Imagining a Kerbal Future: What Would the Future of Kerbals Look Like? (Chapter XLIII: Epilogue)

[MatterBeam]

@SaturnianBlue:

Good write-up so far.

The main advantage of a mass driver is that you can launch or deliver payloads without attaching rocket engines, propellant tanks, propellant, guidances systems ect. to them. The initial investment is huge, but you make it up by saving the difference between bare rock and a miniature, self-sufficient spaceship in each delivery. Huge amounts of energy are required, yes, but its just a matter of accumulating it. Flywheels do a good job, much better than batteries or supercapacitors. As you've noted, producing electricity is cheap in a world with fusion reactors.

For depicting it in KSP, I'd use a small number of welded parts and just apply a speed boost through HyperEdit to simulate a launch.

Space elevators on Kerbin can be made of Zylon or even plain regular Kevlar. These are quite cheap for their weight and strength. Climbers will have to work like trains - the main limitation is the resistance between wheels and track. Going fast is dangerous because there's not a lot to dampen vibrations like with ground trains. Maglevs will work but they have a very high mass per meter. A 2868km climb at fast railway speeds (300km/h) will take over 9 days. 

Skyhooks on Earth can reduce the deltaV to orbit from 9.5km/s to less than 6km/s. There's a concept called a staged rotating tether, where the spinning tethers are mounted on the tips of a larger rotating tether. At the bottom of the two stages, the tip velocity adds up. For example, if each tether can only achieve 2.5km/s from the characteristic velocity of Zylon, then two stages can achieve 5km/s. This allows for the use of cheaper materials than carbon nanotubes. Watch out for the tethers hitting each other when they pass by!

Representing skyhooks in KSP is going to be very difficult due to the limitations of the physics engine. I think the absolute maximum distance where two parts can interact with each other is 22.5 km. 

[SaturnianBlue]

10 hours ago, MatterBeam said:

@SaturnianBlue:

Good write-up so far.

The main advantage of a mass driver is that you can launch or deliver payloads without attaching rocket engines, propellant tanks, propellant, guidances systems ect. to them. The initial investment is huge, but you make it up by saving the difference between bare rock and a miniature, self-sufficient spaceship in each delivery. Huge amounts of energy are required, yes, but its just a matter of accumulating it. Flywheels do a good job, much better than batteries or supercapacitors. As you've noted, producing electricity is cheap in a world with fusion reactors.

For depicting it in KSP, I'd use a small number of welded parts and just apply a speed boost through HyperEdit to simulate a launch.

Space elevators on Kerbin can be made of Zylon or even plain regular Kevlar. These are quite cheap for their weight and strength. Climbers will have to work like trains - the main limitation is the resistance between wheels and track. Going fast is dangerous because there's not a lot to dampen vibrations like with ground trains. Maglevs will work but they have a very high mass per meter. A 2868km climb at fast railway speeds (300km/h) will take over 9 days. 

Skyhooks on Earth can reduce the deltaV to orbit from 9.5km/s to less than 6km/s. There's a concept called a staged rotating tether, where the spinning tethers are mounted on the tips of a larger rotating tether. At the bottom of the two stages, the tip velocity adds up. For example, if each tether can only achieve 2.5km/s from the characteristic velocity of Zylon, then two stages can achieve 5km/s. This allows for the use of cheaper materials than carbon nanotubes. Watch out for the tethers hitting each other when they pass by!

Representing skyhooks in KSP is going to be very difficult due to the limitations of the physics engine. I think the absolute maximum distance where two parts can interact with each other is 22.5 km. 

 Didn't think of hyper edit—I don't use that function often, but it should work, and I should try it out.

As for space elevators, wouldn't it take more like 9 hours at 300km/h? That's about a day and a half in Kerbin days, which isn't too bad.

I don't think I've heard of the staged rotating tether, but it should work for Kerbin, and would be even more effective since orbital velocity there is so much lower than for Earth.

There are mods that extend the interaction range a lot, but the limitations of the VAB's editor is hard enough.

[MatterBeam]

2 hours ago, SaturnianBlue said:

 Didn't think of hyper edit—I don't use that function often, but it should work, and I should try it out.

As for space elevators, wouldn't it take more like 9 hours at 300km/h? That's about a day and a half in Kerbin days, which isn't too bad.

I don't think I've heard of the staged rotating tether, but it should work for Kerbin, and would be even more effective since orbital velocity there is so much lower than for Earth.

There are mods that extend the interaction range a lot, but the limitations of the VAB's editor is hard enough.

My mistake on the hours/days. 

Kerbin's orbital velocity is so low that you don't need staged tethers. 

Try hangar extender mod for VAB.

[SaturnianBlue]

Just now, MatterBeam said:

My mistake on the hours/days. 

Kerbin's orbital velocity is so low that you don't need staged tethers. 

Try hangar extender mod for VAB.

I do use the hanger extender mod, but eventually the nodes for moving parts around just disappears at a certain distance.

[MatterBeam]

16 minutes ago, SaturnianBlue said:

I do use the hanger extender mod, but eventually the nodes for moving parts around just disappears at a certain distance.

I'll see if the Hangar Extender's limits can be increased. Players have build monorails all the way from KSC to the island airport as single objects, so there must be a solution.

[SaturnianBlue]

A question for readers: what topics would you like to see be covered in this story? Keep in mind that I generally want to cover topics as applied to the KSP setting, since certain topics are made somewhat redundant by other (and admittedly better) sites.

Edited September 4, 2017 by SaturnianBlue

[MatterBeam]

1 hour ago, SaturnianBlue said:

A question for readers: what topics would you like to see be covered in this story? Keep in mind that I generally want to cover topics as applied to the KSP setting, since certain topics are made somewhat redundant by other (and admittedly better) sites.

Hard to say. The limits of the KSP engine are currently your biggest obstacle to presenting fascinating technologies such as space elevators and aerovators. 

Perhaps you could start on that turn-based model-representation game?

[SaturnianBlue]

26 minutes ago, MatterBeam said:

Hard to say. The limits of the KSP engine are currently your biggest obstacle to presenting fascinating technologies such as space elevators and aerovators. 

Perhaps you could start on that turn-based model-representation game?

Good idea, I've been thinking about a space warfare series, and I could probably write a whole chapter for that. Before I start on that though, I've been thinking about a dedicated chapter for designing a ship.

[Skylon]

Edit: Ignore the below, I hadn't read your most recent post. Brilliant as always, by the way

If you are in need of a mass driver, there's always this mod If you don't like the modelling or texturing you could always cover it up with panels 

Edited September 5, 2017 by Skylon

[SaturnianBlue]

Non-Rocket Spacelaunch—Part Two

For now, I conclude this chapter on non-rocket space launches, which covers launch loops and orbital rings.

Launch Loop

How It Works

    The loop in the name comes from how the structure runs in the upper atmosphere, before looping around and moving along that same path in reverse, before looping back. When the structure is deactivated, it lies on the ocean, which means that it can be assembled there, too. This loop is mere centimeters in diameter, with an iron tube known as a rotor, which moves at over orbital velocity, surrounded by the sheath, and separated by a vacuum. The rotor moves at a speed higher than the normal orbital velocity, so it begins to rise as it is sped up, supporting the structure’s weight. At a certain height, the stream is deflected by anchors to travel parallel to the surface.

    There are two stations on both ends of the elevated section, and payloads are brought up on a cable to the one on the west side. The payload is then accelerated by taking momentum from the rotor to orbital velocity, where it is then released or it runs to an even higher speed. Each loop can launch dozens of vehicles each hour. The launch loop can also be used to land vessels, and the kinetic energy can be used to power a launch.

Disadvantages

    At full power, the loop would be carrying a tremendous amount of energy. However, a catastrophic failure would likely only damage part of the loop, due to its sheer size. Since the structure is built over an ocean, falling portions of the launch loop would be unlikely to cause serious damage, and parachutes could lessen the effects.

Uses

    The launch loop is best used for atmospheric worlds, where one must get over the atmosphere to reach orbit. This makes it useful on Kerbin, and especially Eve, since its high gravity makes tensile structures like space elevators more difficult to build, and launch loops in the gas giants will only need to elevate the endpoints, while the active support the rotor produces elevates the upper portion. Another benefit is the small diameter of the loop, making the structure light, which is very important for the gas giants, where one must resort to vacuum balloons. A variant of the launch loop, the power loop, can be used to store energy.

How Can It Be Achieved In KSP?

    The launch loop would probably be best depicted by drawing or just describing it, but perhaps you could create segments of the track, and show only those in the screenshots taken. That said, the launch loop would probably be impossible to see, except for possibly the station. It is easy to portray what happens after taking off the launch loop—just use hyperedit to boost the ship to the ideal velocity. Many vessels may use a rocket motor at the apoapsis to raise the ship’s altitude, so at least that can be portrayed well.

Orbital Rings

How It Works

    A metal ring is built around the planet, which can be built at any inclination. If a current runs through the material, it is possible to build around it, and that structure will remain stationary relative to the ground. However, this means more mass is added, with no change in momentum. To compensate, the ring is spun faster than orbital velocity. To allow a connection to the surface and to keep the ring stable, we can build cables out of Kevlar or Zylon, which can be used to bring cargo and people up. These cables can also connect directly to cities, and allow for quick commutes between distant cities, using maglevs on the ring to get to the other side of the world in minutes. The circular nature of the ring allows speed to be built up slowly and steadily, as a ship makes its way around the ring. Even though the ring is not straight, its large turning radius makes certain forces acting on an accelerating vehicle quite low.

Orbital rings can be elliptical as well.

Disadvantages

Built like a skyscraper block.

    Though such a ring could probably be built around Kerbin with “modern” technology, there simply isn’t the demand to build such a thing. Additionally, gathering the resources for the construction of the ring will be difficult, and a robust mining industry on the Mun will have to exist, since bringing up resources from Kerbin or any major planet would be difficult, even with the construction of launch loops and other systems—the sheer volume of resources that will be sent from the Mun will outweigh that.

    

In the case of a failure, the orbital ring would fall, but parachutes would be used to slow it down. As for the spinning sections, they would likely shoot outwards, due to its speed.

Uses

  The orbital ring doesn’t just make space travel cheap like an airplane ticket—it would probably like a rather short train ride in cost. Not only would it open up day long trips to space possible for just about anyone, it allows them to get to anywhere near the path of the ring in little time, and especially large versions allow for massive amounts of freight to move around as well. Perhaps they would usher in a final stage in globalization, with millions commuting on them to work, everyday. When applied to other worlds, we can see that it allows workers to live in spinning orbital habitats, and they will only have to experience low gravity during work, greatly reducing the effects of prolonged exposure to microgravity.

    Multiple rings can be built outwards from Kerbin, connected by tethers, allowing a direct connection to Kerbostationary orbit, and even the Mun.

    An extreme use of the orbital ring would be to create a huge strip above the planet, and use it as living space in a concept known as a supramundane planet, which could allow mass settlement above a gas giant.

How Can It Be Achieved In KSP?

3,800 kilometers of this?!

    Again, it is very difficult to actually portray the entire thing in-game. The fact is, it is much simpler to create sections of the ring—besides, by the time you can look at the entire ring, it would likely be barely visible, or drawing a few lines may be all that is necessary. Unfortunately, the section of the orbital ring portrayed would have to be stationary relative to the surface, which is clearly unsustainable, and even if you could build a ring around Kerbin or even GIlly, who knows how it may react, especially since the physics behind a real orbital ring aren’t simulated in KSP.

End of Chapter XXII

Thanks for Reading!

Next: Ship Design

 

[SaturnianBlue]

@MatterBeam For the next chapter, I've been working on a interplanetary passenger vessel. The propulsion is a tokamak drive (the same one from the fusion propulsion chapter). What would be the ideal electrical generator for that variety of rocket? 

Edited September 8, 2017 by SaturnianBlue

[MatterBeam]

Nice write-up as always. Loving the artwork!

A few notes:
-Floating in gas giants doesn't necessarily require vacuum balloons. Hot hydrogen works well enough and would allow for equalizing the pressure between the inside and outside of the balloon, allowing for vastly thinner envelope materials. 

-Personally, I am skeptical of Lofstrom loops. They are massive moving structures requiring constant upkeep and expensive hardware running at high temperatures throughout. Every single aspect is risky, costly or both. A space fountain at least is much smaller, and Robert L. Forward's suggested modification is even better: shoot the mass stream straight upwards and have spaceships ride them. Vacuum tubes at the bottom protect them from too much drag, and the stream is deflected downwards at the top. My own modification would be not to bother at all with a physical structure at the top. Just angle the stream to 45 degrees through a vacuum tube 10km tall and 10 long and you can have spaceships just ride the stream to a large fraction of orbital velocity. I'll write up a 'stream rider launch system' blog post soon. 

-Orbital rings can have a spinning inner section and a stationary external hull. The hull can be connected to the ground with towers. More importantly, you can portray the immobile exterior of the ring around Kerbin. 

For the interplanetary rocket:

A tokamak is a closed 'fusion bottle'. The heat of the fusion reaction must escape somehow. Tokamak designs have the heat be absorbed by a high-temperature coolant loop, run through a heat exchanger, and into a coolant loop of containing a pressurized fluid just above boiling point. The latter fluid is allowed to boil and expand through a turbine for electricity. It is the electricity which is then used to power the rocket engine. So basically, the tokamak is you big electricity generator and the rocket engine is how you use the electricity. Alternatives include the use of thermocouples moving heat from the tokamak wall to the radiators, or a magnetohydrodynamic generator that bleeds off plasma from the reactor. 

[Kosmonaut]

I made a concept for an interstellar vessel for eight, recently, and within the next few months, I will be engineering it for school. What I did, is I had a massive Tandem-Mirror Nuclear Fusion Engine using Helium-3 and Deuterium, which can be taken from the Moon. That would do an initial, massive burn, and accelerate the ship to around 0.2c. Then, there would be a large array of Ion Engines, which would burn for the duration of the trip, accelerating up to the 0.75 point in the trip, before it turns around, and starts to decelerate. The rest of the deceleration could be done using the Fusion Engine, Aerobraking, and Gravity Assists.

It's a low-tech, and relatively cheap way of doing it.

You could also consider using the Ion Engines coupled with an Antimatter Engine, or the Tokomak Engine

[SaturnianBlue]

7 hours ago, MatterBeam said:

Nice write-up as always. Loving the artwork!

A few notes:
-Floating in gas giants doesn't necessarily require vacuum balloons. Hot hydrogen works well enough and would allow for equalizing the pressure between the inside and outside of the balloon, allowing for vastly thinner envelope materials. 

-Personally, I am skeptical of Lofstrom loops. They are massive moving structures requiring constant upkeep and expensive hardware running at high temperatures throughout. Every single aspect is risky, costly or both. A space fountain at least is much smaller, and Robert L. Forward's suggested modification is even better: shoot the mass stream straight upwards and have spaceships ride them. Vacuum tubes at the bottom protect them from too much drag, and the stream is deflected downwards at the top. My own modification would be not to bother at all with a physical structure at the top. Just angle the stream to 45 degrees through a vacuum tube 10km tall and 10 long and you can have spaceships just ride the stream to a large fraction of orbital velocity. I'll write up a 'stream rider launch system' blog post soon. 

-Orbital rings can have a spinning inner section and a stationary external hull. The hull can be connected to the ground with towers. More importantly, you can portray the immobile exterior of the ring around Kerbin. 

For the interplanetary rocket:

A tokamak is a closed 'fusion bottle'. The heat of the fusion reaction must escape somehow. Tokamak designs have the heat be absorbed by a high-temperature coolant loop, run through a heat exchanger, and into a coolant loop of containing a pressurized fluid just above boiling point. The latter fluid is allowed to boil and expand through a turbine for electricity. It is the electricity which is then used to power the rocket engine. So basically, the tokamak is you big electricity generator and the rocket engine is how you use the electricity. Alternatives include the use of thermocouples moving heat from the tokamak wall to the radiators, or a magnetohydrodynamic generator that bleeds off plasma from the reactor. 

True—floating in  the gas giants doesn't require vacuum balloons, but hot air balloons don't produce much lift.

Lofstrom loops are supposed to be decently cheap—in the several billions of dollars, which would be even less on a Kerbal scale. Building a floating gigawatt power station might be a bigger concern, especially without fusion. I'm a bit curious as to what you mean by space fountains being smaller—I haven't found too much on the topic, but a lot of sites imply having it going all the way to geostationary, though having ships ride mass streams is a rather simple idea that wouldn't require that tall a structure, admittedly. I'm excited to see the steam-rider post—I might even add it to this chapter.

With the tokamak I was imagining that the products would be heated directly by the fusion products, since I was imagining an afterburner fusion engine specifically. Also, what fusion should I use, considering I have D-D, D-T, T-T, He3 Catalyzed D-D, D-He3, D-Li6 available.

@Kosmonaut I don't think ion engines would work for that task—using a low thrust antimatter drive or just fusion would be more effective, and the fact that it doesn't have to use antimatter for the whole trip is helpful. If you've got a massive laser installation on the other end, you could use it to slow the vessel down.

Edited September 8, 2017 by SaturnianBlue

[Kosmonaut]

4 hours ago, SaturnianBlue said:

 

@Kosmonaut I don't think ion engines would work for that task—using a low thrust antimatter drive or just fusion would be more effective, and the fact that it doesn't have to use antimatter for the whole trip is helpful. If you've got a massive laser installation on the other end, you could use it to slow the vessel down.

Yes, I suppose- I was just going for cheap and easy exploration. The way I designed it was as the first starship, so it wasn't really meant for laser installations at the other end

https://imgur.com/a/xpnwh

A mission profile of the launch profile of the IISEV Madame de Pompadour

Edited September 9, 2017 by Kosmonaut

[SaturnianBlue]

Just now, Kosmonaut said:

Yes, I suppose- I was just going for cheap and easy exploration. The way I designed it was as the first starship, so it wasn't really meant for laser installations at the other end

https://imgur.com/a/xpnwh

A mission profile of the launch profile of the IIEV Madame de Pompadour

I suppose that name is a Doctor Who reference? 

Maybe you could use an Orion drive for an initial boost, before activating the fusion engine. The WIP Far Future Technologies mod has a Gasdynamic Mirror drive, which is a type of tandem mirror, so maybe you could use that for KSP.

[MatterBeam]

4 hours ago, Kosmonaut said:

I made a concept for an interstellar vessel for eight, recently, and within the next few months, I will be engineering it for school. What I did, is I had a massive Tandem-Mirror Nuclear Fusion Engine using Helium-3 and Deuterium, which can be taken from the Moon. That would do an initial, massive burn, and accelerate the ship to around 0.2c. Then, there would be a large array of Ion Engines, which would burn for the duration of the trip, accelerating up to the 0.75 point in the trip, before it turns around, and starts to decelerate. The rest of the deceleration could be done using the Fusion Engine, Aerobraking, and Gravity Assists.

It's a low-tech, and relatively cheap way of doing it.

You could also consider using the Ion Engines coupled with an Antimatter Engine, or the Tokomak Engine

Hi Kosmonaut!
I believe deuterium is plentiful in our oceans as an isotope of hydrogen contained in 'heavy water', and being able to produce tritium out of lithium industrially does favour D-T over D-He3 until we start mining the Moon. 20% of the speed of light is for interstellar travel! It would also need extremely high exhaust velocities, since you'd need a minimum deltaV of 120000km/s. Even with a mass ratio of 1000, the exhaust velocity is  17300km/s! D-He3 cannot produce something that fast! You'd have to be running a particle accelerator as an engine with terrible efficiency and absolutely pitiful thrust. 

Aerobraking, which can maybe shave off 10km/s from the trip if you use massive heat shields,  shouldn't even be in the same book at 0.2C. 

Maybe if you greatly reduced the speeds the spaceship reaches? At 500km/s, you're still cutting down the trip from Earth to Jupiter to two weeks...

3 hours ago, SaturnianBlue said:

True—floating in  the gas giants doesn't require vacuum balloons, but hot air balloons don't produce much lift.

Lofstrom loops are supposed to be decently cheap—in the several billions of dollars, which would be even less on a Kerbal scale. Building a floating gigawatt power station might be a bigger concern, especially without fusion. I'm a bit curious as to what you mean by space fountains being smaller—I haven't found too much on the topic, but a lot of sites imply having it going all the way to geostationary, though having ships ride mass streams is a rather simple idea that wouldn't require that tall a structure, admittedly. I'm excited to see the steam-rider post—I might even add it to this chapter.

With the tokamak I was imagining that the products would be heated directly by the fusion products, since I was imagining an afterburner fusion engine specifically. Also, what fusion should I use, considering I have D-D, D-T, T-T, He3 Catalyzed D-D, D-He3, D-Li6 available.

@Kosmonaut I don't think ion engines would work for that task—using a low thrust antimatter drive or just fusion would be more effective, and the fact that it doesn't have to use antimatter for the whole trip is helpful. If you've got a massive laser installation on the other end, you could use it to slow the vessel down.

The difference between the lift produced by a vacuum balloon and a hot hydrogen balloon is very very small, at least in the rarified atmosphere of a gas giant. Saturn has a gas density of 0.19kg/m^3. A vacuum balloon can lift 0.19kg per m^3 of balloon. A hot hydrogen balloon might be able to lift 0.15kg/m^3, approaching 0.19kg/m^3 as you increase the temperature. Very small difference!

A lofstrom loop has to cover thousands of kilometers of land with a 'danger, risk of falling accelerator' signs. People won't want to live under it or near it and it would cost a lot to build. A space fountain has a much smaller footprint... but that's not a big advantage in the long run, I agree. 
I doubt my stream-rider post will appear this month! I've got a lot of my plate and other subjects queued, so don't hold your breath

D-T fusion is the easiest and using a neutron-absorbing shell around the fusion products, either on the fuel pellets themselves or on the reactor walls, allows you to recover most of  the fusion energy. Proton-Boron11 is aneutronic and powerful, and you could deal with current ignition issues by using massive proton accelerators to bulldoze your way past any obstacle, but you'll have to deal with X-rays leaking and wasting a lot of the fusion energy.

Tokamak is a torus-shaped, closed reactor. Its a glorified coal boiler to provide heat for electrical generators. You could use the electricity to power and electric rocket. 
A fusion rocket is an open reaction chamber. Its a rocket engine with a very hot core and lots of propellant coming in through the top and out the bottom.

The designs are incompatible! One or the other. 

 

 
 

[Kosmonaut]

@MatterBeam an interesting point about the exhaust velocities- I hadn't thought of that.

However, the aerobraking would only be at the end of the journey, and it would decelerate towards the planet before hand. The amount of thermal energy released from slowing down from 0.2c to 2750 m/s would be incredible

Deuterium-Tritium is used in Hydrogen Bombs today, but H-3 would be more effective.

I was thinking that if I could magnetically accelerate the H-3 and Deuterium to incredible speeds with a 500 meter long engine, it may work. Would that be possible?

[SaturnianBlue]

17 minutes ago, MatterBeam said:

Hi Kosmonaut!
I believe deuterium is plentiful in our oceans as an isotope of hydrogen contained in 'heavy water', and being able to produce tritium out of lithium industrially does favour D-T over D-He3 until we start mining the Moon. 20% of the speed of light is for interstellar travel! It would also need extremely high exhaust velocities, since you'd need a minimum deltaV of 120000km/s. Even with a mass ratio of 1000, the exhaust velocity is  17300km/s! D-He3 cannot produce something that fast! You'd have to be running a particle accelerator as an engine with terrible efficiency and absolutely pitiful thrust. 

Aerobraking, which can maybe shave off 10km/s from the trip if you use massive heat shields,  shouldn't even be in the same book at 0.2C. 

Maybe if you greatly reduced the speeds the spaceship reaches? At 500km/s, you're still cutting down the trip from Earth to Jupiter to two weeks...

The difference between the lift produced by a vacuum balloon and a hot hydrogen balloon is very very small, at least in the rarified atmosphere of a gas giant. Saturn has a gas density of 0.19kg/m^3. A vacuum balloon can lift 0.19kg per m^3 of balloon. A hot hydrogen balloon might be able to lift 0.15kg/m^3, approaching 0.19kg/m^3 as you increase the temperature. Very small difference!

A lofstrom loop has to cover thousands of kilometers of land with a 'danger, risk of falling accelerator' signs. People won't want to live under it or near it and it would cost a lot to build. A space fountain has a much smaller footprint... but that's not a big advantage in the long run, I agree. 
I doubt my stream-rider post will appear this month! I've got a lot of my plate and other subjects queued, so don't hold your breath

D-T fusion is the easiest and using a neutron-absorbing shell around the fusion products, either on the fuel pellets themselves or on the reactor walls, allows you to recover most of  the fusion energy. Proton-Boron11 is aneutronic and powerful, and you could deal with current ignition issues by using massive proton accelerators to bulldoze your way past any obstacle, but you'll have to deal with X-rays leaking and wasting a lot of the fusion energy.

Tokamak is a torus-shaped, closed reactor. Its a glorified coal boiler to provide heat for electrical generators. You could use the electricity to power and electric rocket. 
A fusion rocket is an open reaction chamber. Its a rocket engine with a very hot core and lots of propellant coming in through the top and out the bottom.

The designs are incompatible! One or the other. 

 

 
 

That's a much smaller discrepancy than I thought.

That is why the Loftstrom loop is built over the ocean, yes? Besides, building it near land would favor certain areas/states over others, and the ocean is usually seen as being international, preventing such conflicts. It would make it a remote location and may require a floating runway capable of servicing passenger jets, but this shouldn't be a challenge compared to the loop itself. I'm fine with the stream-rider taking a while, I can always go back and edit the post later.

Is there anything on Deuterium-Lithium fusion? It appears to be aneutronic but I haven't read much on it. There isn't an option for boron fusion in the reactor i'm looking at, so I suppose Deuterium-Tritium is the easiest, but it does require a thick shadow shield, while D-He3 is expensive. If the D-Li fusion isn't effective, i'd imagine D-D fusion is the best, since there is no concern of half-lives, while the fuel is fairly common and cheap to use.

When I was thinking of the engine design, I was looking at the Discovery II concept and one of the engines from the fusion engine post I made a while ago. Perhaps I did a disservice by referring it as a "Tokamak", since spherical torus reactor would be more accurate. 

Edited September 9, 2017 by SaturnianBlue

[SaturnianBlue]

Nearly done with the next chapter—here's the ship that was built for it. 

[SaturnianBlue]

The Ship Design Process I

   In this next set of chapters, we’ll explore the steps to designing realistic, functional ships in KSP.

Setting

    The setting of where this ship is being designed is everything—it’ll determine the ship’s purpose, and it’s design. For this chapter, i’ll design just one ship—hopefully, you’ll be able to apply the steps to your own design. So let’s start!

    The Kerbals have spread out to the many planets of the Kerbol system, with millions settling the surface, the air, and space, with corporations and countries settling. Kerbals have yet to unlock the power of high-g, high delta-V fusion rockets, but perhaps soon...

Purpose

    Since I haven’t covered space warfare, yet (I can’t get BD Armory to really work, for one thing), this design will be a civilian one. By this point, most interplanetary freight is probably launched by mass drivers, and many likely take advantage of Hohmann transfer orbits—the supply of many resources is likely to remain consistent, barring major changes that would likely be anticipated. Perhaps a few products may require more gentle accelerations, such as electronics and especially complicated equipment, but these can simply use longer mass drivers, or freighters, which can afford to take a fairly slow route. So where does this leave us? Passenger ships. Most people travelling between the planets aren’t going to bother with traveling for hundreds of days—they would much rather prefer paying higher for a quicker trip. Though this is bound to take more propellant, it would save some mass on food and other various amenities. This ship should be flexible enough to travel different routes, according to demand.

    Let us put some requirements for this vessel.

        -Must be able to reach Jool in at least 75 days

        -Must have enough thrust to operate inside the planetary systems themselves

        -Carry at least 1000 passengers in comfortable condition

        -Avoid the use of particularly expensive materials

        -Modular capability, allowing a freight setup

Payload

    We will begin with the payload, as it is what the rest of the ship will be built around. The payload? 1000 passengers and whatever is needed to support them for an extended period of time. In order to find the needs of the passengers, I turn to the Kerbalism mod for help.

    For a 70 day trip, the water and food a kerbal requires adds up to around 300 kg. Considering this has to be multiplied by 1000, this means that the rations alone will be 300 tons. A more obscure factor is the volume required so that passengers don’t experience psychotic breaks. A NASA report suggests a minimum acceptable net habitable volume of 25 cubic meters per person, but because kerbals are smaller, I assume that they can afford to live in smaller quarters. Kerbalism suggests that the space available would be 40 cubic meters, but I reckon that to be much too inefficient—this isn’t a cruise ship, we’re just trying to get people to be where they need to be! Instead I go for around 14 cubic meters.

With Kerbalism, I find what it takes for the passengers to be comfortable, and how much tonnage would be required per kerbal. This was done with a small sample of 9 kerbals, since doing this on a scale of a thousand passengers is very time consuming. The result? Around 2.8 tons. I would imagine that due to the economies of scale, this would be significantly reduced when the amount of passengers is on the order of a thousand. Additionally, inflatable habitation space would significantly decrease this, but the same mods that add such habitats (MKS, Tokamak Industries) are the very same ones that cause the game to crash. Factoring that in, I therefore presume the tonnage will be closer to 2 tons. This gives us a result of around 2 kilotons.

Now for the volume. Since the volume is about 14m3 per person, we end up with 1000 times that. Of course, this ignores the used space, which is essentially everything else. Inflatable habitats would be even more helpful for boosting space, so theoretically the kerbals could have much more for less. To be on the safe side, I will assume that the used space will be as much as 50% of free space, since I’m not exactly sure how much space will be taken up. This leaves us with 21,000 m3 of space, or approximately a cube 28 meters on each side.

I know, it looks rather flimsy...

We will split the habitable space in two, as we are putting the passenger sections at the end of two arms of a centrifuge. Since a variety of passengers from many backgrounds are likely to ride on this ship, we will keep the spin gravity at 0.3 G, which should be tolerable for kerbals who lived on worlds like the Mun, while assuaging the effects of zero-G. While we want to reduce the nausea induced by the Coriolis effect, we also do not want the arms to be too long, since this would increase the mass, and force the ship to be longer, in order for the arms to stay in the shadow shield (I’ll explain that later). Passengers should be able to adapt to 2 RPM with no problem, and achieving that with 0.3 G gives us an arm radius of 70 meters. On the end of this, we will mount the habitation modules, which will be connected to each other by a long, pressurized tube running the entire length of the arms.

Propulsion

    What we are looking for in propulsion is something that can produce lots of thrust when necessary, but also capable of very high velocities, so the distant planet can be reached in a useful amount of time. Electric propulsion produces low thrust and fairly mediocre exhaust velocities when considering such a thing. A solid-core nuclear rocket produces a lot of thrust, but they have low exhaust velocities. Gas-core rockets provide a fair load of thrust, but they have a fairly low Isp. That leaves us with fusion. As the setting has noted, thrusters like the “Kerbstein” drive are still out of reach, further narrowing our best choices to the VISTA and the Tokamak.

    The VISTA engine produces excellent thrust, and an Isp of 15,678, which can be increased to 27144 in return for lower thrust. On the other hand, the Tokamak can produce decent thrust, but can adjust the Isp from around 12,000 to nearly a million in return for lower thrust. In terms of performance, the Tokamak is the better option, as is more flexible in terms of delta-V, and therefore the destination—a close destination can be reached quickly by increasing the thrust, while distant targets can take advantage of the higher exhaust velocity, all for similar amounts of fuel. Additionally, the VISTA performs best with Deuterium-Tritium fusion, which is the easiest to achieve, but also the one that produces the most neutron radiation.

  For a more exact, precise method of finding the best Isp, acceleration, and delta-V for a mission, I highly recommend this.

Keep in mind that I chose a rather arbitrary size for the reactor—we'll have to adjust that later...

    This passenger vessel will use liquid hydrogen—not only is it the only fuel usable with the magnetic nozzle part, it is the most efficient propellant available, something that is particularly valued on a vessel that needs to achieve as high a velocity as possible. The propellant is necessary for achieving the higher thrusts.

Electricity, Radiators, and Radiation Shielding

    The torus reactor that is utilized for propulsion can also be used for electricity generation. Electricity is provided with the help of a magnetohydrodynamic generator, which operate at high temperatures with no moving parts, and uses some of the plasma in the Tokamak and converts the heat into electricity.

    KSP-Interstellar allows various types of fusion to be used in this specific reactor, leaving us with a few options. Deuterium-Tritium is the easiest to achieve, but without the use of a neutron-absorbing shell (which I presume aren’t modelled in the mod), much of the fusion energy is wasted in the form of neutrons. Deuterium-He3 produces considerably less neutrons, but the amount will still necessitate the use of a shadow shield, and the rarity of Helium-3 makes this a less economical option, and limiting the routes of our vessel to just locations with considerable deposits of helium-3, or huge fusion reactors. Though Deuterium-Lithium fusion requires a very high temperature to occur, we will use it, as it produces the least amount of neutrons. It also produces the most thrust in-game, for the same mass reactor.

    A fusion reactor generates considerable waste heat that must be removed, or the spacecraft will heat up, melting the ship. With no way to conduct or convect heat in space, our vessel must use radiators to get rid of the waste heat. Due to the laws of thermodynamics, the radiator coolant cannot be hotter than the system itself, and certainly not as hot as the melting point of the material.

    While there are many types of radiators, the ones in-game appear to be solid radiators. In a nutshell, such radiators are small pipes that pump in hot coolant in and cooled coolant out, before returning back to the system they cool. Since fusion reactions take place at very high temperatures, we do not have to worry about the radiators being hotter than the thermal source.

An assortment of radiators.

    The radiators from KSP-Interstellar are either made of graphite, graphene, or titanium. Since the graphite/graphene radiators are capable of operating at a higher temperature, we will choose those. In-game, they can operate at temperatures as high as 3700 Kelvin. To be on the safe side, I will go with a radiator that operates at 3000 Kelvin. Despite the gigawatts of heat produced by the reactor, this ensures that the radiators do not have to be very large and heavy, which can be the result with some nuclear reactors (especially in Children of a Dead Earth…)

 

    The passengers on the vessel create a lot of heat, which must be radiated away at room temperature, requiring particularly large radiators despite the heat only being in the range of a few hundred kilowatts (an estimate I took from Children of a Dead Earth, though a Kerbal’s small size means less heat is generated compared to that of a human). Though this factor is not actually accounted for in-game, I managed to find the amount of radiators I would need by sticking on some “Blanket Photovoltaic Solar Power Receivers”, which generate about the amount of heat (630 KW) I was looking for. I then added enough radiators to drop the radiator temperature to about room temperature (294 K). Usually the weight of the radiators would be around 2 tons or so.

    Though fusion reactors located on the surface or in space stations can afford to heavily shield their reactors, this cannot be said of spacecraft, where each gram counts. “But,” you might say “then the crew will be exposed to the radiation, yes?”. That’s true, and this is where the shadow shield comes in. They stop the gamma and neutron radiation released from the reactor, particularly on the top side. This will not protect nearby vessels, but it does a good job of protecting the crew.

Despite the fusion type, we still need some radiator protection. The structural pylons mark the "shadow" created by the "shield" represented by an adapter.

    The radiators and the propellant tanks are angled to fit inside the shadow shield’s protective cone. Why? Exposure to neutron radiation can cause the structure to embrittle, seriously weakening the integrity of the ship. Another threat is neutron activation, where a neutron is absorbed by a harmless isotope and is mutated into a radioactive one. The crew will not be protected from the shadow shield from that danger.

    Another way we can lessen the danger of radiation will be by placing the propellant tank in between the reactor and the kerbals, since doing so basically puts more stuff in the way, which is basically how the shadow shield works, too.

Structure

    In order to help reduce the radiation exposure the payload (passengers) experience, they will be mounted at the front of the ship, significantly far away from the reactor. This also increases the diameter of where the shadow shield’s protection is effective, which will be especially useful later. This will require a long truss section, but a lightweight material like aluminum graphite/epoxy should provide the strength to support the vessel, while amassing a few tons. In-game, I will represent the truss with the KSP-I E truss, which is similarly light. 

 

Command

    There is little for a crew to do during the long interplanetary voyage, so it therefore makes sense to automate ship operations, perhaps by utilizing AI. The mass savings associated with this would be significant. However, there may still be a need for crew, in the form of flight attendants, in the case that robots and AI are still incapable of serving the functions of these jobs. For better or for worse, having a crew will probably best for a story, as kerbals will probably be cared for more than an AI.

Communication

Two for redundancy!

    Fairly straightforward. Since this vessel is meant for a variety of interplanetary destinations, the transmitter must have a high range, and with many kerbals onboard, data transmission must also be high. For those reasons, the vessel will include large communication dishes.

Control

    The powerful fusion engine onboard would provide significant thrust for gimballing, but operating the fusion engine near populated areas would place many in harms way, so we must seek alternative methods for control. Reaction wheels are a popular method of turning in stock, but they are considerably overpowered compared to their real-life counterparts. The monopropellant reaction control system is an alternative, but this requires the storage of another fuel, one that is very reactive. The best choice for maneuvering is likely a resistojet or an arcjet. Both use electrical power to heat a propellant, and because the fusion reactor produces a tremendous amount of electrical power, we can use some of it for this. I choose to use arcjets, since they can reach a high exhaust velocity. Both can use hydrogen, which is already used for the fusion rocket, negating the need for the storage of more fuels.

Docking Ports

This shot shows the docking port, the arc jets, the AI, and the antennas.

    This is probably required for this ship—I don’t see any good way the kerbals would get out of the ship, much less get in! Going with a sensible design, we will place the docking port right above the centrifugal arms, so passengers are not required to move very far, and can actually get out (KSP lets you put docking ports anywhere, even next to the engine). We will also place small docking ports on the propellant tanks, to allow tugs to push the vessel a significant distance away from the station.

After a few modifications, this is the finished result.

Next time, we’ll put the vessel into testing to find the shortfalls, and the typical operations of the ship.

Thanks for Reading!

Next: The Ship Design Process II

 

Edited September 27, 2017 by SaturnianBlue

[MatterBeam]

I'm looking forwards to more!

A few notes:

-Bare minimum human food requirements are 0.8kg of oxygen per day, alongside 0.6kg of food and up to 30kg of water. Both oxygen and water can be recycled to a very high efficiency, so all you really need to carry is 1 day's worth of oxygen, food and water, plus emergency reserves, plus recycling equipment (441kg/1.9kW) and luxury food. The 0.6kg figure is actually nearly pure sugar and/or fat and protein mix. Not very tasty! You'll want to bring along packaged and dried food for your guests. If kerbals only need half the supplies humans need, then I get a 0.3kg per kerbal per day of essential non-recyclable consumables, plus 220kg per kerbal of life support equipment, plus about 100kg for a safety margin against losses. That's a total of 352 tons for your 1000 crew. 

[Kosmonaut]

@MatterBeam That's not actually that much... it's amazing what science can do

@SaturnianBlue If you want to read through this report, it's a modern-day (so a bit in the past) concept that I did for school last year. However, it may help. I spent a good quarter year working on that thing (and ended up getting a 100%), so it's very refined word-wise, but there may be some info you want. 

https://docs.google.com/document/d/14wcTrGn4DNq0DCRU1ejzGKgtE5AJfCg539nl3jyfHco/edit?usp=sharing

[MatterBeam]

1 hour ago, Kosmonaut said:

@MatterBeam That's not actually that much... it's amazing what science can do

@SaturnianBlue If you want to read through this report, it's a modern-day (so a bit in the past) concept that I did for school last year. However, it may help. I spent a good quarter year working on that thing (and ended up getting a 100%), so it's very refined word-wise, but there may be some info you want. 

https://docs.google.com/document/d/14wcTrGn4DNq0DCRU1ejzGKgtE5AJfCg539nl3jyfHco/edit?usp=sharing

Those numbers are derived from NASA's Transhab project. 
https://www.nasa.gov/content/life-support-systems

[SaturnianBlue]

3 hours ago, Kosmonaut said:

@MatterBeam That's not actually that much... it's amazing what science can do

@SaturnianBlue If you want to read through this report, it's a modern-day (so a bit in the past) concept that I did for school last year. However, it may help. I spent a good quarter year working on that thing (and ended up getting a 100%), so it's very refined word-wise, but there may be some info you want. 

https://docs.google.com/document/d/14wcTrGn4DNq0DCRU1ejzGKgtE5AJfCg539nl3jyfHco/edit?usp=sharing

Nice report! The effort really shows, though you did get the Isp thing mixed up in the engine section. I quite enjoyed the crew member files.