Ian Ferguson's Analysis of Sand in Traveller

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Ian Ferguson produced a document about Sand and its use in Traveller spaceship combat. He posted the document to the CT-Starships group on Yahoo, and got a number of comments. He updated the document and reposted it. He gave me permission to host his document here in HTML format.

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SANDCASTERS IN CLASSIC TRAVELLER

After some discussion of the rules for sandcasters on ct-starships, I decided to conduct a thorough analysis of the rules given in Book 2: Starships (B2), Book 5: High Guard (B5), and the reprinted version of Book 2: Starships in Books 0-8: The Classic Books (RB2). Note that I found no difference between B5 and the reprinted version of that book. Complete references are given at the end. It quickly grew to become much larger than I had intended, but I have retained the entire discussion. This has been primarily to help me clarify these issues for myself, but others might be interested in these musings.

COST AND INSTALLATION

Sandcasters cost Cr250,000 (B2 p. 16, 21; B5 p. 25; RB2 p. 23). Sand is "generally prepacked in a sandcaster canister" (B2 p. 18) or "replacement canisters of this special sand weigh about 50 kg" (RB2 p. 17). The cost of one canister is Cr400 (B2 p. 18; RB2 p.17).

"Each launcher... has an inherent capacity for three... canisters. When a launcher's... canisters are exhausted, it may be reloaded by the turret's gunner in one turn." (B2 p. 30; RB2 p. 30) Sand may be launched during the Ordnance Launch phase (B2 p. 23, 30; RB2 p. 29-30), only one canister may be launched from one sandcaster in one Ordnance Launch phase (B2 p. 30; RB2 p. 30). The programs Launch and Target must be running to launch sand canisters (B2 p. 30, 32; RB2 p. 29, 39, 41).

Sandcasters may be mounted in one-ton turrets (B2 p. 15, 21, 24; B5 p. 21, 25, 26, 29, 30; RB2 p. 15, 27). Sandcasters may also be mounted in small craft (B5 p. 36) but then does not require a gunner (B5 p. 34).

COMPOSITION AND FUNCTION

The "sand" of sandcasters is "abrasive particles" (B2 p. 15, 18) "of a special composition, combining prismatic crystals and ablative particles..." (B2 p. 18), or "a granular agent" (B5 p. 18) in the early rules sets. This implies a mixture of glass-like grains that refract light, opaque grains that will vaporize with heat, and abrasive grains (possibly the first two types are also abrasive and there is no separate abrasive type of grain). That description suggests something that looks and feels much like sand, and does not contain metal strips or flares or other components, however "ordinary sand or particles are not considered to be an adequate substitute." (B2 p. 18)

This image is re-enforced by the indicated function of sand: "lessening the effectiveness of lasers, disrupting missile fire, and interfering with enemy ship flight" (B2 p. 15), "allows interference with laser beanms[sic] and pulses, as well as inflicting minor damage on ships which it touches" (B2 p. 18), "Defense DMs [for laser fire] result from such circumstances as obscuring sand" (B2 p. 29), "Laser Fire DM... Per ½" of obscuring sand... -3" (B2 p. 30), "obstructs light, when fired it interferes with incoming laser or energy weapon fire" (B5 p. 18), and provides defences against missiles, lasers, and energy weapons (B5 p. 45).

Note that there is no indication that sand interferes with sensors, despite such indication for force fields (B5 p. 43). Further, sand has less effect on energy weapon fire than on laser fire (B5 p. 45), and no effect at all on particle accelerators or meson guns (B5 p. 45). If sand was decreasing chances to hit by interfering with sensors (even in part), we would expect all weapons to be affected (at least to some extent). It might be argued that the influence of relative computer size on penetration success (B5 p. 45) suggests that an influence on sensors is included in the sand DM, but this is inconsistent with the lack of any DM for particle accelerators and meson guns, and in any event increased computer power could allow the firing ship to identify and exploit areas of the sand cloud that are thinner.

Sand both refracts laser beams and absorbs laser energy, resulting in a DM to hit. Energy weapon attacks are not refracted but energy is still absorbed, thus suffer a smaller DM to hit. Particle accelerator beams have sufficient energy to punch through sand, and suffer no DM. Mesons are unaffected by matter, and also avoid any DM from sand.

Sand damage against ships is not addressed, other than being called "minor." Since beam lasers do not seem to do "minor" damage, sand does less damage than a beam laser and so should not inflict a "hit" as described in the combat system. Perhaps sand would cause a system to cease functioning for one turn (no repair roll required, no cost). Drives would be exempt, perhaps roll 2D for damage on the table for lasers but add +3 to the roll. Hull hits could indicate a slow leak. Alternately, the system would only suffer a DM for one turn.

MISSILES

Book 2: Starships does not provide any rules to deal with how missiles are affected by sand. One interpretation is that any missile passing through sand is neutralized ("disrupting missile fire"), but this is not stated. Book 5: High Guard includes rules that deal with the effect of sand on missiles: just like lasers dedicated to anti-missile fire, sand reduces the number of missiles that affect the target. In fact, sand is usually better at stopping missiles than are beam lasers:

TL7

TL8

TL10

TL13

(computer ratings equal)

This suggests that a simple roll should be made for each missile passing through sand, similar to the roll made for the ECM program, but with a chance of success similar to that of a beam laser engaged in anti-missile fire. On the other hand, the tables in Book 5: High Guard also indicate that sand is almost as effective against missiles as it is against lasers:

TL7

This suggests that the roll proposed above should have a chance of success just a little lower than the chance of stopping a laser. The chance that the sand will stop a laser attack may be estimated as the chance that a laser hit will be turned into a laser miss by the sand DM. This will depend on various other DM's that may influence laser success, but there are other issues to consider.

LASERS

The DM indicated for laser fire is -3 "per ½" " (800 km, B2 p. 30) or "per 25 mm" (2500 km, RB2 p. 31). This clearly implies that sand is stackable: the DM increases linearly with amount of sand. The tables in Book 5: High Guard also imply a linear increase in sand DM, as the effectiveness of sand in those tables increases in much the same way as that of lasers (and other weapons) which inflict increased damage with increased numbers of weapons in a linear fashion (B5 p. 45).

The rules do not indicate how many canisters would provide 800 km (or 2500 km) of sand, nor the shape of the sand cloud. How long the cloud lasts is not addressed either, but it is implied that it lasts more than one turn: "Sandcasters dispense abrasive particles into the path of enemy targets,... interfering with enemy ship flight" (B2 p. 15), and "During the ordnance launch phase, missiles or sand which contacted a target in the preceding movement phase now explodes or takes effect." (B2 p. 30). This might refer to ships that are following so closely that they are hit by the sand within one turn of it having been launched, but such a situation seems unlikely. More to the point: "only one missile or sand canister may be launched from a launch rack or sandcaster. The launched item does not actually move until the following friendly movement phase" (B2 p. 30), and "Intruder Movement... Ordnance (missiles and sand) which he has launched in previous game turns is moved at the same time" (B2 p. 23). This implies that sand lasts at least two turns, and possibly is permanent (at least for combat purposes).

PERSISTENCE

With sand lasting several turns, and being stackable, it will be relatively easy to generate enough DM's from sand to completely block any laser attack. This suggests that the DM for a single sand canister should be as low as possible (for example, if each canister was responsible for a -3 DM, one fully-loaded triple sandcaster turret could lay down a cloud of sand with a -27 DM). On the other hand, for a single sandcaster to be useful in a dynamic combat each canister must generate at least -1 for laser fire. If one canister provides a -1 DM, then it may be inferred that one canister generates a cloud of sand 1/3 of 800 km (B2) or 2500 km (RB2). The simplest shape to work with for a sand cloud is a sphere (a circle on the playing surface). This would mean that a single sand canister would form a sphere about 1/6 inch = 267 km (B2) or 8.33 mm = 833 km (RB2) across, and which would impose a -1 DM to hit for laser fire passing through it. Presumably two canisters fired together could form a sphere of the same size but with twice the density, providing a -2 DM.

Even with this approach, sand DM's can quickly climb to become insurmountable. One fully-loaded triple sandcaster turret could still lay down a cloud of sand with a -9 DM, and a few such turrets could easily be mounted on a small warship. In addition, the idea that sand persists for several turns causes other problems. The additional book-keeping would be considerable, making combats with sandcasters cumbersome. It may sometimes involve the third dimension that is usually ignored in table-top games, as ships look for a route around drifting sand (without the third dimension, a wall of sand might be laid down across space relatively easily in two dimensions). It also opens up the possibility of cargo ships full of sand laying down defences that make the game dull.

It should also be noted that the persistence of sand clouds is not necessarily realistic. For a sand canister less than one metre across to expand to a cloud 267 km (B2) or 833 km (RB2) in diameter, the sand has to be expanding in all directions with a speed of at least 133 km per turn (B2) or 417 km per turn (RB2). It will expand to 533 km (B2) or 1667 km (RB2) by the second turn, and have 1/8 the density: lasers will pass through twice as much cloud and so will encounter 1/4 the sand. It is also possible that previous laser fire (even if it was missing the ship) may have destroyed some of the sand, and the attacking ship will have had time to map the drifting sand in the cloud and fire more effectively through it. One might keep track of the changing cloud size and DM, but this just adds to the book-keeping problems that persistent sand is already imposing. Note that by the third turn the cloud would be ½" = 800 km (B2) or 25 mm = 2500 km (RB2), with a DM only 1/9 the original.

It is trivially easy to avoid these drifting sand clouds unless a ship is just hiding behind them without maneuvering. This introduces tactics that would not be otherwise available. For example, rather than fleeing a pirate attack, a merchant might lay down as much sand as is carried aboard the ship, then try to stay behind the cloud until help arrived. There are problems with such tactics (for example: the three-dimensional aspect, and the inability of the 10-minute/1000-second turns to handle fine-scale maneuvering).

Given the lack of realism, the capacity to build very high DM's, the extra book-keeping, and the tactical problems, I must conclude that sand should only last one turn after being launched. Of course, each GM must make their own determination, and mine is no more right than anyone else's.

LASER DMS

Even with sand that only lasts one turn after being launched, very large DM's may be generated against laser fire. For example, a warship of 5,000 tons could easily carry eight triple sandcaster turrets: enough to generate a -24 DM for three turns (then reloading would be required). Such an array of sandcasters could generate a DM of -12 as long as the sand magazine (20 canisters per ton) held out, with half the turrets reloading at any given moment.

One way to prevent excessively large sand DM's is diminishing returns with increasing numbers of sandcasters. There are numerous ways to achieve this, but perhaps the most straightforward is to multiply the number of additional sandcasters required for each increase in DM by a factor. The size of this factor will determine how quickly the DM increases.

Number of sandcasters required for given DM's:

These sorts of progressions are intuitively appealing: it is easy to imagine that protection provided by sand would actually increase in this way. Still remaining would be selecting a factor. A smaller factor (such as 1.5x) allows differences between single, double, and triple sandcaster turrets, but very high DM's are still possible to achieve in larger ships (e.g. a 5,000-ton ship with 14 triple sandcaster turrets: -9 DM). This may be acceptable, depending on the GM. Higher factors make it much more difficult to obtain these very high DM's (e.g using factor 2x, a 5,000-ton ship with 22 triple sandcaster turrets gets a -7 DM), but then differences among lower numbers are sometimes lost (e.g. using factor 2x, there is no difference between a ship with a double sandcaster turret and one with a triple sandcaster turret).

Note that the rules indicate that it is possible to launch enough sand to make it impossible to hit a target with a laser (B5 p. 45). However, the same tables allow some chance with massed laser fire against any amount of sand.

Another approach to limiting sandcaster effectiveness is putting a cap on the DM's. This is perhaps less intuitively appealing, but remains no more unrealistic than many other game rules. It has the benefit of allowing differences among lower numbers of sandcasters while preventing very high DM's. The only disadvantage is that large ships will not benefit from large numbers of sandcasters. Of course, a cap may be imposed on a linear or diminishing series.

Once that is decided, the DM cap must be selected. Presumably it must be at least -3 (since that value is given in the rules (B2 p. 30; RB2 p. 31). It is probably pointless to make it greater than -12, as this DM would already make laser hits impossible under most circumstances. Even -9 would mean a roll of 12+ on 2D at point blank range firing with Predict-4, Gunner Interact, and a gunner with Gunnery-2 against a target that is not evading. Perhaps something like -6 is reasonable: it allows differences among just about any sandcaster array likely to be seen in a smaller ship, and it insures that targets may be hit by a ship with modest abilities (e.g. 12+ to hit with Gunner Interact and a gunner with Gunnery-2).

Perhaps the best approach is a 'soft' cap: a more or less linear increase up to a cap, then a sharp non-linear increase after that. For example, increase linearly up to 6 sandcasters but jumping the prime number 5 (5 sandcasters doesn't come up much), then increase the numbers of sandcasters rapidly, say by an increasing factor:

With this set of DM's, a 5,000-ton ship with 16 of its 50 turrets being triple sandcaster turrets can generate a -7 sand DM for attacks coming from one direction, for three turns. Even assuming that this ship obtained a -2 DM for evasion, an attacker could still hit with beam lasers, Predict-4, Gunner Interact, and a gunner with Gunnery-2 (and of course after three turns could hit very easily while the sandcasters are reloaded). Even a 600,000-ton ship would have to dedicate more than one third of its weaponry tonnage to sandcasters to get a -9 DM against lasers for three turns.

Of course, these DM's apply to any laser fire through the sand, from any direction. This means that sandcasters make laser fire more difficult for both the ship casting sand and its enemy. Anti-missile fire is assumed to take place on the missile's final approach, which may be assumed to be past the sand (only missiles that have survived the sand need be engaged, and there is no sand DM).

ENERGY WEAPONS

Energy weapons gain a +2 DM to penetrate sand (B5 p. 45). This seems a reasonable adjustment: reduce the DM by 2 (minimum 0). Thus a plasma gun would be unaffected by less than three sandcasters, and would suffer a -4 DM if the target ship was protected by 12 sandcasters.

DISRUPTING MISSILES

Above it is suggested that a roll to neutralize a missile should have a chance of success just a little lower than the chance of stopping a laser, which may be estimated as the chance that a laser hit will be turned into a laser miss by the sand DM. This may depend on a number of factors, but in a simple attack with no other DM's, the chance to hit with and without sand is:

Therefore, one sand canister should have a little less than a 33% chance of neutralizing a missile. Given that 33% is between 8+ and 9+ on 2D, and anti-missile laser fire will hit and destroy a missile with a roll of 8+ on 2D (no DM's, B2 p. 29-30, 32), perhaps a simple roll of 10+ on 2D would be required to destroy any missile passing through sand. This should change with increasing sandcasters (as suggested by B5 p. 45), perhaps 11+ on 2D with the laser DM above. That would result in the following:

Perhaps increasing the required roll by one would prevent sand from being too effective, and insure that complete immunity to missiles would remain unattainable. Even this would make sand very effective against missiles, even more effective than the ECM program with large numbers of sandcasters, and that is consistent with the rules given (B5 p. 45).

It may be argued that missiles could maneuver around sand. Maneuvering around a cloud of sand in the final approach to the target (at high velocity) would be problematic, and could be argued to warrant the same DM as going through the cloud. Maneuvering around a cloud in the middle of the flight would be trivial, and is one more argument against the utility of persistent sand. Maneuvering around a cloud just after launch would be simple, as the missile could be launched to the side and would have little initial velocity (relative to the sand). Thus, unlike for lasers, sand can protect you from enemy missiles while not interfering with yours.

AREA DEFENSE

Since sand will affect any attack passing through the sand cloud, it should be possible for one ship to protect another by launching sand in front of it. This may be difficult unless the protecting ship is close to the target ship, as the attacking ship may be able to maneuver so as to fire past the sand cloud. In any event, missiles would only be affected by sand immediately adjascent to the target. The DM for a sand cloud is calculated by summing the sand canisters (possibly from more than one ship) and then calculating the DM, not summing the DM's.

TECHNICAL DETAILS

The packaging of sand ("sand canisters") is not described, but the rules imply that the canister is a simple case of material that disintegrates on firing (perhaps heavy cardboard) full of sand, with no guidance or explosives. There are a number of references to sandcasters that "dispense abrasive particles" (B2 p. 15-16) without explicit mention of any canister, but more compelling is this quote: "Sand must be procured from arms merchants, generally prepacked in a sandcaster canister" (B2 p. 18). The implication here is that sand is sometimes procured in bulk, not "prepacked in a sandcaster canister," and perhaps could even be loaded into a sandcaster as 'loose sand.' Of course it is possible that packaging in a canister is required even though the sand is available 'loose,' but the rules do not resolve this either way.

I could find no mention in the rules of anything other than "sand" in a sand canister. The requirement of the Target and Launch programs for launching sand might be taken to imply that a sand canister is guided towards a target, but it is probably more reasonable to interpret this to mean that the sand is being launched with the vector that maximizes its interposition between the firing ship and the target ship. There is certainly no explicit mention of sand guidance, nor any stated or implied maneuver or explosion associated with sand canisters.

I conclude that the sandcaster is a mechanical device that pushes the sand out with such force that it bursts the canister, and the sand disperses like a shotgun discharge.

Given that a sandcaster creates a sand cloud 267 km (B2) or 833 km (RB2) across within 10 min (B2) or 1,000 sec (RB2), the average muzzle velocity of the sand would be about 222 m/s (B2) or 416 m/s (RB2). For comparison, the famous 88 mm flack gun of the WWII Germans had a muzzle velocity of about 1,000 m/s. With 50 kg of sand, the muzzle energy of a sandcaster would be about 1.2 MJ (B2) or 4.3 MJ (RB2). The German 88 mm fired a 10-kg projectile for about 5.0 MJ of muzzle energy.

The momentum of the launched sand would be 11,100 m-kg (B2) or 20,800 m-kg (RB2). I don't wish to become mired in a discussion of the mass of a "ton" of Traveller starship, but this momentum means that firing a single sandcaster would result in a ship of 1,000 tons mass (a 100 ton ship with the approximate density of a naval ship) moving in the opposite direction with a speed of 1 cm/s (B2) or 2 cm/s (RB2). For comparison, the momentum of the projectile from the German 88 mm is about 10,000 m-kg.

I conclude that people on board a vessel, especially a small vessel, will hear and feel the firing of sandcasters.

SUMMARY

Sandcasters cost Cr250,000 each, and may be installed in any one-ton turret. Each holds three sand canisters ready, may fire one each Ordnance Launch phase, and take one turn to be reloaded by the gunner. Launch and Target programs are required for launching sand. Each canister is 50 kg of abrasive, refractive, and ablative particles and costs Cr400.

Once launched, the rules indicate that sand persists for at least several turns, but I recommend that it last only one turn.

The rules indicate that sand DM's increase in a linear fashion, but I recommend a system such as:

These DM's apply to laser attacks to and from the ship (through the 267 km diameter cloud), except anti-missile fire. Energy weapons reduce the DM by 2.

Sand is very effective against missiles. I recommend a system similar to ECM effects: roll 12+ on 2D + laser DM to neutralize each missile which passes through the cloud.

Sand is unlikely to contact a ship. If it does, roll for one damage location with a +3 DM, but damage done is minor: treat turret or computer hits as normal hits which self-correct after one turn; treat hull, hold, or fuel hits as slow leaks which will have little effect on combat.

As usual, each GM will make different decisions regarding these rules, based on what makes the game most enjoyable for them and their players. These are no more than my own musings on the subject.

REFERENCES

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