Re:Elon Musk’s plan to build one Starship a week and settle ...
by m4rtink on Thursday March 05, 2020 @09:58AM
(#22493995)
It turns out orbital launchers scale rather well with size.
The rocket is already 90+% propellant (fuel & oxydizer), with the few percent left being the engines, structure and payload. So if you want the rocket to have a meaningful payload, it needs to be big.
For example the Falcon 9 weights 350 tons and can place 22 tons to low earth orbit (LEO). So about 6% of initial launcher weight ends up in orbit.
If you want to place the 100+ tons estimated for a reasonable Mars trip, your launcher will be either huge or you will need to do a lot of launches and assemble your ship in orbit with all the overhed that requires.
Starship also aims to be fully reusable, which will eat to your payload yet again but provides a huge benefit of not throwing away any part of your rocket, just burning a lot of propellant, which is dirt cheap compared to rocket hardware (estimates say about 5% of conventional rocket launch is fuel, the less is hardware that you normally simply crash into the ocean after use).
So in short - big payload -> big rocket. Reusable rocket with big payload -> humungous rocket that is really really cheap to operate.
The rocket is already 90+% propellant (fuel & oxydizer), with the few percent left being the engines, structure and payload. So if you want the rocket to have a meaningful payload, it needs to be big.
For example the Falcon 9 weights 350 tons and can place 22 tons to low earth orbit (LEO). So about 6% of initial launcher weight ends up in orbit.
If you want to place the 100+ tons estimated for a reasonable Mars trip, your launcher will be either huge or you will need to do a lot of launches and assemble your ship in orbit with all the overhed that requires.
Starship also aims to be fully reusable, which will eat to your payload yet again but provides a huge benefit of not throwing away any part of your rocket, just burning a lot of propellant, which is dirt cheap compared to rocket hardware (estimates say about 5% of conventional rocket launch is fuel, the less is hardware that you normally simply crash into the ocean after use).
So in short - big payload -> big rocket. Reusable rocket with big payload -> humungous rocket that is really really cheap to operate.