I passed along a bunch of your common questions to Dr. Pekka Janunen, and here's what he had to say: 1. Can we combine them with a solar sail to get the best of both worlds? *Maybe, but we don't have such concept under active planning. At one point we considered using small solar sails to control the spinrate of E-sail tethers.* 2. Could the tethers work as antennae, to help communicate with Earth? *Not really. The tether wires are so thin that their ohmic resistance per length would reduce their efficiency as antennas. Also, nowadays one prefers high radio frequencies. Such frequencies do not call for long wires antennas, but instead smaller directive antennas like parabolic dishes*
I hate to disagree with Dr. Janhunen, but electric sail wires would make excellent antennas. There is a type of antenna, called a Beverage antenna (see: www.google.com/search?source=hp&ei=prM8XYH1NuqF0wKOr5qgBw&q=beverage+antenna&oq=Beverage+antenna&gs_l=psy-ab.1.0.0l10.1830.9150..13246...0.0..0.314.2241.0j16j0j1......0....1..gws-wiz.....0..35i39j0i131j0i10.cBEvc9cDTrY ), which is a long wire-a *really long* wire-that is many quarter wavelengths long. When an antenna wire becomes many quarter wavelengths long (1/4 wavelength is the minimum self-resonant length of an antenna, either above a ground plate or plane, or as one half of a dipole antenna [whose total length is 1/2 wavelength at its self-resonant frequency]), the antenna pattern is such that the signal fires almost entirely off the far end of the wire. (For receiving, such an antenna is also very sensitive to signals arriving at its far end, moving parallel to the wire’s orientation, because the transmit and receive antenna patterns are identical.) Also:
Like a spin-stabilized satellite with an electrically-despun antenna (the USAF pioneered such multiple-antenna spinning satellites, as I covered in *this* www.centauri-dreams.org/2018/05/18/immortal-interstellar-probes/ article about interstellar probes), an electric sail-equipped interstellar probe-like Project Dragonfly’s design-could use the electric sail wires as electrically-despun, highly-directional antennas. Either each electric sail wire could be “worked against” the spacecraft’s body (using it as the RF-Radio Frequency-ground), or each opposing pair of electric sail wires could be worked against each other, forming what is called a doublet antenna. (A doublet antenna is a dipole antenna-with a dipole antenna pattern--*only* at the antenna’s self-resonant frequency, but a doublet antenna works on other frequencies-both higher and lower than its self-resonant frequency-with the help of an antenna tuner.) As well:
At typical spacecraft radio frequencies (S-band, X-band, etc.), the wires of an electric sail are hundreds, thousands, or even tens or hundreds of thousands of wavelengths long, so they would be very high-gain antennas, firing transmitted signals in a very narrow lobe off the far end of the wire (or wires, if opposing pairs of wires were employed as doublet antennas), and they would be equally directionally sensitive for receiving. Using a variable antenna tuner would enable the wires to resonate over a very wide band of frequencies, making the electric sail wires ideal for an interstellar probe’s radio science/plasma wave instrument, and-on a Bracewell interstellar messenger probe-for listening for any intelligently-generated signals from a potentially inhabited planet in a probe’s target star system.
This technique has seen really great investments compared to the recent lightsail. In 2013 Estonian students build a 1 kg cubesat which should test a 10 meter electric sail but it failed because the winding mechanism did not work. The cubesat costed around 100 000€. The official reason was to prevent space junk.
I imagine re-orienting the spin, and retaining the spin would probably be quite difficult as receiving the winds with any angle other than perpendicular is likely to cause an un-even distribution of force.
When travelling near the speed if light, colliding with small particles is dangerous as you said before. Could we use the same technology from a warp drive to bend the space with the particles in so they don't collide with the ship?
Growing up in the 70s and 80s I had a dream over time in my childhood that mankind would have have races in space in solar sail spaceships that people would build and run. I never knew where I came up with the idea of them .. but I even drew them up on paper too and just daydreamed about it. Then they had one in an episode of Star Trek Deep Space Nine much later along about the Siskos travelling in one across the stars. . Such a great idea if mankind had the technology to build it and still be able to protect the people in them. It won't likely happen in my lifetime ... but maybe in the next century? It could be a really cool way to get people to travel into space ... if it was feasible and people were protected enough. This episode kind of brought back memories of that. Thanks for another great episode.. I love your videos by the way!
Some solar sail-including interstellar probe and starship studies from the 1970s and more recently have called for using a solar sail (some were all-metal ones) that would be electrically charged in order to brake against the interstellar wind and the stellar wind of the destination star.
Might it be possible to create such a sail without using solid material? Could we create the same thing using a pure energy field that could somehow capture all that solar wind?
Well I guess it would have to transmit force back to the spacecraft via either strong, weak, gravity, or electromagnetic. Of these only EM has the distance, repulsive direction, and strength. The EM force is transmitted via fields -- which feels rather like a "pure energy" idea that ya mentioned. An electric or magnetic sail, whatever its matter source, *would* continue to catch & transmit particle force a bit past its solid edges -- but would drop off quickly as an inverse square.
Fascinating! Robert Forward suggested other ways to use tethers to harness power for exploration (e.g., in Jupiter's magnetosphere to move things between Io's or Europa's surface and low orbit).
Very interesting. Could we send an electric sail to outside the solar system, or even to another star if we get the trajectory right? Great video, can't wait to see this technology in use.
Electric sail is what they use in the serie by Nathan Lowell where I now am reading the second book (free books that you can get on Itunes and other places. Just include Podiobooks in the search). Freight ships "sail" in and out of the star systems :-).
Nice video Fraser! One issue: I think the electric sail mostly taps into the momentum carried by positively charged solar wind particles (not electrons as you mention around 2:50). Makes sense, since the solar wind has both positive and negatively charged particles, but protons are so much more massive than electrons.
There is a Box Kite shaped model, that has wire loop on the top of the frame. When a current is passed through it, it hovers above the ground. This sounds like that
@@frasercain Some interstellar probe designs combine both sails, for braking at arrival at the target stars--either a combination of a solar (stellar, in this case :-) ) photon sail and an E-sail, *OR* a photon sail that is positively charged, so that it "bounces back" both the star's light ^and^ the positively-charged stellar wind (mostly protons, and some helium nuclei). It is even a "double feature" for arrival braking in some starship designs (as long as the photon sail is large and light enough [ditto for an E-sail, if also used in a particular starship design], effective braking can be done).
Hello Frazier I'm a big fan of your show and astronomy cast. I know this isn't the forum for show ideas for astronomy cast, but... a while ago you did a series on amazing women in astronomy. I would love to hear an episode about Pamela, and her story. I know she has said it all, but not all at one place in one time. As far as inspirational women in astronomy, no one stands out more to me than Pamela gay. She has inspired me to learn in a greater way than any one person in my life. I would be willing to bet that other listeners would agree. Thanks for your time and all your hard work. You are my entire education above the atmosphere
Hey so, pulsars, neutron stars, and magnetars are all supposed to have insanley powerful magnetic fields, right? Could we use a magnetic sail there as a sort of electromagnetic parachute to decelerate ships going a decent fraction of the speed of light? If we accelerate them to .20c with the starshot proposal, and decelerate them using pulsars as magnetic brakes, we could have very fast interstellar probes, with almost no propellant needed
They can make the sail positively charged or negatively charged. Do you think, they make the sail positive charged because it will repel positive charged protons ( Protons are heavier than electrons) from sun. Protons repelling will cause more acceleration to the space craft. But as you go further and further, these proton concentration reduces and the propulsion.
That's right. Protons (or other positive ions) are repelled while electrons are attracted to the sail. That's why the electron gun is needed to maintain a positive charge. As for the proton concentration, check out this paper: arxiv.org/pdf/1707.02801 It's about magnetic rather than electric sails, but it discusses the effect of low proton density on such craft.
9:18 It's not fuel-free, Fraser, it's propellant-free. You still need to come up with energy. Fuel is what you burn to obtain energy. Propellant is what you throw out the back to gain momentum. Only sometimes they're the same. www.projectrho.com/public_html/rocket/misconceptions.php#id--Fuel_Is_Not_Propellant www.projectrho.com/public_html/rocket/engines.php#id--Rocket_Engine_Components
What about the EMdrive? I didn't see you list that one. Is there a reason you left it off of the list? it would be really cool to hear you talk about that concept. =)
I still haven't been convinced that it's actually a thing yet. If it does work, it violates the laws of physics, so we're going to need some solid evidence.
Could you use an Asteroid like A 2017/U1 to get to high speeds? I.e. you could get a dampened hit, or shoot a grappling hook at the Asteroid to get pulled
Fraser, I seem to recall you discussing the importance of Rest Mass in equations like Einstein’s e=mc2… is there such a thing as Rest Energy (or some comparable state)?
What would be good Units, that would be useful to use when colonizing the Solar System/Galaxy? Like years, light years, AU, days, hours, etc. These are different wherever you are(technically speaking, they all have exact definitions)
Electric sails! First time I’ve heard of this. Very cool. Adding a large electric sail to any spacecraft should not be a problem. Even a manned mission could use this technology, how much of a shielding affect would this provide?
Thanks. At first, I wasn't sure about the electron gun shooting electrons. But after rewatching it, it was clear to me. I should stop watching videos late at night.
Didn't they do that in Back to the Future? The only thing that we can maybe do fusion with is a flavor of hydrogen. So we're not at the point that we can fuse trash yet.
Fraser Cain yeah they did do that in back to the future. But i do think that if we had a big enoug reactor and maby jumpstart the reactor with hydrogen et would be hot enough for trash molicules to fuse
A thought: Given that these craft would already be equipped with long, conductive lines, couldn't those be used as transmitters and receivers, essentially big radio antennas? If you're already carrying what is effectively a 20 km radius circle, wouldn't it be relatively simple to use that for sending and receiving signals? On top of which, while cruising from one asteroid to the next, couldn't they use the sail's radio interactions to function as a huge radio observatory?
I mean, that just seems odd. All you need for a big transmitter is a big conductive thing. Seems like they should be able to use the sails as transmitters and receivers.
Do you have any news about the picture they were going to take of a black hole this year? I didn't find anything new on google, maybe you could talk about this in your next video.
If there is one star right behind another star, from our perspective, would we still be able to see it due to gravitational lensing or sth. else? Would it cause some anomalies like weird luminosity, mass, metallicity etc?
I would say that the electric sail is the only way to explore our solar system. It may be the only way to traverse the distance between stars. At some distance from the sun, the electric sail would stop accelerating the spacecraft. That would be the maximum speed the electric sail could generate. It would have to do a sort of sling-shot effect to get the velocity it needs to go to another star. It would have to accelerate away from our sun, then turn the sail around and head into sol - accelerating the whole way then orbit around the sun and accelerate away from the sun. Then and only then would it have any kind of velocity needed to go to another star. Could it decelerate when it got there?
Have you ever looked at the Princeton Satellite System's Fusion Engine that produces 20 to 40 newtons of thrust and 30,000 kilowatts of electricity for going to Pluto or even another star?
Oh! this is awesome! Again, combine this technology with BFR - and you can launch 50 or 100 of those is one go. A stupid question - could there be a magnetic version of this, that exploits magnetospheres of planets? Those sound much more energetic, or are they not?
I have to disclose, that I 'learned' physics online, I've read sci-fi books throughout my years in physics classes at school, so this might be totally impossible. But.. if you could launch a spacecraft, to just charge it's huge battery with free solar energy (ah, shit, batteries are heavy, aren't they?) - and then just to fire up a huge electromagnet, could you use our magnetosphere as a launch loop?
ok, last question, pinky promise: Why couldn't we use both chemical propulsion and this thing... It does not look too complicated or heavy. You do your burn to wherever you are headed; You deploy your electric sail to pick up more speed along the way... Hell If I understood this correctly, you could actually use this to sort of break... You would want to have a spin on your ship one way or another - you could get simulated gravity that way. Would you need a 'mast' though? Or just hundreds of tiny 100 km long wires coming directly from the walls of the spacecraft?
I think you'll use some kind of booster stage that gets them outside the Earth's magnetosphere, and then they'll deploy their tethers and catch the solar wind.
Yip, I understood the concept, watched the videos (ok, got distracted midway though the Finish scientist's talk, still have it in my tab:), but why couldn't it be combined with your ordinary spacecraft with engines? Just add enough km of electric sails to have some extra boost when you are mid flight, retract them back when you are 'there'. Or is the thrust so small that it's unreasonable for anything above several kg?
How is it that photon have momentum without having mass?Since p= m*v then photon momentum should be 0 * C = 0. What did I get wrong? PS Excuse my poor english. I hope my question is understandable.
momentum is not the product of mass and velocity,. Momentum is the product of energy and velocity. Inserting factors of c, the relativistically correct relation between momentum p and velocity v is c^2p=Ev This holds for non-relativistic massive particles (total energy dominated by rest-energy: E=mc2, and therefore p=mv) as well as for massless particles like photons (v=c and hence p=E/c). I could be wrong about everything I've said, but I'm fairly certain it's correct :)
Note that E=mc^2 is only part of the most famous equation. E^2=(mc^2)^2+p^2c^2 That's the full equation. If m = 0 then you are left with E^2 = p^2c^2 E = pc p = E/c Photons have energy, which gives them momentum.
There may be a slight issue with the description of how the electric sail works in the video. I don't think the solar wind has a net negative charge. If it were negatively charged, a positive charge on the solar sail would not produce thrust (or would do so toward the oncoming plasma). Rather, the positively charged sail repels the relatively more massive positive ions in the solar wind while attracting the electrons. Hence the need for the election gun to maintain the positive charge.
Boats uses an under water wing to stere sideways relative to the wind direction. This is how they can navigate at more than 90 deg from it and come back. Since there is no such force in space, how could such a magnetic sail give you thrust other than away from the sun. Also, in order to be repelled by the solar wind, such a sail would need to be positively charged. You mentioned that this could be achieved by throwing out electron, thus giving the hole ship a positive charge. How could they get negatively charged in order to be attracted by this same wind. Does a proton gun exist? And by the way, since the hole craft would be magnetically charged, turning it around would have no effect. Am i wrong?
Something doesn't seem right here a positively charged sales when you attract negative ions to slam into it or is it negatively charged antenna that repels negative ions from it
Could a circular Electric Sail also double up as an antenna and if so wold it be feasible for a swarm of such ships to relay data between themselves on it's way back to earth?
Does the fabric of space adjust the direction of light along the plane/disk of a Galaxy? I imagine light entering the Galaxy straight but shifting with the rotation of the Galaxy?
It would run out of acceleration once it got past Uranus, so it wouldn't be the best way to get to another star. You could knock a few thousand years off the travel time, but it would still be terrible.
Fraser Cain could you potentially use the little amount of wind coming from interstellar space to give it a tiny bit of acceleration or would it coming from all angles mess it up?
Matthew Thompson You'd have to "tack", as you do in a sailing ship, but I think it would be feasible - the problem is that the "galactic solar wind" would be very diffuse, and probably wouldn't provide enough acceleration to be worth it. Interstellar travel will probably depend on ionic propulsion, which means SLOW travel, with low accelerations, unless we can get fusion working as a source of propulsion.
I was thinking of a magnetic solar sails when I clicked on this video, but I guess this one (electric sail) is better than the magnetic sails because it can be steered (slanted sideways). I was particularly hyped about the idea where you create a miniature magnetosphere around a manned spaceship which doubled as a solar sails because it can trap & deflect charged particles, but apparently that idea is going nowhere unlike electric sails...
Fraser Cain and by some point you mean when spacex hypes everyone to the point of the masses wanting more space stuff forcing the government to comply which should take about a decade to be in effect
Why not use a combination of chemical rockets and electrical / solar sail? You could accelerate fast with the rocket and then use the sail for additional longterm acceleration
Can one use hydrogen balloon (eg weather balloon) to get to mid stratosphere, then deploy solar or electric sail? Would such a sail work in the atmosphere?
I have a great idea: Put a link to the playlist in the video description. That way viewers wouldn't have to hurry to click the in-video-link, and can watch the video to its end.
Hey, Fraser. I was wondering about when Phobos crashes into Mars. Will Phobos be going fast enough to completely meld with the planet, or will it be something like a half-spherical protrusion?
But would it, say, reflect off of Mars and fling itself out into space, albeit with a significantly reduced mass; or maybe it will fling itself back into space only to collide again? Perhaps it will just break into large particles of dust?
Yo [Fraser Cain]? [do] you check your facebook still? cos I had a cool idea about radioactive "stars" made out of fissionable uranium, at massive scales...[fringe blackhole level mass/density] ...and I wanted to know what their cores looked like... 😢
Sometimes? So many places to look. Keep in mind that I'm not an astrophysicist, just a journalist. You'll want to take your ideas to actual scientists.
Fraser Cain ...yeah... *sigh* I know, but I'm not cool enough to know any... ...so it's hard you know? (I'm serious, not trolling, just attempting to lighten the mood with a humorous tone)
I assume it can be used together. Speed would be greater when the spacecraft is closer to the Sun because of the solar sail getting more of a push when it is closer to the Sun but when it is further away, solar sail will be receiving less, if not no push, but the e-sails should still work.
Does that not mean that after the electric sail has passed the heliosphere it won't be able to get anymore thrust from the sun because the interstellar wind is now as strong as the solar wind? Would you encounter turbulence at the heliosphere if you had a ship designed to crash into all those charged particles?
This will work ok for the solar system but for interstellar travel you may still need something more powerful. Ten years is still way to slow because this would mean at least 15000 years to get to the nearest star. Dont get me wrong this could be a very helpful technology but the end game is still interstellar travel. I suppose if you could find an even better method using similar technology that might be a step in the right direction. There are problems though if you wanted to use this tech for interstellar travel. In interstellar space you will have less and less of that solar wind and thus you would have to hope that perpetual motion in space would keep it going at a constant speed. Your first problem is you are going to eventually run out of solar wind. What will move the ship after that? The interstellar medium contains some helium and a lot of hydrogen and space dust and small rocks and this could create drag on any large sail. The interstellar medium does, however, have radiation so I suppose you could make use of that. Drag though is a real problem and the more surface area a sail covers the greater the drag. You need speed to reach that next star. This requires having more energy than this solar wind can provide unless we could perhaps find better ways to harness it like maybe focusing it. At the rate mentioned it would still take thousands of years to reach even the closest star. I suppose perhaps a much larger sail might do the trick but you are still going to be depending on low drag and constant motion. All told this is a promising idea for inner solar system travel but I am wondering how it could translate to interstellar travel. This is why I have proposed a magnetic pulse engine that would generate a large electrified magnetic hoop field in front of the ship out of thin air and thus the ship would move through the hoop. The ship would keep generating new hoops pulling the ship through and thus accelerating the ship in a manner similar to what a particle accelerator does. It would not run out of solar wind and there would be no large sail to create drag and thus slow down the ship. In fact these hoops would be mostly energy and not connected to the ship. Still though the disadvantage of my idea would be some source of energy would be needed to create the hoops. Humor me a little here. I wonder if there might be some why to combine your idea with what I am saying and thus reduce drag and increase speed. Seems to me the alternative is just making much bigger sails... but sails are made of something and that can create drag. Hmmmm. Just wanted to put my own thoughts on the table there to add to the conversation. Let me know what you think of this concept vs the sail.
Toats fascinating! How about this, can we set up a solar system subway? We build huge spaceships powered by electric sails that go in loops throughout the solar system. Yes it will take a bit to get them up to speed but once they are there we can hop onto them when they're near earth and then go anywhere in the solar system!
Disasterina They're called Cyclers. One big ship that cycles between two or more places. The advantage is that you would only need a small spacecraft to match velocities with the very big one; used for the long flight.
Could dark energy be an artifact of natural charge imbalances? Would we know if our solar system as a whole had extra protons or electrons turning IT into a giant sail in some galactic wind?
It all depends on the orbit you take. I highly recommend you play Kerbal Space Program to understand the different kinds of orbits there are out there. I learned more about spaceflight from that game than I did from nearly 20 years of space journalism. :-)
Does the radiation coming from other stars past the heliosphere interfere with the electric sail? Im guessing the method is not meant for interstellar travel.
Here's what I suspect: the first time this is used for a "production run", there will be bugs in the system. This happens all the time. But this thing is too small to communicate with Earth, so we won't know what happened, or when, or where the vehicle is; it will simply disappear. We won't know enough about what went wrong to make sure we fix it before the NEXT try. Sorry, but I'm a pessimist about these kind of things -- particularly new, complex machinery being tested in hostile environments. It's nice to be able to engineer a fix from Earth, as has proved crucial for many missions, notably Galileo.
I think the description of how this works is somewhat problematic. The solar wind isn't negatively charged, at least not until it gets to the spacecraft. Rather, the protons are deflected and the electrons are attracted, both of which creates a force accelerating the sail.
Yes they both accelerate the sail. The protons bounce off and give their momentum that way, but the electrons accelerate towards the sail stealing some of the momentum. But then the electrons get to the positive tether and since the wind goes at a much higher velocity than the sail the electron has plenty of forwards momentum and the net force from both those interactions means even the electron is giving much forwards momentum to the sail, but the proton has more mass so it is more important. One final piece of the puzzle- the electron gun spits the electrons back towards the sun so over all it's like the electron did the same thing as the proton and all the momentum from both of them is reversed and by conservation must have gone to the sail.
Alright, so if solar wind and light pressure can overcome the gravity of the star producing it, could you therefore build a solar sail big enough, assuming you had materials strong enough (which, of course, we don't, but theoretically), to move an entire planet?
You could, but an even cooler idea is that you could move an entire star with this technique. Build a huge solar sail, and the gravity of the star will pull it down, but the light will push it away. The whole star will move.
The M2P2 concept of Professor Wiggley. A magnetic field 30 km wide created by small device. The needing a kilo of ionized helium per day. The solar wind would strike the 30k magnetic bubble instead of a physical sail What happened to that idea?
Anyone else use Fraser's soft voice to lull them into a dreamless slumber every night? Fraser, can you start a second channel where you read us bedtime stories?
Question: If we have a stick 10 billions light years long straght. Ignoring all the forces that can effect the stick or the force required to push it, but If I push the stick 5mm, would the stick move 5mm on the other side 10 billions light years away instantly? If it doesn't move instantly, would the person other side of the stick 10 billion light years away when will he know that I pushed the stick from other side?
When you move the stick you are actually making a low frequency sound wave. Though solids have slightly higher speed of sound than air, it is ridiculously low compared to the speed of light, which itself is utterly inadequate compared to the size of the universe.
If you put a timer to an off and on switch function you would experience any travel time like a zap. If you clock down the CPU you could make subjective time flow arbitrarily fast.
![Everything NASA Discovered from James Webb's First Year in Space [4K]](http://i.ytimg.com/vi/nbDQEo0uA0Q/mqdefault.jpg)
I passed along a bunch of your common questions to Dr. Pekka Janunen, and here's what he had to say:
1. Can we combine them with a solar sail to get the best of both worlds?
*Maybe, but we don't have such concept under active planning. At one point we considered using small solar sails to control the spinrate of E-sail tethers.*
2. Could the tethers work as antennae, to help communicate with Earth?
*Not really. The tether wires are so thin that their ohmic resistance per length would reduce their efficiency as antennas. Also, nowadays one prefers high radio frequencies. Such frequencies do not call for long wires antennas, but instead smaller directive antennas like parabolic dishes*
I hate to disagree with Dr. Janhunen, but electric sail wires would make excellent antennas. There is a type of antenna, called a Beverage antenna (see: www.google.com/search?source=hp&ei=prM8XYH1NuqF0wKOr5qgBw&q=beverage+antenna&oq=Beverage+antenna&gs_l=psy-ab.1.0.0l10.1830.9150..13246...0.0..0.314.2241.0j16j0j1......0....1..gws-wiz.....0..35i39j0i131j0i10.cBEvc9cDTrY ), which is a long wire-a *really long* wire-that is many quarter wavelengths long. When an antenna wire becomes many quarter wavelengths long (1/4 wavelength is the minimum self-resonant length of an antenna, either above a ground plate or plane, or as one half of a dipole antenna [whose total length is 1/2 wavelength at its self-resonant frequency]), the antenna pattern is such that the signal fires almost entirely off the far end of the wire. (For receiving, such an antenna is also very sensitive to signals arriving at its far end, moving parallel to the wire’s orientation, because the transmit and receive antenna patterns are identical.) Also:
Like a spin-stabilized satellite with an electrically-despun antenna (the USAF pioneered such multiple-antenna spinning satellites, as I covered in *this* www.centauri-dreams.org/2018/05/18/immortal-interstellar-probes/ article about interstellar probes), an electric sail-equipped interstellar probe-like Project Dragonfly’s design-could use the electric sail wires as electrically-despun, highly-directional antennas. Either each electric sail wire could be “worked against” the spacecraft’s body (using it as the RF-Radio Frequency-ground), or each opposing pair of electric sail wires could be worked against each other, forming what is called a doublet antenna. (A doublet antenna is a dipole antenna-with a dipole antenna pattern--*only* at the antenna’s self-resonant frequency, but a doublet antenna works on other frequencies-both higher and lower than its self-resonant frequency-with the help of an antenna tuner.) As well:
At typical spacecraft radio frequencies (S-band, X-band, etc.), the wires of an electric sail are hundreds, thousands, or even tens or hundreds of thousands of wavelengths long, so they would be very high-gain antennas, firing transmitted signals in a very narrow lobe off the far end of the wire (or wires, if opposing pairs of wires were employed as doublet antennas), and they would be equally directionally sensitive for receiving. Using a variable antenna tuner would enable the wires to resonate over a very wide band of frequencies, making the electric sail wires ideal for an interstellar probe’s radio science/plasma wave instrument, and-on a Bracewell interstellar messenger probe-for listening for any intelligently-generated signals from a potentially inhabited planet in a probe’s target star system.
What if there was a way to use very powerful magnets to manipulate electromagnetic forces and use them for propulsion?
Is that a thing? Can that be a thing? That would be very cool. I don't know how good of an idea it is to have a powerful magnet in space though.
This technique has seen really great investments compared to the recent lightsail. In 2013 Estonian students build a 1 kg cubesat which should test a 10 meter electric sail but it failed because the winding mechanism did not work. The cubesat costed around 100 000€. The official reason was to prevent space junk.
Yup, I think the electric sail idea has a lot of promise.
Really appreciate the playlists you put together, Mr Cain. Excellent idea. Thank you, as ever
I'm glad you're enjoying them. :-)
Im so watching your entire playlist this week. Other weeks ive started and forgotten myself. But i plan to watch these multiple times
Excellent episode, Lightsail was cool but the electric sail is even cooler. Informative video keep up the good work.
Thanks for watching. I'm pretty excited to see where this technology goes.
I imagine re-orienting the spin, and retaining the spin would probably be quite difficult as receiving the winds with any angle other than perpendicular is likely to cause an un-even distribution of force.
When travelling near the speed if light, colliding with small particles is dangerous as you said before. Could we use the same technology from a warp drive to bend the space with the particles in so they don't collide with the ship?
4:18 I love how you put the Argentinian sun
That asteroid swarm mission sounds AMAZING. Fund it yesterday! All your space rocks are belong to us!!!
Growing up in the 70s and 80s I had a dream over time in my childhood that mankind would have have races in space in solar sail spaceships that people would build and run. I never knew where I came up with the idea of them .. but I even drew them up on paper too and just daydreamed about it. Then they had one in an episode of Star Trek Deep Space Nine much later along about the Siskos travelling in one across the stars.
. Such a great idea if mankind had the technology to build it and still be able to protect the people in them.
It won't likely happen in my lifetime ... but maybe in the next century? It could be a really cool way to get people to travel into space ... if it was feasible and people were protected enough.
This episode kind of brought back memories of that. Thanks for another great episode.. I love your videos by the way!
Love your videos Fraser, I listen to your podcasts aswell. Pamela knows everything!
Thanks Fraser, this is one of the coolest ideas in years that could actually work!
nice never heard about an electric sail. sounds awesome and simple at the same time
Yeah, I really enjoy the technology.
this is so marvelous - such a clever way to sail to the stars
Some solar sail-including interstellar probe and starship studies from the 1970s and more recently have called for using a solar sail (some were all-metal ones) that would be electrically charged in order to brake against the interstellar wind and the stellar wind of the destination star.
Might it be possible to create such a sail without using solid material? Could we create the same thing using a pure energy field that could somehow capture all that solar wind?
Well I guess it would have to transmit force back to the spacecraft via either strong, weak, gravity, or electromagnetic. Of these only EM has the distance, repulsive direction, and strength. The EM force is transmitted via fields -- which feels rather like a "pure energy" idea that ya mentioned. An electric or magnetic sail, whatever its matter source, *would* continue to catch & transmit particle force a bit past its solid edges -- but would drop off quickly as an inverse square.
The Finns, smart people! Cool people ;-) What a great concept, and it does make a lot of sense!
Yup, I'm a big fan. :-)
Fascinating! Robert Forward suggested other ways to use tethers to harness power for exploration (e.g., in Jupiter's magnetosphere to move things between Io's or Europa's surface and low orbit).
Yeah, that's a high magnetic environment.
Very interesting. Could we send an electric sail to outside the solar system, or even to another star if we get the trajectory right? Great video, can't wait to see this technology in use.
It stops accelerating beyond the orbit of Uranus and Neptune, so it's not great for going beyond the Solar System.
Electric sail is what they use in the serie by Nathan Lowell where I now am reading the second book (free books that you can get on Itunes and other places. Just include Podiobooks in the search). Freight ships "sail" in and out of the star systems :-).
Nice video Fraser! One issue: I think the electric sail mostly taps into the momentum carried by positively charged solar wind particles (not electrons as you mention around 2:50). Makes sense, since the solar wind has both positive and negatively charged particles, but protons are so much more massive than electrons.
Interesting, I'll take a look at that.
There is a Box Kite shaped model, that has wire loop on the top of the frame. When a current is passed through it, it hovers above the ground.
This sounds like that
Electric sail with solar sail between the filaments .
I've seen a bunch of people recommend this. I'll take it to the research team.
I get first ride, though.
@@frasercain Some interstellar probe designs combine both sails, for braking at arrival at the target stars--either a combination of a solar (stellar, in this case :-) ) photon sail and an E-sail, *OR* a photon sail that is positively charged, so that it "bounces back" both the star's light ^and^ the positively-charged stellar wind (mostly protons, and some helium nuclei). It is even a "double feature" for arrival braking in some starship designs (as long as the photon sail is large and light enough [ditto for an E-sail, if also used in a particular starship design], effective braking can be done).
Hello Frazier I'm a big fan of your show and astronomy cast. I know this isn't the forum for show ideas for astronomy cast, but... a while ago you did a series on amazing women in astronomy. I would love to hear an episode about Pamela, and her story. I know she has said it all, but not all at one place in one time. As far as inspirational women in astronomy, no one stands out more to me than Pamela gay. She has inspired me to learn in a greater way than any one person in my life. I would be willing to bet that other listeners would agree. Thanks for your time and all your hard work. You are my entire education above the atmosphere
Hah, great idea, I'll pass that along to her.
Hey so, pulsars, neutron stars, and magnetars are all supposed to have insanley powerful magnetic fields, right?
Could we use a magnetic sail there as a sort of electromagnetic parachute to decelerate ships going a decent fraction of the speed of light? If we accelerate them to .20c with the starshot proposal, and decelerate them using pulsars as magnetic brakes, we could have very fast interstellar probes, with almost no propellant needed
It's not about the magnetic field, it's about having a powerful solar wind. So they wouldn't really be that helpful.
What is the limiting factor on thrust? Voltage? Wind density?
Yeah, it's the amount of interaction with the solar wind.
They can make the sail positively charged or negatively charged. Do you think, they make the sail positive charged because it will repel positive charged protons ( Protons are heavier than electrons) from sun. Protons repelling will cause more acceleration to the space craft. But as you go further and further, these proton concentration reduces and the propulsion.
I'm not sure, maybe there's a way they could do both?
That's right. Protons (or other positive ions) are repelled while electrons are attracted to the sail. That's why the electron gun is needed to maintain a positive charge. As for the proton concentration, check out this paper: arxiv.org/pdf/1707.02801 It's about magnetic rather than electric sails, but it discusses the effect of low proton density on such craft.
Wow this idea is very awesome!!! Please follow up on this!!!!
Will do. :-)
Could they combine this with the regular solar sail idea?
Does interstellar space have an electric charge? If so this would also be a great way to get to other stars in a short amount of time.
There are charged particles, but they're going in many different directions, so you wouldn't be able to get a consistent thrust in any one direction.
9:18 It's not fuel-free, Fraser, it's propellant-free. You still need to come up with energy. Fuel is what you burn to obtain energy. Propellant is what you throw out the back to gain momentum. Only sometimes they're the same.
www.projectrho.com/public_html/rocket/misconceptions.php#id--Fuel_Is_Not_Propellant
www.projectrho.com/public_html/rocket/engines.php#id--Rocket_Engine_Components
Great point, thanks!
What about the EMdrive? I didn't see you list that one. Is there a reason you left it off of the list? it would be really cool to hear you talk about that concept. =)
I still haven't been convinced that it's actually a thing yet. If it does work, it violates the laws of physics, so we're going to need some solid evidence.
Could you use an Asteroid like A 2017/U1 to get to high speeds?
I.e. you could get a dampened hit, or shoot a grappling hook at the Asteroid to get pulled
Fraser, I seem to recall you discussing the importance of Rest Mass in equations like Einstein’s e=mc2… is there such a thing as Rest Energy (or some comparable state)?
Can this be used to give a little extra thrust to an ion drive? It wouldn’t be much, but ion drives don’t produce much thrust anyway.
If the solar sail is one charge and the electro sail opposite, is there a way to make a hybrid and use the opposite charges in some way?
What would be good Units, that would be useful to use when colonizing the Solar System/Galaxy?
Like years, light years, AU, days, hours, etc.
These are different wherever you are(technically speaking, they all have exact definitions)
Brilliant. Thank you.
Thanks for watching!
Electric sails! First time I’ve heard of this. Very cool.
Adding a large electric sail to any spacecraft should not be a problem.
Even a manned mission could use this technology, how much of a shielding affect would this provide?
Yeah, I really like the idea.
New to the channel, how did you get your knowledge on all this ‘space stuff’ , did you study a certain thing at uni or are you like ex-nasa?
Is it possible to calculate the specific impulse of this? Or it doesn't matter because it has almost unlimited dv.
Yeah, it doesn't give off a thrust, it all depends on the speed and density of the solar wind going past it.
Thanks. At first, I wasn't sure about the electron gun shooting electrons. But after rewatching it, it was clear to me.
I should stop watching videos late at night.
hey fraiser would it be posible to create energy with all that trash in the oceans with fusion?
Didn't they do that in Back to the Future? The only thing that we can maybe do fusion with is a flavor of hydrogen. So we're not at the point that we can fuse trash yet.
Fraser Cain yeah they did do that in back to the future.
But i do think that if we had a big enoug reactor and maby jumpstart the reactor with hydrogen et would be hot enough for trash molicules to fuse
A thought: Given that these craft would already be equipped with long, conductive lines, couldn't those be used as transmitters and receivers, essentially big radio antennas? If you're already carrying what is effectively a 20 km radius circle, wouldn't it be relatively simple to use that for sending and receiving signals?
On top of which, while cruising from one asteroid to the next, couldn't they use the sail's radio interactions to function as a huge radio observatory?
I'm not sure how well they'd work as antennae, but I know the asteroid missions ones won't be able to communicate back home from the asteroid belt.
I mean, that just seems odd. All you need for a big transmitter is a big conductive thing. Seems like they should be able to use the sails as transmitters and receivers.
What do you think about electroweak stars and the q-stars(aka Gray Holes)?
Do you have any news about the picture they were going to take of a black hole this year? I didn't find anything new on google, maybe you could talk about this in your next video.
If there is one star right behind another star, from our perspective, would we still be able to see it due to gravitational lensing or sth. else?
Would it cause some anomalies like weird luminosity, mass, metallicity etc?
It depends on the distances. If you get things to line up perfectly, you'll get that gravitational lensing.
Great idea!!!
Yeah, pretty exciting.
You should do a video on antimatter propulsion
I would say that the electric sail is the only way to explore our solar system. It may be the only way to traverse the distance between stars. At some distance from the sun, the electric sail would stop accelerating the spacecraft. That would be the maximum speed the electric sail could generate. It would have to do a sort of sling-shot effect to get the velocity it needs to go to another star. It would have to accelerate away from our sun, then turn the sail around and head into sol - accelerating the whole way then orbit around the sun and accelerate away from the sun. Then and only then would it have any kind of velocity needed to go to another star. Could it decelerate when it got there?
Why would the effective area the further it goes out? Seems like it would remain the same unless the wires were longer.
Have you ever looked at the Princeton Satellite System's Fusion Engine that produces 20 to 40 newtons of thrust and 30,000 kilowatts of electricity for going to Pluto or even another star?
Oh! this is awesome! Again, combine this technology with BFR - and you can launch 50 or 100 of those is one go. A stupid question - could there be a magnetic version of this, that exploits magnetospheres of planets? Those sound much more energetic, or are they not?
I have to disclose, that I 'learned' physics online, I've read sci-fi books throughout my years in physics classes at school, so this might be totally impossible. But.. if you could launch a spacecraft, to just charge it's huge battery with free solar energy (ah, shit, batteries are heavy, aren't they?) - and then just to fire up a huge electromagnet, could you use our magnetosphere as a launch loop?
ok, last question, pinky promise: Why couldn't we use both chemical propulsion and this thing... It does not look too complicated or heavy. You do your burn to wherever you are headed; You deploy your electric sail to pick up more speed along the way... Hell If I understood this correctly, you could actually use this to sort of break... You would want to have a spin on your ship one way or another - you could get simulated gravity that way. Would you need a 'mast' though? Or just hundreds of tiny 100 km long wires coming directly from the walls of the spacecraft?
For those asteroid missions, you could launch them all from a single rocket. It wouldn't have to be that large.
I think you'll use some kind of booster stage that gets them outside the Earth's magnetosphere, and then they'll deploy their tethers and catch the solar wind.
Yip, I understood the concept, watched the videos (ok, got distracted midway though the Finish scientist's talk, still have it in my tab:), but why couldn't it be combined with your ordinary spacecraft with engines? Just add enough km of electric sails to have some extra boost when you are mid flight, retract them back when you are 'there'. Or is the thrust so small that it's unreasonable for anything above several kg?
How is it that photon have momentum without having mass?Since p= m*v then photon momentum should be 0 * C = 0.
What did I get wrong?
PS Excuse my poor english. I hope my question is understandable.
P=hk/2Pi
h planck's constant and k is related to the direction of the photon
momentum is not the product of mass and velocity,. Momentum is the product of energy and velocity.
Inserting factors of c, the relativistically correct relation between momentum p and velocity v is
c^2p=Ev
This holds for non-relativistic massive particles (total energy dominated by rest-energy: E=mc2, and therefore p=mv) as well as for massless particles like photons (v=c and hence p=E/c).
I could be wrong about everything I've said, but I'm fairly certain it's correct :)
There you go, some answers below. Thanks Trashy and Jeppe!
Note that E=mc^2 is only part of the most famous equation.
E^2=(mc^2)^2+p^2c^2
That's the full equation.
If m = 0 then you are left with
E^2 = p^2c^2
E = pc
p = E/c
Photons have energy, which gives them momentum.
This video might help you as well ua-cam.com/video/ueuwWiR-Dw4/v-deo.html
I got tingeling sensations in my bodyports by watching this video!!!! Great...
There may be a slight issue with the description of how the electric sail works in the video. I don't think the solar wind has a net negative charge. If it were negatively charged, a positive charge on the solar sail would not produce thrust (or would do so toward the oncoming plasma). Rather, the positively charged sail repels the relatively more massive positive ions in the solar wind while attracting the electrons. Hence the need for the election gun to maintain the positive charge.
Frick yeah! I dig this new idea
Me too. :-)
Could an artificial beam of electrons be created like a laser? If so would this be another option for breakthrough star shot?
They can be, I'm just sure if that would be an effective way to boost it faster, though.
David Bland
Should be possible, it would require a BIG particle accelerator in space, though.
Boats uses an under water wing to stere sideways relative to the wind direction. This is how they can navigate at more than 90 deg from it and come back. Since there is no such force in space, how could such a magnetic sail give you thrust other than away from the sun. Also, in order to be repelled by the solar wind, such a sail would need to be positively charged. You mentioned that this could be achieved by throwing out electron, thus giving the hole ship a positive charge. How could they get negatively charged in order to be attracted by this same wind. Does a proton gun exist? And by the way, since the hole craft would be magnetically charged, turning it around would have no effect. Am i wrong?
Something doesn't seem right here a positively charged sales when you attract negative ions to slam into it or is it negatively charged antenna that repels negative ions from it
You want to make a bigger target for the negative ions.
Could a ship use a light sail and an electric sail? Maybe you could reel in the wire when your in the inner solar system?
Could a circular Electric Sail also double up as an antenna and if so wold it be feasible for a swarm of such ships to relay data between themselves on it's way back to earth?
I haven't heard anyone propose this. In fact, as I said in the videos, these microsatellites won't have any way to communicate, so I'm guessing no.
Fraser Cain why are the wires so thin?
Fantom Slobode because costs and them not being hit by objects
Fantom Slobode at least I'd assume those are reasons
The obvious reason, to me, is the weight and the reduction of cost in getting the instrument into space.
What can be done to accelerate the industrialization and habitation of Low Earth Orbit and our LaGrange points?
If someone could make a profit, like through asteroid mining or space power, that would do it.
Does the fabric of space adjust the direction of light along the plane/disk of a Galaxy? I imagine light entering the Galaxy straight but shifting with the rotation of the Galaxy?
How long would it take for an Eletric Sail to reach Alpha centauri? Assuming it can travel in interstellar space
It would run out of acceleration once it got past Uranus, so it wouldn't be the best way to get to another star. You could knock a few thousand years off the travel time, but it would still be terrible.
Fraser Cain could you potentially use the little amount of wind coming from interstellar space to give it a tiny bit of acceleration or would it coming from all angles mess it up?
Matthew Thompson
You'd have to "tack", as you do in a sailing ship, but I think it would be feasible - the problem is that the "galactic solar wind" would be very diffuse, and probably wouldn't provide enough acceleration to be worth it.
Interstellar travel will probably depend on ionic propulsion, which means SLOW travel, with low accelerations, unless we can get fusion working as a source of propulsion.
I was thinking of a magnetic solar sails when I clicked on this video, but I guess this one (electric sail) is better than the magnetic sails because it can be steered (slanted sideways). I was particularly hyped about the idea where you create a miniature magnetosphere around a manned spaceship which doubled as a solar sails because it can trap & deflect charged particles, but apparently that idea is going nowhere unlike electric sails...
Yeah, I'm actually working on an episode about that idea next. Well, the artificial magnetosphere part.
I wonder if solar sails and electric sail can be combined? Thoughts?
I'm not sure if they compete somehow, it's a cool idea, though.
Do you think Planck stars are plausible?
Why not create a hybrid system which uses both solar and electric sails?
I'm sure that'll be in the works at some point.
Fraser Cain and by some point you mean when spacex hypes everyone to the point of the masses wanting more space stuff forcing the government to comply which should take about a decade to be in effect
Whould ion engines make sences when going to mars. Or is that to close?
Sure, ion engines would help if you wanted to take a longer time with less fuel. The SMART-1 spacecraft flew to the Moon with ion engines.
About time they started making fleets like that. I have been wondering for a while why they didn't always use this method.
It's a pretty great idea.
What about a Spore Drive that taps into the mycelial network?
You just need to find a tardigrade to operate it for you.
Fraser Cain Are you proposing animal cruelty? ;)
Why not use a combination of chemical rockets and electrical / solar sail?
You could accelerate fast with the rocket and then use the sail for additional longterm acceleration
Can one use hydrogen balloon (eg weather balloon) to get to mid stratosphere, then deploy solar or electric sail? Would such a sail work in the atmosphere?
What a stellar video you magnificent bald man, thnx for your hard work!
Thanks, I'm glad you enjoyed it. :-)
I have a great idea: Put a link to the playlist in the video description. That way viewers wouldn't have to hurry to click the in-video-link, and can watch the video to its end.
Great suggestion, I'll start doing that.
Thank you!
Could you use radiation belts to slow down?
Hmm, if they've got the right charge and velocity, I guess so. That's a really interesting question.
But you wouldn't want to though right? If your craft is manned.
Hey, Fraser. I was wondering about when Phobos crashes into Mars. Will Phobos be going fast enough to completely meld with the planet, or will it be something like a half-spherical protrusion?
It'll create a big crater. Like a BIG crater.
But would it, say, reflect off of Mars and fling itself out into space, albeit with a significantly reduced mass; or maybe it will fling itself back into space only to collide again? Perhaps it will just break into large particles of dust?
Would this sail keep accelerating past the heliosphere?
Yo [Fraser Cain]?
[do] you check your facebook still?
cos I had a cool idea about radioactive "stars" made out of fissionable uranium, at massive scales...[fringe blackhole level mass/density] ...and I wanted to know what their cores looked like... 😢
Sometimes? So many places to look. Keep in mind that I'm not an astrophysicist, just a journalist. You'll want to take your ideas to actual scientists.
Fraser Cain
...yeah... *sigh* I know, but I'm not cool enough to know any... ...so it's hard you know?
(I'm serious, not trolling, just attempting to lighten the mood with a humorous tone)
Could a solar sail and an electric sail be used in conjunction with each other
I assume it can be used together. Speed would be greater when the spacecraft is closer to the Sun because of the solar sail getting more of a push when it is closer to the Sun but when it is further away, solar sail will be receiving less, if not no push, but the e-sails should still work.
Does that not mean that after the electric sail has passed the heliosphere it won't be able to get anymore thrust from the sun because the interstellar wind is now as strong as the solar wind?
Would you encounter turbulence at the heliosphere if you had a ship designed to crash into all those charged particles?
My eastern neighbors have some exciting ideas :-) Eris, Sedna and Planet 9, here we come!
So will the Webb telescope effectively act like a solar sail?
Not intentionally, but it will be getting hit by both the light pressure and solar wind from the Sun.
This will work ok for the solar system but for interstellar travel you may still need something more powerful. Ten years is still way to slow because this would mean at least 15000 years to get to the nearest star. Dont get me wrong this could be a very helpful technology but the end game is still interstellar travel. I suppose if you could find an even better method using similar technology that might be a step in the right direction. There are problems though if you wanted to use this tech for interstellar travel.
In interstellar space you will have less and less of that solar wind and thus you would have to hope that perpetual motion in space would keep it going at a constant speed. Your first problem is you are going to eventually run out of solar wind. What will move the ship after that?
The interstellar medium contains some helium and a lot of hydrogen and space dust and small rocks and this could create drag on any large sail. The interstellar medium does, however, have radiation so I suppose you could make use of that. Drag though is a real problem and the more surface area a sail covers the greater the drag.
You need speed to reach that next star. This requires having more energy than this solar wind can provide unless we could perhaps find better ways to harness it like maybe focusing it. At the rate mentioned it would still take thousands of years to reach even the closest star. I suppose perhaps a much larger sail might do the trick but you are still going to be depending on low drag and constant motion.
All told this is a promising idea for inner solar system travel but I am wondering how it could translate to interstellar travel. This is why I have proposed a magnetic pulse engine that would generate a large electrified magnetic hoop field in front of the ship out of thin air and thus the ship would move through the hoop. The ship would keep generating new hoops pulling the ship through and thus accelerating the ship in a manner similar to what a particle accelerator does. It would not run out of solar wind and there would be no large sail to create drag and thus slow down the ship. In fact these hoops would be mostly energy and not connected to the ship. Still though the disadvantage of my idea would be some source of energy would be needed to create the hoops.
Humor me a little here. I wonder if there might be some why to combine your idea with what I am saying and thus reduce drag and increase speed. Seems to me the alternative is just making much bigger sails... but sails are made of something and that can create drag. Hmmmm. Just wanted to put my own thoughts on the table there to add to the conversation. Let me know what you think of this concept vs the sail.
So, all the superefficient propulsion systems are also super-weak? Aren't there any powerful, exotic superefficient propulsion methods?
Ayush Sharma Nuclear rockets. High thrust and efficiency.
Toats fascinating! How about this, can we set up a solar system subway? We build huge spaceships powered by electric sails that go in loops throughout the solar system. Yes it will take a bit to get them up to speed but once they are there we can hop onto them when they're near earth and then go anywhere in the solar system!
Disasterina They're called Cyclers. One big ship that cycles between two or more places. The advantage is that you would only need a small spacecraft to match velocities with the very big one; used for the long flight.
Thanks for the info I'll search for some videos on them!
Could dark energy be an artifact of natural charge imbalances? Would we know if our solar system as a whole had extra protons or electrons turning IT into a giant sail in some galactic wind?
How do you slow down?
It all depends on the orbit you take. I highly recommend you play Kerbal Space Program to understand the different kinds of orbits there are out there. I learned more about spaceflight from that game than I did from nearly 20 years of space journalism. :-)
Does the radiation coming from other stars past the heliosphere interfere with the electric sail? Im guessing the method is not meant for interstellar travel.
That radiation is very weak compared to the Sun's radiation.
Question: why do people think White holes are a thing? Don’t black holes just crush things and then radiate them off?
Hey fraiser, what are you going to be for Halloween? Going as Fraiser has surely gotten old. How about Ick-Kerbal-b Crane?
20 kilometers and 25 microns ? From what material can you build such a electrically conductive wire and not have it break ?
What if we like combined an electric sail and a solar sail, best of both worlds?
I'm sure this kind of hybrid idea is in the works.
Did he say 20km tether? The cost of that alone would be a significant part of the whole project.
Here's what I suspect: the first time this is used for a "production run", there will be bugs in the system. This happens all the time. But this thing is too small to communicate with Earth, so we won't know what happened, or when, or where the vehicle is; it will simply disappear. We won't know enough about what went wrong to make sure we fix it before the NEXT try.
Sorry, but I'm a pessimist about these kind of things -- particularly new, complex machinery being tested in hostile environments. It's nice to be able to engineer a fix from Earth, as has proved crucial for many missions, notably Galileo.
I think the description of how this works is somewhat problematic. The solar wind isn't negatively charged, at least not until it gets to the spacecraft. Rather, the protons are deflected and the electrons are attracted, both of which creates a force accelerating the sail.
Yes they both accelerate the sail. The protons bounce off and give their momentum that way, but the electrons accelerate towards the sail stealing some of the momentum. But then the electrons get to the positive tether and since the wind goes at a much higher velocity than the sail the electron has plenty of forwards momentum and the net force from both those interactions means even the electron is giving much forwards momentum to the sail, but the proton has more mass so it is more important. One final piece of the puzzle- the electron gun spits the electrons back towards the sun so over all it's like the electron did the same thing as the proton and all the momentum from both of them is reversed and by conservation must have gone to the sail.
hmm the solar panels would put a bit of energy into the electron so they are less negligible from their lower mass.. but still the protons ...
Alright, so if solar wind and light pressure can overcome the gravity of the star producing it, could you therefore build a solar sail big enough, assuming you had materials strong enough (which, of course, we don't, but theoretically), to move an entire planet?
You could, but an even cooler idea is that you could move an entire star with this technique. Build a huge solar sail, and the gravity of the star will pull it down, but the light will push it away. The whole star will move.
Ah yeah, I think I recall Isaac Arthur talking about that. So cool, thanks for reminding me! :D
The M2P2 concept of Professor Wiggley. A magnetic field 30 km wide created by small device. The needing a kilo of ionized helium per day. The solar wind would strike the 30k magnetic bubble instead of a physical sail What happened to that idea?
Anyone else use Fraser's soft voice to lull them into a dreamless slumber every night? Fraser, can you start a second channel where you read us bedtime stories?
Usually people use Pamela's voice, not mine. :-)
An electrifying video.
Indeed.
Has such a positive vibe, too.
Question:
If we have a stick 10 billions light years long straght. Ignoring all the forces that can effect the stick or the force required to push it, but If I push the stick 5mm, would the stick move 5mm on the other side 10 billions light years away instantly? If it doesn't move instantly, would the person other side of the stick 10 billion light years away when will he know that I pushed the stick from other side?
No, the movement of the stick would still be limited by the speed of light, as would the knowledge about the stick being moved.
When you move the stick you are actually making a low frequency sound wave. Though solids have slightly higher speed of sound than air, it is ridiculously low compared to the speed of light, which itself is utterly inadequate compared to the size of the universe.
Upload my mind to a computer, put it inside an electric sail powered satellite, and let me sail the cosmos!
Sounds good. I'll let you know when all that tech is ready to go.
If you put a timer to an off and on switch function you would experience any travel time like a zap. If you clock down the CPU you could make subjective time flow arbitrarily fast.