UWP clarification

[Spartan159]

For world size codes, is it the average, ie 7 = 6,500mi to 7,499 mi diameter, or is it the lower limit, ie 7,000 mi to 7999 mi? I'm also looking at the T5 chart G (page 413 of my PDF) and wondering about gas giant sizes in the same light.

 

[Spartan159]

When in doubt check the Wiki. Looks like it could use some data from T5 though. I guess for gas giants I will interpolate the data I have.

 

[tjoneslo]

Thanks for pointing out the table in T5 to extend that table.

The problem with the Gas Giant table (5.09 rules page 413) is that the size of Jupiter (90,000 miles diameter) is about as large as Gas Giants get. The more massive ones (1 to 1.6 Jupter masses) will be only slightly larger than Jupiter (110,000 miles or so maximum). At greater masses, the gravity begins to compress the core into degenerate matter and the more massive GGs are smaller.

Once you get to Brown Dwarf stars, where the core is fusing Deuterium may be larger because the pressure balance is different. And Radius is measured somewhat differently.

 

[Spartan159]

Thanks for pointing out the table in T5 to extend that table.

The problem with the Gas Giant table (5.09 rules page 413) is that the size of Jupiter (90,000 miles diameter) is about as large as Gas Giants get. The more massive ones (1 to 1.6 Jupter masses) will be only slightly larger than Jupiter (110,000 miles or so maximum). At greater masses, the gravity begins to compress the core into degenerate matter and the more massive GGs are smaller.

Once you get to Brown Dwarf stars, where the core is fusing Deuterium may be larger because the pressure balance is different. And Radius is measured somewhat differently.

Sure thing. There's also the point that with T5 Generation it's possible to get size 15 planets, aka big worlds. In fact if you happen to roll that the main world is a satellite in a system with no gas giants, it calls for a big world to be placed in the habitable zone for the main world to orbit.

And on to the Real Life _tm is stranger than fiction, there's this:

 

[tjoneslo]

I looked looked through the list linked. All of the larger than Jupiter planets are either brown dwarf possibilities or hot Jupiters with orbital period of three days. So the T5 table is not wrong, just missing a good explanation. A good part of the radius of the gas giant depends upon the temperature. It's one of the reasons I don't like the "radius determines safe Jump distances".

 

[Spartan159]

I looked looked through the list linked. All of the larger than Jupiter planets are either brown dwarf possibilities or hot Jupiters with orbital period of three days. So the T5 table is not wrong, just missing a good explanation. A good part of the radius of the gas giant depends upon the temperature. It's one of the reasons I don't like the "radius determines safe Jump distances".

No arguments from me, I don't have the knowledge to throw in the ring. As to safe jumps, radius? mass? gravity? any or all? I just don't know.

 

[tjoneslo]

No arguments from me, I don't have the knowledge to throw in the ring. As to safe jumps, radius? mass? gravity? any or all? I just don't know.

For safe jump distances, I've had good luck with tidal force. Calculate G * M / R^3 -> you want this below a specific, very small, value. Too large and the stress on space due to the mass causes your jump drive to flake.

The advantage of this is you can calculate safe jump distances for all sorts of weird things like nebula, the galactic core, red giant stars (you can end up inside of them), black holes, two similar mass gas giants, one in a close order the other at 200 AU.

 

[Timerover51]

How about adding this to the mix. A HOT Jupiter.

http://www.space.com/33551-jupiter-...ak&utm_medium=email&utm_campaign=20160727-sdc

That fuel you have been skimming from the local gas giant might be a tad hot, and not in terms of radioactivity.

 

[maksimsmelchak]

When in doubt check the Wiki. Looks like it could use some data from T5 though. I guess for gas giants I will interpolate the data I have.

One more thing to update! Yeah! More to do!

Shalom,
Maksim-Smelchak.

 

[Spartan159]

One more thing to update! Yeah! More to do!

Shalom,
Maksim-Smelchak.

*Grin, duck, and run very fast while dodging* :devil:

 

[whartung]

For safe jump distances, I've had good luck with tidal force. Calculate G * M / R^3 -> you want this below a specific, very small, value.

So, using Earth as an example, and kg for mass, and km for radius.

G * M / R ^ 3

= 6.674e-11 * 5.972e24 / ((12742km * 100) ^ 3)

= 3.9857e14 / 2.0688e18

= 0.00019266

What's odd is when I run it through Wolfram:

https://www.wolframalpha.com/input/?i=G+*+5.972e24+kg+/+(12742km)+^+3

I get, essentially, the same number, but it's:

0.0000001927, so a few order of magnitude off.

Not sure where the discrepancy is, or if Wolfram is doing something with the units (and the resulting units are really strange).

I simply mention this number, either way, so that if someone was looking for a guideline as to what Tidal number you wanted to work with, 100D from Earth I think would be an adequate benchmark. You can round it up to 0.0002.

Using that number, the safe jump distance for the sun is 72,653,630km, which works out to just over 104D.

Mind, for most every other planet in the system, is much too far. Jupiter is 51D, Saturn is 41D. The other rocky planets between 70 and 85D.

 

[tjoneslo]

https://en.wikipedia.org/wiki/Tidal_force

The original version of this has an extra radius (in meters) term, giving the final set of units as m/s^2 (acceleration). Tidal acceleration increases on the outer edges of the object as it gets larger.

When I've done this in the past, the assumption is the second radius term is a default size 1 meter.

Your calculations about the safe jump distances around gas giants and other planets matches my memories of previous calculations. The earth (and other iron core planets) have the largest safe jump distances, where less dense planets are smaller.

 

[Hemdian]

No arguments from me, I don't have the knowledge to throw in the ring. As to safe jumps, radius? mass? gravity? any or all? I just don't know.

I did a little investigation (back in 1995) of the minimum safe distance to jump. Starting out assuming it was based on simple gravity and calculating for different sizes and densities. The subsequent discussion on the TML (Traveller Mailing List) led to the conclusion that the minimum safe distance to jump was actually based on tidal force.

Both sets of calculations (gravity and tidal force) can be found here: http://sol.trisen.com/default.asp?topic=10&page=29 (and uses MT task difficulties).

 

[tjoneslo]

Both sets of calculations (gravity and tidal force) can be found here: http://sol.trisen.com/default.asp?topic=10&page=29 (and uses MT task difficulties).

Thank you for posting this. I had a vague memory of this, but not clear enough to remember where.

 

[kwyjibo]

G * M / R ^ 3

= 6.674e-11 * 5.972e24 / ((12742km * 100) ^ 3)

In the denominator, you should have multiplied by 1000, not 100, to convert from kilometers to meters. The Wolfram result is the correct one.