NERVAfan

That's why you need to use thin films, not traditional solar panels, for electric propulsion beyond the asteroid belt. Well, certainly, because the total delta-v needed is small enough that chemical propulsion is feasible. This would only really be useful if you were doing a very high-delta-v mission that would require unworkable mass ratios with chemical rockets. I think it might end up competitive with nuclear at least out to Jupiter given the existence of thin films, and maybe workable even at Saturn someday if nuclear remains politically difficult.

If you had a solar-system-wide civilization and unlimited time and resources, it could work. Extract deuterium from the comets, use that for fuel for a high-specific-impulse fusion engine to move them into trajectories that get an Earth gravity assist, which will change the Earth's momentum. It's just that when we do spacecraft gravity assists the spacecraft mass is small enough that the momentum lost by the planet is completely insignificant. But if you used millions or billions of comets, you might get a noticeable effect. (Or use a smaller number of larger icy bodies like the outer planet moons and KBOs.)

A few other thoughts... I don't know how we are going to fit a microscope and camera into this. THere's an awesome looking Celestron mini-microscope with a built in camera (http://www.celestron.com/browse-shop/microscopes/digital-microscopes/mini-handheld-digital-microscope) but it's 89mm long... so that would be really squeezing to fit both it and the petri dish in, as the petri dish would be 5-10mm thick itself... I don't know if that would work. If we got an 8mm petri dish, that would leave 3mm for the thickness of both walls. Is that plausible? I see mini-microscopes for iPhones; maybe someone electronics-competent (K^2?) could take the camera out of an iPhone and use that? there may be some misunderstanding here. Phytoagar is a growth medium, not a mesh netting.

I don't think that will be too much of a problem. The top/bottom difference probably will be small since the moss will be, and the side-to-side thing is unavoidable with a cubical spacecraft, I think (and a fancy curved petri dish would mean we can't use existing ones). It'll still be a fairly decent simulation of Lunar gravity, I think. We need an actual design, though. I think K^2 would be the one to know about the electric components etc. - we'd need to know what space is available for petri dish, microscope, camera etc.

Argh. What I meant, but forgot to add, was: An order of magnitude estimate is possible from that; assuming the cells are about silicon density of 2000 kg/m^3 and assuming 10% efficiency, you'd get about 20 m^2 / kg ~135 Watts/m^2 or ~2.7 kW/kg at 1AU ~5 Watts/m^2 or 100 W/kg at 5.2 AU (Jupiter's distance from the Sun) I don't know how much mass the cables/wires to transmit the power would be, though.

Nothing's official yet. But from the information Mazon Del posted, I think that makes the most sense. Thermal control will be necessary, yes. (But I think heat will be at least as big a problem as cold; space isn't really 'cold' - a vacuum has no temperature. In sunlight it will get hot, in shadow it will lose heat by radiation.) All these conditions except the gravity can be easily replicated on Earth. (The thermal control should prevent radical temperature swings.) Yeah, that sounds about right. I don't think we'd need an unusual gas mix or anything. Well, a 1U cubesat is a 10cm cube. This artificial gravity calculator (http://www.artificial-gravity.com/sw/SpinCalc/SpinCalc.htm) suggests 53.5 rotations per minute to produce 0.16 g with a radius of 0.05 m. That's less than one rotation per second; doesn't sound TOO insane. Well, we can't do both at once in the same cubesat*. We could switch partway through, but this experiment is probably sharply time-limited due to orbital decay. Maybe we should just do Moon gravity, and if we have enough funding follow it up with a Mars gravity "Kerbsat-2" or whatever? *well, I think technically a rotating object will have 0 rotational gravity at the axis of rotation and maximum at the edge, so yes, you can have different rotational g's in the same spacecraft. However, that sounds really ambitious for something this small.

Mercury (and Venus) are so underappreciated.... (I do agree with your point, though. Europa and Enceladus are probably the best hopes for extraterrestrial life in the solar system, and Titan is awesome.)

Awesome! Is it altitude limited or altitude and speed limited?

No, but I think that one may be mainly a solar sail with just some of the area covered. We know that IKAROS' thin films were 25um thick First to use solar power for electric propulsion, yes, but not first to use solar power at all; Juno is a solar-powered mission to Jupiter.

I agree that origin shouldn't count for planet vs brown dwarf since it can't necessarily be determined. I think the 13 Jupiter masses thing is good enough. I don't really mind Pluto being "demoted", but clearing the neighborhood is IMO problematic since (as I understand it) really far away bodies wouldn't have had time to clear their neighborhood - a Mars-size body in a Sedna-like orbit wouldn't be a planet. IMO, if the barycenter is outside the more massive body it's a double planet, if it's inside the more massive body it's a planet/moon system.

Mazon Del said that it doesn't need light, it can live using O2 respiration instead of CO2 photosynthesis for this timeframe. Similarly, I think it will just live on the sugar+water in the growth medium, with no provisions for supplying more, and there probably won't be waste disposal. It'll only survive a few weeks anyway due to orbit decay. And no thrusters (at least for the first mission). And the petri dish can be quite quite small, probably <10% of the volume of a 1U cubesat easily if we need it to be that small. Moss is low growing.

Isn't E class the biggest? Wow, that's light. I thought E classes were supposed to be dense? LOL. Sneeze to escape velocity.

Asteroids have much lower delta-v to launch from than the Moon, though. If you're looking for an outpost to make other destinations easier, asteroids are better than the Moon.

What makes the kerbals do that stretchy thing? I've seen screenshots of that before...

It's certainly more expensive than Dawn's engine and solar panels, but I'm not sure it's that crazy if you use the "expanded IKAROS" model I'm talking about. The solar array is super-thin-film (IKAROS's was 25um thick) on an even thinner backing, and is deployed by spinning the spacecraft. I don't see why that's massively complex. A megawatt at 1 AU is (assuming the solar panels are even 10% efficient) something like 7400 square meters of solar panel, or 86 meters on a side. I don't think that's all that crazy for these very thin films (although the wiring to carry the power will add mass). Here's the JAXA brochure I was referring to (it's at the bottom of the second page): http://global.jaxa.jp/activity/pr/brochure/files/sat28.pdf "Next plans The second mission will take place in the late 2010s. It will involve a large-sized solar power sail with a diameter of 50m, and will have integrated ion-propulsion engines. The destinations of the spacecraft will be Jupiter and the Trojan asteroids"

I dunno. Due to the square-cube law, balloons/airships actually perform better when bigger*. According to my (very limited admittedly) understanding, we don't have ultra-huge balloons/airships due to cost/lack of much real use, not because the technology isn't there. *You can have much tougher/heavier envelope for a bigger one, since the surface area to volume ratio decreases as the size increases. I think it's actually one of the better places in the solar system to colonize. There is C/H/O/N (the main elements of life) available in the atmosphere/clouds (from CO2, N2, and H2SO4) and temperature and pressure are Earthlike. The Earthlike pressure means the colony doesn't need a pressure hull, only a thin skin, and if there is a leak air won't rush out or Venus atmosphere rush in - if there is equal pressure on both sides the atmosphere will mix only by diffusion, vastly slower than a leak when you have vacuum or Mars atmosphere outside. (Also, gravity is Earthlike, which some people think is very important -- though I tend to think long term exposure to Mars gravity will be fine; you could just wear weighted clothes to get an Earthlike effect if necessary...)

Sure, but I was talking about the possibility of native microbial life living suspended in the Earthlike temperature/pressure region of Venus' atmosphere, and how the biggest difficulty would be water supply. Importing water from Earth for human use is a whole different question.

Hopefully it will just fall in the ocean somewhere, or Antarctica or something.

That is a bit of an overstatement, though. Even depleted uranium's radioactivity is definitely measurable with a Geiger counter.

Seem ridiculous, maybe... but if you can deploy the huge area by spinning like IKAROS's solar sail, is it necessarily a problem? It's not that bad at Mars's orbit; about 40-50% the power at Earth's orbit, I think. Dawn is using solar-electric propulsion at Ceres and Vesta, which are significantly farther out than Mars. Well, as I say, JAXA was talking about a solar sail/ion mission to Jupiter and the Jupiter Trojan asteroids.

dbmorpher is right, there are actual sulfuric acid droplets. As I understand it, the acid and the super-high temperatures are not in the same place. The upper atmosphere has tolerable temperatures (at about 30 miles, as dbmorpher says) but sulfuric acid, while the surface is incredibly hot but the acid boils away long before reaching it. Yeah, but you still need another source of water, since you need water to make the sucrose in the first place. If all the sucrose is being used to produce water, then the lifeform can't use any of it for energy.

I thought the original Orion people suggested that an advanced version could get to several percent of lightspeed? There's also the Robert Zubrin "nuclear-salt-water-rocket" concept, which IIRC supposedly could be optimized to a few percent of lightspeed as well, but I don't know if anyone else has ever really studied that. IIRC the Orion people talked about some kind of ablative coating that burned away to protect the pusher plate itself. I don't know if it's enough though...

We could do a Kickstarter to fund the balloon/gas, I think they're a couple thousand at most. I would definitely contribute.

xenomorph555 is right, uranium IS radioactive (all elements heavier than lead* have no stable isotopes). But it is much less radioactive than the fission products with short half-lives. A nuclear reactor will be enriched uranium and thus more radioactive than a random lump of uranium, but even uranium-235 has a half-life of 703.8 million years (as opposed to, say, 87.7 years for the plutonium-238 in Curiosity's RTG). *bismuth-209, though, is stable-for-all-practical-purposes (half-life of about 20 quintillion years) RTGs are launched fairly regularly, so launching a not-yet-used reactor doesn't sound that scary to me (although the Russian Proton rocket has had some issues recently...) IMO we as a society are way more concerned about nuclear/radiation stuff than the risk really justifies, compared to how we react to, say, air pollution from coal power plants (which probably leads to far, far more deaths from respiratory problems every month than the Chernobyl accident). EDIT: It would be interesting to know how the radioactivity of the amount of uranium in this reactor (in Curies) compares to that of the plutonium in an RTG.

OK, so maybe figuring out the volume and so on the next thing we need to do/decide on. A 1U cubesat is 10cm on a side (1 liter volume). K^2 (or anyone else who knows), how much of that space will the electronics and structure and so on take? It may not be an issue though... if we simply grow the moss in a petri dish, that should be easy to fit in. It'll probably be the microscope/camera etc that will be trickier.