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.
The "Red Dragon" missions are planning on the cheap approach, using a flattish (indeed rising in places) trajectory to extend the aerobraking long enough to be effective, combined with supersonic retropropulsion. We've got a lot better at fluid dynamics and lifting-body physics in the last few years, and SpaceX in particular is cleverly developing a lot of experience using the same "EDL technology stack" for their booster landings on Earth.
Not everyone reads the articles. I usually skim the comments first to find out if the article might be worth reading; defining the abbreviations definitely helps.
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.
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.
You don't need to get the entire mass of the elevator down initially. Just the harpoon and cable.
Many of the ideas for visiting other planets could and should be tested on earth first. I think we need to get comfortable with visiting the moon and performing large scale industrial projects in space before we have any chance of visiting remote planetary bodies and returning.
>You don't need to get the entire mass of the elevator down initially. Just the harpoon and cable.
That's what I said. The trouble is there's no "just" about it. A cable long and strong enough is going to be extremely heavy, never mind the "harpoon". In a traditional "harpoon" the cable is a small fraction of the total mass - you can't really afford that kind of design (shoot heavy thing, drag negligible thing behind) so it's not clear how the orbital dynamics would work. You'd be looking more along the lines of little tug rockets spaced along the length of the cable.
>Many of the ideas for visiting other planets could and should be tested on earth first.
Quite. This Mars stuff is completely pie in the sky. Let's see a self-sustaining habitat in a desert on Earth, never mind even the moon. As an incidental benefit of solving this we would be able to perform sustainable agriculture anywhere on Earth.
The harpoon could be a big heavy thing. Perhaps we crash an astroid into Mars that is trailing a cable. That doesn't really jive with the planetary protection principals but it might be the kind of thing we need to consider to get the job done.
> As an incidental benefit of solving this we would be able to perform sustainable agriculture anywhere on Earth.
True. Although sustainable on Earth usually also means economical. I would like to see a sustained habitat on the moon.
I feel like a good first step would be setting up an orbital base/space station that orbits mars. It might be be a little easier than habitation On the planet itself, and more risk for the astronauts involved. However, if we set that up using knowledge gleaned from the ISS, I think its a viable path to take.
The attractive thing about landing on dirt is that the raw materials mean that a closed life support system isn't needed. There are relatively accessible supplies.
Space stations anywhere, be that LEO, lunar orbit, Mars orbit, deep space, or floating in Venus' atmosphere, lack that option.
As I told the robotics people at Stanford who were talking about something similar on the moon in the 1980s, "how soon can you do it in Arizona?" The machines sent to Mars so far are very small and wimpy. Because they're semi-teleoperated, and have very limited solar power, they're really slow. If you want to do any high-power activity on Mars, you'll probably have to send a nuclear reactor.
Alternatively, send a probe that generates LOX and liquid methane from water ice and CO2 on Mars using solar power to create the fuel needed for ascent.
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.
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
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 :)
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.
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.
> no perfectly rational, mentally healthy human would volunteer for such a mission
That depends entirely on what they value. If they value their own safety, comfort, and health, then it wouldn't be rational for them. But if they value the advancement of future humans, honor, fame, legacy, scientific discovery, adventure, and so on (which may seem to be irrational things to value for someone in the first group) then it would be rational.
There are some people who will be excited about the fictitious ad from Earnest Shackelton "Men wanted for hazardous journey, small wages, and bitter cold, long months of complete darkness, constant danger, safe return doubtful, honor and recognition in case of success."
>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.
How are they going to come back? All realistic plans I've seen are for one-way trips.
The thought of dying isn't the inherently problematic part, but rather the extreme isolation. People who go to war are there for only some months and have plans for going home, back to friends and family. People who dive and explore the oceans are isolated for a few days at worst; perhaps months in a nuclear sub, but there you have already a pretty large crew around you. Compared to decades spent isolated with a handful of people, and no return ticket to the rest of humanity, those are nothing.
>How are they going to come back? All realistic plans I've seen are for one-way trips.
Huh?
"The first crewed Mars mission would be expected to have approximately 12 people, with the primary goal to "build out and troubleshoot the propellant plant and Mars Base Alpha power system" as well as a" rudimentary base." In the event of an emergency, the spaceship would be able to return to Earth without having to wait a full 26 months for the next synodic period."
Wow, that is so hard I didn't think it was being seriously considered. They're going to send a Mars surface-to-orbit launcher as payload in one piece, without fuel, and then produce >30 tons of rocket fuel on Mars? My hat's off to them.
Musk hasn't discussed the exact details of his plan, but it seems like the unmanned missions in 2018, 2020, 2022, and possibly 2024 (if there's no manned mission that year) are meant to establish a rudimentary fuel production infrastructure and start producing fuel in anticipation of a manned mission.
NASA, I believe, is currently trying to solve the problem with more efficient engines for interplanetary travel. Ion drives seem to be the preferred method, but there is still some research going on in nuclear thermal rockets.
Exactly. Who is going to want to live underground in a freezing wasteland for the rest of their lives after the initial novelty of 'being on Mars' wears off? Nobody even does that here on Earth, so why would they want to do it on Mars?
Floating around in aerostats on the cloud tops of Venus where it's roughly room temperature at 1 atm on the other hand... or living on the Moon where you can at least communicate with Earth in roughly real-time and are only 3 days away...
A floating station (eventually a city?) in the atmosphere of Venus would also be fine. On certain height, the temperature and the pressure are close to Earth's surface, and sun shines brightly enough for plants to generate oxygen. There's plenty of carbon dioxide in the atmosphere to feed the plants.
The access to solids is definitely a problem. One approach might be digging them from the surface and lifting up using balloons. High temperatures don't help, but without the need to stay on the surface for very long periods, the digging robots may probably accumulate enough cold while high in the atmosphere, and then dive down for a short while, managing the temperature e.g. by melting and boiling the coolant, then go up again.
The lifting gas can be initially transported in a highly pressurized form (e.g. liquid helium). It would be enough to support a small initial platform. That platform can generate lighter gases right from the atmosphere, using solar energy. CO2 is pretty heavy, so even oxygen and nitrogen would be lifting gases. Hydrogen is also somehow available for extraction from the atmosphere. These gases could be used to support more and more incoming structures as they arrive from orbit. (Yes, easier said than done.)
The bigger problem would probably be compounds like sulfuric acid, hydrogen chloride and fluoride, etc, that would readily react with many construction materials, especially metals.
Given the atmosphere composition, it's probably even possible to synthesize both fuel and oxidizer for a rocket, e.g. hydrocarbons and O2 or HNO3. Launching a large rocket from a zeppelin is tricky. Launching a rocket from a plane has been shown to work on Earth, so it's possibly also doable from Venusian cloud tops. Again, easier said than done.
"Is Mars really the best target? Sure it's close but there are moons around Saturn that are interesting as well. Titan for example."
First, for what is worth, I share your Mars questioning. But then I can't just let you downplay the distance factor with "sure it's close" glossing-over. One can find interesting tools out there¹ that may help grasping the astronomical distances better. The bottom line is that it just makes more sense to take our chances with planets closer to us and so far, at least with the landing on Moon, the humans respected in this regard their species' "rational" self designation.
>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.
You seem to imply that the issue of radiation should cause us to reconsider whether Mars is worth it. But the same, and worse, problem people will have with Saturn too.
Titan may be a very good bet. It has an atmosphere so you aren't worrying if your water resources may boil away, or if a small tear in your suit hapens, you have more time to fix the situation.
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.
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).
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).
The amount of energy required to lower the orbits of enough asteroids (e.g. 20% of Mars total mass) is probably enough to melt a significant portion of Mars. Unfortunately, collisions would mostly heat up the surface, not the core. Even if you could precisely deorbit enough asteroids to hit Mars, the results of the bombardment would probably take a long time to settle.
Planetary-scale engineering is not only hard, it's inevitably slow.
I think cleaning up the atmosphere of Venus by spreading CO2-eating anaerobic air-suspended algae is more realistic, and the results would likely be nicer.
It's not pressure but heat from mostly radioactive decay and also tidal stresses from the Moon that allow the Earth's core to be liquid. More mass allows for more insulation and more decaying Uranium, Thorium, etc so tends to lead to higher internal temperatures.
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.
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.
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.
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?
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.
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.
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.
"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?
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
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.
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.
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).
>"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.
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.)
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).
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"?
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).
I think he's just expressing a healthy degree of skepticism, with a touch of hyperbole for flavour. He's likely just a bit sick of being asked his opinion on the drive until there's further experiments and research conducted on the matter.
I'm not dismissing your interest and excitement in the topic either. I'd love for it to be functional, and for us to learn new information on the way our universe works. The bar for entry is set particularly high on this, that's all :)
Unfortunately - even if you had some weird results that didn't fit the prevailing theorems, publishing would likely destroy your professional credibility. See: Fleischmann/Pons and their publications of abnormal results that others speculated might be related to cold fusion, the decades of slander and defamation of them as quacks (despite the fact that they themselves had not claimed anything of the sort), and their recent vindication.
> Perhaps most surprising is that, in the formative years of atomic science in the early 20th century, some scientists reported inexplicable experimental evidence of elemental transmutations. In the 1910s and 1920s, this research was reported in popular newspapers and magazines, and papers were published in the top scientific journals of the day, including Physical Review, Science and Nature. The experiments, using relatively simple, low-energy benchtop apparatus, did not use radioactive sources so the results defied prevailing theory. Several researchers independently detected the production of the gases helium-4, neon, argon, and an as-yet-unidentified element of mass-3, which we now identify as tritium. Two of these researchers were Nobel laureates.
To think that our current models adequately explain every phenomenon in the universe is truly the height of hubris. They can't even explain every phenomenon that has been observed on Planet Earth, let alone universally.
Of course extraordinary claims require extraordinary proof - but we do a tremendous disservice by disincentivizing scientists from ever reporting a novel finding that disagrees with the prevailing theories.
Sure, but it's not about whether or not the thing works. When I read his comment, I thought to myself, "What else has this guy missed in his work with such a dismissive attitude?" It's a messy mentality IMHO. And, you know, all seriousness aside, here he is saying the EmDrive is impossible, yet he's actually working on the hyperloop. Badum-psh!
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.
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.
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.
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...)
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.
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.