Radioisotope Thermal generator

[Carlobrand]

Radioisotope thermal generators use heat produced by decay of a radioactive mass to generate power. At TL6, the RTG uses a thermocouple to generate electricity; at higher tech levels, infrared-sensitive photovoltaic cells of increasing efficiency are added to convert more of the heat to electricity. They provide little power for their size but will do so for decades with no maintenance, typically losing no more than about 1-2% of power per year. This makes them useful for low-level long-term emergency power and for powering items that may need to function for years without maintenance.

Among the more commonly chosen materials for this purpose is plutonium-238. PU-238 does not fission; it decays by alpha emission (very fast helium nuclei) into U-234, whose half life is 2800 times longer and which mostly also decays by alpha emission (except for a wee bit that undergoes spontaneous fission), so it is not a significant radiation hazard unless ingested or inhaled. (A very large number of RTGs in one location may pose a slight radiation risk due to gamma emission from the occasional fissioning U-234 atom.)

However, a RTG can produce a lot of waste heat. The radioactive mass radiates at temperatures in excess of 1000 degrees C (1800 degrees F), and at TL6 the generators are about 8% efficient in converting energy to electrical power. For this reason, an RTG will be rather large compared to the radioactive mass it contains: a 50 kg, 200 liter unit may only contain a 0.4 liter 8 kg radioactive block, but the surface of a TL6 unit of that size may still radiate in excess of 100 degrees C.

Each kiloliter of RTG masses 250 kg and at TL6 generates 2 kilowatts (0.002 Mw) of power. They are not cheap, costing Cr100,000 per kiloliter in the Imperium (much more on lower tech worlds with limited production of radioactives). At higher tech levels, the RTG is more efficient at generating power.

	Power	Cost
TL	(Kw/Kl)	(Cr/Kl)
6	2	10,000,000
7	4	5,000,000
8	6	1,000,000
9	8	100,000
10	10	100,000
11	12	100,000
12+	14	100,000

RTGs smaller than 0.1 kiloliter are proportionally less efficient. For example, the power output of a 0.075 Kl RTG is 75% of normal (i.e. at TL6, 75% of 0.15, or 0.1125 Kw), and the power output of a 0.025 Kl RTG is 25% of normal (i.e. at TL6, 25% of 0.05, or 0.0125 Kw). An RTG can be as small as 0.01 Kl (at TL6 generating 10% of 0.02, or 2 watts).

 

[kilemall]

Sounds like a perfect subsystem to incorporate into power plant costs for emergency life support- if it is rerouted to other uses (fusion reactor restart, comms, avoid the incoming rock thruster use etc.) provision must be made from limited suit resources.

 

[HRLMT]

RTGs - a little history.

Here in the US during the Cold War in the late 1950's to the early 1960's, the government was very optimistic on the peaceful uses of the atom. One such program was called the Small Nuclear Applications Project - or SNAP for short. They were also referred to as "SNAP Generators."
They were used during the Apollo space program. You know all those science packages we left on the moon? Would you like to take a guess at what their power source was? Yes, that's right - RTG's. Now take a look at all those space probes we have sent out to the outer solar system. On all of those probes you will
see a long framework boom, and at the end of that boom is, yep, you guessed it another RTG.
And they are still today, in the newer space probes and missions to Mars. RTG's are usually the back - up for those land - based solar - powered Martian explorers.
Just this little bit of back story to add to this technology to the Traveller universe, enjoy !

 

[Enoki]

Sounds like a perfect subsystem to incorporate into power plant costs for emergency life support- if it is rerouted to other uses (fusion reactor restart, comms, avoid the incoming rock thruster use etc.) provision must be made from limited suit resources.

The downside to an RTG is you can't turn it off or put it in storage really. Once it's assembled, it works and keeps on working. You can't stop the radioactive decay of the generator.
So, as an occasional emergency source it's a bad choice. There are high density batteries that would be better here. They don't take up a lot of space and can store a charge for a long time while sitting idle. That's what you need for an emergency power source if you don't have something like a back up generator.

Where the RTG shines is you need a reliable power source for like a decade or two of continuous use. Then these are the best thing since sliced bread. They run for a very long time and are completely reliable. The only drawback is they are radioactive bigtime. But, in space that's no big deal. I'd assume with a couple of millennia of further development they'd be safe to use just about anywhere.

 

[Spartan159]

I could see RTGs being used as emergency power for Cold Sleep berths, especially for sublight colony ships.

 

[tjoneslo]

The downside to an RTG is you can't turn it off or put it in storage really. Once it's assembled, it works and keeps on working. You can't stop the radioactive decay of the generator.

Once you add a nuclear damper you can shut down, or at least slow down, an RTG. So you can have a very short half life radioactive source, allowing a high power output, but then use that to power the Nuclear damper to slow the decay reaction.

Now you can have a very long life "backup" power source which is still capable of putting out a lot of power if and when needed.

 

[Enoki]

Once you add a nuclear damper you can shut down, or at least slow down, an RTG. So you can have a very short half life radioactive source, allowing a high power output, but then use that to power the Nuclear damper to slow the decay reaction.

Now you can have a very long life "backup" power source which is still capable of putting out a lot of power if and when needed.

Sounds more like a perpetual motion machine to me. Why bother with a means to keep it shut down that itself requires continuous power to shut it down? Seems simpler to provide a long life battery instead. If you need it for just emergencies, wouldn't a few hours of power be sufficient?

 

[whartung]

Sounds more like a perpetual motion machine to me. Why bother with a means to keep it shut down that itself requires continuous power to shut it down? Seems simpler to provide a long life battery instead. If you need it for just emergencies, wouldn't a few hours of power be sufficient?

The ships main power maintains the damper. When the main power fails, that's the "dead man" switch that kicks in the RTG to maintain the low berths. If it kicks on for show periods during maintenance or other cut overs, no big deal -- the RTG is a long term unit.

 

[aramis]

The downside to an RTG is you can't turn it off or put it in storage really. Once it's assembled, it works and keeps on working. You can't stop the radioactive decay of the generator.
So, as an occasional emergency source it's a bad choice. There are high density batteries that would be better here. They don't take up a lot of space and can store a charge for a long time while sitting idle. That's what you need for an emergency power source if you don't have something like a back up generator.

Where the RTG shines is you need a reliable power source for like a decade or two of continuous use. Then these are the best thing since sliced bread. They run for a very long time and are completely reliable. The only drawback is they are radioactive bigtime. But, in space that's no big deal. I'd assume with a couple of millennia of further development they'd be safe to use just about anywhere.

You don't start them, either. They're running from the second you put them together. The decay runs no matter whether there's draw or not.

As for reliability - not quite true. Voyager suffers from (strongly suspected) corroded themocouples, resulting in much reduced electrical output.

 

[whartung]

As for reliability - not quite true. Voyager suffers from (strongly suspected) corroded themocouples, resulting in much reduced electrical output.

Just can't get 50 years out of a space probe any more.

 

[Lycanorukke]

You don't start them, either. They're running from the second you put them together. The decay runs no matter whether there's draw or not.

They had that problem with the new horizions probe. Due to the Los Alamos shutdown, they had to recycle PU from older backup RTGs from prior missions. As a result they had about 15% less power available due to decay and insufficient high grade material. And on top of that there isn't much PU238 to go around anymore, which is why they are looking at Americum and other substitues.

And the real fun is what if some idiot finds a RTG and thinks it makes a great heater, a source of free metal, or a great device to steal and power his illegal still. Hello incident with the North sea RTG lighthouses. But if you want decads of power with minimal maintenace, RTGs are they way to go.

For Hi-tech it may be better to hook a F+ module to a battery. The F+ charges the battery and shuts down when it is full. The battery then drains, and then the F+ module switches on again. I'm not sure how long a F+ device lasts though at full output however, but I remember it is a considerasble period of time..

 

[Spartan159]

If you are talking about Fusion plus on a T5 starship, it runs for a full year before needing refueling. Has anyone created Fusion plus for MgT? I would like to hook up the system you suggest to long term cryoberths. Hmm, was Fusion plus detailed in T4 any?

 

[Lycanorukke]

If you are talking about Fusion plus on a T5 starship, it runs for a full year before needing refueling. Has anyone created Fusion plus for MgT? I would like to hook up the system you suggest to long term cryoberths. Hmm, was Fusion plus detailed in T4 any?

Using T5 (don't have T4).

A standard (Q=5) low berth has an integrated power cell with 6 months duration. Power cell recharge is 12 hours.
F+ module has integrated fuel tank with 1 year of fuel

So if nothing went wrong, you could keep a berth running for 365 years using the charge/discharge method with one module, two modules 730 years, and so on. Though more likely the degradation of power cell reliability would probably catch you long before the fuel ran out.

 

[Carlobrand]

The downside to an RTG is you can't turn it off or put it in storage really. Once it's assembled, it works and keeps on working. You can't stop the radioactive decay of the generator.
So, as an occasional emergency source it's a bad choice. There are high density batteries that would be better here. They don't take up a lot of space and can store a charge for a long time while sitting idle. That's what you need for an emergency power source if you don't have something like a back up generator.

Where the RTG shines is you need a reliable power source for like a decade or two of continuous use. Then these are the best thing since sliced bread. They run for a very long time and are completely reliable. The only drawback is they are radioactive bigtime. But, in space that's no big deal. I'd assume with a couple of millennia of further development they'd be safe to use just about anywhere.

Gotta disagree there - somewhat. Even the high density batteries deplete pretty quickly once you start drawing on them. A kiloliter of tech-15 batteries stores 7 megawatt-hours per MT and (approximately) Striker. (Can't speak for the newer Traveller versions.) That feeds basic life support for a stateroom for a bit under 130 hours, if you're using the MT data. For emergency power in decent quantities, I turn to those little fusion microplants unless I'm seriously cramped for space. Same volume nets you a 90 liter little TL 15 plant delivering enough power for 2 1/2 staterooms with fuel for 100 hours at better than 1/5 the cost of the batteries - and assuming your main power fuel tanks are intact, you can go for a couple months for each dTon of fuel available. Handy thing being able to draw on your original fuel source for your back-up power (assuming whatever killed the main plant didn't also rupture your fuel tanks).

The real weakness of RTGs is not that you can't turn them off. Assuming the rest of the machinery can survive that long, the decay rate means you're still getting decent output a couple decades later. Given that the ships are undergoing annual maintenance, you aren't going to get any significant loss before the next maintenance cycle sees them changed out and reprocessed. The real weakness is the output is so low for the size of the things. Good long-term emergency power for a couple of key systems, but even my very, very hopeful TL12 projection would need 4 kiloliters to give basic life support to a stateroom. A ship could only carry enough for the barest of necessities before it started eating into your cargo capacity.

As for radioactivity, the plutonium versions at least are primarily alpha emitters. Takes very little to shield from that. Pu-238 alpha decays into U-234, which is also mostly an alpha emitter and has a 2400 year half life. There's a bit of gamma, I think because the U-234 does occasionally shed gamma, but for the most part this stuff is only dangerous if you ingest it, breathe in particles, or some such thing. I understand they were experimenting with the idea of using the stuff for pacemakers, at one point.

(Being somewhat short of capital at the moment, I am unfortunately not equipped with the T5 rules, so cannot comment on their options.)

 

[kilemall]

New development in this arena- direct radiation power generation.

https://www.newscientist.com/article/dn13545-nanomaterial-turns-radiation-directly-into-electricity/

Could be useful for main fission reactors, secondary cogeneration off a radioactive fusion plant, facilities close to a radiation source, or our radioisotope batteries.

 

[Straybow]

New? Article from 2008, apparently not much progress since...