DFM
I suggest that you give up the "Space Elevator" fantasy.
Mon Dec 4, 2017 4:47pm
162.192.201.157

It will never happen. I think that it is probably physically impossible let alone practically impossible.

The "Royal Road to Space" is with the air-breathing "Space Plane" with ramjet for as high as feasible, and modest sized rocket for the rest. Recall that low Earth orbital speed is about 8km/sec, but there is an additional delta V required to get up that high so the real delta V needed is about 9.4 km/sec.

Also remember the Tsiolkovsky Rocket equation:
Here
E = empty weight of rocket
F = full weight of rocket
V = exhaust velocity
U = final velocity, in case of low Earth orbit, U = 9.4 km/sec.
U/V = exp(F/E)

VH = exhaust velocity of hydrogen + oxygen = 4.6 km/sec. Hydrogen is very bulky, so I will omit it below.

VK = exhaust velocity of liquid hydrocarbon (kerosene) + oxygen = 3.4 km/sec.

Here are some sample numbers just to give you a feel.

Payload is, in all cases, 100 tonnes.

Ramjet Speed km/sec Remaining Boost Exhaust Velocity 3.4 Empty Weight Full Weight Fuel Weight Full Weight Relative
to No Ramjet Percent
0 9.4 3.4 283 4492 4,209 100
1 8.4 3.4 257 3,043 2,786 68
2 7.4 3.4 234 2,061 1,828 46
3 6.4 3.4 213 1,396 1,184 31
4 5.4 3.4 193 946 753 21
5 4.4 3.4 176 641 465 14
6 3.4 3.4 160 434 274 10
7 2.4 3.4 145 294 149 7
8 1.4 3.4 132 199 67 4
9 0.4 3.4 120 135 15 3


The effect of the ramjet boost on the size of the rocket is overwhelming.
At ramjet boost of 3 km/sec (which HAS been achieved) the rocket weights only 31% of the no-boost weight.
At ramjet boost of 5 km/sec (which HAS been achieved) the rocket weights only 14% of the no-boost weight.
At ramjet boost of 7 km/sec (which HAS been achieved) the rocket weights only 7% of the no-boost weight.
At ramjet boost of 8 km/sec (which HAS been achieved) the rocket weights only 4% of the no-boost weight.
At ramjet boost of 9 km/sec (which HAS been achieved) the rocket weights only 3% of the no-boost weight.

In plain language:
Ramjet boost of 7km/sec permits a rocket with payload of 100 tonnes to weigh only 294 tonnes.
Ramjet boost of 8km/sec permits a rocket with payload of 100 tonnes to weigh only 199 tonnes.
Ramjet boost of 9km/sec permits a rocket with payload of 100 tonnes to weigh only 135 tonnes.

A rocket carrying 100 tonnes payload to low Earth orbit that weighs only 135 tonnes is positively TINY.
It is also inexpensive, particularly if it can be reused with short overhaul period.

DFM

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    • I suggest that you give up the "Space Elevator" fantasy. — DFM, Mon Dec 4 4:47pm
      • Why do you think I'm focusing on itEx-News Junkie, Mon Dec 4 5:10pm
        Because I KNOW it won't be done by anyone alive today. Which leaves it wide open.
        • It won't be done by anybody EVER. (nm)DFM, Tue Dec 5 4:28pm
          • e the idea of a space elevator. Rockets carrying an handful of astronauts will play a small role in the future I envision, but generally they will be obsolete.
            • Space Elevator cannot possibly be made to work. DFM
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      • Whoops.DFM, Mon Dec 4 4:51pm
        I wrote "(which HAS been achieved)" too many times. It should only be at 3km/sec. Higher speeds have NOT yet been achieved, or at least not published. DFM
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