DerekL1963

No, I was being critical of the idiots who are trying to map the current Chinese onto the 1950's Soviet Union - and then use that as a justification for reigniting the Space Race. But the problem is, the Chinese aren't racing. There's no value to be had in it, as space is no longer the proxy from ICBM's and technological superiority of political systems. Instead, what have is the more normal sort of international competition. where they're trying to been as equals or maybe modestly in the lead. The latter is a particular point to pay attention to, as while space 'racing' doesn't have much international value it still has considerable internal propaganda value. Much more so in China than in the US, where it's propaganda value is essentially zero if not negative.

Um, so what? I didn't say they weren't. I said they weren't pushing the boundaries, and they aren't starting a race. No offense, but did you actually read what I wrote? Because nowhere did I write anything that could possibly be understood as claiming that nobody took them seriously. In fact, I very specifically wrote that they were trying to be taken seriously.

First China has to be in a race. They aren't, and aren't going to be anytime soon. They've got just (barely) enough of a space program to be considered a Major Nation and not a yuan's worth more. The whole idea of China being in a race is created of whole cloth by clueless space fanboys who want to relive Apollo.

Yep. And there's a reason why industry took off like gangbusters when we switched from charcoal to practically unlimited coal. As somebody said above, our civilization is built on the abundant availability of cheap energy. Biofuels are a complete non starter, as they require considerable technology, infrastructure, and energy to produce.

No, and no. With a railgun, drag will slow the projectile very, very quickly. With lasers, the ocean is too dense (and the wrong color for many lasers).

Yeah, a reliability statistically insignificant from practically any other vehicle is "flawed".

Not using that design, no. With so little compression, essentially zero confinement or tamping, and already being so close to criticality... it'll blow apart and fizzle. (Even making the assumption that the 'control rods' will be ejected rather than being captured.) Nor will the pressures rise to anywhere near that needed to trip the core over into fusion (since they'll be barely more than you can generate with just high explosives).

Define non-critical... I mean, the ice cream machine is certainly non-critical, but what about the refrigeration equipment? Without it, we don't die per se, but we could lose almost all the electronics that support our reason for being there (refrigeration equipment chills the water used to chill the air used as a heat exchange mechanism). The same equipment also chills the chill box (a giant refrigerator) and the freezer that holds most of our food... Losing that won't kill us (we can always fall back on dry goods and dehydrated goods), but it will sharply limit mission duration. It sounds silly, but it's a serious question. There is a broad range of varying shades of grey between white ("successful mission completion") and black ("everyone evacuates or dies"). A large amount of maintenance effort goes into maintaining systems that aren't critical to the immediate or short term goal of keeping us alive, but which are critical to completing the mission. And that's not including the hours spent on routine housekeeping, inventory and tracking stores, on administrivia such as updating documents, etc... etc... Those miscellaneous non maintenance tasks are why I keep hammering on the difference between "maintaining the station" and "performing maintenance on the station". The two terms are not equivalent. The latter is a subset of the former.

No, critical mass isn't a hard physical property. But critical mass isn't the topic of discussion here - a self sustaining chain reaction with power extraction (a reactor, not a "reactor") is the topic of discussion. And it's the power handling and extraction machinery that dominate the design. Though the heat was generated by criticality rather than spontaneous decay, those reactors were really just fancy RTG's - and they weren't self mobile as specified by the OP. (Not that there's any particular reason they can't be...)

It was never built, and the reactor "design" never advanced beyond the most basic assumptions and bar napkin calculations. The smallest operational (mobile) power plant that I'm aware of would be NR-1's... And that looks to be about sixty feet long and twelve feet in diameter.

Assuming that "five man days are required for maintaining the station" refers only to maintenance. As I pointed out above, that's a shaky assumption. Having served four years on a SSBN, I can easily understand how much maintenance might be required. Especially given that the systems on ISS are a) essentially first generation, and b) almost certainly not well designed for maintenance. (Submarines have been at it for over a century now, and we're still getting a handle on that. It's a Very Hard problem when you're sharply space limited.) Your house isn't even a fraction as complex as the ISS. Extrapolating from one to the other is... well, there's no single word in the english language expressing how ludicrous it it to even try. Not to mention it's not particularly small, I've heard it quoted that it contains the same volume as the cabin of a 747 - which clocks in at 5k odd sq ft (or 460 m^2). And that understates the matter, as ISS uses all four walls of a given space for equipment.

"Maintenance" != "repairs". It also refers to preventative and periodic maintenance. For example, I performed corrective maintenance (repairs) to restore suction on our vacuum cleaner this last weekend by tightening a loose internal hose connection... but since I had it apart anyhow I also performed my periodic maintenance and cleaned the filters. My preventative maintenance on my car (oil change) isn't due for another 4,000 miles. And that's all assuming that "maintaining the station" (to quote you quoting your source) means only "maintenance" and doesn't include housekeeping and operating tasks. Which isn't actually a problem so long as you have enough cargo capacity. Or, to put it more clearly it's easy to misunderstand their point... Which is that the problem with Mars One wasn't that it needed so many spares, (AIUI) it's that it had insufficient cargo capacity.

"Maintaining the station" != "life support". The latter is certainly a subset of the former, but it's emphatically not the whole of the former. And without knowing how those man-days of maintenance are spent, it's hard to extrapolate to a Mars vehicle. (A Mars vehicle won't have parts that are decades old for example.)

Exactly what is your definition of "sustainable"?

Precisely. A friend of my who works at the nearby naval shipyard was a part of a recently completed project to replace a pair of motor generators (originally designed in the 1970's) on each Ohio class SSBN/SSGN with a pair of new design switchable static inverters... because it was cheaper to replace them entirely than to restart and requalify the production lines needed to replenish the spares pool. If for some insane reason I was tasked with re establishing MR or MA capability... I'd start with a clean sheet. Anything less is madness.

Ayup.

It's a... mixture of fact, fantasy, and outright repurposed bovine waste.

I know they're broken, but have not had the time to fix them. (It's several hours of time I haven't had with other projects on my plate.) They are not broken because Photobucket is buggy, they're broken because Photobucket changed it's image hosting policy.

Maybe, maybe not. It's not just nuclear theory you need, but chemistry and metallurgy. (And a way to deliver the weapon - something were just barely capable of doing in WWII.)

True for the more-or-less "guided" probes we've sent to date. Not necessarily true in the future and emphatically not true of a guided and piloted vehicle departing from orbit (rather than dropping straight in as had been the general practice to date). Quoted for truth.

Retracting what I said above, it does look like 300m/s is achievable. However, due to gunpowder's slow burn rate I suspect the weapon will be much larger than Little Boy as the projectile has to reach full insertion speed before it reaches the criticality zone. Because both portions of the core have to be near criticality for any reasonable efficiency, that zone extends some distance up the barrel. In the case of Little Boy, the core went critical while the projectile was still 25cm from the target. (The reference is unclear as to whether that measurement is from face-to-face or from face-to-fully seated.)

If by "much more plausible" you mean "still laughably implausible", sure. Gunpower of that era, essentially black powder, isn't going to generate enough force to propel the masses together fast enough... It'll fizzle. But the real problem, as @DAL59 pointed out, is enrichment. That's all but impossible in the gunpowder era. They might be able to get a thermal diffusion plant running - if they can figure out how to handle fluorine. But it's still going to require enormous inputs of conventional fuel.

SSBN launch tubes and eject systems aren't nearly as sensitive to weight as they are to volume, and the ducting takes up a lot of volume. You also add considerable mechanical complexity. You'll need a base fairing to prevent eject gas from simply 'blowing by' the missile via the ducts. You can't eject the base fairing (which will have to be fairly hefty) too early lest you potentially foul the hatch, which means to avoid serious drag and having to lift the weight of water in the ducts you'll need an upper fairing as well. That means a lot of heavy debris created at ignition, which could pose a danger to subsequent missiles. (The existing closures (at least in US practice) are essentially just lightweight bits of fiberglass and some styrofoam, they don't pose a hazard.) Pretty much everyone had gotten rid of surfaced launched strategic systems by the early-mid 60's. And the history of SLBM's is a history of increasing range... This reduces transit time to where they can hit targets, and by giving them a larger area of ocean to hide in makes the other side's ASW problem significantly harder.

Actually, the RD-107/108 is long since retired. Like pretty much everything else in the Soyuz booster and Soyuz spacecraft, it's been replaced by an updated and modified version.

Did you actually read that before linking? Here is the relevant part (emphasis added) "Table 8‑1 Theoretical maximum energy density of some possible flywheel materials", and "These values could be achieved if the shape factor and all alpha factors would be unity. This is unfortunately not possible, at system level the achievable energy density is between 2‑12 % of the above theoretical one". Or, in other words - not only does your source fail to support your claim that Zylon wheels can "reliably" do do... It plainly states that the achievable energy is actually a fraction of what you claim.