Let us consider two launch vehicles - "A" and "B". If "A" has a larger wet mass than "B", does this imply "A" has a higher payload capacity to a particular orbit, from a particular launch site than "B"? Is it possible for "B" (a lighter launch vehicle) to have a significantly higher payload capacity than "A" (a heavier launch vehicle)?

Or is there any fixed rule like "A launch vehicle heavier than the other can definitely lift more compared to the other one"? I think, a launch vehicle having greater wet mass has higher potential energy than a lighter launch vehicle, at the launchpad. By using the law of conservation of energy, I claim the rocket heavier lifts more into orbit than the lighter one. Could you please tell whether I am correct or not? If not, why shouldn't we apply the law here?

Further, are there any medium (heavy) lift launch vehicles lighter (considering the wet mass) than small (medium) lift launch vehicles?

Are there any such examples in real life? If yes, kindly specify them with appropriate quantitative parameters (wet mass, payload capacity, etc.) if possible.


1 Answer 1


In general, heavier launchers can send more mass to LEO, but as described in this QA, the correlation isn't very strong. Different engine technologies used in modern rockets have different mass/impulse/cost tradeoffs.

One particular example is Delta IV Heavy versus Ariane 5.

Delta IV Heavy is 733 tons on the pad, 28 tons to LEO, for a payload mass ratio of 3.8%.

Ariane 5 ES is heavier, at 760 or 777 tons (I found conflicting figures), but delivers less mass to LEO, about 21 tons, a payload mass ratio of 2.7%.

Delta IV Heavy uses only hydrogen-oxygen engines, which produce a high mass-specific impulse, 360 seconds at sea level. Ariane uses hydrogen-oxygen for the core engine, but most of the mass is in solid rocket boosters, which deliver a lot of thrust for low cost, but have relatively poor specific impulse, about 242 seconds at sea level.

I believe D4H has the highest payload mass ratio of any launcher currently in use. At the opposite end are launchers using only solid rocket motors, such as Minotaur IV with a payload mass ratio of 2%, or Vega with a ratio of 1.8% -- less than half that of the D4H. Thus the payload capability of two different rockets of similar launch mass can vary over a factor of 2:1.

I don't know if there are specific cases of a small-lift launcher that outweighs a medium-lift launcher, or a medium-lift that outweighs a heavy-lift, but it's theoretically possible.


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