My understanding is that rockets are good at getting a small mass to move really quickly. They will never win moving a lot of mass within the atmosphere. The fuel costs are radically different.
A 747 can lift and land ~80% of Starship's design cargo but uses something like 7 times less fuel.
Elon thinking is that on long distance flight you increase moved cargo per vehicle per unit of time.
He was saying that flying to the other end of the world will be 20x faster vs. airplane.
So if you move 20x more cargo per unit of time, then cost of cargo per vehicle + static infrastructure are proportionally lower.
But we need to take into account that number of cycles of a rocket engine may not be as good as jet engines, ground / water infrastructure seems a lot more complicated, fuel costs are higher etc. etc.
I doubt the math will close on it taking everything into account, but maybe there will be some limited use cases. USA army seems to be thinking about it. Extremely rapid deployment capability all around the world may be worthwhile for them.
Yeah, I've kept a close but unfortunately deeply skeptical eye on that technology. Seems that all the tolerances are razor thin and all the failure modes catastrophic. Like, water vapour in the pre-cooler tubes? This is waaay out there in engineering terms IMHO.
Reading the recent heat exchanger news [1] the are very careful to talk about Mach 5 airflow temperatures, not velocity. Surely it the product of these two that produce the mind-boggling heat flux that the pre-cooler is tasked with cooling. It feels like they're going to keep carving out smaller and smaller targets until they run out of money.
If you look at the cost the calculated originally for the Skylon, it doesn't actually beat Falcon 9 even.
And when I listened to some presentation with the people involved, it seem they had no real understanding of some of the complexity involved. Their history is mostly in academic and British space industry, and all the project they worked on before are canceled paper studies that were kicked around in Britain.
When asked about the structure of Skylon the answer was vague hand waving about some new materials that might exist. Nothing at all concrete that has even begun being tested for high complexity air frames and high requirements.
Elon himself was asked about this when he presented in Britain. And he answered by saying that investing massive amount of complexity in the easiest part of your flight was counter productive.
Pushing the thrust of your traditional rocket engine a little bit higher, is far, far easier then engines.
And if you are really optimizing to that kind of extreme, doing even more advanced version of second stage engines and structural optimization on the second stage would likely always have a higher pay off per complexity invested.
SpaceX vs Skylon/Sabre, feels a bit like the Henry Ford quote about "faster horses". I do appreciate the scale of the engineering problems and neither is easy, but SpaceX and rocketry just seems like another "faster horse", whereas Skylon/Sabre is something totally new. But I don't have much hope given how long it's taken to get to where we are now. It's the space equivalent of tech - get to market first with something that works, not something that's a tech tour-de-force.
https://en.m.wikipedia.org/wiki/Thrust-specific_fuel_consump...
My understanding is that rockets are good at getting a small mass to move really quickly. They will never win moving a lot of mass within the atmosphere. The fuel costs are radically different.
A 747 can lift and land ~80% of Starship's design cargo but uses something like 7 times less fuel.