NERVAfan

Actually, I think turning (large parts of) the Sahara into farmland is quite viable as megaprojects go - it was apparently mostly grassland, with some lakes and stuff, up till ~7000 years ago. So it might not take much to push it back into that state. It shouldn't mess with climate or ecology too much, as the climate/ecology of 7000 years ago wasn't much different from today. Massive desalination and pumping water inland (by solar or nuclear power) would be the first step, basically a "Canals of Mars" setup. Making the soil better would probably be the hardest part.

If the ship really masses 100,000 metric tons (10^8 kg), then to accelerate it at 15 m/s^2 is 1.5 x 10^9 N (1000 Mainsails worth of thrust!) The force from radiation pressure (assuming a perfectly reflective light sail) is 150 megawatts per newton. So 1.5 x 10^9 N * 1.5 x 10^8 watts/N = 2.25 * 10^17 watts, 225 petawatts, somewhat more than the entire power reaching the Earth from the Sun (174 petawatts). It's still miniscule compared to the Sun's total power output though. If this laser actually hit the Earth... well, a megaton of TNT is 4.184 x 10^15 joules. So this is the equivalent of 53.8 megatons of TNT per second (the largest nuclear test ever was 51 megatons of TNT equivalent).

Yeah, exactly. I wouldn't expect fossils you could see without a microscope. Only a tiny portion even of those.

Because there isn't really all that much interest in Venus compared to Mars, and a Venus rover would have an extremely short lifetime and wouldn't be cost effective (it wouldn't last long enough to use the ability to "rove"). It's not just power limitations but surviving the temperature.

I think biofuels are very promising for some applications (where high energy density is important e.g. aviation fuels) but current corn ethanol production isn't really any environmentally better than fossil fuels (since corn growing is fossil-fuel-heavy) and competes with food. What you need is biofuels made from "waste" materials e.g. biodiesel from waste oil or cellulosic ethanol. Solar... can't be used for base load, true, but it can produce so much energy ultimately that storage might be worth it in the long term.

Greenhouse gases trap more of the Sun's heat. The waste heat contribution from human activities is small in comparison (roughly 1 in 10,000 of the Sun's energy reaching the Earth, IIRC). Yeah, climate problems are much more pressing than running out. OK, I entirely agree that global warming is a real problem, but... ...that seems unlikely. CO2 levels were at 1500-1800 ppm during the Cretaceous, and maybe as high as 4000 ppm during the Paleocene-Eocene Thermal Maximum (though this latter one is very debated & poorly constrained) and warm-blooded animals were just fine (OK there were some extinctions during the P-E TM, but not literally "stuff dying of heatstroke"). (In hotter geological eras, there was much less temperature gradient with latitude, so the planet became - in the extreme cases like the warmer part of the Eocene - mostly tropical rather than the tropical regions reaching 60C or something crazy.)

That's why you use the NTR only in space, as an upper stage. As architeuthis pointed out, there's almost certainly more radioactivity in an RTG than in an un-activated NTR reactor (the reactor is bigger, but the half-life is 10 million times longer so vastly less radioactive).

Precambrian fossils are really hard to find on Earth (OK, some of that is due to rocks that old being relatively rare, but not nearly all of it). I think it's way too early to say we "should" have found fossils if they were there - we've only geologically inspected a miniscule part of Mars (the orbiters don't have enough resolution for that). And life could totally have survived. Endolithic forms of life would do fine on Mars if there's even an ultra-tiny trickle of liquid water in the subsurface. (I don't know how long it would take to evolve an endolithic mode of life though.) I agree it's still very unknown whether Mars was watery long enough to develop life (of course, we don't know how long that takes either - it could have developed practically immediately once Earth had liquid water. There are few to no rocks that old.)

It's worse than that - hydrogen is generally industrially produced not by splitting water but from methane by "steam reforming" (CH4 + H2O -> CO + 3 H2, then CO + H2O -> CO2 + H2) which uses fossil fuels both for the methane feedstock and to provide the heat required for the reaction (though I guess you could use biogas or something). The environmental benefits of hydrogen fuel (in rockets, cars, or anything) are really questionable. Hydrogen (H2) isn't found naturally on Earth in useful quantities, so it's never really a source of energy, only a storage medium. In the vast majority of cases, it would make more sense to directly use whatever energy source you'd use to make hydrogen (like just using the methane as fuel directly). Rockets are sometimes an exception since specific impulse is really important due to the exponential nature of the rocket equation; but storing liquid hydrogen is a giant pain which is why SpaceX doesn't use it and doesn't plan to. The "hydrogen car" people are talking about using solar power to split water and using the hydrogen just as a storage medium - but battery energy densities are improving rapidly so IMO electric cars will end up making more sense (also, there isn't anyone with the stature/resources of Elon Musk/Tesla pushing hydrogen car technology.)

The methane release event is REALLY interesting. Martian "algal bloom"?

IIRC the VentureStar isn't a pure reaction drive ship, it's launched by lightsail powered by laser banks in the Solar System and only uses the (antimatter/fusion) rockets to decelerate... which halves the on-board delta-v requirement. 70% of lightspeed is really really fast though. --- As for the heat problem: you don't transfer the heat into any kind of solid engine component that remains attached to the ship, you use pulse propulsion (like Project Orion). If the "engine component" (IE 'pulse unit'/bomb) only has to last a nanosecond then it can be a trillion degrees and who cares? You run into this problem way before getting to significant fractions of lightspeed, BTW - the melting point of the reactor is what limits NERVA type NTRs to specific impulses in the 750-1000 seconds range. That's why a gas-core NTR or a fission Orion would have much better specific impulse than a NERVA type (solid core) NTR.

Hmmm. I still disagree that it has to be nearly that big. (Biosphere 2 was very inefficient - I'm pretty sure you could make something significantly smaller work - and it's much smaller than a 1000-person base would be.) Sadly, I don't have $1-$2 million or so to actually prove this. (I think you could theoretically fit it into the mass/volume of a smallish RV per person, or less, for that matter, with careful choice of species - but there wouldn't be much margin, and it would be a pretty monotonous diet.) EDIT: I'd say the ISS/Mir/Skylab is right about "too small to make it practical", but something 5-10 times bigger would probably be better served with an at least partially biological system.

I am quite skeptical they will fly anything to orbit any time soon. IMO something like Nanoracks is probably a more workable option.

Well, NASA just gave SpaceX the contract for TESS, and that was $87 million - 42% more than the $61.2 million base price.

I don't see why that price is so impossible, either. I don't believe it's mostly labor costs, because if it were, Russia and India would be launching F9-sized rockets for under $10 million, since their labor costs are something like an order of magnitude lower than SpaceX's (especially as SpaceX is in one of the more expensive cost-of-living parts of the US). Yet they clearly are not. Also, once they get up to full launch cadence (quite possibly next year) the labor costs for F9 could be pretty low.

I don't think there's any confusion. He said 70% of the cost. So assuming a constant profit margin, they could lower the price that much if all savings were directly translated into lowering the launch price.

That would have been a huge problem when the OST was written, and for e.g. the Viking experiments, but not really anymore; stuff like metagenomics can distinguish these days. Also, it would be pretty improbable for any bacteria brought to spread across the planet in a short (decades) time scale.

In 10 years, if reusability works out? I'd expect them to be more like half of current price - $30 million for a F9, ~$40 million for a FH with all 3 boosters reused. Significant, but not utterly game changing. But ... in 10 years there is a good chance the next, fully reusable, rocket will be flying (Elon Musk recently said 5-6 years; assuming slips, 10 years seems realistic). And that may really change everything. Only very small ones. Elon Musk was recently talking about a 700-satellite constellation. Because they would actually have something to sell... They are specifically waiting on Commercial Crew to be available. Since no one has ever lowered launch prices very significantly before ... how can you (or anyone) possibly know that? Sure, people will not suddenly launch 5 times as many commsats or whatever. That's not the point. People will find new ways to use space as the price drops to make it accessible.

IIRC the increase is no more than inflation alone (obviously not between 2013 and 2014, but since they first put up the original price). That would seem extremely pessimistic to me. Elon Musk said the first stage is ~75% of vehicle cost. I really think vehicle cost is much more than 20% of the price. (If labor costs made the difference, the Russians, with their enormously lower labor costs, would be several times cheaper.)

A very important question... which someone professional should really be looking into. (Seriously, why hasn't there been an actual attempt to find life on Mars from NASA since the 70s????) It would probably be hard, but it is IMO critical to answer the question of whether it's transferred-from-Earth or a genuinely independent origin of life.

That's a very good idea. Let's leave this thread for the satellite itself and broader design questions (Where things fit, mass/center of gravity limitations, power limits etc.) I've started a thread here for the experiment, sensors, moss survival conditions. http://forum.kerbalspaceprogram.com/threads/103462-KSP-Community-Cubesat-Project-The-Experiment-Moss-survival-conditions-etc?p=1606234#post1606234 Somebody who knows something about programming or communications (not me) should start those threads.

TO attempt to make the huge (currently 189 page) KSP Community Cubesat project/thread more readable, Newt suggested we should create separate threads for different parts of the project. So here we go. (Introduction for those not familiar with the project: The current plan is for a 1U Cubesat (10cm x 10cm x 10cm, maximum mass 1.33kg) in Low Earth Orbit. The experiment will involve spinning the satellite to create centrifugal "artificial gravity" and observing the response of moss grown inside the satellite to low gravity levels. Funding will probably be by Kickstarter, but we need a good plan and design first.) Original thread, which is currently mostly covering 3D models and how to place the parts within the Cubesat: http://forum.kerbalspaceprogram.com/threads/86010-KSP-Community-CubeSat/ General project Google Doc: https://docs.google.com/document/d/1jR2B_M67cITTBtV_PDMoioVQp3bnCTR85ecQeVKmpWI/edit This thread is for discussing the experiment itself - the moss, the camera and sensors used to measure it and its growing conditions, the environmental control needed to keep it alive. Mazon Del was discussing the experiment with an actual scientist who studies moss. The leading contender for a moss species to fly is Physcomitrella patens (Is that still correct?)

It's not that precise. Plants are not photosynthesizing at 100% of capacity constantly, etc. There is a significant degree of compensation built in, because of the fact that living things respond to different conditions differently. And you can help that along by altering light levels and stuff. (Also, don't use one pump for 1/2 your whole system! And things don't usually die instantly in a situation like that; there should be time to fix things.) Also, I wouldn't use aeroponics, but... There will be some uncertainty, but in a well designed system for this purpose (NOT Biosphere 2*) there will be much less than you would think from Earth examples, since the system is closed and tightly controlled. No weather, no floods, no droughts, no diseases or pests introduced. *To be fair, Biosphere 2 was trying to do a lot of things at once. It was not specifically an attempt to create a space life-support-system. However, I think it has given a very skewed picture of how difficult the problem really is. There would indeed be some margin, but not so much that it would be problematic. Also, the system is self balancing to some degree. It won't be forever. But neither is the Earth, technically. You can get 2-3 years reliably, 10+ years sometimes, of successful closure in an ecosystem the size of a basketball or smaller (they're sold commercially as Ecospheres). I don't see why several thousand years in something the size of a base/colony should be so impossible. Either this will be on a mission/spaceship, in which case you probably only need it to work for single-digit number of years. Or it will be on a base of some sort, in which case it doesn't have to be 100% perfectly closed, as you can introduce extra water/carbon/etc. from the Moon ice or Mars ice/atmosphere or whatever body you have the base on. Then why didn't the earth run out of nutrients billions of years ago? Because the losses are miniscule when the system is considered as a whole - the biosphere has a way of re-harvesting almost everything. You don't immediately get 100% of the gas back, but over time the biologically fixed nitrogen that is emitted as nitrogen gas is fixed back into biologically useful forms, etc. Things are only lost from the system when they are removed from the habitable parts of the Earth entirely (water split by lightning or UV and the hydrogen escapes to space, carbon trapped in deep layers as fossil fuels), or, currently, turned into certain technological chemicals that life can't use. Pretty much all wastes are recycled. No way. Even Biosphere 2 did enormously better than that. OK, true, but not relevant to what we are talking about. Technically the right term for the systems we're discussing is "materially closed" as the matter cycles but you need new energy from outside. Not really. Yes, volcanoes emit CO2, but CO2 is geologically lost as carbonate rocks too, and IIRC this is actually a net loss of carbon. Anyway, this is irrelevant. The abiotic / geological carbon cycle (and the creation of fossil fuels) matter on a timescale of millions of years or more. It's not relevant to a life support system on a human scale. On human timescales (without fossil fuel burning involved, anyway), the carbon cycle really is: carbohydrates + O2 -> CO2 + H2O (respiration) balanced by CO2 + H2O -> carbohydrates + O2 (photosynthesis) I'm not really talking about designing for geological time scales. Getting it to last 6,000-8,000 years or so (the whole history of human civilization) ought to be just fine

I'm kind of skeptical of finding biosignatures as such. It seems really a stretch that complex molecules would survive that long, even without Earth-style decomposers. Microfossils are more likely (but those are rare even on Earth and would be hard to unambiguously identify). I think looking for present life is key. (And if Mars ever had life at all, there's a pretty good chance it would have survived, IMO. Also, nutrient broths would probably only work if the lifeforms were 'organotrophs' - getting their carbon from previous biological sources. Since Mars probably doesn't have much of an ecosystem, it's pretty likely Mars life would just fix carbon directly from CO2 - it wouldn't necessarily be able to metabolize a nutrient broth. You would at least have a good chance; I would think cell sizes would likely be comparable. They can only be so small before there simply isn't room to fit in the complex molecules... I think the smallest Earth cells (200nm-300nm) are too small to see well with light microscopes though, since this is less than the wavelength of visible light (~400nm-700nm).

Not right now. But given development times, we're not talking about the market now but the market 10 years from now. By then, we'll probably have partial reusability, we'll almost certainly have Commercial Crew, we'll probably have more space tourism and Bigelow stations, we'll probably have big LEO satellite constellations... Not right now, maybe, but IMO building the infrastructure for large-scale human spaceflight is what NASA human spaceflight should be for. The cost is tiny on the scale of the US government, and the potential rewards are overwhelming.