Jumping while underway

[phavoc]

I suppose it depends on how accurate you think jumps should/could be. I think one of the deep-space supplements brought up the concept of jump 'shoals' and some other things that are relatively new to the rules overall. I need to go back and read up on them again.

Personally I think if you were to count on the 100D limit to precipitate yourself out of jump space then there'd be a 'bouncing off' penalty. The rules talk about how you can be pulled out of J-space if you get within 100D of a large enough gravitational object (generally a planet or a star, but at some point a large enough asteroid or planetoid could trigger it as well). If you were to always end up at the 100D limit by hitting it, then your astrogation would be pretty easy - aim for the planet and you are good. Seems to me that gets in the way of the spirit of the game and purpose of being able to accurately plot your jump.

 

[MasterGwydion]

I suppose it depends on how accurate you think jumps should/could be. I think one of the deep-space supplements brought up the concept of jump 'shoals' and some other things that are relatively new to the rules overall. I need to go back and read up on them again.

Personally I think if you were to count on the 100D limit to precipitate yourself out of jump space then there'd be a 'bouncing off' penalty. The rules talk about how you can be pulled out of J-space if you get within 100D of a large enough gravitational object (generally a planet or a star, but at some point a large enough asteroid or planetoid could trigger it as well). If you were to always end up at the 100D limit by hitting it, then your astrogation would be pretty easy - aim for the planet and you are good. Seems to me that gets in the way of the spirit of the game and purpose of being able to accurately plot your jump.

Always thought that it was dumb that you never knew where you would come out. Even at TL-16 where they figured out how to create artificial sentience, they still can't navigate any more accurately than, "You appear somewhere near 100D from your destination".

 

[Condottiere]

Uncertainty.

 

[MasterGwydion]

Had jump technology from TL-9 up to Vincennes at TL-16 and accuracy has never improved. Not in thousands of years of jump improvements. Unless you count being able to jump fractions of a parsec at TL-10.

 

[Condottiere]

Jump governors regulate fuel consumption.

Fractional jumping would be possible at factor/zero, going by Interstellar Wars, upto a quarter parsec.

My interpretation being, possibly a customization penalty, aimed at jump drive prototypes.

 

[Endie]

Something else is that the zero velocity rule is relative to the nearest planet, but that planet is going to possess a velocity itself. If you launch from Terra and burn out to 100D, slowing to zero (relative to Terra) then you’re still travelling at about 18 miles every second relative to the sun.

Even if the primary star of the planet you jump to is moving at roughly the same speed relative to the galactic core (and the centre of an expanding universe) the target planet, in the same orbit around a similar sun, could easily be at the opposite point of its orbit, meaning you’re travelling at c. 36 miles every second relative to it. This is equivalent to accelerating at 1G for about 1.6 hours.

Edit: MonsterX mentioned this already: I missed that.

 

[Fluffy Bunny Feet]

I would interpret 0 as versus the velocity to be in orbit at the distance you are. Too fast and your orbit rises too slow and your orbit falls. Just right and the orbit is stable.

 

[rinku]

If you travel to 100D your zero velocity will be relative to the origin world's orbit. Your ship matched orbits with it in order to land, and is still basically in that orbit.

But you could vary your burns to alter that on the way out.

Really, there's a lot of things you *could* do that end up having no practical effect. At some point on the way to jump you set up the vector you want; during your intercept of the destination you match orbits.

Your residual momentum carries over into the post jump location, and your ship is IMMEDIATELY subject to new forces from local gravitation. Pull from the star. Pull from the destination world. Maybe pull from a moon or three. But almost always these will be small compared to your big arse M-Drive and dealing with them is just part of calculating that destination intercept course.

For simplicity's sake, we just use the burn, turnover, burn travel formula, because it's still going to give us a useful time factor (Minutes? Hours? Days?). The exact timing would need far more maths than I'm prepared to work out for a game, and require you have ephemeris for all the major bodies involved.

In the rare occasions that the exact time to arrival is required, the Referee should just state something reasonable. Mostly you just need to know "will they catch us? will we catch them" and "is this fight going to be close to the destination or not?" The three dimensional nature of space and the vagaries of orbital mechanics put this in Referee's decision territory anyway. Something as simple as your ship emerging with a vector at right angles to the orbit of the waiting pirate might give you enough time to add enough distance that they won't bother chasing you.

 

[Condottiere]

Relative to the local gravity wells.

Or the nearest significant one.

 

[rinku]

The destination world is always the most significant one

 

[MasterGwydion]

The destination world is always the most significant one

I think he meant that if you jump to an empty hex. Hence, there is no destination world.

 

[Condottiere]

If I had to find a (funny) comparison:

 

[Condottiere]

As regards to empty hexes, I tend to think that's more game mechanics driven.

The game doesn't want you to use them as short cuts for monoparsec starships, so it disallows it.

I don't recall what the official explanation was, but I'll assume that means that jump drives need a large gravity well as some form of light house.

Nowadays, that's somehow been overcome.

 

[rinku]

Empty hexes don't have any significant gravitational effects for these purposes.

Even at Earth's orbit, the Sun only exerts 0.0006G.

But in an empty hex, it's extremely difficult to fix your exact location. You have no real way of determining if you came out exactly where you aimed, or 6000km that away, or 60,000km that other way. You have no way to measure your current vector except by educated guesswork. You *will* be drifting in some direction, and the faint pull of distant stars will in fact contribute.

At best, with really good astronomy gear, you might be able to get an accurate fix over months of observations. Maybe a survey ship specifically designed to do that stuff might be able to manage it quicker. Although having said that, a rough fix on identifiable stars will quickly tell you if you're in the hex you were aiming for or not.

So as I run it, jumping out of an empty hex will inherently be an inaccurate jump, only reliably capable of jumping to a target star unless there are heroic skill rolls made (never say never. You can TRY to jump in to a specific planet...)

 

[MasterGwydion]

Empty hexes don't have any significant gravitational effects for these purposes.

Even at Earth's orbit, the Sun only exerts 0.0006G.

But in an empty hex, it's extremely difficult to fix your exact location. You have no real way of determining if you came out exactly where you aimed, or 6000km that away, or 60,000km that other way. You have no way to measure your current vector except by educated guesswork. You *will* be drifting in some direction, and the faint pull of distant stars will in fact contribute.

At best, with really good astronomy gear, you might be able to get an accurate fix over months of observations. Maybe a survey ship specifically designed to do that stuff might be able to manage it quicker. Although having said that, a rough fix on identifiable stars will quickly tell you if you're in the hex you were aiming for or not.

So as I run it, jumping out of an empty hex will inherently be an inaccurate jump, only reliably capable of jumping to a target star unless there are heroic skill rolls made (never say never. You can TRY to jump in to a specific planet...)

How hard is it to plot your position in 3-D space using 6 coordinates? The position of every star visible from Charted Space should have already been plotted on a constantly updating model. Why? Because you cannot navigate in 3-D space without an accurate map. So, you just find the positions of 6 stars and you know your position. More stars you can see, the more accurate your position. The computer should do this automatically and rapidly after every jump. Plotting your position in space should be extremely easy for a starfaring civilization. Toddlers should be able to understand the concept in a TL-10+ society.

 

[rinku]

It's a matter of observational error. You simply can't fix positions accurately and quickly enough for a quick turnaround.

Yes, you will know where you are to a fair degree of precision. Sufficient to make a jump to a nearby star. But it is highly unlikely that you can reduce the margin of error of where you actually are to the degree required to make a jump to another object around that star. Not impossible, no, and definitely doable with enough specialised astronomical resources and time.

 

[MasterGwydion]

It's a matter of observational error. You simply can't fix positions accurately and quickly enough for a quick turnaround.

Yes, you will know where you are to a fair degree of precision. Sufficient to make a jump to a nearby star. But it is highly unlikely that you can reduce the margin of error of where you actually are to the degree required to make a jump to another object around that star. Not impossible, no, and definitely doable with enough specialised astronomical resources and time.

How so? If the sensors can detect the positions of one million stars as datapoints and compares the distance of their separation, that will be pretty damn accurate. It takes a 360-degree camera, otherwise known as sensors, and a Ship's Computer with whatever software they use to determine the ship's position in space. Computers will need seconds to calculate all of those equations, including accounting for gravitic lensing.

 

[rinku]

It's about how precisely a ship's sensors can measure the angles. There will always be error, and error always compounds.

But hey, you do YTU with immaculate measurements.

 

[Condottiere]

It depends on how jumping actually works.

In theory, barring misjumps, if you plot the course specifically on distance travelled, you should come out in an empty hex, more or less, where you wanted to.

 

[rinku]

"More or less" is the kicker.

I'm really only talking about the issues of accurately jumping to a world from an empty hex, where your ability to fix your position and vector to the precison required is challenging. If more than one empty hex jump is involved the error compounds, although if you have the time and equipment to do some serious astronomy you can largely reset that, I guess.

But cutting through all that, you will know where you are well enough to jump to a star's 100D, and maybe the rough vicinity of a planet. But be prepared to travel, Traveller.