sevenperforce

As I understand it, there is more readily accessible precursor material on Mars, and the atmospheric shielding and higher gravity make it more hospitable to major operations. If you're going to build a large fuel-mining operation, large enough to need manned support, Mars is a much easier and stabler place to live than trying to survive on the moon or in a space station.

And if we're going with a reusable SSTO design, you can afford to use some more expensive and slightly heavier materials to dissipate heat from compression, especially if you can manage to get your thrust augmentation high enough. Not to mention that re-entry of an SSTO with so many surfaces would be an aerospace engineer's dream. Using atmospheric air seems to be the only way of augmenting thrust and augmentation simultaneously. We already use teh atmosphere as the primary reaction mass for re-entry; why not try to do the same thing for launch as well? Beats trying to coax lift out of a hypersonic vehicle, that's for sure. I'm interested in figuring out the limits of bypass ratio in a central design like this. I can imagine massive ring-shaped engines significantly wider in diameter than their axial thickness....

Simpler is better. As the OP mentioned, colonization of virgin land has almost invariably been associated with the exploitation of a very small number of very valuable resources. Colonization of Mars will make sense when a sustainable market exists for such a resource. As it turns out, there's a market already: fuel. Currently, space missions invariably drag all their fuel along with them because lifting fuel into LEO separately makes no sense. Low Martian orbit, on the other hand, requires only 4.1 km/s of delta-V, and so if you can manufacture fuel on the surface of Mars, you can get it into Martian orbit far more easily than you can get fuel from Earth's surface into LEO. Once the fuel is in orbit, high-efficiency ion thrusters can transfer lots of fuel to LEO at very low cost. An active fuel depot transfer network makes larger space stations and orbiting spaceports feasible, and missions which require high thrust (e.g., manned missions) can pick up fuel at an orbiting depot, vastly driving down the overhead for launch itself. For example, if you want to plan a manned mission to virtually anywhere in the solar system, would you rather design and build a really, really, really ridiculously big rocket to carry all your fuel up at once, discarding entire stages as you go, or simply launch your crew and craft up to LEO and then purchase a couple of fuel tanks from a depot? Of course, most of this process would be automated by robots (definitely the transfer from Martian orbit to LEO), but you'd probably need a human presence on Mars to assure reliability and fix the inevitable problems that would arise.

First post here; joined to discuss rocket designs, SSTO, and reusability. Air-augmented rockets (also known as ejector jets or ducted rockets) are a sort of cross between turbofan jet engines, ramjets, and pure rockets. Ramjets depend on a ram-compressed flow of atmospheric air for combustion, making them useless for launch and for orbital insertion. An air-augmented rocket uses a stream of atmospheric air only as added reaction mass, greatly increasing specific impulse in a fashion similar to a turbofan bypass. They can afford to use fuels with greater energy density, because so much of the reaction mass is external. Best of all, because their core is more or less an ordinary rocket, they have no problem functioning from a standstill or in a vacuum. (For reference, there was a prior forum post on air-augmented rockets here, though it didn't go into many details.) The most efficient turbofan engines are built with extremely high bypass ratios, exceeding 10 kg of bypass air for every 1 kg of airflow through the central turbojet. Of course, the primary difference between a turbofan and an air-augmented rocket is that the power is delivered to the air mechanically in the former case, but thermally in the latter case. Air-augmented rockets have not historically been very successful. In most cases, adding a shroud around the outside of an existing rocket was a large weight cost in exchange for only a modest increase in thrust specific fuel consumption, and because they weren't optimized for using the air as reaction mass, most of the added thrust was the result of secondary combustion between the fuel-rich rocket exhaust and the atmospheric air, making them essentially very inefficient ramjets. If, however, an air-augmented rocket engine were designed in an inside-out configuration with a central bypass rather than an external bypass, you'd end up with a much simpler, more compact, potentially much more efficient design: Such a design could allow a really, really high bypass ratio, causing thrust specific fuel consumption to drop ridiculously low. The combination of really high thrust and really high specific impulse is pretty nice. I wonder whether this could be made large enough that the thrust augmentation more than overcomes additional drag. Thoughts?