Heh also came to say the same thing. On reddit it would have obviously happened asap but I thought maybe there's less snarky humor on HN. Guess we couldn't resist this one though.
Does anyone else think NASA should reconsider their plans for a manned mission to Mars? With Europe, Ceres, Enceladus, Ganymede and many more promising moons out there it seems kind of a waste to spend time, effort and capital in Mars now.
Mars would be the first long-term space based mission. If you've only made a pillow-fort (ISS), or stayed in a tent in your backyard (moon), wouldn't you try to camp in your local state park before backpacking into the wilderness?
Europa is a lot further away than Mars [1]. Every extra 4600 m/s of delta V in the mission means another factor of e in the ratio of initial to payload mass. At least until we develop better high efficiency rockets.
In practice, the ΔV differences are actually way smaller than that chart suggests. Those figures are for direct transfers (per the legend). But if you allow indirect trajectories with gravity assists [0], that makes things drastically cheaper. To intercept Jupiter, you can steal much of the needed ΔV from flybys of the inner planets (at the tradeoff of time, waiting to go around the sun multiple times). And maneuvering within Jupiter's gravity well can be practically free, by flybys of the Galilean moons. The map tells you 8,890 m/s to intercept Europa, which would be horrifying, but none of that actually needs to be propulsion.
Keep in mind, for a human mission, you want to minimize time, rather than deltaV. Gravity assists will take a lot of time, as you spend a lot of time waiting for the encounter.
Furthermore, that chart is likely computed via a direct Hohmann transfer, which is one of the most efficient transfer maneuvers available. It also will take a lot longer.
For practical human travel to destinations farther way, you need to perform the so called "star wars maneuver", which is going essentially from A to B in a more or less straight line, which will cost a LOT of delta V.
> Keep in mind, for a human mission, you want to minimize time, rather than deltaV. Gravity assists will take a lot of time, as you spend a lot of time waiting for the encounter.
True, but we could throw the big ship with all the supplies into a flight path that gains a lot of momentum around the inner planets and intercept it with a much smaller craft only loaded with enough fuel to get the astronauts to the transit ship (and back, if necessary).
There is exploration and there is colonization, which to some degree are orthogonal and to some degree complementary to each other, but they are not the same thing. Manned missions to Mars would mostly be about colonization, though exploration would be a significant side benefit. Mars is by far the most promising candidate for colonization (with the potential for using local resources to enable an early level of significant self-sufficiency, increasing over time) which would help kickstart our capabilities in interplanetary spaceflight in general, both manned and unmanned.
For manned missions when a major "location" of the mission is the space in-between Earth and the destination, Mars becomes a much more lucrative first destination because the duration in transit is much shorter.
It's at least 13 months to get to Jupiter for a probe, and reasonably much longer for a man-rated craft.
I saw some students prove that water can be an effective radiation barrier. The only problem is that it's heavy. If we were already going somewhere with a lot of water...
Absolutely. We can learn much more about life in our universe by exploring Europa, Enceladus and Titan. All can be explored for much less than a Mars mission.
They are completely separate missions. Mars is about sending humans somewhere other than the moon. It's less about scientific discovery and more about engineering and exploration discovery - we're doing it to learn about Mars sure, but moreso we're doing it to see if we can.
Mars is the next step in humanity's long term (hundred of thousands of years) survival. If we ever intend not to be at the mercy of gravity, we have to get off earth. We've been to the moon, which is gravitationally constrained to earth, and is only a three day journey (with many chances for safe aborts). We've conquered LEO and now know more about our planet than we could have dreamed up 20 years ago. Mars is a completely different challenge, and by going to Mars we'll develop the first bits of technology that will help us off our deathtrap of a cradle.
These two missions can coexist. We haven't developed the technology to send humans that far out into the solar system so we should continue to send probes.
Growing up this was a huge question that nobody knew the answer to. I don't remember the first discovery of water but I do remember reading one after another water finding. Back then water = life and if we found water it was very likely we would find some form of life. I've already read articles talking about microbial life but I think we will soon discover a variety of living forms.
That being said I don't think our solar system contains a more advanced being than humans. But what life, in some form, demonstrates is that it is possible, in some place very far away, there are living beings as advanced or more than we are. I would really love to be alive to meet them.
>But what life, in some form, demonstrates is that it is possible, in some place very far away, there are living beings as advanced or more than we are. I would really love to be alive to meet them.
Assuming that they are benign and non threatening but I wouldn't take my chances. I dont hope for this.
I understand where this concern comes from. But what I'm unable to reconcile is if a life form can get more "advanced" or even survive long without knowing co-operation and in general being more civilized - Live and let live? Or to point the question inward, let's say humans continue(d) their indiscriminate slaughter of fellow humans and animals around us would we still survive long enough?
Yes, these are flowing oceans. On Ganymede, it's an ocean between two layers of ice. On Enceladus, it's water below an icy crust and on top of a rocky core.
Has anyone thought much about an (admittedly near impossible) probe to burrow and submarine around in the oceans of some of the juicier Galilean and Saturnian moons?
Georgia Tech had a team in Antarctica recently doing field tests of robots designed to explore under very thick ice sheets, specifically to prepare for a Europa mission.
I work on this project under Bill Stone's company Stone Aerospace [1]. One of the projects, VALKYRIE [2], is a laser powered cryobot to melt through ice in order to launch a vehicle in the water underneath. ARTEMIS is the AUV for SIMPLE, and is the third generation following the AUVs DEPTHX & ENDURANCE. VALKYRIE has been field tested and ARTEMIS goes to Antarctica this fall.
>It avoids most genre cliches, apart from the very ending maybe.
Yeah, by being fully made of those. [SPOILER ALERT]
* lack of crew psychological cross-matching
* some ludicrously exoggerated hydrazine drama
* chloroplast-equipped organisms in the environment which ambient light spectrum is slightly inclined towards gamma radiation (not to mention the meat-packed space vessel itself, brightly shined up by very same light)
* _one_ central computer with sole purpose to be heroically repaired on the _outer_ shell of the vessel (you see, no EVA - no drama)
* (mentioned ending) transferring at least tens of gigabytes from Europe to Earth in a matter of seconds (via that special hero-driven central computer) despite being unable to establish uplink for past several months already due to the broken trasmitter (of course, unreserved)
---
Well, I understand that this is just a movie, but look, why not to put it in agreement with some common sense?
Disorganized team/crew of what first have seemed to appear as "professionals", imho, is a curse of most sci-fi movies (I could hardly recall any movie with more than one actor, where characters won't behave like a bunch of strangers gathered together under some unfortunate circumstances).
Exoggerated drama (i.e. dramatic action out of nothing or due the course of highly regulated procedures (eg. EVA)) is harder to evaluate: sometimes that drama looks quite plausible. Nevertheless, action sci-fi without some sort of team member sacrificion/unexpected death is hard to imagine, at least for me. Hell, it is not even specific to sci-fi: just take a look into any action movie out there - pretty high chances to become a witness of the dramatic death.
Very frivolous treatment of the laws of physics in general. I am pointing out that instantaneous information transmission specifically. Well, pretty much of cliche either, isn't it?
Stupid reasons for "heroicity". Are you a script writer in a search for the rationale to balance around the case of dramatic death of one or more characters? Director struggling with producers demand for fancy attention-binding activity you might be. What to do? Easy! Just place some important peace of equipment in a morbid place and there you go - engineering have been favored out by thrill.
Life. Remember that in "Babylon 5" most of aliens were anthropomorphic? Well, 90th there were, no fancy CG, and, besides, convergention one may say, right? Second decade of XXI century, Wikipedia is here and accessible in a matter of keystrokes. Why not chemothrophs, why?! Although, phototrophs could be plausible even in a shady world, convergention one may say...
They would need to be a certain weight for the rocket they would ride on, be able to withstand radiation, generate power or install a different power source, be able to withstand various extreme temperatures, ensure it can "swim" in different oceans (Titan's ocean is not H2O). Not to mention they need to develop a way to deliver the sub to the water safely. I think there are lots of changes here.
They come to the surface, then get a gps fix (err) and then is picked up by the boat then the data uploaded..... Ok its going to need some minor modifications.
You also need to get from the surface to the water, and from the water back to the surface. Inbetween is a rather huge layer of ice. On Europa it's though to be 10-20 kilometers thick, though there's indications it could be as "thin" as 3km some places
You're misunderstanding the relevance here. Water the molecule is common throughout the solar system, typically as ice. It makes up a significant fraction of the mass of many of the moons of outer planets. It's a common component of comets and other minor planetary bodies. Titan, for example, is about half water ice, but it is so cold there that it is effectively a rock.
What we've been learning is that there is water ice in some places we didn't necessarily expect it before (such as in the form of permafrost underlying much of the Martian surface) and most importantly that liquid water is not as uncommon as we once thought. Liquid water is what's most interesting from the point of view of looking for environments that can support life forms. Previously we thought that the presence of liquid water required not only the presence of water as a material but also overall planetary temperatures in a temperate range, the so called "habitable zone". Which, as it turns out, is a fairly narrow zone. But we've learned that there seem to be numerous circumstances that allow the existence of substantial quantities of liquid water in conditions that otherwise would not support it. Europa, for example, has frigid surface temperatures (150 to 200 degrees C below freezing) but it has a sub-surface ocean due to tidal interactions with its neighbors. That sort of thing seems to be much more common than we knew previously.
It's surprising (water is perceived to be scarce) because:
- oxygen just as readily binds to everything else, to form metal oxides (the well-known rust on Mars) or silicates (rock) or just CO2 (Venus)
- hydrogen is so light it readily escapes into space from anything smaller than Earth
- H2O as solid ice is common anyway, but not as liquid water, which is more relevant for potential habitability and life. The conditions for the liquid phase of water are a remarkably narrow area on the phase diagram. That we have found in few locations, and it's news when a new such place is discovered.
If there is both vapor and ice, there must always be at least some water. If water is plentiful, space is cold, and planets are hot, liquid water should be common, regardless of how narrow the temperature conditions for it are. All temperatures from cold space to molten rock are well represented on planets.
Yes. The pressure of space is not sufficient for liquid water, regardless of how hot or cold it is. This means that regardless of how much ice or vapor exists on separate terrestrial bodies, we cannot assume that there is liquid somewhere in between.
Now, if there was a single planet that had both ice and vapor water, and that planet had an atmospheric pressure of greater than 0.006 atm, then I agree that there must be some liquid water somewhere on that planet. But ice and vapor on a single planet with a sufficient atmosphere is a much higher bar to clear than two totally separate places that combined have both ice and water vapor.
If you actually read what I wrote, you would have understood I was referring to water on planets. Obviously there is not likely to be liquid water in the vacuum of space. The "space is cold" "planets are hot" might have been a pretty sure clue that I was referring to water between a planet's hot core and cold vacuous space.
However, I get the cringes every time an article about space exploration uses those atavistic units like Royal Hangnails (length), Princely Bladders (volume), Regal Farts (speed) and Fornicating Fever (temperature) for measurement. Hasn't the metric system arrived yet on planet USA?
@mitchty, I don't see how the Beagle probe relates unless parallel but different measurement systems caused that, and I'm not seeing anything to indicate this (but let me know if I'm missing something, I'm curious).
"The primary cause of this discrepancy was that one piece of ground software supplied by Lockheed Martin produced results in a United States customary unit ('American'), contrary to its Software Interface Specification (SIS), while a second system, supplied by NASA, that used those results expected them to be in metric units, in accord with the SIS."
The Beagle 2 and Mars Climate Orbiter are not the same thing. It is unknown why Beagle 2 failed and there is no reason to believe it was due to any unit mismatch. It may be that two of the solar panels failed to deploy.
It's well known that the metric solar panels failed to deploy. The imperial solar panels opened successfully, but that did not generate enough electricity to keep going.
How so? If I build something that doesn't conform to specifications, what does it matter if it happened to be unit conversions? They could have skipped a decimal point and not noticed, because they didn't conform to the specification. More importantly it never got checked or tested or simulated further on up the chain to catch the issue.
Look at the Araine 5. Unit conversions had nothing to do with a computer saying "gimbal an engine 90 degrees".
I'm sorry but this canard of two units being the problem is missing the entire point.
Its an engineering issue and management failure. Just like the space shuttle O rings before them, space is hard. Distilling things down to "america should have used metric cause reasons" is trying to pass off complex problems with bite sized quotes. The only issue is it is wrong.
This is a smart comment. It sucks to have to keep repeating this comment every time someone trots out this supposedly easy example.
Sure, the units issue was the root cause, but the resulting navigation errors should have been acted upon. They were noticed ("The discrepancy between calculated and measured position, resulting in the discrepancy between desired and actual orbit insertion altitude, had been noticed earlier by at least two navigators, whose concerns were dismissed."), but the issue wasn't acted upon. This is a management and budget problem.
Even if the units are given as SI, there are always interface issues -- which coordinate system to use, where the origin is, does z point up or down, degrees or radians. It can be hard to appreciate unless you have had experience with hard-to-find failures due to subtle numerical problems.
I'd love to use metric. It'd save a slew of annoyances converting back and forth, and it's the easiest thing to screw up, because no one has an intuitive sense of a millionth of an inch. But as long as I work at the New York Times and New York is part of the United States and the United States isn't metric, I'm stuck with inches, miles, pounds and gallons.
Why? Units are mostly arbitrary anyway. Actually, having more than one system is a good reminder of that. And Fahrenheit is supposedly more efficient for describing weather.
That's just a blatant rationalisation because people don't like change. There's nothing natural about understanding either metric or imperial, so suggesting that humans inherently are born with more understanding of one is silly.
Metric only wins in my book because it is much easier to convert units (there are no magic numbers for conversion factors). However I'd laugh at anyone who suggest metric is better because people inherently internalise it better, just as I laugh at people who suggest the same for imperial.
The US should switch, there are no legitimate arguments against it except perhaps [short term] costs. Certainly not "because F is easier to understand." It is only easier because you grew up with it and are used to it...
> However I'd laugh at anyone who suggest metric is better because people inherently internalise it better
I disagree. Once you've been taught a base ten counting system, units that change based on orders of magnitude is very easy to understand. Since almost everyone has a base ten counting system internalized, metric is MUCH easier.
But 12 is evenly divisible in thirds and quarters. Actually pretty useful for a bunch of things. Really it's just too bad we have 10 fingers instead of 12.
Yep, but 10 fingers is what most of us have. I like 12 too but unless you can persuade people to start counting in astrological symbols instead of decimal digits then metric is the way to go.
I think, if you don't even know that the US doesn't use "Imperial" units, but that the system of units is actually called "US Customary", then you don't know enough about systems of units to be able to comment on the issue.
Don't get me wrong, I like the metric system. But US Customary units aren't that hard to deal with. Seriously, we're software developers, we don't memorize shit. We create type definitions and routines to convert between them.
The same arguments you make for why it's not that big of a deal to switch are the same arguments for why it's not that big of a deal to not switch.
>>There's nothing natural about understanding either metric or imperial
That's not true at all. The metric system is more intuitive because it is a Base 10 system, which is very intuitive and natural for humans because we have ten fingers. Base 10 also makes things a lot easier because calculations are simply a matter of adding/removing zeroes/decimals.
10 fingers/base 10 isn't inherently any more "natural." There are cultures that use(d) base 12 (and count using the 12 finger segments on one hand) and probably others.
I'm not allowed to edit this anymore, so let me reply instead. To those downvoting I ask: do you think this comment wasn't serious? You think there aren't at least 47 senators who would filibuster a bill to, say, convert the US highway signs to metric because it's "unamerican"?
Beer and soda bottled or canned for individual servings still use imperial units (12oz/16oz/20oz). Oddly, water bottled for such has mostly moved over to metric. Keg beer also still uses imperial.
In Finland you can always order 0,568 liter beer. (Imperial pint) Or traditional large beer which is 0,5 liter or euro beer which is 0,4 liter. You decide.
Are you kidding? It was traumatic enough when we switched from cubits, scruples and fortnights.
And what good is a system of measurement that you can't use to bamboozle customers? ("That's not an ounce, ma'am, that's a Troy ounce...")
If we move to anything, it's going to be Donald Knuth's Potrzebie system (see http://en.wikipedia.org/wiki/Potrzebie). It seems more well thought out than most.
