Does removing modules allow longer jumps

[Sageryne]

Hi,

I have been working on a large 10,000 dTon modular freighter.

The ship has a manoeuvre-1 drive (100 dTons), jump-2 drive (505 dTons), power plant (300 dTon), fuel (2000+30 dTon), bridge (60 dTons), crew and passenger areas, plus other misc items total 4,000 dTons. My design includes six 1000-dTon cargo modules, resulting in a ship totally 10,000 tons.

Jump-2 requires 5% of 10,000 dTons + 5 dTons = 505 dTons. It also requires 20% of 10,000 dTons of fuel = 2,000 dTons.

My question is, if the ship does not have the six 1000-dTon modules attached, does it now becomes a 4,000 dTon ship?

Jump-5 requires 12.5% of 4,000 dTons + 5 dTons which ALSO equals 505 dTons. It would require 50% of 4,000 dTons of fuel which ALSO equals 2,000 dTons.

Does that mean the 4,000 dTon "core" ship can now do jump-5?

I am curious what that would do to the economics? Let's say you had a resource world Jump-4 away from an industrial world. You could jump there "empty" without the six modules attached in a single jump, and then return "full" (with six 1000-dTon cargo modules) in two jumps.

Am I calculating this correctly?

Thanks

Edited to clarify my question.

 

[MonsterX]

Yes, you can detach modules to do longer jumps. And faster maneuver. Whether your math is right, I didn't check but the principle is ok.

 

[Starglim]

I am curious what that would do to the economics? Let's say you had a resource world Jump-4 away from an industrial world. You could jump there "empty" in a single jump, and then return "full" (with six 1000-dTon cargo modules) in two jumps.

If the resource world had six cargo modules of the correct design ready to fit, yes. I don't think attached but empty cargo modules would reduce the effective size.

 

[ottarrus]

Provided you have a drive and fuel tankage to reach the extra parsecs, yes you can.
But a J-drive that's only rated at J-2 for a megafreighter will still only go J-2 no matter how many modules or cargo cans you pull off. Where you save by Jumping with lighter tonnage is in fuel costs. Strip enough modules off and your fuel tankage will allow two J-2 without refueling.

 

[Sageryne]

If the resource world had six cargo modules of the correct design ready to fit, yes. I don't think attached but empty cargo modules would reduce the effective size.

Yes, that was my thought, the resource world would built and fill the cargo modules.

I agree, empty modules would still count towards the ship's volume. If you jumped with the module's attached (but empty), they would still count.

Provided you have a drive and fuel tankage to reach the extra parsecs, yes you can.
But a J-drive that's only rated at J-2 for a megafreighter will still only go J-2 no matter how many modules or cargo cans you pull off. Where you save by Jumping with lighter tonnage is in fuel costs. Strip enough modules off and your fuel tankage will allow two J-2 without refueling.

That is the crux of my question. Is a drive only able to jump the maximum distance it was designed for, or does the volume matter.

In the ship design rules, it talks about buying a certain tonnage of jump drives rather than a specific range of drive. You can always jump less right?

If the ship had a Jump-5 drive installed, it could jump-5 when it was 4,000 tons and jump-2 when it was 10,000 tons?

 

[AnotherDilbert]

My question is, if the ship does not have the six 1000-dTon modules attached, does it now becomes a 4,000 dTon ship?

MgT "modules" are internal, the hull stays the same size.
See Cutter:



If you use external hulls carried in docking clamps or drop tanks, the ship changes size with or without them and hence drive performance and fuel consumption changes.
See Jump Shuttle, HG p177.

 

[Sageryne]

Hi AnotherDilbert,

Ah-ha, that was the information I was missing. Modules are internal, thus, regardless of whether they are present or not, the overall volume of the ship remains the same.

Excellent. Thank you.

OK, now that that is sorted out, it raises a new question:

Does a "ship" attached with docking clamps need to be anything more than a box?

Going back to my example vessel, if I have a 4000 dTon ship with six Type IV docking clamps (rated at 301 - 2000 tons), can I attach a "ship" (i.e. a huge 1000 dTon box) with a hull, but no drives or power plant, just a plain empty box?

For example:

Standard, boxy hull, 1000 dTons, cost 50 MCr. Completely empty, no other systems, just 1000 dTons of cargo space.

Based on description from page 57 of High Guard:

4000 dTon ship with six Type iV docking clamps could attach six 1000 dTon "empty box ships" to the outside of the ship.

So, if the original ship was a jump-5 vessel at 4000 dTons, I would have to recalculate its jump capability based on its new size of 10,000 dTons, thus reducing it from Jump-5 to Jump-2 as per the calculations shown above.

 

[Vormaerin]

It is more explicit in other editions of Traveller that modules are internal and/or part of the hull. IIRC, in some editions, the ship can have issues operating without modules in place.

As far as external docking clamps go, you can clamp anything that has a spaceworthy exterior and can be held by the clamp. It doesn't need to be a "ship" per se.

 

[Sageryne]

Looking back on it, I guess I just re-invented the cargo version of the battle rider.

 

[Anstett]

See also this long thread on cargo ship possibilities.

Efficient space only freighter design

I was thinking about how to make a space-only freighter ad efficient as possible to load and unload. But also taking into account that to fully use all available cargo space you have to store your freight basically container to container. And if you do that, how do you that with limited dock...

forum.mongoosepublishing.com

 

[Condottiere]

1. Depends on the definition of module.

2. If it's external to the primary,then yes.

3. If it's internal, then by default, no.

4. Optionally, you leave the module cargo doors open, which theoretically exposes the empty cargo space, and in accordance to High Guard design rules no longer counts as internal spacecraft volume.

 

[Sageryne]

Hi Anstett,

Yes, thank you. That is a great thread. It is one of the things that got me thinking about this idea.

I appreciate all the ideas people have shared.

My idea has "evolved."

The 4000 dTon Cargo-Tender ship contains manoeuvre drive, jump drive, power plant, main bridge, computers, sensors, limit weapons (20 triple beam laser turrets grouped into batteries of five), four 20 dTon launches, six Type IV docking clamps, 145 staterooms, 60 low berths, and a generous common area. Without any Cargo-Riders attached, it can do manoeuvre-2.5 and jump-5.

It can carry six Cargo-Riders. I have designed ones to carry containers, bulk goods (ore, grain, etc) and fuel. The fuel tanker comes with fuel scoops and fuel purifiers that purify the fuel during the jump.

The Cargo-Riders are now sub-light ships with the absolute minimum equipment, including manoeuvre-1, power plant, bridge, computer, basic sensors, and staterooms for one pilot and one engineer. I am assuming they will spend most of the jump in the Cargo-Tender.

The concept is that the Cargo-Tender can park in orbit. The Cargo-Rider can fly down to the surface under their own power. The pilot and engineer then transfer to another Cargo-Rider that is already full, fly it back up to orbit, dock and the ship is ready to go.

The Cargo-Rider can then be loaded or unloaded at the starport's leisure, and be ready to go when the next Cargo-Tender arrives. If the starport is at least Class-B, they can build the Cargo-Riders. Then, the Cargo-Tenders can come without any Cargo-Riders attached (thus allowing them to go Jump-5), load up and return at the slower pace.

 

[Galadrion]

Agreed that you can build this concept as a tender/rider setup, designing the tender with docking clamps and the riders as normal ships (star- or space-). As for improving the drive performance by detaching the riders: yes, within limits. First, your computer (and software) has to be able to handle the task. Second, the drive has to be designed from the outset to meet the required performance - primarily, this means that the tech level has to be high enough to allow that level of drive. (It doesn't matter how many modules you strip off of the ship, a TL-12 ship is not going to be able to make Jump-5... except via misjump; not a recommended strategy.)

One important consideration, though: streamlining can become an issue. The riders can be streamlined without any real restriction, but if the riders were designed to be carried externally (that is, in docking clamps), the combination is not streamlined. For a streamlined combination, you need an enclosed docking space - docking bay, hanger, whatever - and in that case, detaching the rider does not change the tender's tonnage.

Edited to add:
And I see that you've already taken these points into consideration. That's what I get for posting before looking at the attachments...

 

[AnotherDilbert]

Does a "ship" attached with docking clamps need to be anything more than a box?

No, not unless you want air and gravity in there.

If you want basic life-support, it costs you the basic 20 Power/100 Dt, or at least half of that as a bare minimum. The carrying ship can provide the power, perhaps with a small battery in the box to cover transitions?

 

[AnotherDilbert]

It can carry six Cargo-Riders. I have designed ones to carry containers, bulk goods (ore, grain, etc) and fuel. The fuel tanker comes with fuel scoops and fuel purifiers that purify the fuel during the jump.

Stretching the rules a bit you can automate them with Virtual Crew, Expert:Engineer, and repair drones, and delete the bridge and staterooms.

Virtual Crew can fly the Rider itself, or it can be remote controlled.

 

[AnotherDilbert]

The fuel tanker comes with fuel scoops and fuel purifiers that purify the fuel during the jump.

You could make the "internal" jump fuel tank into a breakaway section, that can detach itself and go refuel. You save having both internal fuel and a tanker. Costs quite a bit though...

 

[Galadrion]

You could make the "internal" jump fuel tank into a breakaway section, that can detach itself and go refuel. You save having both internal fuel and a tanker. Costs quite a bit though...

And you would almost certainly want a little bit of a buffer tank on the main section, enough to allow that section to run while the breakaway tank is elsewhere. Probably two or three days' worth of fuel tankage would be enough, unless you're planning for the fuel run to go to or from the outer system. Maybe a week, just for redundancy.

 

[AnotherDilbert]

And you would almost certainly want a little bit of a buffer tank on the main section, enough to allow that section to run while the breakaway tank is elsewhere. Probably two or three days' worth of fuel tankage would be enough, unless you're planning for the fuel run to go to or from the outer system. Maybe a week, just for redundancy.

I would generally split both the power plant and power plant fuel between the breakaway sections, so that both have the regular 30 days fuel supply.

HG'22, p12:
Breakaway Hulls: A ship can be designed so it can operate as two or more independent vessels, breaking or splitting away from one another. Each section must have an appropriate bridge and power plant to operate it.

 

[phavoc]

Hi Anstett,

Yes, thank you. That is a great thread. It is one of the things that got me thinking about this idea.

I appreciate all the ideas people have shared.

My idea has "evolved."

The 4000 dTon Cargo-Tender ship contains manoeuvre drive, jump drive, power plant, main bridge, computers, sensors, limit weapons (20 triple beam laser turrets grouped into batteries of five), four 20 dTon launches, six Type IV docking clamps, 145 staterooms, 60 low berths, and a generous common area. Without any Cargo-Riders attached, it can do manoeuvre-2.5 and jump-5.

It can carry six Cargo-Riders. I have designed ones to carry containers, bulk goods (ore, grain, etc) and fuel. The fuel tanker comes with fuel scoops and fuel purifiers that purify the fuel during the jump.

The Cargo-Riders are now sub-light ships with the absolute minimum equipment, including manoeuvre-1, power plant, bridge, computer, basic sensors, and staterooms for one pilot and one engineer. I am assuming they will spend most of the jump in the Cargo-Tender.

The concept is that the Cargo-Tender can park in orbit. The Cargo-Rider can fly down to the surface under their own power. The pilot and engineer then transfer to another Cargo-Rider that is already full, fly it back up to orbit, dock and the ship is ready to go.

The Cargo-Rider can then be loaded or unloaded at the starport's leisure, and be ready to go when the next Cargo-Tender arrives. If the starport is at least Class-B, they can build the Cargo-Riders. Then, the Cargo-Tenders can come without any Cargo-Riders attached (thus allowing them to go Jump-5), load up and return at the slower pace.

From a pure cost perspective, making the cargo riders as stand-alone ships interjects a much higher cost model into the equation. In the late 1960s the Lighter Aboard Ship (LASH) was implemented. It was basically a barge that you could take upriver to smaller ports but that it could be loaded on an ocean-going ship to take anywhere there was a seaport in the world. These were, essentially, barge-sized containers that, in theory at least, would make it cheaper to get your cargo closer to it's final destination.

They looked great on paper. But in operation they had some economic flaws. The main thing being that there were many costs and issues associated with moving/maintaining these barges - and containers quickly eclipsed them with lower costs and flexibility. Something to keep in mind is that bigger (generally) means lowering your costs-per-ton. So bigger (tankers, bulk carriers, some container runs) is cheaper and more efficient. But for higher cost or specialized goods you simply don't have enough volume to justify costs. Think it's cheaper to move coal, oil, iron ore in big barges/ships. But you'd never fill up ships of that size with iPads or watches.

So your cargo riders are going to have all the costs associated with a cockpit, sensors and engines - but be possibly sitting around unused. You still have to pay for all that while it's waiting around - and cost will have to be accounted for in higher prices for cargos moved in them. If you just need to drop off a pod/cargo while it sits for periods of time you'd be better off having a basic cargo module and then a cargo lighter (or some pod-type vehicle that's essentially a cockpit and engines) to move the pod and then go back to the ship for the next one.

To be fair, there ARE some efforts to do something similar. You see it in driverless trucks that some are working on. And there is an effort to do it with railcars (one idea is to have mini-trains of these cars that take smaller sets of cargos more frequently to their destination than the 8'000 to 15'000 foot train you see in the US today - but none of these are available and none have gone beyond concept to prove if they are actually cost-effective or not). You can do a cost model by estimating what you think is a fair dwell time for your cargo-riders to wait around and project that over a 12month period for your maintenance costs vs. what it would cost for basic cargo. And keeping the same revenue per ton for each to make a fair comparison.

 

[Condottiere]

Prior to the, possibly still current, pandemic, the global economy worked on off shoring and just in time logistics.

I wouldn't depend on just in time logistics for interstellar trade in Traveller.