I tried calculating this, but it gets too complicated.
Assume, we have a Moon orbit station and ISS on Earth orbit. We have a Moon base. We want to send a tourist for a week on the Moon and back. We need to launch only the oxygen/fuel cells and the fuel for trans-lunar and trans-earth injection.
The lunar lander lands and takes off in one piece (we don't need a pile of used stages on the lunar base). It can be lighter than 10 metric tons of Apollo LEM. Fuel cells (200 kg each) may go, because now we have solar panels.
So, how low can we get with newer technologies? And the main question, how small can the launch weight be? Is this doable with conventional Soyuz or Proton rocket?
Assume, we might have a coilgun to do trans-Earth injection right from the lunar surface. Delta-v of 2.7 km/s means 90 km of rail and accelerating @ 5g, if I remember my calculations correctly.
Some data from Wikipedia:
- Apollo Lunar Module
- Ascent stage 4,547 kg of which 2,353 kg is propellant
- Descent stage: 10,149 kg (8,200 kg of propellant for 2,500 m/s delta-v)
- Command and Service module
- command module 5,809 kg
- service module 24,523 kg
all together 46,980 kg
- Saturn V
- 1st stage with fuel: 2,300,000 kg
- 2nd stage: 480,000 kg
- 3rd stage: 120,800 kg
The third stage fired only partially (165 + 335 seconds) to get to LEO, and then was used for TLI.
So, 120 tons were sent to LEO, and only 47 tons left after TLI. How low can the latter get?
The lunar module will be orbiting the Moon and reused. This means several tonnes less for TLI and Lunar orbit injection. But the fuel for it has to fly from Earth.
If CM gets smaller, this can also make the vehicle lighter.
Service module can be reduced by using inflatable materials, and it can be reused and stored at ISS. So we save 25 tons x 9 km/s (launch from Earth), but add 3km/s of delta-v to park it after the way back.
So, all together, we need to launch
- the Earth landing module (CM analog)
- fuel for
- lunar landing and takeoff
- fuel to park SM in LEO
If coilgun is used, we don't need takeoff and TEI fuel. (Hm... we need to launch the SM back too :)
How much does this weigh?