shynung

dV requirement is not reduced. Propellant requirement is reduced, because rather than dV-ing an entire habitation module into transfer orbit, one would simply dV a small capsule carrying only crew and supplies, without the actual hab module itself (which is presumed to be lighter). At the destination, the capsule aerobrakes or otherwise decelerates itself to enter the planet's orbit, while the cycler continues on to intercept the planet-of-origin again. The tractor beam would pull the cycler towards the capsule as it closes in. In order to keep itself on the same trajectory, it would have to expend propellant. There's no other way around that. A much easier, and simpler way is to keep the cycler where it is (as in, don't pull/push other things with tractor beam, or fire the engines), and have the capsule do the final approach on RCS. In a scifi setting, using arcjet thrusters as RCS blocks wouldn't seem out of place.

Uh, the capsule's main engines? Because, like, that's how orbital rendezvouses are done; accelerate to target, match trajectory, and bleed off relative velocity as the capsule gets closer.

Ah, I see. Too bad most politicians aren't scientifically passionate. Or literate. It's not entirely unreasonable; there's a WIP less-lethal weapon system developed by the US military, the Active Denial System, that works on the same principle, though on a different frequency. That, combined with the fact that the microwaves are powerful enough to lift rockets into orbit (in the scale of megawatts) would make them politically dangerous to develop; it'd be just as useful as a propulsion system as it is as a directed-energy weapon. Imagine if one of them accidentally swiped at a passing airliner... I think it'll be cheaper when technology demonstrators have been fired/flown, mass-produced, and after many spaceports have gyrotrons installed, launching microwave thermal rockets regularly. Until then, I suppose we can only wait. Great, some progress. I hope they succeed in whatever they end up doing.

A few dozen m/s would be expensive propellant-wise if the hab module has a low specific impulse engine and is pretty massive. Of course, we can always slap engines like VASIMR on it. Really? Then why haven't I seen news of any organization attempting to make a serviceable version? If the tech is as simple as you described, why has no one attempted to make pre-production prototypes, like what Ad Astra is doing with VASIMR?

Trust me, he knows. And he's right in one aspect: correction burns on every pass will be needed, though it won't be as much as a typical Mars transfer burn. I think you should hold back on microwave-beam thermal rockets for now. Yes, it's plausible, but I don't see any new engines working on that principle being developed as of now, so it's still far-future stuff. I think we'll have more to say about it when the first engine has been successfully test-fired (or explodes on the test rig. It happens occasionally).

One could, say, limit the radiation shielding to some sort of 'storm cellar' for the astronauts to hunker in whenever the Sun spits out a nasty flare. The rest of the living space can be inflatables, or otherwise built out of lighter materials, shielded just enough to block background cosmic radiation, with additional rad-shielding in the form of water bags. A lot of them would be needed on such a long trip anyway, might as well use them as shields.

I suspect it is. The cycler is a strictly orbit-to-orbit ship, with plenty of time for maneuvering burns. We can fit it with more efficient engines than typical chemical engines, like nuclear thermal or nuclear electric engines that, despite being ultimately heavier, can lower the propellant needs for maneuvering burns at each pass. Though, I think that ultimately our suspicions on whether the cycler scheme is worth the trouble compared to an integrated hab module depends entirely on how massive the hab module actually is, compared to the supply/crew ship.

Oh, we're not saving on dV here. We're saving on propellant. In other words, rather than dV-ing an entire habitation module, along with all the hardware associated with it, we're just dV-ing a smaller spacecraft carrying only crew and supplies, but no habitation hardware. Other than the first time the cycler is set off, the fuel requirements for each subsequent trip is lowered because we're sending less mass on transfer orbit, despite the dV requirements being almost the same. Whether it's worth the trouble of sending the cycler ship off in the first place depends on how often trips to Mars are undertaken. A yearly voyage between Mars-Terra would certainly be a solid reason for such a ship. Since there are no such thing as of today... well, you get the idea.

So, is it safe to say that a non-torch-drive ship (not able to accelerate to near-light-speed without 'warp' drive) can warp all over the solar system without experiencing significant time-travel effects (that is, not larger than a few hours) throughout its mission?

We should send a rover there.

Any progress so far? No explosions, I hope?

Surely there'd always be a niche application for them that still works? One wouldn't use nuclear thermal rockets as RCS thrusters, for one.

Won't work. Rocket motor tests have been done (there's an entire chapter devoted to borane in J.D. Clark's book, labeled 'Exotics'), and give a lower specific impulse than theoretical. Also, the exhaust includes B2O3, which is a solid anywhere below 1800 degrees C, which will the gunk the chamber, throat, nozzle, turbopump, and pretty much everything it touches.

Ox/fuel ratio depends on the combustion temperature you're aiming for. Basically, the lower the O/F (more fuel), the cooler it burns, easing the hardware requirements at the cost of energy produced. If a high performance motor is the objective, you'd run it close to, or at, the stoichiometric O/F. Though, that'll put more stress on the hardware, so you'd probably need a sturdier casing. EDIT: I messed around with an online calculator, and found this reaction: 4 KNO3 + C3H8 = 2 K2CO3 + CO2 + 4 H2O + 2 N2 Don't take my word for it, test it before attempting an O/F of 4.

That's for you to find out, unfortunately. Most amateur rockets that use KNO3 mix it with sugar rather than silicone sealant. Hybrid rockets are also commonly designed with solid fuels and liquid oxidizers, rather than the other way around. So, what you're making is a kind of reverse-hybrid rocket. Which AFAIK no one has ever developed before, at least none that got through my news feed. You're practically in an uncharted territory here. But don't let that stop you. Go on with your project; find the optimal ox/binder ratio, then the ox/fuel. Then burn away. After that's done, It'd be wonderful if somebody else tried it with hydrogen and PTFE. Not as a binder, but as the primary oxidizer.

I suppose further oxidizer tests are required. I'd try to torch the mixture, to see if they react.

I agree with K^2's suggestion. Silicone should be the way to go. Well, technically, it'd be a fuel, but it's relatively inert compared to the actual fuel. That might be good enough for government work.

I don't have anything to compare it to, but I know that Teflon is available for the general public in many forms. I'm not sure I know how to get it legally though, in your locale at least. Whether you're OK with having fluorine compounds out your nozzle, that's up to you.

I'd recommend to avoid anything that has a hydrocarbon group. That's going to be a fuel in the resulting solid grain. What you're looking for in an oxidizer are halogen-group elements, things like oxygen, fluorine, and chlorine.

Make sure you're using some remotely-operated mechanisms when testing it. I've known a few persons in my lifetime who has lost fingers due to fireworks.

Maybe not by heat. PVA in wood glue has the chemical formula (C4H6O2)n. The carbons and hydrogens would be the fuel atoms. Try testing it with an open flame; be careful when doing so. If it didn't react with KNO3, then it shouldn't burn as a fuel, and I'd be wrong.

Hence the warning. Teflon starts to deteriorate at around 260° C, byproducts of which have been known to be lethal to birds. Though, we're using it as an oxidizer mix here. Temperatures are going to be significantly higher, and there'd be fluoride compounds going out the nozzle. If the fuel is a hydrocarbon, probably most of them will be HF. EDIT: PVA would qualify as a fuel rather than oxidizer. It'd work as a binding agent, though you're practically making a solid propellant mix rather than a solid oxidizer.

I think PTFE (Teflon) can be considered as a binding agent. According to the Wiki, it's a polymer that melts at 327 degrees C, and fairly non-reactive. It has been used as an oxidizer in pyrotechnic compounds with powdered metals as fuels, producing mainly elemental carbon (soot) and metal fluoride, along with lots of heat. Often used as igniters in common solid-propellant rockets. Watch out for those fluorines, though.

I don't know if there's any solid-fuel binders that is stable when mixed with KNO3, yet can safely disintegrate under combustion without the substance being fuel itself. So in the end, if you make a solid oxidizer, whatever binder you'd use to bind it would be part of the fuel.

Actually, it's more through mass production than vertical integration. SpaceX's Falcon 9 rocket has almost identical engines throughout the stages. The lower stage has 9 Merlin engines, the upper stage has 1 Merlin with a nozzle extension. Since a single rocket requires 10 engines, they can mass-produce the Merlins and cut costs by economies of scale. Furthermore, using only one engine design cuts R&D costs, since the engineers have only one engine type to worry about; most of the tooling can be specified for this engine alone. The only other engine SpaceX makes are the Draco engines used in Dragon spacecrafts, which are simpler hypergolic thrusters mostly used as OMS/RCS.