Crashing ships as weapons

[kilemall]

What drives that need?

The whole 'must survey spacetime ahead of time before accurate jumps are possible' mechanic IMTU, coupled with wanting a reasonable time for opening of new systems vs. doing risky wildcat jumps.

If it takes 30 years to cross a parsec people won't bother, they'll just eat the risk and reward the lucky.

Creates a hardline of 'civilized space' vs. crazy/desperate people out on the edge. Part of that in the Oort Cloud, want more on the edge of the frontier.

 

[nobby-w]

A couple of questions have sprung to mind:

where did the 250MW=1EP come from other than a made up number in Striker - put another way is the output of fusion reactor in Traveller something we could redefine?

how big are the fission reactors used on subs and carriers today and what is their maximum energy output?

I did just that. 250MW=1EP is a lot of juice, and really a 250MW laser is Yuuuuuge. I have done 50 or 100MW, assuming that you need to add access ways in order to maintain your power plant on a starship, and the space is not just a solid lump of metal.

 

[whartung]

The whole 'must survey spacetime ahead of time before accurate jumps are possible' mechanic IMTU, coupled with wanting a reasonable time for opening of new systems vs. doing risky wildcat jumps.

What happens if you don't survey? Does the jump fail? Or can you jump ahead, arrive "poorly", make a "better survey" since you're "closer", jump back (to your accurately surveyed starting point), rinse and repeat until the survey is complete?

 

[kilemall]

What happens if you don't survey? Does the jump fail? Or can you jump ahead, arrive "poorly", make a "better survey" since you're "closer", jump back (to your accurately surveyed starting point), rinse and repeat until the survey is complete?

The average surveyor/scout ship can do the job, but has to be in the system and within typical sensor ranges for CT. The survey data degrades as time goes on, so in civilized systems there is a continuing effort to update the information.

Note that this means that if the space around Earth is surveyed but say Mars isn't, it's a misjump going to Mars.

If one wildcat jumps into an unsurveyed area, one risks misjump at a near certainty, with the old school randomized multi-parsec penalty.

Only luck AND exceptional navigation skill would allow a safe jump.

So this means something like the Oort Cloud is partially protected by a lack of up-to-date surveying, and jump data for say naval fuel dumps between systems are a national secret.

There is a brisk business in getting or selling survey data for places peoiple normally do not/should not go, and many a corporate black op hinges on getting this data.

A typical mission profile for a scout cruiser is to decel halfway to target, jump back several courier ships, the scout cruiser eventually jumps back and a forward fuel dump is established. A new cruiser jumps out and completes the last leg to the target system.

Typically two scout cruisers make the trip to each new system.

 

[sudnadja]

That's really interesting.

Anyone want to do the math to determine relative velocity attained at 5G in 13 million km? Check my math.

So final velocity = 0.3% the speed of light when the M-drive stops really adding to the velocity.

What I didn't do is the calculus required to account for the reduction of gravitic push as it diminishes from 100% at 0 diameters to 1% at 1000 diameters, as an inverse-square function of distance. That is, I assumed a constant 5G acceleration for the entire trip, which is not at all the case.

The description of the problem isn't very clear, but basically I set up the math like this:
{x''[t] = 9.8 pf - G M x[t]^-2, x'[0]==0, x[0] == R}

Where pf is a piecewise function that provides 5 when distance is <= radius of the planet, a linear falloff from 5 to 0.05 (1% of the original value) at 1000 diameters from the surface of the planet (1000.5 diameters from the center) and an even 0.05 after that. G is the gravitational constant and M is the mass of the planet. I used earth mass and radius for these.

as you see, I am presuming a launch from the surface of the planet, do not compute atmospheric drag but do take into account the gravitational field of the planet reducing as you get further away.

100 diameters from the center of the planet is attained at 7337.81 seconds, at which time net acceleration is 4.50285g, velocity is 343516 m s^-1 and position relative to the center of the world is, of course, 100 diameters. 0.114585% c.

I don't know what the gravatic interaction rules are supposed to be though - is it a linear fallof with distance from the world or is it presumed that M drive thrust is (in the case of a "5g" ship) 5*whatever acceleration by gravity is at any particular point?

 

[aramis]

I don't know what the gravatic interaction rules are supposed to be though - is it a linear fallof with distance from the world or is it presumed that M drive thrust is (in the case of a "5g" ship) 5*whatever acceleration by gravity is at any particular point?

Under CT...
Misjump on 13+ and Destroyed at 16+ on 2d6+DM's
DM+1 unrefined fuel in in non-scout/navy ship
DM+5 at under 100 diameters
DM+15 at under 10 diameters.

So, even if you don't stack the 100 and 10 diameter limits, given the min roll of 17, from inside 10 diameters, BOOM.

 

[sudnadja]

Under CT...
Misjump on 13+ and Destroyed at 16+ on 2d6+DM's
DM+1 unrefined fuel in in non-scout/navy ship
DM+5 at under 100 diameters
DM+15 at under 10 diameters.

So, even if you don't stack the 100 and 10 diameter limits, given the min roll of 17, from inside 10 diameters, BOOM.

Oh, I think I misunderstood. I had taken the thread to be regarding the performance of a maneuver drive as related to the strength of the local gravitational field, thus I was computing liftoff from a world at 5g and accelerating to 100 diameters with the drive performance degrading as a liner function of distance.

In our own games, for jumping "inside" of 100 diameters, we had been using homebrew rules where the performance of the jump drive, and the chance of a misjump, were related to the local tidal gradient. Thus you would generally have to get to 100 diameters, but you could cut corners a little bit, and there were often strategic jump points well inside the 100 diameter zone - for example where a large moon and the planet's gravities effectively cancel each other, or between the planet and its primary, but those positions tended to occupy a fairly small volume of space.

 

[aramis]

Oh, I think I misunderstood. I had taken the thread to be regarding the performance of a maneuver drive as related to the strength of the local gravitational field, thus I was computing liftoff from a world at 5g and accelerating to 100 diameters with the drive performance degrading as a liner function of distance.

In our own games, for jumping "inside" of 100 diameters, we had been using homebrew rules where the performance of the jump drive, and the chance of a misjump, were related to the local tidal gradient. Thus you would generally have to get to 100 diameters, but you could cut corners a little bit, and there were often strategic jump points well inside the 100 diameter zone - for example where a large moon and the planet's gravities effectively cancel each other, or between the planet and its primary, but those positions tended to occupy a fairly small volume of space.

the canonical implies a gradient. It doesn't actually provide one.

If we take the -5 as the midpoint of the 10-100, so 55 diameters, and the -15 as the midpoint of 0 to 10, or 5 diameters...
that implies a 1 step in a 10 x base 10 log scale ... call the mystery function ƒd()
so we need
ƒd(100)=0
ƒd(55) = 5
ƒd(10) = a
ƒd(5) = 15
pattern solve implies ƒd(10)=10

 

[sudnadja]

the canonical implies a gradient. It doesn't actually provide one.

If we take the -5 as the midpoint of the 10-100, so 55 diameters, and the -15 as the midpoint of 0 to 10, or 5 diameters...
that implies a 1 step in a 10 x base 10 log scale ... call the mystery function ƒd()
so we need
ƒd(100)=0
ƒd(55) = 5
ƒd(10) = a
ƒd(5) = 15
pattern solve implies ƒd(10)=10

Approximately, linear regression would have f(10) = 13.5 or so.

In[622]:= p=Predict[{100,55,5}->{0,5,15}]
Out[622]= PredictorFunction[Input type: Numerical
Method: LinearRegression

]
In[623]:= p[10]
Out[623]= 13.5196

close enough!

But what I meant was a subtle change in rules, or a description of the limitations of jump drives being related to the local gravitational gradient (generally called "tides" - first derivative of gravitational force over distance). Too steep of a gradient and jump drives become dangerous and unpredictable. I'd also attempted to describe the necessity of perfectly aligning the principle axis of the jump drive with its destination - knowing that the destination has moved considerably in the 3-18 years it's taken for light of the target to reach the jump point, requiring that even tiny torques applied by being in anything other than a very weak gravitational field would supply additional misjump possibility.


I have run across descriptions in the past of this sort of thing, but I'm sure that's mostly the domain of "IMTU" stuff though.

Unfortunately, I have only very scattered knowledge of the vast breadth of the various traveller rules that have appeared over time, so it's nice to see people talking about this kind of thing in forums like this.

 

[aramis]

But what I meant was a subtle change in rules, or a description of the limitations of jump drives being related to the local gravitational gradient (generally called "tides" - first derivative of gravitational force over distance). Too steep of a gradient and jump drives become dangerous and unpredictable. I'd also attempted to describe the necessity of perfectly aligning the principle axis of the jump drive with its destination - knowing that the destination has moved considerably in the 3-18 years it's taken for light of the target to reach the jump point, requiring that even tiny torques applied by being in anything other than a very weak gravitational field would supply additional misjump possibility.


I have run across descriptions in the past of this sort of thing, but I'm sure that's mostly the domain of "IMTU" stuff though.

Not "mostly" - entirely. Canonically, it's the diameter, period, and it's for any solid or liquid, and even dense gas body larger than the jumping ship. Marc's stuck with that, even for stars (but note that the corona doesn't count).

Mind you, I prefer the tidal gradient model, but it's not canon.

 

[sudnadja]

Not "mostly" - entirely. Canonically, it's the diameter, period, and it's for any solid or liquid, and even dense gas body larger than the jumping ship. Marc's stuck with that, even for stars (but note that the corona doesn't count).

Mind you, I prefer the tidal gradient model, but it's not canon.

I suppose that comes down to what "dense" means in terms of a dense gas body. The hydrogen halo around the milky way center is fairly dense, and counting that would make jumping impossible anywhere in charted space. That's probably overly pedantic though.

 

[aramis]

I suppose that comes down to what "dense" means in terms of a dense gas body. The hydrogen halo around the milky way center is fairly dense, and counting that would make jumping impossible anywhere in charted space. That's probably overly pedantic though.

comparable to Earth's stratosphere, I believe.

 

[whartung]

comparable to Earth's stratosphere, I believe.

Cassini is about to get a first class lesson in density in a couple of days.

 

[Adam Dray]

Found a really cool relativistic star ship calculator (JavaScript-based, no download required).

I was able to plug in a scenario where a ship jumps into the Sol system somewhere around Neptune (30 AU) and hard-burns at 1G constant acceleration on an intercept path to Earth (1 AU), for a total trip of 29-31 AU.

Because the calculator assumes a flip-and-burn to decelerate at its destination, I doubled the distance to 60 AU.

The calculator computes time on board and time on Earth (both roughly 22 days), maximum speed (3.1% c), and maximum kinetic energy (44 million megajoules per kg).

For comparison, large asteroid 99942 Apophis (Wikipedia) has an estimated mass of 6.1E+10 kg and a velocity of 20 km/s.
Wikipedia says it would hit the Earth's surface with 750 megatons (3.138E+12 MJ) of kinetic energy and produce a 4.3 km crater.

So as soon as that ship starts the hard burn from Neptune, Earth would realize that it was intending to kill them and have 22 days to do something about it, but if they failed, they'd have serious problem on their hands.

A ship of 71,318 kg (71 metric tons) would have the same impact.

 

[Carlobrand]

...So as soon as that ship starts the hard burn from Neptune, Earth would realize that it was intending to kill them and have 22 days to do something about it, but if they failed, they'd have serious problem on their hands...

The longer they have to react, the easier it is to react. They just have to put something in the ship's way, far enough out that the impact - and the resulting cessation of drive thrust - causes the attacker to miss the target. The faster the attacker goes, the harder it is for the attacker to steer around the obstacle, and the less useful its own weapons will be in clearing the obstacle. The attacker detecting an obstacle two light-seconds out isn't much help if it's four seconds from impact because he's at half light speed.

For that matter, causing the attacker to prematurely vaporize into expanding gas could be sufficient if done far enough out. A cloud of pebbles sown in the attacker's path could be a dandy obstacle. A well-aimed particle beam could do the job from quite a distance away, given that the attacker can't effectively evade while on a days' or weeks' long dive.

This is one of those situations where a deep stellar shadow can be a help. Assuming you haven't already drafted a house "no near C jump" rule, a planet deep in a stellar shadow is going to get more warning than one that has no such protection.

 

[JFGarber]

Canonically, that is the elephant in the room that nobody talks about, because no one that I am aware of has a plausible solution.

IMTU, and violating canon, vessels bleed energy in Jump, and emerge at zero velocity relative to the nearest "large" body. IMTU, and knowingly violating canon.

It also makes my urge for pirates a little more practical, since merchants start at zero velocity somewhere "out there".

 

[Adam Dray]

The longer they have to react, the easier it is to react. They just have to put something in the ship's way, far enough out that the impact - and the resulting cessation of drive thrust - causes the attacker to miss the target. The faster the attacker goes, the harder it is for the attacker to steer around the obstacle, and the less useful its own weapons will be in clearing the obstacle. The attacker detecting an obstacle two light-seconds out isn't much help if it's four seconds from impact because he's at half light speed.

Sure! This assumes that the planet has sufficient TL to detect and meet the threat, in any case. Obliterating half a million people on a backwater planet still hurts.

I assume that any sufficiently motivated attack force could put a dozen 1000-dTon ships in near-c-crash-vector trajectories, all coming from different angles. Would a reasonably-high-TL planet have the capability to stop all of them?

 

[McPerth]

Sure! This assumes that the planet has sufficient TL to detect and meet the threat, in any case. Obliterating half a million people on a backwater planet still hurts.

If you try to use such a weapon, it's likely yo want a worthy target, as one of the sure effects would be retaliation (be in the same way or simply by nucking your planets) and nullifing any previous treaties...

I assume that any sufficiently motivated attack force could put a dozen 1000-dTon ships in near-c-crash-vector trajectories, all coming from different angles. Would a reasonably-high-TL planet have the capability to stop all of them?

See that this would be quite difficult in YTU, where the sungates would forcé all ships to appear from a single point (or several nearby ones), and the ships move along some defined spacelanes in system.

 

[Adam Dray]

If you try to use such a weapon, it's likely yo want a worthy target, as one of the sure effects would be retaliation (be in the same way or simply by nucking your planets) and nullifing any previous treaties...

Assuming you know who it is. If there's a war on, you probably know. If it's just an aggrieved starship captain or some crazy splinter group, who knows?

See that this would be quite difficult in YTU, where the sungates would forcé all ships to appear from a single point (or several nearby ones), and the ships move along some defined spacelanes in system.

Correct. Most planets are going to drop rings of mines around exit points and keep a visible presence near the exit gates to control who comes through.

However, if a ship is way out in the gas giants, scooping fuel, it could decide to 2G burn towards the home planet. Then we're back in the "how quickly can a planet react to a high%-c threat?" scenario.

And did you say "forcé"?

 

[MontyLovering]

IMTU, I don't do the 'Jump at near zero velocity', because whatever is 'near zero velocity' (LOL at the idea) in system A is not in system B.

I also don't do the 'M-drives stop working at 1,000D' thing.

IMTU, a whole bunch of technology all work on various extrapolations of the McGuffin Effect, which allows artificial gravity 'pushes' (fusion, grav cells, grav plates (they're in the ceiling!), repulsors, inertial capacitors), M drives (which unlike grav cells have a rather viscous flux round the back of a ship's drive plates, but can work outside of significant grave fields, unlike grav cells), and J drives (which use gravitics to rip a hole in N space to allow access to J space).

However, the efficiency of the McGuffin Effect falls at any significant relativistic speed. Thus, a 6G ship will accelerate for after about a week to 0.1c, but would take five years to reach 0.5c. This and a few other logically consistent (given the handwavium of the McGuffin Effect) rules stop relativistic planet killers

Jumping at above 0.05c is simply impossible (well, maybe we will find out what happens to those who tried one day… ).

Jumping at above 0.0025c has a navigational error two orders of magnitude higher than normal - say about a moon orbit.

Ships Jumping at above 0.002c will precipitate out of Jump at around 1,000D.

The screening from particle damage that the M drive supplies also becomes largely ineffective at above 0.002c, meaning that most in-system travel outside of 100D (see below) takes place below this speed even if the distance covered would allow a higher velocity before turn-around.

Basically, I hold that any major system (A, B and C Starports) has a defined inward vector for ships Jumping in. They may Jump in at a velocity equal to the maximum velocity at which a ship can attain a safe orbit after decelerating from 100D at 1G. This would be c. 150 km/s or 0.0005c for an Earth-sized planet. Nothing is allowed to exceed this velocity within 100D, or 'controlled planetary space'.

Ships leaving planet A do so on a vector that after arrival in system B will leave them on the stipulated approach vector and velocity for planet B.

It means that Customs vessels can easily intercept inward-Jumping traffic for inspections, and that ships are travelling out to Jump and in from Jump for c. 9 hours instead of 12 hours 45 minutes when compared to 'Jump at near zero velocity'. It also means that anyone 'breaking the speed limit' or Jumping in-system on a different vector is automatically going to attract attention and, if a weapon of terror aimed at a planet, deal with by planetary defences. And if inbound ships arrive in a calculable volume of space relative to the planet's orbit and position to allow for Customs intercepts, other vessels can Intercept them too…

Given the limits on velocity entering Jump, greater navigational error and exiting Jump at 1,000D means a ship arriving at 0.05c that is somehow on a collision vector with a planet will be over eight hours out, and will be assumed hostile and treated accordingly.

Less advanced systems may have uncontrolled planetary space, and be less able to defend against weapons of terror aimed at a planet arriving at less than 0.002c, but still have at least a half-hour to take action. And obviously at these velocities it's only 1.000002 as energetic as at rest, so no biggie.