Recently I was taking a hard look at the Traveller Map data for a handful of Aslan sectors. Afawahisa is a sparse border region three sectors from Dark Nebula and really only developed in Mongoose’s The Great Rift boxed set (2017). Given that the sector had been subject to such a recent publication I was surprised to find that the Afawahisa data was still listed on Traveller Map as “In Review.” But what does that mean?
Much of the sector data for the Charted Space setting was originally developed in the 1980s and the 1990s using a wide range of world generation methods. The resulting data was of highly varying quality and consistency, and in some cases reflected dramatically different historical periods such as The New Era setting. As people began to collect these different datasets and place them side-by-side the glaring differences in data became increasingly apparent.
For over a decade all sector data for the Official Traveller Universe has been subject to ongoing review as part of the T5 Second Survey project. The T5SS is an informal, fan-run effort originally coordinated by Don McKinney, who described it on the Citizens of the Imperium boards as “driven by Marc Miller to stabilize, correct, and control the UWPs of the OTU so that there’s a solid canon base of data for future reference.” The T5SS updated the legacy sector data to reflect both Traveller5 worldgen and a consistent 1105 dating. Since 2013 Joshua Bell’s Traveller Map has hosted the results.
One common change a T5SS review pass would make to sector data would be to adjust world size to reflect the Atmosphere code in the Universal World Profile. As described over on the Zhodani Base, “A problem with the random generation of worlds in Traveller is that small worlds (where size < 4) … might get an ordinary breathable atmosphere. This is a problem, since the minimum molecular weight retained for a [small] planet shouldn’t allow that.” Basically, small worlds cannot retain most atmospheres over billions of years: the constituent gases escape the gravitational pull of the planet and dissipate into space.
Don McKinney came up with a very elegant hack to fix this common problem. As he described it in comments on the Zhodani Base post, “I prefer changing the UWPs: if Atm 1/A/B/C, Size 3+; if Atm 2/3, Size 4+, and if Atm 4-9, Size 5+.” The great benefit of Don’s adjustment is that it neatly addresses the size problem without affecting the trade codes or (usually) past write-ups of the world. I was surprised to find, then, that the adjustment wasn’t made to the Afawahisa data.
Sadly, Don passed away unexpectedly in 2015 and I suspect that Afawahisa just didn’t receive a full T5SS review while The Great Rift was in development. I wanted to write this blog entry because Don’s nifty size hack was never well publicized and even today folks will occasionally wonder why Traveller Map UWPs don’t line up with the published UWPs from early GDW supplements like The Spinward Marches.
One problem with the way the size hack was generally applied to UWPs was that the Size code was often adjusted to the lowest possible result, which inadvertently created an inordinate number of worlds with Size 3 and Atmo 1, Size 4 and Atmo 2 or 3, and Size 5 with Atmo 4–9. This drove me nuts working on Magyar and Dark Nebula, and is a good example of how, when working with sector data, it’s very easy to accidentally create new problems when trying to fix old ones.
I wanted to develop a simple table that would allow me to apply Don’s hack but also introduce a random element to the revised Size code. In traditional Traveller worldgen planetary size is generated with 2D - 2, which creates a range from 0 to 10 (A) with a median result of 5. The distribution of results falls along a bell curve, with a 16.66% chance of producing a Size 5 world and a 2.77% chance of producing a Size 0 or 10 world. A Size of 5 is roughly 6 times more likely than a result of 0 or 10. Atmosphere is then generated by Size plus Flux, which can create an Atmosphere code ranging from 0 to 15 (F).
| World Size | Surface Gravity (Gs) | Odds |
|---|---|---|
| 0 | – | 2.77% |
| 1 | 0.05 | 5.55% |
| 2 | 0.15 | 8.33% |
| 3 | 0.25 | 11.11% |
| 4 | 0.35 | 13.88% |
| 5 | 0.45 | 16.66% |
| 6 | 0.70 | 13.88% |
| 7 | 0.90 | 11.11% |
| 8 | 1.00 | 8.33% |
| 9 | 1.25 | 5.55% |
| A | 1.40 | 2.77% |
To create a Size adjustment table that included some variability, I first looked at what world Sizes were appropriate for each Atmosphere code from 1 to 9. I zeroed out the inappropriate results and then prorated the percentages for the appropriate entries. The proration maintains the relative frequency of world sizes: for a world with a thin oxygen-nitrogen Atmosphere (5), a Size of 5 is still roughly 6 times more likely than a Size of A.
A trace oxygen-nitrogen Atmosphere (1), for example, requires a minimum world Size of 3 with a maximum Size of 6. So I removed results of 0–2 and 7–A and prorated the percentages for Sizes 3–6. A Size of 5 is still the most common result (30%), with a Size of 3 being the least common (20%).
| Atmo Code | World Size | |||||||
|---|---|---|---|---|---|---|---|---|
| 3 | 4 | 5 | 6 | 7 | 8 | 9 | A | |
| 1 | 20.01% | 25.00% | 30.00% | 25.00% | - | - | - | - |
| 2 | - | 25.00% | 30.00% | 25.00% | 20.01% | - | - | - |
| 3 | - | 21.74% | 26.09% | 21.74% | 17.40% | 13.04% | - | - |
| 4 | - | - | 30.00% | 25.00% | 20.01% | 15.00% | 9.99% | - |
| 5 | - | - | 28.58% | 23.81% | 19.06% | 14.29% | 9.52% | 4.75% |
| 6 | - | - | 28.58% | 23.81% | 19.06% | 14.29% | 9.52% | 4.75% |
| 7 | - | - | 28.58% | 23.81% | 19.06% | 14.29% | 9.52% | 4.75% |
| 8 | - | - | 28.58% | 23.81% | 19.06% | 14.29% | 9.52% | 4.75% |
| 9 | - | - | 28.58% | 23.81% | 19.06% | 14.29% | 9.52% | 4.75% |
I then recast the table to use a d20 to generate adjusted world Size based on Atmosphere code. (I know, I should have reformulated this as a native 2D table but a straight d20 was so much easier—and I primarily use this in an Excel lookup table.)
| 1d20 | Atmosphere | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | |
| 1 | 3 | 4 | 4 | 5 | 5 | 5 | 5 | 5 | 5 |
| 2 | 3 | 4 | 4 | 5 | 5 | 5 | 5 | 5 | 5 |
| 3 | 3 | 4 | 4 | 5 | 5 | 5 | 5 | 5 | 5 |
| 4 | 3 | 4 | 4 | 5 | 5 | 5 | 5 | 5 | 5 |
| 5 | 4 | 4 | 5 | 5 | 5 | 5 | 5 | 5 | 5 |
| 6 | 4 | 5 | 5 | 5 | 6 | 6 | 6 | 6 | 6 |
| 7 | 4 | 5 | 5 | 6 | 6 | 6 | 6 | 6 | 6 |
| 8 | 4 | 5 | 5 | 6 | 6 | 6 | 6 | 6 | 6 |
| 9 | 4 | 5 | 5 | 6 | 6 | 6 | 6 | 6 | 6 |
| 10 | 5 | 5 | 6 | 6 | 6 | 6 | 6 | 6 | 6 |
| 11 | 5 | 5 | 6 | 6 | 7 | 7 | 7 | 7 | 7 |
| 12 | 5 | 6 | 6 | 7 | 7 | 7 | 7 | 7 | 7 |
| 13 | 5 | 6 | 6 | 7 | 7 | 7 | 7 | 7 | 7 |
| 14 | 5 | 6 | 7 | 7 | 7 | 7 | 7 | 7 | 7 |
| 15 | 5 | 6 | 7 | 7 | 8 | 8 | 8 | 8 | 8 |
| 16 | 6 | 6 | 7 | 8 | 8 | 8 | 8 | 8 | 8 |
| 17 | 6 | 7 | 7 | 8 | 8 | 8 | 8 | 8 | 8 |
| 18 | 6 | 7 | 8 | 8 | 9 | 9 | 9 | 9 | 9 |
| 19 | 6 | 7 | 8 | 9 | 9 | 9 | 9 | 9 | 9 |
| 20 | 6 | 7 | 8 | 9 | A | A | A | A | A |
A world with a UWP of X164000-0 has a standard oxygen-nitrogen Atmosphere code of 6 that could not be retained with a Size of 1. To adjust the Size, roll a 1d20 and consult the column for Atmosphere 6. A result of 4 produces an adjusted Size of 5. A result of 17 produces an adjusted Size of 8.
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