Quote:
Originally Posted by michaellxv
Lifting to L.E.O. and travelling around space are 2 different problems and would be best served by specific solutions.
Comercial projects like Virgin Galactic will be able to take care of the L.E.O lifting.
Dedicated Space vehicles can shuttle back and forth between Earth and Moon. Being permanently in space and only needing to be lifted once they won't be limited in design to fitting inside the nose cone of a traditional rocket.
Ideally this vehicle would be capable of landing on the moon without the need for a separate lunar landing vehicle.
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I agree that private entities, not just government agencies, would be needed for successful space travel in the future.
A dedicated spacecraft would still require servicing and repairs. There's no way you could do intermediate or depot level maintenance in orbit; so they've got to come down at some point and that would depend upon the servicing cycle (number of operational hours versus reliability). This would mean re-entry, and that means specific design philosophy (heat shields and aerodynamic concerns), which of course means additional weight.
The contest to find the 'Mode' of landing on the moon (Lunar Orbit Rendezvous or Direct Assent) and returning to the Earth by using a single vehicle or two dedicated vehicles was fought and won back in the late 50's. In the end, the design physics called for both Lunar Orbit Rendezvous and Earth Orbit Rendezvous.
It all comes back to a very simple physics principle; for every kilo of additional mass you take to the lunar surface and bring back to Lunar Orbit, add 5 kilos of propellant. Add 6-7 kilos of propellant if you want it to come back to Earth Orbit (these figures do not include the initial lift to Earth orbit, which becomes extreme). So if the combined vehicles' dry-weight is 20% greater, then the all-up weight will be double that of a combined two vehicle solution. There's not much chance of using a single 'multitask' vehicle; it becomes too massive to do the job, and additional mass means extensive trade-offs in payload. I haven't introduced additional structural mass or larger power-plant for a single vehicle, but that would have to increase the single vehicle design by at least 40-50%, not a mere 20%.
If it were possible to construct a single vehicle, which traveled from Earth Orbit to the surface of the moon and returned to Earth Orbit, and that it was a mere 20% heavier, would require a Booster Rocket on the launch pad at least twice the size of the Saturn V.
I didn't want to introduce Mars, but just to give you an idea of the complexity and real world contingency plans that would be required, I wouldn't be surprised if going to another planet in our system called for at least 6 separate unmanned service vehicles to make the journey first. The construction of an orbital station, at least two Mars escape vehicles on the planet itself and two habitat stations. Then there's fuel, water and food depots, a maintenance workshop, vehicles for mobility, a medical surgery...the list is endless!
The reality of space travel becomes apparent when you realise that every single leg of the journey requires a dedicated, specifically designed technology, and then that technology must fit-in with the whole design...so a vehicle that lands on Mars cannot land on Titan or even our own moon.