So, if the Maximum Drive Potential Table says "6" the ships jump number is 6, no more, no less.
A J-6 drive can of course also do J-5, but it is still a J-6 drive requiring 0.1MJn Dt jump fuel.
Still not allowed by LBB2:
LBB2'81, p15:
At a minimum, ship fuel tankage must equal 0.1MJn+10Pn, where M is the tonnage of the ship, Jn is the ship's jump number, and Pn is the ship's power plant rating.
It's silly, but LBB2 rather insists on it.
You can presumably bypass this with demountable or drop tanks.
You can install a too small computer, so the ship is limited to J-5, but it must still have fuel for J-6 as built...
Note:
If
@AnotherDilbert is correct (which he's not ... but let's humor him
), the Type-J Seeker (LBB S7, p27-29) is
flagrantly illegal and illegitimate despite being published RAW.
After all, if
@AnotherDilbert is correct
(which he's not) ... you
CAN'T have a 100 ton hull with A/A/A drives (codes: 2/2/2) with anything less than 40 tons of fuel (20 tons for J2 plus 20 tons for power plant).
And yet ... as designed and published ... the Type-J Seeker has only 30 tons of fuel (10 tons for J1 plus 20 tons for power plant) with an OPTION for demountable internal fuel tanks to increase the accessible fuel load by +10 tons (back up to the original 40 tons of the Type-S Scout/Courier). An option which is NOT installed by default, I would point out.
What makes this example especially hilarious (for example purposes) is that if a 100 ton starship has 30 tons of fuel in it, it's capable of J2 (20 tons of fuel consumed) and will still have 10 tons of fuel reserve remaining for endurance (whether accelerating under maneuver or not) ... and as we all know (or at least, I hope we all do ...
), maneuver drives "have no purpose or use" while in jump between origin and destination. Likewise, weapons and screens that require EP have "nothing to engage" while in jump between origin and destination. In other words, while a starship is in jump, the only (1+) EP that must be supplied by the power plant during jump transits is for the computer to keep the computer operational (and model/1-2 computers use EP=0).
Therefore, while starships are in jump between origin and destination, power plant output can be "throttled back" to providing Basic Power (housekeeping for life support, effectively) and enough EP to keep the starship's computer operational (model/3+ require EPs). In other words, keeping the power plant ON and running "full blast" during the entire time while in jump is ... unnecessary (and wasteful).
While you're in
jumpspace, you're "in another dimension" ... because ...
"we're not in N-space anymore, Toto" ... which means that everything about the journey through J-space is determined when the
jump flash occurs. So it's not like the jump drive needs to "keep pushing" (or "thrusting" if you prefer) while the starship is in J-space in order to reach the destination.
The jump drive probably does require some modicum of "basic housekeeping power" being continuously supplied to it in order to maintain the (protective) jump bubble/field externally around the starship, so you can't turn the jump drive (completely) OFF (cold) while in jump, but we aren't talking "EP relevant" levels of power production required to do that. Therefore, the jump drive needs to be "operational" (at minimal power levels) and the starship computer needs to be "powered" (with EP) and "basic power for housekeeping purposes" to keep the lights/life support on is all that is required while a starship is in jump space.
And why do I say that?
Because once you're IN jump, the only ways to breakout from jump are either to "complete the journey" OR to intercept a gravity well/jump shadow "along the way" (that will precipitate your starship out of jump before reaching your intended destination). Presumably there are "other,
more catastrophic" ways to precipitate out of jump, but since those tend to fall into the category of "never heard from again"
we'll conveniently step over those possibilities as being "not relevant to routine/repeatable operations" for purposes of this discussion.
Continuous Thrust = Continuous Velocity is something that only applies when moving through a medium that imposes drag (which solids, liquids and gasses tend to do).
As (I hope) we all know, the "drag" force of vacuum tends to be pretty minimal ... except when you're dealing with
NAFAL type applications where approaching the speed of light has "implications" for the density of matter in a vacuum (along with the relativistic implications for mass calculations).
To my knowledge, there has NEVER been anything published for
Traveller that imputes or implies that there is any kind of "drag force" (continuously) applied to starships while they are in J-space (or any other "not N-space" context). If there is ...
citation needed.
If there's "no drag force" in J-space ... ipso facto there is no need for "continuous thrust" from jump drives while in J-space in order to reach the destination (just sustain the jump bubble around the hull).
All of the above reasoning is why I maintain that the LBB2 fuel requirements "settings" are less about what is REQUIRED TO OPERATE (at all) and more about safety regulations. The regulations are "biased" to force smaller craft to have larger fuel fractions for reasons of endurance in an emergency/mishap condition, rather than because drives installed into smaller craft are "fuel wasters" that become horrifically inefficient.
A Type-S Scout/Courier (for example) will consume 100/2000=0.05 tons of fuel per week for basic "housekeeping" power ... and 2*0.35=0.7 tons of fuel per week producing 2 EP for continuous acceleration @ 2G/Agility=2. Therefore, a Type-S Scout/Courier will consume a maximum of 0.75 tons of fuel while maneuvering continuously at maximum acceleration, per 7 days.
Therefore, 4 weeks/28 days of continuous acceleration at maximum power will consume ... 3 tons of fuel.
So why is a LBB2 designed Type-S Scout/Courier REQUIRED to have 20 tons of power plant fuel?
Simple.
Q: If a fuel hit (for ANY reason) occurs, what is the minimum fuel loss that can occur?
A: 1% of total fuel load or 10 tons, whichever is larger.
So, by requiring 20 tons of power plant fuel, a 100 ton starship with a Power Plant-A (code: 2) drive, such a minimalist starship could withstand 1x fuel hit and still have SOME fuel remaining to self-recover with. It's a safety margin.
Likewise, a Type-S Scout/Courier that jumps into a star system and refuels will have 40 tons of fuel onboard. At 3 tons of fuel consumption per 28 days/4 weeks/1 month (maximum) ... after 13 months/1 imperial year ... at maximum fuel consumption the Type-S Scout/Courier will have consumed 39 tons of fuel. So the Scout/Courier will have 1 ton of fuel margin remaining to maneuver to a location to (wilderness) refuel and then jump out of the star system.
In other words, that 20+20=40 tons of fuel requirement gives a Scout/Courier 1 year of maximum maneuver endurance on station in N-space before needing to refuel (assuming no mishaps during that time). Endurance of longer than 1 year becomes "problematic" for reasons of annual overhaul maintenance requirements.
Is this explicitly spelled out anywhere the way I'm presenting this information?
No ... this is a
read between the lines that requires access to LBB2, LBB5 and CT Beltstrike to reach these conclusions, but the math checks out (after the fact).
