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  #11  
Old February 22nd, 2021, 08:09 PM
AnotherDilbert AnotherDilbert is offline
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Quote:
Originally Posted by Leitz View Post
That's what I don't really want. I'm looking at "I need to be there as soon as I can, how long is that?" Turn and burn assumes you end up with zero velocity.
That is generally what you want. If you accelerate all the way you won't "be there", you will fly by (or crash into) at very high speed, without any real chance of interacting with the target.


But if you just want to accelerate all the way it is D=At or time t=SQRT(2D/A).

So, one million km (=one billion m) at 3 G (≈30 m/s) would take t = SQRT(21000000000/30) ≈ 8164 s ≈ 136 minutes.

At that point you would travel at 30 m/s 8164 s ≈ 244949 m/s ≈ 245 km/s ≈ 881816 km/h or approx. 550000 mph.
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  #12  
Old February 23rd, 2021, 01:31 AM
Grav_Moped Grav_Moped is offline
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Quote:
Originally Posted by Leitz View Post
That's what I don't really want. I'm looking at "I need to be there as soon as I can, how long is that?" Turn and burn assumes you end up with zero velocity.
Quote:
Originally Posted by AnotherDilbert View Post
That is generally what you want. If you accelerate all the way you won't "be there", you will fly by (or crash into) at very high speed, without any real chance of interacting with the target.


But if you just want to accelerate all the way it is D=At or time t=SQRT(2D/A).

So, one million km (=one billion m) at 3 G (≈30 m/s) would take t = SQRT(21000000000/30) ≈ 8164 s ≈ 136 minutes.

At that point you would travel at 30 m/s 8164 s ≈ 244949 m/s ≈ 245 km/s ≈ 881816 km/h or approx. 550000 mph.
If Leitz is asking something like "how long does it take to get to the 100D limit if you're jumping 'hot' (a 'running jump')" it makes some kind of sense.

Though if you assume away relative motion between origin and destination (and simplicity says you might want to), the "turn and decelerate" point could be on either side of the Jump. Exactly where, depends on the relative world sizes (that is, the 100D limits for each world may be different, and the trip distance is 100Dorigin + 100Ddestination). If the origin world is larger than the destination world, you flip and retro-burn before Jumping; if it's smaller, you flip after Jump exit.
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  #13  
Old February 23rd, 2021, 08:56 AM
Werner Werner is offline
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Quote:
Originally Posted by Grav_Moped View Post
If Leitz is asking something like "how long does it take to get to the 100D limit if you're jumping 'hot' (a 'running jump')" it makes some kind of sense.

Though if you assume away relative motion between origin and destination (and simplicity says you might want to), the "turn and decelerate" point could be on either side of the Jump. Exactly where, depends on the relative world sizes (that is, the 100D limits for each world may be different, and the trip distance is 100Dorigin + 100Ddestination). If the origin world is larger than the destination world, you flip and retro-burn before Jumping; if it's smaller, you flip after Jump exit.
If someone is chasing you, if you flip and start decelerating, he will catch you, but since you are accelerating to a jump point, there is nothing physical to crash into, you just reach the required distance and you press the jump button. Of course when you drop out of jump space at the 100 diameter limit you may have a problem, because you are still going at that speed, which you need to slow down from if you do not wish to crash into your destination. You know where this is a real problem, when you are trying to accelerate to the 100 diameter limit of a gas giant and your destination is a terrestrial planet. Do you have two choices, you can accelerate so you miss the planet and then slow down, accelerate towards the planet and then slow down again or you decelerate much faster that you accelerated away from that gas giant, and I'm assuming since it was a chase, your ship was accelerating away at its maximum capacity, so this second option is not usually available.
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  #14  
Old February 23rd, 2021, 12:12 PM
whartung whartung is offline
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So, for the 100D Earth scenario at 1G:

t = sqrt(2d/a)

t = sqrt(2 * 1,200,000,000 / 10)

t = sqrt(240,000,000)

t = 15492s / 3600 = 4.3 hours

Velocity is v = at

So,

v = 10m/s * 15492s

v = 154,920 m/s

If you happen to arrive at the destination system with it's Earth like body.

t = d/v

t = 1,200,000,000 / 154,920

t = 7,745s / 3600 = 2.1hrs before you "arrive" at the planet, going far to fast to do anything.

This is not a problem, however. When you plot your jump, you simply orient the ship to arrive not vectored toward anything dangerous as you work on slowing yourself down, ideally out of danger from whatever is pursuing you.

With Book 2, a turn is 1000 seconds.

So, in the first scenario, there's potentially 15 turns of combat that can take place on your way to Jump.

In Mayday, a turn is 100 minutes, 6000 seconds. That means there's 3-4 turns of combat.

I would ask your pirates to use the Mayday rules instead of the Book 2 rules .

Better chance of surviving 3-4 rounds of continual laser fire than 15.

In Brilliant Lances, it's 30m per turn, so 9 turns.
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  #15  
Old February 23rd, 2021, 12:57 PM
Grav_Moped Grav_Moped is offline
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Quote:
Originally Posted by Werner View Post
If someone is chasing you, if you flip and start decelerating, he will catch you, but since you are accelerating to a jump point, there is nothing physical to crash into, you just reach the required distance and you press the jump button. Of course when you drop out of jump space at the 100 diameter limit you may have a problem, because you are still going at that speed, which you need to slow down from if you do not wish to crash into your destination. You know where this is a real problem, when you are trying to accelerate to the 100 diameter limit of a gas giant and your destination is a terrestrial planet. Do you have two choices, you can accelerate so you miss the planet and then slow down, accelerate towards the planet and then slow down again or you decelerate much faster that you accelerated away from that gas giant, and I'm assuming since it was a chase, your ship was accelerating away at its maximum capacity, so this second option is not usually available.
If you're running, you burn the whole way to Jump Limit and expect to overshoot the destination. The extra fuel burn to finish slowing down as you pass the destination world, then travel back to it from your stopping point, is just the cost of doing business.

The other thing here is that if "running" jumps are standard, the flight path ought to give you a chance to predict the ship's destination based on velocity at Jump. The vector (handwaving the relative stellar motions issue) tells you something about the relative size of the destination world compared to that of the origin world.
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  #16  
Old February 23rd, 2021, 02:14 PM
Condottiere Condottiere is offline
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Running depends on how fast the pursuer is closing, and most commercial spaceships don't appear to have a larger engine than factor two.
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  #17  
Old February 23rd, 2021, 10:27 PM
Werner Werner is offline
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Quote:
Originally Posted by Condottiere View Post
Running depends on how fast the pursuer is closing, and most commercial spaceships don't appear to have a larger engine than factor two.
Of course the players might be running from Imperial Patrol Cruisers because they are pirates and don't want to be caught.
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  #18  
Old February 24th, 2021, 09:19 AM
Condottiere Condottiere is offline
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Time to either change the transponder, or go into stealth mode.
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  #19  
Old February 24th, 2021, 12:52 PM
sudnadja sudnadja is online now
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Quote:
Originally Posted by whartung View Post
So, for the 100D Earth scenario at 1G:

t = sqrt(2 * 1,200,000,000 / 10)
I don't know that it is important to your analysis, but it looks like you are using about 94 diameters rather than 100, and you don't seem to be accounting for force applied by Earth's gravity. Velocity at 100D from the surface (201 radii from the center) would be more like:

1/2 v = ∫ -G earthmass/r + 10 {r,6378135,201 * 6378135} and that ends up being about v=159337 m/s. Time to 100 diameters from the surface is more like 18555 seconds, unless planetary gravity is handwaved - but page 37 of book 2 of the LBB implies that it should not be.

How is this typically done in practice in most games?
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  #20  
Old February 24th, 2021, 05:20 PM
Condottiere Condottiere is offline
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Most inhabited worlds in Traveller are less than Terran norm.

So default one gee drives have some room to manoeuvre.
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