I still do not know what to do with all of the Liquid Hydrogen required for the Jump. I just figure that it is part of the game, and proceed to march.
Disclaimer: IMTU
On Earth's first Jump ships, this was done using a "jump field generator" which projects a charged field around the ship. This consumes enormous quantities of electric power so requires the power that only fusion can provide. It also leads to Bad Things (tm) if the generator fails for even a moment. It allowed for pre-jump ships (used to ply the solar system or earth orbit) to be retrofitted to become interstellar starships and was forgiving of irregular hull shapes and so on.
The Vilani came to a different solution (though there's evidence they used jump field generators early on as well). By installing a special grid in the hull of the starship, then charging it, the Vilani found that Jump stability could be maintained as well. Through fooling with different preparations of materials to make the grid, they discovered that Lanthanum yielded the best combination of holding the charge, material stability, and low cost. The charged grid, unlike the field, holds its charge and doesn't collapse the moment electrical power fails. Depending on the robustness of the grid this can hold sufficient charge for days of safety even if the power plant fails, this combined with a "dead man" switch on Vilani vessels meant that a Vilani vessel could make a successful journey even if their power plant failed halfway through the trip, though as the field weakened, the hull would slowly erode away; Vilani ships tend to have very thick "armored" hulls with robust grids within them, even on civilian ships to buy more time in the case of a power plant failure. Because the field is bound by the physical hull, IMTU Vilani ships tend to be compact, somewhat rounded, and lack protrusions such as communications and sensors arrays and so on. The preponderance of very simple geometric hull shapes for many Traveller ships is because of this with extruding fixtures being withdrawn into the hull before Jump.
During the Rule of Man, the hydrogen bubble technology was developed, though it would not mature until research resumed in the Third Imperium. It was found that hydrogen gas could be released around the ship then be charged. This allowed ships with irregularly-shaped hulls and protruding hull fixtures like communications and sensor arrays. The hydrogen gas envelope held a charge, but not as well as a Lanthanum grid. At the same time, the charge also held the integrity of the gas bubble, keeping it from dissipating (though things don't dissipate in jump space as fast as it would in normal space). If power failed, the envelope would erode away in Jump Space, much like the hull on jump grid designs. However, because it was cheap hydrogen gas, the ship itself would not be damaged. At the end of the trip, upon re-entering normal space, the hydrogen bubble dissipates into the vacuum of space (a ship with fuel scoops can retrieve a lot of this hydrogen for re-use if desired; this is common practice amongst Solomani ships as the Solomani have "conservationist" thinking and see dumping hydrogen into space as somehow wasteful, but is nearly unheard of in the Third Imperium where hydrogen is considered basically unlimited as it's the most common element in the universe).
IMTU, the "modern" Third Imperium, most ships utilize both the hull grid and hydrogen bubble for redundant, extra safety (the Vilani are into this kind of overengineering). However, it is legal to operate a ship with just the hull grid; it is not legal to operate a ship with just the hydrogen bubble in the Third Imperium (it is legal elsewhere). Nobody in their right mind uses jump field generators anymore.
Note that power plant and jump field generator failures don't happen very often, but understandably, people are concerned about it happening so like redundant safety measures.
