11 ms·

Confronting the Credibility Gap for Crewed Exploration of Mars

101 points by apsec112 10y ago

fapjacks 10y ago
"And then you have the EM/reactionless drive, which is less efficient than a Hall effect thruster, and also impossible." I could sense this was coming, and I stopped reading here.
- NickBusey 10y ago
  For those of us who aren't experts in the physics of theoretical space travel, care to share why?
  - XorNot 10y ago
    It violates conservation of momentum (i.e. why solar sails work). This is a pretty big problem with any evidence purporting that it does work because it requires a massive reinterpretation of our understanding of existing physical laws: i.e. it's mechanism of operation has to simplify to existing theory in such a way as to also explain why the effect is undetectable at the staggeringly high resolutions of measurements we've been making of other physical constants for decades now. This is a big ask. This is a huge ask.
    - mannykannot 10y ago
      As far as I can tell, the quote given by fapjacks is saying that the reactionless drive is impossible. Note that it is in a paragraph that begins "The other major kind of shonky coverage covers mythical propulsion..." (I had to look up 'shonky', but it is consistent with the above reading.)
      - Daneel_ 10y ago
        Correct - Casey believes that the drive is impossible, given our understanding of physics. Given his background and credentials, I'm happy to defer to his opinion on the matter, over my own optimism. Both he and I are firm believers of the scientific method though, so if researchers can show it experimentally then that's where the fun really begins. To my knowledge, the experiments until now have been fairly poor, with barely significant results (on the edge of noise).
        fapjacks 10y ago
        But that's not what he's saying, now is it? He is dismissing it entirely as "impossible". Care to point me to the part of the scientific method which says "Feel free to dismiss outright things that don't make sense to you"?
        daveguy 10y ago
        Everything in science starts out impossible. It doesn't even get considered in science unless it has a chance of being impossible. Then it is up to the scientist to demonstrate that it is possible and explain how it is possible. Edit: The 1) demonstrate and 2) explain parts are critical and it's not science unless you have 1). Preferably 2) also. EM has neither to match the magnitude of the claims until they can push something across the solar system and back (such that loss of mass is ruled out and the propulsive effect is without a doubt not instrument error).
        jack9 10y ago
        > EM has neither to match the magnitude of the claims until they can push something across the solar system and back That is hyperbolic. Pushing something around in orbit is sufficient to move forward (pardon the pun).
        daveguy 10y ago
        Good point, but it would need to accelerate and decelerate in orbit enough to confirm that mass loss isn't driving it.
        avmich 10y ago
        I think, given the structure of phrase, we can assume some irony there - not only baseless dismissal. EM drive remains pretty controversial, and does present significant problems with explanation, and as an extraordinary device requires extraordinary evidence. So it could be conceivable not to focus too deeply on a remark which isn't the main point of the article.
        10y ago
      - omegaham 10y ago
        I'm pretty sure that fapjacks believes that the reactionless drive is possible, and all of the "No, this is silly" folks are just contrarian deniers who are holding back progress. Gotta love starry-eyed futurology people.
        f0urtyfive 10y ago
        Woah there horsey, you're basically sticking anyone that thinks reactionless drive might be possible into the crazy conspiracy theory category, and there are plenty of people that are interested in honest reproducible research on the topic. Just blanket suggesting that it is in no way possible without any evidence is no better than blanket suggesting it is possible without any evidence (well, it's a little better, since the laws of physics are on your side, but...)
        fapjacks 10y ago
        Right. That's the spirit of my original comment. There are obviously people here with some serious investment in their own educations and egos that think this thing is impossible. Yet, here we are, peer-reviewed evidence[0] mounting. [0] http://arc.aiaa.org/doi/10.2514/1.B36120 http://arc.aiaa.org/doi/10.2514/1.B36120
      - Symmetry 10y ago
        That, and that the amount of energy you put in to produce a unit of impulse with a theoretical EM drive is 10 times larger than the amount of energy required to produce that same impulse with a Hall effect thruster. For the journey to Mars that means the EM drive would tend to be much slower in practice even if it worked.
    - techdragon 10y ago
      There is a big difference between "does violate" and "appears to violate". The orbital motion of Mercury "violates" Newtonian gravity. There are other examples but I'm not trying to make a history lesson. I just want to point out, that science moves forward by impartial investigation of EVERYTHING. It's misguided to assume we know all and that there cannot be some thing we don't understand. I'm as sceptical as anyone else about the EM Drive, but I want to understand "what the heck is going on with this thing that appears to move" more than I want to dismiss it as "not possible and obviously flawed because $ABC" There are plenty of possible ways the drive could operate, and if it does work, it has the potential to significantly advance several fields of physics in a way no less valuable than other large expensive "hope this works" experimental physics experiments that no one is complaining about.
      - XorNot 10y ago
        The Relativity of Wrong [http://chem.tufts.edu/answersinscience/relativityofwrong.htm http://chem.tufts.edu/answersinscience/relativityofwrong.htm] Mercury's motion does violate Newtonian gravity. General Relativity however simplifies to Newtonian gravity for various low-dimension applications though (i.e. an Apple falling from a tree, the orbit of the moon for most astronomical guidance purposes over that distance etc.) In much the same way we don't account for the curvature of the Earth when building a house's foundations. That's my point though: when you violate a fundamental physical law, it can't just be wrong. You have to somehow also account for why it doesn't happen all the time elsewhere (i.e. the effect is small to within experimental error over common measurement cases) and by necessity the new theory to explain it has to encompass the predictions of the old i.e. the benefit of Newtonian gravity was that it easily recovers the behaviour of nested epicycles of orbital motion (and made new predictions successfully where epicycles could not).
        nonbel 10y ago
        >"General Relativity however simplifies to Newtonian gravity" I still don't see how this is possible. In GR gravity travels at the speed of light, in Newtonian mechanics it is instantaneous. I have been unable to find an acceptable explanation for how these two very different universes can be compatible.
    - deleted 10y ago
      [deleted]
- chandmer 10y ago
  Sorry to come across as grumpy. It wasn't really the venue or topic to argue about exotic propulsion. There are many excellent resources online explaining why EM cavities are reactionless. You can write down the Poynting vector and then use Green's theorem, it's a neat result. With dire consequences for wish-powered spacecraft. -C
  - deleted 10y ago
    [deleted]
  - james-watson 10y ago
    Don't be sorry. We need scientists to be skeptics when it comes to absurd assertions which violate the most fundamental principles of physics. Extraordinary claims require extraordinary evidence.
    - fapjacks 10y ago
      There's actually a difference between being skeptical and calling this thing -- with peer-reviewed research[0] -- "wish-powered". [0] http://arc.aiaa.org/doi/10.2514/1.B36120 http://arc.aiaa.org/doi/10.2514/1.B36120
Daneel_ 10y ago
If you'd prefer to watch it, Casey's talk is available on Youtube: https://www.youtube.com/watch?v=c0a7eR8Wi4Y https://www.youtube.com/watch?v=c0a7eR8Wi4Y
kirrent 10y ago
ITS is conspicuously absent in this post but has been discussed by the same author in another post. http://caseyexaustralia.blogspot.com.au/2016/09/spacex-mars-plan-analysis.html http://caseyexaustralia.blogspot.com.au/2016/09/spacex-mars-...
nickparker 10y ago
There's a very enjoyable discussion in the comment section with my (brilliant) former colleague Max Fagin. He points out that Casey's first draft of this post neglects the curvature of Mars, and when you account for it Casey's model predicts the craft punching out the other side of the atmosphere.
- chandmer 10y ago
  Always appreciate careful criticism! It turns out the ratio of centrifugal-gravitational force to aerodynamic force is about 10:1, so punching through the atmosphere is a solvable problem. I love Max's videos! -C
  - nickparker 10y ago
    Oh man, I hadn't seen those videos before. That's gold. Off-topic, but your post popping up with the Hyperloop One name attached helped me decide[1] to sign w/ you folks instead of another company for Summer 2017, so see you in a few months! [1] I was probably picking Hyperloop anyway, a cool Mars post + vague affiliation with Max just made it easier :)
- aedron 10y ago
  Can't see those comments. Were they deleted?
  - chandmer 10y ago
    They shouldn't be!
  - chandmer 10y ago
    They're on the ITS post.
avmich 10y ago
The document linked at the end of the talk currently contains summary regarding the radiation problem on the way to Mars. I've heard of the following approach. The spacecraft generates a magnetic field which spreads around it in flight, having some substantial size (order of kilometers). Relatively small amounts of matter (some gas) are constantly emitted from spacecraft, get ionized and trapped in the magnetic field. Such a low density thick "cushion" of ions makes the radiation shielding. I'd like to learn more about effectiveness of such an approach.
- Symmetry 10y ago
  You really want to be piling some dirt on top of your shelters for pressure containment reasons anyways.
  - avmich 10y ago
    That idea was for travel time, not when the spacecraft is already landed on Mars and the crew want protection on the surface. There, dirt will help, but in flight there is nowhere to get it from.
robbiep 10y ago
I had the pleasure of attending high school with Casey. He (and his brother as well, who i worked under as a doctor) are both capital G geniuses. Anyone wanting to be highly informed on interesting topics like the hyperloop (with his potential biases due to involvement with Hyperloop one), terraforming, space travel or other similar things would do well to follow him on quora.
- chandmer 10y ago
  That's too kind! Say hi on fb some day.
Animats 10y ago
Landing is really hard. Not enough atmosphere for aerobraking, and too far from home to have enough fuel for a powered landing. It's a fuel problem. There's the expensive approach. Send multiple unmanned tanker ships into Mars orbit and have them rendezvous into an orbital supply depot. Send landing tanker ship to rendezvous with them and refuel with enough fuel for a powered landing. Landing ship descends. Repeat to build up fuel reserve on Mars surface. Manned ship then docks with orbital supply depot and crew switches to lander. Lander descends, lands near fuel reserve, and refuels for ascent. Ascent is to Mars orbit and docking with the orbital supply depot. Crew switches back to long-haul ship, refuels it, and goes back to Earth.
- chandmer 10y ago
  All kinds of problems! The ITS gets around a lot of them - the trick is to have a lifting body. But there's still a lot of problems.
- jcoffland 10y ago
  How about we harpoon Mars and pull down one end of a space elevator?
  - pilom 10y ago
    The biggest problem with a space elevator on Mars is that the orbit of one of its moons is closer than the minimum height of a space elevator to be stable. Eventually the elevator cable will get hit.
    - dTal 10y ago
      Hang the cable from the moon and let the end trail?
  - dTal 10y ago
    Interesting proposal. You still need a lot of delta vee to get a harpoon+cable from orbit to the surface. You can't just fire it straight down, you have to cancel most of your orbital velocity (which would have to be way out at geostationary). Dunno what the strength requirements of the cable would be either, but I imagine the answer is "not small". Doing the same trick to Earth probably wouldn't be that much harder than Mars. So maybe, once you've solved the hard problems, you wouldn't have to worry so much about mass-to-orbit anyway.
gurneyHaleck 10y ago
"Do you realise the astronauts will run out of nitrogen on day 59 and die?" So Mars One isn't really funny, it has probably set back the credibility of the movement by a decade. I realize it's not meant to be a truly quantifiable statement, but I'm always curious why people regard incidents like this as producing serious damage to progress. There are definitely crucial moments in political science, when an absurd gaff completely botches a carefully crafted image, completely imploding the efforts of hundreds of people, and sinking an entire team permanently. Cringey things that seem to matter to the echo chamber of a 24 hour news cycle. But I don't feel like hard science works that way. When it comes to real engineering feats, if one company tries to trade on faulty calculations, and their charade is laid bare, the smoke and mirrors disappear only to reveal the same bald truth that had always been there from the start: hard problems defy shenanigans. A political failure doesn't deflate an engineering problem. Not in the same way it deflates a PR campaign. If the hard science was not respected, then there was no investment in a decade of progress to begin with. So, these swindlers then maybe blew a decade of real funding, only to burn their investors with bogus project plans and proposals, ripping off charity and fomenting skepticism and suspicion? I think skepticism in this sphere is actually healthy, and separates the children from the adults. Waste is a bad thing, and maybe real money disappears, but maybe that kind money came from the kinds of people who might have just as soon blown their cash on personal assistants, vacations and clothes. Clearly such investors were not "buying science," or they'd have known better. So, then the only thing left is that maybe there's the premise that admirers of the charade would not have loitered on the sidelines, simply yearning to lend their support to the parlour trick they were true believers in. That they would have stepped up to the task, had they known progress was stalled. I don't buy that. No matter what, I don't think there has even been a decade of effort spent on crewing a mission to Mars. It's all been so much conjecture. It's never seemed to be an easier idea than an underground moon base, and no one seems to be giving lunar round-trips or installations much more consideration than mars. Space shuttle accidents and launchpad explosions cast the true hazards in a much more severe relief, but knowing that people are even trying and failing feels like much more significant progress than a lot of talk and faulty plans. So was there really any "damage" done by some of these PR goof ups?
james-watson 10y ago
What gets forgotten here, and something that I keep bringing up, is the lack of a Martian magnetosphere. This means long term human settlements have to be artificially shielded. This means living underground, which defeats the point of going to Mars in my opinion. Elon mentioned using a local magnetosphere generator, which is one of those ideas that is theoretically possible but whose practicality seems questionable. How powerful a magnetosphere generator is required to deflect ionizing radiation? How much power generation capacity will a Martian colony have to spare? Will this require a Fusion reactor? The only hope I have for Martian settlement is that Musk and his engineers are some of the most audacious and brilliant people on the planet. I will never bet against their success, and I wish them the best of luck. I have been a space exploration fan since as long as I can remember, I just worry that humans have a tendency to focus on the wrong goals when ideals and emotion cloud our judgement (e.g. the Space Shuttle).
- Symmetry 10y ago
  One of the aspects of Mars that makes living there hard is that Mars is very cold. But that same aspect makes it somewhat easier to establish big magnetic fields on the surface since it means that superconductors will require less cooling. If you're using a superconductor to generate a magnetic field you don't need any continuous input of power.
- LeoDox 10y ago
  Mars has an iron core; it's just not molten which prevents it from being ferromagnetic. I have three questions: 1. Is it merely a question of mass? That is, if Mars were larger would the increased gravity increase pressure at the core and keep it molten? 2. If it IS merely a question of mass, is there any way to add mass to Mars which doesn't disturb its orbit? Because if you could, then you simultaneously solve both the problem of low gravity AND lack of magnetosphere, which together solve the problem of maintaining atmosphere. Basically the whole planet becomes extremely Earth-like 3. If increased mass wouldn't necessarily wreck its orbit, could something be done to "steer" asteroids from the Main Belt into collision courses with Mars? I really don't know anything about orbital mechanics so maybe there's an obvious flaw in this (aside from the energy required to reroute that many asteroids).
jcoffland 10y ago
Radiation is a huge problem. Both en route and on Mars. A lot of these problems beg the question. Is Mars really the best target? Sure it's close but there are moons around Saturn that are interesting as well. Titan for example. Sure it's cold but it has a lot of atmosphere. Presumably landing would be easier. If we could learn to live underwater we could possibly visit Ganymede or Europa.
- semi-extrinsic 10y ago
  Radiation, as you mention, is a very big problem which is independent of destination. Human psychology is another, perhaps even bigger problem, also independent of destination. We've had various experiments with prolonged isolation, but none where the subjects know that they're never coming back to Earth. I'd say psychology has a >50% chance of wrecking the first manned missions to other planets/moons, unless we send huge ships with hundreds of people. In the Red Mars trilogy by Kim Stanley Robinson, the author has come to the very astute observation that a) no perfectly rational, mentally healthy human would volunteer for such a mission b) there will necessarily be extensive psychological screening to ensure we only send rational people thus c) the people who will be selected are likely to be non-rational actors very good at concealing their non-rationality from psychologists. Also known as people with psychopathic tendencies.
  - coldtea 10y ago
    >Human psychology is another, perhaps even bigger problem, also independent of destination. We've had various experiments with prolonged isolation, but none where the subjects know that they're never coming back to Earth. Who said they're never coming back to Earth? >no perfectly rational, mentally healthy human would volunteer for such a mission That's an easy problem to solve, as there are no "perfectly rational" and/or absolutely "mentally healthy humans", and have never been anyway. And people can still be quite rational and mentally healthy and yet cherish the possibility to take such a mission, even if there's a possibility to die, etc. In fact, it's needs no more troubled people than those that go to the army and are OK to be sent to war, or people that dive and explore the oceans, etc etc.
sjbase 10y ago
Is a no-return mission something worth considering, on a purely technical & logistical level? Has anyone seen a really good analysis of this? My sense is that the social, political, and psychological barriers could be overcome for such a thing.
brilliantcode 10y ago
Why Mars though? Why not build a lunar base on the moon? Maybe even a hotel on the moon, I'm sure people will enjoy watching earth from the moon. I just fail to see this obsession with Mars. We don't even have manned landing on Mars and we are already having questionable stuff like "Mars One" And finally (one for the conspiracists): nearly 50 years ago we landed on the moon without any of the technology we have today. Why hasn't there been any strides? Shouldn't it be cheaper to go to the Moon vs Mars? Shouldn't it be possible to colonize Moon more easily and faster than Mars?
- woah 10y ago
  I think part of it is that mars has an atmosphere
  - dTal 10y ago
    An atmosphere that provides none of the benefits of appropriate pressure, temperature and gas mix but all of the challenges of weather and airborne dust.
    - namlem 10y ago
      The martian atmosphere does have the benefit of having created much less abrasive dust over the years. Moon dust causes much more wear to moving parts. Mars also has accessible carbon, which the moon does not. The martian atmosphere can supply plants with the CO2 they need, enabling agriculture.
- dwaltrip 10y ago
  My understanding is that the Moon has far less useful resources. Sustaining any kind of base or colony on the Moon would require a larger degree of constant imports and may be much harder to sustain. Another huge factor is the lack of consistent solar power. 14 out of every 28 days have zero solar. Mars doesn't have this problem. There are other lesser factors as well, off the top of my head: weaker gravity which may affect health, the psychological problems with 2 weeks of solid darkness every month, and less scientifically interesting. However, it may be still worth considering.

101 points by apsec112 10y ago

"And then you have the EM/reactionless drive, which is less efficient than a Hall effect thruster, and also impossible." I could sense this was coming, and I stopped reading here.

NickBusey 10y ago
For those of us who aren't experts in the physics of theoretical space travel, care to share why?
- XorNot 10y ago
  It violates conservation of momentum (i.e. why solar sails work). This is a pretty big problem with any evidence purporting that it does work because it requires a massive reinterpretation of our understanding of existing physical laws: i.e. it's mechanism of operation has to simplify to existing theory in such a way as to also explain why the effect is undetectable at the staggeringly high resolutions of measurements we've been making of other physical constants for decades now. This is a big ask. This is a huge ask.
  - mannykannot 10y ago
    As far as I can tell, the quote given by fapjacks is saying that the reactionless drive is impossible. Note that it is in a paragraph that begins "The other major kind of shonky coverage covers mythical propulsion..." (I had to look up 'shonky', but it is consistent with the above reading.)
    - Daneel_ 10y ago
      Correct - Casey believes that the drive is impossible, given our understanding of physics. Given his background and credentials, I'm happy to defer to his opinion on the matter, over my own optimism. Both he and I are firm believers of the scientific method though, so if researchers can show it experimentally then that's where the fun really begins. To my knowledge, the experiments until now have been fairly poor, with barely significant results (on the edge of noise).
      - fapjacks 10y ago
        But that's not what he's saying, now is it? He is dismissing it entirely as "impossible". Care to point me to the part of the scientific method which says "Feel free to dismiss outright things that don't make sense to you"?
        daveguy 10y ago
        Everything in science starts out impossible. It doesn't even get considered in science unless it has a chance of being impossible. Then it is up to the scientist to demonstrate that it is possible and explain how it is possible. Edit: The 1) demonstrate and 2) explain parts are critical and it's not science unless you have 1). Preferably 2) also. EM has neither to match the magnitude of the claims until they can push something across the solar system and back (such that loss of mass is ruled out and the propulsive effect is without a doubt not instrument error).
        jack9 10y ago
        > EM has neither to match the magnitude of the claims until they can push something across the solar system and back That is hyperbolic. Pushing something around in orbit is sufficient to move forward (pardon the pun).
        daveguy 10y ago
        Good point, but it would need to accelerate and decelerate in orbit enough to confirm that mass loss isn't driving it.
        avmich 10y ago
        I think, given the structure of phrase, we can assume some irony there - not only baseless dismissal. EM drive remains pretty controversial, and does present significant problems with explanation, and as an extraordinary device requires extraordinary evidence. So it could be conceivable not to focus too deeply on a remark which isn't the main point of the article.
        10y ago
    - omegaham 10y ago
      I'm pretty sure that fapjacks believes that the reactionless drive is possible, and all of the "No, this is silly" folks are just contrarian deniers who are holding back progress. Gotta love starry-eyed futurology people.
      - f0urtyfive 10y ago
        Woah there horsey, you're basically sticking anyone that thinks reactionless drive might be possible into the crazy conspiracy theory category, and there are plenty of people that are interested in honest reproducible research on the topic. Just blanket suggesting that it is in no way possible without any evidence is no better than blanket suggesting it is possible without any evidence (well, it's a little better, since the laws of physics are on your side, but...)
        fapjacks 10y ago
        Right. That's the spirit of my original comment. There are obviously people here with some serious investment in their own educations and egos that think this thing is impossible. Yet, here we are, peer-reviewed evidence[0] mounting. [0] http://arc.aiaa.org/doi/10.2514/1.B36120 http://arc.aiaa.org/doi/10.2514/1.B36120
    - Symmetry 10y ago
      That, and that the amount of energy you put in to produce a unit of impulse with a theoretical EM drive is 10 times larger than the amount of energy required to produce that same impulse with a Hall effect thruster. For the journey to Mars that means the EM drive would tend to be much slower in practice even if it worked.
  - techdragon 10y ago
    There is a big difference between "does violate" and "appears to violate". The orbital motion of Mercury "violates" Newtonian gravity. There are other examples but I'm not trying to make a history lesson. I just want to point out, that science moves forward by impartial investigation of EVERYTHING. It's misguided to assume we know all and that there cannot be some thing we don't understand. I'm as sceptical as anyone else about the EM Drive, but I want to understand "what the heck is going on with this thing that appears to move" more than I want to dismiss it as "not possible and obviously flawed because $ABC" There are plenty of possible ways the drive could operate, and if it does work, it has the potential to significantly advance several fields of physics in a way no less valuable than other large expensive "hope this works" experimental physics experiments that no one is complaining about.
    - XorNot 10y ago
      The Relativity of Wrong [http://chem.tufts.edu/answersinscience/relativityofwrong.htm http://chem.tufts.edu/answersinscience/relativityofwrong.htm] Mercury's motion does violate Newtonian gravity. General Relativity however simplifies to Newtonian gravity for various low-dimension applications though (i.e. an Apple falling from a tree, the orbit of the moon for most astronomical guidance purposes over that distance etc.) In much the same way we don't account for the curvature of the Earth when building a house's foundations. That's my point though: when you violate a fundamental physical law, it can't just be wrong. You have to somehow also account for why it doesn't happen all the time elsewhere (i.e. the effect is small to within experimental error over common measurement cases) and by necessity the new theory to explain it has to encompass the predictions of the old i.e. the benefit of Newtonian gravity was that it easily recovers the behaviour of nested epicycles of orbital motion (and made new predictions successfully where epicycles could not).
      - nonbel 10y ago
        >"General Relativity however simplifies to Newtonian gravity" I still don't see how this is possible. In GR gravity travels at the speed of light, in Newtonian mechanics it is instantaneous. I have been unable to find an acceptable explanation for how these two very different universes can be compatible.
  - deleted 10y ago
    [deleted]
chandmer 10y ago
Sorry to come across as grumpy. It wasn't really the venue or topic to argue about exotic propulsion. There are many excellent resources online explaining why EM cavities are reactionless. You can write down the Poynting vector and then use Green's theorem, it's a neat result. With dire consequences for wish-powered spacecraft. -C
- deleted 10y ago
  [deleted]
- james-watson 10y ago
  Don't be sorry. We need scientists to be skeptics when it comes to absurd assertions which violate the most fundamental principles of physics. Extraordinary claims require extraordinary evidence.
  - fapjacks 10y ago
    There's actually a difference between being skeptical and calling this thing -- with peer-reviewed research[0] -- "wish-powered". [0] http://arc.aiaa.org/doi/10.2514/1.B36120 http://arc.aiaa.org/doi/10.2514/1.B36120

Daneel_ 10y ago

If you'd prefer to watch it, Casey's talk is available on Youtube: https://www.youtube.com/watch?v=c0a7eR8Wi4Y https://www.youtube.com/watch?v=c0a7eR8Wi4Y

kirrent 10y ago

ITS is conspicuously absent in this post but has been discussed by the same author in another post. http://caseyexaustralia.blogspot.com.au/2016/09/spacex-mars-plan-analysis.html http://caseyexaustralia.blogspot.com.au/2016/09/spacex-mars-...

nickparker 10y ago

There's a very enjoyable discussion in the comment section with my (brilliant) former colleague Max Fagin. He points out that Casey's first draft of this post neglects the curvature of Mars, and when you account for it Casey's model predicts the craft punching out the other side of the atmosphere.

chandmer 10y ago
Always appreciate careful criticism! It turns out the ratio of centrifugal-gravitational force to aerodynamic force is about 10:1, so punching through the atmosphere is a solvable problem. I love Max's videos! -C
- nickparker 10y ago
  Oh man, I hadn't seen those videos before. That's gold. Off-topic, but your post popping up with the Hyperloop One name attached helped me decide[1] to sign w/ you folks instead of another company for Summer 2017, so see you in a few months! [1] I was probably picking Hyperloop anyway, a cool Mars post + vague affiliation with Max just made it easier :)
aedron 10y ago
Can't see those comments. Were they deleted?
- chandmer 10y ago
  They shouldn't be!
- chandmer 10y ago
  They're on the ITS post.

avmich 10y ago

The document linked at the end of the talk currently contains summary regarding the radiation problem on the way to Mars. I've heard of the following approach. The spacecraft generates a magnetic field which spreads around it in flight, having some substantial size (order of kilometers). Relatively small amounts of matter (some gas) are constantly emitted from spacecraft, get ionized and trapped in the magnetic field. Such a low density thick "cushion" of ions makes the radiation shielding. I'd like to learn more about effectiveness of such an approach.

Symmetry 10y ago
You really want to be piling some dirt on top of your shelters for pressure containment reasons anyways.
- avmich 10y ago
  That idea was for travel time, not when the spacecraft is already landed on Mars and the crew want protection on the surface. There, dirt will help, but in flight there is nowhere to get it from.

robbiep 10y ago

I had the pleasure of attending high school with Casey. He (and his brother as well, who i worked under as a doctor) are both capital G geniuses. Anyone wanting to be highly informed on interesting topics like the hyperloop (with his potential biases due to involvement with Hyperloop one), terraforming, space travel or other similar things would do well to follow him on quora.

chandmer 10y ago
That's too kind! Say hi on fb some day.

Animats 10y ago

Landing is really hard. Not enough atmosphere for aerobraking, and too far from home to have enough fuel for a powered landing. It's a fuel problem. There's the expensive approach. Send multiple unmanned tanker ships into Mars orbit and have them rendezvous into an orbital supply depot. Send landing tanker ship to rendezvous with them and refuel with enough fuel for a powered landing. Landing ship descends. Repeat to build up fuel reserve on Mars surface. Manned ship then docks with orbital supply depot and crew switches to lander. Lander descends, lands near fuel reserve, and refuels for ascent. Ascent is to Mars orbit and docking with the orbital supply depot. Crew switches back to long-haul ship, refuels it, and goes back to Earth.

chandmer 10y ago
All kinds of problems! The ITS gets around a lot of them - the trick is to have a lifting body. But there's still a lot of problems.
jcoffland 10y ago
How about we harpoon Mars and pull down one end of a space elevator?
- pilom 10y ago
  The biggest problem with a space elevator on Mars is that the orbit of one of its moons is closer than the minimum height of a space elevator to be stable. Eventually the elevator cable will get hit.
  - dTal 10y ago
    Hang the cable from the moon and let the end trail?
- dTal 10y ago
  Interesting proposal. You still need a lot of delta vee to get a harpoon+cable from orbit to the surface. You can't just fire it straight down, you have to cancel most of your orbital velocity (which would have to be way out at geostationary). Dunno what the strength requirements of the cable would be either, but I imagine the answer is "not small". Doing the same trick to Earth probably wouldn't be that much harder than Mars. So maybe, once you've solved the hard problems, you wouldn't have to worry so much about mass-to-orbit anyway.

gurneyHaleck 10y ago

"Do you realise the astronauts will run out of nitrogen on day 59 and die?" So Mars One isn't really funny, it has probably set back the credibility of the movement by a decade. I realize it's not meant to be a truly quantifiable statement, but I'm always curious why people regard incidents like this as producing serious damage to progress. There are definitely crucial moments in political science, when an absurd gaff completely botches a carefully crafted image, completely imploding the efforts of hundreds of people, and sinking an entire team permanently. Cringey things that seem to matter to the echo chamber of a 24 hour news cycle. But I don't feel like hard science works that way. When it comes to real engineering feats, if one company tries to trade on faulty calculations, and their charade is laid bare, the smoke and mirrors disappear only to reveal the same bald truth that had always been there from the start: hard problems defy shenanigans. A political failure doesn't deflate an engineering problem. Not in the same way it deflates a PR campaign. If the hard science was not respected, then there was no investment in a decade of progress to begin with. So, these swindlers then maybe blew a decade of real funding, only to burn their investors with bogus project plans and proposals, ripping off charity and fomenting skepticism and suspicion? I think skepticism in this sphere is actually healthy, and separates the children from the adults. Waste is a bad thing, and maybe real money disappears, but maybe that kind money came from the kinds of people who might have just as soon blown their cash on personal assistants, vacations and clothes. Clearly such investors were not "buying science," or they'd have known better. So, then the only thing left is that maybe there's the premise that admirers of the charade would not have loitered on the sidelines, simply yearning to lend their support to the parlour trick they were true believers in. That they would have stepped up to the task, had they known progress was stalled. I don't buy that. No matter what, I don't think there has even been a decade of effort spent on crewing a mission to Mars. It's all been so much conjecture. It's never seemed to be an easier idea than an underground moon base, and no one seems to be giving lunar round-trips or installations much more consideration than mars. Space shuttle accidents and launchpad explosions cast the true hazards in a much more severe relief, but knowing that people are even trying and failing feels like much more significant progress than a lot of talk and faulty plans. So was there really any "damage" done by some of these PR goof ups?

james-watson 10y ago

What gets forgotten here, and something that I keep bringing up, is the lack of a Martian magnetosphere. This means long term human settlements have to be artificially shielded. This means living underground, which defeats the point of going to Mars in my opinion. Elon mentioned using a local magnetosphere generator, which is one of those ideas that is theoretically possible but whose practicality seems questionable. How powerful a magnetosphere generator is required to deflect ionizing radiation? How much power generation capacity will a Martian colony have to spare? Will this require a Fusion reactor? The only hope I have for Martian settlement is that Musk and his engineers are some of the most audacious and brilliant people on the planet. I will never bet against their success, and I wish them the best of luck. I have been a space exploration fan since as long as I can remember, I just worry that humans have a tendency to focus on the wrong goals when ideals and emotion cloud our judgement (e.g. the Space Shuttle).

Symmetry 10y ago
One of the aspects of Mars that makes living there hard is that Mars is very cold. But that same aspect makes it somewhat easier to establish big magnetic fields on the surface since it means that superconductors will require less cooling. If you're using a superconductor to generate a magnetic field you don't need any continuous input of power.
LeoDox 10y ago
Mars has an iron core; it's just not molten which prevents it from being ferromagnetic. I have three questions: 1. Is it merely a question of mass? That is, if Mars were larger would the increased gravity increase pressure at the core and keep it molten? 2. If it IS merely a question of mass, is there any way to add mass to Mars which doesn't disturb its orbit? Because if you could, then you simultaneously solve both the problem of low gravity AND lack of magnetosphere, which together solve the problem of maintaining atmosphere. Basically the whole planet becomes extremely Earth-like 3. If increased mass wouldn't necessarily wreck its orbit, could something be done to "steer" asteroids from the Main Belt into collision courses with Mars? I really don't know anything about orbital mechanics so maybe there's an obvious flaw in this (aside from the energy required to reroute that many asteroids).

jcoffland 10y ago

Radiation is a huge problem. Both en route and on Mars. A lot of these problems beg the question. Is Mars really the best target? Sure it's close but there are moons around Saturn that are interesting as well. Titan for example. Sure it's cold but it has a lot of atmosphere. Presumably landing would be easier. If we could learn to live underwater we could possibly visit Ganymede or Europa.

semi-extrinsic 10y ago
Radiation, as you mention, is a very big problem which is independent of destination. Human psychology is another, perhaps even bigger problem, also independent of destination. We've had various experiments with prolonged isolation, but none where the subjects know that they're never coming back to Earth. I'd say psychology has a >50% chance of wrecking the first manned missions to other planets/moons, unless we send huge ships with hundreds of people. In the Red Mars trilogy by Kim Stanley Robinson, the author has come to the very astute observation that a) no perfectly rational, mentally healthy human would volunteer for such a mission b) there will necessarily be extensive psychological screening to ensure we only send rational people thus c) the people who will be selected are likely to be non-rational actors very good at concealing their non-rationality from psychologists. Also known as people with psychopathic tendencies.
- coldtea 10y ago
  >Human psychology is another, perhaps even bigger problem, also independent of destination. We've had various experiments with prolonged isolation, but none where the subjects know that they're never coming back to Earth. Who said they're never coming back to Earth? >no perfectly rational, mentally healthy human would volunteer for such a mission That's an easy problem to solve, as there are no "perfectly rational" and/or absolutely "mentally healthy humans", and have never been anyway. And people can still be quite rational and mentally healthy and yet cherish the possibility to take such a mission, even if there's a possibility to die, etc. In fact, it's needs no more troubled people than those that go to the army and are OK to be sent to war, or people that dive and explore the oceans, etc etc.

sjbase 10y ago

Is a no-return mission something worth considering, on a purely technical & logistical level? Has anyone seen a really good analysis of this? My sense is that the social, political, and psychological barriers could be overcome for such a thing.

brilliantcode 10y ago

Why Mars though? Why not build a lunar base on the moon? Maybe even a hotel on the moon, I'm sure people will enjoy watching earth from the moon. I just fail to see this obsession with Mars. We don't even have manned landing on Mars and we are already having questionable stuff like "Mars One" And finally (one for the conspiracists): nearly 50 years ago we landed on the moon without any of the technology we have today. Why hasn't there been any strides? Shouldn't it be cheaper to go to the Moon vs Mars? Shouldn't it be possible to colonize Moon more easily and faster than Mars?

woah 10y ago
I think part of it is that mars has an atmosphere
- dTal 10y ago
  An atmosphere that provides none of the benefits of appropriate pressure, temperature and gas mix but all of the challenges of weather and airborne dust.
  - namlem 10y ago
    The martian atmosphere does have the benefit of having created much less abrasive dust over the years. Moon dust causes much more wear to moving parts. Mars also has accessible carbon, which the moon does not. The martian atmosphere can supply plants with the CO2 they need, enabling agriculture.
dwaltrip 10y ago
My understanding is that the Moon has far less useful resources. Sustaining any kind of base or colony on the Moon would require a larger degree of constant imports and may be much harder to sustain. Another huge factor is the lack of consistent solar power. 14 out of every 28 days have zero solar. Mars doesn't have this problem. There are other lesser factors as well, off the top of my head: weaker gravity which may affect health, the psychological problems with 2 weeks of solid darkness every month, and less scientifically interesting. However, it may be still worth considering.