How strong is my Starship Hull (was Starship Hulls)

[atpollard]

I moved the conversation to a new topic to avoid further drift of the other topic.

Small objects moving at those glacial speeds (orbital) wouldn't even be noticed by a space ship hull in Trav.

Is it possibe that small Ultra High Velocity objects punch thru starships travelling to Jupiter with some frequency, only the tiny hole is little more than a petty maintenance problem. The odds of hitting someone are ... astronomical. :wink:

Umm, no. People don't live long after what just passed through the hull, passes through them. Fuel tanks may be self sealing, people aren't.

You misunderstand my statement, of course it will hurt (probably kill) anybody hit by hypervelocity sand.

However, 99.9% of the office space where I work is NOT a human being. A single random hypervelocity grain of sand passing through my office would have less than a 1 in 1000 chance of hitting me. If one random hypervelocity grain of sand struck the 20 person building where I work every year, then over a 10 year period the odds of ANYBODY being struck by it are still only 1 in 100 and the odds of it striking ME are 1 in 2000.

By volume people occupy less than 1/1000 the volume of a typical starship. A ‘reasonable’ hull will deflect or stop most small objects that it encounters. Those 6-G trips to gas giants are rare. Space is mostly empty, etc ...

... Would it really change the game so much if hulls were not made of impenetrable handwavium? The chance of a serious impact are small and the chance of a death from that impact are even smaller.

I can live with 1 in 1000 spacers die from hull penetrations during their career. It is better than the normal rate of cancer deaths on Earth (1 in 500).

The point is simply that the impenetrable hulls that people like to complain about while quoting energy in kilotons or megatons, don't actually NEED to be impenetrable. The event just needs to be uncommon enough to not be worth modeling in game terms.

You're forgetting about how much of the "non-spacer" volume of a starship, equally vulnerable to the damage, which contains elements critical to keeping ALL the spacers inside the hull alive. Some elements of which will do much more direct and widespread damage to the said spacers if hit. So yes, you pretty much do need a nigh impenetrable hull or some effect to prevent that from happening.

AND, take any Fusion PP, M-Drive, J-Drive, computer, Life support equipment, etc., etc. it hits.

No, it wouldn't work as a viable platform if it was vulnerable to that type of threat. If you do the math, no bank would finance a space ship without MASSIVELY high insurance payments needed. Say a ship gets hit once every 10 years, you'd be easily paying insurance equivalent to 3-4 times the cost of
your mortgage payment...

So if hulls MUST be impenetrable (to avoid astronomical insurance payments) why is 'self sealing' an option for hulls? The question is rhetorical.

The real question is:
Since this Rock-Paper-Scissors problem (Weapon penetrates Hull, Hull resists Near-C Pebble, Near-C Pebble has greater energy than Weapon) creates a paradox somewhere, why decide to make the Hull Impenetrable to pebbles but vulnerable to mass drivers, rather than say super resilient ship systems or a bow gravity wave to clear pebbles or subsidized insurance?

Why that contradiction vs another?
The rules seem neutral on the "hows".

[I only ask because your answers seem so emphatic.]

 

[atpollard]

Ok, just for fun I did the math and here are the results:

GIVEN:
density of space dust at 1,000,000 molecules per cubic meter of space
1 gram of hydrogen = 6 x 10^23 molecules

THEN:
There is 1 gram of interplanetary dust per 3 x 10^17 cubic meters of space

Let us assume that all of this dust is a single object weighing 1 gram (a bad assumption since the density of large objects is orders of magnitude lower than that of molecular dust but it gives us a starting point), then a spacecraft travelling between worlds will strike an average of 1 object weighing 1 gram per 3 x 10^17 cubic meters of swept volume (the frontal area of the ship times the length of the trip).

For purposes of this discussion, we will assume that a 1 gram object will pose a threat to the ship’s hull.

The good ship FRED, a 200 dTon merchant ship, has a frontal area of 200 square meters (a high estimate) and will travel 6 x 10^11 meters (600 million km) to a gas giant to refuel. Thus the volume of space swept by FRED is 1 x 10^14 cubic meters per trip. Dividing the 1 x 10^14 cu. m. by the 3 x 10^17 cu. m. yields a 1 in 3000 chance that the ship FRED will strike a 1 gram object on a trip to the Gas Giant.

If the good ship FRED makes this trip every 2 weeks, then it should strike a 1 gram object every 115 years.

If the hull of good ship FRED is only dinged by a 1 gram object and requires a 1 kg object to penetrate the hull, then the good ship FRED should strike one dangerous object every 115,000 years.

I must conclude that the danger from striking interplanetary objects has been greatly exaggerated and the need for super-impenetrable hulls has been overstated.

 

[apoc527]

I haven't joined in on these discussions in the past because they seem to really generate a lot of passion, along with noise and light.

To me, the idea of these nigh-impenetrable starship hulls is not only unbelievable, but silly. If I can engineer ships with hulls this powerful, I either need to be able to generate weapons capable of penetrating them or just forget about space combat (what would the point be)?

Now, start adding in the whole vehicle-ship distinction and this begins to matter a lot more. Why? Because if vehicles are constructed on some hugely lesser scale, they are always impotent versus ships but the fluff behind this seems weak, at best.

This is why I have recalibrated ship:vehicle damage in my games. Rather than 50:1, I'm thinking of 20:1 or even 10:1. So, I've determined that I'd rather not have unrealistically and magically tough hulls in my game. What do others do, for those that don't buy the crazy hull theory?

(by the way, if it were that big of a problem, impose an interplanetary speed limit! Also, what's wrong with magnetic deflectors that shove aside incredible low mass threats and small lasers that zap anything bigger?)

 

[apoc527]

Or ablative ice shielding sprayed on to the hull before a long interplanetary trip?

 

[rust]

The usual Traveller concept of a starship hull is a hard shell of hullmetal.
I never liked this, so in my settings a starship hull consists of several dis-
tinct layers of different material, and the "core" of the hull is a kind of gel
which "captures" most of the particles which manage to penetrate the ou-
ter hull and distributes their impact energy over a wider area. Another
layer of the hull is a kind of liquid plastic which hardens and closes any
punctures whenever it comes into contact with oxygen, the self sealing
part of the hull.

 

[phavoc]

I thought around TL12 and up starship hulls were made of collapsed materials?

 

[atpollard]

I thought around TL12 and up starship hulls were made of collapsed materials?

Yes, but the strength of the hull only increases a little which suggests that the super alloy is applied in a thinner shell that only increases the total strength by a little (over that of titanuim).

 

[far-trader]

It is really all quite elementary, and iirc described (though only briefly and incompletely iirc) somewhere in canon, though originally and before that came to my attention I worked it out myself, largely borrowed from various sci-fi and given a wider explanation. From memory, possibly forgetting a point or few...

Hull material is strong yes, but not nearly strong enough to resist even small hyper velocity material impacts. Fortunately as a side effect of the maneuver drive field all such material is harmlessly passed around the hull. Usually. Rare cases have been recorded but in general as long as the power plant is providing energy to a functioning maneuver drive space craft are invulnerable to this hazard.

Ah, what about using it for deflecting missiles and such launched in anger? Why do the rules permit such devices to ignore the field effect and only worry about the actual armour or lack of?

Also elementary, because they are designed to do so. Missiles employ their own maneuver drive that generates its own field (and so is also able to ignore debris collisions). The fields interact in such a way that they ignore each other.

EDIT: Felt I should clarify this (the missile solution) was a much later addition. Up until the question was asked I hadn't considered it. I felt the questioner's solution fit quite well with my thoughts though, so I adopted it.

This also permits ships to dock while under way without being repelled by each other's fields. And it prevents simple Vacc-Suit boarding actions until the maneuver drive is disabled (though a boarding craft might attempt it, under serious threat to the ship simply ramming said craft). Oh yes, ships may ram other ships ignoring the field effect.

A downside? Well yes in fact. The field also creates a kind of subspace friction that limits the maximum attainable velocity to significantly sub-c (a vague measure about equal to a 6G trip of about 500 million km). Maneuver drives are also limited to 6G max by the same effect, so far. Not that it's much of a drawback given jump drives but it does make the maneuver drive less practical for STL interstellar voyages. And on the upside it means near-c attack runs are impossible using maneuver drives. While possible with other thrust agents they are for all practical purposes also impossible.

The same field also provides for inertial compensation (up to the thrust applied, as it is applied, no felt thrust from maneuvering, if all is working right) and generates the internal artificial gravity (fixed strength and orientation when the hull is laid down). Collisions and combat hits are felt as they are not part of the field response, so in combat it's a good idea to strap in even if you don't loose IC or AG.

(all MTU of course, though imo well within the spirit if not the rules of Traveller)

 

[apoc527]

You can't tell, but I'm golf-clapping for that post (immediately above).

 

[Colin]

Jovian Chronicles used a laser-based point-defense system: dozens of small emitters all over the hull, but concentrated on the bow. They were also effective against incoming missiles, but railgun rounds (Kinetic Kill Weapons) were too heavy to be affected by the low-power emitters. However, they were powerful enough to deflect any incoming fine particles.

2300AD sidestepped the issue entirely, as stutterwarp had pseudovelocity only.

In Traveller, i always ruled that there was a reason most ships had laser turrets, as particulate point defense. I never liked the idea of starships as flying tanks. Traveller D20's 5:1 ratio is more reasonable, I think.

 

[DFW]

So if hulls MUST be impenetrable (to avoid astronomical insurance payments) why is 'self sealing' an option for hulls? The question is rhetorical.

Your stated assumption (hulls MUST be impenetrable) is incorrect. Therefore, the self sealing option doesn't make sense to you.

 

[far-trader]

One of those forgotten points in my notes above, and related to some recent discussion as well, presuming you're of the school that adopts maneuver drives can float the ship at a hover indefinitely (as long as there's fuel for the power plant)...

Ships that intend to land on a world need beefy landing gear and a very solid surface (starport field or bare bedrock to be safe), or buoyancy in a suitable body of liquid.

Why? Because you can't just hover on your maneuver drive if you intend to do any business as the field effect will prevent any casual contact with the hull. So procedure generally requires one to set down and safe the maneuver drive before you can exit, start offloading cargo, hook up fuel feeds and such.

Handy for added protection in the wilds though, if you can afford the operation. Simply idling the maneuver drive will keep the local aggressive flora and fauna (and the restless natives of course) off the hull and out of the ship...

...usually. There are rumours of... ah, never mind, I'm sure they're just tall spacer tales

Most Downports take a dim view though of Captains idling the maneuver drive once they've set down until they are ready and have clearance to lift. A very dim view. One typically backed up with a parsec of red tape or more lethal force.

On the other hand Highports expect docked ships (as opposed to those in hangers aboard) to keep their maneuver at idle. The Highport has their own field and station keeping maneuver drive (at a minimum) just like ship so they can interact with ships with their maneuver drive idling, through docking arms.

Kudos if you realize that many Downports and Highport hangers can (and will) clamp a landed ship once the maneuver drive is safed to prevent said ship from successfully powering up the maneuver drive. The field interference will prevent it, ground it, and short out the maneuver drive in the process (one hit at a time until the drive is totally burnt out). You know, so you can keep the players from simply running every time they get in trouble

 

[atpollard]

So if hulls MUST be impenetrable (to avoid astronomical insurance payments) why is 'self sealing' an option for hulls? The question is rhetorical.

Your stated assumption (hulls MUST be impenetrable) is incorrect. Therefore, the self sealing option doesn't make sense to you.

MY stated assumption?

Is it possible that small Ultra High Velocity objects punch through starships travelling to Jupiter with some frequency, only the tiny hole is little more than a petty maintenance problem. The odds of hitting someone are ... astronomical. :wink:

No, it wouldn't work as a viable platform if it was vulnerable to that type of threat. If you do the math, no bank would finance a space ship without MASSIVELY high insurance payments needed. Say a ship gets hit once every 10 years, you'd be easily paying insurance equivalent to 3-4 times the cost of
your mortgage payment...

 

[rust]

Ships that intend to land on a world need beefy landing gear and a very solid surface (starport field or bare bedrock to be safe), or buoyancy in a suitable body of liquid.

Indeed. The Lockheed Hercules, about the biggest aircraft that can land on
most kinds of unprepared ground, has a maximum weight of ca. 70 tons,
but (according to GURPS Traveller data) even a scout ship has a loaded
weight of ca. 380 tons, and a free trader of ca. 600 tons.

However, in my setting the maneuver drive does not produce any kind of
protective field, and on many worlds the ships are ordered to keep their
maneuver drives on, both to reduce the ground pressure of the ship to
prevent damage of the frontier starport and to feed energy from their po-
wer plant into the local network - "we give you fuel, you give us electri-
city".

 

[atpollard]

Indeed. The Lockheed Hercules, about the biggest aircraft that can land on
most kinds of unprepared ground, has a maximum weight of ca. 70 tons,
but (according to GURPS Traveller data) even a scout ship has a loaded
weight of ca. 380 tons, and a free trader of ca. 600 tons.

It is not as bad as it seems.

Crystalline bedrock can support 60 tonnes per square meter.
Sedimentary rock can support 30 tonnes per square meter.
Sandy gravel or gravel can support 25 tonnes per square meter.
Sand, silty sand, clayey sand, silty gravel, and clayey gravel can support 15 tonnes per square meter.
Clay, sandy clay, silty clay, and clayey silt can support 10 tonnes per square meter.

So a Free Trader (600 metric tonnes) designed to land on a type E Starport with a landing pad of compacted sand would require 600/10 = 60 square meters of bearing surface (landing skids or the bottom of the wheels). If the ship were designed to land on a class E starport with a landing pad of natural bedrock, then it would require only 600/60 = 10 square meters of bearing surface.

A high tech landing pad might be made out of some super-slab material that can spread a concentrated load (like from a single landing strut) out over the entire slab [while resisting having the landing strut punch through the slab]. A 50 x 50 meter Super Slab over sandy soil would be able to support a 25,000 metric ton (roughly 6250 dTon) Starship.

This could also be done with common concrete, but the required slab would be pretty thick (and therefore expensive) – like airport runways only more-so. We can assume that a ‘starship’ (for purposes of landing pad design) weighs 4 metric tonnes per displacement ton and has 1 load bearing landing strut per 50 dTons (200 metric tonnes) of starship. Since concrete will support over 1500 tonnes per square meter (before the concrete crushes), each landing strut must spread its 200 metric tonne load over 0.14 square meters (a 0.4 x 0.4 meter landing skid). However, the sandy soil beneath the landing pad can only support 15 tonnes per square meter, so the concrete must spread the 200 tonne load over 13.4 square meters (3.7 x 3.7 meters of soil). Concrete distributes the concentrated loads at a 45 degree angle, so the concrete slab will need to be about 1.7 meters thick (for sandy soil). If the landing pad were built over bedrock, the slab would only need to be 0.75 meters thick.

A thought occurs to me that since Streamlining includes provisions for wilderness refueling, it might also include the larger landing skids (or more landing struts) to land somewhere other than a proper starport landing pad. A Standard configuration would not include provision for wilderness refueling and, therefore, no larger than normal landing skids. Just another possible difference for your 10% cost.

 

[atpollard]

I was curious about landing on tires instead of skids, so I did a little research. Truck tires are rated at about 2 metric tonnes per tire, so the 200 tonne load-bearing landing strut mentioned above would require a 0.4 x 0.4 meter landing skid for a starport landing pad, or a 1.8 x 1.8 meter landing skid for a natural bedrock landing pad, or a 3.7 x 3.7 meter landing skid for a compacted sand landing pad, or 100 truck tires!

I was surprised and thought that others might be interested.

[PS:]

Ships that intend to land on a world need beefy landing gear and a very solid surface (starport field or bare bedrock to be safe), or buoyancy in a suitable body of liquid.

Indeed.

It is not as bad as it seems.

[Ok, I guess that it is pretty bad, but there are at least alternatives to needing to run the MD all of the time.]

 

[rust]

I ran into this problem when I attempted to design a floating starport for
my water world setting and had to realize that the "flight deck" would ha-
ve to be truly massive to be able to carry even a normal free trader. In
the end I gave it up and decided that all starships designed to land on the
planet would require "aquafitting", with cargo doors above the waterline,
sonar sensors and all that - much easier to design in a plausible way than
a "spacecraft carrier" for anything heavier than a modular cutter with its
ca. 200 tons.

 

[atpollard]

In the end I gave it up and decided that all starships designed to land on the
planet would require "aquafitting", with cargo doors above the waterline, sonar sensors and all that - much easier to design in a plausible way than a "spacecraft carrier" for anything heavier than a modular cutter with its ca. 200 tons.

Dtons are such a strange measure, what is the density of water (in tonnes per dTon)?
I wanted an idea of how high/low a starship floats in the water and figured that you already did the conversion math.

Have you seen the sea-launch concept that uses a partially flooded hollow tube to provide buoyancy and stability. The result is a small stable platform atop a very long tube. Strange from the side view but not bad from the water-line up. The Saturn V first stage and undersea floating tunnels will give an idea of the largest practical diameter for the tube (at the current TL).

[EDIT: The more I think about it, the more I realize that a floating starport is a REALLY good design problem ... a worthy challenge.]

 

[rust]

Dtons are such a strange measure, what is the density of water (in tonnes per dTon)?

Water has a density of almost exactly 1,000 kg / 1 ton per cubic meter,
and a dton has almost exactly 13.5 cubic meters, so 13,500 kg or 13.5
tons per dton should be good enough.

 

[atpollard]

So part of the annual maintenance for your free trader might involve the purchase of 400 new tires for the landing gear.