Lore question: orbital periods

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nweismuller
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Lore question: orbital periods

Postby nweismuller » Mon Aug 14, 2017 11:36 am

I assume that when orbital periods are listed for bodies, the 'days' measuring the period are 24-hour Earth days, rather than whatever the local rotational day is?

Also: are orbital periods around M-class stars supposed to be that short? I've seen orbital periods shorter than Luna's on some worlds. Are orbits around a more massive central body slower at a given orbital distance? I find it hard to swallow that colonisable planets are orbiting closer to their star than Luna is orbiting to Earth...

Edit: And I just noticed that the orbital period of Fargone I is listed as 3 minutes, which cannot possibly be correct.

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Arioch
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Re: Lore question: orbital periods

Postby Arioch » Mon Aug 14, 2017 5:48 pm

nweismuller wrote:I assume that when orbital periods are listed for bodies, the 'days' measuring the period are 24-hour Earth days, rather than whatever the local rotational day is?

I assume so as well, though I haven't looked at the code. The numbers looked okay to me, and they're irrelevant to gameplay, so that's as deep as I got into it. But if I know Sven (and I do), he based them on real mathematical orbital models.

nweismuller wrote:Also: are orbital periods around M-class stars supposed to be that short? I've seen orbital periods shorter than Luna's on some worlds. Are orbits around a more massive central body slower at a given orbital distance? I find it hard to swallow that colonisable planets are orbiting closer to their star than Luna is orbiting to Earth...

The more massive the bodies, the shorter the orbital period at the same radius. M type stars tend to be very small and dim, and so for a planet to be in the habitable zone it would need to be at a roughly similar orbital distance as Mercury, which would usually mean an orbital period of ~80-130 days. However, planets can and do orbit much closer; a known example such as Kepler-186 is an M1V star with its closest planets having orbital periods of 3.9, 7.3, 13.3 and 22.4 days, respectively. The closest of these planets are much farther from the primary than the Earth-Moon distance, but orbit faster because even a small a star is orders of magnitude more massive than Earth.

The numbers that I see looking at a selection of planets look reasonable to me.

nweismuller wrote:Edit: And I just noticed that the orbital period of Fargone I is listed as 3 minutes, which cannot possibly be correct.

There's something obviously wrong there. I'll check it out. I think the preset systems have hard coded values, so there's probably an error there.

The smallest known exoplanet orbit is PSR J1719-1438 b, which has an orbital period of 2.2 hours, and an orbital distance of 0.004 AU (about twice the Earth-Moon distance). It appears to be a carbon planet in orbit around a pulsar.

nweismuller
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Re: Lore question: orbital periods

Postby nweismuller » Mon Aug 14, 2017 7:07 pm

Thanks for the information, and your quick answer. I feel more comfortable with most of the class-M orbital periods now (although, of course, the Fargone orbital periods seem questionable).

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sven
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Re: Lore question: orbital periods

Postby sven » Tue Aug 15, 2017 4:43 am

nweismuller wrote:Thanks for the information, and your quick answer. I feel more comfortable with most of the class-M orbital periods now (although, of course, the Fargone orbital periods seem questionable).


The trouble with Fargone is essentially a lack of sanity checking. All the data is extrapolated from real star examples, but the reference star used by Fargone appears to be a bit unusual. While it's spectral type is 'M' -- i.e., it looks like a red dwarf to most astronomers, it's only 0.06 solar masses. That's tiny -- significantly smaller than most red dwarfs, and small enough that having a satellite close enough to be something like 'hot' in the language of the game is pretty implausible. And yet, Fargone I has some low-level config data that's setting it up as a relatively 'hot' planet. So the engine goes ahead and solves for an orbital period what would make the math work out. Um, and in this case, that math implies a 3-minute orbit.

I think having Fargone effectively a boarderline brown dwarf isn't necessarily wrong -- but I'll change the definition of the human starting system so Fargone I is significantly cooler. That should stop orbiting at such ridiculous speeds in new games ;)

nweismuller
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Re: Lore question: orbital periods

Postby nweismuller » Tue Aug 15, 2017 5:16 am

Thanks for the fix! I continue to love your game, and eagerly look forward to future improvements. Maybe sometime soon the AI will get a bit smarter about dealing with Marauder factions, or at least the tech gain on Marauders will be toned down... it seems silly when the cutting edge of military technology pretty much rests with the Marauders for centuries.

zolobolo
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Re: Lore question: orbital periods

Postby zolobolo » Tue Aug 15, 2017 7:59 am

My hopes exectly :)

Not sure, but it might be that hte tech advantage to the Marauders is inteded so advanced tech can be won from engaging them, or to balance out AI on highest difficult level. Luckily tech advantage, can toned be down if the above is not true, but players can also do this directly in the lua file (still also hope for a canon solution ;))

Altogether, the AI could avoid Marauders better and calculate its expected tactical outcome better to not waste ships on futile attacks, but think a much easier fix would be to have >50% probability for AI to pay off Marauders if they can afford it and display this information on the Marauder faction diplomacy screen:
- Display who has payed how much for the Marauders to havee them leave their colony alone
- The demanded amount would increase with each payment making for a fun minigame, transparency for AI behavour and realistically scaling the costs as the game progresses.
- Naturally the more payment a Marauder faction gets, the more budget it should have to aquire new ships. Thus Marauders who are payed off are stronger afterwords :) This is fun, as a wealthy empire could potentialy pay them off, while they weaken everyone else around them and thus the Phidi lore desc would come into reality

nweismuller
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Re: Lore question: orbital periods

Postby nweismuller » Tue Aug 15, 2017 12:45 pm

Also to be hoped: that AI Gremak Empires will start actively buying slaves from neighboring Marauder groups, and that they'll have their AI actively weighted to establish peace with Marauders. This then makes the description of the Gremak relying on Marauders as a pipeline for slaves a reality...


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