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Comment by bryanlarsen | Hacker News Reader

Yup, the thrust improvements were expected. The BE-4 engines have quite a low chamber pressure for their engine class, so they can gain significant performance just by increasing chamber pressure.

Additionally, the New Glenn fairings are very large for their weight capacity. New Glenn has 3x the fairing volume compared to the Falcon Heavy, but can throw less mass. So many expected that BO designed it this way because they expected to increase performance of their engines in the future, making the weight/volume ratio of their fairing more balanced.

New Glenn has 45t of capacity now. Increasing thrust by 15% should increase that to 51t, thus making New Glenn 7x2 also just barely a Super Heavy booster. Perhaps they didn't call that out because that would overshadow the 9x4 announcement.

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Falcon Heavy is a huge outlier, and has never actually demonstrated the capability to lift close to its nameplate capacity to LEO. Falcon 9 is already volume constrained to LEO outside of Starlink or Dragon launches, and Starlink is packed incredibly densely to get to that point. When I ran the numbers some time back, New Glenn was similar to Falcon 9.

Increasing thrust by 15% doesn't just increase payload by 15%. I don't know a simpler way to estimate this than to run a simulation, and I don't have one with numbers I can toggle.

The really big change will be launch thrust to weight ratio. Going from ~1.2 to ~1.35 gives you 75% more thrust at launch which means you spend less time fighting gravity, less time in the thick parts of the atmosphere, and less time to get past the trans-sonic region.

There are other constraints on how quick the vehicle should be, even when engine performance allows: you probably won't want to hit maximum dynamic pressure in too-thick air.

> New Glenn has 3x the fairing volume compared to the Falcon Heavy, but can throw less mass.

To be fair, the Falcon Heavy has way too little fairing volume for it's lift capacity (and apparently it is in the process of getting an extra 50% or so?)

I believe that a larger fairing and vertical integration capability for Falcon is in the works as a result of the last round of the National Security Launch Contracts that SpaceX won.

Because the falcon boosters have to be road transportable.

The fairings aren't constrained to the diameter of the booster, they already have a larger diameter than the booster.

The small size of the Falcon Heavy fairing is probably due to the fact that they are the same size as the Falcon fairing, and it was designed when Falcon could throw < 1/2 the mass it can currently throw, let alone the Falcon Heavy.

Theoretically the fairing could be any size, but there is a limit to how much bigger than the rocket it can be.

I'm sure there's a limit, but it's not really that big an effect as you'd think. The fairing is lifted almost entirely by the first stage, and as SpaceX increased confidence in the landings they were able to reduce to fuel margins, leaving move for a heavier fairing. The aerodynamic effects are secondary to the added weight, and are only a really a bother for a few seconds at max q. In fact, the larger volume to surface area makes designing for max q easier in some respects, such as audio energy.

The numbers:

BE-4 is 140 bar chamber pressure vs SpaceX Raptor 2 at 350 bar. Thrust to weight of BE-4 is 80:1 vs Raptor2 at 140:1.

I don't think the capabilities are as different as those numbers imply. I believe that it's due to the conservativeness of Blue Origin and SpaceX's willingness to blow up hundreds of engines on the test stand to iteratively push the margins.

I believe Raptor 2 operates at a lower chamber pressure. According to Wikipedia, Raptor 3 is 350 bar, and its thrust to weight ratio is 183.6:1.

BE-4's chamber pressure is low for its design, but it would be very difficult to increase it to Raptor's levels. Full-flow staged combustion causes the propellants to be gasses when they enter the combustion chamber, and chemical reactions in gasses happen more quickly, allowing for efficient combustion in a smaller combustion chamber. The smaller volume makes it easier to contain higher pressures.

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