KSP2 and the need for speed

[SciMan]

You don't "NEED" antimatter to make a torch-ship drive, per se.

The nuclear salt water rocket is VERY MUCH a torch drive, at least when you do the math using weapons-grade enriched uranium (typically enriched to 90% or greater).

Pulse-fusion ICF drives (like Dadelus but using a magnetic nozzle and much faster pulse repetition rate) can also be Torch drives, it's just a matter of increasing the mass flow rate and power output to a high enough level.
Something that can help with increasing that mass flow rate is operating these pulse type drives in "afterburning" mode (injecting extra hydrogen into the exhaust to "shift gears" by trading away some fraction of the total ISP of the drive to gain a lot more thrust output, the energy provided to the propellants remains the same because the rate of consumption of fusion fuel remains the same).
With this, it's theoretically possible to build a drive that can accelerate a quite large ship at very close to 1 G for months on end or longer. And if that's not a torch drive, I don't know what is.

Pretty much all drives "can" shift gears in this way.
Oddly, even chemical engines can "shift gears" like this, at least to some extent.
For a somewhat odd example the RS-25 SSME runs notably fuel-rich.
I'll start off with why it's an odd example. Running fuel rich with hydrolox propellants means that the engine is actually able to "up-shift", trading thrust for ISP.
That's unusual because most times when an engine is capable of "gear shifting" like this, it will be an extremely high ISP drive and you dump "something extra" into the exhaust to LOWER ISP and INCREASE thrust, but the exact opposite is happening with the RS-25 SSME.
In any case, running fuel rich with hydrolox increases specific impulse because given a constant temperature and pressure in the combustion chamber, if the exhaust products are of a lighter molecular weight they will have a higher linear velocity out the exhaust nozzle, which is exactly the same thing as saying "higher average exhaust velocity" and that translates directly to an increase in ISP since ISP is directly correlated to exhaust velocity (no matter what system of units you're using).

Even a lowly nuclear thermal rocket running on pure hydrogen propellant can "gear-shift" to the point that it becomes an engine with a high enough TWR to be able to launch directly to orbit, switching at altitude to hydrogen-only use. What does it inject into the exhaust to get all this extra thrust? Oxygen! Now it's true, that basically turns the NTR into a "hydrolox rocket with extra steps" in the lox-augmented mode, but that's fine, the performance advantages of the "NTR only" mode outweigh the disadvantages of the more complex plumbing that happen because of the LANTR mode addition.

So too can electric propulsion systems like ion engines, hall effect thrusters, and others shift gears. Most of the time they do this by switching propellants, because any kind of electric propulsion system should in theory be able to use any noble gas as a propellant. Xenon is chosen because of its low ionization energy and high atomic mass, meaning it actually is the "lowest gear" for an electric thruster.
SpaceX with their Starlink satellites quickly figured out that if they were to use Xenon they would consume more than the world's yearly production of the stuff, and so for logistical reasons they chose the next best candidate noble gas, Krypton. Krypton is still a very "heavy" gas as far as the noble gases go, but the electric thrusters on Starlink satellites did take a hit to the thrust output. This is part of the reason that SpaceX lost a batch of Starlink satellites a few months ago, the increased solar activity at this time of the roughly 12-year solar cycle made the earth's atmosphere extend to a higher altitude than normal, which increased atmospheric drag to the point that the electric propulsion systems couldn't even orient the sattelites correctly so that their solar panels faced the sun enough to generate enough power for the electric thrusters to raise the orbit, so they all reentered within a few days (with maybe one or two survivors out of around 60 satellites).
Even the highest power electric thrusters we have, running on Xenon (so highest thrust possible) generate less thrust force than the gravitational force of a single sheet of letter/A4 paper resting on your hand. Electric thrusters literally only work because there's no real "opposing" drag force in space.

Edited August 18, 2022 by SciMan

[t_v]

Right, sorry, that was a miscommunication. The topic was whether torch ships should be there to get a resource or the other way around, and I was using antimatter as a stand-in for “torch ship fuel.” In a previous post I specified that the type of torch ship was an antimatter torch ship. 

[JadeOfMaar]

On 7/29/2022 at 10:44 PM, Strawberry said:

Its been stated that torch ships (the end game engines) are sometimes less efficient then your previous engines and are focused on speeds. The thing is, why? Why the need for speed. With timewarp, going faster is roughly the same speed as going at a slower speed for the player.

Torch drives will, at first glance, be less efficient because the basic thing anyone knows about engine performance is that you trade impulse for thrust. You cannot simply pile on both. But a torch will, by definition, have enough thrust for a manned mission AND the impulse to allow it to burn as long as desired to promise a short or more comfortable ship (see: Thrust gravity).

On 7/29/2022 at 10:44 PM, Strawberry said:

Certain resources decaying with time seems like it would offer good justification for torch ships, the obvious one here is antimatter, however I can see something like maybe a manufactured element that's in the island of stability that while it passively decays, it makes a great structural component for rocket parts. Even this raises more questions though, if it's antimatter or some other unstable fuel what's the point of going fast just to be able to transport your own rocket fuel.

On 7/30/2022 at 5:08 AM, t_v said:

The one resource I see having a time limit is Uranium

Uranium doesn't have such a short half-life. What you're actually thinking of is Tritium. This is a radioactive variant of Hydrogen, with a half-life of just 12 years, and with Deuterium, makes the easiest fusion fuel mix to ignite in an engine or power source. For a period in your space program you could have a D-T fusion economy going, and express delivery between the mining base on an inner system metal world and a settlement on an outer ice planet where solar is utterly dead, is absolutely necessary because if you use Hohmann to transport it, half of it will have fizzled out by then.

The true and first incentive that KSP2 should have for torchships is finite lifespans for kerbals. Let them age and eventually die. No more perfect immortality, then players can't casually "Forget them in a Mk1 pod" or "Maximum gravity slingshot" for mass-efficient ships. (This doesn't even fall under life support. Just add a proper life cycle system so eventually Jeb has to step down and you can legit have his son or his choice pupil take his crown when he's retired or poofed. We know about "boom events" where kerbals are born, but that just means more kerbals. But anything that's born...eventually dies. Fact of life.)

And about Antimatter: The highest form of it we may only ever produce (or use) is Anti-Deuterium. There isn't going to be an "Anti-Uranium." You can't magnetically confine most materials and generally, the thing about Antimatter is that it's stable, but it will annihilate if it touches anything that's not Antimatter. As long as you have power to confine it, you can technically store it indefinitely, right?

I don't expect the KSP2 devs to come up with some Taurusfecallium resource to try to justify torchships. They'd be going against practically the same reason they're not making warp drives. It's too out there. It's far from being perfectly resolved in Math and Physics calculations and until then it violates known Physics.

Edited August 25, 2022 by JadeOfMaar

[SciMan]

I see now, thank you for clarifying. Torch ships should be there to get a resource.

But the resource should be "literally any resource". The sole advantage is that it doesn't take as long. That's it. That's all there is. Nothing else.

If there was something else, that "something else" would break physics in some way.

And that's because none of the elements that we're interested in have a half life shorter than 500 years. Not even uranium-235 or plutonium-239. Go look it up, they have surprisingly long half-lives, how else do you think the US has been able to get away with not making any new nuclear warheads for roughly 30-40 years now?

Chemical fuels just plain don't react if stored properly.

About the only thing that could possibly expire that quickly is fresh food. But there's 2 problems with that:
1. Because we humans need to eat pretty much every day from birth to death, we've invented TONS of technologies that allow us to preserve food for extremely long periods of time. So "Fresh food" is something you'd be getting from the greenhouses at a colony, not something you'd be packing for a 10-year journey.
2. Because KSP 2 is set in the near-future, I'm absolutely certain that if we do get life support as a gameplay mechanic, it will be with parts that allow the life support loop to be closed almost completely, without needing to keep track of 10 different resources that are only used for the life support systems and nothing else. So maybe you will be able to have fresh food on that 10 year journey after all. But the majority of that will be stuff you didn't have with you when you started, instead it will have been produced from the closed-cycle life support system.

Everything else is about as inert as a cargo of rocks, in fact the important ores we'll be looking for and potentially shipping around are literally "just somewhat special rocks".
Ok, maybe oil isn't a rock, you got me there. But here me out:
Coal is just "rocks that can burn", Radioactive ores are just "rocks that emit invisible energy", metal ores are just "rocks that can be melted down to make shiny rocks", the list goes on.
Even water can be a special kind of rock. What do you think Ice is? Ice is just "Rocks that you melt and then drink".

Point is, there isn't any "unstable resource" that out-and-out REQUIRES transport by torch ship or you don't get hardly any of it because it decays in transit.

 

EDIT: Having read @JadeOfMaar's reply that was posted before mine, I have something to add on the topic of Tritium:

You won't be mining Tritium. Instead, you'll be creating it as you need it, if you need it at all and we're not just presented with fusion drives that solely use Deuterium and Helium-3 as fuels.

How? Tritium is easy to create if you have a potent source of neutron radiation, and some Lithium.
If you know how modern thermonuclear weapons work, you know what's coming next.
Exposing Lithium to a high neutron flux does something useful. The neutrons smash apart the Lithium nucleus, for every Lithium nucleus split, one Tritium nucleus and one Helium-4 isotope are produced (with Lithium-6 the reaction is as indicated and slightly exothermic, with Lithium-7, you also get an extra low-energy neutron and the reaction is instead endothermic).

Assuming you use a molten blanket of Lithium surrounding your fusion engine or reactor, you should be able to siphon off the produced tritium and helium. It shouldn't be hard to separate the tritium from the helium, you just need to introduce some Oxygen and ignite the mixture (or send it thru a fuel cell). Then harvest the tritium water from that reaction, and dump the helium either into the exhaust nozzle of the fusion engine or just vent it overboard without the intent to produce extra thrust, you don't need it anymore.
Obviously the tritium is then stored and metered into the reaction chamber of the fusion reactor or engine, where it is fused with Deuterium.

If tritium production is insufficient, or you're trying to get the thing started, you can use a fission reactor (obviously fueled by uranium or plutonium) to supply the neutrons. There will still be more than enough neutrons to go around to do the job, assuming a fission reactor that is depending on Fast neutrons to continue the chain reaction.

And like I said, that's not even considering that these fusion reactors and engines might not even be using D-T fusion.
They might be using D-He³ fusion instead.
I know, D-He³ fusion doesn't output as much raw power. That's fine, what you lose in raw power you gain in "not needing to worry about Tritium" and "a heck of a lot less neutron radiation", both things that can reduce the dry mass of the propulsion system of your vessel (yes I'm lumping the radiation shielding in with the propulsion mass, maybe that's wrong, but since you always need the radiation shielding when you have both crew and a radioactive drive system I figured it made sense).
Not only does D-He³ fusion produce a lot less neutrons (there's still a little bit of it, thanks to some unavoidable D-D fusion happening in side reactions), but the charged reaction products are more energetic as well, which means higher specific impulse, and therefore greater fuel efficiency overall.

EDIT 2: Having now fully read Jade's reply, I agree that Kerbals should eventually get old and pass on (if they don't want to put the concept of death in the game, they could just say that they retired from spaceflight to go teach the next generation).

Edited August 25, 2022 by SciMan
Tritium isn't a problem, allow me to explain why.

[Strawberry]

On 8/25/2022 at 10:50 AM, JadeOfMaar said:

And about Antimatter: The highest form of it we may only ever produce (or use) is Anti-Deuterium. There isn't going to be an "Anti-Uranium." You can't magnetically confine most materials and generally, the thing about Antimatter is that it's stable, but it will annihilate if it touches anything that's not Antimatter. As long as you have power to confine it, you can technically store it indefinitely, right?

Magnetic confinement would keep it stored indefinitely, provided you could prevent every particle from getting enough energy to touch the containment, so in practice you're not going to get no decay (though you can easily get very close and while this decay can be bumped up for gameplay reasons in reality itd likely be minimal).  Also producing anti uranium would be possible, antimatter is just normal matter with an opposite charge and thus you could run it in a fusion reactor, this would make it more energy dense but be very inefficient (I doubt this will be in game). 

The main thing for life support is it will be balanced around rocket parts, not torch drives. The life support system has to be forgiving enough for aging to allow for relatively easy early game planetary exploration, and unless the distances vastily increase for late game interplanetary (which to be fair could easily happen considering the scale of some stars), I dont really see faster ships being much of an aid in late game due to life support probably being a solved issue and most transport at this point probably being cargo (Also this thread is half so I can dream about interesting gameplay options). 

[SciMan]

Anti-oxygen would be a good candidate for storable antimatter, now that I think of it.
Oxygen in its liquid and solid O2 forms is at least a little bit diamagnetic, meaning that a specially configured and/or modulated (time-varying on a static cycle, or actively controlled with something like pulse-width modulation) magnetic field can repel it.
Surround a mass of solid anti-oxygen (so no boil-off) with such magnetic fields (to keep it away from the container walls) and you've made yourself a way to store antimatter quite densely, which is one of the chief problems with storing antimatter. To extract it from this storage, hit the mass with a high energy laser at a favorable point, and then use those same magnetic fields to direct the created anti-oxygen plasma where you need it to go.

Simple in concept, but probably a nightmare to pull off in practice. But at the same time, if I can think of this and I'm just a college drop-out, either there's some real physicist waiting to tell me why this won't work, or the idea is at least feasible.

[t_v]

14 minutes ago, SciMan said:

meaning that a specially configured and/or modulated (time-varying on a static cycle, or actively controlled with something like pulse-width modulation) magnetic field can repel it.

You technically need active control when storing antimatter magnetically. The reason is that, even though antimatter doesn’t decay at a meaningful rate, stray atoms of it will inevitably hit the walls despite magnetic containment. If the antimatter were perfectly stabilized this wouldn’t be a problem, but if the antimatter is oscillating even a tiny bit, as it gets closer to a wall, the interactions with that wall will increase and impact the antimatter more, pushing it in the other direction at a higher speed than it came in. As the antimatter starts seriously oscillating and accelerating, it flings off larger clumps of atoms into the walls, amplifying the amount of force it generates by orders of magnitude. Think of it like someone pushing off of walls as they near it, building up more and more speed until their reaction time fails and they hit one of the walls. It is kind of cool that antimatter stores so much energy that it will literally give itself kinetic energy just by the minuscule amount of interaction it has with anything around it. 

[Pthigrivi]

 

On 8/25/2022 at 11:50 AM, JadeOfMaar said:

The true and first incentive that KSP2 should have for torchships is finite lifespans for kerbals. Let them age and eventually die. No more perfect immortality, then players can't casually "Forget them in a Mk1 pod" or "Maximum gravity slingshot" for mass-efficient ships. (This doesn't even fall under life support. Just add a proper life cycle system so eventually Jeb has to step down and you can legit have his son or his choice pupil take his crown when he's retired or poofed. We know about "boom events" where kerbals are born, but that just means more kerbals. But anything that's born...eventually dies. Fact of life.)

Despite this and your idea for crispy-brown hibernation>death consequences for depleted LS being pretty good ideas Im going to disagree on them being part of default/normal gameplay. How long would it take for kerbals to die of natural causes? 80 years? That would mean its not really a factor through most of the game until you’re colonizing multiple star systems and at that point why start creating a random die-off that restrains population growth? Its not compelling anything, or adding anything, so why not just let them live forever and ignore it? 
 

If you want to create a real and consistent time pressure it needs to kick in much sooner, and be more easily manipulated through tech development. Whatever else people say players are in it for the parts. If lack of LS reduces science output and therefore reduces the rate at which parts unlock then LS becomes the hand on the throttle. Thats the direct line on fundamental game incentives. Anything punitive beyond that is overkill. 

Edited September 2, 2022 by Pthigrivi

[GigFiz]

2 hours ago, Pthigrivi said:

If you want to create a real and consistent time pressure it needs to kick in much sooner, and be more easily manipulated through tech development. Whatever else people say players are in it for the parts. If lack of LS reduces science output and therefore reduces the rate at which parts unlock then LS becomes the hand on the throttle. Thats the direct line on fundamental game incentives. Anything punitive beyond that is overkill. 

I am very much with you there. Complicated and/or punitive life support systems are a terrific ground for interesting and fun (YMMV a lot) mods, and it the behind the scenes framework should absolutely allow them to do that (which I am certain that it will), but that stuff should stay way the hell away from the stock game.

There will definitely be mods for it, and people that want that kind of thing will seek them out, but in base game, plenty of people would just get bogged down or overwhelmed or discouraged, which just stops being fun, and then what's the point? So even if it could be toggled, it can't be on by default, and I bet you that most people would never switch it on, so then it's just a waste of time to implement and we have circled back around to -----> mods

[Starwaster]

On 8/30/2022 at 2:12 PM, SciMan said:

Anti-oxygen would be a good candidate for storable antimatter, now that I think of it.
Oxygen in its liquid and solid O2 forms is at least a little bit diamagnetic, meaning that a specially configured and/or modulated (time-varying on a static cycle, or actively controlled with something like pulse-width modulation) magnetic field can repel it.
Surround a mass of solid anti-oxygen (so no boil-off) with such magnetic fields (to keep it away from the container walls) and you've made yourself a way to store antimatter quite densely, which is one of the chief problems with storing antimatter. To extract it from this storage, hit the mass with a high energy laser at a favorable point, and then use those same magnetic fields to direct the created anti-oxygen plasma where you need it to go.

Simple in concept, but probably a nightmare to pull off in practice. But at the same time, if I can think of this and I'm just a college drop-out, either there's some real physicist waiting to tell me why this won't work, or the idea is at least feasible.

Liquid oxygen is paramagnetic, not diamagnetic. And I'm not sure its antimatter equivalent would be different. Assuming that it would in fact be repelled, the repulsive force would be very weak. Probably too weak to overcome inertia whenever the craft accelerates. Definitely too weak to overcome planetary gravity.

Edit: Also, just keeping it away from the tank walls won't be enough to prevent boiloff losses through radiation. You need to keep the walls cooled and this magnetic containment scheme is also generating heat.

Edited September 3, 2022 by Starwaster

[SciMan]

OK so I got my terms mixed up regarding how oxygen is affected by magnetic fields. Point was, you do NOT need to IONIZE oxygen to get it to respond to a magnetic field.
And yes, I know that you'd have to have active cooling in place to keep the antimatter contained.

But you know what? You don't have to explain all that to the player to be able to use antimatter. Just say "antimatter will always react with normal matter, so to keep it contained you need to supply power to the antimatter storage vessels".
The key is to know when to stop explaining to avoid confusing the player, and also to avoid opening up any holes in your argument.

In any case, I personally don't think that antimatter will be introduced into KSP 2.
Fusion propulsion is more than capable, and if there is some form of "thrust generating means that doesn't use fuel" then that will also be useful.

Of note, you don't need to invoke "warp drives" to get a way to produce motion without consuming reaction mass.
You can always use a solar sail to do that. It works even better if you aim a lot of lasers at that sail, rather than depending on the star to provide all the energy. And it works best if you can direct a beam of particles at the sail (so-called mass-beam technology, because instead of a beam of light it's a beam of particles that have mass). With the mass-beam idea, you don't even need a physical sail anymore, you can use a magnetic field. That same magnetic field can be used to decellerate at the target star by using that star's own magnetic field and the charged particle radiation that star outputs as a source of momentum to impart on the interstellar vessel.

There's also the potential to build a series of mass drivers in deep space in order to accelerate things to interstellar velocities in a much shorter time period than is tolerable by crewed vessels, this would obviously be useful for sending bulk commodities and specially braced or reinforced infrastructure equipment ahead of sending actual crew to potentially operate that equipment (so you could have the "base in boxes" sent to the other star at the same time as the crew, but the base would get there first because it was sent at a higher acceleration even if the cruising speed was the same).