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Sorry, But Lasers Aren't Taking You To Mars Anytime Soon
An anonymous reader writes: It's long been a dream of humanity to travel interplanetary distances at great speeds, or to make it to another star system within a human lifetime. Until recently, technologies to get us there — antimatter propulsion, wormholes or warp drive — have all been composed of physically unrealistic solutions. But recent developments in laser technology make directed energy propulsion a feasible solution. By building a giant laser array in space and developing a new type of solar sail that reflects the laser light with incredible efficiency, a laser sail, this propulsion system is scalable to arbitrarily large powers. There are many technical obstacles to be overcome, and so it's unlikely we'll see the fruit of this anytime in the next few decades (despite the promises of some), but this may well be the technology that takes us to the stars in the coming centuries.
Lasers would get me to Mars faster than I would click on a Forbes link.
Seven puppies were harmed during the making of this post.
Another Ethan Siegel blogspam that will take you to Forbes which HAS BEEN KNOWN TO deliver malware via their adserver. Do not follow the Forbes link!
"Scalable to arbitrarily large powers" = "I haven't thought about this very hard"
I recall there was some trick at the turnover about charging the sails an using the lasers for deceleration too.
Screw that.
Also, as long as Elon Musk goes to Mars and shuts the hell up, I'll chip in a few bucks to make that happen.
Slowing down isn't the problem. Slowing down and staying in one piece is the tricky bit. Just ask the Mars Climate Orbiter team.
Nuclear is still the best way to get to Mars. If it weren't for the fact that the words "nuclear rocket" in the same sentence is somehow horrifying, we would have been there a while ago. I mean, it isn't even going to be on Earth people. If you really want we can even have it dock with the ISS so we just have to carry it up.
If interested in this potential star-reaching tech, read Robert L. Forward's book Rocheworld.
Non-Linux Penguins ?
"...how would you slow down when you get there? "
Radio ahead to make a deal with the locals to build a similar laser for when you arrive.
I was always worried about being kidnapped by lasers to another planet.
when doing something new, should we begin with an untested unknown technology, or with existing technology modified to meet the need ?
imo the second method. and in this case, choosing that way would probably get us to mars in decade or three, but choosing first will only delay it ever further (though it would allow us to paint and write cool impotent pictures to pass the time).
and we are not doing a new potential technology a service by saddling it with solving complex task start with.
XKCD covered this and came to the conclusion that laser propulsion just isn't practical, even by the lofty standards of theoretical intrastellar space travel.
I read the internet for the articles.
Enter orbit, fly back towards the beam as you come around a few times. Or just take a chemical rocket, it's still a huge weight saving. There is atmospheric braking as well, it depends how fast you need to decelerate.
const int one = 65536; (Silvermoon, Texture.cs)
SJW, n: "Someone I don't like, and by the way I'm a fuckwit" - AC
Crazy Eddie!
Sorry, But Lasers Aren't Taking You To Mars Anytime Soon
a) I didn't think they were going to; this is the first I've heard of it at all
b) Well, not with that attitude.
C'mon, Slashdot, put a positive spin on it. Lasers might take you to Mars some day.
systemd is Roko's Basilisk.
Light sails don't work just one-way. Wind-based sailors have known for millennia how to tack into the wind; the same basic idea works for light.
What works in practice is that you slow down by turning your motion, relative to your destination, into heat.
Science, bitch. Now spare use your hand waving.
"His name was James Damore."
Tacking works because of the reaction of the keel on the sea water. Unfortunately, there is no sea water in space.
The biggest technical hurdle to human spaceflight is enabling them to survive the experience. Robots are far more likely, I think, for the next few centuries at least. Of course, some new disruptive technology could change that picture.
This posting is provided 'AS IS' without warranty of any kind, implied or otherwise.
Unfortunately you are traveling faster than escape velocity. Therefore you CANNOT "enter orbit". The planet will only deflect your path. The laser idea is just that an idea. Interesting but totally impractical and unworkable. Better to put a liquid salt thorium nuclear reactor and ion drives onboard the space craft. Or use an EM massless drive if it turns out to be real and not an experimental error. The light weight thorium reactor could use both ion drive for long haul low acceleration to conserve reaction mass and for a burst of high acceleration you could use the thermal output of the reactor to heat reaction mass and expel it directly. Interesting idea for a hybrid nuclear rocket system.
By building a giant laser array in space BLAH BLAH BLAH unlikely we'll see the fruit of this anytime in the next few decades
You had me at giant laser array 3
8 of 13 people found this answer helpful. Did you?
do you even Kerbal?
you know how much of a pita gradual atmospheric breaking would be on mars too? you don't have to worry about your components melting... but you've also barely got an atmosphere to work with.
don't think a parachute would do much unless it were impractically large either.
How do you stop at the other end?
Sailing into the wind relies on the keel to resist any sideways motion of the hull so that the only component of force remaining is one which points into the wind. You cannot do that in space. The only way I can think to do anything close to that in space is to use a gravitational field which will be very different to wind-based sailing.
For example no tacking is required: if you want to move closer to the sun use your solar sail to slow your orbital velocity and then just retract the sails and fall. However if you are powered by a laser bank then getting bank to Earth will be a lot trickier since there is no gravitational field to pull you in at inter-planetary distances. You will likely need good timing and rely heavily on complex orbital maneuvers in which case it is hard to see how it is better than a rocket.
If we are talking about sending very small micro satellite or slightly larger sized probes, then who cares about slowing down? You can get good data without slowing down.
I think that disposable probes is where you start. Sending small probes (anywhere) for a few million each to get you to a proof of concept.
Just play with them in Earth orbit to start.
>> ("lay-zers") may well be the technology that takes us to the stars in the coming centuries
I, for one, welcome our new shark overlords.
Or use an EM massless drive if it turns out to be real and not an experimental error.
It is absolutely not real.
SJW n. One who posts facts.
The faster your trajectory, the closer you need to get to the mass that you're slingshotting (not orbiting) around. If you want a solar sail to survive, then you want to make sure that this radius is outside of the radius of the outer atmosphere. If you want the spacecraft to survive, then you need to make sure that this radius is outside of the planet's crust. Otherwise, you'll just end up with a smallish deflection and go off in a totally useless direction.
I am TheRaven on Soylent News
Nobody reading this today is going to Mars.
It's time for you all to accept that and just move on.
You are welcome on my lawn.
The limiter in space communications, and in the space-sail-propulsion application, is diffraction. Don't think additive diffraction, as in crystallography, but the basic mechanism.
Waves diffract (change path) when they pass near the edge of an aperture. This is how nature works.
You might tightly collimate your beam, but the more you do so, the greater the 'spread' of the beam over long distances. For reference, see The Opticks, by I. Newton. (I hope you can read Latin!)
Well you could then spend 3 years aerobraking - can't get too deep into that Martian atmosphere at 0.3c so it's going to take a while...
Seven puppies were harmed during the making of this post.
At 0.3c you are not entering orbit. At best Martian gravity will put a slight kink in your trajectory but at that speed it's either hit the planet or miss it completely.
Seven puppies were harmed during the making of this post.
Or use an EM massless drive if it turns out to be real and not an experimental error.
it is absolutely not real.
So we have multiple experiments showing it is, but you're not linking to what debunks it. Why?
Don't disappoint your bird dog. Go to the range.
Er.... ok I'll bite. What's the other component, apart from wind, that keeps a sailboat on course? I'll give you a hint - racing yachts and modern sailboats have something called a keel. I DARE you to try to sail your "light sail" against the "wind" in space. What are you going to push against? Physics fail.
Seven puppies were harmed during the making of this post.
Entering orbit requires decelerating. Any speed which gets to a planet is way too high to orbit it. You want your periapse as close to the planet as possible and you burn at periapse so gravity helps you break but you still need to slow down or you will just escape again (ina different direction)
Unicode killed the ASCII-art *
I will ignore the obvious joke about going faster than the speed of light, but I wonder if we could do a similar effect using a solar sail? Anyone know if you can use a solar sail to get 'lift' as well as push?
excitingthingstodo.blogspot.com
I can't judge if laser propulsion will become workable but external propulsion (as opposed to onboard) certainly makes sense. That is, between two of 'our own' locations, with a 'cannon' on both ends.
So you would need a stage of slow ships taking ages to reach the target and brake. Then they build the 'braking laser' and then you can get much faster traffic.
Solar sails would work differently than wind sails, as has been pointed out vehemently by others, but while it certainly is impossible to use the sail to move towards a sun, it is an interesting question whether a solar sail can be made that can push you sideways when flying towards the sun. after all, a mirror can deflect light sideways.
So we have multiple experiments showing it is, but you're not linking to what debunks it.
No we don't, we have several experiments which show that there is no effect larger than the current experimental errors.
Why?
Seriously? Would you expect me to provide a link if I claimed timecube is bunk? Anyway, start here:
Noether's Theorem.
SJW n. One who posts facts.
...how would you slow down when you get there? Acceleration without deceleration won't work.
Your light sail splits in two. The outer ring being lighter is accelerated ahead of your ship and is flexed to cause it to focus the light back onto the smaller remaining sail on the ship, decelerating it.
...Inverse Square Law? Fer ******* sakes! Even a "focused" beam spreads out over distances. Those who dream of "laser propulsion" might think of a huge laser onboard, but the power source to drive it would be immense!
Is it April 1st, yet?
... Better to put a liquid salt thorium nuclear reactor ... The light weight thorium reactor...
There seems to have developed a nerd cult of the "liquid salt thorium nuclear reactor" which is apparently endowed now with quasi-magical powers, the answer to all possible questions about power sources. The proposed "liquid salt thorium nuclear reactor concept, none of which has every been built, is an idea for large scale fixed power plant designs, and is a very complex system as conceived (involving circulating molten salt fuel, on-line fission product removal systems from the fuel, etc.) that only makes sense - if it is practical at all - as part of a world-wide nuclear power industry. It has absolutely no features of value for a space travel power source.
The notion that such a system could ever be "light weight" is ridiculous - tacking those words on to "thorium reactor" does not make it any sense.
Any real space-flight ready reactor use ceramic highly enriched uranium fuel (negligible hazard until the reactor core turns on for the first time in space), fast neutron operation (moderator is heavy), and as few moving parts as possible. Something more like this.
Starships were meant to fly, Hands up and touch the sky - Nicky Minaj
Though if it was sturdy enough the sail could conceivably double as a parachute/kite. Whether it can be that sturdy (even for mars) and still light enough to be practical as a light sail is left as an excercise for Werner Von Kerman.
Unicode killed the ASCII-art *
just put a big superconducting ring around the sun, that can twist up a big streamer of plasma and then make it lase in ultraviolet. "they had a weapon bigger than worlds. Hindmost, I think Im going to feint."
or maybe faint eh?
Why try to make all that laser energy on Earth. The Sun has all we need. Just...
collumate the light into a beam to power your ships.
For quick reference, you can't collimate incoherent light into a beam that doesn't diverge-- the "collimated" beam of solar light will still fan out with a solid angle exactly equal to the solid angle of the incident solar light no matter what you do to it optically. If you get closer to the sun, the intensity is higher but the solid angle is higher; if you get farther from the sun the solid angle is narrower but the intensity is lower.
This is the "law of conservation of etendue" (which if you want to, you can derive from thermodynamics. Or from the Liouville theorem, take your pick.). That's a little bit obscure, I'm afraid, but if you just think of it as the brightness theorem, you've got the important part of it.
http://eckop.com/illumination/...
http://www.geoffreylandis.com
Seriously? Would you expect me to provide a link if I claimed timecube is bunk?
Actually, yes.
Disclaimer: I'm not the OP or GP or OG or anything like that.
I would expect it because Slashdot is a mixed crowd and some people (GASP!) actually read comments to get a better understanding of what's at hand. You, as a random Slashdotter, have no real standing with me. Not that I dislike you but I don't know you from Adam. You could be making up whatever you talking about or, worse, repeating something from someone else who also is just as clueless but now you've got an idea in your head that you're passing on as facts to others.
Telling someone their wrong in what could be a forward thinking forum would also carry the obligation of explaining why they would be wrong. Any jerk can make flippant remarks and be smug about it but it takes real knowledge to put something out there that will point the way to a better understanding for all involved.
I don't know why people around here think it's such a burden to discuss ideas with one another but is somehow acceptable to bad mouth others on matters that have very defined truths about them.
Anyone know if you can use a solar sail to get 'lift' as well as push?
"Lift" is defined relative to the direction of motion (it is the component of force on a wind perpendicular to the airflow). The force on a lightsail is defined relative to the incident direction of the beam.
If you were to define "drag" as force in the direction of the beam, and "lift" as force perpendicular to the beam, then, yes, you can have lift on the sail.
Nobody actually does define lift and drag on a lightsail that way, but if you think of the laser (or solar) beam as the "incident wind", then in fact it is exactly analogous to the lift and drag on a wing, in the Newtonian approximation.
http://www.geoffreylandis.com
Getting the speed solves the lifetime problem. By 5% of lightspeed time is moving a lot slower (at 100% it stops entirely). 80 years may pass on earth but your astronaught would experience only mabe 30. Trouble is when he gets home 160 years have passed on earth. Everyone he knows is dead. His country is now a province of the empire of the grand Pumba of Jakarta. Pizzabagels have become the worlds prinary food supply. Nobody remembers sending him and on the way he probably got passed by another mission launched 100 years after he left with a new 20% lightspeed drive which is already on the way back. The problems with high sublight travel isnt aging and the technical difficulties are utterly dwarfed by the political and psychological difficulties. And this wont conceivably change until we colonize at least our nearby neighbours.
Unicode killed the ASCII-art *
Any real space-flight ready reactor use ceramic highly enriched uranium fuel (negligible hazard until the reactor core turns on for the first time in space), fast neutron operation (moderator is heavy), and as few moving parts as possible. Something more like this.
Maybe it's not great for "launch failure" scenarios, but plutonium cores are nice and compact.
The laser sail is already impractically large (ever try to collimate a laser beam for delivery at 10+ miles?) why not an impractically large braking sail? Better still, make them the same sail, the laser sail may have a larger outer portion, but the structural braking sail could already be deployed as a central portion of it - you'll just need to execute a 180 degree rotation just in time for atmo-braking... Make sure you don't catch Phobos or Demios while you're at it.
You'd probably have a more conventional propulsion system for slowing down. So you'd carry fuel or perhaps deploy your giant blast shield and use nukes to slow down. You may not want to nuke the shit out of your own solar system, but no one cares about some backwater like Alpha Centauri.
Seriously, though. Even if you had to carry fuel to brake with a rocket propulsion system, you'd only have to carry half the amount, which would be a pretty big win.
And obviously, for two way travel, you can certainly build one in your destination, if you had sufficient reason to set one up there.
Of course, this doesn't get you FTL travel, or even high relativistic velocities, so this isn't exactly the birth of the Federation here.
gotta sky crane it, apparently aerobraking, and parachute won't do too well... though airbags might work good.
but powered descent is probably still necessary with a sizable payload.
yay
I came to Slashdot many years ago to read about new and exciting technology and when an announcement was made or a proposal was evaluated there was a lot of excitement by everyone, criticism was common, but it was constructive criticism, almost as if the readers were interested and excited.
Now days, not so much, most posts are either haters that hate everything, or people trying to out negative everyone else by pointing out how "it will never happen".
sigh...
I've seen plans that involve an outer portion of the sail separates from the inner disk, continues forward while the backside reflects light back to the sail, but hitting the opposite side and slowing it down. It might have involved slewing the vehicle with the inner portion of sail around 180 degrees, and using the same reflective surface it used for most of its journey. This would alleviate having to re-rig the sail if the photon pressure came from the opposite side, for example relocating trusses or whatever they use to secure sail to vessel to account for the force to be coming from the complete opposite direction. They might have that part figured out, been a while since I read about it in detail and am too lazy to look it up now ;-)
But... But... The ether!
I've thought about this a lot. Once a person/society goes 'relativistic' there's essentially no going back (at least to a recognizable land).
There could be other ships/societies that are also relativistic and you could potentially meet them somewhere in space-time. One ship goes 20% the speed of light and the other goes 15% to get to the same space at the same time.
How the relativistic societies would communicate is still somewhat of a pickle though, as there's be some pretty huge delays, even with the signals going the full speed of light.
I guess I should have read all the comments before I posted a redundant one. That was the first thing I thought of when I saw this.
Cheaper too.
We make fusion reactors here on campus, it's not that hard, plus there are a few space companies nearby.
-- Tigger warning: This post may contain tiggers! --
If you're going to another star, you dive in towards the sun and use it as a light source for your sail. If you're going to Mars, because of the way solar sails and orbital mechanics works, you can use the Earth-based laser to "slow down" (actually, speed up) to enter Mars orbit as well.
Better to put a liquid salt thorium nuclear reactor and ion drives onboard the space craft.
That's an insane idea. Even regular SEP has better T/W ratio than a nuclear heat engine, and a laser-boosted SEP would be even better (and is probably one of the better. laser-related ideas in the realm of space propulsion).
Ezekiel 23:20
It is unlikely to be real but your claim that the error level is higher than the measured effect is AFAIK wrong.
Not really, the experiments all have major flaws.
But your post is strictly anti-scientific
Except no it isn't. Noether's theorem means that breaking conservation of momentum means that the physical "constants" vary over space. There have been many attempts to accurately measure physical constants and none have shown any variation.
It's not unscientific to trust many very very carefully done experiments over a small number of flawed experiments.
SJW n. One who posts facts.
Time dilation is insignificant at 5% of light speed. It's about 1/10 of 1%.
Unfortunately you are traveling faster than escape velocity. Therefore you CANNOT "enter orbit".
Did you forget about aerocapture? https://en.wikipedia.org/wiki/... It would probably be about as viable as building giant lasers to propel a spacecraft.
...how would you slow down when you get there? Acceleration without deceleration won't work.
Laser propulsion systems usually are intended to decelerate by breaking off a section of the solar sail and sends it forward. The laser now hits that section of sail and bounced back to hit the main body, causing it to decelerate. So, just like a rocket, accelerate halfway there, then decelerate the second half. For added efficiency, the laser can continue be be bounced between the two making them separate even faster. Of course they could use that method to accelerate faster in the first half too.
Lasers aren't ever going to lift a ship up from the surface of the earth via a light sail. It is not entirely impossible that ground-bound lasers cannot be directed into an ablative material in the base of a ship that then vaporizes, superheats, and emerges as a plasma drive, but even that is highly speculative and requires extremely precise alignment of thrust vectors and the ship's vertical axis in the presence of both turbulence and coriolis effects during liftoff.
The place light sails become arguably useful is in orbit (however you get there). At that point, IF one can generate a light sail shroud on the order of 1 km^2, one can start to get some nontrivial acceleration for a not completely absurd payload not from lasers, but from the sun. At that point, one can get order of 10 N of thrust, which for 1000 kg of payload yields an acceleration of 0.01 m/sec. This doesn't sound like much, but every two to five minutes one can add a meter/second to a selected vector. Every day one can add hundreds of meters/second. Sunlight is free, and for certain payloads (not humans) you don't care how long it takes.
A light sail is perfectly capable of promoting metric ton scale payloads from Earth orbit to Mars orbit, even if it takes a year or more to get there. By filling a queue of such payloads -- firing one off per day, for example -- one could transport substantial physical resources from Earth orbit to Mars over the course of a year or two and use them to build an orbital platform and/or drop them down to a targeted site on Mars. The only cost is the standard 32 MJ/kg net energy required to get to near-Earth orbit.
So the real question is: Can we use lasers plus ablation (not light sails) to reach near Earth orbit with less than the 1000 or so to 1 energy/fuel penalty associated with rocket launches? And that is not at all clear. It will have to compete with alternative solutions, as well, such as fusion drives (assuming we get fusion at some point) or electromagnetic cannon mass launchers.
The problem with reaching Mars, or Jupiter, or the stars themselves, isn't getting there from Earth orbit. It is getting TO Earth orbit. That's half of escape energy right there, and once you are in orbit and away from atmospheric drag, even low thrust solutions become efficient provided one can maintain them for long periods of time, and light sails or (maybe) high efficiency ion drives are both candidates for moving non-living mass around on timescales uncomfortable for humans but just fine for human food, or water, or other resources required for the colonization of space or at least the nearer planets or their moons.
This is all very expensive, to be sure, but it isn't infeasible from the physics point of view and as always, economies of scale or technical improvements may lower the costs over time. Grabbing a nickle-iron asteroid as it passes near the Earth and attaching one of the in-system drives might let us use resources already at the top of the orbital gravity well and avoid the cost of lifting all of that mass up entirely.
rgb
Even when the experts all agree, they may well be mistaken. --- Bertrand Russell.
It does. But light pressure is the Poynting vector divided by c. What that means is the thrust in Newtons is basically the power of the laser divided by c. That means that a megawatt laser can produce less than 0.001 Newtons of thrust, which applied to a mere 1000 kg payload gives you less than a millionth of a meter per second squared acceleration. One can grow old and die before building up a reasonable delta V, at 30 million seconds per year, assuming your 1000 payload could sustain a MW output for a lifetime.
Take that same MW, run it for one second, and turn it into a 1 kg reaction mass with a million joules of energy and it gives you a momentum change of order 1000 Newtons (per second), or accelerates your 1000 kg payload at 1 m/sec^2. But then you only have 999 kg left.
It's all the brutal arithmetic of moving around in space. Light is easy to generate with an energy source but it produces irrelevant thrust until you start to talk about gigawatts of power, sustained. Throwing reaction mass makes far more thrust per unit of energy, but you LOSE the reaction mass you throw. No free lunches, sorry. The arithmetic is sustained almost independent of what kind of mass you throw or what you use as an energy supply.
A light sail using free sunlight MIGHT be marginally productive, provided that you can build kilometer-square shrouded lightsails with (substantially) less than a metric ton of mass. That's a million square meters, which means in turn that if it is a mere 1 mm thick it has a volume of 1000 m^3. Any reasonable density means that it is already up there in the general ballpark of your desired payload, and very order of magnitude difference adds a LOT to transit times. And then there is the shroud.
Is the material science problem for building a light sail solvable? Perhaps, but it isn't going to be easy, and we can't do ones capable of substantially shifting orbits at this point, although NASA is testing them for being able to fix the decaying orbits of near-Earth satellites, where one has only to compensate for micronewtons of drag with micronewtons of light sail force. Even 1 N/1000 kg is enough acceleration to be very useful, but 0.001N/1000 kg is nearly useless.
rgb
Even when the experts all agree, they may well be mistaken. --- Bertrand Russell.
Sigh. Newton lived in vain, I see.
Pardon me, I have to grab myself by the scruff of my neck and lift myself up out of my chair and go teach physics.
rgb
Even when the experts all agree, they may well be mistaken. --- Bertrand Russell.
Ok, you say:
Not really, the experiments all have major flaws.
Then please identify those flaws, or cite a link that does that
If you cannot provide evidence then you are just another fraud making claims with no evidence
It is unlikely to be real but your claim that the error level is higher than the measured effect is AFAIK wrong. We also have replication in 3 separate places with separate groups of people using different hardware which reduces some error sources.
No, sorry, but I will challenge that last statement. There are three separate groups which have produced different results which are inconsistent with each other.
Most recently, the NASA Johnson "Eagleworks" group has tried to replicate both the EM drive proposed by Shawer and a result on a similar concept in China claimed by Yang-- and falsified both of these results. The EM drive proposal stated that the purported drive worked because of a specific asymmetry, but the Eagleworks test showed that the result was the same whether or not the asymmetry is present: the Shawer driver does not work as proposed. They also tested the Yang result, and got a result... but the result was orders of magnitude different than the claimed Yang result. The net answer is that neither result was replicated.
Also, the test that was reported at a conference was not done in vacuum (although they only mentioned this detail in the "further work" section of their paper.) There has been a post to an internet forum saying that they have now tested it in vacuum, and gotten yet different results-- but internet forums are not scientific publications.
I'm in favor of good experimental work testing these ideas... but so far, it's way premature to suggest that the results have been replicated. They're not. The results are very, very small, and no two experiments seem to show the same thing.
Here's a Wired article from last year (which was the last anybody heard anything new) with some more discussion. (Sorry it's in Wired, which apparently everybody hates now, but that's where it is.) http://www.wired.com/2015/05/n...
http://www.geoffreylandis.com
They did build and run a molten salt reactor, using fuel bred from thorium (although not in the same reactor.) The program grew out of a perceived need for a compact, lightweight reactor for nuclear powered aviation. The ability to operate at atmospheric pressure, and utilize the fuel bearing salt as the coolant gave it a huge advantage in that regard.
Wiki for the proof-of-concept reactor.
https://en.wikipedia.org/wiki/Molten-Salt_Reactor_Experiment
Funny how many people said basically the same thing, but you win the "snarkiest while not an AC", so I'll respond to you.
What's the other component, apart from wind, that keeps a sailboat on course?
What's the other component, apart from its own thrust, that keeps a spacecraft on course? I'll give you a hint: Everything in the solar system moves in a great big ellipse around the biggest source of it in our system.
What are you going to push against? Physics fail.
You can "push" (or maybe in this case "pull" makes a better choice of words) against the Sun's gravity from anywhere in the solar system. I'll consider my physics grade corrected, thanks.
It does seem unlikely that EM drives work, especially as stated, but it doesn't matter what Noether's or anyone else's Theorem states. After all it might be wrong, just as the vast majority of theorems to date have been shown to be wrong, or at least incomplete.
All that matters is whether or not an anomalous force is actually being produced in the experiment. If so, then the theorems will be updated or replaced as needed, or we will develop an alternate explanation for the effect that allows it to exist within the framework of existing theorems. After all nothing says that any of the current conjectures as to its means of operation are correct either, it may be that it actually does conserve momentum - for example perhaps it can only operate within a sufficiently curved space, and imparts an equal-and-opposite force upon the body producing the curvature. (wild speculation, don't bother refuting unless it's interesting)
That is the essence of science: the experiment is the ultimate authority, all else must be brought into accordance with it.
And point in fact, a number of research groups have claimed positive results far beyond the margin of error for their measuring apparatus. Many have found it perplexing that the guys at NASA have been testing such an extremely low-power version of the device rather than at power levels where far more dramatic results have been claimed.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
Indeed. There are far better fission reactor designs for space, such as the Russian TOPAZ reactor.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
This concept is totally cool, and apparently at least possibly workable for microsats. - Make 100,000 or so microsats, with a quantum entangled thingamabob (however that is done, I have no idea, but someone is doing it somehow) - Send 1000 to each nearby star...yes, they will flyby the star - figure out how to tweak trajectory a bit - send pictures back of planets in those systems.
A regular Stanford Encyclopedia of Philosophy has better Tesla per Watt ratio than a nuclear heat engine?
Please, your extremely generic capital letters are hard to follow.
You are mistaken about theorems. They're not scientific theories, they are mathematics. I the case of Noether's theorem it proves mathematically that for conservation on momentum to hold then certain symmetries must be present. That's maths and it's proven in an absolute sense.
Where it connects with science is if the physical world has those symmetries. If it does, then momentum is conserved. For momentum to not be conserved, then physics as we know it does change over time or space. That link is inescapable.
You're right that the experiment has supremacy, but so far all other experiments have shown no variation I physics over time or space. I other words, both cannot be correct. I'm very much inclined to believe the mass that show nothing over the very few that show a tiny, tiny effect.
And as for the low power thing: consider the difference in scale between kilowatts and milli Newtons. It's that scale difference, not the absolute size which matters. It's incredibly difficult to dump 1kW into something without generating small forces. Consider heating of the wires and other things, coupling of the high current to magnetic fields, electrostatic forces generated be nearby bits at different voltages etc. Don't forget that even common insulation materials like pvc exhibit the piezoelectric effect so voltage gradients can cause forces.
Dumping more power in will generate a larger force if this is real, but it will also increase the size of the confounding effects. And reading more about it there are confounding things all over the place.
SJW n. One who posts facts.
Gravity doesn't work that way.
Gravity has a time component because it's an acceleration. If you're moving close to the speed of light (I mean this was the point, right?), you are going to be very far away before gravity (even the sun's gravity) has any chance to act on you. The other problem with being further away - you're further out of the gravitational field. Divided by r SQUARED, remember? So exactly how were you going to use this "force"?
Not to mention the fact that you are allowed two and only two directions: Faster than the Earth (which will get you to the outer planets and eventually out of the solar system) and slower than the Earth (which will get you to the inner planets and eventually into the Sun). Now, if you're going to go really fast (the fraction of the speed of light that has been mentioned), the Earth will not have moved much around the sun before you need to slow down again. Oops. If you were counting on some weird trigonometry with the Earth in a special position on the other side of its orbit, er, well, that's not going to happen in a day or so.
Of course you could go slower and loop around planets, etc, before you get your magical "set-up" that allows you to shine your beam at the sail ship. Then you'll find that although you partially correct one velocity component, you've added even more to the ones that say "away from the sun". It's a tangent thing, you know? You can only make a bigger circle from inside a smaller circle...
Only way this would work would be to have some laser at your destination waiting to slow you down. And THEN we can get into details about how much acceleration your craft can stand and for how long. Anything biological is out, for starters...
Seven puppies were harmed during the making of this post.
anyway, the historical accuracy of mathematics is compelling to convincing, but there's always that niggling doubt, that horror at the back of my mind, that 2+2 doesn't equal 4.
You might want to look at Galois fields (finite fields). There, 1+1=0 in GF(2) and 2+2=1 in GF(3).
SJW n. One who posts facts.
all i know is i must try this in KSP now... thanks asshole.
If the EM massless drive turns out to work, we can probably do much better at exploiting what's in the gaping holes in our fundamental understanding of physics than that silly drive.
I'm going to need a LOT of evidence before I stop believing in the Law of Conservation of Momentum (or, more precisely, its relativistic combination with Conservation of Energy).
"When you have eliminated the unacceptable, whatever is left, however improbable, must be the truthiness" - Holmes
The truth of mathematics is NOT the truth of reality, so don't try proving the contrary. Mathematics is extremely useful in modeling reality, and, significantly in this case, providing a handy way to come up with consequences of a theory. If we can't get consequences out of a theory, we can't do science, because we can't perform experiments and/or observations to distinguish one theory from another.
2+2 == 4 not because of some fundamental principle of the Universe, but because that's how we've defined integers. You can find lots of physical cases where you take two X, add another two X, and don't get four X. Suppose you have two droplets of water on a rubber sheet. Drop another two droplets onto the sheet. You can get quite a few different numbers of droplets on the sheet that way, depending on where you drop the water and what happens next. Perhaps they combine with the previous two and form one large droplet. Perhaps they splash on impact and we've got dozens. We don't have a law of conservation of droplets. We do have a law of conservation of mass that works in Newtonian physics, since we've observed that.
Noether's theorem is correct. The Law of Conservation of Momentum does depend on physical laws being invariant throughout space. (Actually, the laws get more complicated when we need to consider relativity, but the basic principles are the same.) It doesn't claim that physical laws don't vary between points in space, and it doesn't claim momentum is conserved, but it does show that the two are related. If momentum is not conserved, then we have to have changes in physical laws from place to place, and that would have consequences that we would almost certainly have observed.
I'm not saying the drive doesn't work. I'm saying that it's going to take a whole lot of evidence to convince people, and I haven't seen a whole lot of evidence.
"When you have eliminated the unacceptable, whatever is left, however improbable, must be the truthiness" - Holmes
The plutonium cores aren't reactors. They're lumps of Pu-238, which are highly radioactive and produce a lot of heat. They're hardened sufficiently to last through any projected launch failure. Mark Watney was overly fearful of the thing in "The Martian", which I'll attribute to it not being his field.
"When you have eliminated the unacceptable, whatever is left, however improbable, must be the truthiness" - Holmes
If you deploy the sail, you create a velocity change away from the Sun. If you furl the thing, you stay in the orbit you previously had, and that orbit isn't going to decay. You might want to play some Kerbal Space Program to get a bit of a feel for orbital mechanics.
"When you have eliminated the unacceptable, whatever is left, however improbable, must be the truthiness" - Holmes
Lots of heat is different from a reactor how?
If it ever got to the point in which they tried to moved a vessel that contained people or a cargo shipment the amount of force leaving the lasers would be very great, especially when trying to accelerate the vessel at greater distances. So they would need to install the lasers on a very large mass or us some sort of engine to maintain the position of the lasers. At that point why not just put the engines on the vessel and skip the transformation of energy.
Orson Scott Card explored this very well in the Ender series, especially in Speaker for the Dead and Xenocide.
Unicode killed the ASCII-art *
A nuclear reactor changes the nuclear reactions within, typically by keeping the neutron flux at a level that causes fission to provide enough neutrons to keep the flux up. This lump of plutonium just decays normally.
"When you have eliminated the unacceptable, whatever is left, however improbable, must be the truthiness" - Holmes
2 + 2 for pure numbers and 2 + 2 for arbitrary groupings are not the same thing, and you know it. Or if you don't know it, you're an idiot.
It's true I tell you, feller at work's next door neighbour read it in the paper.
Ah, so lots of heat - no potential for super-criticality - why, then, isn't this a good power source for a long trip?
There are a lot of other techniques using beamed propulsion other than just using photons to push tiny masses around. Ablative laser propulsion for example. It can have enough thrust to weight to get to orbit and it has like twice the ISP of a chemical rocket.
Problem is lasers aren't cheap or high powered enough. Yet.
These are good power sources for long trips, and NASA likes to use them when solar power won't work. One problem is that the Pu-238 was a by-product of something else, I seem to remember weapons production, and we have been using it faster than we've been replacing it, so it's getting more expensive. (I assume the stuff's already expensive, having once looked for depleted uranium on eBay.)
"When you have eliminated the unacceptable, whatever is left, however improbable, must be the truthiness" - Holmes
With the right connections, people will pay you to take DU...
You either dive into the star for maximum deceleration or you detach part of the sail and use it to reflect the beam back.
Robert L. Forward suggested this 30 years ago:
https://en.wikipedia.org/wiki/...
Solar electric propulsion.
Ezekiel 23:20
I also understand that some people got DU sent them for free by the US Army, in some of the recent unpleasantnesses in the Middle East.
"When you have eliminated the unacceptable, whatever is left, however improbable, must be the truthiness" - Holmes