So we like landed on Mars, and stuff

[Starfisher]

but will we do that before our great grandchildren are old and grey?

Options:
1) Send rovers (could actually happen)
2) Send people (dodgy technically and impossible politically)

So which one results in ANYTHING getting done?

[Carl]

@Starfisher: that’s naive in the extreme. Certainly setting up a colony is a hugely difficult problem, but sending a shorter term mission to establish a base and spend a few weeks on the surface is vastly more viable from a technician PoV. As for the political realities, I seriously doubt they're going to persist till our great grandchildren are old and grey. The rovers vs manned debate isn't about weather we should send a manned mission now, (duh difficult as all hell), it's about if we should ever send one at all. Or at least that was my reading of Black's post.

[Nurizeko]

Options:
1) Send rovers (could actually happen)
2) Send people (dodgy technically and impossible politically)

So which one results in ANYTHING getting done?

Sending people isn't 'dodgy' technically, it's dooable. Countless people keep telling the world why it's dooable, intelligent qualified people.

Politically...well, that is political will and doesn't impact on our capabilities, merely the will of our current leaders to get the ball rolling.
I could go on a tangent as to why NASA should have a bit more freedom from the whims of political leaders since they work on timescales a tad more considered than the next election cycle, but that might require some basic ring-fencing of NASA I don't know, suffice to say that's a political debate lol.

I hate to bring it up again but the Apollo programme and NASA itself had a lot to do with politician's will.

[Starfisher]

Someone find me a plan for sending someone to Mars and bringing them back. Right now there isn't one because we have no idea if we can actually make fuel on Mars yet. (Ie we should be sending more rovers to figure that out)

This is why people bring up a colony as "easier". Not bringing people back simplifies the issue. We just keep launching stuff to Mars forever! Which is of course massively naive politically, and yes, it's still technically "dodgy". Intelligent people are great at thinking up ways that might work. We don't know that they'll all work, and even so there are still fundamental issues to maintaining any long term presence on Mars which are unanswered. We've been over this repeatedly.

The point where we send a manned mission is the point where rover missions have exhausted their scientific usefulness and would cost the same as a manned mission to go anyway. That, or we discover some way to actually profit from a manned Mars mission. Until either or both criteria are met, there really isn't any point beyond "YEAH AWESOME" in sending people. And so we won't.

[Retroboy]

@Retro: I'd disagree on the timescale stuff. Unless we suddenly have an Nth generation rover design show up that drastically up's the exploration rate we'll still be trying to answer vital questions about the solar system a centaury or more from now.

With the caveat that I'd love to see a manned Mars mission, what are some of the vital questions that it will answer that can't be answered through other less expensive means? Honest question - not disputing the value of the science, but what does "vital" mean, what are the truly practical benefits beyond making the next space exploration mission easier, and why should it influence the timeline to advance this as rapidly as possible?

======

One of the other challenges is leaving Mars' surface for the return trip. They did okay with it on the Moon because the gravity is about 1/6th that of Earth. On Mars, surface gravity is a little more than double that of the Moon's, and because it's larger its gravity extends out further meaning more fuel and acceleration is required. Even with an orbital rendezvous craft that keeps most of the mass off-planet, there's still a lot of fuel required to visit the surface with any reasonably equipped team and then come back with samples. Assuming they can get a decent Ion Engine built, the fuel for the interplanetary voyage doesn't really have a lot of mass, but that technology doesn't provide sufficient acceleration to escape a gravity well from the planetary surface so you need something else.

In my book, one thing that would help the cause tremendously is to get fusion working. Having near-limitless safely generated power would make a huge number of problems go away. But I think that working fusion is still 20-30 years away if we ever do actually achieve it.

[Stripe7]

There are many technologies that have to be worked out before a manned mission to Mars is possible. Unfortunately the scope of the project would be politically impossible for the west. The only governments I can think of with stability for a long term project such as a Manned Mars mission would be either Japan or China. The US business thinks long term is 1 year, and a US politician's idea of a long term is the span of his/her term in office. China's long term goals cover generations, so I figure the US should design the project and let China swipe the plans and build it. <is there an emoticon for sarcasm?>

The MSL had its radiation detectors active for the entire Mar's trip. NASA should have an idea as to the radiation hazards an 8 month trip entails. They need to develop some kind of radiation shield. It could be in the form of a small bunker for humans and sensitive equipment, or more active measure like a cold plasma shield or high powered magnetic fields that create a charged ion barrier a long distance from the spacecraft or maybe a combination of two or all three.

I think a powered flight would be more feasible than just an orbital sling shot. They need to develop engines, for without them they would need consumables that last for 3-5 years exposed to cosmic rays. NASA paper on food for a Mars trip. The sheer mass needed to be launched of just food would be enormous.

I think building a ferry system and sending a stream of robots to Mars to eXplore possible landing sites for raw materials and then have them eXploit the resources by building radiation shelters and habitats in preparation for the human landing. Once we have eXpanded onto Mars, the Mars astronauts can do all the usual things human explorers do.

[Retroboy]

Gotta watch out for the rats, though. They get everywhere and you need to eXterminate them.

...yeah, I noticed.

======================

Interesting current-news fusion article, as an extension to my previous post. http://www.bbc.com/future/story/2012...eate-the-sun/1

Synopsis: An international consortium is building a giant Tokamak-technology fusion reactor in France, slated to go on-line in 2040. They're hoping it's sufficiently scaled to surpass the energy-in/energy-out break-even point.
Relevance: So unless a different architecture or controlled-fusion process can be developed while this thing is being constructed, my comment about fusion helping the Mars-visiting process won't be relevant for quite some time.

[Elukka]

I think the most feasible high performance engines in the near term would be nuclear thermal rockets. The US developed a working one back in the 60's and the Soviets had a more advanced one in the 80's. The US again flirted with the idea in the 90's but didn't get any hardware built. The technology involved is well understood and all that would be needed is a new design.

VASIMR is good too but would require some serious work on space nuclear reactors to power it. Not that it's not doable, it's just a bit less ready. It has the potential to be even faster than nuclear thermal rockets but getting to that point would take a while.

Either way you go you're gonna need nuclear power. If you only use the reactor in space it would be very safe to launch (arguably safer than the RTG's we launch all the time) as unused nuclear fuel isn't particularly radioactive in general.

You might also go Zubrin's way and do it old school with chemical rockets. That would probably be the fastest option for a less ambitious mission.

[korpisoturi]

In my book, one thing that would help the cause tremendously is to get fusion working. Having near-limitless safely generated power would make a huge number of problems go away. But I think that working fusion is still 20-30 years away if we ever do actually achieve it.

The problem of fusion concerning space exploration is that it doesn't scale down very well (if it did, we would already have fusion reactors in use). You'll need a Death Star for a fusion reactor to be a feasible solution.

[Retroboy]

The problem of fusion concerning space exploration is that it doesn't scale down very well (if it did, we would already have fusion reactors in use).

Disagree in that the problem is substantially more basic: we don't have net-positive-energy fusion at all yet, even in laboratories where they're just testing the concept of energy output-vs-input. The ability to turn the energy output into something useful and add it to the grid is another whole problem.

As for miniaturization, there are alternate fusion technology approaches that are a good deal smaller than the "death star" (and I realize that was a deliberate size exaggeration). A good self-contained fusion plant design will recycle most of its power into the next generation sequence, much as a car engine uses the rotational energy of a camshaft to compress gas vapour for the next cycle. Hooking your fusion reactor up to a 'starter' to initiate the cycle, like those trucks that help start many smaller commercial airliner engines, and then disconnecting it once it's running, might reduce the mass requirements tremendously.

[TDATL]

Space elevator + orbital construction is the way to go for long distance space travel.

[CommissarRezail]

Yeah i like to see orbital boundaries my self smelting ore from the belt.

[ajlsunrise]

In light of the recent mars landing.... I thought that this was funny

[marmoo]

http://www.youtube.com/watch?v=uF9qM...eature=related

Can't believe i'm the 1st to put this obviously pointless but fun link

Cookie for me

[Nurizeko]

So the thread has come to this then?

Aight..

[Guilliman]

That's just awesome.

[Misiok]

The sword and helm would pass, but the Tireme just stands out.

[marmoo]

You doubt Nurizeko's evidence?
Do you not believe your own eyes?

[Derivative]

We're going to Mars in a rowboat!! Beat that one, buddy!

[Stripe7]

That is like totally awsome, Nurizeko!

[Moe]

That's not a trireme. That's a goat throwing viking longboat.

[Carl]

@Everyone: sorry for how late this is. Had a week off work so been chilling out doing my own thing and this got a bit forgotten, sorry.

@Starfisher: look back about 5 posts from your last one. Any decent draughtsman should be able to lay out the basics and the eggheads at NASA could easily refine it into a workable spacecraft. It fills all the basic elements of radiation shielding, living space, and structural elements. All you need is to figure out the mass of the final setup and then you can figure out what kind of propulsion it needs to achieve the pre-specified thrust in the structural design. Again something NASA is eminently qualified to do. The problems aren't really technical, they're political. Such a design while doable now is very much a case of brute force engineering, that means it's heavy as all hell, getting the funding across the many years it would take to assemble for the number of launches is just not going to happen right now. Especially since I tracked down a figure for the dimensions on the ISS modules and did some math, try adding a pair of zeros to my original weight estimations.

I also aren't sure why your hung up on making fuel at mars. NASA has a stated policy of never sending a manned mission without the fuel to bring them home, (another thing that would kill a 1 way colony trip that I forgot to mention). They might experiment with making fuel when they get there, but they'll never rely on it.

@Retro: I thought we'd been through the whole practical applications thing, (by we I mean the forum, i don't think i was too involved in that one personally), about immediate practical applications. I'm sure a full blown expert in the field could find a few points. But like a lot of pure science it's done with the hope of discovering new thing's, practical applications are often side aspects of this that no one expects, (because no one's too sure of what they'll discover). That said much of the hard physical stuff used to build this thing is distinctly usable for a whole range of other things, weather you ship it all from earth, or otherwise.

@Retro & Stripe7: The fuel for takeoff and landing and food mass are both relatively minor weight expenses TBH. As I’ve pointed out before, no one is going to risk their astronauts on an energy shield system on the assumption that it will never ever fail. At that point the radiation shield stops merely being a part of the spacecraft, sans engines and fuel tanks it will be the spacecraft. I just did some math, using 88 ISS modules with a total maximum capacity of 1180 tons, the mass of the rad shield hit's 62,000 tons. You can tighten that down a bit by reducing inter-module connectivity and making servicing of module exteriors impossible, (so no exterior only serviceable parts allowed), but you can only get it down so much. Though the ratios of module mass to shield mass do get better as the size increases, the overall shield weight still goes up, (for example at 512 modules, (6900 tons), the shield still only grazes 200,000 tons). Square cube law and all that.

@Stripe7: Decreasing the time to mars shouldn't have a significant effect on radiation exposure, due to solar flares and their unpredictability it is necessary to include adequate shielding against said flares. At that point their average dose over a trip isn't going to vary much with trip time, (assuming the sun is at the same point in it's 11 year cycle for both trips).

@Elukka: The problem with spaceborn reactors isn't what happens when they undergo a normal re-entry. You can have them in cold shutdown and safely bring them down due to that. It's when there is an uncontrolled re-entry that issues arise. There's no time to get it sufficiently shut down and it will inevitably suffer a meltdown during or immediately after reentry. That said I do agree it’s the most advanced and well understood of the high end rockets available. There's even an advanced "lightbulb" form that’s been theorized out that would be able to achieve ISP values equivalent to VASMIR's best. But the inherent danger is always going to be off-putting.

@TDATL: when we get a space elevator, sure. But that’s then. This is now. For now the best option that we can actually build is a moon base shipping lunar rock to the L4 or L5 point for refining via mass driver. A space Elevator is a great idea, but it's still the same distant dream that usable fusion is, and will likely remain so for some time to come.

@Aj, e.t.c: hehe

[Nurizeko]

So ronry...

[CommissarRezail]

Wall - E what are you doing on Mars?

[Liljagare]

Getting prepped for our arrival..

[Retroboy]

But like a lot of pure science it's done with the hope of discovering new thing's, practical applications are often side aspects of this that no one expects, (because no one's too sure of what they'll discover). That said much of the hard physical stuff used to build this thing is distinctly usable for a whole range of other things, weather you ship it all from earth, or otherwise.

That could very well be true, but that type of gamble does not make a sound investment strategy. There are a ton of already-identified directions where the payback from significant scientific and innovation advancement is more predictable given many billions of dollars of investment. Some of them, like asteroid mining or fusion, would assist in the ability to put a footprint on Mars at minimum by making the trip more feasible.

The reason some billionaires are kicking funds into asteroid mining is because the payback would be immense AND it's a feel-good project that advances humanity. Plus - bonus - it can be done completely with robotics that aren't too far away from what we have now, which means very little human risk.

62,000 tons (required shielding)

The cost of lifting that much payload from Earth using conventional technologies would be colossal. For comparative purposes the entire ISS weighs 49000 tons according to Wikipedia and that took a lot of years and a lot of flights to construct.

Seems to me that unless the design changes away from high-mass physical shielding, either the astronauts would have to accept the gamble, or there would have to be a smaller "bomb bunker" onboard to squeeze into for any radiation storms.

[Moe]

Retro, the ISS weighs 450,000 kilograms, which is about 450 tons. You're off by two orders of magnitude - not sure where you're getting that from. I'm guessing 62,000 tons is closer to the sum total of every object we've shot into orbit so far.

[Stripe7]

The definition of a heavy lift vehicle is the ability to lift a minimum of 50,000 kilo's into orbit. So about 50 tonnes. (metric). So that would be 1240 launches just for the infrastructure using heavy lift rockets. Add to that the launches for consumables for 5 years and you are looking at a political and economic impossibility.

There are major power issues with Vasimr thrusters but I think a Mars spaceship using one with a Stirling Radioisotope Generator power source could make the trip in 40-50 days. Using plasma and magnetic shields for normal space radiation and a bunker for solar flares would cut down the mass requirements. There would be less issues with radiation degradation of the food stores as well as less consumables overall.

There is a major issue of the US running low on Plutonium for power cores due to the lack of new Nuclear power plants coming online. How this will affect space exploration has yet to be determined.

[Retroboy]

Moe, I'm getting that from being stupid and posting after a relatively sleepless night that obviously impaired my normally fairly reasonable mathematical abilities to count zeroes, tell the difference between metric and imperial, and divide by 2000. My bad.

[Carl]

@Retro: there are countless projects going on right now, (of which the search for higgs boson is/was just one), that are of that nature and that are consuming or have consumed huge amounts of money. Just because it's not a definite return on investment doesn’t mean it shouldn't be pursued. I'm sure the other more sciencey forum members could point to numerous science projects throughout history that where pursued with no obvious benefit but whose findings where/are fundamental to everyday life as we knew/know it. I understand where your coming from of course . But it doesn’t marry up with reality very well.

Wiki for me lists the ISS at 450 tons, I think you've confused KG's and Tons there . I'm not disagreeing btw that it would be politically untenable.

This is why we need the moon base and mass driver. For 40,000 tons to the moon plus the mass of the mass catcher you can ship a million tons of moon rock to NEO's a year. Another 40,000 nets you a space refinery and construction shack. It might be expensive to initially establish. But it takes manned mission costs and basically trivializes them. Even if you just use lunar rock for rad shields it cuts the mass to orbit by large amounts. Add in Oxygen extraction for fueling and it starts dropping several orders of magnitude, (fuel is likely to be the only thing nearly as massive to lift as a rad shield).

Using a web source LEO costs are somewhere between 4.3 and 3 thousand US dollars per KG. That means you can build one rad shield a launch cost of approx 250 Billion US dollars. Or a Mass Driver and Catcher capable of supplying rad shielding for 16 ships a year at 172 billion US dollars setup, (works out at around 10 billion per ship, or about the same as a year and a half’s worth of CERN funding, or 77$ per pound, about 55 times cheaper than the rocket that put them on the moon). Go for a full blown refiner and construction shack and your looking at maybe a half a trillion setup, but you now only have to ship the modules and engines from earth, (and theoretically you could avoid that and go for a better design), the structural frameworks, rad shields, fuel tanks, and pipe work are all built in space. The personnel cost and occasional electronic module needing to be shipped out, (plus supplies of food), will produce upkeep costs, but relative to what they'll let you do they're quite cheap compared to doing it all from the ground. Of course since it involves far more technologies that would require development it would never cost just the launch costs and maintenance costs. But even with that cost inflation, spread it out over 10 years and it becomes very workable, (quite aside from the fact that mass launching of stuff would have a strong negative effect on cost and that the designs represented there are a long way from the ideal in terms of cost per KG to orbit).

Solar Flares are far too frequent to simply "take the gamble" and whilst a bunker might do for flares it does nothing about the continuous low level ambient radiation which over a several year period could be quite an issue, especially the ion nuclei. Another issue is that even if the flare shelter is there and you've got the day to day exposure sorted, the fact that most of the craft gets hit by high doses of radiation is going to kill any attempts at a space farm, as well as recycling air, water, e.t.c. via any kind of organic means, (you can carry everything though, it's just less efficient, mostly due to excess mass and volume for the storage), there's also the issue of what that kind of systematic long term exposure is going to do to ships systems. Some things have been put on probes and will be just fine, but other systems are unique to manned craft and have never been put through that kind of systematic testing. In particular if your doing it this way the durability of the CO2 scrubbing system is vital. Other waste recycling is also going to have to be considered carefully. Also long term irradiation issues on the longer missions show up. Plus of course that NASA study pretty strongly indicates letting the food stores get heavy exposure is very non-ideal. Another finial issue is how it limits the ability of missions to be conducted during the peak periods in the suns 11 year cycle, flares jump from once a week or less at the low end of it's cycle to several a day, (wikipedia for source). That could result in them barely being able to leave the bunker for days at a time. That could become an issue to say the least.

Mars also presents issues here. The surface isn't anywhere near as well protected and I would fully expect a rad shielded landing unit and (if you want them to explore any serious distance), equally well shielded rovers to be necessary. That’s going to add 1000's of tons to a mars mission any way you cut it. Even parring down to bare minimum you probably couldn't scrape much under the 1,000 ton mark, and at that point your so limited in what you can do on mars it's not really worth going. The need to bring a 100 tons or so of satellites to mars to make sure you can spot flares in enough time isn't going to help matters.

@Stripe7: Again, compared to the weight of the shield the food and water and oxygen are totally incidental. A human needs about 10 pounds of food and water a day, and a source on the web says a human at rest breathes the equivalent of about 550 liters of pure gaseous oxygen every day. Lets quadruple that up to cover actual work and possibly a faulty source, add on food and water and then a 20% safety margin. It comes out at 16 Pounds per head per day. Or 320Lb's per day for a 20 man crew. Even on a 5 year mission it's only 261 tons. Compared to the rad shield it's incidental, especially if your able to recycle any of this in some way or another.

As for VASMIR on RTG's, it all comes down to how much mass per watt VASMIR can move to mars in X timeframe. Certainly if you can do it, stuff like VASMIR eliminates the second most massive item, (fuel for acceleration and deceleration of the main spacecraft).

EDIT; Fixed consumable figures. Forgot to factor in 1 mole of gas = 24 liters first time round, same excuse as retro, late night maths .

[Moe]

So apparently there was a plan to land a motherfucking boat on Titan and have it float around in the methane lake. Sadly, that mission got axed before it went past the planning stage, but that would have been pretty fucking awesome. Instead, we're now sending a drill to Mars in 2016. Bruce Willis will not be available to run it though.

[Nurizeko]

We'll never make depth without the best but most personally dysfunctional drill-team on earth.

That robot is the biggest mistake in the history of NASA.

[Derivative]

Why'd they pick Mars yet again? We've sent plenty of probes to Mars. Their other choices were the boat and a probe to a comet right? I would pick a boat to Titan over Mars at any time. Plus if that boat had oars for maneuvering, then we could safely say that we went to Titan in a rowboat.

[Misiok]

I guess we didn't send that boat because we've got no real vikings anymore, and sending anyone but them wouldn't be manly and our race would be seen as weak, sending silly scientists/robots with on it.

[Aesaar]

I've always found Titan more interesting than Mars, so NASA passing on that is disappointing.

[SpitfireMK461]

Venus and Mars are the spiritual siblings of Earth, in that they are the planets most like Earth. Venus is an extremely harsh planet to work with, so Mars is the logical planet to explore the most. It has many geological features that interest us for the purpose of learning more about the solar system. It is a planet that has easily accessible ice and obvious evidence that liquid water was present in large flowing quantities. That makes, at the moment, the most likely place to find life or evidence of past life. It is also a relatively easy planet to work with as there are no giant millennium old storms, acid rain, massive winds, corrosive atmospheres, or complete cloud cover, and it is close. That is why we spend so much time looking at Mars.

Titan is certainly interesting because it has active weather and lakes and oceans, and it "looks" a lot like Earth. Unfortunately, those lakes and the weather are all methane. It looks great, but it isn't the most hospitable climate. It is possible there is life there, but there are better places. If you want to talk of other places to explore, higher on the list, I think, are Europa (oxygen atmosphere, covered in ice, possible oceans of water), and Enceladus (thinner sheet of ice, oceans of water underneath, geologically active).

[Moe]

That makes, at the moment, the most likely place to find life or evidence of past life

There's always Europa. That would actually be a really cool mission, but the flight time is kind of long.

[Carl]

@Spitfire: Titan's actually got the building blocks of life just lying around though, plus it has lower surface radiation than those two AFAIK. A lot of the work on throwing together a mission to our watery neighbors seems to have ground to a halt with that realization. They'd need to send a remote probe quiet deep under the ice to reach the parts of the oceans free of that radiations. Gas Giants and their Van Allen belts eh.

Io Is a prime candidate for study just for it's sheer volcanism, but that same volcanism means it's amongst the harshest of radiation environments in the solar system.

[SpitfireMK461]

Don't get me wrong, Titan has the possibility of holding life, but its environment is not one that we would consider having the highest chance of holding life. Our current standard for the most productive environment to contain life is the rich oxygen/nitrogen/CO2 atmosphere with liquid water. We KNOW life thrives there. Other environments we know contain life, and others we figure CAN contain life, but we only know of one where it thrives, so it is natural to look closest at those environments. Everything we know about Mars says it used to be similar to Earth, so it is natural for us to look there. Titan, while it looks like Earth, is also extremely different. There is certainly much to learn from it, and I hope in the future we study it closely, but in terms of looking for life, it isn't at the top of the list.

And yes, Europe and Enceladus explorations would take quite a bit of work, having to design a drilling probe, but it looks like we could be getting that practice on the next Mars mission. If I were NASA, I'd be asking for two or three of those probes for the purpose of sending them to Europa and Enceladus.

I'd also like to see another look taken at Venus. It is an obviously inhospitable place now, but evidence suggests it may have once had a climate similar to Earth but was eventually destroyed by, wait for it, runaway global warming, something that we may want to research. For exploration, its atmosphere could be helpful as a floating probe could be used instead of a rover. That avoids the issue of destructive pressures and allows us to see much more of the surface.

[Retroboy]

Why'd they pick Mars yet again?

Four reasons: it's the most "earthlike" body that fits within the potentially habitable zone around a star, it's closer so the timeframe between launch and landing is short, it's the planet that people are most curious (pun intended) about, and due to its firm placement in our SF literature everyone would just love it to death if we actually discovered martians of one form or other.

Extraterrestrial exploration has as much to do with marketing as it does with science. The more that you learn (key words) in short order, the more you galvanize public awareness and interest, and thus the greater your budget for the next mission and the better your chances of not losing your NASA job or gubmint research grant. The Moon has already been ambled around on more than 30 years ago so it's way, way done, leaving Mars as easily the best current target for all of that inspiring stuff.

[Carl]

@Spitfire: the problem is that based on our current knowledge, for life to form certain basic (but incredibly complex), chemical interactions have to take place. We don't have the exact reactions panned out yet, but we know what the basic chemicals are. AFAIK it's fairly unclear weather euroepa actually has that mix, and with the radiation any attempt to find life, even if it exists would have to go very deep. Where talking the equivalent of building an autonomous ROV submersible craft capable of operating at the deepest points on earth for years and remotely transmitting it's data to an orbital satellite, (not easy through that much water and ice), all without ever receiving any human intervention. It's far beyond anything we've ever conceived of right now.

Titan on the other hand confirmably has all the stuff needed, The cold amongst other things might well limit the probability of actual life, but it's still a good shot for finding it, and there's a high chance we'll find "part built" life there, the intermediary steps between pools of chemicals and single celled life that we currently lack. That alone represents a discovery of incalculable magnitude.

I'd also point out something else. Whilst I don't believe titan's methane is in any way indicative of anything, when NASA sent the Galilieo probe of on it's journey to Jupiter, just before they sent it off they performed a churlish littlie experiment. Point it's sensors at earth and look for signs of life . The only sign of life it found was a chemical analysis of the atmosphere. I contains significant quantities of both Oxygen and Methane. The two substances are highly reactive, unless something is continuously replacing both they cannot co-exist. That replenishment is all that shows life exists here. From the PoV of a space probe all the great works of men are invisible. Galileo couldn't even say there was intelligent life. (i now have this image of the probe sitting there pondering the "is it intelligent question" whilst also wondering how it can be receiving orders and weather that’s evidence one way or the other ).

Venus however is a definite bust. Evidence from ground scanning radar indicates that Venus periodically undergoes a mass volcanic eruption that literally erases the existing crust. In addition that highly toxic atmosphere would have reacted with any traces of life on the surface destroying it even if the lava didn't. Life may have existed at one time on Venus, but if it did we'll never be able to prove it. All trace has been lost forever. A floating probe sounds nice, but again we've never created anything like that for long term work. Also Venus has extreme upper atmosphere wind speeds, whilst the lower atmosphere is still blisteringly hot, (on Venus it rains liquid lead, but the rain evaporates before it reaches the ground).

[SpitfireMK461]

I think we can agree that exploring these planets/moons is quite difficult for various reasons. Notice now how Mars seems like a relatively easy and reasonable choice for exploration? It has a bit of everything going for it.

And clarification on Venus - We obviously wouldn't explore it for life reasons. It would be geological/atmospheric research. There is interest in research why Venus has the atmosphere it does, due to the belief runaway global warming occurred there.

[Carl]

Ahh gotcha. Agree Venus is intresting for that .

And yes most places besides mars are really arkward, the Gas giants have huge magnetic feilds that produce intense radiation hazards before you even start to deal with the individual moons issues, (though we did drop a probe right into jupiter. Survived for 51 minutes on us). Venus is just a plain hell hole. Mercuarys Radiation will be high but mostly it's just plan hell to get to due to the delta V required, and Pluto and beyond are just so dammed far away. IMHO i'd love a detailed study of Uranus. To quote one source i read on it: "To build a working model of how this world and it's moons formed from Voyager 2's observations requires more miricales than anyone is willing to accept".

[Nurizeko]

Titan is just too cold tbf, it has a weather cycle of sorts, happy days. Weather isn't life, and the building blocks for life are pointless if they're in a deep freeze.

Venus' atmosphere is like what, 98% CO2? Earth's is a fraction of 1% and Venus is closer to the sun so we have our run-away greenhouse explained. A shame really, if Venus had been lucky enough to avoid run-away greenhouse we might be able to look at a truly sister planet to Earth, maybe even bearing life. Venus interests me a lot if only because of the sheer potential it had to be the true second life bearing world in the solar system. Fuck you Venus for killing our dreams you selfish hot bastard.

Europa and the sorts are interesting, their deep oceans might just be the place we want to look but as has been said, humans are pretty lazy so waiting all that time and making the right probe would require some effort to stop being that lazy.

mercury is a burnt metalic ball without an atmosphere, no chance.

Mars is cool in that it's the closest we have to an Earth like environment in the solar system but on the other hand Mars is small and it seems like it was inevitable it's magnetic dynamo would wind down, and thus we'd end up with a dead dry rock with a piddling remnant atmosphere. The wonder is Mars ever had running water at all and maybe even life because of it. Mar's was never going to have a long and storied relationship with life-bearing conditions.

[OpelFalcon]

Whenever Titan is mentioned. I'm always reminded of this clip.

[Stripe7]

Titan may seem too cold but what goes on down beneath its crust? What about exploring Europa? It has a layer of liquid ocean under its crust. Dropping a probe near one of its many ice volcano's could give us a glimpse of what is under the ice crust.

[Elukka]

@Elukka: The problem with spaceborn reactors isn't what happens when they undergo a normal re-entry. You can have them in cold shutdown and safely bring them down due to that. It's when there is an uncontrolled re-entry that issues arise. There's no time to get it sufficiently shut down and it will inevitably suffer a meltdown during or immediately after reentry. That said I do agree it’s the most advanced and well understood of the high end rockets available. There's even an advanced "lightbulb" form that’s been theorized out that would be able to achieve ISP values equivalent to VASMIR's best. But the inherent danger is always going to be off-putting.

If you're using the reactor for the trip to Mars and back there's very little chance it could ever make an uncontrolled re-entry. I suppose it's theoretically possible you'd have some kind of catastrophic navigation failure on the way back and you'd randomly hit a tiny target (the Earth) but it really doesn't seem very likely. And during launch, when it's not yet operational, it wouldn't be particularly dangerous.

Where do you get those numbers for radiation shielding? I've never heard of any concept where the shielding mass would approach the mass of the rest of the vehicle, and I've especially never heard of a case where the shielding would utterly eclipse the ship's mass!

[Carl]

@Nuri: True the deep freeze certainly doesn’t help the chances of life on Titan, but there's still all those chemicals there that may hold clues to how things start, and even at that low temperature, reactions still take place, i find it unlikely anything capable of surviving there would have developed, but i'm not going to discount it either. Besides, we already put a more basic probe on titan, so we at least know how to do it .

@Elluka: I used this module as the basis for the prospective "modules" of a theoretical mars craft, (it's used as the basis of a few ISS modules so seemed the obvious choice). After working out a very rough basic layout for them i worked out the peal exterior dimensions on a calculator, added a bit for clearance then worked out the surface area of a cylinder. At that point it was just a case of working out the surface area X tonnage per square meter.

The tonnage comes from this page. Specifically:

But six feet of soil over all 440 exterior acres of the Stanford torus is a rather large pile. It is 10 million tons...

You can backwork that to the mass per square meter, and since radiation absorption is a factor of material and thickness we know that the same thickness on any other craft will provide the same level of protection. So as long as you now have the surface area worked out you can work out shield mass.

[Moe]

Where do you get those numbers for radiation shielding?

Also, you can separate the reactor from the rest of the craft and have it dangling on a tether. Flux will drop with the square of the distance. Furthermore, unless you're revolving around the reactor, you really only need to put a shield between it and the rest of your ship. Nobody really cares about radiation leaking out "backwards".

[Inquisitor Lok]

So remember that low quality black and white descent video that was posted a while back after it landed. Well they released a colour HD version!