Jump Arrival Point

[Bardicheart]

A bit of premise first...
Lately I've been going over the trade rules from Merchant Prince and tweaking my house rules. In Traveller games I've played in or refereed, piracy is often very difficult or impossible to pull off. In my experience a ship leaving a planet and approaching the 100D limit can generally jump out before a pirate attack can succeed in disabling the ship. Ships arriving generally jump in somewhere just beyond the 100D limit and move in from there which also makes them a difficult target. So for piracy to work, the target ship needs to be further away from the main world / starport. It also means non jump capable craft moving in the outer system are more likely pirate targets.

This got me to thinking, where exactly do ships normally arrive and why? What are reasons they might jump in to the outer system instead of the main world?

Thought it might be interesting / fun to discuss that.

For example maybe they have a cargo marked for deliver to an outpost in the outer system. So the players have a choice, either jump in to the main world and refuel then travel out. Or jump in to the outer system, make their delivery and then head in.

In some systems, for example under developed or low tech worlds, the outer system might be where you'd normally head (trading with belters for example).

If they're carrying something "questionable" maybe they choose to jump into the outer system with the intent of refueling at a smaller outpost or station to avoid customs checks (maybe the outer system has a lower law level than the inner system / main world... the cargo is legal at the out post but not on the main world).

Pirates set up the trader, part of the cargo they picked up is to be delivered to an outpost 2 parsecs away. Turns out there is no outpost, just a few pirate ships waiting for them to make their delivery. The pirates intend to attack them, take their cargo and get away before any Navy patrols can respond (being further out and much larger distances, this has much better odds of working).

Any other ideas?

Another thought, though I can't think of a justification for it, what if most traffic normally did jump in further out for some reason? That would certainly give pirates more of a chance. Creates more work for the Navy as well. Might start straining the life support for many ships though.

[AndrewW]

Another thought, though I can't think of a justification for it, what if most traffic normally did jump in further out for some reason? That would certainly give pirates more of a chance. Creates more work for the Navy as well. Might start straining the life support for many ships though.

Some condition prevents jumping closer in?

Binary star system, the twin gravity fields prevents it.

Dangerous conditions such as debri from a long ago battle or asteriods make it a bad idea.

Some rogue object with a strong gravity field.

Nervous system that forbids it, wanting to have more notification of any system traffic?

[Lord High Munchkin]

Ships wanting to refuel at an outer-system gas giant.

[locarno24]

The simplest answer;

Stars also have a 100D limit - it's not uncommon for a mainworld's orbit to fall inside it (Earth is only about 10% outside it). Mercury/Venus equivalent worlds would not be jump-able to directly.

Equally, as noted, refuelling at a gas giant is slower but also free (although since it takes something like two days to complete the process it's kind of a false economy if processed fuel would be available elsewhere).

[Condottiere]

1. I haven't figured out the sensor/detection formulas, but the pirates discover the likely route the ship takes to the jump point, have military grade stealth and are on silent running, Once the ship approaches, they jump it.

2. I hear rumours of jump disruption missile.

3. Corrupt astrogation so that they jump into an empty hex, or an insystem jump that's far enough removed so that the prates can have their wicked way with the wayward vessel without unexpected visitations.

[locarno24]

I haven't figured out the sensor/detection formulas, but the pirates discover the likely route the ship takes to the jump point, have military grade stealth and are on silent running, Once the ship approaches, they jump it.

True, but lurking in the 'commercial emergence zone' is dangerous, and jumping in elsewhere in the system still means you're probably going to pass through that region of space anyway.

2. I hear rumours of jump disruption missile.

Jumpbreaker missiles. However, they're something for use on a ship trying to jump out, not jumping in.

[alex_greene]

A Jump that close to the destination world increases the risk of the Jump point forming in the exact same spot as another ship (outbound or inbound) - or worse yet, the Jump point intersecting with another opening Jump point, again whether outward bound or inbound.

It could be easier for the ship to enter the system anywhere within one or two light hours of the mainworld, preferably in the wake of the world, and accelerate briefly to catch up with it.

[CosmicGamer]

Any other ideas?

The not uncommon occurrence that the star of the departure or destination is blocking a direct jump to/from the 100d limit.

[CosmicGamer]

There is a lot of space "above", "below", all around...

A Jump that close to the destination world increases the risk of the Jump point forming in the exact same spot as another ship (outbound or inbound) - or worse yet, the Jump point intersecting with another opening Jump point, again whether outward bound or inbound.

Jumping takes a not so exact amount of time. IMTU the exact location of exiting jump, in relation to moving objects, varies too. Three hours off? The destination is at point X in their orbit instead of Y.

It could be easier for the ship to enter the system anywhere within one or two light hours of the mainworld, preferably in the wake of the world, and accelerate briefly to catch up with it.

What reason is this preferred? I always preferred jumping to a location in advance of the orbit and letting the world come to me. Saves fuel and time vs chasing it down, no?

[alex_greene]

What reason is this preferred? I always preferred jumping to a location in advance of the orbit and letting the world come to me. Saves fuel and time vs chasing it down, no?

If your ship drops out a little late in the trailing wake of the planet, it adds maybe a day extra to the travel time to catch up with the planet that's a little further along its orbit than planned.

If you try and aim your ship to arrive ahead of the planet, and you're three hours late, your Jump point could form in the upper atmosphere and your ship plough right into the ground.

Assuming it's not a gas giant you were aiming at.

[CosmicGamer]

If you try and aim your ship to arrive ahead of the planet, and you're three hours late, your Jump point could form in the upper atmosphere and your ship plough right into the ground.

Above, below, just inside or outside the orbit. Lots of space in advance of the orbit without being directly in it's path.

On a separate note, I thought being within the 100d limit would force the ship out of jump?

[alex_greene]

On a separate note, I thought being within the 100d limit would force the ship out of jump?

Well, if the ship was coming out of Jump anyway ...

[Condottiere]

While looking at it from a tactical view for a marauder, I got the distinct impression that it's not a pleasant experience.

[Bardicheart]

On a separate note, I thought being within the 100d limit would force the ship out of jump?

Well, if the ship was coming out of Jump anyway ...

This just gave me a thought.

Time spent in jump is variable by 6-36 hours, so you cannot know exactly when you'll come out of jump. It occurs to me that it'd be pretty nuts to sit there at the controls for up to 36 hours waiting to emerge so either:
a) either you have no warning about emerging from j-space meaning for 36 hrs there's a tense watch as pilots switch off so there's always someone at the controls (otherwise the ship emerges with no one at the helm).
b) part of the whole jump drive system includes sensors that can detect when the jump "bubble" is about to collapse, so the crew normally gets some warning. But, an unexpected gravity could yank a ship out of J-space with little or no warning and possibly some nasty side effects.

Now supposing some enterprising individuals took a look at some astrogation charts, noting what the incoming vectors from another system would be at a given time, did a lot of number crunching... and say dragged a chunk of rock into that general area. Unexpected gravity starts spitting some very surprised merchant traffic out of J-space in the outer system where...

Just a thought.

[CosmicGamer]

Now supposing some enterprising individuals took a look at some astrogation charts, noting what the incoming vectors from another system would be at a given time, did a lot of number crunching... and say dragged a chunk of rock into that general area. Unexpected gravity starts spitting some very surprised merchant traffic out of J-space in the outer system where...

Just a thought.

Where did our moon go? It was here last night.

[Condottiere]

Creation of an artificial gravity field, which theoretically should be possible post TL9.

[Bardicheart]

Where did our moon go? It was here last night.

LOL... I was thinking something a little smaller. Say a few asteroids a couple of hundred meters across giving a 100D of about 20-25 km each. Spread a few out so they make a "gravity net" of sorts and...

Not saying it would catch everything, but then you wouldn't really want it to. But it did set me to thinking that if you knew the departure point and time (and thus the astrographic location) you could plot their course and possibly set up said "gravity" net to catch anything departing within maybe a a few hours of that departure time and location. Whatever ships jumped from system X at Y time to system Z (where your trap is) would pass through your "net" and get dumped out unexpectedly. (The math on this would be challenging so I'm thinking make an Astrogation Check, Edu, Very Difficult) You've got a 36 hr window to wait around (the variable time as to when the ship actually hits the net), so you could probably manage to hang around while looking mostly harmless. Maybe even claim to be belters, etc. as a cover.

Ships jumping in from other systems or who jumped maybe a day earlier or later would not be affected. That would actually benefit pirates, secret agents, inquisitors, or whoever is pulling this off since they wouldn't want to catch everyone... last thing you need is 50 ships popping out on top of you.

Down side is the Imperial Navy would be watching for such stunts. On the other hand its difficult to detect... those chunks of rock are harder to spot so unless a navy patrol catches you moving one, they may not notice until its too late and the GKs are going out. Even if they do spot you, if you're set up as a belter, you could try and BS about a mining operation, maybe harvesting planetoids for hulls, etc. Succeed and the patrol goes away, fail and they discreetly watch you (which means if you're planning piracy you may end up with 20 intercept fighters on you 30 sec after you fire the first shot... oops). On the other hand if the Navy task force left system yesterday for their next stop on their patrol route...

Now all you need is a ship(s) that can push a 300,000 to 1,000,000 dT rock around in a relatively short amount of time... never said this was going to be easy.

Just brain storming.

[alex_greene]

dragged a chunk of rock into that general area. Unexpected gravity starts spitting some very surprised merchant traffic out of J-space in the outer system

That could happen naturally, if the planet has a moon - and even without a moon or moons, every planet has a L4 and L5 point, where matter tends to naturally collect.

[Bardicheart]

Could but I'm guessing in most cases the planet's moon is within the planet's 100D limit.

Example: Earth (size 8 ) has a 100D limit of about 1,274,200 km. Our moon at apogee is only 405,503 kilometers distant, well inside that limit.

Of course a very small planet might have a moon outside it. But even in these cases mapped systems would include nav charts that detail the orbital periods of all planetary bodies. I would assume part of plotting a jump means plotting a course that avoids all these. Keeping these nav maps updated and accurate is part of what the Scout service does.

Going back to my original topic question; this suggests to me that if a system is particularly "crowded", maybe it has lots of planetary belts for example, may force ships to jump in system beyond them because there's just too many objects to make plotting a course around them feasible. Not official of course but its an interesting idea to make a specific system unique and add some more flavor to your games.

It also raises another point. Suppose a 300 dT asteroid or rogue comet happens to wander across the jump path of a incoming ships. I could see it completely dumping a 200 dT free trader out of jump space. A 2000 dT freighter might be thrown off course, coming out other than where they expected but not necessarily at the comet (treat as an inaccurate jump). Meanwhile a 75,000 dT cruiser would hardly notice (maybe an alarm goes off) but it completes its jump as planned. Again, nothing official indicates this, I'm just considering that if the ship is larger than the object it seems reasonable that it would be less affected and as some point where the ship is far larger any effect by a small chunk of rock would be hardly noticed.

[alex_greene]

Could but I'm guessing in most cases the planet's moon is within the planet's 100D limit.

It distorts the 100D sphere into a shape roughly like a butternut squash lying on its side.

All the more argument for setting the Jump exit point to be about a light hour out, at least, from the planet, in open space, in the wake of the planet, rather than trying to Jump in at exactly 100 D from the world. - the envelope's shape would he just too unpredictable.