MCT seems to be about reducing cost by taking advantage of low launch costs to use a simple chemical based architecture. SEP adds complexity, vehicle cost and operational difficulties to reduce IMLEO - which is exactly the one thing you don't need to optimise for if you have cheap launch.
Because brute-force "abundant chemical" architectures with fully reusable super-heavy-lift launchers carrying "cheap propellant" would apparently make SEP look complex, expensive, and obsolete by comparison.MikeAtkinson:QuoteMCT seems to be about reducing cost by taking advantage of low launch costs to use a simple chemical based architecture. SEP adds complexity, vehicle cost and operational difficulties to reduce IMLEO - which is exactly the one thing you don't need to optimise for if you have cheap launch.
High power SEP is more or less required for large scale colonization of the asteroid belt and/or mercury. For Mars, it allows transport to Mars outside of the very limited launch windows that chemical is subject to, and with good enough solar arrays it can reduce travel times relative to chemical.The BFR does not reduce the viability of electric propulsion at all. It just increases our presence in space, which is strictly beneficial for the development of pure in-space propulsion. The complexity argument is mostly unwarranted because SEP is a much simpler technology than your typical staged combustion chemical engine, with space storable propulsion and practically no moving parts.
Quote from: Nilof on 01/09/2018 11:49 pmHigh power SEP is more or less required for large scale colonization of the asteroid belt and/or mercury. For Mars, it allows transport to Mars outside of the very limited launch windows that chemical is subject to, and with good enough solar arrays it can reduce travel times relative to chemical.The BFR does not reduce the viability of electric propulsion at all. It just increases our presence in space, which is strictly beneficial for the development of pure in-space propulsion. The complexity argument is mostly unwarranted because SEP is a much simpler technology than your typical staged combustion chemical engine, with space storable propulsion and practically no moving parts.SEP requires very large steerable solar arrays with complex electrical conduits from arrays to some sort of storage system then to the engines. Somehow don't see a direct feed of electricity from the arrays to the engines. Also you need a cooling system for the waste heat from the solar arrays. So high power SEP is not simple or non-complex, therefore not cheap.Don't see high power SEP entering service in the near to mid time frame. However maybe nuclear electric propulsion will be economical beyond Jupiter's orbit and away from the propellant depot network.
Does shipping still have a future? (If airplanes are successful?)Oceanliners are pretty much a thing of the past since the invention of winged machines that go over 10 times faster. However, a gargantuan amount of the worlds trade is still conducted with far slower vessels over the world's waters. I fully expect a similar dynamic to develop for human expansion into the solar system. Bulk cargo being hauled by slow but efficient umanned craft, people being sent by faster and pricier means.Although propellant is a small part of the cost of launch today, in any large settlement effort it would rapidly become a large portion of the costs of the endeavour. Fuel costs put enormous strain on "rapidly reusable" airliners today even though jet fuel is relatively cheap and the oxidizer is free, courtesy of the atmosphere. More efficient ways to use the same amount of resources will always have a future.
Quote from: Zed_Noir on 01/10/2018 12:22 amSEP requires very large steerable solar arrays with complex electrical conduits from arrays to some sort of storage system then to the engines. Somehow don't see a direct feed of electricity from the arrays to the engines. Also you need a cooling system for the waste heat from the solar arrays. So high power SEP is not simple or non-complex, therefore not cheap.Don't see high power SEP entering service in the near to mid time frame. However maybe nuclear electric propulsion will be economical beyond Jupiter's orbit and away from the propellant depot network.You don't need to actively cool solar arrays, that is the weirdest thing that I have ever heard of. They radiate heat passively. Large chemical engines on the other hand may need hundreds of megawatts of active cooling to prevent their combustion chamber from melting.
SEP requires very large steerable solar arrays with complex electrical conduits from arrays to some sort of storage system then to the engines. Somehow don't see a direct feed of electricity from the arrays to the engines. Also you need a cooling system for the waste heat from the solar arrays. So high power SEP is not simple or non-complex, therefore not cheap.Don't see high power SEP entering service in the near to mid time frame. However maybe nuclear electric propulsion will be economical beyond Jupiter's orbit and away from the propellant depot network.
Electric propulsion has a bright future in the form on powering launch loops and orbital rings. The economy just needs to get to the point where BFR is not enough.
SEP only will make sense if commodity transport to LEO/EML-1/2 is never realized, or if 'N'uclear becomes the power supply for the 'EP'. BUT the OP isn't about NEP...
Because brute-force "abundant chemical" architectures with fully reusable super-heavy-lift launchers carrying "cheap propellant" would apparently make SEP look complex, expensive, and obsolete by comparison.
Another one is solar sails driven by lasers from larger solar satellite. Forgot name of project buts one that wants to send nano size probes interstellar. Same concept can work for larger payloads at slower speeds, if driven by 100MW-GW significant payloads can be sent between earth and moon.This could be one way to build larger GEO space solar power satellites for beaming power to earth. The same satellites can use some of there power for delivering cargo to GEO to build more. The vehicles can be very simple, large sail, cargo container, avoinics and some cold gas thrusters. As vehicle spirals out, GEO SSPS spaced around earth take turns boosting it.
This is not really true. Since something like 75% of what is delivered to orbit is fuel, 75% of the cost of launch is 'fuel' cost (plus the few $100k to buy the fuel itself). This is the argument for SEP... don't have to bring as much fuel to orbit when launching a fully fueled spacecraft. The counter argument is that bulk commodity deliveries of fuel to orbit could become very inexpensive... in that case, launch the spacecraft dry, and fuel it on orbit. This gets you a factor of a few more spacecraft for the launch costs.
Quote from: AncientU on 01/10/2018 12:29 pmThis is not really true. Since something like 75% of what is delivered to orbit is fuel, 75% of the cost of launch is 'fuel' cost (plus the few $100k to buy the fuel itself). This is the argument for SEP... don't have to bring as much fuel to orbit when launching a fully fueled spacecraft. The counter argument is that bulk commodity deliveries of fuel to orbit could become very inexpensive... in that case, launch the spacecraft dry, and fuel it on orbit. This gets you a factor of a few more spacecraft for the launch costs.There are more costs than just launching propellant propellant. A trip to Mars would tie up an BFR craft for years. If another type of craft did the trip say SEP then the BFR could focus on generating more revenue via Earth launches. The BFR would deliver an bulk delivery of propellant to orbit it just would be propellant for SEP. In addition on Mars the ISRU could just produce enough propellant to move things to Mars Orbit instead of to escape and Earth landing. For Space X however attempting to develop SEP for MARS would be a bad idea and abundant chemical is probably the best idea for an initial landing. However given enough development and demand SEP could find a use as the colony grows. It would depend on the economics of how much the SEP costs, how many trips could it do and how much does maintenance cost.