Why X-Boat tenders

[Condottiere]

Manoeuvre drive with Thrust 0 consumes tonnage equal to 0.25% of the space station’s total hull and costs MCr1 per ton. Enables the station to make flight corrections to stay in orbit.

 

[tytalan]

The bridge has two weeks of life support and battery power, while emergency thrusters give it basic manoeuvring capabilities, equivalent to Thrust 0. A detachable bridge is even capable of soft-landing on a planetary surface.

That’s actually a very specific case and it does not say maneuver 0 can do that it says the maneuver drive on a detachable bridge can. Your making unsupported assumptions

 

[Condottiere]

Three cases, four, if you include solar sails.

Soft planetary landings would tend to vary by how far you can lower the velocity when touching down, which should vary between one done on the Moon, and another on a heavy gravity planet.

Another aspect to consider is if a Scout Ship tows a Subsidized Merchant: two hundred thrust tonnes divided by five hundred tonnes volume, would be forty percent of thrust factor/one, which could be defined as thrust/zero?

There doesn't seem to be a definite value, or even a range.

As regards reaction control system, the rules say that the manoeuvre drive can vector it's thrust, though with diminishing returns.

And, possibly, Kentucky Fried Crewmen.

 

[rinku]

For what it's worth, the JWST thrusters (which in Traveller terms are a reaction drive 0) can generate a few Newtons of thrust. That's enough to keep it on station if it starts to drift too far out of line, but it only masses 6500kg. One Newton of thrust would impart an acceleration of 0.00015 metres per second squared. 1G of thrust is about 10 metres per second squared, so that's about Thrust 0.000015.

Space combat and ship construction keeps things in round figures for ease of play, but there's no reason you can't deal with fractional thrust. The travel time formula can cope, for example - if a scout towing a subby has effective thrust 0.4, you can work out how long it's going to take to haul it to the starport, move between range bands etc.

But any constant thrust will move you. 0.000015G would take about 16 million seconds to go 1 million km, or 4500 hours. 189 days, or around 6 months.

Now, in the case of JWST, it will run out of propellant well before that. But an M-Drive 0 can happily keep reactionless thrusting for ever, as long as the power holds up and nothing breaks down.

An M-Drive 0 of 0.001G rating would only take 2 million seconds to travel 1 million km, or about 43 days.

 

[tytalan]

For what it's worth, the JWST thrusters (which in Traveller terms are a reaction drive 0) can generate a few Newtons of thrust. That's enough to keep it on station if it starts to drift too far out of line, but it only masses 6500kg. One Newton of thrust would impart an acceleration of 0.00015 metres per second squared. 1G of thrust is about 10 metres per second squared, so that's about Thrust 0.000015.

Space combat and ship construction keeps things in round figures for ease of play, but there's no reason you can't deal with fractional thrust. The travel time formula can cope, for example - if a scout towing a subby has effective thrust 0.4, you can work out how long it's going to take to haul it to the starport, move between range bands etc.

But any constant thrust will move you. 0.000015G would take about 16 million seconds to go 1 million km, or 4500 hours. 189 days, or around 6 months.

Now, in the case of JWST, it will run out of propellant well before that. But an M-Drive 0 can happily keep reactionless thrusting for ever, as long as the power holds up and nothing breaks down.

An M-Drive 0 of 0.001G rating would only take 2 million seconds to travel 1 million km, or about 43 days.

I think it’s best to keep to game mechanics and not start Home Brewing thing for this type of conversation. It opens things to Al sort of things that will only complicate the conversation

 

[Condottiere]

It doesn't make sense, because Mongoose homebrewed it themselves.

Unless it's partly borrowed from Tee Five.

 

[rinku]

It's not homebrew if it's physics.

All I'm using here is the travel formula that's been in every edition of Traveller since 1977, and which has nothing to do with game rules. Its real world stuff. Page 163 of MGT2e22.

Time = 2 * SQRT(distance/acceleration)

I was using seconds, metres and metres per second squared, but the units don't matter. You could use miles, hours and miles per hour squared should you wish.

Thrust 0 is left undefined, but sometimes you might need to know what the actual acelleration is. How long will it take your solar sail to get you there? Is a solar flare or collision going to push your space station out of orbit? Be prepared for arguments if you don't put a value on it and do some quick maths.

 

[Condottiere]

If it's actual Einsteinian universe physics, it can be defined, and written down simply enough so that the reader can understand it.

In theory, you could soft land a space station.

Atmospheric reentry.

The space station version seems closer to performance costs, though a tad inefficient.

Arguably, you could permanently just attach a tug, with a type five docking clamp, on top of it.

 

[rinku]

I finally worked out what was bugging me about the idea of hanging a station above the north pole of a star.

The physics does work out - and for what it's worth the gravitational pull of the sun at 100D is something like 0.0006G, so well within "Thrust 0" territory - but it's horribly unstable (solar weather, gravitational influence from planets or even light pressure from the star is going to push it around and need even more correction). And if the power or M-Drive fails you'd immediately start to spiral in towards the star.

So it's like placing a transmission source in a helicopter, or maybe more like a dirigible whose gas bag doesn't completely offset gravity and needs lift support from propellers. Yep, you can get great coverage (except for being thousands of km away from everyone tuning in...). But for most situations it makes more sense to place it at a stable position (i.e. a normal orbit) and maybe use relays to cover blackspots and outlying areas.

 

[gylesw]

Yeah, IMTU the different vector and velocity of star systems (relative motion) is a thing and Jumps are normally done after matching the ship's vector and velocity to the destination system to produce the desired vector and velocity on arrival there.

This means:

• Ships outbound to 100D normally do so on the appropriate vector and by doing so give a strong clue of their destination (IMTU you can't guess destination just by observing the Jump).
  • But you can Jump and adjust for relative motion on arrival, it just is more time consuming.
  • It also means if there are three systems within Jump range you can act like you're heading for System A and actually go to System B
• Ships inbound in a system with class C+ Starport will be aware of the standard approach vector and velocity to that world and the arrival box, which is basically a cube of space ships are expected to arrive in. No, jumping on top of another ship is not an appreciable risk because maths.
  • The approach velocity on emergence is no higher than a 2G drive could decelerate from into a geo-orbit to await clearance to land on-world or dock with the high port - this clearance may be given before entering geo-orbit but that is where you head for.
  • Any ships arriving too fast, or any ships arriving in the inner system outside of the Jump Box will get attention.
  • Ships arriving in the outer system operate on SabS (See and be Been); transponders on, standing watch on bridge, do what you like.
  • In-system traffic will follow approach protocols when nearing inhabited worlds which can be broken down to 'if it looks like you can't decelerate to a geo-orbit at 2Gs then you will get attention.\
  • This allows safe inbound traffic and makes in-space inspections of ships far simpler
• Imperial ships (i.e. of the services) can operate under their own recognisance.

What it also means is the canon X-boat doesn't work... unless you assume that X-boat tenders work rather differently:

• The X-boat network will have their own Jump Box in system. This is typically near a source of fuel - a point 105D out from a gas giant in the direction of the mainworld of the system is normal:
  • Busy networks will have two tenders and attendant fuel shuttles (well, they have at least three as they have two on duty at any one time). They alternate between retrieval of inbound X-boats and 'pitching' outbound X-boats to match to the required velocity and vector of the X-boat Jump Box in the destination system. This is very simple; X-boat in bay, accelerate to required V&V, open bay doors and stand off 100D+ (yes ships can make ships misjump) and wait until the X-boat Jumps, return to Jump Box.
  • Quieter systems will have a single tender on duty at anytime (with two in each system).
  • Typical duty cycle is three weeks on, one week off, but off-duty X-boat tenders are subject to recall at any time.
  • Off-duty X-boat tenders will not normally go to the system's mainworld, as this would potentially mean they could not return to duty within a reasonable period. If the gas giant has any inhabited satellites they will be used to regular arrivals of Scout off-duty. If there is no possibility of planet fall within a reasonable recall time (24 hours), they will normally 'pick a pretty orbit' and
  • X-boat pilots (colloquially known as 'the great unwashed') have a similar duty cycle, three weeks on, one week off. If they are lucky, they will be picked up by an X-boat tender that is due to go off-duty. X-boat schedulers on busy routes can make sure Scouts they like have this happen far more often than chance, or ensure a Scout they dislike doesn't leaves a ship for the four years of a term.
  • The great unwashed are renowned for an adventurous approach to personal hygiene, mental health issues, being avid hobbyists, carrying at least a exabyte of encrypted data storage crystals and a collection of pot plants (in both senses of the word) with them. When they finally do get planet-side they can be a little excessive.
  • The expression 'what happens in the Express Boat Service Branch, stays in the Express Boat Service Branch' is well deserved. Comparatively low levels of work, and what work there is being repetitive means boredom and ennui are ever-present. Crews get to know each other... very well, often on multiple occasions. The understanding is that if your turn around times are under four hours no one cares if you have a small herd of goats on a tender, if the ship has a 'no textiles' policies, or if its the corridors get turned into hydroponic bays dedicated to the cultivation of recreational pharmaceuticals. There is an unspoken understanding that an X-boat tender will be given adequate notice of any inspection and that the ships will look adequately normal when they come in for their annual servicing.
  • X-boats themselves are taken out of service for maintenance (for 24 hours but it's actually closer to 8 hours of work) every three Jumps - this does not necessarily coincide with a X-boat pilot's duty cycle and would mean an X-boat pilot swaps ships on a regular basis. However, some pilots find a ship they like and synchronise their duty cycles to the ship's maintenance cycle, finding some mysterious issue that prevents the ship returning to service until the end of their break or volunteering to return to duty early. For the week-long annual maintenance period (actually five days work) serious creativity on the X-boat pilots part, understanding maintenace chiefs, and the fact that there is a surplus of X-boats (every node has at least one kept powered down but fuelled and ready to Jump within one hour) means that some X-boat pilots stay on the same ship for years. The current record is claimed to be held by 'Old Stinky' aka Terry Butcher who allegedly did not leave his X-boat 'Mabel' for 37 years - and as he disappeared in a mis-Jump he may still be on it, some where or some when. There are occasional claimed sightings in this system or that, and claims that X-boat tenders will refuel Mabel, send over supplies, and send her on her way with no questions asked (and no data transfer) and delete all records of the occurance. Other stories are similar, but basically imply that the crew are compelled to lend assistance and have their own memories altered along with the ship's, If true then Old Stinky and Mabel have been moving around beyond the Claw spending c. 98% of their time in Jump for over sixty years since the alleged misjump, which would mean Old Stinky is around 120. Many people will say this is exactly the sort of bullshit you'd expect hearing from the Express Boat Service Branch, a bunch of social misfits with permanent ship fever. Others notice that Express Boat Service Branch members agree with this very quickly and enthusiastiucally.

 

[Condottiere]

Tenders should be able to fully service, and remedy anything short of catastrophic damage, of their charges.

Whether a kilotonne is enough, would be another issue.

You could view them as mobile bases, that locate themselves at the most convenient point to serve the express boat network.

 

[Fluffy Bunny Feet]

I do question the Jump 1 ability of the standard tender. They can't easily reach worlds not on the same main they are on. Unless of course the empire is maintaining fleets of Jump tugs to move the Tenders around. So how do they recover stranded X-Boats?

 

[Sigtrygg]

They don't, the jump 1 drive is mostly for insystem jumps... perhaps.

 

[Condottiere]

If an express boat misjumps into an empty hex, the pilot's best chance is to do a Ripley, with or without a cat.

 

[tytalan]

Busy networks will have two tenders and attendant fuel shuttles (well, they have at least three as they have two on duty at any one time). They alternate between retrieval of inbound X-boats and 'pitching' outbound X-boats to match to the required velocity and vector of the X-boat Jump Box in the destination system. This is very simple; X-boat in bay, accelerate to required V&V, open bay doors and stand off 100D+ (yes ships can make ships misjump) and wait until the X-boat Jumps, return to Jump Box.

In a hub system 4+ lines you can have as many as 24+ x-boars come and go in any 4 hour period more if it’s an import System much much more in trouble times. You two tenders can’t handle the load no where near, by the way that’s according to the description of the X-boat network.

Then big problem is that the number of tenders is much greater than most of you think. It’s literally said in the book that you can have multiple x-boats entering a system per hour. So say on a four line system if you only have 3 x-boats entering the system in a hour you also have 9 leaving the system since a tender can only resupply 1 x-boat per hour and can only refine 2.5 x-boats worth of fuel a day plus has to pick up and dock a unpowered X-boat before it can refuel it your looking at something like depending on the system 120 tenders to handle the load in any high traffic system. While a space station and giving the X-boats maneuver drive you can handle multiple incoming and outgoing X-boats with heavily trafficked systems having bigger stations to handle the load while saying vast amounts of credits over all.