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Which of these (listed below) is the best method for sublight space travel?

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21 minutes ago, sevenperforce said:

One of the nice things about NSWRs is that if something DOES go horribly wrong, it becomes an impromptu single-pulse Orion. So structure your vehicle accordingly, and you're fine.

 

Meh. You mean you could blow up the ship while another part surives as a lifeboat?

A one pulse use only Orion does not appeal to me.

I would not wanna sit inside a NSWR. 

If I had to choose, I would chose to sit in Orion.

 

Edited by Spacescifi

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6 hours ago, sevenperforce said:

Yes, I am aware. You need not inform me of the difference between pressurized reactors, molten salt reactors, and a NSWR.

No, not necessarily.

You go on to list many of the very real challenges, which are readily acknowledged. They are by no means solved. But they are not significantly more challenging than the early materials and engineering hurdles for pressurized nuclear reactors. They are different challenges, obviously, but they are not dramatically more different. It is nothing whatsoever like the challenges in creating a Halo drive, for example.

Again, um.... no.  The hard thing about conventional reactors was designing a controllable core that wouldn't explode or melt without a long chain of unlikely events happening.  Once they had the core design, everything else was existing technology, or nearly so.  For instance, in a PWR, the most extreme water conditions for the coolant are about 2200psi at about 650^F.  This is actually easier to handle than the 1200psi, 950^F superheated steam then being made every day by the thousands of standard oil-fired naval boilers of the 1950s because steel starts getting soft above 900^F. (red heat), as any blacksmith can tell you.  So yeah, the PWR had about twice the pressure of a 1200psi steam plant but regular steel was better able to withstand it because it wasn't hot enough to get soft.  Thus, the PWR didn't need new materials or alloys invented, which was the case for the 1200psi steam plants, it just needed thicker walls of whatever existing alloy was cheapest.

The NSWR has nothing in common with any of this, however.  The operating principle of the NSWR can be summarized as having a continuous nuclear explosion going on in the combustion chamber, obtained simply by pumping nuclear saltwater into it.  It has to be an explosion because otherwise you're just making relatively low-pressure (because it's uncontained due to the open nozzle) steam like with the non-explosive NERVA.  Otherwise, the NSWR wouldn't offer the advantages over the NERVA that Zubrin claims.  So, it's a given that having enough fuel in 1 place to make this continual explosion happen means you can't store it in 1 place in that quantity.  This is why the fuel tank has to be so unworkably complex, essentially being a giant conventional nuclear reactor core you can't even use, just lug around.

Basically, with the NSWR, Zubrin envisioned a machinegun version of the single-shot Hiroshima bomb.  In that bomb, you had 2 separate sub-critical masses of uranium far enough apart not to set each other off.  An actual gun fired 1 of these masses into the other, resulting in the big boom.  Hence the liquid form of the radioactives in the NSWR concept.  Just keep spraying this mixture into an environment where the neutrons can do their work unimpeded and voila, constant explosion.

Setting aside the dubious ability of any known nozzle material other than metastable neutronium to withstand such "mundane" forces as a continuous nuclear explosion going on within arm's reach, you have to consider the back-pressure that such a continuous explosion would induce up the necessary myriad of fuel tubes (to prevent the explosion from happening in the tanik) leading into the combustion chamber.  Which tubes, as mentioned above, have to be skinny to avoid the fuel going critical even under zero-G.  That's without considering the centrifuging the dissolved uranium salts would experience due to the thrust of the running NSWR engine and the resulting mixture imbalances in the combustion chamber.  But even if this can be overcome, you still have the back-pressure from the continuous nuclear explosion which the feed pumps have to overcome in the the volume required to run the engine despite the friction loss inherent in long, skinny tubes,  And all this pressure somehow handled without rupturing the fuel tubes just from the feed pump pressure.  It simply can't work.

Zubrin is either demonstrably insane or crazy like a fox in trying to get rich off preaching to the gullibility of the masses.  You can always see the madness in his eyes on TV, despite the multiple takes and edits before the show airs.  And he's always preaching, never discussing.  He always preaches his demonstrably incorrect theme that colonizing Mars will save humanity by making us a 2-planet species, and that achieving this goal is only a few legislative votes and a couple of "minor" tech advances away.  The multiple fallacies inherent in his sermons should be appallingly obvious to anybody not hypnotized by his crazy eyes.  Colonizing Antarctica would be several orders of magnitude easier than colonizing Mars and would have a more positive result on the human species, but nobody is preaching for that happening because it's obviously a stupid thing to do.  Colonizing Mars is therefore even stupider.  All the extra effort required there as opposed to Antarctica won't make us a 2-planet species, it would make us  (at best) 1 huge subspecies on Earth with a tiny, troglodyte, utterly dependent subspecies on Mars.  But ignoring these obvious facts, Zubrin concocts utterly unworkable schemes like the NSWR to keep deluding the delusional, which includes himself IMHO.

 

6 hours ago, Spacescifi said:

I still think project Orion is better than NSWR.

I wholeheartedly agree.  The allure of the NSWR, which has beguiled so many who haven't thought it through, including Zubrin, is that it relies on a SUBSET of the well-known properties of uranium and water, without considering the rest.

Edited by Geschosskopf

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5 hours ago, sevenperforce said:

One of the nice things about NSWRs is that if something DOES go horribly wrong, it becomes an impromptu single-pulse Orion. So structure your vehicle accordingly, and you're fine.

Snort :) Why has like been disabled ?
And yes NSWR is kerbal^2 

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Spoiler
2 hours ago, Geschosskopf said:

Zubrin is either demonstrably insane or crazy like a fox in trying to get rich off preaching to the gullibility of the masses.  You can always see the madness in his eyes on TV, despite the multiple takes and edits before the show airs.  And he's always preaching, never discussing.  He always preaches his demonstrably incorrect theme that colonizing Mars will save humanity by making us a 2-planet species, and that achieving this goal is only a few legislative votes and a couple of "minor" tech advances away. 

He's just trying  to return back to home, to Mars.

 

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28 minutes ago, kerbiloid said:
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He's just trying  to return back to home, to Mars.

 

LOL!  Yet another on the tab for when likes come back.

Edited by Geschosskopf

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3 hours ago, Geschosskopf said:

Again, um.... no.  The hard thing about conventional reactors was designing a controllable core that wouldn't explode or melt without a long chain of unlikely events happening.  Once they had the core design, everything else was existing technology, or nearly so.  For instance, in a PWR, the most extreme water conditions for the coolant are about 2200psi at about 650^F.  This is actually easier to handle than the 1200psi, 950^F superheated steam then being made every day by the thousands of standard oil-fired naval boilers of the 1950s because steel starts getting soft above 900^F. (red heat), as any blacksmith can tell you.  So yeah, the PWR had about twice the pressure of a 1200psi steam plant but regular steel was better able to withstand it because it wasn't hot enough to get soft.  Thus, the PWR didn't need new materials or alloys invented, which was the case for the 1200psi steam plants, it just needed thicker walls of whatever existing alloy was cheapest.

The NSWR has nothing in common with any of this, however.  The operating principle of the NSWR can be summarized as having a continuous nuclear explosion going on in the combustion chamber, obtained simply by pumping nuclear saltwater into it.  It has to be an explosion because otherwise you're just making relatively low-pressure (because it's uncontained due to the open nozzle) steam like with the non-explosive NERVA.  Otherwise, the NSWR wouldn't offer the advantages over the NERVA that Zubrin claims.  So, it's a given that having enough fuel in 1 place to make this continual explosion happen means you can't store it in 1 place in that quantity.  This is why the fuel tank has to be so unworkably complex, essentially being a giant conventional nuclear reactor core you can't even use, just lug around.

Basically, with the NSWR, Zubrin envisioned a machinegun version of the single-shot Hiroshima bomb.  In that bomb, you had 2 separate sub-critical masses of uranium far enough apart not to set each other off.  An actual gun fired 1 of these masses into the other, resulting in the big boom.  Hence the liquid form of the radioactives in the NSWR concept.  Just keep spraying this mixture into an environment where the neutrons can do their work unimpeded and voila, constant explosion.

Setting aside the dubious ability of any known nozzle material other than metastable neutronium to withstand such "mundane" forces as a continuous nuclear explosion going on within arm's reach, you have to consider the back-pressure that such a continuous explosion would induce up the necessary myriad of fuel tubes (to prevent the explosion from happening in the tanik) leading into the combustion chamber.  Which tubes, as mentioned above, have to be skinny to avoid the fuel going critical even under zero-G.  That's without considering the centrifuging the dissolved uranium salts would experience due to the thrust of the running NSWR engine and the resulting mixture imbalances in the combustion chamber.  But even if this can be overcome, you still have the back-pressure from the continuous nuclear explosion which the feed pumps have to overcome in the the volume required to run the engine despite the friction loss inherent in long, skinny tubes,  And all this pressure somehow handled without rupturing the fuel tubes just from the feed pump pressure.  It simply can't work.

Zubrin is either demonstrably insane or crazy like a fox in trying to get rich off preaching to the gullibility of the masses.  You can always see the madness in his eyes on TV, despite the multiple takes and edits before the show airs.  And he's always preaching, never discussing.  He always preaches his demonstrably incorrect theme that colonizing Mars will save humanity by making us a 2-planet species, and that achieving this goal is only a few legislative votes and a couple of "minor" tech advances away.  The multiple fallacies inherent in his sermons should be appallingly obvious to anybody not hypnotized by his crazy eyes.  Colonizing Antarctica would be several orders of magnitude easier than colonizing Mars and would have a more positive result on the human species, but nobody is preaching for that happening because it's obviously a stupid thing to do.  Colonizing Mars is therefore even stupider.  All the extra effort required there as opposed to Antarctica won't make us a 2-planet species, it would make us  (at best) 1 huge subspecies on Earth with a tiny, troglodyte, utterly dependent subspecies on Mars.  But ignoring these obvious facts, Zubrin concocts utterly unworkable schemes like the NSWR to keep deluding the delusional, which includes himself IMHO.

 

I wholeheartedly agree.  The allure of the NSWR, which has beguiled so many who haven't thought it through, including Zubrin, is that it relies on a SUBSET of the well-known properties of uranium and water, without considering the rest.

 

I do not know Zubrin. Nor did I know he was alive. At any rate, here is a video of him.

He does seem... literally mad here (not crazy, just angry).

 

On some level I sympathize with him. Since he is implying NASA could have done better with developing new space technology for colonization than they have.

True they could have.

Yet unlike Zubrin, I am not set on colonizing other worlds just yet.

We are not ready. Not yet anyway as race.

One day, I have faith that we will be, and then I will seriously consider colonization of other worlds.

Right now all we would do is transport our creed and greed to the stars. Our love too.

Have to crawl before you can run.

Edited by Spacescifi
Vid

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1 hour ago, kerbiloid said:
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He's just trying  to return back to home, to Mars.

 

 

Actually that would make an excellent scifi story. Zubrin is an alien in disguise who is so disgusted with NASA's primitive human space program because his starship is on the surface of Mars.

All he has to do is get there and he can finally leave this ghetto civilization and rejoin his Star Trek level Federation solar system with replicators, holodecks, and green space women!

That was a joke. I do respect Zubrin and do not think he is crazy. But I could not resist. His anger and and frustration is so palpable it begged for me to fictionalize it!

 

However this:

 

He is compelled by various assumptions, which if actually false, he would be supporting wasting a lot of time and money to get an answer that we can guess already.

The movie Ad Astra is uniquely poignant about this.

No I won't spoil the ending. But I will say this.

When you look up at the sky at what is far beyond your reach, remember to look back down at what is near and reach for that.

Edited by Spacescifi

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His plans look doable in their first part: just get to the Mars.
Further phases look like they are just to hype expendable companions.

Spoiler

Like in J. Vance's The Eyes of the Overworld. / The Pilgrims.

 

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23 hours ago, Geschosskopf said:

Um, no..    Not.  At.  All.  The NSWR has NOTHING in common with a normal (or even molten salt) reactor, other than they both involve uranium.  Thus, the challenges are ENTIRELY different.

In the conventional reactors you mention, the uranium is solid, in the fuel rods, and doesn't move.  The pressurized water or molten salt is merely coolant, absorbing heat from the solid core and carrying it away to keep it from melting.  As this fluid circulates through the fuel rods, it picks up bits of radioactive solids so is usually not the actual working fluid---otherwise you'd contaminate the turbines, which would complicate maintenance.  So instead, the coolant goes through a heat-exchanger to pass the heat on to the actual working fluid, which is water in a separate set of pipes.  This water turns to steam, spins the turbines to make electricity, condenses, gets cooled in the big towers, and back into the heat exchanger.

In a molten salt reactor, the active elements are molten.  Of course you don't have the same issues as NSWR as only a small amount of your fuel has been bred into U233, and so you just filter it out of the thorium and dump it into the core to breed more.  But even a vat of U233 solution is safe, as it needs the moderators to slow down the neutrons so they can interact efficiently.(the fail-safe is a plug of salt that is kept solid through active cooling, and should it melt, all the working fluid drains into an underground vat, where, with no moderators, it will slowly lose U233 to radioactive decay, but otherwise be just fine to pump out and start up the reactor again unless you leave it there long enough to 'freeze')

We actually had one working from 1965-1969 (even if they skipped the thorium breeding blanket in preference of taking measurements, they did use thorium bred to U233 as a fuel in later stages)

https://en.wikipedia.org/wiki/Molten-Salt_Reactor_Experiment

 

Not quite as easy as a solid-core NERVA, but then again, you might be able to stack the 'frozen' fuel salts along the corridors of the hab if you were really pressed for space.

(probably want to wrap it in plastic-wrap to reduce floride leaking into the air, but external stacks held down with cargo-netting would work too)

 

Edited by Terwin

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18 hours ago, Spacescifi said:

 

I do not know Zubrin. Nor did I know he was alive. At any rate, here is a video of him.

He does seem... literally mad here (not crazy, just angry).

 

On some level I sympathize with him. Since he is implying NASA could have done better with developing new space technology for colonization than they have.

True they could have.

Yet unlike Zubrin, I am not set on colonizing other worlds just yet.

We are not ready. Not yet anyway as race.

One day, I have faith that we will be, and then I will seriously consider colonization of other worlds.

Right now all we would do is transport our creed and greed to the stars. Our love too.

Have to crawl before you can run.

That's not a rant, that's an incredibly generous rationalization of the pathetic state of NASA, and its systemic mismanagement that in a more reasonable society would be considered criminal.

He's like a prosecutor laying out irrefutable evidence of first degree murder, and then recommending a sentence of community service.

 

We have their words, their deeds, and their signatures.

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14 minutes ago, Nothalogh said:

That's not a rant, that's an incredibly generous rationalization of the pathetic state of NASA, and its systemic mismanagement that in a more reasonable society would be considered criminal.

He's like a prosecutor laying out irrefutable evidence of first degree murder, and then recommending a sentence of community service.

 

We have their words, their deeds, and their signatures.

 

I did not title the video. Someone on youtube did. I just posted the shortest video on Zubrin that came up and it was this.

Really, NASA being government run tends to shift it's priorities.

For example... what do you think goverments care most about? Colonizing the solar system or maintaining their power on Earth?

I honestly think space agencies the globe over are far more interested in orbital spy satelites, GPS, early warning satelites, and ICBM's than they are about space colonization.

Since they have the capacity to do more but would rather protect their own soveregnty from attack by rivals.

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4 minutes ago, Spacescifi said:

Really, NASA being government run tends to shift it's priorities.

For example... what do you think goverments care most about? Colonizing the solar system or maintaining their power on Earth?

I honestly think space agencies the globe over are far more interested in orbital spy satelites, GPS, early warning satelites, and ICBM's than they are about space colonization.

Since they have the capacity to do more but would rather protect their own soveregnty from attack by rivals.

I'm not disputing that assertion, I'm saying it's evidence of their culpability.

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45 minutes ago, Nothalogh said:

I'm not disputing that assertion, I'm saying it's evidence of their culpability.

 

I am not worried really. NASA definitely won't be the force behind the future of human space exploration.

But I am positive we will... get out there in the future when conditions for space flight are far more favorable than they are now.

Edited by Spacescifi

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21 minutes ago, Spacescifi said:

when conditions for space flight are far more favorable than they are now.

Physical conditions, or political conditions?

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4 minutes ago, Spacescifi said:

 

Both... and yet more.

The physical limitations are practically non-existent

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12 minutes ago, Nothalogh said:

The physical limitations are practically non-existent

 

Um .. we only wish that were true.

Gravity is the enemy of space flight. If we could somehow toggle it on/off then all of our nuclear rocketry would be more practical to utilize.

As matters are now, great thrust means great heat, which requires great cooling. Which makes great weight.

We could have ALL the benefits of nuclear rocketry if we could negate the pull of Earth's gravity. As we could then pile on the cooling equipment with minimal engine thrust losses.

I know that is not possible now, but if it ever is... it would be game changer.

 

Edited by Spacescifi

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If the physical limitations were non-existent, that would be just an object of trade for the political ones.

Edited by kerbiloid

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19 minutes ago, kerbiloid said:

If the physical limitations were non-existent, that would be just an object of trade for the political ones.

 

Yes and no I think.

Yes: Nations who lack a way to toggle planet gravitational pull on/off are going cry out and say it is a threat to global security.

No: Superpower nations will expand their military forces with nuclear rocket spaceships, all thanks to the power to toggle gravity on or off. The major powers may not go to war directly, but they no doubt would fight proxy wars and hammer down on old but weaker foes who would either placate them or fight to the bitter end.

 

Edited by Spacescifi

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23 hours ago, Terwin said:

In a molten salt reactor, the active elements are molten.

I was unfamiliar with the liquid core versions so point taken :)  But using molten salt to cool a solid core (also called MSRs) have been around a long time.  Some Soviet subs reportedly had them.

 

Quote

Of course you don't have the same issues as NSWR as only a small amount of your fuel has been bred into U233, and so you just filter it out of the thorium and dump it into the core to breed more.  But even a vat of U233 solution is safe, as it needs the moderators to slow down the neutrons so they can interact efficiently.(the fail-safe is a plug of salt that is kept solid through active cooling, and should it melt, all the working fluid drains into an underground vat, where, with no moderators, it will slowly lose U233 to radioactive decay, but otherwise be just fine to pump out and start up the reactor again unless you leave it there long enough to 'freeze')

Yeah, this type of reactor can't be a torchship because the fuel isn't macho enough.  The fuel properties you outline are the exact opposites of what you want in a rocket engine.  It might work well to power a VASIMR, though.

Edited by Geschosskopf

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On 9/14/2019 at 10:55 PM, Geschosskopf said:

In the classic Niven and Pournelle book The Mote in God's Eye, the jumpdrive-capable human empire encounters its first intelligent aliens in the form of a sublight beamed-power ship.  This ship solved the deceleration problem by being a huge solar sail.  It was sent on its way with a massive battery of lasers then planned to stop by using its sail to brake during a close pass by the destination star.  The main problem the aliens had with this scheme was political.  They didn't have a single world government and their civilization was never stable due to internal pressures.  So they'd nuked themselves back to the Stone Age MANY times in their very long history.  One such episode happened while this ship was en route, with its launching lasers being used in their nth world war.

That's the main problem I see for humans and beamed power, too.  All spacedrives worthy of the name are also WMDs, due to being able to direct the vast amount of energy required in the desired direction.  I see beamed power as more vulnerable to misuse than most other schemes where the power is aboard the ship.  For example, an Orion ship is a high-capacity nuclear bomber in orbit but it can be built and fueled far enough away to pose little real threat.  Even if it does some start dropping nukes on Earth, there's time to intercept them.  With beamed power, OTOH, all you need is a few mirrors in orbit and brief flicking of the beam to them, and you can vaporize anything you want without significantly slowing the ship.

Except that that would not work in practice. Logically they could dipped close to their sun for the boost instead of using the lasers, however this would not give enough trust for the travel time. In Avatar the starship was laser powered up to speed, it then used antimatter engines to slow down. 
Both Mothe and Avatar has an problem with the energies required as in need to be an K1 civilization. This solves the problem with pollution in avatar, that is outside of heat pollution :)

Mote in the gods eye is 1/10 less as payload was way smaller as in pilot and some other crew hibernating.  They also have the overlaying issue of have to reproduce. 

And beamed power is not an major security issue. Nuclear bombs are much easier to make. Easier than putting an man in orbit. 
You don't need anything more than them for security. 
Yes you can used beamed power to propel high speed impactors however this will be pretty visible.
 

Edited by magnemoe

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15 minutes ago, magnemoe said:

And beamed power is not an major security issue. Nuclear bombs are much easier to make. Easier than putting an man in orbit. 
You don't need anything more than them for security. 

It's not the ease of making it, it's the ease of using beamed power as a weapon.  Lets say you only fuel an Orion out beyond the Moon.  The skipper goes rogue and starts shooting nukes at Earth.  They'll be several days in transit at least, plenty of time to shoot them down before they arrive.  With massive lasers, you can just reorient a mirror here and there, and POOF, instantly vaporize any target you want.  No way to stop that.

This accidentally happening has always been a major downside of putting massive solar collectors in orbit to beam power to the ground.  If the platform wobbles even a little,, the beam will laser-etch a lot of real estate around the ground station.

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46 minutes ago, Geschosskopf said:

It's not the ease of making it, it's the ease of using beamed power as a weapon.  Lets say you only fuel an Orion out beyond the Moon.  The skipper goes rogue and starts shooting nukes at Earth.  They'll be several days in transit at least, plenty of time to shoot them down before they arrive.  With massive lasers, you can just reorient a mirror here and there, and POOF, instantly vaporize any target you want.  No way to stop that.

Assuming it's a laser beam. Particle beams can be deflected by magnetic fields and are actually more efficient than photon beams for propulsion purposes.

49 minutes ago, Geschosskopf said:

This accidentally happening has always been a major downside of putting massive solar collectors in orbit to beam power to the ground.  If the platform wobbles even a little,, the beam will laser-etch a lot of real estate around the ground station.

Uh... only if you use laser beams. Microwave beams tuned to a specific frequency and kept at a low enough irradiance will be no more of a threat than normal sunlight. Even if you used laser beams the beam irradiance will not be high. To be honest, this just isn't possible unless you specifically designed the "solar power station" to be a weapon of mass destruction.

Another aspect to consider is that the immense power of beams for propulsion is that they're inherently chained to large facilities. Yes, mirrors could deflect the laser beams to hit a target, but doing so will be difficult and will be easily visible. Not to mention the easily visible heat rejection and other unavoidable results of activating the laser beam station. Any and every entity worried about it will keep a lot of firepower trained on the station. As soon as they try something, it'll be turned into slag. 

Propulsion beams don't make good weapons. Yes they can cause immense damage, but really they're just huge targets.

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20 hours ago, Spacescifi said:

As matters are now, great thrust means great heat, which requires great cooling. Which makes great weight.

We could have ALL the benefits of nuclear rocketry if we could negate the pull of Earth's gravity. As we could then pile on the cooling equipment with minimal engine thrust losses.

Cooling is not a problem for NTRs.

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48 minutes ago, sevenperforce said:

Cooling is not a problem for NTRs.

Solid core NTRs, yes. Gas core might require cooling to get better performance.

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