williatw wrote: ↑Thu Oct 15, 2020 3:24 am
First you have to locate the asteroid containing the volatiles you are looking for then cost/time to reach it and setup operations there. After you deplete said asteroids' limited resources you have to locate the the next one and repeat the process. We already know where Saturn & Titan are and would only have to setup operations there once.
That unfortunately is not so straightforward.
While we have a rough idea about Titan composition, but we do not know the exact chemical nature and real composition of the environment where the operation will take place. This includes eventual trace of other chemicals/materials that might influence the extraction/transformation/catalytic process of the end product we need to extract/manufacture.
Like all mining activities we will need to send a prospect team to verify and test the area and the process to be implemented before even evaluating the possibility to set up a full human mission.
The real main limit I see on implementing operations on such a large time scale, is the extreme startup costs, and in the end it might be order of magnitude cheaper to just source them from earth (He3 being the exception, but we still need to prove that there is enough there to be economically mined).
williatw wrote: ↑Thu Oct 15, 2020 3:24 am
Didn't think we were talking about that long of a trip time to Saturn with a modified Z-pinch delivering several thousand seconds SI and high thrust operated in something approaching a "torch-ship" mode. The longer the intended trip the longer the acceleration/deceleration boost phase; nothing close to a linear relationship for ship travel time with distance.
Yes, I already put that into account.
With our actual level of technology an high ISP/high thrust engine design has the trade-off of a huge increase in mass (for energy generation/ancillary equipment) that will generally nullify the extra ISP (or the extra thrust) benefit. Any engine proposed so far that overcome one of these limits is designed with technologies we do not posses yet nor we are anywhere near to posses.
The consequence is a very slow acceleration even in the most optimistic scenario where you can use the engine 24h/365d. To to gain speed will take a very long time, to the point where for short distance travels (say Mars or the asteroids) a chemical rocket is more "time wise" efficient.
The same proposed ZAP engine is a good example of these limits and if you run some calculations (by estimating what could be the thrust duration in a given second) you can see it clearly where my numbers come from.
It is true that we do not have any official number from ZAP about engine repetition rate, but existing technology puts strong limits on the range of those numbers.
The time frame I gave you is in truth a very very optimistic one. In a real application I doubt we will get even near to those numbers due to the limits of ship mass /repetition rate as I mentioned above.
We can open a new thread if you are interested in going through the calculations.
williatw wrote: ↑Thu Oct 15, 2020 3:24 am
A ship (once the facilities were operational) could arrive at the Saturn virtually empty refuel then boost from Titan/Saturn with full tanks of propellant/fuel/cargo. Unlike an Asteroid you wouldn't need to carry fuel/propellant for the round trip to the asteroid and back, or just gamble you can find fuel/propellant as needed on said Asteroid.
Any engine operating on ISP of 370.000 does not have many fuel issues for such a short (distance wise) round trip.
For a 30000 tons ship (say 20000 Tons of infrastructures and 10000 Tons payload) it would take between 1000 and 1600 tons of fuel (depending on engine repetition rate), so is still manageable in respect to total ship mass.
The problem is still the time for the humans onboard.