Wednesday, January 30, 2019

Jump Drives in Traveller - An Illumination

This post grew out of discussion with certain others about handwavium technologies in RPGs, with a specific focus on interstellar travel constraints in Traveller. As someone who is always interested in how genre constraints are perceived in-character by PCs, and who was weaned on robust technobabble, I wanted to try to address the operation of the default Traveller jump drive. This is written without reference to OTU assumptions, working mostly from the relevant pages of the LBBs. 

If anyone has any critiques of this description in relation to the mechanics of the LBB jump drive, let me know in the comments.



When activated, the jump drive produces a bubble of ‘realspace’ within jumpspace, and in forming the bubble imparts to it the mathematical equivalent of a ’ballistic trajectory’ in reference to realspace-jumpspace coordinate correlations. By way of analogy, the jump drive is like a nuclear pulse rocket, using a single release of energy to lift off from the surface of a planet. Following this analogy, the fuel consumption and gravity-well distance is the minimum necessary to achieve realspatial ‘escape velocity’ for the jump-bubble. Because the formation of the jump-bubble occurs while the ship is in reference to realspatial coordinates, the course must be plotted before the activation of the jump-drive. No means of affecting the trajectory of the jump-bubble from inside, once created, is known, although research continues. (This may have something to do with causal issues related to the realtemporal-jumpspatial issues described below.) A major part of the trajectory calculation requires the jump-bubble’s surface to collapse, ‘re-entering’ realspace, in relation to the energetic level of the bubble at the moment of intersecting with gravitational warping of jumpspace — hence the ‘empty space problem’ of navigating without relation to gravity wells, and the requirement to climb out of a gravity well to form a jump-bubble.

The bubble’s extent in realspatial dimensions is related to ship size, but jump-capable ships currently require a minimum of 100 tons of displacement (although this is likely to be a constraint of power and fuel needs in relation to materials engineering rather than jumpspatial physics). The bubble’s minimum extent in realtemporal dimensions is subjectively between 150 and 185 hours (approximately 605 000 seconds, on average). The temporal size of the bubble appears to be related to the minimum density for realspace bubbles within a jumpspace ‘medium’; decreasing subjective jump time would require a method of adjusting realtemporal density without risking the bubble’s jumpspatial surface tension. (Given the time spent in the jumpspace bubble during a misjump, it is possible there’s an inverse relationship to realtemporal ‘density’ and jump-bubble surface tension.) It’s often assumed that the time spent in jumpspace also corresponds to travel time ‘within’ jumpspace, but the lack of ability to perceive jumpspace except as a theoretical mathematical construct means that this is likely to be a mere projection of sophont realspatial assumptions.

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