10% decrease in fuel consumption would give you the same 10% in payload increase. That includes the orbital stage weight, though. Not just cargo.
I don't see where you are getting 30% from.
I don't see where you are getting 30% from.
That's called hand-waving. How do you get 200%. Show me the numbers that say 200% or something in the ballpark at least. How much drag? How big is the impact of initial velocity? How much does higher initial velocity increase drag? Give me numbers.
Higher altitude launch decrease drag and allows for a higher rate of acceleration.
High end velocity could be as much as 5% of total orbital speed if high altitude lift craft is constructed.
Wings on craft will also reduce fuel consumption.
All of these things both decrease the amount of fuel necessary...but then less fuel means less weight...which then again means less fuel needed, which is again less weight. It snowballs a bit.
I'm pretty sure that you could get 100% increase in payload just from abandoning a vertical ground launch. Throw in all the other factors and I'm fairly confident in the 200% number. As I said, it's ball park, and without an actual craft to begin running numbers on that's the best that can be done.
Maybe you just don't understand what estimate means. It's not a number you make up. It is a number you get from computations using a rough model.
Your "rocket fuel" comment won't fly. Shuttle doesn't use expensive fuels, except for the boosters. It's using LOX/LH2, which is pretty cheap. It is comparable in cost to Jet A, which is what your lifter is using, and if fuel cell tech takes off, it will be cheaper than Jet A. Proposed SSTO craft don't use boosters. So it's just the cost of LH2.
And what do you mean you can't estimate the fuel consumption? You can work out all that stuff for a rocket, but you can't figure out how much Jet A the lifter is going to take up? How about I help you with some base figures?
Take glide ratio to be about 5.
Take efficiency of jet engines to be about 50%. That's pretty generous for the task.
Take thrust/weight to be about 1/2. (That's thrust = half the weight of the lifter).
Take lifter weight to be about equal to orbiter weight.
Look up the energy/weight of Jet A. (Use figures for Kerosene if you can't find Jet A).
Use what you know about glide ratio to figure out how long it will take to climb to 10 miles and then how much fuel would be consumed.
Maybe after running these, you'll have some idea why the proposal for a Shuttle to be launched from a modified 747 sans boosters was scrapped. Boosters turned out to be cheaper.
Take glide ratio to be about 5.
Take efficiency of jet engines to be about 50%. That's pretty generous for the task.
Take thrust/weight to be about 1/2. (That's thrust = half the weight of the lifter).
Take lifter weight to be about equal to orbiter weight.
Look up the energy/weight of Jet A. (Use figures for Kerosene if you can't find Jet A).
Use what you know about glide ratio to figure out how long it will take to climb to 10 miles and then how much fuel would be consumed.
Maybe after running these, you'll have some idea why the proposal for a Shuttle to be launched from a modified 747 sans boosters was scrapped. Boosters turned out to be cheaper.
As for cost...don't forget the recover proceedure for the boosters. A lifter will just fly back and land on the same air strip it left from and can be refueled and take off again within the day. How long does it take to refit boosters? There's more to cost of operation than simple fuel prices.
Also, the cost of fuel to weight of payload increases exponentially the larger the payload you use. There is a limit when the rocket just gets too big to launch. Because of this, air launch will always yield larger payloads than vertical ground launch.
Again, you can't do calculations for a craft that doesn't exist. But you can do a basic logical comparison.
Rocket = lift through 100% thrust.
Air launch = lift through thrust + wings.
Based on this simple principle, winged craft will always require less fuel than rockets...type of fuel and current cost are another matter.
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