For All Mankind (AH Tv series at Apple TV)

If anyone's interested, he you go.


There was only a difference of nearly one month.

In OTL, the Moon landing occurred on July 16, 1969, while in FAM, it occurred on June 26, 1969.
 
Lol was re-watching with a friend and we hit that scene where the cosmonauts are in the outpost. The astronaut asks the cosmonaut what music he likes and he says he likes, “automobile crash category” and I’m trying to figure out what the hell that could be.

It sounds like a badly-translated band name (“category” could be “band” or “group”). Is there a band whose name might be mis-translated as “automobile crash” you can think of? I tried to look for anything Soviet it might be but came up pretty blank.

Maybe it’s just a weird, one-off joke. I looked up the underground poetry journal printed in Pam’s back flap bio, and it was real and utterly obscure (like no web presence and just one google mention of its existence second-hand). So maybe the writers are just being obscurists. It’s driving me crazy, though!:openedeyewink:
 
Lol was re-watching with a friend and we hit that scene where the cosmonauts are in the outpost. The astronaut asks the cosmonaut what music he likes and he says he likes, “automobile crash category” and I’m trying to figure out what the hell that could be.

It sounds like a badly-translated band name (“category” could be “band” or “group”). Is there a band whose name might be mis-translated as “automobile crash” you can think of? I tried to look for anything Soviet it might be but came up pretty blank.

Maybe it’s just a weird, one-off joke. I looked up the underground poetry journal printed in Pam’s back flap bio, and it was real and utterly obscure (like no web presence and just one google mention of its existence second-hand). So maybe the writers are just being obscurists. It’s driving me crazy, though!:openedeyewink:

There's a whole vast array of songs about car crashes, maybe that's what was meant?
 
Related, I love almost every line delivery from those two cosmonauts. “We would like...hamburgers” is maybe the best delivery of the season, followed closely by, “Do you have...Jack Daniels?” Just note perfect acting from the...I was gonna say Russian, but IMDb says he’s Serbian. Looks like he’s got a big role in Stranger Things coming up as another Russian.

Heh, always so weird to me how someone will get so specifically typecast.
Showrunner: We need someone to play a sympathetic Soviet military guy in the 1980s, officer class but not general staff.
Casting Director: I’ll call Nikola.
 
i have issue with Pathfinder main engine
They say clearly NERVA, but those have NOT the thrust level needed to bring Pathfinder into Orbit !
You Are Not Alone, Michel!

I actually think the Pathfinder is where the series goes full on ASB; we seem to have a magic spacedrive that scorns all known physics, a la Shuttlecraft on Star Trek.

The trouble with holding that Pathfinder has an engine that is any kind of rocket whatsoever starts for me when we consider that unlike the real Orbiter of OTL, but like such works of movie fiction as the Moonraker Shuttle in the James Bond movie of that name, the engines don't seem to require any sort of propellant! There is no external propellant tank, so if Pathfinder is using a rocket engine, presumably some kind of nuclear thermal setup, it has to rely on propellant stored somewhere within the airframe of the shuttle itself. Lo and behold we notice those little swellings in the wing root area--presumably these are prop tanks.

As you might guess knowing me I have been going to town with Isps and propellant candidate densities, trust me when I say what follows is the short version!

1) I don't think the "speed bump" swellings on the wing roots of Pathfinder can hold a lot of volume--at a wild guess, say 40 cubic meters tops.
Nor does the layout of Pathfinder--similar to OTL Orbiter, crew space in the nose area, big cargo bay taking up the whole volume of the middle fuselage, engines and darn little room for much else in the tail section--leave much. OTL an Orbiter stored a variable amount of OMS hypergolic propellant in the tail region, call it 20 cubic meters tops with scrounging for more volume. Presumably with a gee whiz ultra high Isp, and yet withal high thrust (gotta be greater than 2 G on launch from the carrier airplane after all) magic engine, we can dispose of the OMS and just use the main engine throttled way down (but probably without Isp penalty, maybe with a bonus a la VASMIR) for orbit changes. Including all the ones in space. OTOH the Orbiter of OTL used the same propellant mix for its low thrust Reaction Control thruster system, except that the nose units had their own separate propellant storage. Could it be that the main engine also has a "hotel power" low output mode using recycled coolant and radiators, and that the electric power from that can drive ArcJet thrusters using something like water (or hydrogen, if we can justify that being the main propellant)? If so that frees up the propellant mass in the nose, plus 100 percent of the storage of hypergolic stuff in the two OMS pods, along with the mass of the OMS thrusters as well as that of the main engines, to be divided between additional propellant and the mass of the main engine itself.

So realistically we have in the ballpark of 50 cubic meters or less for propellant storage--I do think 20 cubic meters on each wing is stretching it even if we can justify as much as 20 in the fuselage somewhere or other.

2) I considered that if we have nuclear reactor/rocket tech way way way better than "NERVA," we might find we can use any damn material whatsoever for propellant.
Osmium say. It has a density 22 times that of water; if we have 50 cubic meters available (and assuming the volume and mass of auxiliary stuff to melt the damn osmium, which is pretty darn refractory to say the least, is not itself a major hit) we can store as much as 1100 tonnes of the stuff in the screen-canon Pathfinder! But let's not be silly; that would raise the mass of the "fueled" Pathfinder to 1200 tonnes or so. To put it mildly, making an airplane that could lift that up to the stratosphere would be a massive budget item in itself, if it can be done at all--we are looking at an order of magnitude heavier aircraft taking off than has ever been built.

Also, it is an open question whether the handwavium "A Wizard Did It!" "NERVA" engine follows thermal principles of operation or not. It could be some bizzaro thing that shoves back mass of any type whatsoever at the same speed per kilogram--in that case we definitely want dense material, if not osmium than say mercury. If on the other hand thermal rocket principles based on ideal gas laws apply at all, then the lighter the molecule, the better the Isp (though the lower the thrust per watt of generated power). Osmium is element 76 and has atomic mass a bit over 192; compared to a hydrogen molecule, atomic mass of 2, this makes for nearly a factor of ten (square root of the molar mass ratio) in Isp between these extremes. But of course liquid hydrogen is very low density, requiring some 14 cubic meters for each tonne, so the lower weight involved with hydrogen propellant also involves many hundreds of cubic meters of storage volume even so. We might do a lot better with say water, but even then squeezing the stuff into the hull as shown would leave a serious reaction mass deficit.

Let's say the reaction mass is water, which is the best stuff from many points of view, and mathematically convenient since 1 cubic meter of water masses one tonne.

Now insist that we must go with what we see on screen as canon. Pathfinder has no external tank storage whatsoever, and so that means we'd be limited to 50 tonnes of water at takeoff--which added to 80 tonnes dry mass and 20 tonnes payload (including crew and their life support supplies) gives us a no-fuel mass of 100 tonnes. Let's kick it up a bit to 120 allowing for the mass of the engine system itself, and assume RCS is done with ArcJets getting say Isp of 400 and using water. 170 tonnes fully loaded is heavier than the OTL Orbiters hauled around by the 747 carrier fleet OTL, but hey, a factor of two in this accomplished with high budgets going to Boeing or Lockheed between say 1975 and 1982 is something I can believe. Denser propellants raising the burden much more though would be definite shark jumping. (Not that Moore seems to care).

3) Delta V is a lot more than just what it takes to reach orbit. On her maiden voyage Pathfinder is supposed not only to reach LEO but to press on to the Moon, then presumably take up low lunar orbit then scoot back to Earth for an aerobraked reentry and landing. All up the beyond LEO delta V must be at least 5000 m/sec, and likely more for maneuvering and contingency. (And with engines like this, lunar landing and takeoff might well be in the design too, adding another 4000 m/sec or so.

With one thing and another, design delta V on one tank filling seems to be in the ballpark of 20,000 m/sec.

4) With a mass ratio of just 17:12, to achieve that delta-V we must have Isp in the ballpark of nearly 6000. Assuming the engine is fundamentally thermal in it operation, and fully cooled by the propellant flow, substituting hydrogen would raise that to 18000.
To reach orbit alone, delta V around 10000 m/sec, would require only 7 tonnes of LH2--but that mass would fill 100 cubic meters. Rather than rely on internal storage of ultra-cold liquid hydrogen it would be better to store it in external tanks of course, and anyway there is no way to reach orbit on just half the 7 tonne load.
Meanwhile show canon does not allow for external tanks! We have to rely on water pretty much, though perhaps loading in 3.5 tonnes of LH2 can be considered for 5000 m/sec delta-V--which is the minimum needed for LEO to Earth atmosphere reentry via entering and leaving LLO (from a Hohmann transfer--we need more for the faster more energetic orbits both NASA generally and the specific plot of the final episode mission requires). Other fluids could be substituted for water in a pinch--ammonia, LOX, hydrocarbon fuels, hypergolic propellants come to mind; their molecules are in similar ballparks (more or less, LOX or liquid nitrogen would give inferior Isp, and I have no idea what the average molar mass of the hypergols would break down into). Water is the go-to preference by far; it is pretty likely to be found in situ in many places NASA wants to go and would be relatively easy to isolate and purify.

Thus, on the same scale as real-world proposed nuclear thermal rockets we could hope to actually produce with known 2020s technology, the best Isp using hydrogen I have ever heard of in a credible design is the Reaction Engines Ltd proposal by Alan Bond and Mark Hempsall for the "Serpent," which can supposedly deliver hydrogen propellant Isp of 1300 sec--noting that the design absolutely requires using hydrogen, though it might possibly be modified to work with water, but then only deliver a mediocre 433, inferior to the Shuttle SSME already. (Though propellant storage would be more convenient of course--a propellant tank to hold 800 tonnes of water would be just 40 percent the volume and presumably somewhat lighter than half the dry weight of a Shuttle ET). Supposing Serpent could run on water is a big stretch if one understands its design at all, though water is a close competitor to hydrogen in heat sink capacity. If the Pathfinder engine normally runs on water and gets Isp of 6000 sec withal, and thus could run on hydrogen for Isp of 18000, we see that in Isp terms it outclasses even Serpent by more than a factor of ten!

Which means of course that to achieve a given thrust, it must produce power at a rate also greater than a factor of ten versus the already stupendous power output of the Serpent fission core.

It should be noted that thrust/weight ratios are a major reason Nuclear Thermal Rockets are a very poor way to put payloads into Earth orbit. Serpent has a relatively high T/W versus credibly attainable realistic alternatives, but this is only 4.4 or so.

Now on the assumption I like that Pathfinder runs on 50 tonnes of water stored internally, to achieve a net "mission delta V" of 20 km/sec we can estimate thrust and power requirements. For total mission delta V on 120 tonnes unfuelled mass, at Isp of 6000, we get as expected 48.6 tonnes of water required, close enough for government work, and it gives a spare margin too (because I kicked Isp up to a round 6 K sec). Thus launch mass is 170 tonnes, and going through a full 10 km/sec (which could be less) to reach LEO, we consume 26.6 tonnes, leaving 23.4 for the rest of the mission which is plenty with margin to spare. On launch then, if the "burn" to LEO takes 500 seconds, comparable to the Shuttle launch, we consume 53.2 kg/sec, times ejection velocity of 58.86 km/sec is 3078 kiloNewtons of thrust force. This applied initially to 170 tonnes gives over 18 m/sec^2 acceleration, rising eventually near cutoff to 20. The force times the exhaust velocity gives power in Watts, which is 966 gigaWatts, practically a teraWatt!

Note that this terawatt of power is being dispersed into the atmosphere; the engine produces a plume that must dissipate this power somehow--we have to wonder how well the launch plane will survive the sudden appearance of such a massive power release just above it, even if we assume the plane dives rapidly and note the spacecraft is speeding away from the launch point quite briskly. As the spaceplane rises the plume will extend farther and farther and eventually blast away from Earth and indeed out of the Solar system, and the disturbance is higher and higher up.

To summarize then--
To achieve the results we see on screen with Pathfinder, assuming as I think most reasonable that it is a rocket and it uses water for propellant we require:
1) achievement of thermal based Isp a factor of thirteen or more greater than any sane proposal of OTL;
2) corresponding great jumps of sustainable power output beyond the most extreme plausible proposals;
3) I have not yet mentioned the neutron and gamma radiation flux from any sort of nuclear core, be it fission or fusion, but suffice it to say these are pretty deadly with sober OTL real world proposals including Serpent, and much of the terribly low thrust/weight ratio of nuclear based systems depends on the attempt to try and get these fluxes down to something we can more or less tolerate
--note not only crew survival is at stake, but also the ability of other spacecraft to come anywhere near the nuke propelled vehicle, and the structural integrity of the craft is undermined by heavy radiation flux as well, never mind that of the core engine itself. The radiation flux of neutrons and gamma rays will be proportional to the power output and so is 13 times worse than would be the case with Serpent--where spacecraft design (the "Scorpion") includes putting crew spaces hundreds of meters away from the Serpent engine, and using the mass of structure, propellant, and cargo to augment the basic plug shield along with plain old inverse square law flux reduction to give the crew a fighting chance with optimistic assumptions about the hazard the flux presents.
This is offset a bit by the fact that thrust requirements will be somewhat lower, but the only way to justify the on-screen portrayal of Pathfinder is to suppose the engine itself somehow or other gobbles up all that stray radiation flux, since shielding mass to account for it would probably outmass the entire rest of the spaceship, by I don't know what factor. I am not aware of any manipulation of nuclei and surrounding electrons in the plasma or whatever further extreme state of matter the engine core material might wind up in that could raise the neutron capture cross section enough to absorb the lion's share of these emitted particles. But we pretty much have to pretend it is done somehow, or the neutron flux alone would fry the crew dead in seconds and destroy the spaceplane structure too.

Now let's just stop a minute and imagine the consequences of NASA perfecting such an engine before 1984 is out!

a) to the space program that ordered this thing, the goal is obviously to achieve fast interplanetary transport. Indeed if we had one of these puppies parked in LEO, and "fueled" it up with 50 more tonnes of water (or rather topped it off with 23 or so) it ought to be able to get to Mars pretty fast.

Pathfinder should be able to go to Mars on a single tank from Earth launch, but slowly; refilling the tank in LEO and being able to fill it up again with water from Mars should allow a rapid return too.

Another thing is that with water available on the Moon, at Shackleton station anyway, Pathfinder could be designed to simply land there. Now I dislike the idea of blasting the landing site with the full power of its main engine, but it should be quite feasible to brake to a dead stop some distance above Shackleton's landing field, and then use auxiliary ArcJet engines which (based on the fact that Serpent relies on such devices to achieve Isp of 1300 sec with hydrogen) should reach Isp of 400 fed with water instead. Such jets should be able to achieve a thrust of 50 tonnes (weight on Earth, that is 500 kN) which is 1/3 the Earth weight of the 150 tonne mass ship--thus double Lunar weight. It would require about 2 gigaWatts of power, and a feed of 125 kg/sec to the various thrusters total, so in 8 seconds we'd consume a tonne of water reaction mass. But there is water to refuel with at the base, and reversing this procedure--that is hopping up to a decent height above the base and then firing the main engines with its plume clear of anything on the Lunar surface--would be plenty to get back to Earth.

Thus, the LSAM can be retired, or converted to a Lunar utility vehicle.

Of course, the Pathfinder drive does not have to be mounted in a spaceplane. We could imagine it is driving a pure vacuum vehicle--and when we imagine this, that we substitute hydrogen propellant for water and thus get even better Isp. Such a vehicle could not take advantage of a planetary atmosphere for braking, so it needs a higher delta-V budget to be sure--though not overall actually. If we leave the job of lifting stuff to LEO to specialized vehicles, to go from LEO to the Lunar surface and back to LEO is under 12 km/sec. We'd probably be much saner to have something more like 2001: A Space Odyssey, with surface-LEO shuttles to LEO stations, where ships more like the sphere-with-legs "Orion" take people and things on to Luna--and pretty well, far beyond.

But that takes us away from show canon!

B) meanwhile back on Earth--if we have a rocket that can generate nearly a terawatt of power, in an assembly that masses under 20 tonnes, and somehow avoids a massive neutron bath of its surroundings, it seems plain we have an advanced nuclear reactor that can generate power.

Per Wikipedia, the entire world generated just a bit over 2 terawatts of electric power in 2013! Now b USA is liable to have been responsible for a large share of that; per another chart in Wikipedia's article on World Energy Consumption, the overall energy consumption of the USA (or rather, North America, but I think we can assume the USA accounts for the lion's share of it) has been pretty stable going back to 1980, with world consumption having grown by 5/3.

Thus, developing a single Pathfinder engine into a power generation system would greatly exceed the total US electric power consumption in 1985, and might well match or exceed the total consumption of all power sources, which is a lot greater than electric power generated.

It seems plain to me that it should be possible to derive appropriately sized generator units which can in various ways provide all the power the USA needs in various forms, at a fraction of the cost of the single Pathfinder prototype!

Self funded or not, NASA must have taken a lot of taxpayer dollars to get Pathfinder built...even so, it seems unlikely to be a really large line item in the total US budget. Whereas of course the revenue that could come to the Federal Government if it were to offer cheap electric power as a commodity .

The Reagan Administration would be unlikely to take that straightforwardly a public-owned approach of course. They'd be more likely to cartelize the whole US energy sector, forming a government-controlled holding company in which investors have a great deal of say, and manage a phased transition from other forms of generation to near total dependency on this one mode of generating it, maintaining remnants of others as contingency reserves. Note how the series indicates that energy independence and shifting toward nuclear powered electricity is already the general drift of public policy and national sentiment anyway.

Even bearing in mind such a gee whiz engine as Pathfinder appears to have is a highly costly item, and that it might involve risks of blowups or the like that would require expensive protections to contain failures--also, the nature of the power grid is that range is limited before power losses over the lines eat up too much of it. But it is hard to see why the technology would not simply scale down; plants generating 1/100 the power of Pathfinder's engine, phased in gradually in dozens, would seem entirely feasible.

Thus, it seems pretty plain that in "designing" Pathfinder, Rule of Cool dominated and engineering was not considered at all.
 
I'm super curious to see how things continue to play out. My biggest surprise to me for the entire Season 2 is that I expected AIDS (and possibly gay rights) to become a bigger deal - especially with Larry and of course the specter of Ellen coming out/being outed. I was fully expecting a plot line along those lines - especially after the early episodes where it showed Larry going out to clubs with his boyfriend of the moment.... For sure it'll come up in some way with Ellen and/or Larry at some point - probably when she takes the step to run for office... It would also be an interesting twist for a character like Kelly as a growth thing for Ed who's as strait laced and conservative as he is...

On the President front for the 90s - I could easily see us with any number of people- Hart, Clinton, Gore and plenty others if we're going back to a Dem administration... but I think we're also straying so far away from RL TL that it's entirely plausible that they start introducing more and more made up politicians rather than splicing old footage and deep faking... I wouldn't be mad at all- they could use a regular actor and it could be entirely plausible at this point...

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 will be very curious to see what the space program of the 90s looks like since IRL it was kinda boring except for the building of the ISS... I'm certainly curious to see what their architecture for getting to Mars looks like, how massively expanded the Moon will be - which we got a taste of in that ending clip- and of course everything with the soviets.

I do wonder if they'll keep using the Soviet Union as the larger foil that lasts longer and longer for the rest of the series or if they'll eventually let it collapse and perhaps switch to say, China. Obviously the Soviet Union will still be around in some form next season- but there's nothing saying they have to keep using the Soviets...

I'm absolutely sad about loosing Gordo and Tracy- but in many ways it makes sense. They can only age up the actors/characters so much and if they're moving decade by decade each season they'll eventually need to introduce new main characters as the new major astronauts and whatnot doing the crazy stuff...
 
You Are Not Alone, Michel!

I actually think the Pathfinder is where the series goes full on ASB; we seem to have a magic spacedrive that scorns all known physics, a la Shuttlecraft on Star Trek.

The trouble with holding that Pathfinder has an engine that is any kind of rocket whatsoever starts for me when we consider that unlike the real Orbiter of OTL, but like such works of movie fiction as the Moonraker Shuttle in the James Bond movie of that name, the engines don't seem to require any sort of propellant! There is no external propellant tank, so if Pathfinder is using a rocket engine, presumably some kind of nuclear thermal setup, it has to rely on propellant stored somewhere within the airframe of the shuttle itself. Lo and behold we notice those little swellings in the wing root area--presumably these are prop tanks.

As you might guess knowing me I have been going to town with Isps and propellant candidate densities, trust me when I say what follows is the short version!

1) I don't think the "speed bump" swellings on the wing roots of Pathfinder can hold a lot of volume--at a wild guess, say 40 cubic meters tops.
Nor does the layout of Pathfinder--similar to OTL Orbiter, crew space in the nose area, big cargo bay taking up the whole volume of the middle fuselage, engines and darn little room for much else in the tail section--leave much. OTL an Orbiter stored a variable amount of OMS hypergolic propellant in the tail region, call it 20 cubic meters tops with scrounging for more volume. Presumably with a gee whiz ultra high Isp, and yet withal high thrust (gotta be greater than 2 G on launch from the carrier airplane after all) magic engine, we can dispose of the OMS and just use the main engine throttled way down (but probably without Isp penalty, maybe with a bonus a la VASMIR) for orbit changes. Including all the ones in space. OTOH the Orbiter of OTL used the same propellant mix for its low thrust Reaction Control thruster system, except that the nose units had their own separate propellant storage. Could it be that the main engine also has a "hotel power" low output mode using recycled coolant and radiators, and that the electric power from that can drive ArcJet thrusters using something like water (or hydrogen, if we can justify that being the main propellant)? If so that frees up the propellant mass in the nose, plus 100 percent of the storage of hypergolic stuff in the two OMS pods, along with the mass of the OMS thrusters as well as that of the main engines, to be divided between additional propellant and the mass of the main engine itself.

So realistically we have in the ballpark of 50 cubic meters or less for propellant storage--I do think 20 cubic meters on each wing is stretching it even if we can justify as much as 20 in the fuselage somewhere or other.

2) I considered that if we have nuclear reactor/rocket tech way way way better than "NERVA," we might find we can use any damn material whatsoever for propellant.
Osmium say. It has a density 22 times that of water; if we have 50 cubic meters available (and assuming the volume and mass of auxiliary stuff to melt the damn osmium, which is pretty darn refractory to say the least, is not itself a major hit) we can store as much as 1100 tonnes of the stuff in the screen-canon Pathfinder! But let's not be silly; that would raise the mass of the "fueled" Pathfinder to 1200 tonnes or so. To put it mildly, making an airplane that could lift that up to the stratosphere would be a massive budget item in itself, if it can be done at all--we are looking at an order of magnitude heavier aircraft taking off than has ever been built.

Also, it is an open question whether the handwavium "A Wizard Did It!" "NERVA" engine follows thermal principles of operation or not. It could be some bizzaro thing that shoves back mass of any type whatsoever at the same speed per kilogram--in that case we definitely want dense material, if not osmium than say mercury. If on the other hand thermal rocket principles based on ideal gas laws apply at all, then the lighter the molecule, the better the Isp (though the lower the thrust per watt of generated power). Osmium is element 76 and has atomic mass a bit over 192; compared to a hydrogen molecule, atomic mass of 2, this makes for nearly a factor of ten (square root of the molar mass ratio) in Isp between these extremes. But of course liquid hydrogen is very low density, requiring some 14 cubic meters for each tonne, so the lower weight involved with hydrogen propellant also involves many hundreds of cubic meters of storage volume even so. We might do a lot better with say water, but even then squeezing the stuff into the hull as shown would leave a serious reaction mass deficit.

Let's say the reaction mass is water, which is the best stuff from many points of view, and mathematically convenient since 1 cubic meter of water masses one tonne.

Now insist that we must go with what we see on screen as canon. Pathfinder has no external tank storage whatsoever, and so that means we'd be limited to 50 tonnes of water at takeoff--which added to 80 tonnes dry mass and 20 tonnes payload (including crew and their life support supplies) gives us a no-fuel mass of 100 tonnes. Let's kick it up a bit to 120 allowing for the mass of the engine system itself, and assume RCS is done with ArcJets getting say Isp of 400 and using water. 170 tonnes fully loaded is heavier than the OTL Orbiters hauled around by the 747 carrier fleet OTL, but hey, a factor of two in this accomplished with high budgets going to Boeing or Lockheed between say 1975 and 1982 is something I can believe. Denser propellants raising the burden much more though would be definite shark jumping. (Not that Moore seems to care).

3) Delta V is a lot more than just what it takes to reach orbit. On her maiden voyage Pathfinder is supposed not only to reach LEO but to press on to the Moon, then presumably take up low lunar orbit then scoot back to Earth for an aerobraked reentry and landing. All up the beyond LEO delta V must be at least 5000 m/sec, and likely more for maneuvering and contingency. (And with engines like this, lunar landing and takeoff might well be in the design too, adding another 4000 m/sec or so.

With one thing and another, design delta V on one tank filling seems to be in the ballpark of 20,000 m/sec.

4) With a mass ratio of just 17:12, to achieve that delta-V we must have Isp in the ballpark of nearly 6000. Assuming the engine is fundamentally thermal in it operation, and fully cooled by the propellant flow, substituting hydrogen would raise that to 18000.
To reach orbit alone, delta V around 10000 m/sec, would require only 7 tonnes of LH2--but that mass would fill 100 cubic meters. Rather than rely on internal storage of ultra-cold liquid hydrogen it would be better to store it in external tanks of course, and anyway there is no way to reach orbit on just half the 7 tonne load.
Meanwhile show canon does not allow for external tanks! We have to rely on water pretty much, though perhaps loading in 3.5 tonnes of LH2 can be considered for 5000 m/sec delta-V--which is the minimum needed for LEO to Earth atmosphere reentry via entering and leaving LLO (from a Hohmann transfer--we need more for the faster more energetic orbits both NASA generally and the specific plot of the final episode mission requires). Other fluids could be substituted for water in a pinch--ammonia, LOX, hydrocarbon fuels, hypergolic propellants come to mind; their molecules are in similar ballparks (more or less, LOX or liquid nitrogen would give inferior Isp, and I have no idea what the average molar mass of the hypergols would break down into). Water is the go-to preference by far; it is pretty likely to be found in situ in many places NASA wants to go and would be relatively easy to isolate and purify.

Thus, on the same scale as real-world proposed nuclear thermal rockets we could hope to actually produce with known 2020s technology, the best Isp using hydrogen I have ever heard of in a credible design is the Reaction Engines Ltd proposal by Alan Bond and Mark Hempsall for the "Serpent," which can supposedly deliver hydrogen propellant Isp of 1300 sec--noting that the design absolutely requires using hydrogen, though it might possibly be modified to work with water, but then only deliver a mediocre 433, inferior to the Shuttle SSME already. (Though propellant storage would be more convenient of course--a propellant tank to hold 800 tonnes of water would be just 40 percent the volume and presumably somewhat lighter than half the dry weight of a Shuttle ET). Supposing Serpent could run on water is a big stretch if one understands its design at all, though water is a close competitor to hydrogen in heat sink capacity. If the Pathfinder engine normally runs on water and gets Isp of 6000 sec withal, and thus could run on hydrogen for Isp of 18000, we see that in Isp terms it outclasses even Serpent by more than a factor of ten!

Which means of course that to achieve a given thrust, it must produce power at a rate also greater than a factor of ten versus the already stupendous power output of the Serpent fission core.

It should be noted that thrust/weight ratios are a major reason Nuclear Thermal Rockets are a very poor way to put payloads into Earth orbit. Serpent has a relatively high T/W versus credibly attainable realistic alternatives, but this is only 4.4 or so.

Now on the assumption I like that Pathfinder runs on 50 tonnes of water stored internally, to achieve a net "mission delta V" of 20 km/sec we can estimate thrust and power requirements. For total mission delta V on 120 tonnes unfuelled mass, at Isp of 6000, we get as expected 48.6 tonnes of water required, close enough for government work, and it gives a spare margin too (because I kicked Isp up to a round 6 K sec). Thus launch mass is 170 tonnes, and going through a full 10 km/sec (which could be less) to reach LEO, we consume 26.6 tonnes, leaving 23.4 for the rest of the mission which is plenty with margin to spare. On launch then, if the "burn" to LEO takes 500 seconds, comparable to the Shuttle launch, we consume 53.2 kg/sec, times ejection velocity of 58.86 km/sec is 3078 kiloNewtons of thrust force. This applied initially to 170 tonnes gives over 18 m/sec^2 acceleration, rising eventually near cutoff to 20. The force times the exhaust velocity gives power in Watts, which is 966 gigaWatts, practically a teraWatt!

Note that this terawatt of power is being dispersed into the atmosphere; the engine produces a plume that must dissipate this power somehow--we have to wonder how well the launch plane will survive the sudden appearance of such a massive power release just above it, even if we assume the plane dives rapidly and note the spacecraft is speeding away from the launch point quite briskly. As the spaceplane rises the plume will extend farther and farther and eventually blast away from Earth and indeed out of the Solar system, and the disturbance is higher and higher up.

To summarize then--
To achieve the results we see on screen with Pathfinder, assuming as I think most reasonable that it is a rocket and it uses water for propellant we require:
1) achievement of thermal based Isp a factor of thirteen or more greater than any sane proposal of OTL;
2) corresponding great jumps of sustainable power output beyond the most extreme plausible proposals;
3) I have not yet mentioned the neutron and gamma radiation flux from any sort of nuclear core, be it fission or fusion, but suffice it to say these are pretty deadly with sober OTL real world proposals including Serpent, and much of the terribly low thrust/weight ratio of nuclear based systems depends on the attempt to try and get these fluxes down to something we can more or less tolerate
--note not only crew survival is at stake, but also the ability of other spacecraft to come anywhere near the nuke propelled vehicle, and the structural integrity of the craft is undermined by heavy radiation flux as well, never mind that of the core engine itself. The radiation flux of neutrons and gamma rays will be proportional to the power output and so is 13 times worse than would be the case with Serpent--where spacecraft design (the "Scorpion") includes putting crew spaces hundreds of meters away from the Serpent engine, and using the mass of structure, propellant, and cargo to augment the basic plug shield along with plain old inverse square law flux reduction to give the crew a fighting chance with optimistic assumptions about the hazard the flux presents.
This is offset a bit by the fact that thrust requirements will be somewhat lower, but the only way to justify the on-screen portrayal of Pathfinder is to suppose the engine itself somehow or other gobbles up all that stray radiation flux, since shielding mass to account for it would probably outmass the entire rest of the spaceship, by I don't know what factor. I am not aware of any manipulation of nuclei and surrounding electrons in the plasma or whatever further extreme state of matter the engine core material might wind up in that could raise the neutron capture cross section enough to absorb the lion's share of these emitted particles. But we pretty much have to pretend it is done somehow, or the neutron flux alone would fry the crew dead in seconds and destroy the spaceplane structure too.

Now let's just stop a minute and imagine the consequences of NASA perfecting such an engine before 1984 is out!

a) to the space program that ordered this thing, the goal is obviously to achieve fast interplanetary transport. Indeed if we had one of these puppies parked in LEO, and "fueled" it up with 50 more tonnes of water (or rather topped it off with 23 or so) it ought to be able to get to Mars pretty fast.

Pathfinder should be able to go to Mars on a single tank from Earth launch, but slowly; refilling the tank in LEO and being able to fill it up again with water from Mars should allow a rapid return too.

Another thing is that with water available on the Moon, at Shackleton station anyway, Pathfinder could be designed to simply land there. Now I dislike the idea of blasting the landing site with the full power of its main engine, but it should be quite feasible to brake to a dead stop some distance above Shackleton's landing field, and then use auxiliary ArcJet engines which (based on the fact that Serpent relies on such devices to achieve Isp of 1300 sec with hydrogen) should reach Isp of 400 fed with water instead. Such jets should be able to achieve a thrust of 50 tonnes (weight on Earth, that is 500 kN) which is 1/3 the Earth weight of the 150 tonne mass ship--thus double Lunar weight. It would require about 2 gigaWatts of power, and a feed of 125 kg/sec to the various thrusters total, so in 8 seconds we'd consume a tonne of water reaction mass. But there is water to refuel with at the base, and reversing this procedure--that is hopping up to a decent height above the base and then firing the main engines with its plume clear of anything on the Lunar surface--would be plenty to get back to Earth.

Thus, the LSAM can be retired, or converted to a Lunar utility vehicle.

Of course, the Pathfinder drive does not have to be mounted in a spaceplane. We could imagine it is driving a pure vacuum vehicle--and when we imagine this, that we substitute hydrogen propellant for water and thus get even better Isp. Such a vehicle could not take advantage of a planetary atmosphere for braking, so it needs a higher delta-V budget to be sure--though not overall actually. If we leave the job of lifting stuff to LEO to specialized vehicles, to go from LEO to the Lunar surface and back to LEO is under 12 km/sec. We'd probably be much saner to have something more like 2001: A Space Odyssey, with surface-LEO shuttles to LEO stations, where ships more like the sphere-with-legs "Orion" take people and things on to Luna--and pretty well, far beyond.

But that takes us away from show canon!

B) meanwhile back on Earth--if we have a rocket that can generate nearly a terawatt of power, in an assembly that masses under 20 tonnes, and somehow avoids a massive neutron bath of its surroundings, it seems plain we have an advanced nuclear reactor that can generate power.

Per Wikipedia, the entire world generated just a bit over 2 terawatts of electric power in 2013! Now b USA is liable to have been responsible for a large share of that; per another chart in Wikipedia's article on World Energy Consumption, the overall energy consumption of the USA (or rather, North America, but I think we can assume the USA accounts for the lion's share of it) has been pretty stable going back to 1980, with world consumption having grown by 5/3.

Thus, developing a single Pathfinder engine into a power generation system would greatly exceed the total US electric power consumption in 1985, and might well match or exceed the total consumption of all power sources, which is a lot greater than electric power generated.

It seems plain to me that it should be possible to derive appropriately sized generator units which can in various ways provide all the power the USA needs in various forms, at a fraction of the cost of the single Pathfinder prototype!

Self funded or not, NASA must have taken a lot of taxpayer dollars to get Pathfinder built...even so, it seems unlikely to be a really large line item in the total US budget. Whereas of course the revenue that could come to the Federal Government if it were to offer cheap electric power as a commodity .

The Reagan Administration would be unlikely to take that straightforwardly a public-owned approach of course. They'd be more likely to cartelize the whole US energy sector, forming a government-controlled holding company in which investors have a great deal of say, and manage a phased transition from other forms of generation to near total dependency on this one mode of generating it, maintaining remnants of others as contingency reserves. Note how the series indicates that energy independence and shifting toward nuclear powered electricity is already the general drift of public policy and national sentiment anyway.

Even bearing in mind such a gee whiz engine as Pathfinder appears to have is a highly costly item, and that it might involve risks of blowups or the like that would require expensive protections to contain failures--also, the nature of the power grid is that range is limited before power losses over the lines eat up too much of it. But it is hard to see why the technology would not simply scale down; plants generating 1/100 the power of Pathfinder's engine, phased in gradually in dozens, would seem entirely feasible.

Thus, it seems pretty plain that in "designing" Pathfinder, Rule of Cool dominated and engineering was not considered at all.
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
 
I'm super curious to see how things continue to play out. My biggest surprise to me for the entire Season 2 is that I expected AIDS (and possibly gay rights) to become a bigger deal - especially with Larry and of course the specter of Ellen coming out/being outed. I was fully expecting a plot line along those lines - especially after the early episodes where it showed Larry going out to clubs with his boyfriend of the moment.... For sure it'll come up in some way with Ellen and/or Larry at some point - probably when she takes the step to run for office... It would also be an interesting twist for a character like Kelly as a growth thing for Ed who's as strait laced and conservative as he is...
I had the same thought about Larry, initially, and I think if this show had been made ten or perhaps even five years ago you could’ve laid down money on a tragic turn of events. It could still happen in the future, after Ellen’s established in politics.

I’d like to think that the show might be interested in showing other sides of gay life beyond a devastating virus. Ignoring it completely would be problematic, but it might be novel to not totally center a gay narrative in the 80s/90s on HIV.

“He’s partying, plus he’s gay, plus it’s the eighties, therefore he will get AIDS” is kind of a terrifying (maybe even puritanical) formula to get a brain trained into. And I hope it’s clear, I’m not casting aspersions on you, I’m saying I had the thought, and I kinda think it’s at least partially because I’ve seen that plot twist a time or fifteen.
 
I binge watched Season 1 and half of Season 2, or more like 2/3 of it actually. So I might have missed it--but is there ever any positive mention of any disease that seems to actually be HIV at all?

As some have noted, in 1983 it was a pretty new thing. But I was there--I graduated high school in 1983, and started my first college semester (well, trimester, as we called it where I went, there being no summer "quarter") that year. I did not finish HS in any sort of great metropolis, it was Panama City, Florida, and I didn't get into the habit of reading weekly news magazines consistently until after I went to college. So the fact I knew that there was a new disease that had some troubling and frightening aspects, and was first associated with immigrants from Haiti before everyone started pointing at various "alternative lifestyle" people instead is I think significant. Not nearly as widely known, feared then understood, as it became over the next couple decades, no. But not unknown to the general public as a thing. And certainly not unknown to politicians. It would certainly be the responsibility of Reagan's medical establishment from Surgeon General on down, mainly via the CDC, to learn as much about it as soon as damn possible.

So I think non-mention by the series has three possibilities:
A) as OTL, except that by virtue of focusing on people with deep preoccupation with other issues of a particularly preoccupying type (that is, intensive NASA stuff, overlapping with intense geopolitical tension) these people happen not to have noticed.

You know who would notice? Wayne, I think. Not that I think he is much into gay sex personally, but I think he might well have good friends who are "out" and others who are not so out, and that he just pays attention to countercultural stuff across the board. And I think Molly would therefore have some nuance about it.

Therefore "AIDS is spreading just as OTL but the show missed mentioning it because it wasn't so Big in common culture yet" is not terribly high probability. It is plausible, and thus possible, but not an obvious compelling slam dunk.

B) it is out there and happening, but delayed. Go back just one year, to 1982, and I think that is when the first mentions in the Panama City News-Herald (which was IIRC a Ridder-Knight paper) turned up, late in the year. Delay it just 18 months or so and 1984 would be the year people start noticing--and of course therefore the initial spread and first "Patient Zero" would be different paths and a different person.

C) higher probability than one might guess, certainly more so than say a Solar major event in 1983--there either is no HIV at all, the virus just hasn't taken a species-jumping form yet or has but it died out and some cousin of it has to evolve eventually, perhaps with enough different characteristics medicine can develop various effective treatments against it early on. Or it exists but has not had the chance to spread into a regional and global pandemic, and might be recognized and checked the way Ebola is.

It is my impression that the event of HIV as we know it today getting out of its obscure central African incubation ground related to social disruption, driving more people to rely on monkey meat. Perhaps a parallel radiation from the 1960s POD makes this region of Africa more politically and socially stable, and the species-jump event does not happen effectively at all.

Certainly choosing path C would be my personal preference from the point of view of "I want to live in this TL!" I am not so sure I would in every respect by the way; if we are on Tracks A or B, there are plenty of other aspects of society and world history that we just haven't seen explored ITTL where a lot of people seem assured it means X (typically expressed as, "this TL has a more socially liberal US culture." Again something I'd like subjectively--but is it true? I don't think that's confirmed, it could just be that just as with HIV spreading, the show focus hasn't turned on ugly stuff going on that actually makes OTL look more decent in some respects.

On track C, a major cultural event that had I believe deep impacts on wide aspects of popular culture will have been bypassed, and indeed this could be consistent, quite hand in hand, with a more "socially liberal" USA.

On track B, essentially the same objective crisis exists, but perhaps different timing with different authorities in charge of things can make a major difference in the narrative about it and the scope of its outcomes.

And for that matter, Track A where the fundamental initial events are as near to OTL as possible, is still happening in a different cultural and political context, and quite possibly the Reagan Administration is handling it considerably better than OTL, despite it being very nearly the same people in the same offices--but people with their ears to a different political ground.
 
I had the same thought about Larry, initially, and I think if this show had been made ten or perhaps even five years ago you could’ve laid down money on a tragic turn of events. It could still happen in the future, after Ellen’s established in politics.

I’d like to think that the show might be interested in showing other sides of gay life beyond a devastating virus. Ignoring it completely would be problematic, but it might be novel to not totally center a gay narrative in the 80s/90s on HIV.

“He’s partying, plus he’s gay, plus it’s the eighties, therefore he will get AIDS” is kind of a terrifying (maybe even puritanical) formula to get a brain trained into. And I hope it’s clear, I’m not casting aspersions on you, I’m saying I had the thought, and I kinda think it’s at least partially because I’ve seen that plot twist a time or fifteen.
yeah, in a way it's nice that they subverted that expectation and didn't go for that kind of tragic (and almost predictable) route and instead went a different way for the story. I'm very curious to see the arc of Ellen (and Larry)'s stories.

I don't remember them ever bringing it up in the show. The only thing they've brought up is that Ellen and Larry have had to remain closeted... and that was why after the 1st season's movement with Women's rights and the ERA I thought that gay rights might have come up even more in season 2 and probably will next season... As to why they never brought up HIV/AIDS- i'm not entirely sure which of those options you brought up is the reason- any of them are entirely possible and plausible.

On a different note I think we're in to start seeing a whole lot of new characters next season having lost two major people and I wouldn't be surprised if we loose Molly very soon for obvious reasons... though a blind Molly hitting people with a cane could make for some comedic moments.
 
Thomas Paine was going to South Korea to talk about forming an "East Asian Space Alliance." I get that this is an excuse to put him on KAL 007, but Korea didn't have a space agency (KARI) until 1989 and no orbital rockets until 2009 (in OTL). While NASDA already had rockets (based on licensed Deltas) and astronauts being trained in the 80s, but Japan's space program wasn't even mentioned.
This seems down to the ATL's more hard-line Cold War mentality. Japan was most definitely a CW ally of the Western bloc--in that US effective occupation gave Japanese government and corporations no choice in the matter--nor do I doubt that the officials of both and the major stockholders in Japanese corporations much preferred the Western side in their self-interest.

But the neutralization of Japan in terms of treaty limits on military power (directly; Japan was vital to supporting Western military power projection in east Asia to be sure, a major source of repair parts and the like) associated with the Japanese government formally flirting with seeking good relations with the rival Communist bloc leaders. On paper of course Japan and the USSR remained at war indefinitely, with no peace treaty signed until the Communists collapsed and the successor Russian Federal Republic did so at long last, half a century after hostilities practically ceased. But by back channels Japan was signaling a desire for peace, and also with the PRC. One can dismiss this as mere show, when the reality of things was that Japan would do what the USA required them to, so such talk was cheap. But the governments kept it up for generations anyway.

South Korea on the other hand was a lot less ambiguous. Their government and vast majority of people were dead against the North, dead against their patrons, one hundred percent Western allied by deep conviction. South Korean politicians could flirt with rapproachment but Cold Warriors like Reagan could trust that when push came to shove, South Korea was going to be joined at the hip with US policy, versus Japan always seeking to demonstrate some independence if only on a symbolic level.

Therefore it the ATL, despite the vast superiority of Japanese capability over South Korean (at this early date; the RoK has of course advanced considerably since 1983 though not quite in Japan's league just yet) I can see why the USA would flatter Seoul, seeking by injection of aid and general promotion of South Korea's capacities and status, to balance and check Japan.

Surely Japan would be a partner in an East Asian/US initiative. I am just suggesting why and how the USA seeks to bring South Korea up to be in the same room with Japan.
 
Murdoch’s more at home in, er, “news” production; it was running a network that was the departure for him IOTL. All his Australian and British tabloids are likely still around. The question is to what extent can he break into the US market, and does he even resemble the Murdoch of OTL if he does?

It really feels like conservative politics in this world are going to have to shift. The GOP is tied to big government, likely higher taxation, more acceptance of multi-culturalism and women’s rights, even immigration to an extent, and an open mind on energy policy. The institutions that fought for conservative causes have been pretty universally sidelined, with the major exception of the national defense establishment.

Murdoch might push red meat to sell papers and get viewers, but he only pushes what people are buying. ITTL, the audience is just going to have different tastes. A conservative ITTL wants to hear about how great the military is, how strong the economy, and how much we’re kicking ass in every field we engage in, whether it’s computers or space or entertainment. Just a big ol arrogant, “What Can I Say Except ‘You’re Welcome’” kinda ideology.

What’s changed is that the fear that is such a big component of Murdoch’s branding is likely directed entirely across the Iron Curtain, rather than at domestic “threats.” But even then, I think readers (or viewers, if it comes to that) will have less fear overall to drive their politics and media consumption.
I think though that if someone is a media mogul who finds his "product" has a market on the right, that either the reason for that is that the product leans right in content because that is what the mogul is pushing, out of personal conviction, and this is why the right wing media consumers buy these papers (and more and more, tune in to his radio programs and TV news). Whereas if a person who had no strong personal commitment one way or the other just happened to notice that skewing his papers' editorial line rightward was a money maker, one of two things would happen--either this formerly apolitical person would be troubled at this extremism and seek to "educate" the public, at best shifting his market leftward and perhaps more likely just sinking it--or, subjectively gratified by this appreciative sector of the public, look into their positions and belatedly decide these good people have to know what they are doing and come to align his personal views with the public that likes his media products.

In Murdoch's case, I presume he started out with pretty right wing ideas and stuck to them out of conviction, and the general rightward drift of the 1970s and onward meant this was very profitable and enabled him to extend his ownership grip wider and deeper. Of course as he did this, he accelerated the trend as farther and farther right views had more and more wide expression while moderate and liberal ones were eclipsed. But I don't think we can say Murdoch invented the rightward drift out of whole cloth, nor do I suppose you are saying that.

What I don't think he'd do is personally trim his sails in a more moderate direction and then capture the same share of market on this basis. Rupert Murdoch I think would stick to his guns, and the winds of profit would fill the sails of more moderate rivals according to their convictions, leaving Murdoch personally less rich and powerful, with fewer papers and other media outlets. But these papers would be little more moderate than OTL; there would just be fewer of them.

And maybe not a lot fewer after all:
Teddy would’ve gotten to replace Douglas as well (who might’ve even retired a bit earlier ITTL). Stevens was seen as pretty liberal IOTL, but I think we can assume Teddy’s choice would be even more to Stevens’ left.

I'm not so sure that the context permits Ted Kennedy to go as far left as he might personally prefer. Winning against Nixon will not have been easy and he'll find himself balancing a center-left base against key moderate supporters he desperately needs to woo.

I'd very much like to believe the USA is socially liberal consistently relative to OTL, but I don't think we've seen a lot of proof of that.

Well, perhaps the simple fact that neither Molly Cobb nor her husband Wayne has been busted for drug "abuse," nor has Mrs Baldwin despite Wayne "turning her on" to marijuana, is a concrete demonstration in one major dimension? OTL, Richard Nixon, as he explained openly in the Frost interviews, used what Reagan would rename "war on drugs" as a cynical political club. Targeting ethnic minority drug use and implying that this was the "center of infection" in what was portrayed as a national disease played well with his chosen political base, which most definitely included unreconstructed racists as well as large numbers of people giving lip service to improving interracial relations who had no intention of actually getting any closer to non-"white" people than they had to. Finding an "objective" trait to criminalize more and discredit the whole group collectively was what Nixon drug policy was mainly about. In fact, the objective major and growing sector of Americans using drugs the government deemed "narcotic" were in fact Vietnam war veterans, of all ethnicities pretty evenly. (FAM, in discussing Danielle's husband Clayton's deterioration and demise, touches on one of several reasons this was so--major PTSD and self-medication).

It is possible then that the Kennedy administration, interrupting a process Nixon and Ford sustained OTL, just might have taken a very different tack and redefined the rise in alternative drug use as a medical matter, and that perhaps a fair degree of success with that approach kept Kennedy from being politically scalped by right wingers whose views on the counterculture would not be moved by any number of facts--but successes in limiting the uglier impacts and stabilizing what might have become out of control spirals OTL created a grassroots moderate consensus that it would be crazy to support Nixonian style drug demonization.

OTOH, surely Molly and Wayne are tiptoeing around NASA's guardians of morals much the way Ellen and Larry have to. Surely even Kennedy did not want it to be known that astronauts, some of them anyway, enjoy the occasional joint of weed, and it would end the career of even the great Molly Cobb to have that become known. And while Reagan might be pragmatic enough not to try to revive the old Nixon coalition on such an unpopular point as zero tolerance drug demonization, he surely won't support normalization of drug culture in his America. He probably prefers to keep the whole topic quiet.

So--improvement on OTL? Yes! Hippie utopia? No, absolutely not.

I think perhaps it is most likely the shift in culture versus OTL is definitely leftward more or less in all dimensions--there is no obvious sphere in which it would be more reactionary even than OTL (except I suppose, perhaps in the strictly political sphere; Americans becoming Marxist might be literally inconceivable). But I don't think conservatives are dead in the water; moderates remain to the right of modern OTL views though to the left of themselves at the time OTL. There are somewhat more leftists who are a little bit louder, but they are on political thin ice all the time, as anything too extremist is easy to portray as a plot of the Kremlin.
 
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
 
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