For All Mankind (AH Tv series at Apple TV)

With regards to Pathfinder- yeah, they're probably stretching physics for the sake of 'rule of cool' and plot, but i'm okay with it. It's one of the best space shows out there besides The Expanse so I can accept that they need to do some things that break physics a bit.
I want to be clear--I've been enjoying the show. Many people who know their stuff have very reasonably objected to this that and other aspect of it, notably the business of sending Space Shuttles all the way to Lunar orbit to rendezvous with the LSAM. (The LSAM itself is also pretty controversial, for good reasons). But until Pathfinder, while I agreed with critics that we saw on screen was not the most probable way the ATL NASA would achieve its goals, I didn't think it would take terribly large retcons to make it possible. (If only the shots of Orbiters we had in LLO happened to show they had an external fuel tank attached, one smaller considerably than the ones they launch with would be fine). Pathfinder is the first thing which, as shown, is practically impossible, and I wanted to stress too--if by some miracle of Yankee ingenuity the damn rocket were actually possible, it would have a hell of a lot more applications, and probably the scheme of using one spaceship one launches from Earth to go all the way to the Moon and Mars, instead of developing a deep space spaceship that doesn't do atmospheric braking and launches from a LEO space station and returns to it, is a silly way of applying it to the deep space mission too. Though given the rocket, it does have its points, just as I think I can defend the idea of Orbiters to Luna (on the grounds that knocking the final delta-V phase of braking off 3 km/sec with rocket thrust to return to LEO is overall more costly than using Earth's atmosphere to enable a heavier vehicle to be sent from Earth to the Moon and back again, and either of these reuse strategies are better than expendable one-way cargo delivery--or anyway, given we do want some mass to return to Earth, the reusable route is worth developing).

Anyway it is more plausible than say Space: 1999 or U.F.O,, and for that matter I can only enjoy Star Trek by ignoring much worse "physics breaking." And while things in the Gerry Anderson stories were most definitely physics breaking, generally speaking one does suppose "engineers can do almost any damn thing, given vision, money and time!" It isn't so much physics breaking as engineering leapfrogging, and again, note that there are other applications for this amazing invention.
Well, they say nuclear, but they never say what kind of nuclear.
Pathfinder obviously runs on a fusion torch drive of the type we expect to see in the 2100s OTL :p
No, we don't actually need fusion to explain it; fission would be no more problematic and less so in some ways.

I don't know how you define a "torch" drive, but I revert to those old Robert Heinlein stories he wrote in the 1940s. It is clear enough Heinlein had a bit of a loose grasp of the concept of nuclear power, seeming to think that total conversion of matter to energy would be just a matter of time, and not worrying too much about what the resulting photon rocket would look like in operation! Another benchmark for me is Larry Niven Known Space stories where the Belters used continuous fusion rockets.

If we could first of all cause nearly 100 percent of a given flow of fusible nuclei to actually fuse, and then harness all the energy that released to drive their own daughter products with that energy in a fairly well collimated rocket stream, we'd have what I would agree would be a Heinlein-Niven "torch" drive good enough for Solar System work, though Heinlein as noted elided it over to total conversion that would logically lead to a photon rocket (or in a version that is kinder and gentler, a neutrino rocket maybe). Whether we can use it for a slower than light starship that approximates light speed and thus gets the benefits of relativistic time contraction, depends on whether it is fusion or total conversion (as we'd get with say matter/antimatter reacted 1 to 1). Sticking with fusion, the idealized exhaust would be flowing out at about 1/10 the speed of light, since fusion involves releasing about 1 percent of the rest mass as kinetic energy of some kind.

Say we could make deuterium and tritium fuse in a continuous, and complete, flow (or make it fuse with pulses, but the pulses come fast enough, say 20 times a second or more, that they look continuous to the human eye). Actually 80 percent of the energy released would be in the form of neutron flux, only 1/5 of 1/100 the total mass-energy of the reactants would take the form of directly energizing the daughter helium nucleus. These nuclei would thus be moving at 1/22 or so the speed of light, half the speed we'd get from ideal fusion. But say we jacketed the core where these reactions are happening with say enough lithium that the neutron flow carrying the lion's share of the power output served to boil the lithium, and we capture all that heat with a helium gas turbine a la the Serpent fission engine, and use the resulting electricity we generate to further accelerate the helium nuclei we produce with fusion--then we can get them up to 1/10 light speed.

Well we could if we could do something about the waste heat the gas turbine would have to output--in a Serpent engine, hydrogen is the heat sink; since we'd have to throw away any hydrogen (or water, or what have you) heat sink material we vaporize to sustain the electric generator, we might as well throw it into the exhaust stream and use the power to accelerate it too. The result will be much greater mass flow but much lower Isp; thrust is higher but we need to consume more total propellant to go anywhere.

So if we had an ideal fusion process, Isp would be 3 million sec! that puts even the gee whiz 6000 I estimate for Pathfinder deep in the shade. We'd be able to burn for a million seconds or so before the masses we use up as propellant approach the mass of the payload (this is what the "seconds" in Isp mean actually, the exponential decay time a given mass of propellant can suspend itself in 1 G). A million seconds is a good long time to sustain acceleration at 1 G in terms of Solar system travel times, which is what the Niven and Heinlein stories were talking about. If you try to use such a drive to push a starship up toward light speed though you have to sustain it for something like 30 million seconds, a whole year--this can work but you wind up using godawful amounts of fuel to do it, making a Saturn V Lunar Apollo mission look frugal. In fact given fixed minimum material masses for tanks and so forth, there are practical limits even with an ideal fusion "torch." Go over to total conversion by some miracle of engineering, turn all your propellant into neutrinos speeding away mostly harmlessly in a rough beam in one direction, and perhaps we can bear the mass ratios and achieve practical sublight interstellar travel, because now the Isp is 30 million seconds.

Vice versa, we might find we need 99 times the mass of the product of deuterium-tritium fusion in the form of hydrogen (plain old proton nucleus hydrogen-1, but in H2 molecules presumably) to cool the power turbine, and then the helium we produce to generate the power is just a fraction of the exhaust mass, which is mostly hydrogen--with Isp of 300,000 sec. Now we can't sustain boost at 1 G for much longer than one day before we are seriously changing the mass of the ship--but that still gets us fantastic delta-V to be sure, and we don't have a proper Heinlein-Niven fusion "torch" but we still have a rocket with 50 times the Isp of the Pathfinder rocket, and can do a lot of Buck Rogers stuff even FAM's Pathfinder cannot.

So Pathfinder, stupendous though its drive is, is hardly a "torch" rocket by any reasonable definition. It falls between somewhere and leaves lots of room for progress, and can easily be a fission powered thing rather than fusion. In fact it isn't the ideal efficiency fission drive--fission processes release about 1/1000 instead of 1 percent of the rest mass, and so if we had an ideal fission rocket its Isp would be surprisingly close to the ideal fusion--a bit under 1/3 the Isp or about one million sec! Again Pathfinder's drive is far less ambitious than that. And I hope, a hell of a lot cleaner-I don't know about you, but I much dislike the idea of an ideal plutonium fueled fission rocket blasting fission daughter nuclei through the System. (To be sure, they would be moving way faster than escape velocity and soon make their way into interstellar space, and of course the mass flow would be low. Call me crazy then, I just think it is messy as hell).
 
First: Good Speed, Michael Collins

Back to monster called Pathfinder
i hab in Secret Project Forum some debate about it
First a Nerva engine has not the 400 metric ton thrust to bring a 300 tons shuttle (C-5 Maximum load) from 7,62 km hight (C-5 maximum) to Orbit
DUMBO nuclear engine had this thrust level, but never got build (there was money only for one project Nerva or DUMBO)

it could be this NERVA was thrust augmented
either LACE were air is suck into Nerva engine (that explain the 7,62 km high, but Jesus christ, the nuclear fallout !!!)
LOX-augmented Nuclear Thermal Rocket here oxygen is injected into Nerva nozzle, the oxygen serve as Afterburner to increase thrust !

Nerva with water
good point Shevek23 !
A Nerva engine could with modification run on Water with ISP 412 sec (SSME 440 sec)
benefits are very low tank volume and option to refuel anywhere in solar system were is Ice
 
Is it possible they could go with Hillary Clinton as a Nineties President. There would be enough material from her appearances as Flotus to fudge the usual presidential appearances from OTL footage. Perhaps her work in 76 on Kennedy's second campaign (OTL Carter's) takes a different direction, Bill doesn't make Arkansas Governor but Hilary makes it to the Senate much earlier, she would be in prime position to run for POTUS by the nineties
 
I want to be clear--I've been enjoying the show. Many people who know their stuff have very reasonably objected to this that and other aspect of it, notably the business of sending Space Shuttles all the way to Lunar orbit to rendezvous with the LSAM. (The LSAM itself is also pretty controversial, for good reasons). But until Pathfinder, while I agreed with critics that we saw on screen was not the most probable way the ATL NASA would achieve its goals, I didn't think it would take terribly large retcons to make it possible. (If only the shots of Orbiters we had in LLO happened to show they had an external fuel tank attached, one smaller considerably than the ones they launch with would be fine). Pathfinder is the first thing which, as shown, is practically impossible, and I wanted to stress too--if by some miracle of Yankee ingenuity the damn rocket were actually possible, it would have a hell of a lot more applications, and probably the scheme of using one spaceship one launches from Earth to go all the way to the Moon and Mars, instead of developing a deep space spaceship that doesn't do atmospheric braking and launches from a LEO space station and returns to it, is a silly way of applying it to the deep space mission too. Though given the rocket, it does have its points, just as I think I can defend the idea of Orbiters to Luna (on the grounds that knocking the final delta-V phase of braking off 3 km/sec with rocket thrust to return to LEO is overall more costly than using Earth's atmosphere to enable a heavier vehicle to be sent from Earth to the Moon and back again, and either of these reuse strategies are better than expendable one-way cargo delivery--or anyway, given we do want some mass to return to Earth, the reusable route is worth developing).

Anyway it is more plausible than say Space: 1999 or U.F.O,, and for that matter I can only enjoy Star Trek by ignoring much worse "physics breaking." And while things in the Gerry Anderson stories were most definitely physics breaking, generally speaking one does suppose "engineers can do almost any damn thing, given vision, money and time!" It isn't so much physics breaking as engineering leapfrogging, and again, note that there are other applications for this amazing invention.

No, we don't actually need fusion to explain it; fission would be no more problematic and less so in some ways.

I don't know how you define a "torch" drive, but I revert to those old Robert Heinlein stories he wrote in the 1940s. It is clear enough Heinlein had a bit of a loose grasp of the concept of nuclear power, seeming to think that total conversion of matter to energy would be just a matter of time, and not worrying too much about what the resulting photon rocket would look like in operation! Another benchmark for me is Larry Niven Known Space stories where the Belters used continuous fusion rockets.

If we could first of all cause nearly 100 percent of a given flow of fusible nuclei to actually fuse, and then harness all the energy that released to drive their own daughter products with that energy in a fairly well collimated rocket stream, we'd have what I would agree would be a Heinlein-Niven "torch" drive good enough for Solar System work, though Heinlein as noted elided it over to total conversion that would logically lead to a photon rocket (or in a version that is kinder and gentler, a neutrino rocket maybe). Whether we can use it for a slower than light starship that approximates light speed and thus gets the benefits of relativistic time contraction, depends on whether it is fusion or total conversion (as we'd get with say matter/antimatter reacted 1 to 1). Sticking with fusion, the idealized exhaust would be flowing out at about 1/10 the speed of light, since fusion involves releasing about 1 percent of the rest mass as kinetic energy of some kind.

Say we could make deuterium and tritium fuse in a continuous, and complete, flow (or make it fuse with pulses, but the pulses come fast enough, say 20 times a second or more, that they look continuous to the human eye). Actually 80 percent of the energy released would be in the form of neutron flux, only 1/5 of 1/100 the total mass-energy of the reactants would take the form of directly energizing the daughter helium nucleus. These nuclei would thus be moving at 1/22 or so the speed of light, half the speed we'd get from ideal fusion. But say we jacketed the core where these reactions are happening with say enough lithium that the neutron flow carrying the lion's share of the power output served to boil the lithium, and we capture all that heat with a helium gas turbine a la the Serpent fission engine, and use the resulting electricity we generate to further accelerate the helium nuclei we produce with fusion--then we can get them up to 1/10 light speed.

Well we could if we could do something about the waste heat the gas turbine would have to output--in a Serpent engine, hydrogen is the heat sink; since we'd have to throw away any hydrogen (or water, or what have you) heat sink material we vaporize to sustain the electric generator, we might as well throw it into the exhaust stream and use the power to accelerate it too. The result will be much greater mass flow but much lower Isp; thrust is higher but we need to consume more total propellant to go anywhere.

So if we had an ideal fusion process, Isp would be 3 million sec! that puts even the gee whiz 6000 I estimate for Pathfinder deep in the shade. We'd be able to burn for a million seconds or so before the masses we use up as propellant approach the mass of the payload (this is what the "seconds" in Isp mean actually, the exponential decay time a given mass of propellant can suspend itself in 1 G). A million seconds is a good long time to sustain acceleration at 1 G in terms of Solar system travel times, which is what the Niven and Heinlein stories were talking about. If you try to use such a drive to push a starship up toward light speed though you have to sustain it for something like 30 million seconds, a whole year--this can work but you wind up using godawful amounts of fuel to do it, making a Saturn V Lunar Apollo mission look frugal. In fact given fixed minimum material masses for tanks and so forth, there are practical limits even with an ideal fusion "torch." Go over to total conversion by some miracle of engineering, turn all your propellant into neutrinos speeding away mostly harmlessly in a rough beam in one direction, and perhaps we can bear the mass ratios and achieve practical sublight interstellar travel, because now the Isp is 30 million seconds.

Vice versa, we might find we need 99 times the mass of the product of deuterium-tritium fusion in the form of hydrogen (plain old proton nucleus hydrogen-1, but in H2 molecules presumably) to cool the power turbine, and then the helium we produce to generate the power is just a fraction of the exhaust mass, which is mostly hydrogen--with Isp of 300,000 sec. Now we can't sustain boost at 1 G for much longer than one day before we are seriously changing the mass of the ship--but that still gets us fantastic delta-V to be sure, and we don't have a proper Heinlein-Niven fusion "torch" but we still have a rocket with 50 times the Isp of the Pathfinder rocket, and can do a lot of Buck Rogers stuff even FAM's Pathfinder cannot.

So Pathfinder, stupendous though its drive is, is hardly a "torch" rocket by any reasonable definition. It falls between somewhere and leaves lots of room for progress, and can easily be a fission powered thing rather than fusion. In fact it isn't the ideal efficiency fission drive--fission processes release about 1/1000 instead of 1 percent of the rest mass, and so if we had an ideal fission rocket its Isp would be surprisingly close to the ideal fusion--a bit under 1/3 the Isp or about one million sec! Again Pathfinder's drive is far less ambitious than that. And I hope, a hell of a lot cleaner-I don't know about you, but I much dislike the idea of an ideal plutonium fueled fission rocket blasting fission daughter nuclei through the System. (To be sure, they would be moving way faster than escape velocity and soon make their way into interstellar space, and of course the mass flow would be low. Call me crazy then, I just think it is messy as hell).

Would it be more workable if Pathfinder refueled in orbit off screen from a big water tank launched by a previous Sea Dragon mission, before thrusting for the moon?
 
@Shevek23
Some very interesting political/cultural theory, and I think all your posits are reasonable.

Further thoughts on Murdoch/political culture:
You’re right to say it would be totally reasonable for him to have very similar opinions to OTL; some true believers really are out there, who build their psyches around particular notions.

However, I think a theory of political culture based on a sort of societal dialogue has a certain appeal (as a theory). We are social creatures, we take cues from each other much more than I think we’re comfortable admitting. We base our decisions on factors observed in our environment. I think it’s more common for a person to base their identity on, for example, holding opinions/beliefs to the right of 90% of the people they encounter in their environment, rather than holding discreet, specific opinions because those opinions/beliefs are stamped onto their psyche. In other words, our opinions are probably more reactive than we often like to think. If you change what people are talking about, those who feel comfortable occupying a certain position relative to others in their environment will shift their opinions and beliefs.

The benefit of a theory like this is we can observe how society has changed over the years and see how a certain equilibrium of relative left, right, and center is maintained (in the presence of stable societies), while views continue to shift. The Overton Window is a related expression of this idea.

So I’m not suggesting Murdoch would moderate himself relative to society- he would still calibrate his psychological GPS to be more right-wing than x% of the people he encounters, and to cater to that demographic in his media. But to maintain his OTL positions and calibrate himself at perhaps (x+10)% when no environmental factors are encouraging it? I’m a little skeptical.

Furthermore, I’m not so sure his audience would shrink, since they’re going through the same relative shift as everyone else. The whole edifice moves, leftist publications and people being further to the left than OTL, the center moving to fill that void to the left, and the right following suit.

It would require observation of a second timeline for anyone to try to fight against this pull, and while we can “see” them, they can’t see us. They wouldn’t be able to triangulate their opinions with their OTL self and ground those opinions for “consistency.”

And keep in mind, this is different from the phenomenon of a personal political realignment based on discreet events. Reagan’s OTL conservative awakening, Ariana Huffington switching camps, even the gradual process of liberalization Supreme Court Justices undergo over a lifetime- all of these shifts are based on observable phenomena.

On HIV:
All of your theories have merit. I’d just like to add in the rather dull factor of narrative space. Maybe they just didn’t have time to get into it? There’s a lot of open questions out there that seem really important. They get left out. Ten-ish hours of tv to explore a world just isn’t much time.
 
Is it possible they could go with Hillary Clinton as a Nineties President. There would be enough material from her appearances as Flotus to fudge the usual presidential appearances from OTL footage. Perhaps her work in 76 on Kennedy's second campaign (OTL Carter's) takes a different direction, Bill doesn't make Arkansas Governor but Hilary makes it to the Senate much earlier, she would be in prime position to run for POTUS by the nineties
Not gonna lie, Hillary as POTUS in the 90s would be kinda cool. Though, would the Lewinsky Scandal be butterflied away? Or would just never be revealed?
 
Not gonna lie, Hillary as POTUS in the 90s would be kinda cool. Though, would the Lewinsky Scandal be butterflied away? Or would just never be revealed?
If Bill is the First Gentleman, it's unlikely they'd ever meet or have enough time together to ever have an affair. It's more likely one of the numerous sexual misconduct incidents he's been accused of being involved in over the years will be the scandal of the Hillary era (if she's the president in this version of the 90s)
 
1983 Time Magazine cover:

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Wonder if Able Archer is called off due to the actual tensions ITTL?
 
With regards to upcoming alt-Presidents, it occurred to me that the show writers could go with Biden in '88 (or earlier, in '84, or maybe he's the new democratic VP in '84 and runs in '92)? Maybe not the most likely choice, but I could see it. From what I've read, the controversies that caused him to drop out stemmed more from poor handling early on by his campaign staff that then got exacerbated when some of his law school issues came to life and other things piled on top. I would argue that the causes were circumstantial enough that they could be butterflied away, especially almost 20 years after the POD in the show's TL. Now, they might not want to go that route because of him being the current president, but I think it would be a plausible choice.
 
With regards to upcoming alt-Presidents, it occurred to me that the show writers could go with Biden in '88 (or earlier, in '84, or maybe he's the new democratic VP in '84 and runs in '92)? Maybe not the most likely choice, but I could see it. From what I've read, the controversies that caused him to drop out stemmed more from poor handling early on by his campaign staff that then got exacerbated when some of his law school issues came to life and other things piled on top. I would argue that the causes were circumstantial enough that they could be butterflied away, especially almost 20 years after the POD in the show's TL. Now, they might not want to go that route because of him being the current president, but I think it would be a plausible choice.
They could also go for broke and have him run and win in 1984 (he probably was actually ready to at that point ) or be Harts VP and then ole Gary still has a sex scandal trouble and VP Biden is nominated and runs and wins in 1988 ? If Biden is a two termer that could effect my Supreme Court wishes but I wouldnt mind seeing that as long as he goes big or at least tries to go big as President in the ATL as he is doing now....
 
I want to be clear--I've been enjoying the show. Many people who know their stuff have very reasonably objected to this that and other aspect of it, notably the business of sending Space Shuttles all the way to Lunar orbit to rendezvous with the LSAM. (The LSAM itself is also pretty controversial, for good reasons). But until Pathfinder, while I agreed with critics that we saw on screen was not the most probable way the ATL NASA would achieve its goals, I didn't think it would take terribly large retcons to make it possible. (If only the shots of Orbiters we had in LLO happened to show they had an external fuel tank attached, one smaller considerably than the ones they launch with would be fine). Pathfinder is the first thing which, as shown, is practically impossible, and I wanted to stress too--if by some miracle of Yankee ingenuity the damn rocket were actually possible, it would have a hell of a lot more applications, and probably the scheme of using one spaceship one launches from Earth to go all the way to the Moon and Mars, instead of developing a deep space spaceship that doesn't do atmospheric braking and launches from a LEO space station and returns to it, is a silly way of applying it to the deep space mission too. Though given the rocket, it does have its points, just as I think I can defend the idea of Orbiters to Luna (on the grounds that knocking the final delta-V phase of braking off 3 km/sec with rocket thrust to return to LEO is overall more costly than using Earth's atmosphere to enable a heavier vehicle to be sent from Earth to the Moon and back again, and either of these reuse strategies are better than expendable one-way cargo delivery--or anyway, given we do want some mass to return to Earth, the reusable route is worth developing).

Anyway it is more plausible than say Space: 1999 or U.F.O,, and for that matter I can only enjoy Star Trek by ignoring much worse "physics breaking." And while things in the Gerry Anderson stories were most definitely physics breaking, generally speaking one does suppose "engineers can do almost any damn thing, given vision, money and time!" It isn't so much physics breaking as engineering leapfrogging, and again, note that there are other applications for this amazing invention.

No, we don't actually need fusion to explain it; fission would be no more problematic and less so in some ways.

I don't know how you define a "torch" drive, but I revert to those old Robert Heinlein stories he wrote in the 1940s. It is clear enough Heinlein had a bit of a loose grasp of the concept of nuclear power, seeming to think that total conversion of matter to energy would be just a matter of time, and not worrying too much about what the resulting photon rocket would look like in operation! Another benchmark for me is Larry Niven Known Space stories where the Belters used continuous fusion rockets.

If we could first of all cause nearly 100 percent of a given flow of fusible nuclei to actually fuse, and then harness all the energy that released to drive their own daughter products with that energy in a fairly well collimated rocket stream, we'd have what I would agree would be a Heinlein-Niven "torch" drive good enough for Solar System work, though Heinlein as noted elided it over to total conversion that would logically lead to a photon rocket (or in a version that is kinder and gentler, a neutrino rocket maybe). Whether we can use it for a slower than light starship that approximates light speed and thus gets the benefits of relativistic time contraction, depends on whether it is fusion or total conversion (as we'd get with say matter/antimatter reacted 1 to 1). Sticking with fusion, the idealized exhaust would be flowing out at about 1/10 the speed of light, since fusion involves releasing about 1 percent of the rest mass as kinetic energy of some kind.

Say we could make deuterium and tritium fuse in a continuous, and complete, flow (or make it fuse with pulses, but the pulses come fast enough, say 20 times a second or more, that they look continuous to the human eye). Actually 80 percent of the energy released would be in the form of neutron flux, only 1/5 of 1/100 the total mass-energy of the reactants would take the form of directly energizing the daughter helium nucleus. These nuclei would thus be moving at 1/22 or so the speed of light, half the speed we'd get from ideal fusion. But say we jacketed the core where these reactions are happening with say enough lithium that the neutron flow carrying the lion's share of the power output served to boil the lithium, and we capture all that heat with a helium gas turbine a la the Serpent fission engine, and use the resulting electricity we generate to further accelerate the helium nuclei we produce with fusion--then we can get them up to 1/10 light speed.

Well we could if we could do something about the waste heat the gas turbine would have to output--in a Serpent engine, hydrogen is the heat sink; since we'd have to throw away any hydrogen (or water, or what have you) heat sink material we vaporize to sustain the electric generator, we might as well throw it into the exhaust stream and use the power to accelerate it too. The result will be much greater mass flow but much lower Isp; thrust is higher but we need to consume more total propellant to go anywhere.

So if we had an ideal fusion process, Isp would be 3 million sec! that puts even the gee whiz 6000 I estimate for Pathfinder deep in the shade. We'd be able to burn for a million seconds or so before the masses we use up as propellant approach the mass of the payload (this is what the "seconds" in Isp mean actually, the exponential decay time a given mass of propellant can suspend itself in 1 G). A million seconds is a good long time to sustain acceleration at 1 G in terms of Solar system travel times, which is what the Niven and Heinlein stories were talking about. If you try to use such a drive to push a starship up toward light speed though you have to sustain it for something like 30 million seconds, a whole year--this can work but you wind up using godawful amounts of fuel to do it, making a Saturn V Lunar Apollo mission look frugal. In fact given fixed minimum material masses for tanks and so forth, there are practical limits even with an ideal fusion "torch." Go over to total conversion by some miracle of engineering, turn all your propellant into neutrinos speeding away mostly harmlessly in a rough beam in one direction, and perhaps we can bear the mass ratios and achieve practical sublight interstellar travel, because now the Isp is 30 million seconds.

Vice versa, we might find we need 99 times the mass of the product of deuterium-tritium fusion in the form of hydrogen (plain old proton nucleus hydrogen-1, but in H2 molecules presumably) to cool the power turbine, and then the helium we produce to generate the power is just a fraction of the exhaust mass, which is mostly hydrogen--with Isp of 300,000 sec. Now we can't sustain boost at 1 G for much longer than one day before we are seriously changing the mass of the ship--but that still gets us fantastic delta-V to be sure, and we don't have a proper Heinlein-Niven fusion "torch" but we still have a rocket with 50 times the Isp of the Pathfinder rocket, and can do a lot of Buck Rogers stuff even FAM's Pathfinder cannot.

So Pathfinder, stupendous though its drive is, is hardly a "torch" rocket by any reasonable definition. It falls between somewhere and leaves lots of room for progress, and can easily be a fission powered thing rather than fusion. In fact it isn't the ideal efficiency fission drive--fission processes release about 1/1000 instead of 1 percent of the rest mass, and so if we had an ideal fission rocket its Isp would be surprisingly close to the ideal fusion--a bit under 1/3 the Isp or about one million sec! Again Pathfinder's drive is far less ambitious than that. And I hope, a hell of a lot cleaner-I don't know about you, but I much dislike the idea of an ideal plutonium fueled fission rocket blasting fission daughter nuclei through the System. (To be sure, they would be moving way faster than escape velocity and soon make their way into interstellar space, and of course the mass flow would be low. Call me crazy then, I just think it is messy as hell).
Pathfinder as a nuclear powered vehicle is a pretty big stretch. Pathfinder as an evolved shuttles design like the Venture Star and its linear aerospike engine would have have been far more acceptable. A nuclear shuttle just brings with it too much overhead. The shuttle would have to be powered by some version of the highly enriched uranium fueled fission engines using liquid hydrogen propellant that the AEC and NASA experimented with in the 60s. Tellingly, ATL "Sally Ride" in one FOAMK scene says that the control drums had been rotated - control drums to control reactivity was a feature of the engines tested at Jackass Flats in the 60s. Designs along this line were drawn up in the 60s but never carried forward - in part - for the same reason that no nuclear powered aircraft was ever fielded. No could ever figure how to economically deal with a returned / recovered vehicle.

Initially, before the core goes "hot", the vehicle and its engine presents no special exposure hazard. Once, the control drums are rotated to the Full Power position and the vehicles flies and returns - the engine is now an INTENSE exposure hazard and the structural materials offer very little protection from the gamma shine from the run core. Some of the structural components have probably been activated by the engine's neutron flux as well. This exposure hazard will persist for a long while - many weeks or longer. The problem worsens with each run of the engine. The only heavy shielding would be the shadow shield that would protect the crew cabin from direct gamma shine placed as a barrier bulkhead separating the engine compartment from the rest of the vehicle. Protection from the neutron flux would be provided (until depletion) by the tanks of LH2 or LH2 slush placed to protect the crew cabin from direct streaming neutron flux. The cargo bay - nestled in the center of the vehicle - would probably receive some neutron dose during nuclear powered lift.

The design for a practical nuclear shuttle would have been massive and if its going to carry a significant payload to orbit being carried aloft by a C5 Galaxy is not going to work since the limit of the whole lifted package would be set by the C5's lift capability. It was intended that the vehicle would either have to launch as a conventional rocket (maybe initially boosted by 4x or 6x strap-on solid rocket boosters) before activating the reactor - OR - much more complex - it was envisioned flying off an airfield using jet engines and after pushing itself high enough, it would transition to reactor power (both modes of flight would draw on the hydrogen propellant). Assuming that the cladded fuel has worn well (not eroded by the dynamics and chaotic thermal environment of a flow of fluid entering at cryogenic temperatures, heated to thousands of degrees, and exiting as an incandescent gas over the length of maybe ~2meters) operation in the atmosphere should present no issue with fission products being dumped into the atmosphere. However, fuel cladding degradation was an issue in tests in Nevada. How that would have been dealt with in the context of operational flight program is a difficult open question.

In addition to possible fission products in the exhaust stream, the issue that proved to be a stumbling block for development of the nuclear ramjet (Project PLUTO), the nuclear powered bomber, and then the nuclear powered shuttle was the issue of after flight servicing (PLUTO actually wouldn't have had the service issue - development was stymied by the related question of where and how a flight test might be conducted safely). The shuttle (or bomber) would have been dangerous to approach after operation and the crew would have been trapped in the crew cabin until some shielded exitway could be mated to the craft. Towing the aircraft would have required a heavily shielded tank. No unprotected person could approach the aircraft for any of the usual after flight inspections. Inspections would have to wait until the aircraft was towed to a shielded hangar complex - the engine end of the craft would have to be sequestered in what would amount to a hot cell and inspections, routine servicing, or repair would have to be done through remote handling procedures. The intense neutron flux might reduce the structural airworthiness of the airframe over several flight cycles over what would be expected to occur with a more conventionally powered airframe.

NASA still has interest in fission nuclear power for applications outside the Earth's atmosphere - like powering a Mars mission - but the engine - UNRUN - would be lifted conventionally and mated with the Mars bound ship (along with tanks of LH2 that would also have to launched up). Once the whole assembly was fit together and ready to depart Earth orbit - then the controls drums would rotate and - off you go.

On a related note - I thought it was silly that the big reveal of this season was the secret US program to make weapons grade Plutonium on the moon. That's just a dumb idea and you wouldn't use a Pu fueled reactor to make weapons grade Pu anyway. And, the writers had to sacrifice two of my favorite characters to keep Shackleton Crater from being made "uninhabitable for a thousand years". On the moon. Preventing the Hollywood meltdown disaster of their too delicate power reactor might save Jamestown Base but even if they'd failed, Shackleton Crater would have been no more uninhabitable after the fact then it has been for the last 3 or so billion years.

Bad writing.
 
And, the writers had to sacrifice two of my favorite characters to keep Shackleton Crater from being made "uninhabitable for a thousand years". On the moon. Preventing the Hollywood meltdown disaster of their too delicate power reactor might save Jamestown Base but even if they'd failed, Shackleton Crater would have been no more uninhabitable after the fact then it has been for the last 3 or so billion years.

Bad writing.
It would've certainly contaminated the ice needed for life support at both Jamestown and Zvezda
 
It would've certainly contaminated the ice needed for life support at both Jamestown and Zvezda
Yeah, you can't overlook the fact that we would need that for life on the Moon. The Moon isn't Mars it has no atmosphere. So if you're going to make a living on the Moon you need a way to make O2 and the ice allows you to do that plus make fuel for later Mars missions.
 
They have to filter that extensively anyway before consuming it. In fact, distillation is probably how they mine it anyway. So contamination isn’t really a huge concern, I would think.
You can distill out nuclear waste? (Zero snark, I am a science fan, not a sciencetition.)
 
Was it ever established why the americans wanted to make weapons-grade nuclear material on the moon? Was it just a case of having them there to threaten the soviets with?
 
You can distill out nuclear waste? (Zero snark, I am a science fan, not a sciencetition.)

You can distill out pretty much anything--it's just a matter of boiling and condensing the water. On Earth, this is, of course, expensive, but on the Moon, it's pretty much just a small additional expense on top of all the other costs of operating a moon base.
 
Was it ever established why the americans wanted to make weapons-grade nuclear material on the moon? Was it just a case of having them there to threaten the soviets with?
My guess? It was a snarky way to get around arms limitation treaties since they probably didn't cover off world production of weapons grade material.
 
It would've certainly contaminated the ice needed for life support at both Jamestown and Zvezda
My guess is probably not - a failure of the reactor would have been a very local event - not something that would have contaminated many square kms of the lunar surface. And, certainly would not have propelled contaminants into the depths 10s of meters below the surface where the ice was found in cave like vents. Jamestown is a small facility - it would have have needed a very small reactor to power it. Small enough that worst of the event might be contained within the structure of a properly designed reactor. In any case while Shackleton was a rich source of water - other sources - in similar dark polar craters might have been developed. But I don't believe that a "reactor meltdown" at Jamestown would have impacted local ice supplies' "cleanliness".
 
My guess? It was a snarky way to get around arms limitation treaties since they probably didn't cover off world production of weapons grade material.
What arms limitation treaties put limits on Pu production? Nothing was ever mentioned in the show and there was no such thing in OTL to my knowledge.

Pu production is a very specialized nuclear process that requires a limited time of irradiation of the Uranium fuel. Leave the fuel in core too long and the Pu intended for weapons is poisoned by other Pu species. Once the irradiated fuel is pulled it is both thermally and radioactively HOT. Storage in water filled cooling pools is required. And, this is even before the processing of the fuel to extract the Pu (which involves a lot of noxious acid based chemistry). Presumably the fuel would then have to be shipped back to earth to a place like Hanford in WA to complete the process of extraction and then from there to Rocky Flats CO or Los Alamos NM to be fashioned into pits.

I say all this to point how silly a plot point is the idea that we would be producing Pu on the moon under such difficult circumstances so far from home and at the end of such a complex transportation line. But, the writers needed to create a circumstance whereby two of the characters would have to sacrifice themselves in order for the season ending episode to have the emotional wallop they were hoping for and this contrived "nuclear meltdown" scenario is whatt they settled on.
 
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