Traveller Fusion maneuver drives

February 18, 2023December 22, 2024 jbhemlock

Maneuver drives in Traveller are one of the “magic” technologies that live in the setting, but let’s try to scrap that and try something new. This setting is an attempt to make a “hard” interstellar science fiction setting for Traveller, and so we’ll look at more realistic maneuver drives.

Rockets!

First thing we’re going to decide: We’re using rockets. Reaction drives. Just like all spacecraft now, our ships will move by blasting stuff really fast out one end, and then Newton’s Second Law will push us the other way. The next question, though… What kind of rockets?

We’re not going to use chemical propulsion. That’s what we use today. Combine fuel and oxidizer in an engine, and hot gasses blast out of the end of it. The problem with chemical propulsion is it’s just not good enough. An Atlas V, which is a pretty common modern rocket, is 590,000 kg of metal and angry chemicals, and it can get at most 18,000 kg into orbit. Once. If you want to get something to Mars, then that 18,000 kg has to include another small rocket that will propel your spacecraft to Mars, so your final spacecraft mass will likely be something on the order of 1,000 kg in Mars orbit… After a journey of years. That’s not going to do it.

We’re not going to use ion engines, either. The problem, you see, is that current rockets really come in two flavors. High thrust, or high efficiency. A chemical rocket produces high thrust, which lets the rocket lift off from the Earth and produce a bunch of acceleration. For a very short time. An ion engine, on the other hand, is very efficient, but it produces minuscule thrust.

No, what we want is a torchship drive! A drive that is both high thrust and high efficiency! One that will let us travel from one planet to another in a reasonable amount of time! We want something that’s in the general ballpark of what a standard Traveller maneuver drive can do… Just with added realism. And that realism will include thermodynamics.

Thermodynamics

Oh God, here we go.

Nothing is 100% efficient. Especially rockets. They generate heat. Often a tremendous amount of heat. Chemical rockets get rid of that heat by sending it out with the exhaust. This works for them because they chew through all their fuel in a very short time – there is a lot of hot mass going out the business end of a rocket engine. Since we want a spacecraft that can produce a reasonable amount of acceleration for a long time while not filling up all the internal space of the ship with fuel tanks, we can’t get away with this. So we’ll need to deal with the heat our engine produces. However much heat that is…

So, let’s start to work out a better definition for a torchship. I’m going off of Winchell Chung’s definition: A torchship is “a spacecraft with more than 300 km/s total delta V and an acceleration greater than 0.01 g.” We know what acceleration is, but now we’ve added delta V. That’s a concept that describes how much a vehicle can change its velocity. It’s essentially a measure of fuel capacity. If our torchship can accelerate at 0.01 g, that’s about 0.1 m/s^2. 300 km/s of delta V, at that acceleration, just means that the ship can fire its thrusters for 300,000/0.1 = 3,000,000 seconds. That’s almost 35 days. The standard Traveller starship can also maneuver for about the same amount of time, so that’s a good definition.

There’s an equation for determining how much power a drive produces: Thrust * exhaust velocity / 2 = power. If our spacecraft masses 1000 tons (which feels like it’s in the Type A Free Trader range, assuming each dton masses 5 tons on the average), then our drive is producing 10,000 newtons of thrust. It’s pretty common with theoretical fusion engine designs to have an exhaust velocity somewhere in the range of 1,000 km/s, so let’s use that. Our drive, then, produces 5 gigawatts of power. Let’s be generous, and assume that we’re only losing 10% of that as waste heat. We still need to radiate 500 megawatts of heat for the entire time the drive is operating. That’s a lot, but it’s doable, especially with exotic, theoretical radiators.

So what do we choose?

I’m going to gloss over all of the time I spent pouring over the Atomic Rockets website. I highly recommend it, though. I wanted to have something that was a low end torchship that was feasible with future technology – something that wouldn’t break the known laws of physics. I wanted something that used some sort of hydrogen fuel, because so much of Traveller revolves around that. That led me to fusion engines. One design that’s fairly well developed is the gasdynamic mirror fusion engine. There have been a couple of theoretical designs done with these as proposed propulsion for manned Mars missions, and they have surprisingly decent performance. Exhaust velocities above 1,000 km/s and thousands of Newtons of thrust. So we’ll pick that. We want our setting to be farther in the future – I picked 2600 AD out of a hat – and so I used that as an excuse to beef up some of the numbers a bit, mostly in the heat dissipation area, and ended up with a drive massing 108 tons and producing 60,000 Newtons of thrust with an exhaust velocity of 1,200 km/s. This drive produces 36 GW of thrust power, and dissipates waste heat through a type of exotic radiator called a Curie Point Radiator which is based on the magnetic properties of hot metal. Most metals lose their magnetic properties when they’re heated above a certain point, called the Curie point. The Curie Point Radiator, then, just flings hot metal out. When it cools down below its Curie point, then it is drawn back by powerful magnets. There are electrostatic versions of this, as well. These are buildable with existing technology, and they’re capable of radiating several MW of heat per square meter, which is pretty good. The gasdynamic mirror drive is a long tube, so there’s plenty of room to mount these things on a framework running along the drive. The drive itself uses powerful electromagnets along the tube, so it’s entirely possible those could do double duty as the magnets in Curie Point Radiators.

The gasdynamic mirror fusion engine fuses deuterium and tritium, both of which are refined from hydrogen. Tritium has a short half life – 12 years – but we don’t care too much about that, because we’re looking at trip times shorter than a month. The only problem with this is that deuterium-tritium fusion produces a lot of neutrons, which are deadly and hard to shield against. And by “a lot,” I mean nearly 80% of the fusion energy is in the form of neutrons, emitted in all directions. So we’re going to bring in a little unobtanium…

Unobtanium

Unobtanium is technology that doesn’t seem like it’s impossible – it doesn’t violate laws of physics – but we have no idea how to make. It’s almost cheating, but not quite. I’m allowing myself a little unobtanium in the setting.

The unobtanium that we’re bringing in is spin-polarization. When a deuterium atom and a tritium atom slam together and fuse, they emit an alpha particle and a neutron in opposite directions. And it turns out that these directions are based on the magnetic spin moments of the atoms. So if you can align them… you can control the direction the neutrons and alpha particles are emitted! You can direct all the neutrons out the nozzle of the rocket! You can direct some of the alpha particles through a magnetohydrodynamic generator for electricity, and use magnets to direct the rest of them back out the nozzle! This not only cuts way down on the amount of shielding you need for this engine, it effectively doubles the thrust! We’re totally doing that!

We’re also going to allow the thrust to be augmented by injecting additional hydrogen as propellant. Basically, we’re using the energy from fusing some hydrogen to heat more hydrogen, boosting our thrust. We can double the thrust of the engine by injecting four times as much hydrogen, reducing the exhaust velocity by half. This gives us some choices, trading off fuel efficiency for thrust.

Extras

This drive produces power, so we can potentially use this as a replacement for both the maneuver drive and power plant. One of the reference designs for this drive described the power required to start it – 1,000 MW-sec – and described this as coming from a capacitor bank that was initially charged up with fuel cells. Once the drive was operating, it would produce the electricity needed to maintain the reaction, as well as hotel power for the rest of the ship, and power to “recharge” the fuel cells. Our drive is smaller and lighter than this reference drive, so I’ve scaled this down to about 250 MW-sec, which can be provided by a 7 ton bank of capacitors, using Book 5 rules. 2 tons of fuel cells can charge these capacitors in about 1000 seconds, which is 1 CT space combat turn, so that seems like a good option.

One downside to this drive is it produces a dangerous neutron stream out the business end of the rocket. This makes decelerating for rendezvous with a spaceship or station tricky. To get around this, we’re going to simply say the standard drive also has a pair of ponderomotive VASIMR thrusters firing along the axis of the drive for “last mile” maneuvering.

The final drive

Here’s what I’m calling our reference drive – something suitable for mounting in a Type S scout/courier or a Type A free trader:

Cost: Mcr 20

Mass (including radiators): 108 tons

Length: 44m

Thrust (N)	Exhaust Velocity (m/s)	Specific Impulse (sec)	Mass Flow Rate
60,000	1,200,000	122,449	0.05
120,000	100,000	0.32	Maximum powered range for 5G2 missile
240,000	150,000	0.5	Normal sensor detection range
600,000	250,000	0.833	Maximum laser range with full accuracy
1,200,000	300,000	1	1 light second

The VASIMR thrusters on this drive produce 1,280 N of thrust, which isn’t much, but it’s better than giving everyone radiation poisoning at the station you’re docking with.

This isn’t really a drive that’s useful for taking off from or landing on planets, but that’s fine for us. This setting is a station-heavy setting, so we’ll assume that our spaceships never land. If players want to go to a planet, they’ll take a shuttle from a station in orbit.

We are keeping jump drives in this setting, and we’ll want to work out the accuracy of those jump drives. It seems reasonable to assume that a typical pilot can jump into a system and land about a million km from a station. That’s a bit more than double the distance from the Earth to the Moon, and a bit less than 100 diameters from the Earth. That’s the sort of distances we’re going to be dealing with in day-to-day use.

Performance-wise, lets imagine a typical ship. We’re using a near stars starmap, and we’ll need a minimum of jump-2 to be able to get around in the vicinity of the Sun, so we’ll call that the standard. In Classic Traveller, a 200 dton far trader is barely profitable, with a 300 dton variant a much better option, so we’ll go with that. 300 dtons. That’s about 1500 tons, using our 5 ton per dton napkin rule. This drive, running at 60,000 N thrust, can travel a million km in about 3.5 days. At 120,000 N, it cuts it down to 2.5 days. 240,000 N gets us there in under 2 days – 40 hours or so. 600,000 N drops it to about 25 hours, but there’s a big drawback. 600,000 N gets us into the station with dry tanks, while 240,000 N only consumes about 30% of our fuel, taking 15 hours longer. 240,000 N feels like the sweet spot, then, for a working trader. With the wimpy “last mile” VASIMR drive, we dock in 2 days. If the station is outside of the 100 diameter limit of a planet, which seems like a reasonable choice for a trade depot, we can just undock and jump, so we get 5 days at the station.

Next Post: What does this drive do to our setting?

Traveller Fusion – A low-magic Traveller setting

February 17, 2023February 18, 2023 jbhemlock

This is the first in a series of posts detailing a new Traveller setting I’ve been playing around with.

It’s been a long time since I’ve updated this blog, mostly because I haven’t had a lot of time to mess around with Traveller recently. A few months ago, though, I had a hard science fiction itch and I started thinking about how to scratch it with Traveller. While Traveller as a game, especially Classic Traveller, sits more on the “hard” side of things, it does rely on a handful of what I would call “magic” additions: Psionics; torch drives that break the laws of thermodynamics; and faster than light travel. Could you strip some of those things away and still have a fun and viable game? Could I do that while portraying a universe that felt gritty and realistic?

Psionics is a no-brainer. They have always felt like add-ons in the rules, and quite a few settings ignore them entirely.

Likewise, faster than light travel is a no-brainer. You pretty much have to leave it in. Without it, there’s no good way to go from system to system. There are settings that leave it out – Zozer’s Orbital 2100, for instance, does a good job of presenting a setting without FTL travel – but I’m interested in a multi-system setting. So I will be leaving jump drives in.

Which leaves the torch drives. The nature of these things isn’t really gone into in the little black books, but you can make some guesses based on the rules around them. In the little black books, they range from 1 to 6 gravities of acceleration, and they’re capable of constant use for about a month on most ships. That’s quite a bit. The bare minimum 1-G drive will take you from Earth to Mars in about half a week even when they are farthest apart. And these drives are magical, in that they produce no heat to speak of, no radiation to speak of, and consume no fuel. Later editions and custom settings sometimes go into reaction drives, but these are still magic: Tremendous performance for fairly small fuel consumption with no heat to worry about.

So I started thinking about a setting with “future realistic” maneuver drives and standard jump drives. What would that look like? Would it be fun?

Future realistic?

What I wanted to do with this is to come up with something that would appeal to the sort of people who enjoy Winchell Chung’s Atomic Rockets website. Something that would appeal to people who play games like Children of a Dead Earth. So the first thing wanted to do is define what it is I’m going for. This is not going to be a modern realistic setting. I don’t want this to be Traveller with Atlas rockets. I don’t want multi-year travel times. Longer travel times are fine, but I want to keep the Traveller feel of interplanetary and interstellar mobility. So I’m looking to the future. I’m looking towards propulsion systems that enable that.

Gritty, realistic universe

I’ve experimented in the past with revamping the Traveller world generation rules to make shirtsleeve worlds rare, and I’ve always enjoyed the result. One of my favorite authors is C.J. Cherryh, who takes this tack with her Alliance/Union setting, so I felt there was a lot of potential for an interstellar setting that doesn’t depend on a lot of planets where you can walk around without a space suit. The last setting I did was an attempt to reproduce the Alliance/Union setting in Traveller, using near star data to create a sector centered on the Sun, and that was really fun. I decided to basically take the exact same physical setting, and use it for this one.

Next post: Traveller Fusion maneuver drives!

Non-deterministic background actions and you – an example

April 21, 2022April 21, 2022 jbhemlock

This was originally part of a discussion of “big fleet” actions in a small ship setting on the Traveller discord, and how to let these actions in the background affect players while not making it feel like the background is just sitting pre-created and waiting to nab them. I mentioned that I make heavy use of GM and NPC emulators for this sort of thing, and someone wanted to see a detailed example.

I love worldbuilding, and this is all based on a custom setting I developed. 24 inhabited systems, linked by about the same number of uninhabited systems, spread out over a few subsectors. Two major polities, a small but centralized one, and a larger confederation. So it’s very much a small ship, small universe setting. It’s also a pretty hostile universe, with only a couple of worlds that are even remotely terraformable, so those are extremely valuable. In this setting, no jump drives capable of better than Jump-2 exist.

Historically, there have been conflicts between the two polities before, and stretches of cold war. The larger polity (the Alliance – I know, lame name) has recently been weakened because of a civil war, and the smaller polity (the UTSC) is taking advantage of this, and has invaded. The UTSC admiral who came up with the plan, Admiral Antonini, was put in charge of the invasion force. I used an NPC generator to give me a one-liner for him:

A proud warrior, motivated to achieve victory, safeguard force, and achieve myths.

The impression I got from this is that he’s an older admiral who’s thinking about his legacy, wanting to return lost UTSC territory to their control (with himself as military governor of the conquered territory, of course). He’s also cautious, prone to probing attacks instead of risky battles.

This is important, because it lets me imagine the possibilities that he would consider. I don’t make any firm decisions for him, however. Those are controlled by a GM emulator – a set of tables that answer yes/no questions.

This example takes place in this area of space

Hai Zhe is the nearest UTSC stronghold. Fomalhaut is a neutral party. Dupree used to be an Alliance system, but the starport station in the system was partially destroyed, and the system held by the UTSC as they drove into Medusa and Aiea. Rasalhague is the jewel of this particular area, home to the only planet in the subsector where food can be easily grown. The UTSC naval forces are stronger than the Alliance forces in this area of strength, but Rasalhague is still heavily defended. The UTSC concentrates its force in Medusa, with a smaller force in Dupree (to maintain the route to Hai Zhe), and a defending force in Hai Zhe which the UTSC will not commit to the invasion.

Alliance Admiral Nieves (A sinful outlaw. Motivated to achieve myths, secure riddles, and associate the church.), in charge of a smaller but significant force rimward (“south”) of this map has been gathering intelligence, and thinks Antonini is overextended. He has been trying to convince Alliance Admiral Hu (A pious courtier. Motivated to conceive the elite, manage enlightenment, and administer the elite.) to link up to invade Dupree, but Hu feels this would expose them to an attack by UTSC reserves rimward. Nieves figures he has to act alone, then, and that if he succeeds Hu will support him.

Nieves has sent a small force to Fomalhaut demanding that they stop allowing the UTSC to stage through their system, or he will consider them to be allies of the UTSC, and treat them as hostile. Fomalhaut is not a wealthy or powerful system, and so they agree. Nieves figures that this might delay the UTSC from resupplying the invasion force, and so he takes this opportunity to make a risky attack on Dupree, capturing the system and cutting off Antonini.

Antonini is currently in Medusa, which is an untenable spot for him. The two options for him would be to either strike Dupree and retake it (which would cost him a portion of his force, limiting his ability to continue the invasion), or strike Rasalhague in the hopes that victory here would push the UTSC into retaking Dupree. Since Antonini is thinking about his legacy, I ask the GM emulator about invading Rasalhague first:

Q: “Will Antoniti attack Rasalhague?”
A: Yes, but…

So he will, but there’s some hesitancy. I probe into this:

Q: “Will he attack this month?”
A: No

Q: “Will he attack next month?”
A: Yes

So clearly he’s gathering his forces, gathering intelligence. The PCs (detached duty scouts) are in Rasalhague at the time. The atmosphere at Rasalhague Station is tense, with people expecting an invasion force at any time. I had already checked if the scout base there wanted to reactivate the PCs, and got the answer “no, but…”, so I figure I will recheck that if conditions change. The PCs are contacted by someone who wants to leave the system, and so they gather some cargo and head out to Serurier. They do their business in Serurier, and end up taking a lucrative contract to bring supplies into Rasalhague. Timing-wise, they will arrive at Rasalhague a few days after Antonini launches his attack, so I need to work that out.

There’s a set of mathematical formula that’s useful in military strategy called Lanchester’s Laws. They basically determine who would win in a fight between unequal numbers of forces. In my setting, the very largest ships are 6000 dton, with no book 5 weapons or anything. Limited to 1 turret per 100 tons, military ships boost their force by carrying fighters and SDBs. Missiles are the primary offensive weapon, with lasers being secondary offensive weapons and anti-missile defenses, and both sides of a battle field similar sorts of forces – lots of fighters, carriers focusing on defense, etc. The battles themselves are mostly contests of fighters, with the winner of that contest engaging the opposing carriers.

This is similar to infantry battles between forces armed with guns (battles at a range greater than contact, with choice of target, and heavy offense versus defensive abilities). Lanchester’s Square Law deals with this and says the side with the greater numbers wins, and that their effectiveness is proportional to the square of their numbers. For instance, if side A brings 300 fighters to a battle, and side B has 400, the ratio is 3/4. But the square of the ratio is 9/16, so side B would win and retain 43.75% of their forces: 175 fighters. This forms the basis for how I determine who wins a big naval battle in my game.

Back to the invasion of Rasalhague! Antonini jumps in with 4 carriers and an assault ship, carrying 427 fighters. The Alliance forces consist of one small carrier, and 284 fighters. I divide the battle into days. Each day I make a roll to see what percentage of the forces engage, and I roll to see how effectively they deploy. Effectiveness is a small fudge factor onto the strength ratio, just to add some uncertainty. I make rolls day-by-day and determine that the battle takes 3 days. At the end of this time, Antonini has lost one carrier and about 230 fighters, while the Alliance carrier fled and the system otherwise fell.

This tells me that when the PCs jump in, the system has been newly conquered. Antonini has been working to organize food shipments to Medusa and Aiea. Time for the GM emulator:

Q: “Is Rasalhague cooperating with the food shipments?”
A: Yes, but…

Q: “Are there problems with merchants being attacked by the UTSC forces?”
A: Yes

Q: “Does this mean that merchant families are getting out of Rasalhague?”
A: Yes

Q: “Does this threaten Antonini’s ability to supply Medusa and Aiea?”
A: Yes

So the PCs jump in to a powderkeg situation. Antonini desperately needs to regain cooperation of the merchant families – in my setting, large merchant ships are owned by families – but he’s also concerned about possible Alliance smugglers. So Rasalhague Station contacts the PCs, informing them that they are now in UTSC territory, and they need to dock at Rasalhague Station to get UTSC trade papers. There is a lot of UTSC naval traffic, so the implication to the PCs is that there is an unspoken “or else…”

The PCs don’t have the fuel to immediately jump out, and refueling at a gas giant would take too long, so they decide to dock at Rasalhague Station. Once there, they are informed that there is a delay processing papers… There are a lot of merchants docked there, and they’re all angry at the delays…

Travel – Interstellar vs insystem

March 16, 2022March 16, 2022 jbhemlock

I’ve been developing a small ship, small universe Traveller setting that’s based on the spread of Terrans from the solar system over a couple of centuries. One of the things I wanted to do with this setting is to make habitable worlds extremely rare. Out of the 50-odd systems in my setting, there is a single planet with a breathable atmosphere aside from Earth. There are 6 other planets which are potentially terraformable, but most human habitation remains in space. This pushes my setting away from the traditional “one main world in an otherwise mostly uninhabited system” feel of standard Traveller, and I wanted to see what that might do to the feel of a system.

So, of course, I decided to dig into the economics of it, first…

Interstellar travel in Traveller requires a passenger starship, and the price of travel is based on the price of running that starship.

The Type A, for instance, has the following costs of operation:

Item	Cost
Crew	6,500/fortnite
Fuel	2,500/fortnite
Mortgage	77,250/fortnite
Maintenance	1,545/fortnite
Total	87,795

We’ve calculated costs per fortnite (14 days), instead of per jump, though this is the same for most commercial starships. For this, it can carry 82 tons of cargo, 6+ warm passengers, and 20 low passengers, and the cargo/passages it sells have to pay this. You can imagine liner variants that carry relatively small quantities of cargo, but have up to 20 more staterooms for warm passengers, but the economics for those remains largely the same.

Adding onto this are the life support costs. That high passage doesn’t give the trader 10,000 credits in profit, because 2,000 of it go towards paying the life support fees. If you imagine about half the passages sold are medium, that’s an average of Cr 7,000 for the ship per passage. Add to that Cr 900 per low passage, and estimate Cr 900 per ton (since it’s rare that a trader fills up the whole hold), and that’s the ship’s income. For our example Type A, that’s about Cr 134,000 per jump Enough to pay for everything, with a profit for the owner.

Now let’s look at insystem travel on a nonstarship or small craft. It’s easy to assume this will fall into an entirely different category of service, but it’s not too dissimilar to interstellar travel. Taking a shuttle from Earth to Jupiter, for instance, is a 4 day trip.

So let’s look at the cost of the shuttle – 95 tons, 71 tons of free space, for MCr 33. The crew of 2 is probably pilot and engineer. To this we’ll add a medic and steward, for limited passenger service. Like the Type A, it could carry more passengers for less cargo, but we’ll try to keep it similar to the Type A:

Item	Cost
Crew	6,500/fortnite
Fuel	200/fortnite
Mortgage	68,750/fortnite
Maintenance	1,375/fortnite
Total	76,825

So far the costs are pretty similar to the Type A, though I suspect a shuttle can easily manage 2 paying trips per fortnite. This allows for something like the 4 day Earth-to-Jupiter transit time, plus a few days in dock to handle cargo transfer, maintenance, and the like.

Since the Type A’s passenger pays on average Cr 7,000 + life support for their passage, and the passage takes twice as long as the shuttle’s flight, the shuttle passenger probably pays something closer to Cr 3,500 + life support for their passage. The life support is probably half as expensive, too, since the trip takes half as long, so that’s probably around Cr 4,500 total for passage on the shuttle.

This is not cheap.

One of the common conceits of Traveller is that interstellar travel is expensive. This allows for individual systems that develop their own cultures, without large scale mixing with other nearby cultures. But we can see here that insystem travel is also quite expensive, and probably contributes to a similar feel within a system. Because of the cost of travel, a habitat at Saturn would likely not see a lot of intermixing with a base on the Lunar surface.

There are all sorts of implications that come out of this. Individual habitats in a system will likely develop their own cultures, their own identities. They might see themselves in competition with the other habitats in the system. There might be tension between habitats, amplified by cultural differences and feeding distrust. It makes individual systems feel roomier, with more for players to do.

Digging into External Cargo

March 16, 2022March 16, 2022 jbhemlock

Ken Pick wrote a fantastic article for Freelance Traveller talking about using external mounts for cargo ships in Classic Traveller. I make heavy use of this in my own small ship settings. Ken’s rules for external cargo are fairly simple – special attachment points are added to the ship when it is built at a cost of MCr 0.01/ton of ship, and that’s it. I like the flexibility of this, but it does give large traders carrying external cargo a huge advantage: Bridge sizes. Book 2 specifies a ship dedicate 2% of its tonnage (minimum 20 tons) to the bridge and avionics, at a cost of MCr 0.5 per 100 tons of hull.

This means that a 2000 ton ship designed to carry 3000 tons of external cargo carries a 20 ton bridge at a cost of MCr 10, while a 5000 ton cargo ship carries a 50 ton bridge at a cost of MCr 25. Sure, the 2000 ton ship also spends an extra MCr 20 on external fittings, but it gains 30 tons of space!

I wanted to balance this out a bit, without getting too complicated, so I decided that in addition to Ken’s cost of external fittings, a ship that carries external cargo needs to have a bridge sized appropriately for the total tonnage it will carry. This makes small ships with external attachment points somewhat more expensive than a dedicated cargo ship of the appropriate tonnage, which seems an appropriate trade off for the added flexibility.

A cheap and easy example: The Duchamp class Scout/Courier

This is one of my favorite ships from my current setting. This is a small ship, small universe set in the year 2552. The standard 4-stateroom Type-S didn’t make a huge amount of sense, but a Scout/Courier equipped for a more flexible mission did, and this is what came out of that:

The Duchamp class Scout/Courier is an older TL A design that is still commonly seen. Designed in 2448 for long duration missions with little support, the ship is well suited for communications, survey, and exploration work. The Duchamp and all its variants feature large staterooms and comfortable living spaces, as well as convenient cargo holds with large belly lifts.

Name	Mass	Cost
Streamlined std 100 ton hull		MCr 2.2
External cargo attachment points		MCr 1
J-Drive A (Jump-2)	10	MCr 10
M-Drive A (2-G)	1	MCr 4
P-Plant A	4	MCr 8
Model/1bis Computer	1	MCr 4
Bridge/avionics	20	MCr 1
Fire control x1	1	MCr 0.1
Staterooms x2	8	MCr 1
Air/raft	4	MCr 0.6
Fuel	40
Cargo	6+5

It’s pretty simple – a Type-S with only 2 staterooms, with the rest of the space as cargo. The cargo bay is split into two connected sections, with the idea that the ship can accept a 5 ton multi-mission payload specific for whatever mission it is on (which can include additional living space, if that is needed for the mission).

The two things to note on this is the addition of the external cargo fittings, and the increased cost of the bridge. This allows the ship to carry a 100 ton external module, reducing its performance to Jump-1 and 1 G acceleration.

Salvaging, rolling dice for credits!

February 18, 2022March 16, 2022 jbhemlock

The Traveller universe is a dangerous place. Pirates haunt trade routes; skirmishes and wars leave shattered hulls and bodies; and even in the absence of a living enemy, space itself is an unforgiving foe. What happens to the remnants of these losses? Enter the salvager.

What is salvaging?

Salvaging is a potentially lucrative profession relying heavily on luck, planning, and excellent sensors. Being hired by patrons to salvage a lost ship is a classic hook for a Traveller adventure. However, even in the absence of connections, salvaging can be done. Not that it will be easy.

Legality

This is the trickiest bit. Historically (and currently) on earth, an arrangement must be made with the owner of a ship in order to salvage it, typically under a “no cure, no pay” clause. The salvager contracts to recover the ship and return it to the owner, in exchange for money. Even when things may seem clear cut, these contracts may get caught up in court for years before the salvager gets their money.

Things can be looser in your Traveller universe, however. In my current setting, for instance, there are several areas where wars were fought during the past couple of years. The victors were pretty good about salvaging their own losses, but enemy losses can be found. Legally, those are considered free to the finder, though the salvager is required to bring along a sealed, untamperable recorder with which to determine the identity of the ship.

Finding your wreck

It’s important to understand that space isn’t simply swarming with wrecks waiting to be salvaged. Wrecks will cluster around trouble spots: War zones (or areas where wars were recently fought); areas of heavy piracy; areas with dangerous environments. A prospective salvager needs to keep their finger on the pulse of the subsector, so that they understand where the likely wrecks are. This, of course, is a fantastic hook for adventure: If wrecks destroyed by pirates are in an area, then there should be an increased danger of piracy in that area. If heavy radiation around a gas giant sometimes wreck ships that are trying to refuel, then that danger lies in wait for the salvager, as well.

Once a likely spot is identified, then the salvager needs to start looking. Wrecks are effectively running silently, so ships are at a disadvantage when scanning for them. Standard civilian shipping normally has a 0.5 light second sensor range. When trying to find salvage, they will be unable to detect a wreck out past 0.25 light seconds. This is an area where a scout ship operating on detached duty has an advantage – their superior sensors can still detect a wreck out to 1 light second.

In my settings, a ship with civilian sensors that is actively looking for a wreck in an appropriate area has about a 2% chance per week of finding one. A ship with scout or military sensors has about a 4% chance per week of finding one. In 2d6 terms, a civilian ship needs to roll a perfect 2, while a ship with scout/military sensors needs to roll a 2 or 3.

Both the 1981 and 1977 ship encounter tables in book 2 result in ship encounters on high rolls. They are both somewhat vague about how often the roll should happen, simply stating that it should happen when a ship enters a system. Since most starships will go straight to the starport, or another planet, I rule that a ship that remains in space will make a roll once a week. Since finding a wreck happens with a low roll and a ship encounter happens with a high roll, the same roll can be used for both. Third party tables, likewise, tend to follow the same pattern. For instance, I personally am a huge fan of the encounter tables in Zozer’s SOLO – the tables go a long way towards establishing motives for encountered ships, and they provide a wide spread of ships in various situations. The tables in SOLO all generate encounters with high rolls, so I’m still able to use the same roll for finding salvage as well. Once salvage is found, simply determine the ship type randomly – I use the same ship encounter table, and just roll again until I come up with a ship type.

Condition of the wreck

A wreck is a wreck because it’s not a functional spacecraft. However, that doesn’t mean that everything on the ship is ruined. Once I know what sort of ship the wreck is, I’ll roll for each major component on the ship – jump drive, power plant, computer, turrets, weapons, small craft/vehicles, etc – using the following table:

Roll 2d6	Result
2-5	Destroyed (Any weapons carried in a destroyed turret are considered destroyed)
6-8	Salvageable for spares
9-10	Disabled but repairable
11	Operational
12	Like new

In addition to the condition of the components, I also roll for the condition of the hull. Roll 1d6. 1 = swiss cheese, 6 = wholly intact. This really only comes into play if the players wish to repair the ship and fly it.

Salvaging the wreck

Once I’ve identified a wreck and determined the conditions of its’ components, my players can begin salvaging. Computers, turrets, and the like can all be salvaged in one week, while larger components (drives, etc) require at least a week each. Roll 8+ on 2d6, applying the most skilled salvagers’ engineering skill as a positive DM. If the salvager is alone, apply a -2. Failure allows the salvager to try again in another week, but a natural 2 results in the component being destroyed. Note, too, in the table that if a turret is destroyed, then any weapons carried in the turret are also destroyed.

Normal salvaging of small components (computers, turrets, etc) can be done with the standard toolkits normally carried on a starship. In Book 3 terms, this is the electronic, mechanical, and metalworking toolkits. Salvaging large components (drives) requires a laser cutter to cut into the hull, as well as thruster packs to maneuver the component out of the ship. Once the component has been removed, it can be loaded into the salvager’s cargo bay.

Gear

Laser Cutter: (TL 10) Cr 10,000. A heavy duty laser designed to be powered by a starship power plant. Cased cutter weighs 50 kg.

Thruster Pack: (TL 9) Cr 100,000. A set of thrusters designed to move a 1-10 dton object over short distances in space. The thruster pack cannot move anything quickly. Massier objects may be moved using multiple thruster packs. Powered by integral power packs, recharged from a ship’s powerplant. Cased thruster set weighs 200 kg.

Pay me my money!

Legal salvage can be sold to a shipyard, scrappers, or other resellers of used components. The sale price for components is based on their condition, and the new price of the component. Disabled but repaired parts may be repaired to increase their value, while (at the referees discretion) components may be scrapped for spares to repair similar components. For instance, a beam laser that is salvageable for spares may be used in an attempt to repair a beam laser that is disabled but repairable.

Condition	Sale price
Disabled but repairable	5%
Disabled but repaired	10%
Operational	20%
Like new	25%

Having a disabled component repaired costs 10% of the new price of the component. This makes it economically unviable to have a component repaired to sell – you will spend 10% of the price of the component in order to make 5% of the price of it. However, a skilled engineer can attempt to repair a component at a cost of 2.5% of the price of the component. Roll 8+ with appropriate DMs, the attempt takes a week. If another similar part is salvageable for spares, roll 8+ to find the parts needed. Failures can be re-attempted at an additional cost in parts.

Selling the location of the wreck

If other salvagers are working an area, they may pay a finder’s fee for the location of a wreck. Depending on the condition of the wreck, its location, and the nature of the other salvagers, expect to be offered between 1 and 5% of the new value of the ship as a finder’s fee. A hull with at least one salvageable drive (not necessarily repairable, just salvageable) should always be worth at least 1% of the new value of the ship. A hull with at least one repairable or operational drive is worth more.

Variant Star System Generation Rules for Classic Traveller

January 27, 2022March 16, 2022 jbhemlock

Star system generation in Classic Traveller favors creating shirtsleeve worlds. The majority of systems that the rules generate are the sort of places you can walk around on. Sometimes you need a filter mask, sometimes you need specialized clothing, but in general they are very livable places. This is all very well understood.

I want to talk about some variant rules that generate systems that don’t fall into this pattern. These are rules that I developed for my own games, to fit the sort of maps that I wanted to play around in. In general, I don’t like to see a lot of shirtsleeve worlds. I like to see hostile systems, and I like games that largely occur in space and in space habitats. I’ve been using the Book 6 expanded system generation rules for decades, so all of these rules are based on that. If you don’t have a copy of Book 6, these rules also exist in similar forms in MegaTraveller, T5, etc.

Expanded System Generation

Book 6 provides a set of rules for generating a complete star system, filled with planets. There are a couple of methods of doing this: the Continuation Method, and the Expanded Method. The Continuation Method starts with a pregenerated main world, and generates the rest of the system around it. The benefit of this is it lets you use an existing subsector. The Expanded Method, on the other hand, generates the star system from scratch. There are some statistical differences between the two, the big one being that the expanded rules are slightly less likely to give you a shirtsleeve world. They still do favor generating shirtsleeve worlds, and they fit very nicely into the feel of a standard Traveller map.

Stellar Class Tweaks

Book 6 generates stellar classes for stars, so you might have a class B star that’s bright and blue in a system, or a planet might huddle close to a dim class M red star. However, the same tables are used for both the continuation and the expanded method, and so they are biased towards sunlike stars set up for shirtsleeve worlds. I’ve come up with a variant table that favors the class M stars that are far more common in the galaxy.

Dice	Result
2	A
3	M
4	M
5	M
6	M
7	M
8	K
9	G
10	G
11	F
12	F

Note that this table will never generate class O or B stars. Those are rare, and should be hand-placed.

Atmosphere Tweaks

The expanded system generation rules apply a small negative DM to the atmosphere type of words outside of the habitable zone of their star. However, they still generate a lot of breathable atmospheres all over the system. One of the things I wanted to address is this. Since I was effectively redefining the atmosphere rules, I wanted to make sure I understood what the various atmospheres meant to me.

Vaccuum and trace atmospheres: These are the familiar class 0 and 1 atmospheres. They are, effectively, what they say on the tin. In terms of survival, both effectively require you to wear a vacc suit.

Shirtsleeve worlds: Atmosphere class 2-9. Some of these require filtermasks, some require compressors, some require both. Yet, breathing apparatus aside, you can walk around in ordinary clothes. There is an implication that the temperature is sufficient to allow someone to survive in ordinary clothes, though “ordinary clothes” might include things like stillsuits, cold weather clothing sufficient for Antarctica, etc.

Exotic: Class A. Exotic atmospheres are unbreathable, but otherwise these are still shirtsleeve worlds. You might have to wear heavy insulative clothes to deal with temperatures, but otherwise you can get by with what are effectively scuba tanks.

Corrosive: Atmosphere class B. Corrosive atmospheres require the use of protective suits or vacc suits. Protective suits are closed environment suits with their own breathing systems, and are basically vacc suits for use in atmospheres. I used to believe corrosive atmospheres were literally corrosive – acid droplets in the air, that sort of thing. In retrospect, looking at them from simply a game-rules point of view, they are merely environments which are so hostile that you need a protective suit. The moon titan, for instance, has an atmosphere that’s largely nitrogen, which is not corrosive at all. I would call it a class B atmosphere, though, because it’s so cold that you couldn’t survive on the surface without a protective suit.

Insidious: Atmosphere class C. Insidious atmospheres are akin to corrosive ones, but they will defeat any personal protective measures in 2-12 hours. The surface of Venus, for example, is hot enough to destroy every lander that made it there within a matter of hours. No matter how good your protective suit, eventually that heat will seep through it and bake you. I would call that a classic insidious atmosphere. But imagine a world with a thick atmosphere of hydrogen – a failed gas giant, perhaps. Hydrogen gets everywhere. It will seep through any material by osmosis. An explorer in a space suit will eventually start seeing hydrogen seeping into their suit, forming a flammable mixture with their breathing air. Because of that, I would categorize that atmosphere as insidious, as well.

All of that, along with my desire to avoid shirtsleeve worlds outside of the habitable zone, led me to develop these tables for the inner and outer atmosphere:

Inner planet atmosphere

Dice	Result
0	0
1	1
2	1
3	A
4	B
5	B
6	B
7	B
8	B
9	B
10	B
11	B
12	C

Outer planet atmosphere

Dice	Result
0	0
1	0
2	1
3	1
4	1
5	A
6	A
7	B
8	B
9	B
10	C
11	B
12	C

Brown Dwarfs

This is the easiest variant rule to make. The Book 6 expanded system generation rules creates star systems with stars of class O-M – stars that shine by fusion. Adding brown dwarfs allows you to add additional star systems, typically without shirtsleeve worlds. To add brown dwarfs, just decide on a ratio of brown dwarfs to regular stars – anything from 1 brown dwarf per 6 stars all the way to 1:1. This makes it easy to determine which systems have fusing stars and which have brown dwarfs. For the most part, brown dwarfs don’t have a habitable zone, so all planets generated should follow the “outer planets” rules.

Brown Dwarf Stellar Class

Dice	Result
2	Y
3	Y
4	Y
5	Y
6	L
7	L
8	T
9	T
10	T
11	Y
12	Y

Reducing Atmospheres

My current Traveller game sets up a universe that draws a lot from C.J. Cherryh’s Alliance-Union universe, and one of the big things about that setting is that planets with breathable atmospheres are rare. This variant simply says “roll a die for any breathable atmosphere to see if it’s actually an exotic atmosphere.” With my current setting, I made 90% of the breathable worlds into class A atmospheres.

Putting it all together

And lastly, here is a subsector that uses all of these rules. None of the planets have been populated, but you can see how there is only a single world with a breathable atmosphere in the whole subsector, and that atmosphere still requires a filtermask. The rest of the planets either have exotic or no atmosphere, and no shirtsleeve world exists around any of the brown dwarfs.

#Hex Name             UWP       Remarks          {Ix}  (Ex)    [Cx]   N     B  Z PBG W  A  Stellar
#--- ---------------- --------- ---------------- ----- ------- ------ ----- -- - --- -- -- -------
0103 all-0103         X000000-0 As Ba Va                                         000 6     FVI VI 
0104 all-0104         X000000-0 As Ba Va                                         000 3     MVI VI 
0105 all-0105         X5A7000-0 Ba                                               004 9     GV V   
0108 all-0108         X4AA000-0 Ba Wa                                            003 6     KVI VI 
0203 all-0203         X000000-0 As Ba Va                                         004 11    GV V   
0204 all-0204         X000000-0 As Ba Va                                         003 7     MV V   
0205 all-0205         X000000-0 As Ba Va                                         011 8     LDD    
0301 all-0301         X000000-0 As Ba Va                                         020 6     MV V   
0303 all-0303         X5A3000-0 Ba Po                                            003 10    FV V   
0306 all-0306         X5A0000-0 Ba De Po                                         004 9     GV V   
0308 all-0308         X000000-0 As Ba Va                                         012 9     GDD    
0309 all-0309         X5A7000-0 Ba                                               014 10    GIV IV 
0310 all-0310         X000000-0 As Ba Va                                         003 9     YDD    
0401 all-0401         X000000-0 As Ba Va                                         000 1     MV V   
0402 all-0402         X000000-0 As Ba Va                                         002 9     GV V   
0403 all-0403         X000000-0 As Ba Va                                         000 1     MDD    
0409 all-0409         X000000-0 As Ba Va                                         000 1     MV V   
0502 all-0502         X000000-0 As Ba Va                                         002 8     MV V   
0504 all-0504         X000000-0 As Ba Va                                         003 9     YDD    
0506 all-0506         X6A7000-0 Ba                                               004 10    MV V   
0508 all-0508         X5A9000-0 Ba                                               003 10    MII II 
0510 all-0510         X6A3000-0 Ba                                               003 8     MV V   
0601 all-0601         X000000-0 As Ba Va                                         000 4     YDD    
0609 all-0609         X000000-0 As Ba Va                                         002 6     GV V   
0610 all-0610         X553000-0 Ba Po                                            005 10    MV V   
0703 all-0703         X000000-0 As Ba Va                                         004 10    AV V   
0704 all-0704         X000000-0 As Ba Va                                         000 1     KVI VI 
0802 all-0802         X000000-0 As Ba Va                                         001 3     MV V   
0805 all-0805         X000000-0 As Ba Va                                         013 11    TDD    
0807 all-0807         X000000-0 As Ba Va                                         000 1     MDD    
0808 all-0808         X000000-0 As Ba Va                                         021 7     MV V

Trade Clans

January 22, 2022March 16, 2022 jbhemlock

I play Traveller a little differently. Marc Miller was heavily inspired by Dumarest and the fiction of Jack Vance. And while I may have “borrowed” the Dirdir, the Pnume, and the Star Kings for past campaigns, most of my science fiction inspiration comes from writers like C.J. Cherryh, Larry Niven, and Bruce Sterling. I tend to favor less hospitable universes and smaller settings.

Which is to say, I really wanted to come up with a good reason to steal the trade clans from C.J. Cherryh’s Alliance-Union setting. It turned out to be easier than I thought.

Starship Economics 101, Traveller-style

Book 2 starship economics is extremely straightforward: If you want a ship, you mortgage your soul with a bank, and end up paying 220% of the price of the ship over 40 years of payments. During that time, you are lucky if you can barely scrape by. Ken Pick wrote a series of articles for Freelance Traveller talking about the economics of scraping by, including the calculation of a ship’s Commercial Efficiency Rating (C.E.R.). The C.E.R. of a ship is simply the Net Tonnage (the cargo/passenger carrying tonnage on the ship) multiplied by the jump range and divided by the cost of the ship in MCr. This is basically a ratio between how much money the ship can bring in, and how much money the ship costs. The higher the C.E.R., the better off the ship owner is. A C.E.R. above 5 is profitable even simply selling transportation at Cr 1000 a ton. A C.E.R. between 3 and 5 can be profitable if they add in speculative trade. A C.E.R. below 3 is pretty much unprofitable, and must be subsidized.

The Type A Free Trader, for instance, has a C.E.R. of just above 3. It’s profitable enough to make someone imagine they could make an honest living with it, but not profitable enough that they can make a living easily with it. Which is exactly what you want for a game of desperate traders.

But why would anyone in their right mind go into that much debt if it was so hard to make a living? I’m not talking about adventurers. I mean, why would Joe Average Trader do so? Especially if Joe is able to save up the 20% down payment on the ship? The down payment on a Free Trader is about seven and a half million credits! That’s enough to live like a king for the rest of your life! Sure, once you pay the ship off, it becomes a big profit factory… But you’ll be eating cup noodles for 40 years while you wait for that to happen!

Which begs the question, after that ship is paid off, how long will it remain operational? Classic Traveller doesn’t really say. Book 1 mentions that, with really good rolls, a Merchant player could end up with a 40 year old Free Trader free and clear. It mentions that the downside is that the ship is 40 years old, but it doesn’t really say anything about that being particularly bad…

How long do starships last?

Commercial aircraft get used heavily, and tend to have a service life of about 20-25 years. It’s not so much the time, it’s the cycles of pressurization. Each time a commercial aircraft is sealed up, pressurized, and flown, it stresses the fuselage and wings. And commercial aircraft get used heavily, so they could see multiple pressurization cycles a day, on short hops. Long haul aircraft, ironicaly, tend to last longer, because they go through fewer pressurization cycles over time. Everything else – engines, avionics, etc – can be maintained pretty much as long as there are parts available.

Book 2 starships, in my mind, are similar to commercial aircraft. If you exclude the High Guard rules, you see ships that carry no armor to speak of, which are made to get a job done. Book 2 starships, however, go through far fewer pressurization cycles than commercial aircraft. True, the pressure difference is more extreme, but it’s not that much more extreme. You see adventures written for Classic Traveller with starships that are quite old – some approaching 100 years old. My suspicion is that, so long as they are maintained properly, a Book 2 starship can easily last that long. There will probably be more expensive maintenance at some point – drive replacement, perhaps – but I think the expectation is that a properly maintained starship should still have plenty of life after the 40 year mortgage is paid off.

Enter the Trade Clan

In C.J. Cherryh’s Alliance-Union setting, merchant ships are often owned by families and trade combines. A combine is simply a corporation, like Oberlindes Lines, so there’s nothing new there. But families… Trade runs in this setting can take a long time. Ships may fly routes that take them from station to station to station, and those routes may be months (or years) long. Ship people, in that setting, tend to be tightly knit, because they’re the only people that they see consistently. The people they meet at stations (or planets) are good for a drink or a fling, but you might not see them again for a year, once your ship casts off.

It sounds a lot like Traveller. It sounds like something that could develop naturally in Traveller.

Say you buy a Free Trader. You mortgage your soul. You live on cup noodles and you scrape by, and you go from world to world. Say you meet someone, and you fall in love, and they come along with you on this spacer’s life. Years pass. Kids come. They grow up, learn to help with the ship… Some of them might leave, but some might stay. And then, forty years later, you pay your last mortgage payment. The ship belongs to you. To your family. Now you’re making profit! And your family is growing. Your kids fall in love with people, and some of those people come along. The ship is getting a little crowded. But, since you know how to make money on the ship, you’re not worried. At some point you’ll retire, hand the ship down to your kids. It makes sense to me – my mother’s side of the family are commercial fisherman, and there’s a family boat. It’s been handed down through generations, and it’s typically crewed by people who are all related to one another.

You see, you’ve learned how to make 200% of the price of that Free Trader in 40 years. Which means you could make the price of another Free Trader in another 20. You’ve taught your kids to do the same. So in 20 years, you buy a second Free Trader, because the family needs it. Or maybe you make enough money to buy a larger ship, free and clear. At this point, after all, you’re effectively making twice as much money as a mortgaged captain, because you own your ship free and clear.

This is how it is in my current Traveller universe. Most trade ships are owned by families and combines. The families, in homage to Cherryh, are called Trade Clans. The successful ones become names, well known. The influential ones have sway with governments. With other Trade Clans.

And the captains with mortgage payments? They’re still the desperate ones. Desperate because they’re barely scraping by. Desperate because of that mortgage payment. Desperate because they don’t have a name, they don’t have a family, they don’t have a clan.

Extending the Classic Traveller Drive Potential chart

January 20, 2022March 16, 2022 jbhemlock

Ken Pick wrote a fantastic article for Freelance Traveller talking about using external mounts for cargo ships in Classic Traveller. I make heavy use of this in my own small ship settings. It’s fairly easy to do with large ships – loading up the 2000 ton Type TJ with a few thousand tons of external pods – but it gets more difficult with smaller ships. A 400 ton ship, for instance, that can carry 400 tons in pods is easy to make, but a 400 ton ship that can carry 800 tons in pods runs afoul of the Drive Potential Table, because it doesn’t have a line for a 1200 ton ship.

Rather than using Book 5 High Guard rules for ship construction, I wanted to stick with simple Book 2 ship construction, so I extended the Drive Potential Table, adding entries for 300 ton, 1200 ton, 1600 ton, and 6000 ton ships. For the 300 ton line, I divided the 600 ton line by 2. For the others, I multiplied the performance of the “half” entries by two, so 1200 ton performance is based on the 600 ton line, etc. The 6000 ton entry doesn’t include a build time, because it’s intended more to provide a line for a Type TJ with 4000 tons of external pods.

There are some oddities in the table, especially when you get into the heavier hulls, and I didn’t try to change those. They’re part of the character of the original game, and I wanted to stick close to that.

Hull (Tons)	A	B	C	D	E	F	G	H	J	K	L	M	N	P	Q	R	S	T	U	V	W	X	Y	Z	Build Time
100	2	4	6	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	10
200	1	2	3	4	5	6	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	12
300	-	1	2	2	3	4	4	5	6	6	6	-	-	-	-	-	-	-	-	-	-	-	-	-	14
400	-	1	1	2	2	3	3	4	4	5	5	6	6	-	-	-	-	-	-	-	-	-	-	-	16
600	-	-	1	1	1	2	2	2	3	3	3	4	4	4	5	5	5	6	6	6	-	-	-	-	24
800	-	-	-	1	1	1	1	2	2	2	2	3	3	3	3	4	4	4	4	5	5	6	6	6	28
1000	-	-	-	-	1	1	1	1	1	2	2	2	2	2	3	3	3	3	3	4	5	6	6	6	30
1200	-	-	-	-	-	1	1	1	1	1	1	2	2	2	2	2	2	3	3	3	4	4	4	6	31
1600	-	-	-	-	-	-	-	1	1	1	1	1	1	1	1	2	2	2	2	2	2	3	4	6	31
2000	-	-	-	-	-	-	-	-	1	1	1	1	1	1	1	1	1	1	1	2	2	3	4	6	32
3000	-	-	-	-	-	-	-	-	-	-	-	-	-	-	1	1	1	1	1	1	1	2	2	4	34
4000	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	1	1	1	2	3	35
5000	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	1	1	1	2	36
6000	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	1	2	N/A

Vector-based starship combat in Classic Traveller

January 19, 2022March 16, 2022 jbhemlock

These notes came out of my attempts to make vector-based starship combat in Classic Traveller easier to grasp. I’ve played the game off and on since I first bought it in 1981, but starship combat as-written has never figured heavily, and when I have played it, I mostly just stuck to lasers (since book 2 doesn’t really explain how to play with missiles).

I returned to Classic Traveller during the pandemic, and (inspired by the “Traveller out of the Box” blog) decided to run a game using just books 1-3, with the rules as written. That series of blog posts also turned me on to the missile rules in Special Supplement 3, at which point everything just clicked. For the purpose of this blog entry, I’m going to be dealing exclusively with Classic Traveller books 1-3 (in their 1981 form), with the Special Supplement 3 missile rules.

One of the problems I’ve always had with book 2 starship combat is the use of different units throughout it. There are light seconds, kilometers, scale mms, and different things are given in different units. Because of all the craziness with different units, I went through and converted things to the same units:

• 1 light second ~= 300,000 km ~= 3000mm

• 0.5 light second ~= 150,000 km ~= 1500mm

• 2 light second ~= 600,000 km ~= 6000mm

• 100 km = 1 mm

• 100D for a size 8 world = 1,280,000 km, ~4 ls

Distances

Distance (mm)	Distance (km)	Distance (ls)	Notes
100	10,000	0.032	1G acceleration for 1 turn changes velocity by this
1000	100,000	0.32	Maximum powered range for 5G2 missile
1500	150,000	0.5	Normal sensor detection range
2500	250,000	0.833	Maximum laser range with full accuracy
3000	300,000	1	1 light second
4800	480,000	1.6	Maximum powered range of 6G4 missile
5000	500,000	1.66	Maximum laser range with -2 DM
6000	600,000	2	Military/scout detection range
9000	900,000	3	Maximum tracking range
9000	900,000	3	Maximum powered range for 5G6 missile
10,800	1,080,000	3.6	Maximum powered range of 6G6 missile
19,200	1,920,000	3.2	Maximum powered range of 6G8 missile
25,000	2,500,000	4.16	Maximum powered range of 5G10 missile

Having everything in one table starts to make things clear. Book 2 space combat takes place at enormous ranges, and the weapons used retain their accuracy to a huge distance. Take a look, especially, at the point at which lasers first get a negative DM: 0.833 light seconds. A pirate who is clever then can achieve the starship version of surprise and hit their target from a point farther out than their target can even see them. The rules don’t say what would happen at this point, but in my game I rule that this counts as detection, so the target can fire back.

Now lets look at missile flight time. Missiles are enormously effective, with the typical missile accelerating at 5-G for six 1000 second turns. Special Supplement 3 gives rules for creating all sorts of different missiles, and so I created a bunch of different ones (ranging from a 5G 2 turn missile with a huge warhead to a 5G 10 turn missile that isn’t great against military targets but can fly for a long time).

Missile travel time (turns)

Distance (km)	5G2	6G3	6G4	5G6	6G6	6G8	5G10	Notes
100,000	2	2	2	2	2	2	2	Max powered range 5G2 missile
150,000	-	2	2	2	2	2	2	Normal sensor detection range
250,000	-	3	3	3	3	3	3	Maximum laser range with full accuracy
300,000	-	3	3	3	3	3	3	1 light second
500,000	-	3	3	4	3	3	4	Maximum laser range with -2 DM
540,000		3	3	4	3	3	4	Max powered range 6G3 missile
600,000	-	-	4	4	4	4	4	Military/scout detection range (2 ls)
900,000	-	-	4	5	4	4	5	Maximum tracking range (3 ls)
960,000	-		4	5	4	4	5	Max powered range 6G4 missile
1,800,000	-	-	-	6	6	6	6	Max powered range 5G6 missile
2,160,000	-	-	-	-	6	6	7	Max powered range 6G6 missile
3,840,000	-	-	-	-	-	8	9	Max powered range 6G8 missile
5,000,000	-	-	-	-	-	-	10	Max powered range 5G10 missile

One thing that surprised me is how long it takes for missiles to travel to their target at long ranges. If a poor, beleaguered Free Trader is attacked by a pirate from 0.8 light seconds away, it would take 3 turns for the missiles it launches to hit the pirate.

What I love about this is that it makes player choices more clear: Do you mount missiles, which can do heavy damage to a target while risking being shot down, or do you mount lasers, which do less damage, but do damage immediately?

Adding to this is the fact that most of the missiles in Traveller are self-guided, so they will track their target even if the firing ship is destroyed. This means that even if the pirate takes out that Free Trader, the missiles the Free Trader launches would still be coming. Pirates need to be careful who they choose as their prey…

Computers

Civilian ships typically don’t spend on their computers. Ditto software. Auto-evade is cheap and small and easy, and gives a nice -2 to being hit. Typically, target and launch are the limits to what is available, offensively. Auto-evade and (occasionally) anti-missile defensively.

Military ships tend to have large computers, and the cost of software systems is small compared to the rest of the ship, so they spend. Maneuver/evade-4, 5, or 6 are common, along with ECM, anti-missile, and return-fire on the defensive. Offensively, the predict software is common, ditto gunner, multi-target, and select.

Paramilitary ships tend to fall one way or the other. Things like a scout courier is probably armed and equipped like a civilian ship, while a Type T patrol cruiser is set up like a military ship.

Fighters

Fighters come with a model/1 computer, which gives them better options than other armed small craft, but it still doesn’t give them the ability to run a ton of software, so they end up looking a lot like (very fragile) civilian ships. This means that fighters are easy targets in military combat, but they can deploy defensively and cut power, making themselves invisible to military ships past 1 light second.

As defensive craft, I could see large numbers of fighters, each armed with triple missile racks, forming a screen around valuable targets. As offensive craft, they would probably simply rely on numbers to overwhelm their targets, launching their full complement of missiles as fast as they can and then breaking off. They end up being less “space fighters”, and more of attack craft. 10 fighters, each carrying triple missile launchers, costs less than MCr 200, and can easily overwhelm a 400 ton Type T or SDB.

Tactics

Finally, the good stuff! On player scale, starship combat is extremely chancy. While something like a Type T has the computer to support a lot of combat software and the toughness to take a few hits to the engines, the more typical Type S or Type A doesn’t. Those ships will not have an easy time hitting their target, while a lucky hit can easily leave them completely dead in the water. This makes combat feel like a desperate gamble for them, which really suits the small-ship Dumarest-style feel of the game.

If you are playing a pirate, you will want to be careful to choose your targets. Take advantage of your sensor range to attack while your target can’t see you. Make use of lasers to try to disable your target in the first turn, and then demand their surrender. If I were playing a pirate, I would probably eschew missile launchers, since there’s too much of a chance of destroying the booty I want to capture.

On the other hand, players in ships like the Type-S or Type-A should probably select their weapons more for their deterrence. A single hit on a pirate ship could cost them millions of credits, while a turret full of missile launchers could potentially destroy them. Remember: You don’t have to be able to defeat a pirate, you merely have to be a harder target than the other ships.