Is hyperfission an easier goal than fusion?

[kerbiloid]

9 minutes ago, KerikBalm said:

Also, we've had Fusion energy since 1951 was it? The Russian's built the largest ever fusion reactor, its energy output was about 100x its energy input.

I'm speaking of course about Hydrogen bombs and the Tsar Bomba. They used a fission reaction to start the fusion reaction, but in the case of the Tsar bomba, the fission reaction only supplied about 1% of the device's energy output, the other 99% was fusion.

Not exactly so. Iirc,
1952 - USA, the first  thermonuke, Ivy Mike. Stationary, useless. Pure liquid deuterium + fission primer.
1953 - USSR, layered fusion bomb. Portable, poorly useful.
1954 - USA, fusion bomb. Useful.
1956 - USSR, fusion bomb. Useful.

AN602 was not pure fusion, its lead plates replaced just the additional external layer of uranium. So, it was "50:50", while with uranium addons it would be "80:20" fission:fusion.

[KerikBalm]

6 minutes ago, kerbiloid said:

AN602 was not pure fusion, its lead plates replaced just the additional external layer of uranium. So, it was "50:50", while with uranium addons it would be "80:20" fission:fusion.

Yes, the weaponized design would have had an additional fission stage. The wisely and thankfully removed that stage to limit the radioactive fallout created. The result was 99% of the energy was from Fusion.

IIRC, the additional fission stage would have doubled its yield, and made it roughly 50:50 fusion:fission.... that is assuming all the added yield came from fission (and not increased fusioning as well), and their calculations were accurate.

As it was actually built and tested it was 99:1 fusion:fission. If we regard the fission reactions as the energy input, then the fusion output exceeded the energy input by about 2 orders of magnitude.

That's far beyond "break even".

Its also an energy output that will destroy cities, not supply them with electricity.

[kerbiloid]

1 hour ago, KerikBalm said:

Yes, the weaponized design would have had an additional fission stage. The wisely and thankfully removed that stage to limit the radioactive fallout created. The result was 99% of the energy was from Fusion.

That's how wiki describes.

Afaik, they've replaced the additional uranium case (the 3rd stage), the passive part of the device, which fissions under the neutron flow from inside, so can be made of absolutely anything. So, you don't need it to test the bomb.
But how could they replace the uranium tamper of the 2nd stage, as it is a significant part of the active part, causing the neutron flow and inner radiation (or gas diffusion) pressure? The fusion just wouldn't run.

So, afaik, the 2nd stage uranium part stays same, and 99% is a misunderstood.

Edited July 29, 2019 by kerbiloid

[YNM]

On 7/27/2019 at 6:45 AM, Spacescifi said:

How about oh... 25% of the atom converted into energy after it is split? Instead of the standard 2%?

Well, how do you control them ? It needs to be sustainable.

Also, to the best of my knowledge, such energy release isn't possible - the energy released are reflected as the difference in mass of the nucleus, and so far I don't see how the binding force would ever contribute to a quarter of the mass-energy. Such an isotope would be terribly, terribly unstable.

Unless you're saying neutron stars, in which case, bad news : they are so immense that they're bonded by something else.

[DDE]

6 hours ago, KerikBalm said:

I'm speaking of course about Hydrogen bombs and the Tsar Bomba. They used a fission reaction to start the fusion reaction, but in the case of the Tsar bomba, the fission reaction only supplied about 1% of the device's energy output, the other 99% was fusion.

Sounds a bit optimistic. But then again, we got 98% out of the Tundra 200 t industrial nuke.

[KerikBalm]

So I checked wikipedia again, and they claimed 97% from fusion, not 99%.

Either way... technically speaking its a fusion reactor that gets well past break-even. It was just a single use fusion reactor :p

[Guest]

@Spacescifi

when do we get to read this book!

[Spacescifi]

4 hours ago, Dale Christopher said:

@Spacescifi

when do we get to read this book!

 

Haha... this was OP was not for that. It was for analysis.

Some will say a fusion powered spacecraft is more realistic than a fictional drive powered spacecraft.

But based on what I read about fusion, fusion powered scif spaceships looking like anything seen in popular media are just as fictional.

Mankind's abilty to generate lots of heat in small packages does not scale with their ability to reject lots of heat in small packages.

Thus, even if we had loads of antimatter and a way to safely store it, a working self sustaining fusion system, and metallic hydrogen, we STILL could not have a scifi spaceship.

Why? Heat. Even fission NTR generate a lotta heat. So the heat from a self sustaining fusion reaction would be likely worse for a spaceship.

Stars were not meant to be put in jars. And that is only one reason why fusion is so hard.

The one way we could have a starship that won't need radiators that are massive is one that essentially blows up mini-stars out the back.

 

AKA project orion. So even with tech we do NOT have, orion is our most efficient bet for a starship that I have seen. 

Unless we dramatically increase our heat rejection abilities for small amounts of mass (currently not possible that I have seen).

Or do the more realustic option of just putting on massive radiators or.. just make an Orion.

 

[Guest]

Hmmm, heat dissipation is a challenge but I don’t see why it’s a showstopper. 

[Spacescifi]

21 minutes ago, Dale Christopher said:

Hmmm, heat dissipation is a challenge but I don’t see why it’s a showstopper. 

 

It is a matter of practicality.

Say I give you a choice of a spaceship propelled by antimatter bombs Orion pusher plate style or one where is it an actual antimatter rocket. Either beam core core or antimatter thermal liquid propelled.

I reckon that either rocket scheme will require more mass (radiators) than the Orion will, since the Orion's push is coming from outside, not inside.

Mass penalty is a big deal with spaceships if it is NOT expendable, and radiators really are'nt.

You need less radiators with an Orion, plus an Orion looks somewhat closer to classic scifi spaceships.

Rather than a massive set of radiator wings stemming from a small vessel.

Edited July 30, 2019 by Spacescifi

[magnemoe]

1 hour ago, Spacescifi said:

 

It is a matter of practicality.

Say I give you a choice of a spaceship propelled by antimatter bombs Orion pusher plate style or one where is it an actual antimatter rocket. Either beam core core or antimatter thermal liquid propelled.

I reckon that either rocket scheme will require more mass (radiators) than the Orion will, since the Orion's push is coming from outside, not inside.

Mass penalty is a big deal with spaceships if it is NOT expendable, and radiators really are'nt.

You need less radiators with an Orion, plus an Orion looks somewhat closer to classic scifi spaceships.

Rather than a massive set of radiator wings stemming from a small vessel.

Still its some work on fusion powered engines, pulsed and they don't go break even but the drive is way lighter than an orion pulse nuclear. you only partially constrict the pulse. Same would work with antimatter at least if you wanted high trust. 

[Nuke]

On 7/28/2019 at 2:06 PM, DDE said:

Direct conversion requires hot gas of absolutely any kind. Even a rocket engine will do - Purnell suggested hooking J-2s to an MHD as a source of a brief power surge for a laser launch system and RD-600 had an MHD coil built into a GCNR’s exhaust nozzle to get a megawatt of power while firing - while there are also proposals for high-temperature gas-cooled spaceborne reactors using just the MHD (e.g. the related EU-610).

charged particle direct conversion is a lot more efficient. 

[Guest]

Also, any kind of low frequency pulsed drive is problematic for crewed missions. Humans do not like changes in accelerations, and sustaining an Orion-style jerky ride even for 10 minutes will drive most of them nuts. Orion a great as an unmanned LV, and maybe an asteroid pusher. The only Orion concept that works for manned travel is Medusa, which uses an extra-long tether to spread the acceleration out so that it feels steady. On the other hand, Medusa is unsuitable for liftoff due to a rather awkward sail mechanism. In orbit to orbit duty, Orion is outperformed by other drives.

Highly optimized NTR spacecraft can have high thrust, exhaust velocity between 6 and 10km/s (depending on whether you're using CH4 or LH2) and no real need for radiators unless you're adding an electricity generating loop. If you're building spaceships in orbit, NTRs are all you need to make spaceships that would be a lot like cruise ships of old. 

21 hours ago, Spacescifi said:

But based on what I read about fusion, fusion powered scif spaceships looking like anything seen in popular media are just as fictional.

Popular media depictions of spaceships are nothing like reality, period. There were some realistic designs in old SF, and they pop up from time to time, but most of the time. The bottom line is, you need radiators, even the ISS has them. They are not too heavy, and in fact can be made surprisingly sturdy if you want to make a space battleship. You can also design them flush with the hull on some designs. Fusion is hard, but very definitely possible. It may not be very economical at the moment (and for the foreseeable future), but it's far more believable to say something expensive became cheap after some time than to say something thought impossible was suddenly found possible.

[mikegarrison]

55 minutes ago, Dragon01 said:

Also, any kind of low frequency pulsed drive is problematic for crewed missions. Humans do not like changes in accelerations, and sustaining an Orion-style jerky ride even for 10 minutes will drive most of them nuts.

Well, that was why the idea with Orion was to have so much mass and also large springs. That would tend to smooth out the acceleration.

That being said, nobody ever said that going to space was going to be like sitting on the couch and watching TV. I've driven down bad, bumpy roads for half an hour just to go hiking. Some people spend hours running a jackhammer because it's their job. I think 10 minutes of annoyingly harsh pulsing would be a small price to pay to go to Saturn.

Edited July 30, 2019 by mikegarrison

[Guest]

13 minutes ago, mikegarrison said:

Well, that was why the idea with Orion was to have so much mass and also large springs. That would tend to smooth out the acceleration.

Not enough. The stroke on proposed Orion variants would not be enough to the acceleration out completely. Medusa is the only one where it really works. We're not talking running a jackhammer, those are fairly high frequency compared to Orion. Nor is it comparable to riding down a very bumpy road (that would Ares I during first stage burn). Far from it. This would feel more like a beginner driver fumbling with the clutch and violently jerking the car forward. Even a few seconds of this is bad. In fact, it's difficult to describe just how terrible that is, go learn to drive stick if you want to check. Only a handful of people would be able to endure it for long enough. Orion is just not feasible for crew launches. Any pulsed drive is suspect for the same reason, unless vacuum-only with a very low thrust, or using a shock absorber with a very long stroke. 

[mikegarrison]

8 minutes ago, Dragon01 said:

Not enough. The stroke on proposed Orion variants would not be enough to the acceleration out completely. Medusa is the only one where it really works. We're not talking running a jackhammer, those are fairly high frequency compared to Orion. Nor is it comparable to riding down a very bumpy road (that would Ares I during first stage burn). Far from it. This would feel more like a beginner driver fumbling with the clutch and violently jerking the car forward. Even a few seconds of this is bad. In fact, it's difficult to describe just how terrible that is, go learn to drive stick if you want to check. Only a handful of people would be able to endure it for long enough. Orion is just not feasible for crew launches. Any pulsed drive is suspect for the same reason, unless vacuum-only with a very low thrust, or using a shock absorber with a very long stroke. 

I'm starting to doubt that you have ever driven down a washboarded road.

And I still say you are crazy if you think a few minutes of unpleasantness would mean "only a handful of people" could tolerate it.

[Guest]

I doubt you've ever driven stick (and really, we've got plenty of crappy roads) or sat in the car with someone who was bad at it. This is a series of violent jolts. Not even stepping on gas then immedietely slamming on the brakes gives you that sort of experience. Acceleration is actually less important here than jerk, and Orion designs I've seen would have problems with that. With very small pulse units and long absorbers you might get it down to "bumpy round" level, but what you don't seem to realize is that frequency is also the key here. We can stand vibrations. What we have trouble with is being slammed in the back every few seconds.

Non-Medusa Orion is not viable as a crew vehicle, period. Disregarding other problems with it (such as inevitable EMP from each pulse unit), it's hard to design one that would be merely an unpleasant ride, as opposed to a torture.

[Spacescifi]

1 hour ago, Dragon01 said:

Also, any kind of low frequency pulsed drive is problematic for crewed missions. Humans do not like changes in accelerations, and sustaining an Orion-style jerky ride even for 10 minutes will drive most of them nuts. Orion a great as an unmanned LV, and maybe an asteroid pusher. The only Orion concept that works for manned travel is Medusa, which uses an extra-long tether to spread the acceleration out so that it feels steady. On the other hand, Medusa is unsuitable for liftoff due to a rather awkward sail mechanism. In orbit to orbit duty, Orion is outperformed by other drives.

Highly optimized NTR spacecraft can have high thrust, exhaust velocity between 6 and 10km/s (depending on whether you're using CH4 or LH2) and no real need for radiators unless you're adding an electricity generating loop. If you're building spaceships in orbit, NTRs are all you need to make spaceships that would be a lot like cruise ships of old. 

Popular media depictions of spaceships are nothing like reality, period. There were some realistic designs in old SF, and they pop up from time to time, but most of the time. The bottom line is, you need radiators, even the ISS has them. They are not too heavy, and in fact can be made surprisingly sturdy if you want to make a space battleship. You can also design them flush with the hull on some designs. Fusion is hard, but very definitely possible. It may not be very economical at the moment (and for the foreseeable future), but it's far more believable to say something expensive became cheap after some time than to say something thought impossible was suddenly found possible.

 

While you may be right about the fission rocket, my point still remains that radiator mass on a vessel with self sustaining fusion would be a large part of the vessel.

Antimatter could also perhaps be made to work without substantial radiatiors, but I believe the high thrust performance would have to be scaled back a bit.

Unless you also know of antimatter designs that do not require massive radiators?

If they are like slow ion drives then not having big radiators is not a plus since ions take forever to get anywhere.

EDIT: Could one not just unfold the medusa net from the ship in orbit.

Some assembly required is how they having been doing for decades now in orbit.

10 minutes ago, Dragon01 said:

I doubt you've ever driven stick (and really, we've got plenty of crappy roads) or sat in the car with someone who was bad at it. This is a series of violent jolts. Not even stepping on gas then immedietely slamming on the brakes gives you that sort of experience. Acceleration is actually less important here than jerk, and Orion designs I've seen would have problems with that. With very small pulse units and long absorbers you might get it down to "bumpy round" level, but what you don't seem to realize is that frequency is also the key here. We can stand vibrations. What we have trouble with is being slammed in the back every few seconds.

Non-Medusa Orion is not viable as a crew vehicle, period. Disregarding other problems with it (such as inevitable EMP from each pulse unit), it's hard to design one that would be merely an unpleasant ride, as opposed to a torture.

 

And I kind of agree with you about Orion being awkward.

You would not have gravity every 3 seconds, so if something or someone lept up high during the 3 seconds of free fall/weightlessness they would come down harder than normal from height alone.

Electromagnetic shoe soles anyone? To keep crew grounded at all times?

Edited July 31, 2019 by Spacescifi
Orbit assembly

[Guest]

Just now, Spacescifi said:

While you may be right about the fission rocket, my point still remains that radiator mass on a vessel with self sustaining fusion would be a large part of the vessel.

Here's the trick with radiators: the hotter they are, the smaller they can be, and this adds up quickly. Fusion involves plasma, which means your radiators can be as hot as you can make them without melting. For carbon composites, this can be very hot. In Children of a Dead Earth (where radiator mass is a very serious concern), I've built ships with one tiny radiator for the crew module, and exactly the same type of tiny radiator cooling a nuclear reactor in GW range. How is that possible? The reactor puts out coolant at 2000K, the crew module at around 300K. A very hot radiator can be made very small, and if you can find a way to use a liquid surface (like in droplet radiators), it can be even smaller.

Also, the more efficient your power plant, the less waste heat you need to radiate. If instead of a thermal engine, you use direct conversion (an MHD generator, for example) to change your hot plasma directly into electrical energy,  you will generate a lot less waste.

As for engines, you can use open-cycle cooling. This reduces Isp, so it is not always suitable, but it can let you make engines that do not need radiators of any kind. Simply put, with open cycle you use your exhaust as radiator/heat sink.

[mikegarrison]

47 minutes ago, Dragon01 said:

I doubt you've ever driven stick

LOL. So very wrong. Every car I've ever owned for the past 30 years. I guess maybe I just know how to use a clutch (and even how to heel-toe)?

Obviously you are hung up on the whole "hardly anybody would put up with something uncomfortable in order to go to space" thing, so we'll just have to disagree about that.

[Spacescifi]

6 minutes ago, mikegarrison said:

LOL. So very wrong. Every car I've ever owned for the past 30 years. I guess maybe I just know how to use a clutch (and even how to heel-toe)?

Obviously you are hung up on the whole "hardly anybody would put up with something uncomfortable in order to go to space" thing, so we'll just have to disagree about that.

 

Still... 3 seconds without gravity could prove injurious without magnetic shoes.

Just imagine how high a ball or a tool can go in 3 seconds with no gravity.

Before crashing down again.

Edited July 31, 2019 by Spacescifi

[mikegarrison]

1 minute ago, Spacescifi said:

 

Still... 3 seconds without gravity could prove injurious without magnetic shoes.

Just imagine how high a ball or a tool can go in 3 seconds with no gravity.

Before crashing down again.

Yeah, you would definitely have to batten down the hatches before firing up the engine. Kind of like the walkthrough on a commercial airliner where (in theory) every bin, every closet, every cart, every seatbelt, every loose item, etc. is checked before takeoff or landing.

[kerbiloid]

5 hours ago, mikegarrison said:

That being said, nobody ever said that going to space was going to be like sitting on the couch and watching TV. I

Can't find the video, but you've just described a scene from an old (1950s ?) Soviet sci-fi movie.
A space station. A woman returns back to her cabin, gets changed, takes her seat on the couch, and starts watching ballet on TV.
The space is so spacy!

Also, there is a couch in Soyuz habitat, lol. And originally it was even bigger.

6 hours ago, Dragon01 said:

Humans do not like changes in accelerations, and sustaining an Orion-style jerky ride even for 10 minutes will drive most of them nuts.

Have a train journey on an old railway. Or a non-American/German autobahn, lol,
If the Orion cascaded springs soften the 2..4 Hz oscillation down to this level, no problem at all, for a pair of weeks.

Another sample: a tiny crewed command cabin in a SILO of ICBM is designed to survive a seismic hit from nuclear explosion in ~200 m from it, with the SILO cap inside the fireball.

Spoiler

Don't underestimate the force of springs.

If use a magnetic field instead of the steel plate, the kicks can be softened even better.

 

6 hours ago, Dragon01 said:

The only Orion concept that works for manned travel is Medusa, which uses an extra-long tether

That's why unlikely Medusa had any chance. Unlike the brutal Orion, Medusa needs enormous sci-fi tethers like a space elevator..And still has to soften the oscillations.
(Though, the project is morally blessed by Dysons' favor.)

Medusa was a pure fantasy. The only way you can uses nukes, even thermonukes together with sail is a solar sail.

6 hours ago, Dragon01 said:

The bottom line is, you need radiators, even the ISS has them.

Does the Earth have radiator panels?

The greater are heat capacity of the ship and the lower is heat conductivity of its nozzle/mirror/plate, the weaker radiators are required. So, a proper balance is important.
And speaking about Orion, it doesn't keep the reaction inside, it just receives kinetic kicks, while the heat gets radiated outside.

So, there is a limit of a drive power which you can contain in an enclosed combustion chamber, when you have to cool it and when most part of energy raises the pressure but doesn't produce  thrust.

To get bigger you have to move the reaction zone outside, behind the ship, and make the nozzle mirror/plate flat, shallow, or immaterial (magnetic).
In this case your engine spends most part of energy outside, to heat the Universe, because the plate/mirror is just a small part of the spherical surface receiving the blast energy.

Next you have to focus your blast prograde, towards the ship. And as a result you inevitably return to Orion, just on higher technical level.
To focus the blast power you have to use pellets and discrete explosions rather than smooth flow of fluid, like Orion.
(Orion has grown not from a rocket design, but from a focused nuke charge project, they just had an idea to use it for propulsion).

And when the blast happens behind, then most part of heat stays outside and doesn't warm the ship.

So, whatever you do in da space, looks like finally you get just another type of Orion.

Edited July 31, 2019 by kerbiloid

[KerikBalm]

On 7/30/2019 at 2:10 AM, Spacescifi said:

AKA project orion. So even with tech we do NOT have, orion is our most efficient bet for a starship that I have seen. 

Ummm but we do have the tech, at least the major parts of it.

Shock absorbers? check

Shaped charge nuclear bombs? check

Materials fur use on the pusher plate? check

Sure there would be a lot of engineering involved in putting the components together, and getting it into a working space ship, but there is no fundamentally new tech that needs to be developed.

On 7/30/2019 at 3:11 AM, Spacescifi said:

Say I give you a choice of a spaceship propelled by antimatter bombs Orion pusher plate style or one where is it an actual antimatter rocket.

...

I reckon that either rocket scheme will require more mass (radiators) than the Orion will, since the Orion's push is coming from outside, not inside.

Orion is a rocket, not a conventional continuous thrust one... and antimatter shaped charge bombs would work as well, so you can have an antimatter orion (but as it will need working mass for the pusher plate, you won't have you exhaust as gamma rays... unless you've got some pretty exotic pusher plate)

10 hours ago, Dragon01 said:

Also, any kind of low frequency pulsed drive is problematic for crewed missions. Humans do not like changes in accelerations, and sustaining an Orion-style jerky ride even for 10 minutes will drive most of them nuts.

...

9 hours ago, Dragon01 said:

Not enough. The stroke on proposed Orion variants would not be enough to the acceleration out completely. Medusa is the only one where it really works. We're not talking running a jackhammer, those are fairly high frequency compared to Orion. Nor is it comparable to riding down a very bumpy road (that would Ares I during first stage burn). Far from it. This would feel more like a beginner driver fumbling with the clutch and violently jerking the car forward. Even a few seconds of this is bad. In fact, it's difficult to describe just how terrible that is, go learn to drive stick if you want to check. Only a handful of people would be able to endure it for long enough. Orion is just not feasible for crew launches. Any pulsed drive is suspect for the same reason, unless vacuum-only with a very low thrust, or using a shock absorber with a very long stroke. 

Un supported assertion. Would it be uncomfortable? yes. Would the ship be perfectly dampened? No. Can crew chairs be dampened additionally? yes.

For interplanetary voyages where high thrust departure is desired, at an average of 1 g, even 1 hour of thrusting gives you 36 km/sec, your crew only needs to endure a about 2 hours of thrust for departure. At these velocities, oberth isn't so important, and you can break it up and have rests.

For interstellar voyages, you can drop the average acceleration down to something like 0.1 G, at which point active damping can easily be made to compensate.

9 hours ago, mikegarrison said:

I'm starting to doubt that you have ever driven down a washboarded road.

And I still say you are crazy if you think a few minutes of unpleasantness would mean "only a handful of people" could tolerate it.

Agreed

[steve_v]

11 hours ago, Dragon01 said:

any kind of low frequency pulsed drive is problematic for crewed missions. Humans do not like changes in accelerations, and sustaining an Orion-style jerky ride even for 10 minutes will drive most of them nuts.

...

16 minutes ago, KerikBalm said:

Un supported assertion. Would it be uncomfortable? yes. Would the ship be perfectly dampened? No. Can crew chairs be dampened additionally? yes.

Indeed. Citation needed and all that.

The original proposal called for a peak acceleration of about 3G IIRC, and apparently this was not considered a problem, at least from what I have read. Some links and stuff.

Edited July 31, 2019 by steve_v