To RTG or not to RTG the size is the question

SpaceNut · 2017-05-23 18:58:09

Its pretty clear to me that we will go with a mix of power solutions to which a Small Nuclear reactor of Space design, with some solar being used for the less critical, with possibly RTG's for portable size energy and or for just in case we need it.

As far as the nuclear materials is by far safer as the quantity is small in comparison to what we would use in a reactor.

https://solarsystem.nasa.gov/rps/rtg.cfm

https://en.wikipedia.org/wiki/Radioisot … _generator

To which I am sure that some sort of trade study has been done.

For landers that are not needing much power (10Kw) solar and batteries will probably do. Think panels like the pheonix from ATK as they would allow for any location or angle with in where humans would want to set up shop.

The RTG's for those landers that would require power levels above the 10Kw but probably less that oh pick a number 75kw or less. These RTG's should be made sort of like a panel or flat battery pack such that we can make them removable as needed.

To which I am thinking that nothing short of humans being present and the ISPP plant would need any source higher than the RTG units. Also if we do require more once the landers are unloaded we can reroute the power from them for other uses.

Oldfart1939 · 2017-05-23 21:31:47

SpaceNut-
The major drawback to RTGs is the cost of the plutonium/KWe. This is a very expensive source of electric power.

kbd512 · 2017-05-24 00:19:27

Oldfart1939,

The new Silicon-Graphite permanent batteries provide better We/kg numbers at costs ranging into the tens of thousands of dollars instead of tens of millions of dollars just for Pu238 production. Once this technology has been successfully demonstrated in a NASA-sponsored endurance test, Pu238 usage will be limited to RHU's for deep space robotic science missions. If mass is not absolutely critical and the probe can tolerate a few tens of kilograms of permanent batteries to provide electrical power and electrical heating, then we may opt to remove any possibility of radioactive contamination entirely.

Dave_Duca · 2017-05-24 02:50:50

POWER PLANTS

Interesting to note Robert Zubrin's phrase of "Living off the Land" was a metaphor.
What's also interesting is that: a single match stick can kick off an entire Forest Fire.

Since our current "engineering trends" are bent on too much in too little of space;
Then, it is easy to realize the techniques of Von Neumann Over Time approach, applies here.

Such as one small RTG positioned adjacent to the best source of water,
From which the Collecting - Melting - Filtering - Electrolyzing - Sabatiering - CH4/O2 Engine Plant Generating
can commence.

This would be: The Pilot Plant

Working Smarter, Not Harder, right?

elderflower · 2017-05-24 03:14:22

We definitely need a demonstration plant operating, before we send men that are going to depend on it, even as back up. This applies to all the new gadgets and systems we design specifically for use on Mars. Rescue missions are not an option.

louis · 2017-05-24 05:56:03

Clearly this is one of those technologies we would want to develop in parallel with the mission, but I wouldn't want to rely on a technology that doesn't yet exist (same goes for the SAFE-400 nuclear reactor).

kbd512 wrote:

Oldfart1939,
The new Silicon-Graphite permanent batteries provide better We/kg numbers at costs ranging into the tens of thousands of dollars instead of tens of millions of dollars just for Pu238 production. Once this technology has been successfully demonstrated in a NASA-sponsored endurance test, Pu238 usage will be limited to RHU's for deep space robotic science missions. If mass is not absolutely critical and the probe can tolerate a few tens of kilograms of permanent batteries to provide electrical power and electrical heating, then we may opt to remove any possibility of radioactive contamination entirely.

louis · 2017-05-24 05:58:43

There are whole swathes of Mars where water ice can be extracted from the regolith at concentrations of around 6%. Why is that not good enough? Why do we have to go to the "best" water source which might not be a good location from other aspects (iron ore, temperature, landing etc).

I favour Chryse Planitia which has a lot of what we need and is already quite a known quantity.

Dave_Duca wrote:

POWER PLANTS
Interesting to note Robert Zubrin's phrase of "Living off the Land" was a metaphor.
What's also interesting is that: a single match stick can kick off an entire Forest Fire.
Since our current "engineering trends" are bent on too much in too little of space;
Then, it is easy to realize the techniques of Von Neumann Over Time approach, applies here.
Such as one small RTG positioned adjacent to the best source of water,
From which the Collecting - Melting - Filtering - Electrolyzing - Sabatiering - CH4/O2 Engine Plant Generating
can commence.
This would be: The Pilot Plant
Working Smarter, Not Harder, right?

louis · 2017-05-24 06:02:06

I agree. We need demonstrations in a Mars Testing Facility, in orbit and in journeys to the Moon. The way I see it, in a ten year programme, the testing phase would be in the 3-8 year range. After 8 years you want everything good to go, because by then you want a couple of years for training and familirisation of the potential pioneers (probably a squad of 20 out of which you pick your 6 actual pioneers).

elderflower wrote:

We definitely need a demonstration plant operating, before we send men that are going to depend on it, even as back up. This applies to all the new gadgets and systems we design specifically for use on Mars. Rescue missions are not an option.

elderflower · 2017-05-24 07:26:24

Yes Louis. Except we should go asap with what we already know. The earliest mission will first do scouting to confirm proposed surface sites. Then rest of the first and the second mission will be setting up a base and a little local exploring. Included in the base set up will be installing and testing things that later missions will depend on. I don't see the enterprise accelerating until at least mission 3.

Dave_Duca · 2017-05-24 08:38:18

Precisely, Gentlemen....
What better way than the Red Dragon Direct Sample Return

That seriously needs an acronym... lol

Last edited by Dave_Duca (2017-05-24 09:51:53)

louis · 2017-05-24 09:45:43

First couple of missions will be slow burn in terms of output, but they will be experimenting a lot with ISRU materials (or perhaps I should say they "should" be).

elderflower wrote:

Yes Louis. Except we should go asap with what we already know. The earliest mission will first do scouting to confirm proposed surface sites. Then rest of the first and the second mission will be setting up a base and a little local exploring. Included in the base set up will be installing and testing things that later missions will depend on. I don't see the enterprise accelerating until at least mission 3.

Antius · 2017-05-24 11:00:28

Strontium-90 in its oxide form would be a much cheaper isotope. A 1GWe nuclear reactor produces about 50kg of it per year. In the UK and France, it is separated during reprocessing and has been used in hospital irradiation sources. It has a high melting point (2600C) and is a lot less radiotoxic than Pu-238. It's mass specific power is 387W/kg - about 5 times lower than Pu-238. For a thermal power of 10KW, sufficient to produce maybe 1KWe using thermoelectric generators, some 26kg would be needed.

Last edited by Antius (2017-05-24 11:40:55)

RobertDyck · 2017-05-24 11:44:06

Dave_Duca wrote:

What better way than the Red Dragon Direct Sample Return

Not a good idea. Red Dragon is a heavy metal shell. Not appropriate for an unmanned Mars lander. Red Dragon is only useful for cargo that requires pressurization. An appropriate Mars Sample Return mission would use a lander based on Mars Phoenix, a rocket with empty propellant tanks, ISPP, an aeroshell for return to Earth based on NASA's Stardust and Genesis missions, and a tiny rover the size of Sojourner to collect samples.

Last edited by RobertDyck (2017-05-24 11:52:14)

Antius · 2017-05-24 11:46:44

Oops. The specific power of Pu-238 is 560W per kg, about 45% more than Sr-90. SrO has about one third the density of PuO2.

So its better than I initially thought. With strontium so cheap and abundant and able to provide 70% of the specific power of Pu-238, I do wonder why plutonium is used at all. There is no global shortage of Strontium-90 - it is one of the most abundant isotopes in fission product waste. Most countries with power reactor programmes would be happy to give it away to a good cause. The UK has about 30 tonnes of it in high level waste stores. France even more.

Last edited by Antius (2017-05-24 11:50:20)

kbd512 · 2017-05-24 17:26:47

Sr90 emits some pretty intense X-rays when it absorbs its own beta emissions. Any Sr-based RTG would require W or DU shielding. DU is a readily available nuclear waste, much like Sr90. I don't think DOE would care if NASA took some off their hands, but it might still charge them. W is pretty expensive, but also available.

SpaceNut · 2017-05-24 19:12:18

I am here to learn so I am going to post basic stuff to fill in followed by any thoughts.

http://www.tech-faq.com/types-of-nuclear-fuel.html

Fission Nuclear Fuels
The known fissile materials are:
Uranium-233
Uranium-235
Plutonium-238
Plutonium-239
Plutonium-241
Neptunium-237
Curium-244
types-of-nuclear-fuelThe most often used fuels are Uranium-235 and Plutonium-239; they become instable when bombarded by slow (also known as “thermal”) neutrons. They are not easy to find or produce materials, and the process to generate them is usually the most expensive part in the creation of a nuclear bomb. Uranium-233 was used in a couple of test bombs in USA and it is supposed to be the main component in India’s bombs. Thorium-232 is also fissile but it needs fast moving neutrons to start the chain reaction.

http://www.world-nuclear.org/informatio … ation.aspx

http://www.world-nuclear.org/informatio … orium.aspx

https://www.caseyresearch.com/articles/ … clear-fuel

https://ieer.org/resource/factsheets/fi … al-basics/

http://cen.acs.org/articles/93/i27/Tryi … orium.html

https://nsuf.inl.gov/Documents/Hayes-Ba … rFuels.pdf

I noticed that the fuels are shaped into rods, pellets, beads and plates for reactor designs but not much is given for shaping an RTG for these....

250 kg of Uranium = 1 kg of Thorium to achieve the same energy output.

https://en.wikipedia.org/wiki/Multi-Mis … _Generator

Thorium fuel cycle — Potential benefits and challenges

RobertDyck · 2017-05-24 20:02:52

If you want to learn, one of the more interesting leading-edge nuclear technologies is Potassium-40. It's technically radioactive, but so low level that it isn't regulated. It's naturally occurring, so production means isolating the isotope. Well, 0.0117% by mass isn't much, but it's there. The interesting thing is it appears to violate one of the principles that scientists used to believe in. Don't you love when that happens? That's called progress. Recent research appears to show that a properly regulated magnetic field can get Potassium-40 to decay much more quickly. Normally K40 decays through electron capture, but the magnetic field can get it to beta decay to Calcium-40, which is stable and the predominant isotope of calcium. A beta-voltaic cell works similar to a photovoltaic cell, but uses beta radiation instead of light.

::Edit:: Oops. One website periodic table says Potasisum-40 decays by electron capture, but Wikipedia gives a more complex description.

Potassium-40 is a rare example of an isotope that undergoes all three types of beta decay. About 89.28% of the time, it decays to calcium-40 (40Ca) with emission of a beta particle (β−, an electron) with a maximum energy of 1.33 MeV and an antineutrino. About 10.72% of the time it decays to argon-40 (40Ar) by electron capture, with the emission of a 1.460 MeV gamma ray and a neutrino. The radioactive decay of this particular isotope explains the large abundance of argon (nearly 1%) in the earth's atmosphere. Very rarely (0.001% of the time) it will decay to 40Ar by emitting a positron (β+) and a neutrino.

Last edited by RobertDyck (2017-05-24 23:34:02)

Oldfart1939 · 2017-05-25 08:35:40

RTGs are a pretty inefficient way to generate power: 6% power conversion. Lots of mass for very small output.

kbd512 · 2017-05-26 13:08:39

Oldfart1939,

The Silicon-Graphite permanent batteries look pretty appealing compared to RTG's.

Si-Graphite Power Cell:
Voltage: 1.5VDC (72F) to 2VDC (max, with heat applied)
Current: 3A continuous, 5A peak
Dimensions: 12” x 12” x .1875”

24VDC Power System:
Cells Required: 24V / 1.5V = 16 Si-Graphite power cells
Output: 24V * 3A = 72We
Volume: 12” * 12” * .1875” = 432in^3 (.25 cubic feet)
Graphite Bulk Density: 48lbs/ft^3
Maximum Cell Mass (Excluding Cell Casing): 12lbs

There are ways to substantially reduce this mass, but this is conventional stacked plate design. It’s the most simple configuration possible, albeit mass-inefficient, and this is something you can purchase as a commercial product. Think of it like fuel cell plates, except it's an extraordinarily high energy density and very low power density battery.

6,250kWe is the input wattage required to drive a 100kWe homopolar generator

6,250We / 62.5We (de-rating cell output for easy math and to account for losses) = 100 Si-Graphite power cells

100 Si-Graphite power cells * 12lbs per Si-Graphite power cell = 1,200lbs (546kg)

Si-Graphite power cells are completely non-toxic and inflammable.

The 100kWe homopolar generator requires mercury brushes to collect the output, so the generator must remain outside the habitat module. I estimate the mass of this generator at about 225lbs (100kg) using permanent magnets and copper conductors. The actual copper mass is only 2kg, but I’m grossly over-estimating what the generators would actually weigh to account for packaging, mounting, and structural reinforcement to handle G loads. I want to stick with a conventional homopolar electric generator design, to the extent practical.

Let’s call the entire setup about 700kg. The 700kg figure does not include power conditioning and distribution electronics or wiring, it’s just Si-Graphite cells with secondary casings (each cell is individually sealed) and the electric generator. Volumetrically, the Si-Graphite power cells consume 25 cubic feet of pressurized volume. Let’s just call this 1 cubic yard with secondary casings and wiring.

It’s possible to save hundreds of kilograms of mass by wrapping the Si-Graphite cell’s active material in a manner similar to a conventional battery, which is what the designer intended. Although graphite is part of the active material, the graphite plates exist to seal individual cells. This would greatly reduce the volume of the cells, too. The 1.5V at 3A plate design is just easier for him to manufacture with the limited facilities at his disposal.

The habitat modules only require life support power, so permanent batteries alone are sufficient. The ISPP plant requires an electric generator and to assure crew return, we pre-stage the plant before humans show up. The plant must fuel the crew return stage before humans arrive. I was thinking that the plant should be integrated with the ascent stage as human-removable modules that the humans discard just prior to ascent.

Permanent battery technology like this mostly invalidates the use of both solar and nuclear for powering exploration missions, both of which have mass requirements that substantially exceed this setup. Ultimately, this technology continues to scale linearly, whereas fission reactors do not.

Realistic Mass-Efficient Technology Uses:
1. Use solar in space to about 2AU if the power requirement is 100kWe or less

2. Use permanent batteries and electric generators at about 2AU+ or if the power requirement is between 100kWe and 1MWe, then switch to fission reactors if the power requirement is greater than 1MWe or distance from the Sun exceeds 2AU

3. Use permanent batteries for surface life support and deep space backup power

4. Use nuclear fission for utility grade surface power

5. Use nuclear fission if process heat is required for manufacturing or to heat bases in cryogenic environments, like the surface of Titan

Oldfart1939 · 2017-05-26 13:50:14

kbd512-

Do you have a reference giving the chemistry of the redox couple involved? These certainly would be very appealing, especially for any vehicular application (Bobcat...er...Marscat, rovers, suit integrated heat and internal electronics, etc.). As this is a new technology, until there are working models available for testing...I am a "Murphy was an Optimist" skeptic.

kbd512 · 2017-05-26 15:50:35

Oldfart1939,

Watch this video:

WORLD'S FIRST - SELF POWERED Q Beta Prototype with Silicon Crystal Graphite Powercells

I probably have some details wrong. For example, it may require as much as 4 times as many cells for continuous output. The masses I gave were for solid blocks of graphite. The active materials in the cells will be nowhere near as heavy as what I calculated. I only attempted to provide the upper limit on what the cell could possibly weigh if they were solid graphite.

The plate geometry cells are only one possible cell geometry. The internal construction of the actual cells would be shaped just like ordinary batteries, which is to say a roll of the material. If the plate geometry is used, then the figures I provided represent the maximum cell volume.

SpaceNut · 2017-05-26 17:41:43

Oldfart1939 wrote:

RTGs are a pretty inefficient way to generate power: 6% power conversion. Lots of mass for very small output.

Is this the same for the same amount of fuel used in a reactor?

What I see is the means to convert the energy from the nuclear materials is the issue. Yes nuclear materials are expensive when coming from Earth but RTG's made insitu on mars not so much and the same is true of using the fuel for reactors as well.

Batteries are still short lived no matter what the energy density is as you must refill it from some source right. They are just due to mass more portable.

kbd512 the Si-Graphite power cells (batteries) are interesting as a cutting edge technology.

Red Dragon is a landing stunt to prove out retro prolpulsion and pin point landing.

tahanson43206 · 2023-12-22 12:01:12

Thanks to SpaceNut for bringing this topic from 2017 back into view.

I'm interested in the "permanent" battery described by kbd512, and am hoping there might be some news about that design/invention/concept since 2017.

I am also interested in RobertDyck's mention of Potassium 40 and it's transition to Argon 40.

There might be news on that front as well, since 2017.

(th)

SpaceNut · 2023-12-22 17:18:53

most batteries are a 1 way discharge design and that is all as a rechargeable requires ions to move with in it and not be recharged in a collider.

SpaceNut · 2023-12-25 07:57:47

thermal heat is used to create an electrical current from the decay process.

Review and Preview of Nuclear Battery Technology

The shortcomings of RTG technology are its poor efficiency of 6%, its low power density, and its large size.

I seem to recal the americium was also doing electrical current with a screen to capture the charge but it was not a great amount.

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#1 2017-05-23 18:58:09

To RTG or not to RTG the size is the question

#2 2017-05-23 21:31:47

Re: To RTG or not to RTG the size is the question

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#18 2017-05-25 08:35:40

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#19 2017-05-26 13:08:39

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#21 2017-05-26 15:50:35

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#22 2017-05-26 17:41:43

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#23 2023-12-22 12:01:12

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