fredinno

Using Amercium RTGs for a reusable Manned Lunar Lander-Could it work?

RTG-Powered landers- worth it?  

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  1. 1. Is an Amercium RTG-Powered Lunar Lander worth it?



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Using Americium RTGs for a reusable Manned Lunar Lander- could it work?

On the surface, this seems very reasonable- the lifetime of a Manned Lunar Lander could easily be extended far into the Lunar Night, beyond the 14 day maximum mission length a current lander would allow for (w/o something like fuel cells or large batteries to store electrical power- though extra supplies would obviously be necessary). It would also heat up the lander, reducing electrical usage, and makes batteries unnecessary (which would reduce the mass.) The increased mission duration also means that NASA could squeeze more science out without more SLS launches (which cost at least $500 Million apiece) including during the night (maybe some sort of Lunar night-specific experiments?)

Amercium RTG use could also be extended to a lunar pressurized rover, increasing distance one can cover in a single mission dramatically-now limited only by consumables and CO2 scrubbers, not power)

However, RTGs would require larger radiators and radiation shielding- also, Amercium RTGs (which have a lower power density, but use much more common material than Plutonium ones) will likely take another decade to develop (which ESA is doing), meaning the first lunar landers will have to use more conventional power sources. However, since Amercium 241 has a longer half-life (432 y), it will take much longer for the heat energy to decline, so long that the RTGs will likely never have to be replaced- it would be replaced with the aging lander itself. Though more common, Amercium RTGs still have a limit to how much you can make- limited by the production of the Amercium Feedstock (a limit I have no idea is :p)

Additionally, Amercium RTGs would have a much lower power density of 2W/Kg, compared to Solar at 10W/kg. On the other hand, the increased capability of the lander and not having to carry O2 and H2 (if using fuel cells) may offset it.

So, is an Amercium RTG-powered Manned Lunar Lander a Good Idea? Or should it go in the dump bin next to RTG-powered Space Stations? (Yes, those things were proposed in the 60s-70s.)

Edited by fredinno

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You would certainly need a lot of battery for the solar panels. I could see the RTG being the better option, despite weighing over 4 times more than solar panels alone.

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49 minutes ago, RuBisCO said:

That is a 2 ton RTG! No one has built such a thing!

No, it's a 2 ton RTG CLUSTER.

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5 minutes ago, SomeGuy123 said:

Why not just stick with plutonium?  

Because we're out of Plutonium-238, it has to be specially produced if you want to build any more RTGs.

Edited by SargeRho

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Ok, so some more googling : the obvious thing to do is to use a heat engine to get more bang from our RTG buck. Instead of using thermoelectric materials, use a sterling engine.

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Americium is a valid replacement for plutonium-238, but the latter is better. It depends on the economy and politics.

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You get plenty of solar power at the moon and there are various designs for how to store energy on the moon that are less effort than an RTG. Hence, even the long nicghts are not that problematic. So I would not use an RTG for a moon base, or only as backup.

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 Stupid nuclear power bill. NASA can't make its own Pu-238, which will mean that its deep space exploration will be put on hold.

Sorry. On topic now...

I still think solars are a better idea. I don't think radiation is a good thing to expose to astronauts, they have enough already.

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16 minutes ago, Sanic said:

 I still think solars are a better idea. I don't think radiation is a good thing to expose to astronauts, they have enough already.

238PU has very little gamma & neutron radiation; most of it is alpha and beta particles which are easily blocked. Americium produces more harmful radiation though.

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15 minutes ago, Kerbart said:

238PU has very little gamma & neutron radiation; most of it is alpha and beta particles which are easily blocked. Americium produces more harmful radiation though.

Which is why solars are better, at least for the Moon lander.

Edited by Sanic

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I dont see the reason for RTGs. How much energy could you store in those 4 tons with lithium batterys? Im sure that would be sufficient. Also: Why would you want to land in the night? Just wait 2 weeks...

I would like to avoid nuclear stuff where its possible. Every bit of gamma radiation escaping adds to the dose of the astronauts, and thats allready a problem without RTGs...

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It was not suggested to land at night, but perhaps the experiments should work more than 2 weeks, in that case you need to bridge the night and not freeze to death in it.

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8 hours ago, SargeRho said:

Because we're out of Plutonium-238, it has to be specially produced if you want to build any more RTGs.

I always wondered why the Pu-238 from pacemaker batteries couldn't be reprocessed into Pu-238 for space use.

7 hours ago, SomeGuy123 said:

Ok, so some more googling : the obvious thing to do is to use a heat engine to get more bang from our RTG buck. Instead of using thermoelectric materials, use a sterling engine.

I was thinking that too, but it's supposed to take 10 years to make Amercium RTGs a reality, then maybe another 6 years to make RTGs large enough for manned applications. Stirling might take another 6 years. Not sure if it is worth it by then.

5 hours ago, lajoswinkler said:

Americium is a valid replacement for plutonium-238, but the latter is better. It depends on the economy and politics.

Though, Amercium does not have the same anti-nuclear stigma as Plutonium...

2 hours ago, Sanic said:

Which is why solars are better, at least for the Moon lander.

Couldn't the CH4 fuel act as shielding (plus a layer of lead.)?

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In fact, production of Pu-238 has just started again:

https://en.wikipedia.org/wiki/Plutonium-238#United_States_supply

3 minutes ago, fredinno said:

I always wondered why the Pu-238 from pacemaker batteries couldn't be reprocessed into Pu-238 for space use.

Old Pu-238 is less pure. If it is not pure enough, it is not very useful anymore. Besides, I doubt that there are enough pacemaker batteries to gain a significant amount.

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2 hours ago, Sanic said:

Which is why solars are better, at least for the Moon lander.

You would need enormous batteries to survive through the 16-day night.

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1 hour ago, Elthy said:

I dont see the reason for RTGs. How much energy could you store in those 4 tons with lithium batterys? Im sure that would be sufficient. Also: Why would you want to land in the night? Just wait 2 weeks...

I would like to avoid nuclear stuff where its possible. Every bit of gamma radiation escaping adds to the dose of the astronauts, and thats allready a problem without RTGs...

Judging from this: https://www.google.ca/search?q=lithium+battery+power+density&ie=utf-8&oe=utf-8&gws_rd=cr&ei=mI2aVvD_CYWIjwOVsJOADA#gws_rd=cr&imgrc=HkOc4XkuB8T9SM%3A

Let's say 200 Wh/kg capacity for the batteries. That sounds like a lot, until you consider Altair uses 9.3 kWh/hour, or 3571.2 kWh over a 16 day night. Since that is also 3571200 Wh, you would need a WHOPPING 17.86 T of battery. Not worth it.

 

Also, Poll added. Debate away!

Edited by fredinno

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14 minutes ago, fredinno said:

You would need enormous batteries to survive through the 16-day night.


Or you could use Fuel Cells. The Space Shuttle was powered by Hydrogen-Oxygen fuel cells, giving it a mission time of 2 weeks or so. The Apollo CSM was also powered by Hydrogen-Oxygen fuel cells, which was sufficient for the more than 12 days that some of the Apollo missions lasted. So, a fuel cell energy storage system would be more than adequate to sustain the base for the night. During the day, part of the solar power would be used to split the Water back into Hydrogen and Oxygen.

Edited by SargeRho

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6 minutes ago, SargeRho said:

Or you could use Fuel Cells. The Space Shuttle was powered by Hydrogen-Oxygen fuel cells, giving it a mission time of 2 weeks or so. The Apollo CSM was also powered by Hydrogen-Oxygen fuel cells, which was sufficient for the more than 12 days that some of the Apollo missions lasted. So, a fuel cell energy storage system would be more than adequate to sustain the base for the night.

Fuel Cells could work, but would still be heavy- using the Apollo ones as a base, you would need 1.17 T of mass for the fuel cell storage system for Altair. Fuel Cells and Solar Panels would raise that to 1.6 T of Mass, or 0.4 T less than RTGs. Of course, that's misleading, since RTGs also heat the spacecraft up, something essential during the cold lunar night, and is not included in these numbers. That would probably put the power system masses to on par or slightly less than RTGs, since RTGs also require shielding.

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12 minutes ago, SargeRho said:

To quote myself: "it has to be specially produced if you want to build any more RTGs."

From the  article:

Quote

The DOE will begin by supplying NASA with 300 to 400 grams of the material per year. Once the process is scaled up, the DOE will supply the space agency with an average of 1.5 kilograms each year, the statement said.

 

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