The benefit is for satellite launches, the increased performance allows for launching heavier satellites.
It's highly debatable if there is a higher risk to human life as well - unlike with rockets where you fuel up before the astronauts board, you don't have people approaching a fueled up rocket which could explode with no possibility of escape. Instead if there is a issue while fueling up, the astronauts are in a capsule with a escape system which should pull them safely away from the rocket if there is a problem.
My understanding is it effectively reduces launch costs by ~25% by getting ~30% more mass to LEO. Really if it increases risks of failure by less than 10% it's probably worth it for unmanned rockets.
PS: High launch costs set up a cost escalation as satellites are so expencive they can't fail. Which means launches need a really high success rate. If you could get 10,000kg to LEO for say 1 million but had a 40% failure rate you would see a very different approach with much lower overall costs.
In addition you are more mission-flexible with the weight expended for fuel. It can be used to either soft land the stage, or give extra boost to a GEO mission or a heavier payload.
Another benefit of larger rockets is the width of the components they can carry. I'm no expert, but larger spacecraft modules seem like a big win for long duration missions.
To me having a particularly heavy rocket to be man-rated is like stepping into Shuttle problems again. That is, trying to make a system both very safe and having a large mass payloads.
Why to have a larger than necessary rocket, which has additional problems with just getting stuff to orbit - FH is more complex than F9 - to carry humans, who requires extra care?
Much better, from the point of safety, is to have a moderate-sized launcher human rated and specializing in bringing humans safely to orbit. After that it's much safer to use whatever means of travel are brought to space by any other launchers, those with focus on economy and less on safety.
A counterargument is usually a variation of "it's very expensive", but that's just, roughly, because human life is valued cheap enough to allow for suboptimal choices.
My guess, and I'm sure someone more knowledgable will chime in, would be efficiencibutton a larger rocket/lift capability-
Defintely with the current 'throwaway' model, where whole rocket costs are ~95%+ cf. fuel; but I believe even with re-usable rockets (as they are aiming for) you have significant cost advantage per kg (or pound if you prefer) from a larger rocket.
So, as I see it, less cost, less launches, less messy construction (larger modules/however the beast turns out)
Exactly. Another way to say this is that this launch requires less Delta V. It's completely different than getting cheaper fuel of the same mass (which would be trivial).
You can run the first stage longer without any extra second stage fuel. Adding performance to either one (within limits) increases the performance of the system. Using the landing fuel for a launch would allow for a heavier payload without changing the second stage. The first stage would do more of the total work.
They have the significant advantage that they get pretty much free mass before the fairing opens (since more mass reduces drag and they aren't fighting the rocket equation until they are out of the atmosphere). As such they can do things like heavily brace the inside of the nozzle without it hurting their payload capacity.
And TSTO has some very practical advantages. The mass ratios of the stages are much less constrained, the payload mass is less sensitive to overrunning the mass budget, and most of the mass of the launcher is recovered at much lower speed, making handling entry much easier. The first stage does have to be returned to the launch site but that's not a terribly hard problem.
My layman’s understanding is that doubling the payload quadruples the fuel requirement. So it is much more efficient to launch multiple rockets with a small amount of fuel than one big one with all the fuel you need. It’s the difference between O(n) and O(n^2).
I understand the whole point of this is that the rocket equation, assuming as it does that you'll be carrying all the fuel you need with you right from the start, doesn't apply until you get to about 28 km up, and once you get to that point you're not starting from zero speed; you're starting at about mach 5.
Anyway, on the the answer to your question. The projected outcome is that the cost per KG of payload into orbit is less. So that's why. Because it will be cheaper.
In case something doesn't work as efficiently as possible. Since these rockets are not specialty designed for each launch you only save a very tiny amount of money/weight by not filling it all the way up.
It's highly debatable if there is a higher risk to human life as well - unlike with rockets where you fuel up before the astronauts board, you don't have people approaching a fueled up rocket which could explode with no possibility of escape. Instead if there is a issue while fueling up, the astronauts are in a capsule with a escape system which should pull them safely away from the rocket if there is a problem.
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