NERVAfan

But if the price drops enough, new space industries - new "needs" - will probably appear. I agree Skylon probably won't be funded in the current environment... but "the current environment" may not last much longer. If SpaceX gets first stage reusability working, and if it saves money, then other companies/agencies will be looking for reusable vehicles.

Specifically, you have to use 300 megawatts of power per newton of thrust. You can do twice as well if you separate the laser from the spacecraft and point it at a reflective solar sail (since the light bounces off in the opposite direction so the momentum transferred is doubled) but then you're limited by the laser (eventually diffraction spreads it out so that not all the beam is hitting the solar sail).

https://www.kickstarter.com/projects/575960623/ardusat-your-arduino-experiment-in-space/posts https://www.kickstarter.com/projects/880837561/skycube-the-first-satellite-launched-by-you/posts https://www.kickstarter.com/projects/zacinaction/kicksat-your-personal-spacecraft-in-space/posts I don't know what kind of backup plan could be viable. Yeah, the thermal stuff will be critical. I'm eager to see what you come up with.

I don't think Skylon will be operating (if it ever flies) in anything like the current market, though. They haven't built an engine yet; even if they get funding really soon, it will be a long time until it flies, probably well into the 2020s at least. By then stuff like Falcon reusability, big LEO smallsat constellations, maybe Bigelow stations etc. will likely have changed the picture quite a bit.

They actually considered dimethylmercury (which is vastly worse than elemental mercury as it passes through the skin vastly more effectively, and even passes through common glove materials like latex, gets into the brain and is horribly neurotoxic). That one didn't get to the test phase, though (thankfully) as sanity prevailed (or rather they couldn't get anyone to make it in the needed quantities). EDIT: The nitric acid isn't nearly as crazy as the other things listed. Hazardous, yes, and there's a very good reason the US uses LOX instead these days, but the Russian Proton still uses massive quantities of N2O4. Strong oxidizers aren't really safe things. (One of the crazier bits was "inhibiting" the nitric acid's corrosiveness by adding a bit of HF. So... yeah, still pretty extreme.)

I love that concept. Sure, but with Isp ~20 times better than chemical rockets, you don't need much of a mass fraction to do anything in the solar system. Totally unworkable to test on Earth, though. I'd try it on the Moon with Lunar thorium. IIRC SpaceX is using it for their next engine (Raptor) because it's better specific impulse and easier to make on Mars (ISRU). I don't know why Firefly Space Systems picked it to work on.

It was tried (in ground tests) but the Isp isn't that good. They tried pretty much every imaginable thing in the 50s and 60s.

It's been done several times before, and the KSP connection probably gives us a very good chance.

US and Soviet atmospheric nuclear tests ended in 1963 with the Partial Test Ban Treaty. However, the lack of demand (as by then NASA budgets were going to be severely cut following Apollo thus no money for a Mars mission) was definitely a (maybe the) major factor in canceling NERVA. The anti-nuclear thing would definitely be a major factor in trying to use NTRs now though. (in the US anyway. I doubt Russia or China would have a problem.)

That may be the political reason, but an inactive reactor almost certainly has less radioactivity than an RTG (which we do launch) since plutonium-239 (half life ~90 years) is many orders of magnitude more radioactive than uranium-235 (half life ~700 million years). The reactor becomes badly radioactive once it's operating... so you don't turn it on until you're safely in orbit.

Yeah, everything I've read suggests the Skylon project has quite significant margins. The money remains the big question... as in pretty much all big technological projects.

Well, I guess the reason I disagree is that I think that if technological civilization lasts another 100 years or so, we'll have significant space colonization, and once you have that I think generation ships are pretty much inevitable eventually - they strike me as a natural extension of space colonies. Something that would be able to raise a vaguely functional human being would be not only enormously more capable than anything we have today, but a fundamentally different kind of capability. Generation ships don't require any fundamental breakthroughs; seed ships do.

I think most if not all of the species that it might be possible to get sufficient DNA to revive were made extinct by humans. DNA doesn't preserve well over geological time (it doesn't even preserve that well over much shorter timescales).

They are IUCN endangered, sure, but that doesn't by itself prohibit anyone from doing anything. The IUCN does not make laws. I would disagree strongly. The capacity is fundamental, sure, but not any particular set of such behaviors. New mammoths would develop a new set of behaviors, not found in Pleistocene ones - but they wouldn't have been uniform over the huge time and space inhabited by Pleistocene mammoths either. Um, how? Taiga/boreal forests are still around, they've just moved much farther north. There are plenty of places on Earth just as cold as mammoth habitat was back then, and plenty of them are dry. Sunlight hitting the Earth hasn't changed much. Why would deep soil be a bad thing? Would it be an exactly 100% perfect recreation of any particular Pleistocene mammoth habitat? No. But woolly mammoths as a pretty widespread species must have had a fairly wide range of habitat tolerance, and I'm pretty sure there are some modern taiga/boreal forests that would fall within that range.

If they can get enough DNA, I think it's probably quite doable with sufficient funding - which is (as usual) the big question. Asian Elephants are regularly used as work animals in the areas they're native to. And IIRC this work is Russian, the laws may be different there. What about putting them in with an elephant herd in a zoo? Or raise a bunch of mammoth calves together, something will probably develop. It won't be identical to behaviors of original mammoths, but does that really matter? It wouldn't prevent cloning them and keeping them in a zoo or fenced preserve. And I don't think the ecosystem is so different that mammoths couldn't survive in the wild, either. 10,000 years or so is not that long in evolutionary time - the most significant changes are the extinction of all the megafauna (which shouldn't prevent revived mammoths from surviving) and the warming of the planet (solvable by putting them farther north, in the areas that currently have the kind of habitat the mammoths lived in in their time).

It would be great if someone could find a way to actually use ozone (which is unfortunately, incredibly dangerous) - it could give much better performance than H2/O2.

Ah, OK. (10 characters)

Ah. I got that from the Sandy Antunes book ("Surviving Orbit the DIY Way") which says: "Most picosatellites are not just limited in weight, but also don’t need to really worry about short-term transient damage like SEUs. Instead, we’ll just take our lumps and hope that the bulk of the data we downloadâ€â€itself just a fraction of the entire data capturedâ€â€will suffice." and "in general, a short-lived picosatellite does not have to significantly worry about the radiation environment for their typically shorter lifetimes." Is that not accurate? EDIT: Also, I thought you were talking about a rad-hard camera, not a rad-hard CPU. Did I misread that? If so, sorry.

I'm sure you know more about this than I do... but I thought rad-hard components were generally unnecessary for cubesats due to LEO magnetosphere protection and having short lifespans anyway?

In low Earth orbit, spacecraft will probably be unmanned, like modern spy satellites. Beyond the Moon, though, I think humans in space probably would be involved somewhere because of signal lag preventing effective remote control and not wanting totally autonomous spacecraft with really powerful weapons. The humans might well be on a mothership a thousand km away controlling drones that do the actual fighting, but they'd be "in the loop", I think. EDIT: However, by the time there's enough human activity in space to make fighting wars over it worthwhile, the technology will be different enough that the actual design of the ships would be much different from something we'd produce now.

Sure I can. Electronic computers are not brains and do not function in the same way at all (and I am skeptical that quantum computers will ever be very practical due to temperature/decoherence issues). Maybe you could simulate a human brain... but I don't think that will be very workable at the level of fidelity needed (largely because I don't expect the current "revolution in computer technology" to last much longer). Technologies tend to start slow, explode, then slow down/plateau again. The late 19th/early 20th century saw an explosion in land and sea transport (trains, ships driven by engines instead of sails, cars, trucks etc.). The early-to-mid 20th century (post WWI to say 1970) saw an explosion in aircraft technology and the development of orbital launch all the way to Apollo. The late 20th century to now is seeing an explosion in computer technology... but it probably won't last forever, or even all that much longer (we've already gone to multi-core computers due to practical limits on CPU speed, IIRC cooling based...) I think the next revolution(s) will be -biotech (arguably it's already happening with things like DNA sequencing getting way cheaper... but the big explosion of consumer applications like we had with computers hasn't happened, and probably won't while people are irrationally terrified of GMO food -- I do expect it to come eventually, but probably out of Asia or maybe Latin America, not US/Europe). But I expect that revolution to be much more limited than some would hope, though maybe more by regulatory/social concerns than actual technological capabilities (I can't imagine any practical way to get longevity drugs by the FDA without decades of testing, for example). -nuclear fusion and everything that leads to Nanobots, maybe someday, but ... by definition at that scale (a couple of nanometers is the scale of large molecules like proteins - atoms and chemical bonds are on the order of 0.1 nm) it's more chemistry than machinery, and so will probably have many of the same limitations as life (needs a medium such as water and specific substrates/"food"/raw materials, narrow temperature range, etc.) If we ever get serious nanobots I expect them to have those limitations, probably be bigger than "classic" nanomachines (more virus or even small bacteria sized), and be derived more from advanced biotech than classic "mechanical" technology. Well, yeah. Humans prove that intelligence is possible, sure. But for the interstellar question, what's relevant is if we can have intelligence without the lifespan and life support requirements of humans -- "biological computers" or fragile quantum computers may not qualify. Not really - I assume such a ship would use advanced biotech to create a new ecology that's far more energy-efficient and efficient at supporting humans. But you could build a (larger) generation ship without that. The thing is that seed ships need a major fundamental breakthrough (not just AI, but AI "human" enough to raise functioning human beings). Every step needed to build a generation ship could be spelled out right now - all we lack is money and will. If we'd done Project Orion in the 60s, we probably could have built a generation ship in the 80s or 90s. (I think the "hardest" problem is ironically super-long-lasting on-board power/lighting to feed the photosynthesis.) EDIT: And again, I'm skeptical of getting a seedship capable of reliably* surviving interstellar travel in a package too small to support a worldship (especially given biotech to "engineer down" the size of the ecosystem needed to support a couple of hundred humans). *because if the AI is "smart" enough to raise humans, it's a person, and therefore its life is valuable too, so it shouldn't be a matter of sending tons and hoping some get through.

That's because of lack of investment and (even more so) fear of nuclear stuff, not technological maturity. That's essentially what I had in mind, though the space colony would probably build a new structure rather than convert their existing one - I doubt a pure O'Neill colony would be built to stand up to thrust, and it would likely be dependent on sunlight. That requires the existence of an AI/non-human system that can raise vaguely functional human beings. That is an extreme breakthrough if possible at all. Not really - but it's a long way to Alpha Centauri. If the stardust probe's dust collector was hit by seven dust grains, even a tiny interstellar ship would probably be hit by millions. It will be eroded away. And one slightly-bigger dust grain or chip of Oort cloud ice and the spacecraft is destroyed. Essentially, yes (and with vacuum layers too like a Whipple shield) - but I'm suggesting to make that composite armor layer, say, 100 meters thick or more. Enough to stand up to, say, a human-sized chunk of Oort cloud ice (100 kilotons TNT equivalent or so).

Anyway, as politics will prevent an Orion launch from Earth, the best way to do it is to mine thorium from the thorium-rich region of the Moon, turn it into U-233, and launch from the Moon.

If it doesn't have noticeable effects on humans, it won't do so for other animals (and plants are quite resistant to radiation). The amount of radiation released, across the globe, is just not that much. Airburst do not produce fallout, and you'd launch from a remote location to avoid this problem. I'd pick one of the unpopulated 'guano islands' of the Pacific that is already effectively a complete ecological dead zone due to most of the island being mined away. The point is that there's no good evidence (no evidence period, really) that this level of increase in radiation dose has any health effect. (And an effect on the level of 1 excess death in billions is in practice unmeasurable.) What non-radiation-related effects? EMP probably would be a major issue, but nothing else. We tend to think of nukes as overwhelmingly powerful - and they are, on a human scale - but to the Earth system, the energy release is nothing. Orion pulse units, especially for use in atmosphere, are very small anyway. --- On a slightly related topic: radiation is not nearly the ecological problem people tend to assume it is, even when it is present in dangerous quantities. The Chernobyl Exclusion Zone is full of animals - there are some detectable effects, but on the whole it's pretty good. This is because for human health we care about individual outcomes, but for ecology we only care about populations, and there are already a lot of animal deaths - a few extra cancers just don't amount to anything ecologically. Short of an actual full-on nuclear war with groundbursts and fallout, radiation will not seriously mess up the ecology.

I don't know where they got that number. I'm pretty sure the Orion people were talking about velocities of several percent of the speed of light (for ultra-advanced versions), which would imply a much higher specific impulse. See, the thing is, nuclear pulse propulsion doesn't require any fundamental breakthroughs. This sort of thing involves quite a few, some of which may not even be possible (I'm not at all convinced you could put a human intelligence in a computer, at least not in any practical way -- brains are not electronic computers and do not work the same way). And it doesn't really help solve the problem anyway, assuming any meaningful level of interstellar dust (and the Stardust probe apparently captured several grains), much less the possibility of hitting a head-sized chunk of Oort cloud object or something. You'll want a huge ship anyway to provide massive armor, so you might as well bring along a "worldship" while you're at it. 1100 years is probably quite workable for a generation ship on this scale.