been used in deep space because of their moving parts and the large radiator surfaces they need. On Mars the radiators could be small.

        -- RobS[/color:post_uid0]

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#4 2003-11-01 22:04:25

Hazer
Member
From: Texas/Oklahoma
Registered: 2003-10-26
Posts: 173

Re: RTGs - And Rovers

[color=#000000:post_uid0]Thanks for the clarification.

A Stirling cycle engine on Mars?  Now that's not a bad idea.[/color:post_uid0]


In the interests of my species
I am a firm supporter of stepping out into this great universe both armed and dangerous.

Bootprints in red dust, or bust!

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#5 2003-11-05 12:24:24

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

Re: RTGs - And Rovers

[color=#000000:post_uid0]Hmmmm so if you packed a 50kg Stirling-Cycle RTG and, say, another 50kg of batteries/generators/shielding though... would 100kg be a small price to pay for a Mars rover with unlimited range and surface duration? Sounds like a bargain to me.[/color:post_uid0]


"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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#6 2003-11-05 13:28:40

RobS
Member
From: South Bend, IN
Registered: 2002-01-15
Posts: 1,695
Website

Re: RTGs - And Rovers

[color=#000000:post_uid0]I don't know how much a Stirling engine putting out a few kilowatts would mass, but I suspect it could be less than 50 kg. Maybe 10 kg? We're only talking about a few horsepower. I doubt it'd be very large, either.

     -- RobS[/color:post_uid0]

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#7 2003-11-06 02:14:13

Free Spirit
Member
Registered: 2003-06-12
Posts: 167

Re: RTGs - And Rovers

[color=#000000:post_uid0]I think we should be very discreet about landing nuclear powered vehicles on surfaces where people or other life might inhabit.  A few pounds of plutonium might not seem dangerous on a planetary scale, but keep in mind that it's one of the most toxic substances out there.  If you inhale even a few atoms of it, your chances of getting cancer are very near 100%.  Anyhow, RTGs don't develop a whole lot of power, usually a few hundred watts if that.  [/color:post_uid0]


My people don't call themselves Sioux or Dakota.  We call ourselves Ikce Wicasa, the natural humans, the free, wild, common people.  I am pleased to call myself that.  -Lame Deer

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#8 2003-11-06 09:40:56

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

Re: RTGs - And Rovers

[color=#000000:post_uid0]How come everybody beats up on nuclear power? The modern RTG is a marvel of durability and safety, and the "threat" they pose is entirely overstated.

"A few pounds of plutonium might not seem dangerous on a planetary scale, but keep in mind that it's one of the most toxic substances out there. If you inhale even a few atoms of it, your chances of getting cancer are very near 100%.  Anyhow, RTGs don't develop a whole lot of power, usually a few hundred watts if that..."

First-first of all, atoms are small. Real small. You would need a million billion billion atoms of Plutonium to even be visible with the best optical microscope. You have already inhaled a few atoms from nuclear testing and Chernobyl.

Plutonium is fairly nasty, but it is not intensely radioactive unless it is being used in a nuclear reactor, which an RTG is NOT. Secondly, the Plutonium is stored as a sinterd metal oxide which is extremely hard, and will only fracture into a few large pieces if broken, not into a fine powder. Thirdly, the US-made RTGs are extraordinarily resistant to damage, and have survived with little or no leakage at all through a battery of torture tests, like terminal velocity impacts, several thousand degree arcjet furnace, sea water immersion, and even firing fairly large bullets at them to simulate a launch disaster. All modern designed RTGs that have accidently re-enterd Earth's atmosphere didn't leak at all. Bet you didn't know some already came back down from failed satelites and Apollo 13's Lunar Module. US RTGs are virtually impenitrable.

The danger of the material itself is greatly overestimated too, the radiation from Pu-238 that you have to worry about is predominantly alpha radiation, which is easily blocked by a thick sheet of paper, much less a RTG hardend casing. Furthermore, the data used to extrapolate the huge jump in lung cancer with inhilation of small quantities by those heralding plutonium as the doomsday poison is shakey if not fraudulent, and consider its source... US and Russian nuclear testing has thrown more Plutonium areosol (and worse things!) directly into the air worldwide than Nasa could dream about putting into RTGs, and yet, we're all still here aren't we?

I would actually think that the small amounts of radiation put off by a running RTG would be a -good- thing, since it would help sterilize the spacecraft after it lands, which would make the chance of us accidently discovering "life on Mars that looks alot like life on Earth near Cape Canaveral" lower.

Solar power, if you haven't noticed, doesn't make a whole lot of power either per weight, and it has one fatal drawback on Mars... the dust adheres to them. The Pathfinder base station probe would still be sending us pictures of Martian sunrises and weather forecasts if its solar panels didn't lose [i:post_uid0]THREE PERCENT[/i:post_uid0] of output a day. While this has improved a little, it hasn't improved much... An RTG need not supply all the power for motors to move around either, if it recharged a battery that was used for motion now and then instead (which is what Nasa rovers do anyway, stop and go) and have a life span of YEARS instead of a few weeks of exploring![/color:post_uid0]


"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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#9 2004-03-11 07:56:35

C M Edwards
Member
From: Lake Charles LA USA
Registered: 2002-04-29
Posts: 1,011

Re: RTGs - And Rovers

[color=#000000:post_uid0]Why don't we forget about those meager little RTG's and solar panels and send a rover that runs on propane/oxygen?[/color:post_uid0]


"We go big, or we don't go."  - GCNRevenger

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#10 2004-03-11 08:54:47

Lars_J
Member
Registered: 2004-02-11
Posts: 82

Re: RTGs - And Rovers

[color=#000000:post_uid0]And how long do you think that propane/oxygen will last compared to an RTG?[/color:post_uid0]

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#11 2004-03-11 16:27:26

C M Edwards
Member
From: Lake Charles LA USA
Registered: 2002-04-29
Posts: 1,011

Re: RTGs - And Rovers

[color=#000000:post_uid4]And how long do you think that propane/oxygen will last compared to an RTG?[/color:post_uid4][/quote:post_uid4]
[color=#000000:post_uid4]*shrug* About as long as a solar powered rover, I guess, only with more available power.[/color:post_uid4]


"We go big, or we don't go."  - GCNRevenger

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#12 2004-03-11 23:10:45

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

Re: RTGs - And Rovers

[color=#000000:post_uid0]Nooope, way lower energy density, days at most for a reasonable mass... high output though.[/color:post_uid0]


"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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#13 2004-03-12 06:31:26

atomoid
Member
From: Santa Cruz, CA
Registered: 2004-02-13
Posts: 252

Re: RTGs - And Rovers

[color=#000000:post_uid0]What would be better, a small RTG charging either a battery or capacitors?

* power needed for experiments VS roving
* weight of battery VS capacitor
= weight advantage (if any) by downsizing the RTG and relying on battery bank (heavy?) for roving VS bigger RTG sized for top roving speed, any experiements needing more current could rely on capacitors, to minimize complexity and weight vs solar panels and yeilding more capacity for experiements... thats right! as cheap backup redundant pairing with the Phoenix lander, send the tried-and-tested Athena platform refitted with RTG and headlights for night roving in 2007!  [i:post_uid0]Hell, why not just send in the Marines!!![/i:post_uid0]
:rant: tongue :band: :bars2: :sleep:[/color:post_uid0]


"I think it would be a good idea". - Mahatma Gandhi, when asked what he thought of Western civilization.

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#14 2017-05-17 23:22:46

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 10,650

Re: RTGs - And Rovers

The marscart would seem to be favoring this power system and not solar

and this is another topic to fix....

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