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BattleTech Player Boards => Fan Fiction => Topic started by: Akjosch on 04 February 2015, 11:46:21

Title: All the pretty stars - Expansion for the AToW:C and IO star system rules
Post by: Akjosch on 04 February 2015, 11:46:21
The current rules of the game wisely limit themselves to just B, A, F, G, K and M-class stars, and outright ignore giants and variable stars in favour of playability. Even the inclusion of B-class stars is kinda a stretch - those don't live nearly long enough to create proper planets of their own. Sometimes though, you just need that "special" one, and that's where I started writing down additional notes.

Brown dwarves: L- and T-class stars

Straddling the divide between "proper" stars and gas giants sit the dark brown dwarves. Too light to ignite pure hydrogen fusion in their cores, they nevertheless produce some light, even though it's mostly in the deep IR spectrum. Spectrographically, they are easy to discern from their bigger M-class brethren by the presence of lithium lines in their spectra - an element which gets "burned" with atomic hydrogen in proper stars in the first 100 million years of their existence or so.

Brown dwarves are, despite their mass, only about the size of Jupiter or slightly larger. As they age, which they do only very slowly, they become colder, less luminous and slightly smaller. They cease deuterium fusion at the transition from L- to T-class and finally go nearly dark after hundredths of billions of years - far in the future of our universe. On the other hand, the more massive of them can manage to ignite into "proper" M-class stars if they are partners of a larger star and siphon off some of its mass.

Rules-wise (since I couldn't find anything else how to calculate those values), their spectrum means that the minimum safe jump distance is limited not by luminosity or radius, but by gravity alone. Recharge times are calculated as the ones at the M9 star, multiplied by how much less irradiance the JumpShip experiences at that distance from the star. In general, it's wiser to just burn fusion reactor fuel instead of waiting for the solar sail to recharge the K-F core, especially at the darker stars where the times easily go into weeks, sometimes months.

I set up the distance to be uniformly at a point where the gravity reaches 180 micro-g. The life zone radii were calculated for a "white" planet (albedo: 0.4) at 310 K (37°C, 98°F) as the inner radius limit and a "dark" one (albedo: 0.1) at 220 K (-53°C, -64°F) as the "outer" one, allowing for the greenhouse effect to raise it to somehow survivable temperatures.

L-class brown dwarves

Ranging from about 13 Jupiter masses (the point where deuterium fusion through gravitational compression starts to be possible) up to about 80 Jupiter masses (where atomic hydrogen ignites in a fusion fire), the unassuming, deep red stars often play the role of satellites to bigger, more easily visible stars. That said, as often as not they are hosts to a planetary system of their own - in some cases even with gas giants. Such "dark" systems are a common find all around the galaxy. Less likely is to find a terrestrial planet inside their life zone: The zones are extremely narrow and even the slightest eccentricity will mean that the planet spends a good part of its orbit being a frozen wasteland or a burning inferno - and sometimes both.

Spectral ClassCharge timeTransit timeSafe jump distanceHabitability mod.Inner life zoneOuter life zoneMass (solar)TemperatureLuminosity (solar)
L9210 days1.31 days31,262,503 km-90.004 AU0.009 AU0.013 M☉1300 K0.000006 L☉
L8151 days1.33 days32,442,633 km-80.005 AU0.011 AU0.014 M☉1410 K0.000009 L☉
L797 days1.35 days33,581,315 km-70.005 AU0.013 AU0.015 M☉1520 K0.000015 L☉
L674 days1.44 days37,794,523 km-70.006 AU0.015 AU0.019 M☉1630 K0.000025 L☉
L561 days1.49 days40,668,992 km-60.007 AU0.018 AU0.022 M☉1740 K0.000035 L☉
L448 days1.57 days45,054,062 km-60.008 AU0.020 AU0.027 M☉1850 K0.000055 L☉
L338 days1.62 days48,276,182 km-50.010 AU0.023 AU0.031 M☉1960 K0.00008 L☉
L230 days1.70 days52,741,556 km-50.011 AU0.026 AU0.037 M☉2050 K0.00012 L☉
L126 days1.78 days58,164,544 km-40.012 AU0.030 AU0.045 M☉2180 K0.00017 L☉
L022 days1.87 days64,303,323 km-40.014 AU0.033 AU0.055 M☉2290 K0.00025 L☉

T-class brown dwarves

Lacking even the mass necessary to ignite deuterium fusion, those are the failed stars. In a lot of aspects, they are simply bigger gas giants - including an atmosphere full of water vapour, carbon monoxide and methane. However, they are still barely above the size of Jupiter despite being at least ten times as massive, and they are still generating heat and light, slowly releasing what was stored during their creation inside their cores and cooling down as billions of years pass by.

Due to the strong absorption of green light in the atmospheric compounds of sodium and potassium, they appear a dark shade of magenta to the naked eye.

You can't really expect life around those stars, but they can give off just the right amount of additional IR radiation to heat up planets orbiting it to "habitable" levels when they are themselves satellites to bigger stars, just outside the life zone.

Spectral ClassCharge timeTransit timeSafe jump distanceHabitability mod.Inner life zoneOuter life zoneMass (solar)TemperatureLuminosity (solar)
T937206 days (a bit over 100 years)1.21 days26,865,052 km-100.000 AU0.001 AU0.0096 M☉500 K0.000000025 L☉
T823738 days1.22 days27,143,454 km-100.001 AU0.001 AU0.0098 M☉550 K0.00000004 L☉
T713842 days1.22 days27,419,029 km-100.001 AU0.002 AU0.0100 M☉600 K0.00000007 L☉
T68985 days1.23 days27,691,862 km-100.001 AU0.002 AU0.0102 M☉650 K0.00000011 L☉
T55598 days1.24 days27,962,033 km-100.001 AU0.002 AU0.0104 M☉700 K0.00000018 L☉
T42935 days1.24 days28,229,618 km-100.001 AU0.003 AU0.0106 M☉800 K0.00000035 L☉
T31495 days1.25 days28,494,691 km-100.002 AU0.004 AU0.0108 M☉900 K0.0000007 L☉
T2889 days1.25 days28,757,320 km-100.002 AU0.005 AU0.0110 M☉1000 K0.0000012 L☉
T1558 days1.27 days29,403,633 km-100.003 AU0.006 AU0.0115 M☉1100 K0.0000020 L☉
T0333 days1.28 days30,036,042 km-100.004 AU0.009 AU0.012 M☉1200 K0.0000035 L☉

(Next on the "todo" list: O-class stars and white dwarves)
Title: Re: All the pretty stars - Expansion for the AToW:C and IO star system rules
Post by: Giovanni Blasini on 05 February 2015, 19:38:00
Tagging this to come back when I'm not on my phone. :)
Title: Re: All the pretty stars - Expansion for the AToW:C and IO star system rules
Post by: NullVoid on 09 February 2015, 14:43:00
This is great, but maybe it should be under Fan Design and Rules (
Title: Re: All the pretty stars - Expansion for the AToW:C and IO star system rules
Post by: snakespinner on 10 February 2015, 02:33:36