Do you dispute my reasoning, or numbers?The reasoning is sound. You pay more for an SEP vehicle. To make that worth it you have to reuse it. That's possible in Earth space where like a boomerang it comes back to you in 6 months or so. Then you get multiple reuses. When you send it to Mars, even if you can get it back, it will take so long that you only get a small number of reuses before its old.
1) a regular hydrolox upper stage2) The difference between a throw away falcon heavy and a fully reusable one is the cost halving you seek3) See 2)Do you dispute my reasoning, or numbers?The reasoning is sound. You pay more for an SEP vehicle. To make that worth it you have to reuse it. That's possible in Earth space where like a boomerang it comes back to you in 6 months or so. Then you get multiple reuses. When you send it to Mars, even if you can get it back, it will take so long that you only get a small number of reuses before its old.
Yes, my numbers dispute your numbers, because mine are based on actual research and quoted prices, rather then numbers that are hand-waved into existence. I using the most obsolete Russian JUNK imaginable and your highly optimistic launch prices they show plenty of room for SEP to be cost effective.
I certainly got a giggle from the logic that says that this TV set costs $100 therefore I can't believe that in a few years it will only cost $50.Also suspiciously absent is any attempt to argue why launch costs cannot fall given reusability or indeed why reusability cannot happen.It'll get better over time. It'll get cheaper with volume. Ok, I believe you but the same still applies to chemical rockets.And the nay sayers merely responded with exactly the same anecdotal evidence without ever really questioning what is the fundamental "materials and energy" cost of building a rocket. It boils down to a few millions of dollars, with volume. That's all I have to say on the matter.And explain to me why sending SEP vehicles off on years-long missions where they will only get reused a few times if at all, makes economic sense.
And my logic still applies. SEP isn't economic if it costs billions and you don't get enough reuse out of it. I've yet to see anyone even acknowledge that the number of times you reuse a SEP vehicle is what makes or breaks it economically. Instead you get the exact same arguments. It'll get better over time. It'll get cheaper with volume. Ok, I believe you but the same still applies to chemical rockets.
Within a SEP tug the solar panels decay in the high radiation environment of space. So assume a 10-15 year lifetime. For a 2 year trip to Mars and 2 years back this means the SEP could make approximately15 / (2 + 2) = 3.75 tripsA 0.75 trip means it could get to Mars but not return. The lower power output and wear out of the thrusters may reduce the viable payload on the last trip.The tug would need refuelling each trip. To improve reliability it may be better to replace the electronics in the guidance system and sensors each trip, fortunately microprocessors and cameras are not expensive.
Quote from: Russel on 07/11/2015 01:03 pmAnd my logic still applies. SEP isn't economic if it costs billions and you don't get enough reuse out of it. I've yet to see anyone even acknowledge that the number of times you reuse a SEP vehicle is what makes or breaks it economically. Instead you get the exact same arguments. It'll get better over time. It'll get cheaper with volume. Ok, I believe you but the same still applies to chemical rockets.When you just pull "Billions" out of the air as a price for what your opposing you can claim anything is too expensive. But I've done the actual MATH that shows your cross-over is at 3.8 Billion using present launch costs and is still half a billion at best case future launch costs. And that is with disposable usage, reuse would raise the cross-over point even higher.What makes your argument bogus is that your assuming EVERY possible technology advancement, volume production improvement and new vehicle development in launch vehicles while assuming nothing for SEP. The anticipated launch cost reductions are going to come from SpaceX, but we KNOW they are about to become a manufacturer of satellites (using SEP) using assembly line production, so it makes no sense to claim incredible cost saving will come ONLY in launch costs when SpaceX is clearly going to be trying to drive both costs down.You don't have any idea what a large volume production of SEP vehicles would cost, no one here can do anything other then estimate. Half of a SEP stage would generally be propellents, Xe is going to be phased out rapidly in preference for Kr which is $300 kg. The rest of the SEP stage is solar-panels, electronic and thrusters which is basically the same kind of stuff a modern satellite is made of. So based on the earlier comparison we would be looking at 62 mT each of propellents and hardware, the propellents would come to $18.75 Million, the hardware I'll compare with a well produced satellite Iridium which uses an assembly line process to get their costs down to 5 million each, the mass is 1500 pounds. This would yield a hardware cost of ~460 million. And thus a total cost of approximately 490 million, right at the cut off price of the optimistic launch cost estimate.
I would also like to reiterate that there is a very big difference between the economics of SEP for Earth-space use which can be reused many times, and doing the same thing on round trips to Mars.
Quote from: A_M_Swallow on 07/11/2015 11:07 pmWithin a SEP tug the solar panels decay in the high radiation environment of space. So assume a 10-15 year lifetime. For a 2 year trip to Mars and 2 years back this means the SEP could make approximately15 / (2 + 2) = 3.75 tripsA 0.75 trip means it could get to Mars but not return. The lower power output and wear out of the thrusters may reduce the viable payload on the last trip.The tug would need refuelling each trip. To improve reliability it may be better to replace the electronics in the guidance system and sensors each trip, fortunately microprocessors and cameras are not expensive.Thanks for writing this. What it says is that the SEP vehicle has to be no more than 3 times the cost of the equivalent tonnage of EUSs that it would replace.
Satellites can afford to fail because they are unmanned.
The moment you consider using SEP for manned flights it has to go through the same level of assurance and testing as any chemical stage. There's your billions of dollars of development folks.
I would also like to reiterate that there is a very big difference between the economics of SEP for Earth-space use which can be reused many times, and doing the same thing on round trips to Mars.I am considering SEP but only for Earth space and only for unmanned flights.
Quote from: A_M_Swallow on 07/11/2015 11:07 pmWithin a SEP tug the solar panels decay in the high radiation environment of space. So assume a 10-15 year lifetime. For a 2 year trip to Mars and 2 years back this means the SEP could make approximately15 / (2 + 2) = 3.75 tripsA 0.75 trip means it could get to Mars but not return. The lower power output and wear out of the thrusters may reduce the viable payload on the last trip.The tug would need refueling each trip. To improve reliability it may be better to replace the electronics in the guidance system and sensors each trip, fortunately microprocessors and cameras are not expensive.Thanks for writing this. What it says is that the SEP vehicle has to be no more than 3 times the cost of the equivalent tonnage of EUSs that it would replace.
Within a SEP tug the solar panels decay in the high radiation environment of space. So assume a 10-15 year lifetime. For a 2 year trip to Mars and 2 years back this means the SEP could make approximately15 / (2 + 2) = 3.75 tripsA 0.75 trip means it could get to Mars but not return. The lower power output and wear out of the thrusters may reduce the viable payload on the last trip.The tug would need refueling each trip. To improve reliability it may be better to replace the electronics in the guidance system and sensors each trip, fortunately microprocessors and cameras are not expensive.
Completely obsolete assumptions. Amorphous silicon solar panels (which are what we would use in thin-film type panels) do not suffer significant performance loss from radiation because of an annealing effect that essentially heals the damage from radiation.
So Argon could easily be produced on Mars, as could solar panels, lets presume that SEP craft can be refurbished at Mars.
Quote from: nadreck on 07/12/2015 04:35 pmSo Argon could easily be produced on Mars, as could solar panels, lets presume that SEP craft can be refurbished at Mars.While Argon propellents are a viable means to re-fill a SEP vehicle when in Mars orbit, I see no need for manufactured components like solar-panels to be replaced at Mars. The vehicle is constantly transiting between Earth and Mars so it can receive maintenance at Earth with the exact same impact on schedule.If solar-panels could be manufactured on Mars (and I am highly skeptical of that), the proper use would be to employ them on Mars surface for power needs, not taking them to orbit to place on a vehicle going back to Earth. The cost of sending anything to Mars and setting up manufacturing their are so high that all outputs need to serve local needs.
I expect that the cost of solar panels made on Mars would be much cheaper in Mars orbit than ones made on Earth in Earth orbit.
Quote from: nadreck on 07/13/2015 05:05 amI expect that the cost of solar panels made on Mars would be much cheaper in Mars orbit than ones made on Earth in Earth orbit.This is quite impossible. If you have some notion that the lower DeltaV to Mars orbit some how compensates for incredible difficulty of manufacturing on the surface you are off by orders of magnitude.This is not going to BE any manufacturing on Mars until Earth launch costs are on the scale of $100 kg, nothing on Mars could compete with that because manufacturing requires massive infrastructure, solar panels on Earth are only the cost they are now because this giant factory called ASIA is being used to make them.
They are still going to be cheaper to make on Mars than to import in the volume needed, at that point the manufacturing facility to make them will be a sunk cost, so the incremental cost to make them and ship them to Earth will be what competes with Earth manufactured ones sent up from Earth. The craft have to come back from Mars virtually empty, why not have them carry a cargo that can be used in LEO. Argon and solar panels would be good candidate exports.