Extracting Power from Nuclear in Space

[Nuke]

it occured to me that any propellant based engine could reject heat by sticking a heat exchanger between the propellant and coolant lines. this would likely also save power and/or increase isp for the engine, all be it slightly, by pre-heating the propellant. it might also be possible to generate power by putting a turbine beyond the heat exchanger since the propellant is expanding. 

Edited December 5, 2017 by Nuke

[shynung]

12 minutes ago, Nuke said:

it occured to me that any propellant based engine could reject heat by sticking a heat exchanger between the propellant and coolant lines. this would likely also save power and/or increase isp for the engine, all be it slightly, by pre-heating the propellant. it might also be possible to generate power by putting a turbine beyond the heat exchanger since the propellant is expanding. 

So, like regenerative cooling, but being used to generate heat instead of cooling the chamber/nozzle.

I don't think putting a turbine past the HX would do much good. That would sap propellant line pressure, and it's needed for thrust. Much simpler to plug a generator at the turbopump shaft instead.

[magnemoe]

https://www.nextbigfuture.com/2017/12/nasa-testing-ultra-simple-small-nuclear-reactors-that-will-power-missions-to-mars-and-beyond.html
This is relevant for discussion, Using an Beryllium oxide reflector to reduce the size of the core, also using heat pipes to an stirling engine. 

[DDE]

On ‎05‎.‎12‎.‎2017 at 6:57 PM, wumpus said:

So instead of being "20 years from now" fusion will be require a steadily increasing size until it exceeds Earth?

Well, eventually they'll just say that it already exists and has been around since forever.

And then they'll try to monetize it somehow.

3 hours ago, magnemoe said:

https://www.nextbigfuture.com/2017/12/nasa-testing-ultra-simple-small-nuclear-reactors-that-will-power-missions-to-mars-and-beyond.html
This is relevant for discussion, Using an Beryllium oxide reflector to reduce the size of the core, also using heat pipes to an stirling engine. 

I still think they should raid SDI's warehouses for Yenisei. Beryllium oxide isn't that innovative, it's being in use in weapons for quite a while. But heat pipes might cost them a lot of efficiency whereas fuel-integrated thermionics will not.

[PB666]

6 hours ago, magnemoe said:

https://www.nextbigfuture.com/2017/12/nasa-testing-ultra-simple-small-nuclear-reactors-that-will-power-missions-to-mars-and-beyond.html
This is relevant for discussion, Using an Beryllium oxide reflector to reduce the size of the core, also using heat pipes to an stirling engine. 

Yes but how are they going to extract water with only 10 kW of power after it has been distributed for personal use?

 

[Nuke]

On 12/5/2017 at 9:04 AM, shynung said:

So, like regenerative cooling, but being used to generate heat instead of cooling the chamber/nozzle.

I don't think putting a turbine past the HX would do much good. That would sap propellant line pressure, and it's needed for thrust. Much simpler to plug a generator at the turbopump shaft instead.

its pretty much exactly the same thing as regenerative cooling. you are transfering heat from the thing you want to cool, to the propellant and then shooting it out the nozzel taking the heat away with it. the only difference is the thing being cooled. should work with any ion drive, nuclear-electric, nerva or fusion engine. i was reading an article on nuclear powered tunnel boring machines for use on the moon. they had a rather novel way of cooling the reactor. they would take resulting rubble and use it as a heat sink, then take it out side and dump it on the lunar surface.

Edited December 7, 2017 by Nuke

[shynung]

16 minutes ago, Nuke said:

its pretty much exactly the same thing as regenerative cooling. you are transfering heat from the thing you want to cool, to the propellant and then shooting it out the nozzel taking the heat away with it. the only difference is the thing being cooled. should work with any ion drive, nuclear-electric, nerva or fusion engine. i was reading an article on nuclear powered tunnel boring machines for use on the moon. they had a rather novel way of cooling the reactor. they would take resulting rubble and use it as a heat sink, then take it out side and dump it on the lunar surface.

AFAIK, on a rocket engine, regenerative cooling was done to keep the nozzle and chamber from melting despite the vigorous reaction happening inside them.

[Nuke]

1 hour ago, shynung said:

AFAIK, on a rocket engine, regenerative cooling was done to keep the nozzle and chamber from melting despite the vigorous reaction happening inside them.

exactly, heat you need to get rid of. so you pump the fuel around the bell. this is essentially a heat exchanger to put the heat of combustion right back into the fuel. but you can use the technique to remove heat from any other part of the spacecraft.

[DDE]

2 hours ago, Nuke said:

they would take resulting rubble and use it as a heat sink, then take it out side and dump it on the lunar surface.

What a waste. A lot of the melt-borer machines tout using heat rejection to melt the wall material into a structurally sound tunnel.

Edited December 7, 2017 by DDE

[shynung]

3 hours ago, Nuke said:

exactly, heat you need to get rid of. so you pump the fuel around the bell. this is essentially a heat exchanger to put the heat of combustion right back into the fuel. but you can use the technique to remove heat from any other part of the spacecraft.

I read that this trick was put to use in the SR-71 spyplane. Some of the outer skin, in particular the chines along the side of the fuselage, are cooled by the incoming charge of fuel.

[Nuke]

10 hours ago, DDE said:

What a waste. A lot of the melt-borer machines tout using heat rejection to melt the wall material into a structurally sound tunnel.

in the paper i read the machine did that. but you still have a lot of surplus heat to reject.

[PB666]

30 minutes ago, Nuke said:

in the paper i read the machine did that. but you still have a lot of surplus heat to reject.

Silicon starts becoming plastic at around 600'F and melts well over 1000'F, many of the other components of rock, particularly the alkali metals will decompose and form a powder when exposed to air that is difficult deal with.

[Mayer]

Fusion is funny until you realize how much energy is released from Deuterium-Tritium and Deuterium-Helium³ reactions. Once i've put their values in the formula of kinetic energy and got around 10% speed of light. I don't think a vessel with solar sails can pull this off, there is no solar wind where Voyager 1 drifts.

[PB666]

9 hours ago, Mayer said:

Fusion is funny until you realize how much energy is released from Deuterium-Tritium and Deuterium-Helium³ reactions. Once i've put their values in the formula of kinetic energy and got around 10% speed of light. I don't think a vessel with solar sails can pull this off, there is no solar wind where Voyager 1 drifts.

It gets even crazier if you learn to harness neutrons, most of the energy in the reaction is in neutrons that wander off an make things heavier. All fusion is simply extracting energy from stuff that holds nucleus together, but real energy comes from converting normal matter to antimatter and then annihilating it. If you can create a fusion reactor that converts neutrons into anti-matter by some step-wise process then you really have a power source. 
The problem with fusion, and in particular unlimited fusion power in space is this as I see it.

In space limitless energy is not exactly unlimited unless it is distributed over time, mass and space or to phase properly we soft fleshy things like to keep our body parts together and so we don't generally take kindly to power conversions of great power in small spaces over brief periods and small heat sink mass. And this is the power problem. The famous example is the big bang, at the beginning there was infinite energy in a point, as soon as you have space-time, energy density becomes finite, and entorpy that ensues sees energy all but disappear the only thing that is less is the non-zero vacuum energy of space. Pretty much the same thing happens with space craft energy. Power is the transformation of energy per unit of time into something that eventually all becomes waste heat. Its not exactly true but basically true. Some of you will say 'yes it becomes heat, but not in a relevant context'. I would argue maybe but we sure don't want unlimited waste energy in our living quarters the food storage coolers. Thus we need to control energy flow very carefully in a space craft, it just can't go anywhere.

Here is why.
When traveling in space the primary outlay of energy is phase transitions from high-energy space-time isoquants to low-energy isoquants and back to high-energy isoquants. The conversions require PE->KE. This is denoted as SKE. unlimited energy - SKE = unlimited energy until you add mass. Unlimited energy - SKE * mass = you're screwed. Here is the proof, suppose we have a 1 TW reactor (10¹² Watts). Now suppose we have a [reaction]mass-less drive system. Ok it has mass we just accelerate the hell out of the mass. N = 2 * P / V_e. So that close to the speed of light the equations becomes N = P/c (i.e the u-r-f-d-and-bad equation) which means you get 3,333N of power, you jump up and down with joy, except . . . . . . . wait that 3 kn of thrust, thats like the tiniest thruster in KSP. Hmm and that TW reactor weighs a >KT (we wont worry about its weight at the moment, the biggest problem is latent heat). In this particular solution we generated pure light - somewhere a billions of light years away some race will see a blip in the MW background energy, i.e. heat. And what you got out of it was 0.00333 m/s². Hmmm, something forgotten, thrusters . . . . . .thrusters that use energy also waste energy, in space they cannot dissipate energy except by radiation. An ION drive is essentially a mass that conducts fuel-mass and heat at the expenditure of power. The heat limit of the device determines the power per unit area (something like 70kw per meter at 80% efficiency means 14 KW per meter is about 10 time more energy than ensolance energy on Earth, some of that goes into the xenon the rest is radiant heat) and the mass. So that you end up with somewhere between 29 and 58 kg of drive per 70 kw per meter. If you have a TW of power you need to get rid of equates to 415 kt of mass. That translates to an acceleration of 0.00008 m/s² (a) of acceleration. When you are talking about interplanetary travel and acceleration, once you get below about 0.01 a your oberth effects are lousy inefficient, in addition you can waste almost half your power trying to spiral out of planetary orbits in order to escape. This can be corrected by raw material ships by kicking and wasting time doing nothing, which for fusion is great because it does not require critical mass like fission reactors. But its very difficult to capture the oberth-like effect for planetary transfer orbits you get from combined burns at low planetary orbits. The savings are almost half of what an infinitely slow ION drive craft would spend. I don't know if this is apparent but let me make it clear, a chemical thruster puts the bomb (the energy conversion over short time and space) into a combustion chamber and expels most of the waste heat as exhaust. A fusion reactor has (for reactor and humans to survive) place most of the energy conversion inside or near the reactor, about 1/3rd is in the thruster and 2/3rds approximately has to be dissipated over a 2-dimensional surface around the reactor into space. The latent heat is an inherant problem with larger amounts of energy (addressed below).

So correcting the problem of the u-r-f-d equation is to add mass to it in the form of lower exhaust velocity. So if we cut the V_exhaust by 625 fold  we bring acceleration up to 0.01 but we add fuel mass. This is an ISP of approximately 50,000 which means we could travel to places in the solar system, carry landers ect. But in handwaving that thrust power into existence I have failed to reveal one tiny detail, yes the thrust is possible, its effects are not. Above we said we are not going to worry about a 1 TW reactors weight, the problem is now we do have to worry, the heat expulsion is heat is expelled through infrastructure mass. In this case we have a reactor, the reactor does not produce high potential electrons that then flow into ION drives, it produces radiation that is converted to heat, hopefully by some state-phase-transition power generator which drops the energy potential by at least half, and maybe another potential that drops it again and so on . . eventually you have reactor waste heat. But in addition you have pesky waste and reactor erosion (very very hot stuff) that will be ejected or accelerated into space. Neutrons could be absorbed by sacrificial boron and ejected along the way however you have heat generated and alot that is expensive to capture. So now we have the big problem. Lets say we had 300 GW of waste heat, now lets say we had a very black transfer foil and we can evolve heat at 1 kg per one meter, the thermal limit is 50 degrees and into the black of 5 kelvin space. Your differential is 293 kelvin. The bottom line is that you need to all but double the mass of your ship, meaning that to maintiain  a, ISP will need to drop by 25000 to about 25000. Im saying this in a future thinking that fusion will be a thing and we will have better ion drives yada, yada. At the moment 10,000 ISP is the practical limit. (because energy density of solar panels is alot less than fusion reactors and cooling mass).  To restate, there is no limit to the ISP of an ION drive like system, the limits lie in its practical application. 

So here is what happened. Fusion power = unlimited energy but not perfect efficiency energy. Thrust conversion is also not perfectly efficient. Thrust  efficiency has a dependency on mass.
a = (Unlimited energy - Power conversion losses - Thrust conversion losses)/ (ISP * thruster mass + reactor mass + converter mass + radiator mass + PL mass + fuel mass/2) = you're screwed.
heat = Unlmiited energy*(power conversion inefficiency + thrust conversion inefficiency + PL waste) = ........

So this is the reason unlimited energy is self limiting, the problem is if we look at space we can think of it as a 2 dimensional manifold that captures heat from whatever 2-dimensional radiators are present.
Lets say we can dissipate power over 1 meter of space, but at most we can fold the surface and double heat dissipation. This means that our effective heat loss is roughly 8* pi * r². For the nay-sayers lets say its 100 * pi * r²

Equally generous lets say the we can dissipate 100 times ensolance (reality is that this would mean glowing orange hot). OK so lets dissipate fusion reactors. (IOW we have some ungodly means of dumping heat in the future)

1 watt reactor generating 0.3 waste heat would require a 'rough' sphere of radiators of r  = 0.00008
10 watt, r  = 0.00026
100 watt, r = 0.0008
1000 watt, r = 0.0026
10000 watts, r = 0.008
100000 watts, r = 0.026
1000000 watts, r = 0.08
10000000 watts, r = 0.26
100,000,000 watts, r = 0.8
1,000,000,000 watts r = 2.6 (yes, I am very generous with the radiative heaters)
10,000,000,000 watts r = 8 meters (the radiators would be visible at many places on the ship)
100,000,000,000 watts r = 26.6 meters (the radiators now completely surround the ship except the radiators
1,000,000,000,000 watts r = 80 meters. (the PL is now buried inside a large manifold of radiators, finding  difficulty to keep cool).

So lets tinker with this lets say the rate of dissipation is 3 times ensolance at best, and we can oscillate the manifold 3 fold.
The equation for 1 TW of power is now 1306 meter in radius. Up to this point for each point in which power presented a problem we have provided a work around that cost mass, but not space.
Now we have a work around that cost space, and the cost of space is mass. So that at some point mass as a function of  heat has a second hyperbolic term. IOW the heat eqaution eventually mutates into this type of thing

radiator mass + structure = k*( KW_heat + 0.00001 KW_heat²)

where k is the radiative heat capacity per radiator mass.

Fundamentally, this drafts the question when we look at Universal events, (big bangs, intergalactic speeds, intra galactic orbital velocities) we can examine these in the context of very high energy events that occur over relatively short periods of time (the accretions of a solar system, a super nova, the initiation of fusion of a star). The speeds that we see are often the result of catastrophic events, for example the momentum created by inflation that is fed into expansion, the particle formation energies and the resulting momentums. IF you want to generate huge relative velocities you have tolerate rather erosive power conversions. IN the case above we might want a 1 TW fusion reactor in a ship, we just would not want to use it much of the time, and we are more mass efficient by having a 1 GW fusion reactor, we can easily scale down the ION drives and heaters. But lets say the smallest fusion reactor is 1GW, then what, you have a reactor that can only be used for a few seconds a minute and the other 57 seconds are devoted to dumping heat.

My bottom line on Space fusion (not ground based fusion) is that it has to be able to generate power, convert power and do so in a specified power range, say 10 MW to 100 MW. The alternatives are
we have to create power transformation fundamentally more advanced in technology than fusion reactor or abandon space fusion.

I want to make this point, we had a 2 year argument about the Cannae drive and how it would answer all the space problems, it lowers the space problems only about a factor of 3. The problem with the massless drives primarily is a time constraint that travel has, to make the point, if you are on the moon and you need to orbit there are no intrinsic electric propulsion system, extrinsic maybe. If you are in GSO transporting underwear and two-by-fours  to Martian GSO, its not a problem, but to transfer from LEO to proxima centauri is the same problem as launching from the moon, except that for the moon chemical propulsion would work, for proxima Centauri your acceleration to 100 years and deceleration another 100 years and of course nobody lived. To utilize Cannae for manned space flight would require many things that would be extremely difficult to do or currently impossible even if there was unlimited power to do those things. Unllimited power, as we see above, limits itself.

 

 

 

 

 

 

[Mayer]

Fusion power is not unlimited energy, it's constrained by fuel and efficiency(how much D, T or He³ actually undergoes fusion). Even a antimatter-matter annihilator, the ultimate mass to energy conversion, would not be unlimited energy.

It's a controlled reaction, you have a specific output. ITER is aiming for 500MW. It's obviously not massless. I agree that cooling will be a challenging problem in space, but so is engineering a form of fusion propulsion in which most heat will be expelled. Your example of a spacecraft which can only operate fusion in small pushes could still benefit from it, because the reactor (1GW) is so large, it will probably have a positive energy output.

I don't quite understand the dilemma in the last paragraph, interstellar voyages are long no matter what. But travelling at 10% of speed of light can cut the travel time a lot. Space travel within the solar system will multiply when more payload can be moved cheaper, enabling exploitation of space resources, higher velocities may be interesting for passenger lines or intercepting a fast object.

[PB666]

2 hours ago, Mayer said:

Fusion power is not unlimited energy, it's constrained by fuel and efficiency(how much D, T or He³ actually undergoes fusion). Even a antimatter-matter annihilator, the ultimate mass to energy conversion, would not be unlimited energy.

It's a controlled reaction, you have a specific output. ITER is aiming for 500MW. It's obviously not massless. I agree that cooling will be a challenging problem in space, but so is engineering a form of fusion propulsion in which most heat will be expelled. Your example of a spacecraft which can only operate fusion in small pushes could still benefit from it, because the reactor (1GW) is so large, it will probably have a positive energy output.

I don't quite understand the dilemma in the last paragraph, interstellar voyages are long no matter what. But travelling at 10% of speed of light can cut the travel time a lot. Space travel within the solar system will multiply when more payload can be moved cheaper, enabling exploitation of space resources, higher velocities may be interesting for passenger lines or intercepting a fast object.

When you get beyond the capacity to harness the power, then power is unlimited, for all intents and power. As for ITER, no, look at Germany Wendlestein. ITER is a big political boondoggle.

My point is that the weight of fusion and the inability to dissipate heat (plus the seed energy for the reactor) may ultimately prevent its use for a while.

Fusion will not get you to 0.1 of speed of light except on paper, see threads from a couple of years ago on fusion, we pretty much covered all the bases.

I could see a fusion design in which ships are couple together in a wide array like a snowflake with the reactor at its core and each branch and subbranch taking a liquid energy converting to power and radiating the waste and going close places like Mars or asteroid belt object. For mercury the sun will suffice to get your there.

This is a 10th scale version, prototype galaxy ship. Check the dV. This added weight for shielding (need at 0.001c and higher, cells for fusion reactors, space for ION drives, the stats are real. A full scale version would hold 2400 individuals because after all we are talking about a generational ship. 0.01c means 444 years to alpha centuari. Above 0.01 c your acceleration is pityful because the ISP used requires acceleration to relativisitic speeds to gain the mass. It took some time to realize there is an acute marginal utility of gain once V_exhaust is above 0.1 C because your waste products are more than exhaust weight. A full sized ship would probably overheat because of inadequate radiant heating.

IIRC maximally you get 4% of the fusion reaction as energy gives a preferred exhaust velocity of something like 80 Mm per second. If the fuel is one third of the weight (remember its got to be liquified hydrogen, very difficult to store in a ship where you are trying to dissipate alot of heat gives a total dV of 22,000,000 m/s for start-stop ip mission it was 0.04c. There are a ton of tradeoffs with fusion powered interstellar, ultimately I decided it would be unlikely that any fusion ship would push higher than 0.005c. The major problem we discussed in the group was risk avoidance (a speck of dust is a nuclear warhead at near light speeds). The shape above is designed to deflect most of the impact energies. The other problem was providing the crew a lifelong livable ship, which means the reactors at the back could be discharged in the even of an emergency (much discussion of fusion instability). The reason for the lower ISP is that power had to be diverted to other ship systems such as life support, food production, waste recycling, cooling. Every bit of power used for these reduces the power that can be devoted to the very hot fuel you needed to get rid of and fast. So pretty much you don't get 0.1c  > members of the group concluded that if 0.005c was as high as could be obtained then interstellar travel would never be possible. Their opinion not mine, but you see what I mean by unlimited power, its limited, power is its own limitation.

[Mayer]

ITER is a half-way finished Tokamak design, the international community is working together on this one. What is so bad about it?

Wendelstein 7-X is just a test reactor in the Stellerator design which will not usable as a power plant because it's too small. The Stellerator design has the benefit of preventing particle instability, but it's still poorly understood. The ITER team has the tools to predict particle instability.

"When you get beyond the capacity to harness the power, then power is unlimited"

Conservation of energy applies. If you have a whole lot of energy and don't do anything useful with it, it has to go somewhere like heating up your ship. Unlimited energy seems quite impossible, like a perpetuum mobile or the massless drive without propellant.

"Above 0.01 c your acceleration is pityful"

Well, with non-nuclear ships like the laser-sail acceleration is pitiful from the start. They can nonetheless go far beyond 0.1c.

"because the ISP used requires acceleration to relativisitic speeds to gain the mass."

How is that relativistic? Relativity comes into play when approaching speed of light. You gain 10% more mass when travelling 0.5c and there it goes up. Meaning you need more thrust until acceleration becomes impossible at 0.99...c

"It took some time to realize there is an acute marginal utility of gain once V_exhaust is above 0.1 C because your waste products are more than exhaust weight. "

The fuel has to be accelerated too and there are waste products, because the reaction is inefficient. Which is why i said 0.1c as maximum, but Project Daedalus could even go 0.12c.

" (a speck of dust is a nuclear warhead at near light speeds). "

With this reasoning you can discard interstellar travel altogether. The interstellar medium is quite empty, cosmic dust is primarily microscopic. You are talking about an event which is highly unlikely to occur and even then it might be possible to divert or suck these particles up. Asteroid 1I/2017 U1 came from interstellar space with slow speed, meaning it had ample time(thousands of years) to crash with fast objects but it survived, proving that interstellar travel is possible.

"Every bit of power used for these reduces the power that can be devoted to the very hot fuel you needed to get rid of and fast"

The very hot fuel contains power by itself, you can use a fraction for the ship's systems and still move the ship forward when getting rid of the fuel, thanks to Newton's Third Law of Motion.

 

[Green Baron]

On 7.12.2017 at 7:23 PM, PB666 said:

Silicon starts becoming plastic at around 600'F and melts well over 1000'F, ...

"Well over" results to 2600°F for dry silicon (if you mean the element Si with atomic number 14) ....

Edited December 9, 2017 by Green Baron

[PB666]

8 hours ago, Mayer said:

Well, with non-nuclear ships like the laser-sail acceleration is pitiful from the start. They can nonetheless go far beyond 0.1c.

The problem is that you are ignoring the fact they need a power supply, and a fusion reactor is incapable of producing that level of ship. The only power supply so far dreamed-up is a black-hole drive, which falls in the realm of science fantasy.

8 hours ago, Mayer said:

How is that relativistic? Relativity comes into play when approaching speed of light. You gain 10% more mass when travelling 0.5c and there it goes up. Meaning you need more thrust until acceleration becomes impossible at 0.99...c

We have been through this exact conversation 2 years ago. This comes under that category of belief that somehow you can wave energy into existence, stabilize it and transform it. As I said previously, talking about power supplies which don't exist and that you couldn't cool even if they did exist does not aid the conversation. Here is the sense of reality, to get a particle to relativistic speeds, requires a type of accelerator that is much more powerful than ION drive. Consider how much heat is wasted per proton to reach 0.8c, sure it gains mass, but you are no longer talking about plates 0.1m thick, you are talking about extremely massive structures and hefty arrays of supercooled magnets.

8 hours ago, Mayer said:

The fuel has to be accelerated too and there are waste products, because the reaction is inefficient. Which is why i said 0.1c as maximum, but Project Daedalus could even go 0.12c.

Daedalus again. " Project Daedalus was a study conducted between 1973 and 1978 by the British Interplanetary Society "-wikipedia. Science fantasy. You claim that Wendelstein 7X 'isn't' a viable fusion reactor, the Daedalus pulse fusion rocket design is a paper design, that its. Its a handwaving argument on how to initiate and contain the reaction, nothing more.

Quote

The current apex of inertial confinement fusion.

"Newly discovered schemes to efficiently frequency triple high intensity laser light discovered at the Laboratory for Laser Energetics in 1980 enabled this method of target irradiation to be experimented with in the 24 beam OMEGA laser and the NOVETTE laser, which was followed by the Nova laser design with 10 times the energy of Shiva, the first design with the specific goal of reaching ignition conditions.

Nova also failed in its goal of achieving ignition, this time due to severe variation in laser intensity in its beams (and differences in intensity between beams) caused by filamentation which resulted in large non-uniformity in irradiation smoothness at the target and asymmetric implosion. The techniques pioneered earlier could not address these new issues." . . . . .

" As of October 7, 2013, the facility is understood to have achieved an important milestone towards commercialization of fusion, namely, for the first time a fuel capsule gave off more energy than was applied to it.^[31] This is still a long way from satisfying the Lawson criterion, but is a major step forward.^[2]"

" In particular, the laser systems need to be able to run at high operating frequencies, perhaps one to ten times a second. Most of the laser systems mentioned in this article have trouble operating even as much as once a day. Parts of the HiPER budget are dedicated to research in this direction as well."  -wikipedia- Inertial confinement fusion.

So at the time Daedalus was proposed the inertial confinement was to be done by electron beams, this has apparently failed. So that now everyone appears to be using lasers, but they can only be powered up at a rate of 0.0001 not the 10 s^-1.  The bottom line is to cause inertial confinement fusion you have to have enough power to initiate the reaction, which as it turns out is very power intensive. Also, the expulsion of waste in the nozzle of a space ship provides no means of recovering that power. I should also note that if ICF worked tomorrow, the raw materials would not be cost effective power production in the commercial market. It is considered one of the more power inefficient fusion methodologies.

8 hours ago, Mayer said:

cosmic dust is primarily microscopic

All it takes is one that isn't. The ships protections are not against things that don't exist. If you imagine a ship whose cross-sectional area is say 10,000 meters and you are traveling to a star 10 ly away. 1E17 then you are covering a space that has a volume of 1E21 in size. If we were to compare this to our solar system it would represent a sphere the volume of the Earth. If you were to then ask the question, scouring the areas outside the solar system what is the likelihood of finding a granule in Earth sized volume of space.   Im not even convinced that the gas encountered by the system in the course of travel would make radiant heating more problematic that my 2 year old calculations.

8 hours ago, Mayer said:

The very hot fuel contains power by itself, you can use a fraction for the ship's systems and still move the ship forward when getting rid of the fuel, thanks to Newton's Third Law of Motion.

But that is wasteful, that which you do need or want on the ship is best accelerated off the ship , if you just dump it, and then you use the energy to pulse light, you have wasted about over 90% of the thrust you could have generated. Oh, and I would like to see the expression on NASA director's face when they are directed to launch a working version of ITER into space. "Uh, Mr. President . . .we don't have " "Well how long to dev . . . . ""15 years"

Edited December 9, 2017 by PB666

[PB666]

4 hours ago, Green Baron said:

"Well over" results to 2600°F for dry silicon (if you mean the element Si with atomic number 14) ....

That was a typo, the natural molecular silicon is almost always found in silicates. I work with borosilicate glass alot and I can assure you I never heated it to 2600'F.
I think you are familiar with amorphous silicon.

[Green Baron]

11 minutes ago, PB666 said:

That was a typo, the natural molecular silicon is almost always found in silicates. I work with borosilicate glass alot and I can assure you I never heated it to 2600'F.

Though it has a higher melting point than Si ?

 

Silica: if there is water in the mineral structure then the melting point is much lower, though not as low as 1000°F. That enables anatexis and thus some forms of volcanism, for example over subduction zones or in back arcs. Or else the temperatures had to be much higher.
 

 

Edited December 9, 2017 by Green Baron

[PB666]

57 minutes ago, Green Baron said:

Though it has a higher melting point than Si ?

 

Silica: if there is water in the mineral structure then the melting point is much lower, though not as low as 1000°F. That enables anatexis and thus some forms of volcanism, for example over subduction zones or in back arcs. Or else the temperatures had to be much higher.
 

 

Amorphous solids do not behave like crystals. Think of glass like glycerol. If you cool it to a low enough temperature it behaves like a solid, increase the temperature a few degrees and it viscocity drops, heat it up enough and it flows. Glass is pretty much the same, before it reaches the point were it glowing red you can flex it; heat to red hot and its often too plastic to mold.

Edited December 9, 2017 by PB666

[Mayer]

10 hours ago, PB666 said:

The problem is that you are ignoring the fact they need a power supply, and a fusion reactor is incapable of producing that level of ship.

About what levels of power supply are we talking about? A fusion reactor is by all means a power generator.

10 hours ago, PB666 said:

This comes under that category of belief that somehow you can wave energy into existence, stabilize it and transform it. As I said previously, talking about power supplies which don't exist and that you couldn't cool even if they did exist does not aid the conversation.

Fusion power doesn't exist? The sun begs to differ

Conservation of Energy! You never wave energy into existence, fusion power is converting the binding force of nuclei.

10 hours ago, PB666 said:

Daedalus again. " Project Daedalus was a study conducted between 1973 and 1978 by the British Interplanetary Society "-wikipedia. Science fantasy. You claim that Wendelstein 7X 'isn't' a viable fusion reactor, the Daedalus pulse fusion rocket design is a paper design, that its. Its a handwaving argument on how to initiate and contain the reaction, nothing more.

That is fiction.., that is utopian.., that doesn't mean anything. The same buzzwords with which rockets and airplanes were disregarded in the past. You need some solid arguments for the infeasibility of the concept.

I for one trust the British Interplanetary Society(if their name is supposed to be funny, remember what a similar sounding Society for Space Travel gave us) and NASA who had a similar idea with Project Longshot.

10 hours ago, PB666 said:

The bottom line is to cause inertial confinement fusion you have to have enough power to initiate the reaction, which as it turns out is very power intensive.

Every form of nuclear fusion is hard to initiate because you have to overcome the Coulomb barrier. That's why we have thermonuclear bombs and large plasma containers. Small fusion pellets would be a big step forward but the technology is still in its infancy.

13 hours ago, PB666 said:

Also, the expulsion of waste in the nozzle of a space ship provides no means of recovering that power. I should also note that if ICF worked tomorrow, the raw materials would not be cost effective power production in the commercial market.

If nozzles are so wasteful, why are we stll using rocket thrusters? The principle behind utilizing a chemical explosion or a nuclear equivalent is the same.

Nothing in space-travel is cost-effective or commercial at the moment, it's a money sink.

10 hours ago, PB666 said:

All it takes is one that isn't. The ships protections are not against things that don't exist. If you imagine a ship whose cross-sectional area is say 10,000 meters and you are traveling to a star 10 ly away. 1E17 then you are covering a space that has a volume of 1E21 in size. If we were to compare this to our solar system it would represent a sphere the volume of the Earth. If you were to then ask the question, scouring the areas outside the solar system what is the likelihood of finding a granule in Earth sized volume of space.

The chance of colliding with a larger object is ridiculously low and you can't compare interstellar space with our solar system because the sun attracts a lot of junk.

11 hours ago, PB666 said:

Oh, and I would like to see the expression on NASA director's face when they are directed to launch a working version of ITER into space. "Uh, Mr. President . . .we don't have " "Well how long to dev . . . . ""15 years"

ITER costs around $24 billion and weights 23,000 tonnes. In the best case, it costs $10,000 to get one pound into LEO. ITER's ~50.7million pounds would cost $507 billion. So it's a 530 billon dollar project, not including resupply missions, maintenance and space work hours. NASA's annual budget is $19.5 billion, you have to subtract $3 billion for the ISS, if they didn't spend it on anything else, they'd have 247.5 billion dollar in 15 years which is less than half.

The NASA director is obviously lying, playing the stupid yes man.

[wumpus]

On 12/8/2017 at 10:56 PM, PB666 said:

Fusion will not get you to 0.1 of speed of light except on paper, see threads from a couple of years ago on fusion, we pretty much covered all the bases.

Is the argument against 0.1c in an [H-bomb based] Orion that you would need 100,000+ tons of dueterium (assembled into H-bombs, natch)?  Because that's one means of harnessing fusion that is ready to go (assuming are either willing to build and take off from Antarctica or build something carrier-sized in space).  If the rocket equation starts to creep up on you, that will be a problem with Orions, as I expect the fuel gets pretty expensive.

It will certainly do the "Mars in 39 days" without issue.  Just don't try to fight the rocket equation.

[Nuke]

iter is why fusion is always 20 years away. thats just how long it takes to build a massive tokamak. so every time a physicist says ' we need a bigger machine' add 20 years to the time table. its also why it will never yeild a fusion reactor that is commercially viable even if demo makes breakeven. it will also never yeild a spaceworthy reactor because tokamaks are massive machines. 'its good science'  but thats all it will be. 

the real breakthroughs are going to come out of the smaller machines. they lend themselves to rapid iteration, many are compatible with direct conversion schemes, and are all small and light enough for spacecraft use. the same makes them viable for commercial application. those are what you want to pay attention to. my money is on polywell and they are giving 3 years instead of 20.