CT Only: Stellar Masking
- Thread starter Supplement Four
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Xerxeskingofking
SOC-13
indeed, although my go-to example would the JumpShip/DropShip model of the BattleTech universe.
in that setting, while large companies and governments maintain their own JumpShip fleets, a lot of the JumpShips are independently owned by small, one or two ship merchant companies and make a living by hiring out docking space to DropShips wanting transport (JumpShips owned by the megacorps and governments also sell docking space as a side-line). Their is enough ships using this "pick up" system that it works well enough to keep many merchant companies afloat without needing to own their own JumpShips (i.e. they can get transport to and form their home and destination worlds reliably enough to turn a regular profit, and Jumpships can turn a profit shifting these Dropships around).
Timerover51
SOC-14 5K
Looking at the original post, is there another "Timerover" on the forum? One does not show up in the members list, but I am not sure how up to date that is.
Second, stellar masking is not mentioned at all in Classic Traveller, and I have never bothered with it. I go with 100 diameters away from the nearest gravitational mass, and then you Jump. Adding the diameter of the star into the equation just complicates things.
Third, since Regina is apparently the satellite of a Gas Giant, which also means that it must be fairly close to the star, what is the appropriate Jump parameter for it?
Lastly, what would be the correct jump distance for a White Dwarf, a neutron star, or a black hole?
I just wish to make sure that I make no claim to originating this thread.
Second, stellar masking is not mentioned at all in Classic Traveller, and I have never bothered with it. I go with 100 diameters away from the nearest gravitational mass, and then you Jump. Adding the diameter of the star into the equation just complicates things.
Third, since Regina is apparently the satellite of a Gas Giant, which also means that it must be fairly close to the star, what is the appropriate Jump parameter for it?
Lastly, what would be the correct jump distance for a White Dwarf, a neutron star, or a black hole?
I just wish to make sure that I make no claim to originating this thread.
mike wightman
SOC-14 10K
Supplement 4 is referring to you - he provides a link to a post you made.
Timerover51
SOC-14 5K
Then where is the 51 following the Timerover.
As I said, I take no responsibility for this thread.
Xerxeskingofking
SOC-13
did you click on the hyperlink to the post he is citing? the one that leads to a thread started by you (specifically, your thread on gas giant skimming)?
he is talking about you, he just didn't put the 51 on the end. Not being Sup4. I can only presume, but I would guess that he thought it unnecessary, Given that their is only one timerover of note on these forums, that being you.
also, he doesn't say the thread was your idea, just that he had the idea while reading your thread, and spun it off form their.
GypsyComet
SOC-14 1K
This was established in Book 6, IIRC. It is hardly new information.
Regina's gas giant, Assiniboia, is in Orbit 4 (1.6 AU) around an F7 V star (1.4 Stellar radii), and so is outside the star's jump horizon. Regina is in orbit 55 (for moons, that means 55 planetary radii) of the gas giant, or 145 radii inside the jump horizon. Using Jupiter's numbers, that is roughly 10 million kilometers inside Assiniboia's jump horizon. Assiniboia is about 40 million kilometers outside the star's jump horizon, for what it's worth.
As an aside, here is the footnote on page 46 of Scouts:
"Solar radii can also be used to determine if a location is more than 100 diameters out from the star for jump purposes."
While masking wasn't called that in CT, necessarily, the concept was certainly in place once there was enough information to make it calculable.
Xerxeskingofking
SOC-13
in a similar vein, my high G shuttles would also be a good fit for this idea, as the long, enforced realspace travel would let them make full use of their 9G drives. I havnt worked out what it would be for one of those 66 day trips, but considering the trip I did work out was about a third the length, I feel it might bring it down to 15-20 days or so.
obviously, MgT2e only, but the idea would work at 6G as well.
Straybow
SOC-14 1K
NO WAY!
The list of travel times for mainworlds in the post linked by Xerxes is off by ORDERS OF MAGNITUDE!
A transit of 1 billion km takes only 7.3 days at 1G. Menorb, for example, is listed as taking 66 days. That would be 81 billion km, or 541 AU. How big did the list maker think Menorb's primary was?
Menorb is K2 V (typically ~0.8 Msol, 0.735 Rsol) which makes the 100.5 diameter jump shadow roughly 103M km. At 2√(D/A) that makes 1G (10m/s²) travel time 56.4 hours (not days) to reach the star. Hab zone edge is approx 0.35AU = 52M km for a differential of only 51M km. Travel time at 1G is only 39.7 hours.
Actual travel time will be less than that. The navigator should plot jump exit behind the planet's orbital position, so that travel to the planet involves catching up to the planet's orbital speed. That means spending more time accelerating and less time decelerating to match speed. For Menorb orbital velocity might be around 40-50 km/s, trimming 2-3 hours off transit time.
One might point out that stellar masking has very little effect if the vector of travel is nearly perpendicular to the plane of the destination planet's orbit. You will come out of jump space a relatively short distance out of the orbital plane. On the other hand, if the star system happens to be close to edge-on from the originating system, then at some times of the year the destination world is on the far side of the star. The jump needs to be planned to skirt the edge of the stellar shadow and drop out of J space some distance out of plane. It wouldn't be clear on the far side of the star, as though the route were restricted to the plane of orbit.
Then again, stellar masking of the originating star system might be more significant. One must travel not only to outside the star's jump shadow, but also where the line of travel to the destination isn't masked.
Without actually making a universal calendar for the orbits of all the inhabited worlds, and putting 3D orbital plane information for each system, it isn't something one can realistically track. I suppose one could build up an almanac of visited worlds, adding this information as players travel. Still maybe more difficulty than it's worth.
The list of travel times for mainworlds in the post linked by Xerxes is off by ORDERS OF MAGNITUDE!
A transit of 1 billion km takes only 7.3 days at 1G. Menorb, for example, is listed as taking 66 days. That would be 81 billion km, or 541 AU. How big did the list maker think Menorb's primary was?
Menorb is K2 V (typically ~0.8 Msol, 0.735 Rsol) which makes the 100.5 diameter jump shadow roughly 103M km. At 2√(D/A) that makes 1G (10m/s²) travel time 56.4 hours (not days) to reach the star. Hab zone edge is approx 0.35AU = 52M km for a differential of only 51M km. Travel time at 1G is only 39.7 hours.
Actual travel time will be less than that. The navigator should plot jump exit behind the planet's orbital position, so that travel to the planet involves catching up to the planet's orbital speed. That means spending more time accelerating and less time decelerating to match speed. For Menorb orbital velocity might be around 40-50 km/s, trimming 2-3 hours off transit time.
One might point out that stellar masking has very little effect if the vector of travel is nearly perpendicular to the plane of the destination planet's orbit. You will come out of jump space a relatively short distance out of the orbital plane. On the other hand, if the star system happens to be close to edge-on from the originating system, then at some times of the year the destination world is on the far side of the star. The jump needs to be planned to skirt the edge of the stellar shadow and drop out of J space some distance out of plane. It wouldn't be clear on the far side of the star, as though the route were restricted to the plane of orbit.
Then again, stellar masking of the originating star system might be more significant. One must travel not only to outside the star's jump shadow, but also where the line of travel to the destination isn't masked.
Without actually making a universal calendar for the orbits of all the inhabited worlds, and putting 3D orbital plane information for each system, it isn't something one can realistically track. I suppose one could build up an almanac of visited worlds, adding this information as players travel. Still maybe more difficulty than it's worth.
Menorb's primary used to be an M5 II, according to the old Spinward Marches Campaign. I suspect it was changed for precisely that reason. The giants made a royal mess of things when people started talking about stellar masking. They changed Cogri too, used to be an M1 II.
Menorb primary as originally conceived would have had a stellar diameter of 712 solar diameters per Book 6. Good ol' Sol is about 1.4 million kilometers in diameter. So, Menorb primary, as an M5 II, would have had a 100-diameter limit out at 712*1.4m*100= 99.6 billion kilometers. Habitable zone at 122 AU, or about 18.3 billion kilometers. So, 81.3 billion kilometers best case. I get T at 2,851,000 seconds from start to turnaround, then the same to decelerate, or about 66 days from 100D limit to mainworld at 1G, and that's rounding 1G up to 10 m/s2. I'm pretty sure the person who made the list was not using 1 m/s2
Is it fair to say that jump masking was a far bigger problem for earlier editions that had much wilder stellar results? So you had a bunch of high pop worlds with native life in the habitable zones of supergiants. Many of these stars have been reconned to something on the main sequence, and for those stars masking isn't much of an issue.
Straybow
SOC-14 1K
Well, the simple solution to Menorb as type II is to say the 100D jump limit shadow only applies to solid, icy, or similarly dense matter that would include a main sequence (type V) star. Various subgiant, giant, and supergiant stars are so rarified that they've expanded to roughly the size of the star's main sequence lifetime jump shadow, yet the mass is probably a little bit less than the star's original mass. Perhaps the jump shadow might expand to double the main sequence lifetime shadow due to greater tidal shear, or maybe not even that much.
100D IS the simple solution.
Many suggest that it's really a tidal function related to mass of the object. That brings in lots of math about density and mass and other things.
Or, you can just take the diameter, multiply it by 100, quip "Boy, Jump Space sure is weird", and call it a day.
How does 100D apply to a black hole? is D the event horizon?
100D from the event horizon of a stellar black hole is about 1000-5000 km. I do NOT want to be there under any circumstances. About 1x106 g's even by classical Newtonian calculation, and tidal forces of about 0.1 g/m unless I miscalculated.
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Menorb primary as an M5 II was 16 solar masses. If we assume it's an older star that's moved off the main sequence, and if we use CT Book 6 as a guide, then it was a bit smaller than a B0 V before it expanded, and the original diameter would have been a bit under 10 solar diameters ... and the star's original habitable world froze up when the star moved off main sequence and expanded. Habitable zone moved inward from orbit 12 to orbit 11, covering a world that had originally been baked. It's an interesting idea, but I'm not certain a world originally in a Venusian orbit would still have any water to speak of by the time things cooled down. Maybe the Ancients flew some ice-teroids into it in a terraforming experiment. But, putting that aside, it would be a cool history; it means Menorb system has a frozen world that might once have had a living ecology. There's adventure fodder in that. Makes it a shame to have changed it - though the idea might be workable elsewhere.
At one time Aramis proposed this idea where the 100-diameter limit evolved from the cube root of some function or another. I wish I could recall the details; I thought it was rather clever.
I confess this is the opposite of what I expected to happen when a star moves off the Main Sequence to Giant phase. For instance, Heya, in the Marches in Regina subsector is an Ag world that orbits a K6 III orange Giant. I’ve been playing for years that millennia ago Heya was a frozen world like Europa or Enceladus and the star’s expansion to Giant phase shifted the HZ outward, immolating the old HZ and thawing out Heya, releasing the budding ecosystems locked under the ice.
Running the numbers with stellar data approximated from GURPS First In, I get an orbital period of over 50 years, creating some interesting flora and fauna life cycles, as well as an interesting and different culture to interact with.
Of course (back to the OT) TL 5, star port B Heya is, under this paradigm, several days’ travel inside the star’s jump shadow for 2G ships, almost a week for 1G vessels... on the coreward Imperial border where many Vargr raiders prowl.
If I am mistaken about how stars leave the Main Sequence and their energy output when they do so, well... Heya’s too much fun to “fix” IMTU.
I believe the 100D limit and the "cube root" being referred to has to do with the gravitational tidal force.
G-Field (Gravitational acceleration):
- ag = -GM/R2 (in mks-units, divide by 10 for units in g's)
- Tg = ∆ag = D x -GM/R3, where D is the length (or diameter) of the object experiencing the tidal force. (in mks-units, divide by 10 for units in g's per meter)
So in this interpretation, it is not necessarily the g-field itself that is the problem, but rather the change in intensity of the field with respect to distance across the dimensions of the ship (i.e. the gravitational gradient). This also means that an accelerating ship would potentially have no problem jumping (as the acceleration would potentially be the same at any point on the ship under acceleration). See: Equivalence principle.
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