Consolidation Thread: Xboats in a System

[robject]

GURPS Traveller, core rules, library data.

The original quote has to be from 1982 or earlier, because that's the date it appears in Library Data: N-Z.

 

[Spinward Flow]

Pretty sure the Imperium can manage lots and lots of XBoats.

The often quoted (but apparently, not entirely accurate) figure of 11,000 star systems in the Third Imperium (pre-shattering) makes for a decent starting point.

Although the Express Network "touches" only a superminority fraction of the star systems in the Third Imperium (since most star systems are not "on" the Network), it then becomes a relatively straightforward question of ... what should be the ratio of XBoats in service to the number of star systems within the border of the Third Imperium?

• 1:1 = 11,000 total
• 2:1 = 22,000 total
• 3:1 = 33,000 total
• ... more?

For the purposes of conversation, I'm thinking that about a 3:1 ratio (so 30,000 to 33,000?) XBoats in service within the Third Imperium feels like a decent guesstimate. Especially if you figure that at least 10% of that number are going to be "out for maintenance" and no longer in circulation at any given time span.

As for the time delay from Neptune to Earth, file that under "who cares".

Well, maybe not YOU ... but I'm reasonably certain that there are going to be other people who would find an 8+ hour round trip between inbound XBoat, transmit to mainworld, send reply from mainworld, load reply onto another outbound XBoat to be "less responsive than it could be" just by virtue of the tyranny of distance (between Neptune and Terra).

If you're viewing the Express Network as more of a "postal service" with what amount to "once a day deliveries" (let alone, once per week!) ... a 4 hours one-way lag time isn't that much of a problem. If you're expecting multiple inbound/outbound cycles per day, a transmission delay lag of that magnitude starts getting harder to defend. And then there's that time to dispatch standard that was cited near the beginning of this thread:

BUT ALSO NOTE that the time between jumps always seems on the order of an hour or two (e.g. more than seven minutes, less than 4 hours); this is probably a reflection on general flight readiness.

An excessively long distance uplink, resulting in network lag of 3+ hours will necessarily cause a certain amount of temporal displacement friction in the network within individual star systems.

Th thing is, if the Express Network runs on more of a "pass the baton" style of operation (XBoat comes in, dispatches need to be going out to other star systems in less than 4 hours as a reaction to that arrival), that's rapidly going to wind up desynchronizing handoffs due to the 150-175 hour duration of jumps (LBB5.80, p17).

It's hard to keep trains "running on time" when they could appear "at any time during a calendar day" (so to speak).

 

[Condottiere]

Express Boats may be the largest class for starships, in Chartered Space.

In fact, I'm surprised that decommissioned Express Boats aren't reutilized.

 

[mike wightman]

Per Dan "Far Trader" Burns:



This is a potential problem, although you could always just mandate return trips being synchronized, rather than ALL ROUTES IN synchronization. It's more doable. It's certainly lazier and still reliable.

You don't wait, you put the new data on the next boat.

 

[mike wightman]

The original quote has to be from 1982 or earlier, because that's the date it appears in Library Data: N-Z.

They wrote new material for the Library Data books, they didn't just recycle previous Library Data, wasn't there a JTAS article about the xboats...

 

[mike wightman]

JTAS 6: 1980
"A ship makes its jump, relays its messages to the station immediately upon arrival by means of a high-speed, tight-beam radio transmission, and then waits to be picked up and towed into the xboat station by a specially built xboat tender, where it will be refueled, refitted, and prepared for its jump to the next destination."

"Xboat Stations: An xboat station is usually located near the edge of a system, where it can pick up the information beamed to it from incoming xboats with the smallest possible delay. The station contains receiving and rebroadcast equipment, to receive the xboats transmissions and send them in turn to other xboats and to the populated world(s) of the system. An xboat station contains facilities for refueling and repair of the xboats and their tenders, as well as quarters for the pilots and the staff of the station."

A quicj note, I do not think your model of an xboat jumping backwards and forwards between two worlds is correct. I believe individual xboats jump down the xboat routes because eventually they have to end up at:

"Way Stations: Major overhaul of xboats is done at way stations, located along the xboat network. Way stations are equipped to perform drive overhauls and other maintenance operations beyond the abilities of the smaller xboat stations. One way station is provided for every eight to ten xboat stations."

Also they jump to each world on the route in turn, or the average speed would be jump 4 not the jump 2.something message speed quoted for Capital to Regina... and I am ignoring that canonically the core sector had jump 6 xboats by 1105, JTAS 2 TAS News)

 

[ady]

We also seem to be suffering from everyone's favorite sci fi writing failure ... distance doesn't matter....

...You really need a 4-6G maneuver drive performance before you can make the transit between Uranus and Terra in less than 7 days. My point being that "personnel transfers" between Uranus and Terra can be done EITHER by Ship's Boat (6G) or Pinnace (5G) or Modular Cutter (4G) or Scout/Courier (J2/2G) in "approximately a week" for the transfer.

That's also how I see it, lots of fast small craft acting as a chain of supply, carrying crew, fuel, supplies and physical mail to and from the various worlds and orbital stations in the system to the distant Tender. You could even have chains of small craft zipping around between the Tenders and X-boats as well, with the Tender acting as a sort of semi mobile space base. It would only need to dock with x-boats for occasional major repairs, with basic between jump servicing and supply being performed by small craft. Artists like Riftroamer have done art of Cutters painted in Imperial colours and they seem perfect for the job, being so adaptable.

 

[Condottiere]

In theory, the Scout Service could have a single hundred tonne hull, and used that for all roles suitable for that tonnage, and fit the mission requisite equipment within.

Whether for four parsec message delivery, or last mile orbital connector.

 

[kilemall]

In theory, the Scout Service could have a single hundred tonne hull, and used that for all roles suitable for that tonnage, and fit the mission requisite equipment within.

Whether for four parsec message delivery, or last mile orbital connector.

Heh imagine getting an xboat for your scout benefit.

 

[Condottiere]

Tadpole entering atmosphere.

 

[Spinward Flow]

That's also how I see it, lots of fast small craft acting as a chain of supply, carrying crew, fuel, supplies and physical mail to and from the various worlds and orbital stations in the system to the distant Tender.

Again, the Tyranny of Distance creates a somewhat unwanted logistics friction factor. The farther "out" in the system the Express Network operation is, the lower the "throughput capacity" of any single craft making runs to it will be (in terms of tonnage delivered per unit of time). You also wind up with LONG supply chains (parts, personnel, consumables, etc.) which then become a security risk due to the increase in locations of opportunity for disruption (piracy, terrorism, or other criminal activity).

It's kind of like how it's possible (now, in the real world) to ship products from the other side of the world ... but that doesn't necessarily make that option "cheaper" than getting the same product from neighboring regions that are local to you. CAN be done is not necessarily the same as WISE (or economical) to be done that way.

You could even have chains of small craft zipping around between the Tenders and X-boats as well, with the Tender acting as a sort of semi mobile space base.

That's basically what I was proposing, earlier upthread.
Essentially, what you want is 2 types of small craft (maneuver tugs and fuel shuttles) specialized for different roles doing most of the "heavy lifting" of the operation. You then set up the Express Tenders as being more of a logistics marshaling/fuel depot plus command & control base of operations for a particular volume of space around a "target" planet where Express Network operations are managed and run. A "fleet" of Express Tenders is then managed from a "desk job" administrative posting (plus staff subordinates) located at a scout station or full on scout base in the star system.

So you wind up with a sort of "mothership to starships and small craft" type of vibe going on with the Express Tenders. The key point, however, is going to be that the tempo of fuel deliveries to the Express Tenders is going to determine how quickly those Express Tenders can turn around XBoats for dispatch. Since (100 ton J4 LBB2.77) XBoats consume 40 tons of fuel every time they jump (regardless of parsecs traveled), that means that any fuel shuttles making regular refueling runs down/up gravity wells to the edge of the 100D jump shadow will need to be incremented in amounts slightly over 40 tons (to account for consumption in transport and sustainment of the Express Tender itself). If a fuel shuttle delivers less than 40 ton increments, it's going to need to make 2 trips in order to deliver the required fuel tonnage to execute 1 jump by an XBoat (which then impacts the tempo of operations). Note that this requirement immediately impacts the suitability of 50 ton Modular Cutters outfitted with a 30 ton Modular Cutter Module configured as a dedicated fuel tank (make 3 round trips to fuel 2 XBoats) for this fuel shuttle mission.

It would only need to dock with x-boats for occasional major repairs, with basic between jump servicing and supply being performed by small craft.

I'm thinking that, bare minimum, refueling would need to be staged through the Express Tenders. Additionally, any and all engineering support/maintenance would be "outsourced" to crew on Express Tenders, rather than putting such crew onto small craft. This would necessarily mean that the engineering department of an Express Tender should be sized to account for not only the drive systems installed on the Express Tender itself, but also any subordinate craft (maneuver tugs, fuel shuttles, XBoats docked inside the internal hangar bay for refurbishment/maintenance) that are assigned to the Express Tender.

My point being that although H/H/H drives may total up to only 85 tons combined, you're probably going to need more than 3 engineering positions (105 tons of drives crew capacity) on the crew roster of any Express Tenders, because they'll be providing crew support services to the drive systems of additional craft beyond just themselves. Typically, engineering crew positions are not mandated for craft that can expect to be receiving plenty of "shore support" at starports (such as free traders and other merchants) ... but for long endurance operations "out in the boonies" away from any starport personnel, you had better have enough engineers (yourself) to "shoulder the load" or you're going to have problems.

If you don't schedule downtime for maintenance yourself, your machine systems will schedule outages FOR YOU ... usually with little to no notice (and often at the Worst Possible Times™).

 

[whartung]

If Jump Shadowing is a Thing (and by Jump Shadowing I mean the planets primary start "getting in the way" of Jump, so that part of the year a planet is in the "shadow" of the star, making routine jump now entail a long trip from around the star, if that is a Thing, then it makes sense to put an XBoat station far from the star. The farther from the star, the less impact of jump shadows.

If not, there's no reason to park the XBoat infrastructure out in the middle of nowhere. "Space is big", there's plenty of room to park it all somewhere near the main population centers, no need to orbit Neptune.

However, if Jump Shadows are a thing, it would likely be better, particularly for more active hubs, to simply have duplicate infrastructure, so there's always a XBoat station "in LOS" of any jump so as to recover and serve the boats more efficiently.

As for the scope of the ships involved, that's base purely on how often they fly. Obviously if they jump every 12 hours instead of every 6, that's half the ships needed. I don't think you can efficiently do "pony express" style of simply jumping as soon as they're ready to go (i.e. XBoat arrives, beams messages, ready boat jump within an hour or so of arrival). The Pony Express wasn't really a network. It was just a line. For a line, that works, for a network, not so much.

I can't find out how often riders left St Joseph/Sacramento (the respective east/west terminus), I'm guessing one per day

Scheduled jump make far more sense, however often that may be.

 

[Spinward Flow]

As for the scope of the ships involved, that's base purely on how often they fly. Obviously if they jump every 12 hours instead of every 6, that's half the ships needed. I don't think you can efficiently do "pony express" style of simply jumping as soon as they're ready to go (i.e. XBoat arrives, beams messages, ready boat jump within an hour or so of arrival). The Pony Express wasn't really a network. It was just a line. For a line, that works, for a network, not so much.

I agree.
The Pony Express works for a LINEAR system with no direct branching.

As soon as you start getting into NETWORKED operations, where each node on the network needs to forward information to multiple locations (except the point of origin for that information, because it already came from there) ... the transmission behavior stops being "baton handoff" in a straight line and turns into more of a "fission chain reaction" type of behavior.

At that point, you can't be thinking in terms of overly simplistic "racetracks" between a mere 2 star systems linking up the chain of the entire Express Network. Instead, each "node" of the Express Network simply forwards data via XBoat Packet Protocol (XPP? ) using whatever XBoats are available after every incoming breakout from jump. This then necessarily means that some "nodes" on the Network will need to dispatch multiple XBoats outbound per each XBoat that arrives inbound ... which then presents a sustainability problem. In order for the Network to remain stable, it needs to balance the number of outbound XBoats to the number of inbound XBoats, otherwise the "stock" of XBoats within any particular star system on the Express Network will (rapidly) deplete their supply of XBoats.

 

[Condottiere]

If you're going to do simple networking, I think three parallel (relative) tracks, that crossover for error correction.

Or, lost packets.

 

[Grav_Moped]

In theory, the Scout Service could have a single hundred tonne hull, and used that for all roles suitable for that tonnage, and fit the mission requisite equipment within.

Whether for four parsec message delivery, or last mile orbital connector.

Heh imagine getting an xboat for your scout benefit.

Yeah... why is the canon XBoat a streamlined "teardrop" rather than a sphere or close structure anyhow?

I'm liking this...

 

[Condottiere]

Comet, I speculate.

 

[Spinward Flow]

Yeah... why is the canon XBoat a streamlined "teardrop" rather than a sphere or close structure anyhow?

Considering that XBoats (by definition) have no maneuver drive, I'm hard pressed to think of a (design spreadsheet relevant) compelling reason why XBoats shouldn't be built as Dispersed Structure (configuration: 7) hulls. I mean, it's not like they're going to be doing much aerobraking/orbital skimming without a maneuver drive.

 

[aramis]

An individual Xboat of need operates on no less than an 8 day schedule. as it's ±17 hours from an ideal 7 day window.
So up to 8 days for jump.

On a 1/week departure, on a chain, you need 2 boats per link, 1 each way, and sanity says you should have a second each way, for four.

On a 9 day routing, you need 2 per link.
On a daily departures, you need 10-11 for a 9 day cycle each way per link. This puts 0-4 at the tender, normally 2... but ensures a daily departure each way.

I've always assumed daily departures.

 

[Condottiere]

Frequency of departure might depend on what the Imperium might consider actionable intelligence, though that might be more the province of fleet couriers.

 

[Spinward Flow]

An individual Xboat of need operates on no less than an 8 day schedule. as it's ±17 hours from an ideal 7 day window.
So up to 8 days for jump.

I'm going to quibble with a few details here, in an attempt to hone in on a more sustainable baseline assumption of the individual XBoat dispatch tempo.

The first question I've got is ... how is the 150-175 hour duration of a single jump determined?
LBB5.80, p17 provides NO GUIDANCE on how to "roll" for a result correctly.

Given that (classic) Traveller is a D6 ONLY game, the only way (that I can think of, well after the fact ) for how to determine how long an individual jump takes would be ... 5D6+145 ... and that tells you how many hours a starship will spend in jump (roll for each jump separately).

Well, if that's the case ...



Rolling 5D6: The Bell Curve Sharpens

When rolling five six-sided dice, the possible outcomes range from 5 (rolling five 1s) to 30 (rolling five 6s). As the number of dice increases, the probability distribution becomes more concentrated around the center.

Number of Possible Outcomes: There are 7,776 possible combinations when rolling 5D6 (6 × 6 × 6 × 6 × 6).
Probability of Each Sum: The probabilities for 5D6 are:

• 5 or 30: 1/7,776 (0.01%)
• 6 or 29: 5/7,776 (0.06%)
• 7 or 28: 15/7,776 (0.19%)
• 8 or 27: 35/7,776 (0.45%)
• 9 or 26: 70/7,776 (0.90%)
• 10 or 25: 126/7,776 (1.62%)
• 11 or 24: 210/7,776 (2.70%)
• 12 or 23: 330/7,776 (4.24%)
• 13 or 22: 495/7,776 (6.36%)
• 14 or 21: 712/7,776 (9.15%)
• 15 or 20: 980/7,776 (12.60%)
• 16 or 19: 1,287/7,776 (16.55%)
• 17 or 18: 1,600/7,776 (20.57%)

The most probable outcomes are again centered, with sums of 17 and 18 being the most likely.



With such a distribution curve of probable jump durations, 17+145=162 or 18+145=163 hours comprises 40.14% of the outcomes, which is decent (although not "perfectly reliable"). My point being that the outlier times (150-155 hours and 170-175 hours) wind up being RARE, even though they're still possible. That means that "regularly scheduled departures" need to account for this amount of variance, but will rarely need to deal with it as a matter of routine operations (see: outlier cases).



The second factor is that I'm (now) honestly of the opinion that XBoats really SHOULD go through a 16 hour routine maintenance check after every jump by a skilled engineer (who is not a part of the XBoat crew). That basically means that they need "servicing" by an Express Tender after every jump.



That means, that in a worst case scenario ... a 175 hour duration jump plus whatever the maneuver time is for recovery+hangar docking plus 16 hours (which in actual operations might routinely turn into something closer to 20 hours) plus maneuver time to deploy for dispatch ... could mean something on the order of 195+ hours per jump cycle of an XBoat (not including maneuvering to/fro times).
195/24=8.125 days

In order to account for any "slop factor" tolerance in individual circumstances and the need to rotate XBoats in and out of service (along with any other operational frictions) it's probably better to assume an operational window of 9 days=216 hours between jump dispatches for individual XBoats. That slightly slower tempo of operations builds in sufficient "margin" to keep the network running smoothly, because there will need to be reserves in play to streamline the logistics of actual dispatch operations.