Interstellar Engines for In-System? (Far distant speculation)

[stephensmat]

So, we know a later expansion gives us interstellar travel. The Devs have made no secret of the fact that the interstellar Engines will be enormous, powerful, etc.

I can't imagine they'd be the standard 'chemical' rockets, needing regular liquid fuel. What little we've seen suggest something new. Something that can burn for 'weeks'.

So I wonder how they'll deal with that inside the Kerbol system. Because any Interstellar Drive I can think of won't have any trouble with 'In-System' distances.

The way I see it, there are two options.

1) Story reasons. They could say that the 'Interstellar Drive' is too powerful, or too delicate, and has to be entirely out of the system before it can be activated.

2) Unlockable 'Easy Mode'. If you could use the 'unlimited range' tech in system, then it's the final unlockable. Something you have to earn through plenty of colonies and plenty of science, and plenty of work. Effectively, once you build up your Kerbol system enough, then you never have to worry about fuel or electricity ever again, and are rewarded for your diligent efforts with a semi-'God' mode.

 

Any thoughts?

[Superfluous J]

3) Just let us use the engines where we want.

[Sea_Kerman]

The balance comes from a beam-core antimatter torch drive being entirely impractical for use on a lander, or possibly in close proximity to other craft, or in-atmo, (and of course antimatter being a pain to manufacture) giving a perfectly valid use case for chemical rockets even into the endgame.

[Scarecrow71]

4) Eve wasn't using Gilly, so we moved it.  To Eeloo.

[Periple]

I expect that interstellar engines will have ridiculously high Isp but very low thrust. They would also be very, very big and very, very expensive (in resource cost). 

So I imagine that you totally could use them in-system, but I'm not sure you'd want to, any more than you'd want to take a nuclear aircraft carrier to go bass fishing!

[Mutex]

1 hour ago, Periple said:

I expect that interstellar engines will have ridiculously high Isp but very low thrust.

That's not going to work if you're going to get to a decent fraction of c with them, you need to have a pretty high acceleration. If you have 1G acceleration, it's going to take nearly a year to reach light-speed (353 days).

[Periple]

5 minutes ago, Mutex said:

That's not going to work if you're going to get to a decent fraction of c with them, you need to have a pretty high acceleration. If you have 1G acceleration, it's going to take nearly a year to reach light-speed (353 days).

As far as I know, most somewhat-plausible engines that could work for interstellar travel would only give you accelerations of a few thousandth of a G, and could reach about 0.1c in ~30 years. We'll see how sci-fi KSP2 goes, but I'm kind of hoping there won't be magic Epstein drives!

[Mutex]

9 minutes ago, Periple said:

As far as I know, most somewhat-plausible engines that could work for interstellar travel would only give you accelerations of a few thousandth of a G, and could reach about 0.1c in ~30 years. We'll see how sci-fi KSP2 goes, but I'm kind of hoping there won't be magic Epstein drives!

With such engines it'd take decades or centuries to reach another star system. I don't remember where I read/heard it but I'm pretty sure they are planning to add torch drives to the game. How they'll balance them is indeed the question, but I'm sure they'll be extremely large and expensive.

Also it depends what you mean by "somewhat-plausible", but there's definitely theoretical nuclear engines with very high ISP and decent (at least 1G) acceleration (nuclear salt-water engines most immediately come to mind), not that we're going to see such engines in real-life anytime soon.

Edited December 14, 2023 by Mutex

[Periple]

42 minutes ago, Mutex said:

With such engines it'd take decades or centuries to reach another star system.

I think it most likely will! I do remember them saying that an interstellar campaign could last a thousand years!

Also nuclear salt-water rockets would have Isp below 7,000 which is still an order of magnitude or so below what’s needed for interstellar propulsion. I think! I’m not an expert though!

Edited December 14, 2023 by Periple

[Mutex]

5 minutes ago, Periple said:

I think it most likely will! I do remember them saying that an interstellar campaign could last a thousand years!

Also nuclear salt-water rockets would have Isp below 7,000 which is still an order of magnitude or so below what’s needed for interstellar propulsion. I think! I’m not an expert though!

Well, we'll see, I'm expecting interstellar trips to be shorter than that for gameplay reasons though, timewarping for decades doesn't seem fun.

I pulled NSW out of my hind-areas tbh, there's loads of other "theoretical" designs, I can't remember the name of the website that named them all... but I definitely remember designs with theoretical ISPs in the millions and high thrust, usually involving nuclear fusion.

[Periple]

1 hour ago, Mutex said:

I pulled NSW out of my hind-areas tbh, there's loads of other "theoretical" designs, I can't remember the name of the website that named them all... but I definitely remember designs with theoretical ISPs in the millions and high thrust, usually involving nuclear fusion.

A citation would be nice!

I don't really know anything about this but most of the stuff I've looked at that seems relatively well grounded in science seems to put the theoretical top speed at around 10% of c, give or take a few %, if you also need to decelerate. Even an antimatter drive would only get you to maybe 40% of c, and that if you're able to somehow deal with the gamma radiation it produces. But maybe I've missed something big!

[Mutex]

23 minutes ago, Periple said:

A citation would be nice!

I think I found the site I was talking about, and it's... much more fiction-orientated than I remember it being:
https://projectrho.com/public_html/rocket/engineintro.php

There's some links to NASA reports in the descriptions of some of the engines, certainly no vaguely solid designs with millions of ISP and >1G acceleration though.

[GluttonyReaper]

5 hours ago, Periple said:

I expect that interstellar engines will have ridiculously high Isp but very low thrust. They would also be very, very big and very, very expensive (in resource cost). 

So I imagine that you totally could use them in-system, but I'm not sure you'd want to, any more than you'd want to take a nuclear aircraft carrier to go bass fishing!

Right, at the very least, you presumably don't want to use up your rare precious resource when collecting more of that resource...

[Strawberry]

Torchships with millions of isp and over 1g tend to be mostly fictional because in order to get that type of performance you need power outputs of hundreds of terrawatts. The entire power output of humanity makes roughly 2 terrawatts. From a physics perspective, its possible to have a spacecraft with this type of power output and have it not melt from its own exhaust, from an engineering perspective though good luck even getting the fusion to react enough in order to get these types of power outputs. 

Anyways, more realistic interstellar designs tend to involve very low thrusts, for example project Daedalus (which seems to be the inspiration for the interstellar engine we have seen), gets an acceleration of roughly .01 G (assuming fully loaded) and also needed a fission reactor to power the thing (You can have a craft with less acceleration and not a terrible loss in performance (only less then 10% of daedelus's mission had it actually using its thrusters). For comparison, DART (which used the NEXT ion thruster with similar isp to ksp's dawn), would've had an acceleration of .00004 G using just its ion thrusters, and Psyche also  gets very similar acceleration.

I think the main reason why you wouldn't want to use interstellar craft in system is theyre kind of a pain. They're not as slow to fly as ion spacecraft sure, but they're huge things that are hard to dock, rotate, and individually they're very expensive. If you were to use them, you'd use them only for routes and materials you need to transfer lots of materials, making them more of space trains, with high setup costs but low maintence costs. Overall I think you can have interstellar engines not break the game just due to the reality of them being heavy, large, slow things.

Edited December 14, 2023 by Strawberry

[Wheehaw Kerman]

13 hours ago, Superfluous J said:

3) Just let us use the engines where we want.

Like the fission pulse engines for large landers in multiplayer.

[mattihase]

I assume the "balance" is the tech tree & cost of setting up colonies to fuel them.

 

Plus like with NERV SSTOs in 2 you probably have the additional balance feature of them relying on awkwardly big or heavy parts that are hard to integrate into craft with more specific purposes like landers and SSTOs.

and, of course radiators and heat management.

[mattihase]

I think there's somewhat of an element too in the game of ultimately things do become obselete as new parts are added. I mean, think of how often we make Jet SSTOs post RAPIER. We can, as a challenge, but most of the time it just isn't worth it.

[NexusHelium]

I imagine you can use these engines in the system but... why would you want to?

Things like laser fusion engines would take up more time and resources than YOUR time and resources is worth. You may have a ridiculously powerful and efficient engine that is (conceptually) able to reach near-light speeds within a few years or so but the other thing to take into account is weight. Weight is everything on a rocket, and you just slapped an engine bigger than the Saturn V on the back of your interplanetary shuttle. It's just not worth it to add something that heavy to something that's only going to, say, Eeloo.

And, I mean, just LOOK at this thing...

Spoiler

 

[regex]

I don't see an issue with using interstellar capable engines in-system, no one's gatekeeping my delta-V expenditures and at some point that interstellar engine has to traverse the system it's in to get out of that system. The problem with them is generally a long acceleration time because engines that are bound to the laws of thermodynamics can pick one of high acceleration or high isp and for interstellar journeys you're going to prioritize isp, so you're wasting a lot of potential by using them in-system with short travel times. There will undoubtedly be mid-point drives with a decent balance of accel/isp because they are stepping stones to true interstellar drives; like I can't imagine you'd skip directly to an antimatter beam core engine without trying antimatter catalyzed fusion, for instance. That beam core is going to get you to the next star while the ACF drive is going to run your interplanetary shipping empire.

Edited December 14, 2023 by regex

[Bej Kerman]

17 hours ago, stephensmat said:

Because any Interstellar Drive I can think of won't have any trouble with 'In-System' distances.

...and?

Let the player do what they want, the entire point  of  KSP 2 is giving players access to powerful engines. Yes, there will be mid-tier torch drives made specifically for smaller in-system vessels, but why would an advanced civilization prevent themselves from using massive interstellar engines for in-system travel should they come up with a use for that? Furthermore, why should the developers come up with an answer for that last question if one of the reasons for creating KSP 2 was to have stock torch drives?

[GluttonyReaper]

14 minutes ago, Bej Kerman said:

...and?

Let the player do what they want, the entire point  of  KSP 2 is giving players access to powerful engines. Yes, there will be mid-tier torch drives made specifically for smaller in-system vessels, but why would an advanced civilization prevent themselves from using massive interstellar engines for in-system travel should they come up with a use for that? Furthermore, why should the developers come up with an answer for that last question if one of the reasons for creating KSP 2 was to have stock torch drives?

And even better - if you're like me, and not really a fan of far-future interstellar tech in KSP, you can just... not use it. The devs so far seem pretty committed to creating a game where the player isn't forced to do anything arbitrarily. 

[NexusHelium]

14 minutes ago, GluttonyReaper said:

And even better - if you're like me, and not really a fan of far-future interstellar tech in KSP, you can just... not use it. The devs so far seem pretty committed to creating a game where the player isn't forced to do anything arbitrarily. 

Well... You can't exactly expect to travel to a place like Debdeb with, say, an RS-25. So you will be forced to use the tech if you want to travel to the other systems.

[GluttonyReaper]

2 minutes ago, NexusHelium said:

Well... You can't exactly expect to travel to a place like Debdeb with, say, an RS-25. So you will be forced to use the tech if you want to travel to the other systems.

Right, but that's not arbitrary. That's physics. 

[Bej Kerman]

22 minutes ago, NexusHelium said:

Well... You can't exactly expect to travel to a place like Debdeb with, say, an RS-25. So you will be forced to use the tech if you want to travel to the other systems.

Feel free to read up on the context because this is not the point being made 

Here's the short version, OP sees a problem with being able to use powerful engines inside a solar system despite there being no real reason to prevent players from doing so, and torch drives already being made a selling point.

[Superfluous J]

53 minutes ago, NexusHelium said:

Well... You can't exactly expect to travel to a place like Debdeb with, say, an RS-25. So you will be forced to use the tech if you want to travel to the other systems.

Challenge accepted.