Crashing ships as weapons

[whartung]

Then there is a bit from the railgun thread that is relevant-ish. If the railgun round would become a plasma ball at around 0.5C, why, how would a ship survive at greater than that without more magic to defend it?

The railgun ammo isn't turned to plasma because it's going 0.5C, it's turned to plasma because of the massive amount of energy involved in accelerating the ammunition to 0.5C in a very short amount of time that turns it in to plasma.

Here is where fuel needs take effect. How many jumps you may do? what about PP fuel?

It's not difficult to design a ship with a J1 drive and 50% fuel space to give that ship "several laps" around the star before finally jumping in to the target system.

You can always add more PP fuel.

The other hard part is that it's essentially a suicide trip unless it's somehow automated, since you need essentially the same process in order to decelerate anyone that wanted to try and leave before the final attack.

But even then, as a "dedicated weapon", you could mount a several hundred ton escape vehicle in the ship that detaches after the final vector is set. This, too, will need to have several jumps of fuel. It'll just be a smaller ship.

 

[pendragonman]

Whartung, are you implying it won't take a massive amount of energy to reach 0.9C? Or even 0.5C?

 

[McPerth]

I think even IMTU there are lots of reasons for ships to head far out to the gas planets: gas mining, asteroid mining, and so on. A normal Brachistochrone trajectory from a gas giant to the home planet is largely indistinguishable from an attack until the flip-and-brake point midway.

And that's the key. Any ship not so flipping and braking should be seen as a hostile and destroyed. You have half the distance from the gas giant to do it.

If the distance is less (let's say from Mars instead that from Jupiter), you have less time to react, but also the built up speed will be quite lesser...

 

[McPerth]

The railgun ammo isn't turned to plasma because it's going 0.5C, it's turned to plasma because of the massive amount of energy involved in accelerating the ammunition to 0.5C in a very short amount of time that turns it in to plasma..

Once again, the railgun ammo speed is irrelevant to stop that incoming ship. It's the own ship's speed that makes it so letal when they collide.

It's not difficult to design a ship with a J1 drive and 50% fuel space to give that ship "several laps" around the star before finally jumping in to the target system.

You can always add more PP fuel.

The other hard part is that it's essentially a suicide trip unless it's somehow automated, since you need essentially the same process in order to decelerate anyone that wanted to try and leave before the final attack.

But even then, as a "dedicated weapon", you could mount a several hundred ton escape vehicle in the ship that detaches after the final vector is set. This, too, will need to have several jumps of fuel. It'll just be a smaller ship.

Let's see...

Using HG:

if you want yout ship to accelerate very fast, you need a good MD, and that means a good PP. If you mount MD (and PP) 6 on it, you'd need 23% of your ship dedicated to it, plus 1% in fuel per four weeks needed (let's say you plan to do it in 10 weeks (incluiding jump time), so 2.5% in PP fuel). So we'd be at 25.5% volume used just for that...

Add to this j1 (2%) and 50% jump fuel (for 5 jumps, as you say), so we're up to 77.5% fuel. Either your escape ship is quite small or your attack ship quite large, but I guess it could be done...

But here I'm afraid my knwledge of fine details about jump are not enough to be sure, but if I understood it well, the timing for jumping must be quite precise. If you are reaching relativistic speeds, time dilatation will begin to affect them, and I'm not sure if this dilatation can be calculated exactly enough for the jump to be safe.

And, as the jump time is not exact, you cannot calculate exactly the time for jump exit. Multiply this uncertainly by 5 (as you perform 5 jumps), and add you nearly null maneuver capacity (due to the same time dilatation and your very high speed), and, IMHO, the possibility to really hit the planet is close to zero.

 

[Quint]

My own answer regarding the accelerate and *then* jump is that given the variable nature of the length of Jump there is no reliable way to create an accurate vector until after the Jump has concluded and the pilot has an exact bearing on where they relative to the system. That's the other reason for slowing to a nominal stop befor Jump because you don't want to unintentionally add to you travel time because you were shooting way off on an tangent before you can correct and get headed to the primary port.

When it comes to in-system defenses, I just imagine it is some variation on a sandcaster. Heck even if they pay every merchant ship to strew their cargo on an intercept path, plus dump sandcasters, it's cheaper than the cost to "build a new planet".

I've always that some obscure Imperial Edict insures that this sort of thing happens.

D.

 

[Adam Dray]

I really don't see how this sandcaster works. I mean, I get that it throws sand really really far. I don't see how that helps. The surface area of the sand increases exponentially (quadratically) with distance, and the density of the sand decreases at the same rate.

You can't just blow up the ship. You need to divert it from its collision course, or you're looking at the same amount of mass colliding with the planet in roughly the same package as it was before. Even if you manage to "vaporize" the ship into whatever, you're either just turning it into a slightly larger cloud of material or igniting it into plasma, which is going to slam into the planet just the same.

 

[Condottiere]

Gravitational distortion sufficient to deviate the flight course.

Maybe a salvo of jumpbreaker missiles.

 

[Brandon C]

I think this is something that sounds game-breaking in theory, but when you try to work out the details, you see that it's so unlikely to work as to not be worth the effort. Frankly, as a terror weapon, a nuclear bomb smuggled on a ship that lands in a starport is a far greater threat but no one is discussing trying to stop that. It's far easier to pull off both because of less demands on the attacker and greater demands on the defender: systems would have to board and search every ship that exited jump. Every one.

 

[Cryton]

Interesting. Here's a question then.

If you arrive at 100D when emerging from Jump (That is how I have always understood/assumed that Jump drives worked), and M drives only work within 1000D. Wouldn't you be spotted a LONG time before ever reaching a fraction of C?

Example: you jump in at 100D, then accelerate out toward 1000D, decelerate to a "stop" so you can turn around as turning is nigh impossible at those speeds,, then accelerate back towards the planet. As there really is no stealth in space, unless you are trying to ram a really primitive planet, you will be spotted and intercepted/destroyed in all but the most EXTREME cases.

I am probably wrong, but I thought the arrival at 100D was standard arrival point regardless of edition, and assumed unchangeable save for a misjump as it is the gravity well at 100D that pulls you out of jump?

Thoughts?

 

[Cryton]

Also, you Physicists, isn't there an effective "speed limit" that's much lower than C due to the increasing power requirements to add velocity the faster an object is moving? IIRC you need near infinate energy to achieve even .1C.

But I could be wrong...

 

[aramis]

A few thoughts here.

First, the Traveller dTon is a measurement of volume, not of mass. A 1000 dTon ship may easily mass more than 1000 metric tons, probably more like between 2000 to 3000 metric tons, unless it is armored, in which case it is going be weight quite a bit more. That is the mass that needs to be accelerated.

More like unloaded freighters might come in at that... Perhaps we can simplify down from striker and MT to get reasonable mass numbers in a HG friendly way.

Reminders on terms:

kl = kiloliter = cubic meter = 1/14 Td
Td = Ton Displacement = DTon (tho' note there is a real world use of DTon which is different than the Traveller Td is)
tonnes = 1000 km = metric tonnes mass. for clarity using Tm in some items.
SG means Specific Gravity = Tonnes/kl
​

working the math inside the spoiler. Results follow.

Spoiler:

Looking at striker and megatraveller - most mechanical systems come in a Vol in kl = mass in tonnes. This includes powerplants.

So tonnes should be about 14 tonnes per Td for drives and such.
Computers mass tonnes = kl/5 So 7 Tonnes per Td.

Staterooms are 1 tonne per Td.
Low Berths are 2 tonnes per td

Control mass is 2x volume. I'd put the bridge as 1/5 controls, 1/5 seating, 1/5 seating & access. Rest in others. Sophont seating for human sized occupants is about 200kg (presumably plus the 40 to 200 kg for the person) so
0.4 Tm/Td controls
0.2 Tm/Td seats
rest "empty", but extra bulkheads.
so call it 1Ton/Td


Stateroom mass is 2 Tonnes per stateroom (or SC Stateroom)... but doesn't include the person, nor the baggage.

Armor TL5-6 SG 8
Armor TL 7-9 SG 7 (HG TL 7-8)
Armor TL 10-11 SG 10 (HG TL 9-12)
Armor TL 12+ SG 15 (HG TL 13-14 and 15+)
Let's assume for the moment that it's only 90% solid.

Hull presumption: 0.1 kl per Td for flooring, with armor density. Subsumed into other systems volumes.

Crew and Passengers should mass about 70kg each on average, but add 100 kg for baggage, and 30 for food... and 50 for slop... each person thus about 0.25 tonnes

The TEU high cube gives us a good limit for real world cargo density...
high cube 43 kl, max gross 24 tonnes, of which 3 tones is tare, but that's immaterial really. So, per Td of cargo, 1 ton tare for containers, 7 tons useful mass... SG of actual carried should be under 0.5... note also, that's TL 7 materials... so we'll reduce for the higher tech materials.

Empty Mass by TL & System, tonnes (metric) per Td[/td]

System	TL9ABC	TLDE	TLF
Hull	0.8	0.7	0.4
Armor	100	200	200
Computer
Bridge
PP, MD, JD
Quarters (SR, SCSR, Bunk, Seats)
Low Berths (LB/ELB)
Weapons
Fire Control w/out
People, each, w/baggage:
Container Cargo	7.5	7.25

[tc=3]0.5[/tc] [tc=3]1[/tc] [tc=3]14[/tc] [tc=3]1[/tc] [tc=3]1[/tc] [tc=3]2[/tc] [tc=3]0.1[/tc] [tc=3]0.25[/tc] [tc]7.75[/td]

Applying this to a Type A with Bk2 drives:

System	Td	Mass
Hull	200	160
Bridge	20	20
Computer	1	0.2
PP	4	56
MD	1	14
JD	10	140
SR x10	40	40
LB x20	10	20
FC	2	0.2
Fuel	30	(30)
Cargo	82	0
People (10 up, 20 cold)	10	7.5
Total Dry
+Fuel & crew
Cargo Alone, containerized TL 9	(80)	620	Containerized cargo, fuel & crew, TL9

[tc=2]450.4[/tc] [tc=2]482.9[/tc]
[tr] [tc=2]1107.9[/tc]

That's about 5 tonnes per Td.
Which, in no small irony, is also about the GRT ...
Note that TNE specifies 10 tonnes per Td as the "no need to recalculate until exceeded" line and the mass limit per cargo ton

 

[aramis]

Also, you Physicists, isn't there an effective "speed limit" that's much lower than C due to the increasing power requirements to add velocity the faster an object is moving? IIRC you need near infinate energy to achieve even .1C.

But I could be wrong...

No. Not Near-infinite...

It's simple time dilation.

Barely noticeable at that point.

 

[Timerover51]

More like unloaded freighters might come in at that

I was thinking of unloaded freighters.

 

[Timerover51]

Also, you Physicists, isn't there an effective "speed limit" that's much lower than C due to the increasing power requirements to add velocity the faster an object is moving? IIRC you need near infinate energy to achieve even .1C.

But I could be wrong...

No, you are right as I pointed out in my earlier post. The energy requirements to reach an appreciable fraction of the speed of light are enormous. That is why Larry Niven used ram-scoop ships a lot. You get around the need to carry fuel by scooping up interstellar hydrogen.

 

[whartung]

Whartung, are you implying it won't take a massive amount of energy to reach 0.9C? Or even 0.5C?

Its not that it doesn't take a massive amount of energy, it the amount of time energy is introduced in to the system. The railgun is accelerating "instantaneously" (for assorted values of "instantaneously") in contrast to acceleration over days.

So, I got my napkin and magic marker out and did some fiddling.

Given a star the size of the Sun to work with for the example, a 6G ship making 3 passes will accelerate to ~34,000 km/s, or roughly 0.1C. It accelerates for about 157 hours. I did not compensate for any additional acceleration or drag caused by the star itself.

And that's the key. Any ship not so flipping and braking should be seen as a hostile and destroyed. You have half the distance from the gas giant to do it.

Or the ship exits jump at .1C at 100D.

As for dealing with the jump time discrepancies, this is not that big of a problem. First, the jump delays during the acceleration phase aren't really an issue. You don't really care when you arrive as long as you get the bulk of your 2000D acceleration run. The only one that matters is the last leg.

But even then, you plot your arrival to be on the ecliptic ahead of the target planets orbit.

The earth, for example, is 12.7km in diameter. However, on the orbital arc, if you look at it head on, where the planet is coming toward you, and thus "turning" to it left (your right), along that axis, during the 32 hrs of jump discrepancy, the planet only moves about 15,000km. If you time your arrival for "12am", and "aim" just a bit to your right of center as you view the planet, the planet will arc in and out of the midpoint during that window -- and frankly is too large to really get out of its own way. So, it's likely (if not guaranteed) that a ship can jump in at 100D going .1C and actually hit the target. Take a basketball, and shift it 3" left then back right. That's about what the planet will do.

I can't speak to the relativistic effects on this. My physics are locked in the 19th century.

"How can you target gas giants or planets?" "Easy! Ya just don't lead 'em so much."

 

[Brandon C]

Given a star the size of the Sun to work with for the example, a 6G ship making 3 passes will accelerate to ~34,000 km/s, or roughly 0.1C. It accelerates for about 157 hours. I did not compensate for any additional acceleration or drag caused by the star itself

It better be doing it in an unihabited system, because a SDB or patrol cruiser will notice this and probably guess what the ship is up to.

Or the ship exits jump at .1C at 100D.

The problem here is that in some editions, the time spent in jump is variable by around half a day either side of a week. The timing will be way off and the ship will be going too fast to correct course. A miss is probable, even if the planet mounts no defense.

Again, a nuke on a free trader landing in a starport is much more likely to succeed.

 

[aramis]

It better be doing it in an unihabited system, because a SDB or patrol cruiser will notice this and probably guess what the ship is up to.



The problem here is that in some editions, the time spent in jump is variable by around half a day either side of a week. The timing will be way off and the ship will be going too fast to correct course. A miss is probable, even if the planet mounts no defense.

Again, a nuke on a free trader landing in a starport is much more likely to succeed.

The accuracy of jump is 3000 km per parsec (3.086e+13 km)... 1 in 1e10, roughly, and it's proportional to distance jumped. (JTAS 24, p34).

If jumping less than 100 AU (1.496e+8 km each), accuracy is pretty much spot on... higher than the temporal accuracy of exit versus most planets.

Earth is whipping a 30 km/second course 'round the sun. 1.08e5 km/hour
±16.6 hours, thus 3.5856e6 km window. Timed correctly, that's reduced to a variation on how long until you impact, as earth is about 12742 km across. Timed wrong, that's a clean miss.

Note that you can hit earth from 2 parsecs, if you time it right, so that the arc of that 1.5° wide arc is aligned to your acceleration direction...

But a scout courier with a 4-week runup at 1 G (this is a suicide mission, after all) and then exit will have been noted at run-up by week two... and a decent astrogator with the course angle will be able to say, "Hey, he's going to jump at this point"... and the computers are likely to note anyone doing any singular course in N-space for 2 weeks+... because once they hit day 16, it's likely they are on an "unstoppable" course. Jump a ship to just ahead of their day 23 position, and drop a missile at them. End of them.

 

[Brandon C]

The accuracy of jump is 3000 km per parsec (3.086e+13 km)... 1 in 1e10, roughly, and it's proportional to distance jumped. (JTAS 24, p34).

Did that make it into any later ruleset, because I don't remember it.

 

[whulorigan]

Interesting. Here's a question then.

If you arrive at 100D when emerging from Jump (That is how I have always understood/assumed that Jump drives worked), and M drives only work within 1000D. Wouldn't you be spotted a LONG time before ever reaching a fraction of C?

Example: you jump in at 100D, then accelerate out toward 1000D, decelerate to a "stop" so you can turn around as turning is nigh impossible at those speeds,, then accelerate back towards the planet. As there really is no stealth in space, unless you are trying to ram a really primitive planet, you will be spotted and intercepted/destroyed in all but the most EXTREME cases.

I am probably wrong, but I thought the arrival at 100D was standard arrival point regardless of edition, and assumed unchangeable save for a misjump as it is the gravity well at 100D that pulls you out of jump?

Thoughts?

I think the idea is (or could be) that you do all of your accelerating (relative to the destination system) while still in the originating system, and once you are up to speed, you then jump and emerge with your high momentum vector toward the planet preserved.

(Presuming that you are going with the idea that momentum is preserved thru jumpspace).

 

[whulorigan]

Also, you Physicists, isn't there an effective "speed limit" that's much lower than C due to the increasing power requirements to add velocity the faster an object is moving? IIRC you need near infinate energy to achieve even .1C.

But I could be wrong...

A continuous thrust-force will produce a progressively decreasing acceleration over time, causing the increasing velocity to asymptotically approach lightspeed as time goes to infinity. This decreasing acceleration with increasing velocity only becomes noticeable at very high speeds. As Aramis noted, at 0.1c the acceleration drop-off starts to become noticeable (but is not overly significant), whereas at about 0.9c upward it becomes quite significant. Of course, as your speed increases, at some point you will begin to encounter noticeable "drag" from the interstellar medium, even if you do have particle screening produced as a side effect of your M-Drive (per Beltstrike).

Another issue is what you are using to produce acceleration. Timerover is correct in the case of reaction-drive systems using reaction mass to accelerate. The amount needed to be carried along would be prohibitive, and would need some type of system similar to a Bussard Ramjet that picks up its own fuel from the interstellar medium along the way. If you are using some type of drive like the gravitic based M-Drive (T4/T5, et al), then you do not have that limitation. But those drives canonically drop to 1% efficiency beyond 1000 diameters. The M-Drive in MT was Strong Nuclear Force based, and had no efficiency drop-off. (Note that T5 has both the NAFAL-Drive (long-range grav-based) and the Dean Drive (with no efficiency drop-off).