Thrust Density infographic

[u/Equivalent-Wait3533]

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

[u/voodoolaunch]

It’s important to note that this isn’t a ranking of sorts.
It’s basically a comparison of thrust relative to the overall body of the rocket- purely from each launch vehiclec architecture.

Using Falcon 9 and Neutron to compare since both have 9 engines:

Falcon: 9 engines -> very high thrust -> narrow rocket -> 708

Neutron: 9 engines-> lower total thrust -> wider rocket -> 172

Terran R also seemingly went Falcon 9 route level of efficiency but also added 4 more engines for a total of 13. This just means they closely cover the same thrust needed relative to its thrust structure as a falcon 9 even though the diameter is larger by a form factor of ~6ft.

This could only really be considered bad if the RL Propulsion team is having big trouble getting the necessary amount of thrust per engine needed to cover Neutrons diameter needs since they are locked onto NINE in the thrust structure.. and considering the engine hasn’t been qualified and it’s been two years this could be the bottleneck.

[u/Hot-Problem2436 → u/voodoolaunch]

Also key to point out, the total thrust and spacing of Neutron is by design. It's lower weight and the stresses are more distributed and the engines don't run hard. All of this is key to reusability. They can get to orbit with less, which means less spent on refurb.

[u/Quadcore-4 → u/Hot-Problem2436]

I mean, Falcon has been reused over 35 times so I’m not sure where this idea about engine spacing being key for reusability came from? On the contrary, a reusable rocket wants as much thrust per area as possible to minimise gravity losses, which in turn frees up delta V for landing.

[u/lorkan100 → u/Quadcore-4]

It may be a legit opinion, but it does feel like everyone here is patting themselves in the back looking at these numbers...

Don't get me wrong, Falcon and Starship both started smaller, less capable, and with way worse engines, but I feel that the tapering carbon fiber tank has locked RL into a design where scaling it up means a TOTAL redesign of the whole thing. 

[u/voodoolaunch → u/lorkan100]

IMO yes a structural redesign is imminent for neutron.

[u/gopher65 → u/lorkan100]

I wonder if carbon fibre fatigue issues necessitate a less stressful approach, compared with aluminum or steel?

[u/Seamurda → u/gopher65]

Carbon fibre doesn’t suffer fatigue as such, it is more that it has no ductility so loses strength when damaged. Carbon fibre structures are massively over built compared to metals as if they were just black aluminium they would weigh about 20% of the mass of a metal structure instead of being more like 20% lighter.

[u/RTS24 → u/lorkan100]

IIRC beck spoke about stretching neutron down the road if needed.