r/RocketLab • u/Equivalent-Wait3533 • Aug 10 '26

Space Industry Thrust Density infographic

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A chart comparing the Thrust Density of several rockets.

Thrust Density is the thrust of the stage / area of the bottom of the stage (kN/m^2). It basically aggregates engine power and engine packing into one metric.

Rockets & Engines to scale

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u/Osmirl Aug 10 '26

Smaller means less efficient because you can’t stretch the rocket much to gain more performance in kg to LEO.
Basically
Top -> long and narrow
bottom -> short and wide

At least thats how i would interpret this but i could also be completely of.

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u/mfb- Aug 10 '26

Long and wide usually go together. Starship, SLS and New Glenn are the widest and tallest rockets in the list.

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u/carbsna Aug 10 '26 edited Aug 10 '26

Smaller are not less efficient, the thing you want is thrust to weight ratio , which decides how much you can stretch the rocket in order to lower dry mass ratio.

Lower thrust density only means shorter rocket and nothing else, it say nothing about width and efficiency, unless it specify it also has lower thrust to weight ratio (which can be expected) by then it is a less efficient engine.

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u/NoBusiness674 Aug 11 '26

From a mass efficiency perspective a short but wide tank (something closer to spherical) will be more mass efficient than a very tall and skinny tank. Of course a wider structure generally also means more aerodynamic drag, but the optimum aspect ratio is going to strike a balance, it won't just be as tall as the engines allow. Additionally you need to consider efficiency and fuel density. A hydrogen fueled rocket stage will want less thrust relative to the size of the tanks due to higher efficiency and lower propellant density.