Imperial Research Station A forum for discussing technology and related topics for use in the Traveller Universe 
February 22nd, 2021, 08:09 PM

Citizen: SOC14


Join Date: May 2008
Location: Stockholm 🇸🇪
Posts: 2,426
Gallery :
0


Quote:
Originally Posted by Leitz
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=½A×t² or time t=SQRT(2D/A).
So, one million km (=one billion m) at 3 G (≈30 m/s²) would take t = SQRT(2×1000000000/30) ≈ 8164 s ≈ 136 minutes.
At that point you would travel at 30 m/s² × 8164 s ≈ 244949 m/s ≈ 245 km/s ≈ 881816 km/h or approx. 550000 mph.

February 23rd, 2021, 01:31 AM

Citizen: SOC14


Join Date: Oct 2016
Posts: 1,156


Quote:
Originally Posted by Leitz
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
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=½A×t² or time t=SQRT(2D/A).
So, one million km (=one billion m) at 3 G (≈30 m/s²) would take t = SQRT(2×1000000000/30) ≈ 8164 s ≈ 136 minutes.
At that point you would travel at 30 m/s² × 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 100D _{origin} + 100D _{destination}). If the origin world is larger than the destination world, you flip and retroburn before Jumping; if it's smaller, you flip after Jump exit.

February 23rd, 2021, 08:56 AM

Citizen: SOC12


Join Date: Sep 2020
Posts: 409
Gallery :
0


Quote:
Originally Posted by Grav_Moped
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 100D_{origin} + 100D_{destination}). If the origin world is larger than the destination world, you flip and retroburn 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.

February 23rd, 2021, 12:12 PM

Citizen: SOC14


Join Date: Nov 2004
Posts: 2,814
Gallery :
0


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/s² * 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 34 turns of combat.
I would ask your pirates to use the Mayday rules instead of the Book 2 rules .
Better chance of surviving 34 rounds of continual laser fire than 15.
In Brilliant Lances, it's 30m per turn, so 9 turns.

February 23rd, 2021, 12:57 PM

Citizen: SOC14


Join Date: Oct 2016
Posts: 1,156


Quote:
Originally Posted by Werner
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.

February 23rd, 2021, 02:14 PM

Citizen: SOC14


Join Date: Nov 2013
Posts: 3,893
Gallery :
0


Running depends on how fast the pursuer is closing, and most commercial spaceships don't appear to have a larger engine than factor two.

February 23rd, 2021, 10:27 PM

Citizen: SOC12


Join Date: Sep 2020
Posts: 409
Gallery :
0


Quote:
Originally Posted by Condottiere
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.

February 24th, 2021, 09:19 AM

Citizen: SOC14


Join Date: Nov 2013
Posts: 3,893
Gallery :
0


Time to either change the transponder, or go into stealth mode.

February 24th, 2021, 12:52 PM

Citizen: SOC12


Join Date: Feb 2017
Posts: 295
Gallery :
0


Quote:
Originally Posted by whartung
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 v² = ∫ G earthmass/r² + 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?

February 24th, 2021, 05:20 PM

Citizen: SOC14


Join Date: Nov 2013
Posts: 3,893
Gallery :
0


Most inhabited worlds in Traveller are less than Terran norm.
So default one gee drives have some room to manoeuvre.

Thread Tools 

Display Modes 
Linear Mode

Posting Rules

You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts
HTML code is Off



