Antares is a subsector capital, with a population of tens of billions.
Cause and effect is important, though.. Presumably Antares doesn't have population of tens of billions because it is the sector capital, it is the sector capital because it has a population of tens of billions and a fairly high tech level. In other words, because of its economic and military power which translates into political power.
It's not some out of the way backwater, and I really doubt that "doesn't trade much with the outside world".
No, it should have considerable trade, but less than it would have if it wasn't so deep into the star's jump shadow. Realspace traffic isn't as costly as jump traffic, but the added cost effectively put it at the equivalent of several extra jumps distance from its trading partners. Starships would jump in, dock at a space station, offload and load, and jump out again. Their cargo would be transferred to in-system shuttles and ferried to the world.
If I was the Duke of Antares, I'd have the sector (and subsector) administration located on a space station outside the jump limit. The planet would be a backwater of a sort, with no one visiting unless they absolutely had to.
Even if the planet is somehow in Antares' habitable zone, that would be at a distance of about 250 AU from the star (let's leave aside the fact that Antares is too young to have planets and that none will form at that distance anyway, and it's incredibly unlikely to have captured a planet in exactly the right orbit), well within its 1000 AU 100D limit.
Your figures are a little off. Jump limit is at 651 AU and the world Antares orbits at 213 AU (assuming the figures quoted on the
Traveller wiki are correct, which I can't say for sure, since no source is quoted).
But you're right that a position deep inside a jump limit is a problem for a world. However, that has nothing to do with jump masking. That's a problem with jump shadowing, and everyone agrees that MM's essay firmly establishes the existence of jump shadowing.
At the very least (if they're on the same side of the 100D sphere as the mainworld), ships would have to travel a minimum of 750 AU under sublight power to get to the planet from the star's 100D limit, which is an 11 billion kilometer journey which I think would take around 2 years at 1G acceleration. Even at 6g it'd take about 316 days (if my calculations are correct. I'm using a formula from Megatraveller's Referees Companion for this).
Wiki article says 87 days a 1G, 35 days at 6G. It also says that Antares is the largest star in Charted Space, so no other world would have quite that severe a problem.
The obvious conclusion is that Antares simply cannot work as described.
What description would that be?
Since the mainworld is pretty much inaccessible at all times, it's a terrible place to have a sector capital and trade is pretty much impossible. And also, the star could go supernova at any time. If the mainworld orbited a distant companion star at a distance of a few thousand AU from Antares (outside Antares' 100D limit) then that would solve many of these issues, but Antares' 100D limit may still be an obstacle to traffic coming in from a specific direction.
I repeat, if you can reach the near side of Antares' jump limit in one jump, you can reach the far side in two jumps. What happens next may justify your claim that the description of Antares (which I don't know in detail; the Wiki article is woefully short) is flawed, but that has nothing to do with the existence of jump masking.
Hans
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