One would suppose mass energy density is even more important for rockets.

In practice, only some rockets use LH2. Many rockets use souped up kerosene (RP1) or, more recently, methane.

Compare https://en.wikipedia.org/wiki/Liquid_rocket_propellant#Hydro... and https://en.wikipedia.org/wiki/Hydrogen-powered_aircraft

Also:

> With materials available in the 2020s, the mass of tanks strong enough to withstand this kind of high pressure will greatly outweigh the hydrogen fuel itself, largely negating the weight to energy advantage of hydrogen fuel over hydrocarbon fuels. Hydrogen has a severe volumetric disadvantage relative to hydrocarbon fuels, but future blended wing body aircraft designs might be able to accommodate this extra volume without greatly expanding the wetted area.

From https://en.wikipedia.org/wiki/Aviation_fuel

The quote concerning mass of tanks is talking about compressed hydrogen storage, which people don't really consider feasible for large aircraft. Cryogenic liquid hydrogen storage is the way.

The need for higher mass density exhaust to provide enough absolute thrust to get off the ground overwhelms H2's energetic efficiency. Thus, SLS, like STS before it, depends on solid-fuel rockets until well clear of the pad, and then jettisons them.

Aircraft operation involves nothing analogous.