Passive Planetary Defenses

[Taav]

So, I'm still curious, what happens if you manage to intercept one of these ships...

1. A destroyed ship is a destroyed ship. It has no effect on the next turn of the starship battle.

2. If you need a reason to discount the mass.... it burns up into the atmosphere if present... if not... it hits a non-critical portion of the planet or planetoid and hereafter is referred to as crater 1105-001.

 

[Garnfellow]

Am I wrong, or is this whole exploit predicated on the idea that a ship accelerates to an extremely high velocity in system A, then jumps to system B and slams into the target planet before any defense systems can engage?

Given the variability in time a ship spends in jumpspace, how accurately can someone be expected to predict the exit vector?

 

[Hal]

So, I'm still curious, what happens if you manage to intercept one of these ships with a spinal mount sized chunk of dense material moving at a high speed? Would they vaporize before hitting the planet? How long do you have to react assuming detection of jump exit?

To sort of give you an answer to your question...

It depends on which Traveller Game system rules you are using.

If you're using the rules that the 100 diameter limit includes Stars, then the maximum distance from a target using a jump where you can PERFECTLY predict the exit vector of a ship leaving Jump space and entering normal space, is 100 diameters from either of the World or the Sun - which ever places the exiting object at 100 diameters furthest away from the target. In other words, if a planet is well within a star's 100 diameter limit, then the sun's limit determines the closest it can get from jump space, otherwise, the planet's determines it.

My problem with Traveller's Jump Exit game mechanics in use since the start of Classic Traveller Onwards, is the lack of precision in what exactly is happening with the Jump and its Variability spent in Jump space.

Time: does time pass at a 1 for 1 ratio within a jump bubble as with the external to jump bubble normal space? For example, if I enter Jump space at 11:00 PM day 23:00:00, 100-1105 (Imperial reckoning by calendar date), and exit jump space after spending an additional 6% time in jump space (7 x 24 x 1.06) or 7 days, 10 hours 4 minutes 48 seconds, will it now be 09:04:48 108-1105? To the people aboard the ship, all of that time passed. To the rest of the universe, did that time pass, or did precisely 7 days pass?

If the former, where the time in jump space bubble matches the time spent in physical universe, the sun that the jump was targeted to end up in, has moved an addition distance that the 6% extra time in Jump space didn't account for. In addition, the planet itself will have moved a given distance to take into account the extra 10 hours, 4 minutes and 48 seconds of its own motion.

In the end, the exit point, having missed its intended target point of precisely 168 hours transit time in jump space, will no longer be pointing at the impact point of its intended target. Between the star's own motion and the planet's own motion, a near-C projectile will miss its intended target even if its original aim had been spot on! So the +/- 10% rules given in CT, largely imply that the object will miss its target.

The real issue is what happens when you take a maneuver drive, connect it to an asteroid, power it up, and point it towards where a given planet will be in a given time required to move the asteroid into a collision course.

WARNING! Talking about near-C rocks, or the issues involved with navigation and/or jump space trip duration and implications therein, will run into the issue that many people, playing different versions of Traveller, will disagree with the analysis or how Jump Drives work.

To give you an idea of how different game systems can truly be with regards to Traveller...

CT had it where you only rolled for miss-jump if your ship did not submit to the once per year maintenance interval, or used unrefined fuel, or jumped within a given distance of a planetary mass.

GURPS TRAVELLER requires that the Pilot make its skill roll on 3d6. The Navigator makes its roll versus skill on 3d6, and the Engineer makes its skill roll on 3d6.

The problem with the GURPS TRAVELLER approach versus CT is that the odds of all three skill rolls succeeding are less than the rules used in CT (which made jumps automatic). The odds of a crew with skill at 12 on 3D6, is a roughly 3/4 chance of success for one roll. But the odds (statistically speaking) of all three rolls succeeding is equal to the odds of each roll times the others. So: .75 x .75 x .75 = .4219 (Call it a 42% chance of successfully entering jump space in one attempt).


I'm sure others can chime in on the oddities of different systems versus the original CT version (not to mention TRAVELLER: THE NEW ERA's version of how the maneuver drives work!)

In the end? It will boil down to what YOU want to do with YOUR game. If people have fun playing in your game universe where the maximum speed of a ship using Maneuver drives is 10% the speed of light, then so be it. If Near C rocks can exist in your Traveller Universe, then so be it.

I will confess however - it is nice when you can ask a physics question and get an answer back.

For me, I guess, in the end, it boils down t the story and having some level of internal self-consistency where it comes to administering a game for my players. I really HATE the jump rules in GURPS TRAVELLER where the stellar masses can cause a ship to drop out of Jump space. It wasn't in the original CT rules, and it annoys me from time to time. My solution? Ignore the rule and not use it.

 

[Carlobrand]

Am I wrong, or is this whole exploit predicated on the idea that a ship accelerates to an extremely high velocity in system A, then jumps to system B and slams into the target planet before any defense systems can engage?

Given the variability in time a ship spends in jumpspace, how accurately can someone be expected to predict the exit vector?

That was answered in part of the math Aramis offered:

...3.456e9 m transit.
Earth diameter 1.2742e7m
100D limit 2.5484e9m diameter sphere...
Distribution is pretty close to standard ... so putting that as a percentage... 73% of the range, but probably 90% of the jumps. We can use the 100D limit, instead.
Note that it's a 6d6 roll, so standard deviation is (per Anydice) 4.18... 31 hour range is thus ±3.708 sigma, and the variability is 22.6 hours worth to hit the sphere in the ±2.7
halving that, 1.28e9 m (rounding up)... looking it up, that's 87%...

I can't recall where the 6D6 roll came from. CT was a straight 7 days, if I recall, though one of the supplements may have added a bit more info. MT was doing 7 days unless you rolled a 1 or a 6 on 1d6, in which case it was 6 or 8 days, and MT Starship Operator's Manual was suggesting 124 + 2d6x6.

 

[aramis]

That was answered in part of the math Aramis offered:



I can't recall where the 6D6 roll came from. CT was a straight 7 days, if I recall, though one of the supplements may have added a bit more info. MT was doing 7 days unless you rolled a 1 or a 6 on 1d6, in which case it was 6 or 8 days, and MT Starship Operator's Manual was suggesting 124 + 2d6x6.

DGP SSOM.

 

[Spartan159]

OK, I'm not being clear. Without going into aiming of near C ship through jump space, what happens if you hit a near C ship with near C large chunk of something dense, will it vaporize the ship?

Could having large mass driver cannons in orbit be a viable defense? Or am I a clueless deer in the headlights here.

 

[aramis]

OK, I'm not being clear. Without going into aiming of near C ship through jump space, what happens if you hit a near C ship with near C large chunk of something dense, will it vaporize the ship?

Could having large mass driver cannons in orbit be a viable defense? Or am I a clueless deer in the headlights here.

A megaton of TNT will pretty much wipe out wet naval ships within a couple miles... it will completely level about a kilometer radius, ruin structures to about 6 km...

A gigaton, thanks to the inverse square, is only about x31 that range...
A Terraton is about x1000 range.

That 1G 100Td ship (at about 350 MT) is likely to make a crater a km across, flatten buildings to 30 km, destroy buildings to 120 km, severely damage to about 200 km, and cause fires to about 180 km, and burn people to about 350 km...

At least all the radiation is going to be in the IR, near-visible and visible ranges... unlike a nuke.
For that 2 terraton 6G, multiply those by about 70... as in, the crater is likely to be some 70 km, the total flat about 210km, buildings destroyed (but not blown over) for about 8400 km... as in, wipe out all structures within a hemisphere... just from the shock.... then the rain of hot death which follows from the splash...

Can we say "Dino-Killer?"

 

[Lycanorukke]

I think he means what happens when the planet notices the C-rock inbound and shoots at it with missiles, mass drivers, shuttles, etc _before_ it hits the planet.

 

[aramis]

I think he means what happens when the planet notices the C-rock inbound and shoots at it with missiles, mass drivers, shuttles, etc _before_ it hits the planet.

Total energy reduced by the intercepting projectile's energy. Which, if it's not enough to shatter cleanly, results in a whole lot of smaller impactors at velocities great enough to cause multi-dozen kiloton or larger impacts.

If the incoming is small enough and slow enough, you can prevent impacts by pushing it all to graze in, and burn up. Still dumps the energy, just not nearly as fast. And damage is more a factor of rate of energy change than of total energy change.

Also note - by timing it right, you can reduce the probability of miss by jumping to about 200 diameters short of median position, and almost assure a hit. Not much they can do will change that, and most things the can to to change it will simply make it a MIRV type hit instead of a single hit...the beaten zone gets FAR worse hit, but the outer zones aren't much effected. And the duration of impact events spreads out over a couple hours instead of a minute...


And if it's not big enough to crack it with the Vr (relative velocity) available, it's not big enough to matter. If it is big enough, it's going to scatter it out, so that hemisphere (well, about a 70° wide area) can break 180°...

... Glancing blows can alter a whole lot more.

Tunguska was only about 10-20 Megatons... 15 is the "best guess" from what I've read... split that scoutship up into about 15 tunguska events on the same day... some of which might throw rock and debris into low orbits...

Oh, and Tunguska caused a 5.0 Earthquake. A scoutship impact is about 6.2 on the Richter scale. A 2 Terraton impactor is doing probably a 9.5 to 10.5 on the richter scale. Think the 1964 Good Friday in Alaska. It caused tsunami damage across a lot of coast... and flattened Valdez, Seward, and several (fairly small) cities. A 10.5 can be felt a few thousand miles from source...

 

[Spartan159]

I think he means what happens when the planet notices the C-rock inbound and shoots at it with missiles, mass drivers, shuttles, etc _before_ it hits the planet.

Yup. I did figure a C-rock would be harder to deal with, but I was hoping a large enough mass hitting a C-ship would result in vaporization.

 

[Carlobrand]

So, the stolen scout, now manned by terrorists, jumps in at ludicrous speed on a direct course for planet Bullseye. Imperial dreadnought Fearless happens to be properly positioned and takes position between planet and oncoming ship, and forces the ship to ram her to reach the planet. Fearless is transformed into a cloud of incandescent spreading debris. Scout becomes a spreading jet of slightly less than ludicrous speed plasma on a course to intercept the world. What happens next?

 

[kilemall]

I would think a lot depends on how many large size chunks make it through that don't burn up in atmosphere. Atmosphere value should matter here, the thicker the atmosphere the more chunks burn up and the thinner atmospheres it goes through.

Conversely, more shockwave action the thicker the atmosphere.

 

[aramis]

I would think a lot depends on how many large size chunks make it through that don't burn up in atmosphere. Atmosphere value should matter here, the thicker the atmosphere the more chunks burn up and the thinner atmospheres it goes through.

Conversely, more shockwave action the thicker the atmosphere.

Burnign up in Atmosphere does impart the same energy, but as heat, rather than kinetic, and spreads it out timewise.

 

[Carlobrand]

I am assuming that the impact energies at collision convert pretty much the entire mass of the scout into plasma at a range at which the full plasma mass strikes the atmosphere. At point of impact, scout's nose vaporizes along with the impacted portion of the dreadnought hull. But that bit of plasma nose still has tremendous velocity and energy, and it's shoving through the dreadnought hull plasma to impact and convert to plasma more hull mass deeper in, while the remainder of the scout is crowding into the now-slowed plasma mass and in turn converting to high-velocity plasma. I'm basically thinking the entire mass of the scout shoves through the dreadnought but vaporizes under the forces involved, so now you've got a ball of superheated dense scout-plasma with a substantial fraction of its former speed, about a second or two away from impacting the planet's atmosphere at - say 20-30 kps. And then ...