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0 pointsJPLeRouzic1mo ago0 comments

Could you tell me more? I suppose a heavy two-stage rocket is not optimized from the point of view of the rocket equation, but I know nothing about this field.

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s1artibartfast1mo ago· 4 in thread

In short, the more stages the better to discard mass once it isnt necessary, and the larger to the better to improve the ratio of (ship+payload) to fuel.

Here is a decent summary.

https://gemini.google.com/share/121466b300c1

kibwen1mo ago

This is only true to an extent. Yes, a larger rocket means a better mass:payload ratio, but a larger rocket also means more mass in absolute terms, and more mass means more fuel, and more fuel means more mass, and more mass means more fuel, and more fuel means more mass, and so on. This is "the tyranny of the rocket equation", and it places an upper bound on the size of rockets that need to carry their own fuel for a given gravity well. And because the larger absolute mass of a larger rocket means more fuel, which means more cost, it relies on actually being able to find enough paying customers to fill out that payload capacity every single time. This is why, for example, despite the existence of jumbo jets (which have a better mass:payload ration than smaller planes), most passenger flights are not on jumbo jets, because there's just not enough demand on most routes.

NetMageSCW1mo ago

No it doesn’t matter if the payload is full or not. If they succeed in full reuse, flying on a mostly empty Starship will be ten times cheaper than flying on an F9 and that means everything will switch eventually.

If a jumbo jet was ten times more efficient than a smaller plane, they would go everywhere. If a giant pickup truck got a 100MPG, why would you take a 30MPG economy sedan anywhere?

murderfs1mo ago

> This is why, for example, despite the existence of jumbo jets (which have a better mass:payload ration than smaller planes), most passenger flights are not on jumbo jets, because there's just not enough demand on most routes.

Airlines used to use a hub and spoke model where it would make sense to have larger planes between hubs and smaller ones to get to and from the hubs, but consumers strongly preferred direct routing, so it didn't work out. For orbital payloads, most payloads probably do not mind too much if it takes a month or more to boost/deboost themselves to their intended orbits.

s1artibartfast1mo ago

You fundamentally misunderstand the implications of the rocket equation. It does not put and upper limit on rocket size for a given gravity. Smaller rockets would not be successful where larger fail.

Due to strucrually efficiency, larger ones suceede where smaller fail due to higher m0/mf ratio

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