NERVAfan

Yeah, LAS are only needed because rockets are unreliable right now. If you had a rapidly reusable rocket, you could test it enough to prove very high reliability.

To expand on that... farms on Earth need lots of nitrogen fertilizer input because the farm is not a closed system. The crop is removed from the farm and consumed far away - nitrogen is lost from the local system. But the Earth is a closed system, and no nitrogen is imported. A space greenhouse would be more analogous to the whole Earth - the nitrogen cycle is completed locally, within the system.

No, it doesn't show that at all. Biosphere 2 was very badly designed. I (or anyone with half a clue about ecology and agriculture) could do much better, especially with their bad example It was designed to mimic Earth ecosystems. But... A) that doesn't work in the first place because on Earth you do not have desert 100 meters from rainforest (and indeed the desert stopped being desert); this is hideously inefficient for human life support if you are mass-limited; you should design like a farm (with air as a "crop") not like a natural system; C) this meant lots of extra work for the crew to try to do stuff like scrub algae off the coral reef. Also, they didn't plan for the day/night and winter/summer carbon dioxide/oxygen variation (easily solved if you know it exists). Also, their structure wasn't inert; the new concrete absorbed oxygen. Erm, how did these plant lice arrive? You only have the species you brought with you. Fire and decompression are catastrophic in any spacecraft. Why would that happen? Fertilization of crops with human waste is hardly some new untried technology. You need some margin, yes. No. Mass is conserved. The nitrogen is consumed from the crops by humans, excreted and returns to the crops. There will be some loss as nitrogen gas, but you include nitrogen-fixers to solve that problem. You will probably actually have extra fixed nitrogen, since the humans will bring food to eat before the first crop is ready to harvest, which will be excreted and added to the plants.

OK, thank you!

$10 million? Maybe with Atlas/Delta, but Falcon 9 can launch 13150 kg to LEO, and the listed price is $61.2 million. That's $4.65 million/metric ton. I've heard the final price is higher when you include other services... but it would have to be 2.15 times higher to reach $10 million. (And Falcon 9's actual performance is higher, the official number includes some margin for reusability testing, IIRC). So this really doesn't sound massively game-changing. Competitive, definitely... but if SpaceX's first-stage reusability turns out to be practical (without massive refurbishment like Shuttle) the costs may drop quite a bit lower.

Yeah. I really do not understand why an algae oxygen-recycling system hasn't been flown yet on ISS (or some earlier station for that matter). It could be pretty simple.

The lower stage thing is an intermediate step. Elon Musk has now said that reusing the 2nd stage of Falcon isn't practical since it goes to GTO and has poor specific impulse, but the next rocket (methane/LOX and much bigger) is supposed to be fully reusable.

I think that's quite an overstatement; each of the MERs was something like $400 million and MSL was something like $2 billion, and something small scale like what is being proposed in this thread (a "lunar Tiangong/Salyut" instead of a "lunar Mir/ISS") would not cost $400 billion-$2 trillion unless it was done with truly hideous inefficiency. You can do initial exploration vastly cheaper with unmanned stuff, yes. But the thing is that a robotic mission that actually gave you comparable capability to a human mission probably wouldn't be nearly as much cheaper -- and probably wouldn't be possible at any price with current tech given the slowness and limitations of current rovers. IE the robots will begin to hit diminishing returns. (And we can't rely on better robotic tech to solve that problem; the acceleration of computer tech can't continue forever.) Not really. Humans are more expensive largely because they require more mass. So as launch costs decrease, it will shift in favor of humans. I expect the picture to look very different in ~5 years, with reusable Falcon 9 first stage, Commercial Crew vehicles and possibly Bigelow stations. That assumes fixed money that can go either to human or unmanned exploration. But I don't think that's a valid assumption -- with humans, there will be more interest and therefore more money. People lost interest in Apollo because of vast social disruptions around 1970 and also because it was set up just "to get to the Moon" with no long term goals. I don't think the same would happen to something like this, unless it got historically unlucky like Apollo did.

Ah, thank you. I figured there should be a way to do that but I could only turn them 90 degrees with Q/E/W/S etc. keys. How do you angle them just a little bit?

Well, other Kickstarted cubesats have asked for much less than that. They might have had other funding sources... I really don't think it needs to be nearly that much though.

True... but the poles are probably where you want your moon base to be anyway due to the perpetually dark craters having the good resources. IIRC Whipple Crater is probably the best place, a perpetually dark crater with a plateau that gets light most of the time right next to it.

Well, it's more to determine IF it is, since there's the possibility of transmission of life from Earth via meteorites. Yes, exactly. No, tis is exactly what the metagenomics experiment resolves! If it is contamination, it will be something we know about or at least a very close relative of something we know about. If it uses our genetic system but is distantly related, then it was transmitted naturally a long time ago. I suppose there could be some ambiguity if it arrived by meteorite very recently... but that seems very unlikely since life has existed on Earth for ~4 billion years and there were more big impacts early on. I doubt there's been any impacts big enough to eject significant rocks to escape velocity in the last few million years (the K-T impact might have, but 65 million years allows significant evolution).

Ah, that would make sense. Well, I'm not sure it's quite THAT bad given that we were very close in 1961 and current engines (Merlin 1D anyway) are way better TWR and somewhat better Isp.

We haven't actually looked for life on Mars since the Vikings (except for the failed Beagle 2) and the knowledge of microbiology was just really primitive back then. (They didn't even know about chemosynthesis when those experiments were designed.) They also didn't know about perchlorates in Martian soil. So here's what I think we should send to Mars next... A lander (doesn't even necessarily need to be a rover - this could basically be "Viking updated" - though a rover would be better) with the following instruments: To look at rocks in-situ/"in the wild": -Microscopic imager to look for microfossils. To extract samples: -Digging tool to get soil from at least a meter or so down. -Drill to extract samples from the interior of rocks (to look for endolithic microbes) To analyze samples: -Raman spectrometer to look for organic molecules/biomolecules. Curiosity's SAM instrument has had problems due to contamination, but IIRC also since it has to heat a sample to analyze it, and Martian soil has perchlorates in it, which react with the organics when heated. (ExoMars rover is going to have one of these... but I am not optimistic of its getting a chance to be used since ESA has outsourced the launch and landing system to Russia, who have a very bad Mars record.) -Metagenomics experiment. Oversimplified, this is basically "grab an environmental sample and analyze any DNA in it". This has been a huge development in microbiology; before, we were basically limited to studying cultured microbes, and we couldn't culture most microbes!

I don't know about the actual theory, but... Maybe it has. We really haven't looked! The Viking experiments were horribly insufficient given modern knowledge of microbiology (which has advanced enormously since then) and haven't been followed up - and the most likely places to find life on Mars would be underground/inside rocks anyway. No one has looked in Europa or Enceladus water. It's possible that life could exist in Titan's hydrocarbon seas, or maybe even in gas/ice giant atmospheres/supercritical "atmo-oceans" (is there a word for that?) but we wouldn't know how to detect it since it would be so different. I think life on Mercury, the Moon, or other airless/waterless bodies can pretty much be ruled out due to the lack of a fluid medium... but everywhere else is still possible, IMO.

Maybe... but I'd like to see the numbers compared to modern solar panels. But it's irrelevant, since you can use thin film panels without hard surfaces - see the Japanese IKAROS solar sail, which had ultra-thin (25 micrometers!) solar cells in the sail.

Oxygen isn't the biggest problem, as it is pretty light - humans use something like 0.8 kg/day (or 0.63 kg/day depending on who you believe... it's probably pretty variable by activity level, body mass etc. anyway). Plus it probably wouldn't be too hard to recycle oxygen with some algae. Water recycling is much more important (and difficult, probably) as much more water is needed (especially when you count in bathing and such).

Maybe so, but it's not clear to me that "noticeable" equates to bad (or that it even would remain noticeable after a while -- often continuous stimuli, like noise or smells, stop being noticed). You adapt to zero-g (stop feeling nauseous) after a while, the same would probably happen to this. OTOH, I don't think it's actually necessary for near-term stuff. Valeri Polyakov spent 14 months in microgravity on Mir and apparently was able to walk out of the capsule upon landing; it's only 8 months to Mars. And IIRC current ISS exercise stuff is dramatically better for bone loss than what they had then; IIRC it's near zero (though there are still some visual effects etc.) So we don't need it for Mars IMO.

Um, really? Falcon 9v1.1 has a starting mass of 505,846 kg with an LEO payload of 13,150 kg (according to the SpaceX website). That's 2.6%. (And IIRC that number includes some margin for reusability attempts, too). Is SpaceX really doing 5x or more better than normal? That seems unlikely, as much as I like the company. It's harder to tell with Delta IV since it has a bunch of different configurations, but looking at the numbers on Wikipedia it seems to be in the 4% range. (The Atlas V article lists a range of payload capacities but only one total mass, so I don't know what to do with that).

Also, developing an orbital launch vehicle is really expensive, so there aren't that many organizations that can do it. If you could develop an orbital LV cheaply, IMO somebody would have made a non-spaceplane SSTO, because even if the payload fraction is much less there are some potential advantages (theoretically you could have higher reliability since there are fewer parts and no staging events). But since developing an orbital LV is super expensive you need a really good justification to develop a new one. --- You might be able to get an interesting (expendable) SSTO by using the Mercury Atlas design with SpaceX's Merlin 1D engines. The Mercury Atlas only dropped engines, not a whole stage, and is probably the closest thing to an SSTO that's ever actually been used. But SpaceX's Merlin 1Ds have much better TWR so you might not need to drop the engines (they seem to have better Isp too). OTOH, the old-style-Atlas balloon tanks probably wouldn't work well with reusability, so SpaceX wouldn't be interested.

Thank you!

Eh, Mars is close enough that you don't really need awesome recycling. People need about 5 kg/day of life support, most of which is water. What are the chances of that happening, though? Seems pretty unlikely. Because putting in that much delta-v would likely make the whole thing impractical. Your point is correct, but Mars is close enough to the Sun that solar-electric would almost certainly win out over nuclear-electric. Solar panel technology is advancing fast and nuclear technology... mostly isn't. IMO nuclear-electric is only for Jupiter and outwards.

Next step: the Mercury Atlas. This is a weird rocket, and by trying to match the functionality, I ended up with something that looked quite different. The Atlas rocket used didn't stage, but it had 3 engines, 2 of which were dropped off during flight - this is probably the closest thing to an SSTO that's ever flown to orbit. Trying to build this in KSP, I couldn't get fuel to flow through a decoupler, so I had to attach a tiny Oscar-B fuel tank to each of the side engines and use a fuel line to feed fuel from the main tank. Similarly, I couldn't use a tricoupler, since that would make its thrust off-center with only one engine. So this rocket has 3 "cores" even though the real Mercury-Atlas rocket only had one. Podlo Kerman was assigned to fly this mission. Here it is launching: Here it is after engine separation: And here's the stable orbit: And firing retrorockets for reentry (these are actually the same separatrons I used to represent the launch escape system): The capsule then parachuted to a safe landing and was recovered.

The lack of hydrogen is right (specifically, the Solar System is in a low-density area, the Local Bubble; IIRC the original calculations used the galactic average), but it's not really a problem with fusion being too low-energy; it's a problem of drag caused by collecting the hydrogen and the extreme difficulty of fusing normal hydrogen (1H), which is the vast majority of hydrogen. So far we can't even get net power out of deuterium-tritium fusion, which is vastly easier. EDIT: No, electrons have rest mass (about 1/1836 that of a proton, IIRC).

Yeah, I've read that too. That's just demonstration of capabilities; doesn't imply actual hostility. Well, sure, there were plenty of tensions between the US and Soviet Union during the Cold War, and several proxy wars (Korea, Vietnam...) But it never turned into outright war between the US and Soviets. And I think those tensions will mostly fade away over the next 20-30 years. Right now the people in power still remember the Cold War. In 20-30 years that generation will have retired. EDIT: There's no really rational-self-interest reason for those tensions as US/China are so intertwined economically that either nation would harm itself by harming the other. IMO it's holdover "we have to support X country against Russia/China" cold war thinking, nothing to do with actual US interests.