Tag Archive for 'science'

[Battletech] Realistic gravity-based Jump Point Distances

I’ve got back into Battletech recently and I’ve been trying to reverse-engineer how the Proximity Limit is calculated (because I like to know how these things work). First, here’s a little background if you’re unaware of how jump works in Battletech. According to the fluff, Jumpships use a “Kearny-Fuchida drive” to travel over interstellar distances almost instantaneously. Traditionally they arrive at the Zenith/Nadir points – above the north and south poles of a star respectively – at the Proximity Limit, which is (supposedly) determined by the gravitational field of the star. These Jumpships usually carry Dropships, which then detach from the Jumpship with their cargo of mechs and head towards their target planet using normal fusion drives. Meanwhile, the Jumpship (which has little more than a few manoeuvering thrusters) generally sits at the arrival point and unfurls a large solar sail about a kilometre in diameter that it uses to recharge its drive in readiness for the next jump, which usually takes around a week (150-200 hrs).

After looking at the latest version of the stellar data table on pg. 100 of Campaign Ops, and I made an interesting observation: the Proximity Limit is not based on gravity. Given all the fluff says that this distance is determined by gravity (e.g. the notes on pg. 122 of Strategic Ops, summarised as “hyperspace fields don’t like gravity”) this is somewhat surprising. It turns out I’m not actually the first to notice this either – a thread on the battletech forums from over a decade ago discusses this too, but no solution to this is presented there. So I wondered – what would it look like if the Proximity Limit was calculated using gravity?

If you just want to skip to the point – here’s the gravity-based Safe Jump Distance table that you can use in your Battletech games instead of the published ones (this is just intended as a variant to use if you want more realistic values):

Table showing recalculated gravity-based Safe Jump Distance values.

If you want to know the technical details behind how I calculated this then read on…
Continue reading ‘[Battletech] Realistic gravity-based Jump Point Distances’

[2300AD] The GDW 2300AD Worldbuilding system: Part 3 – Final version!

2300AD Celestia output!

2300AD Celestia output!

I’ve been tinkering around a little bit more with my 2300AD worldgen script – I was actually adding the capability to generate Celestia versions of the systems that the program creates (as you can see from the screenshot above, I was successful!), but while I was at it I figured I’d make a few tweaks to some parts of the the system that I wasn’t too happy with. I think the results are much better now.

World Density: First I added a new rocky core density category so that worlds between 4000 and 7000km radius had densities between 0.75 and 1.00 Earths – previously they could go down to 0.5 Earths and I was ending up with habitable planets with unrealistically low densities for their size as a result. Worlds smaller than 4000km radius still have densities between 0.5 and 1.00 Earths, and worlds over 7000km radius have densities between 0.8 and 1.3 Earths as before.

Icy Core size: I wasn’t happy with the Icy Core size either – I was getting a lot of Titanian and Iceball worlds with the first realistic system and that didn’t make much sense to me – in the outer zone it should be easier to accrete material and you’d be much more likely to end up with gas giants instead of Titan and Pluto-like bodies. “Iceballs” don’t really make much sense to have as planets either – they’re really just the equivalent of Dwarf Planets, which would be found in a Kuiper Belt (which is usually assumed to be present but not mentioned). So now Icy Core radii range linearly from 3d6 to 8d6 times 500km, instead of starting at 1d6 – this means we end up with larger icy bodies, and a greater chance of gas giants (though there are still a small number of iceballs created, mostly below 3000km radius).

Snowballing: One limit from the original system was that ‘snowballing’ into a gas giant couldn’t happen within the Inner Zone if the MMW was greater than 2. This seemed a bit arbitrary to me, so I removed that limitation to allow it to occur at any planet where the MMW is greather than 2. As it turned out, changing it didn’t actually seem to make any significant difference to the output! Presumably this is because it’s very hard to get an inner zone planet that would be massive enough to have an MMW over 2 in those conditions.

Gas Giants: I’ve now subdivided Gas Giants into new World Types based on their sizes. Failed Cores are still under 12000 km radius. Small Gas Giants are between 12000 and 40000 km radius (this includes Uranus and Neptune). Gas Giants are larger Jovians that are larger than 40000 km radius but less than 2 Jupiter Masses (2 MJ) – this includes Jupiter and Saturn. Superjovians are over 40000 km radius but have masses between 2 and 13 MJ. Finally Brown Dwarfs are jovians that have masses over 13 MJ. This adds a bit of variety to the systems generated (and lets me use different textures in the Celestia output!)

I also changed how these gas giants are created. I still stick with the ‘snowballing’ idea, but something that always bugged me about that was the fact that the the original core density is assumed to be the density of the resulting gas giant, which can’t be right since all that extra hydrogen and helium has a much lower density than the icy/rocky core and would reduce the density of the resulting jovian. Now, if a planet snowballs into a Gas Giant then its density is re-rolled on a new density table depending on its final radius – this allows Superjovians to be 2-12 Jupiter masses, and Brown Dwarfs to be between 15 and 65 Jupiter Masses. It’s not the prettiest system since values are rolled and then rerolled, but it seems to get the right kind of results.

Garden Worlds: I realised that the lowest mass F V star has a total main sequence lifespan of 4 billion years, which means that garden worlds aren’t really likely around them. So while Pre-Garden, Post-Garden, or Frozen worlds are an option in their habitable zones, Garden worlds and Glaciers (which are just Garden worlds in a temporary ice age) are now no longer possible there.
Continue reading ‘[2300AD] The GDW 2300AD Worldbuilding system: Part 3 – Final version!’

[2300AD] The GDW 2300AD Worldbuilding system: Part 2 – Realistic Version

Sunrise on a new world (created in Space Engine)

Sunrise on a new world (created in Space Engine)

In the first part of this series, I looked at the distribution of systems that the default 2300AD system generated, and examined some of the issues and assumptions that it made. In this article, I’ll present the results of a modified system that addresses these issues and corrects the flawed assumptions, and explain why I made the changes.


Orbital Zones: The Outer Zone now begins at 2.5356*SQRT(L) AU from the star. This is roughly where the “frost line” is (where the blackbody temperature is 175K), beyond which volatiles can condense and gas giants are more likely to form. The new zone between the outer edge of the habitable zone and the inner edge of the outer zone is called the Middle Zone, and cold rocky planets are likely to form there (Mars is located in the Middle Zone in our Solar System, and Jupiter and the more distant gas giants are in the Outer Zone).

The boundaries of the Habitable Zone also need to be adjusted. The K multipliers used in the Life Zone equation in 2300AD don’t match the values shown in the table there – the values in the equation are K=0.72 and 1.45, but the table shows values for K=0.82 and 1.2. Unfortunately, those are both pretty unrealistic! Recent papers have put the inner boundary much closer to 1 AU than 2300AD assumed (between 0.9 and 0.99 AU) and while the outer boundary is less well defined but seems to be around 1.4 to 1.6 AU (see the Circumstellar Habitable Zone wikipedia article).

I will assume here that the habitable zone goes from K = 0.9 to K = 1.4 – this lets us have a full range of environments in the habitable zone without things getting too extreme. So K = 0.9 for the inner edge of the Habitable zone, K=1.4 for the outer edge of the Habitable zone, and K=2.5356 for the border between the Middle and Outer Zones.
Continue reading ‘[2300AD] The GDW 2300AD Worldbuilding system: Part 2 – Realistic Version’

[2300AD] The GDW 2300AD Worldbuilding system: Part 1 – Investigation

Gas Giant orbiting a triple G V system (created in Space Engine)

Gas Giant orbiting a star in a triple G V system (image created in Space Engine)

Now that I’ve got the Realistic Near Star Map Project out of the way I thought I’d take a look at the world generation system from the original GDW 2300AD Directors Guide, which I haven’t really examined in detail before. To do this, I automated the generation system so that I could generate thousands of systems and go over the statistics of the results.

However, I had to make a few tweaks to the system while writing the program so it’s not entirely faithful to the original system in the Directors Guide. First, the 2300AD system was designed to be used with existing stars, so I had to add a stellar generation system to generate those on the fly. I used a slightly modified version of my Revised Stellar Generation Tables (the original is available on my Worldbuilding page), that only generated solo stars (largely because it was easier to program that way). I used the stellar data tables from 2300AD to determine the stars’ luminosity and radius, but I just used the mass from the “V” column since in reality stars don’t change their masses significantly when they evolve into sizes II, III and IV. I also assumed fixed masses for the II and III Giants (1.5 Ms) and the White Dwarfs (0.5 Ms).

Another issue was that 2300AD is missing an Orbital Zone – there is a gap between the outer edge of the Habitable Zone and the inner edge of the Outer Zone. This “Middle Zone” is where Mars is located in our own Solar System, and cold rocky bodies (as opposed to icy bodies) would dominate there.

Additionally, in the original system, Gas Giants could snowball to immense sizes – the radius multiplier could go up to 16x the original rolled radius, which meant that you could potentially get Gas Giants with a radius of up to 384,000 km – over half the size of Sol! Obviously, this is not realistic – in reality, the maximum radii of jovians (that aren’t in star-hugging “Torch orbits”, at least) is between 70,000 and 80,000 km, because at that point adding more mass just causes them to self-compress further. In other words, Jupiter is about as big as a Gas Giant can get in terms of radius, though more mass can be piled into it and it wouldn’t get much bigger. So I set the upper limit at 70,000 – 80,000 km here, which results in an upper mass limit of about 8 Jupiter Masses (still too small for a Brown Dwarf though).

Finally, I simply calculated the MMW (and blackbody temperature and mass) of each planet instead of attempting to encode the tables directly. The MMW table in the book isn’t accurate in a general case anyway – this is discussed further in the Observations section.

Aside from these changes, I was able to translate the worldgen rules pretty faithfully into the program. Once that was done, I could set up runs that would generate 100,000 systems to investigate how many of which types of stars and worlds were created.

Continue reading ‘[2300AD] The GDW 2300AD Worldbuilding system: Part 1 – Investigation’

[2300AD] Realistic Star Map Project Update #2 (corrected American Arm!)

Yes, it’s another update! After I did the last update to the French and Chinese Arms, I was pointed to some new data that changed the locations for some of the Brown Dwarfs used here. Most of the affected BDs shifted only slightly (not enough to change their positions in the subway map), but a few of them did change significantly, and one of the ones that moved significantly was WISE J1541-2250, whose location changed from being about 9 ly from Sol to being 44 ly away! Unfortunately, that was one of the systems at the start of the American Arm so an update was required for the American Arm – now the American Arm is back to sharing its first few systems with the Chinese Arm. All of the changes that resulted from the new data are described below:

– Since WISE J1541-2250 is no longer in the right place, the American Arm now starts at Sol and then follows the Chinese Arm through Alpha Centauri (Tirane), Barnard’s Star, Ross 154 and AX Microscopii. Serurier is now at Ross 154 (as it is in canon), and Broward is now at AX Microscopii. The American Arm now continues through the binary brown dwarf system SCR 1845-635(7), the very young red dwarf Gliese 674, and then rejoins the rest of the Arm at 36 Ophiuchi (DM -26 12026).

– As a result of these changes, Broward is no longer located at Wolf 1061, and Wolf 1061 is no longer considered part of the American Arm (though it is still accessible from it). Serurier is similarly no longer at WISE J1049-5319 (though that system is still on the French Arm and is now just a waystation on the way to Nyotekundu).

Ross 458 has been removed from one end of the Pentapod Arm, since it is now out of range because of the new data – the Pentapod Arm now ends at Gliese 516 A.

– The brown dwarf WISEPA J1828+2650 is no longer located between Mu Herculis (Hermes) and Gliese 745 (the BD is now out of range and further away from Sol). This means that a Stutterwarp Tug is necessary to access Gliese 745 from Mu Herculis, and then from Gliese 745 another Stutterwarp Tug is required to reach Gliese 748 in the Beta Aquilae Cluster. This makes it somewhat harder to reach the Cluster, since there are no longer any brown dwarfs to bridge even part of the distance to it.

– The subway maps for all three Arms have been updated with these changes, so be sure to check them again!

– There is also now a “secret route” between the Antares and Beta Canum branches of the French Arm. I haven’t shown this route on the French Arm subway map because it’s not actually terribly useful, but I mention it here for completeness. The route goes from Gliese 518 on the Antares branch to Gliese 486 to WISEP J1217+1626 (a new Brown Dwarf) to Gliese 436 to (61 Ursae Majoris, Gliese 450, and Xi Ursae Majoris). The star Denebola can also be reached directly from J1217+1626. I originally thought that the existence of this new route might allow the Kafers to reach to Beta Canum to attack it during their invasion of human space, but it’s very unlikely that they would be able to actually locate such a dim object with their technology. It could allow a human force to travel between the arms, however.

You can check out the updated American Arm here: http://evildrganymede.net/wp/2013/09/09/2300ad-realistic-star-map-project-part-iv-the-new-american-arm/.

Hopefully this will be the last update to this 2300AD Realistic Star Map Project – I don’t intend to make any further changes or additions unless there’s something really major to update (new brown dwarfs near Sol, radically updated distance etc)!

[2300AD] Realistic Star Map Project Update (corrected French and Chinese Arms!)

tl;dr version: I inadvertently placed a Brown Dwarf near Sol in the wrong position on the Realistic Star Maps, which messed up the start of the French and Chinese Arms. But I’ve now fixed that and made a few other changes too, so be sure to check the updated pages!

The long version: A commenter here (thanks, Schutze!) pointed out that I’d made an error in the location of the brown dwarf WISE J1049-5319, which I previously placed at the start of the French and Chinese Arms. It turned out that I had used the Co-ordinate Converter from my Stellar Mapping page to calculate the location of that one system, but I’d forgotten to convert from the Galactic XYZ co-ordinates that it outputs into the Astrosynthesis XYZ format – so it ended up in the wrong place since everything around it was (correctly) in Astrosynthesis XYZ co-ordinates. There shouldn’t be any more errors like that in the maps – I’m pretty sure that was the only system for which I could have used the Galactic co-ordinates since everything else was converted using the Bulk Converter spreadsheet (which explicitly has Astrosynthesis XYZ columns that I copy the values from).

As a result, J1049-5319 was placed on the map in the wrong position, and fixing that really changed the start of the French Arm and somewhat changed the start of the Chinese Arm too. On the plus side though, the correct position of the J1049-5319 bridged the gap between Sol and Wolf 359 so that actually fixed that issue with the French Arm, and the new position also meant that the start of the Chinese Arm was more like it was in 2300AD canon.

Aside from the changes to the start of the French and Chinese Arms (involving the addition, removal and/or re-ordering of some systems), I’ve also significantly revamped Kafer Space by moving the Kafer homeworld to Psi Serpentis and adding a fictional Brown Dwarf between Psi and Lambda Serpentis, for reasons explained on the updated New French Arm page (it makes more sense like this now, and actually allows the Kafers to access human space!).

I’ve now updated the maps and descriptions on the New French Arm and New Chinese Arm posts, and also updated the Overview and Introduction posts to make all the preamble consistent (the New American Arm is unaffected by this, so it remains as it was).

So please be sure to check out the updated pages for the corrected information, and I’m sorry for missing that!

[2300AD] Realistic Star Map Project: Part V – The New Chinese Arm (v2.0)

NOTE: This is version 2.0 of the New Chinese Arm – it has been updated from its original version. See here for the full explanation for the change, otherwise read on for the updated Arm!

Finally, here’s the final part of my Realistic Star Map Project: the New Chinese Arm, and its associated branches! There are a lot of systems in here – 115 in total – and as you can see from the 3D map, it sprawls across a large region of space!

New Chinese Arm top view

3D Map of the New Chinese Arm (view from “above”).

As usual, the “subway map” makes this a little easier to digest:

Chinese Arm Subway Map

Subway Map of the New Chinese Arm.

The “Chinese Arm” is actually divided up into six main regions, with two more ‘extensions’ beyond those. The Chinese Arm itself is shown in green on the maps above. The Latin finger now has its own significant extension to expand into, and the Canadian ‘finger’ also has more systems and should now more properly be called the Canadian Arm (or maybe the “Canadarm”, but that’s already taken I guess 😉 ). The Sung finger is longer, and the Kormoran finger has now been corrected. Finally, the Full Eber Arm and its extensions map out the route to the true Eber homeworld of Zeta 2 Reticuli, and can be consider to be extensions of the Chinese Arm.
Continue reading ‘[2300AD] Realistic Star Map Project: Part V – The New Chinese Arm (v2.0)’

[2300AD] Realistic Star Map Project: Part IV – The New American Arm (v2.0)

NOTE: This is version 2.0 of the New American Arm – it has been updated from its original version. See here for the full explanation for the change, otherwise read on for the updated Arm!

Next, here’s a look at the New American Arm in the realistic star map. Here’s what it looks like from “above” Sol:

3D Map of the New American Arm (view from "above")

3D Map of the New American Arm (view from “above”)

And here’s an easier to understand “subway map” of the Arm:

American Arm Subway Map

Subway Map of the New American Arm

The New American Arm is not too different from the original one. One of the biggest differences is that it now only shares the Chinese Arm up to Broward (which is now AX Microscopii). Also, Davout (Gliese 682) is now exclusively on the Chinese Arm.

Some stars have been replaced by different ones, because of errors or different astrography:
– Serurier is still Ross 154, but Broward is now AX Microscopii (both stars are shared with the New Chinese Arm).
– Gliese 661 (Red Speck’s original star) is also off-track, so Red Speck is now 2MASS J1835+325 – a young M8.5 Brown Dwarf, somewhat more appropriate for the name of the system!
– Ross 863 (Gliese 655) was also in the wrong spot on the original map – it’s actually located beyond Kingsland on the Extended Australian Arm, not before it. Its spot is now taken by WISE J1738+2732 (another dim Y0 Brown Dwarf).
– Ellis is now 61 Cygni, which is actually quite accessible (it was described as being beyond 7.7ly and ‘inaccessible’ from the network in 2320AD, but on the realistic map it’s very straightforward to get to).

Otherwise, the American Arm remains the same as before – the only other differences are the extensions, which add a lot more systems to it:

– There is a small ‘extension loop’ of systems that can be explored between Clarkestar (Wolf 630) and King (Gliese 673).

– The Australian Arm now extends out for many systems beyond Kingsland, so there’s plenty of room for them to expand into. It also loops around ‘behind’ Kafer Space, providing an opportunity to access a ‘backdoor’ into their systems. The closest system to Kafer Space on the Extended Australian Arm is SDSS J1628+1804, which is 8.56ly from 2MASS J1553+1532, a binary brown dwarf system that is about 7ly from both Gamma and Lambda Serpentis.

– The Beta Aquilae arm branches from Mu Herculis (Hermes). There is a gap of 9.35 ly between Gliese 745 and Mu Herculis (Hermes), which requires a Stutterwarp Tug (there are no brown dwarfs in this region) – another Tug is then required to traverse the 10.9 ly gap between Gliese 745 and Gliese 748 (both Tug routes are shown as dotted lines on the subway map). Gliese 748 is the first accessible system in the Beta Aquilae Cluster (Delta Aquilae is the Aquilan homeworld). Note that nobody is aware of the Aquilans yet in MGT 2300AD, but they are of significant interest in 2320AD.

– The Vega Extension doesn’t contain many particularly interesting stars (Gliese 706 is a K2 V, the rest are M dwarfs), but it’s extra space to expand into.

– Red Speck’s Extension leads to Altair, which would be of scientific interest.

– Gliese 1245’s extension leads to Sigma and Chi Draconis – both potentially habitable systems (G9 V and F7 V respectively). Gliese 1245 is not present on the original maps, and is an ‘extra system’ between Red Speck and Ellis.

– One significant change to canon that I would propose is that the Extension that branches off from 61 Cygni should now be the new Bayern Route (used with the permission of the Americans) – this would make far more sense than the original route, since it actually points directly towards the Pleiades (unlike the canonical route, which goes all the way ‘up’ towards and beyond Aurore on the French Arm before coming back down again). Littlendia would be one of the systems on this route – probably Gliese 75 (a G9 V star similar to their canonical home system).

Interestingly (and unlike the New French Arm), the New American Arm contains several systems that are currently known to have planets – Alpha Centauri has at least one earth-sized planet in a torch orbit around the dimmer B star, there are several superearths orbiting the C component of Gliese 667 (Avalon would be 667Cd or Ce), and Vega has a protoplanetary debris disk and possibly a distant jovian.

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[2300AD] Realistic Star Map Project: Part III – The New French Arm (v2.0)

NOTE: This is version 2.0 of the New French Arm – it has been significantly updated from its original version. See here for the full explanation for the change, otherwise read on for the updated Arm!

Following on from my overview of what 2300AD’s Arms could look like on a realistic starmap, let’s take a closer look at my reinterpretation of the French Arm (as well as Pentapod and Kafer space) by starting off with a general overview (and some 3D maps!):

View of the French Arm from above.

3D Map of the New French Arm (view from “above”).

This new 3D map shows what the revised “New French Arm” looks like in the realistic starmap, as seen from “above”. The solid blue lines show the explored and colonised parts of the French Arm, the red/pink section is Kafer Space, and the light pink section is Pentapod Space. Dotted lines are “extensions” that haven’t been colonised yet but provide space for future expansion. Sol is located at the bottom left corner of the network, and Pentapod and Kafer space are “above” Sol, closer to the viewer.

While a 3D map is nice to look at to get an idea of the real layout of the stars, they are a little hard to interpret! Fortunately, the nature of the Arms is such that they can be represented using a much simpler “subway map” (shown below) that displays all of the connected systems in and around the French Arm much more clearly. This map was made using the very handy subway map generator at http://beno.org.uk/metromapcreator/ – it has a few quirks (such as not saving the maps properly – some screen capturing and assembly in Photoshop was required!) but it works pretty well once you get used to it.

Subway Map of the French Arm and Alien Space

Subway Map of the French Arm and Alien Space

The subway map shows the Arms and branches much more clearly. I’ve tried to arrange it so that the lines vaguely agree with reality, though in doing so it looks a little un-intuitive – I had to put Sol at the bottom right end of the dark blue line (with the French Arm extending to the left from it) in order to get the Beta Canum Branch on the same side of the map as the Arcturus Branch.

I’ve also had to move some of the named systems around to get the history working with the new map, and also had to incorporate the systems that were at fictional stars or stars that turned out too distant to be usable. I tried to fit the systems to similar stars, but there may be some differences (that probably matter less in the grand scheme of things than their placement on the arms).

So. What do we have now? We’ll actually start from the top of the arm and work down towards Sol.
Continue reading ‘[2300AD] Realistic Star Map Project: Part III – The New French Arm (v2.0)’

[2300AD] Realistic Star Map Project: Part II – Overview

So what could humanity’s expansion to the stars in 2300AD look like with a realistic star map? It could look like this…

The Realistic Arms of 2300AD

The Realistic Arms of 2300AD (click to expand)

The map above shows all of the stars within 60 lightyears of Sol, though only the stars on the French, Chinese, and American Arms are labelled (as well as those of all of the other space-faring nations and alien races). Obviously there’s a lot to digest in there – I’ll be discussing the arms individually in later posts, but in this post I’ll be providing an overview of what’s going on. As I pointed out in my previous post, this is merely my own personal (obviously non-canonical) interpretation of where the Arms would go – I’ve tried to keep as many systems in common with the original arms as I could given the more realistic stellar distribution, but this is by no means the only path the Arms could take.
Continue reading ‘[2300AD] Realistic Star Map Project: Part II – Overview’