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Light Sail Propulsion Could Reach Sirius Sooner Than Alpha Centauri (arxiv.org)
RockDoctor writes: A recent proposition to launch probes to other star systems driven by lasers which remain in the Solar system has garnered considerable attention. But recently published work suggests that there are unexpected complexities to the system. One would think that the closest star systems would be the easiest to reach. But unless you are content with a fly-by examination of the star system, with much reduced science returns, you will need to decelerate the probe at the far end, without any infrastructure to assist with the braking. By combining both light-pressure braking and gravitational slingshots, a team of German, French and Chilean astronomers discover that the brightness of the destination star can significantly increase deceleration, and thus travel time (because higher flight velocities can be used). Slingshotting around a companion star to lengthen deceleration times can help shed flight velocity to allow capture into a stable orbit. The 4.37 light year distant binary stars Alpha Centauri A and B could be reached in 75 years from Earth. Covering the 0.24 light year distance to Proxima Centauri depends on arriving at the correct relative orientations of Alpha Centauri A and B in their mutual 80 year orbit for the sling shot to work. Without a companion star, Proxima Centauri can only absorb a final leg velocity of about 1280km/s, so that leg of the trip would take an additional 46 years. Using the same performance characteristics for the light sail, the corresponding duration for an approach to the Sirius system, almost twice as far away (8.58 lightyears), is a mere 68.9 years, making it (and it's white dwarf companion) possibly a more attractive target. Of course, none of this addresses the question of how to get any data from there to here. Or, indeed, how to manage a project that will last longer than a working lifetime. There are also issues of aiming -- the motion of the Alpha Centauri system isn't well-enough known at the moment to achieve the precise maneuvering needed without course corrections (and so, data transmission from there to here) en route.
This is a Thought Experiment, not a real plan to go anywhere... we aren't going to travel between the stars until we figure out something a whole lot better than chemical rockets and probably FTL drive...
Everything else is just fantasy...
Thats how it begins. a "Thought Experiment" that is. 70 years is a great amount of knew tech... we will likely have something in 40 years that will sail right past our sail ships.,,, hmmm
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So you have to replace the apostrophe with a dwarf apostrophe?
Ezekiel 23:20
We are lucky enough to live at the right time where we can say yes Im 45 now and in 40 years I may not look a day older than I do now.... stem cell research :)
[($)]
Presumably, if you can decelerate faster you can also accelerate faster. Given that you have to take all the fuel for deceleration with you but not (or at least less) the one for acceleration, I can see how having the destination help decelerate is useful ...
No, this is a way to significant increase BRAKING power. The speed up is tied to Sol no matter where we point a light sail, by changing the destination we can slow down a LOT faster.
Getting a person there with something better than chemical rockets is just fantasy since if you got the vehicle to move fast enough even the cosmic background radiation will be shifted enough to irradiate people to death.
Of course, a different fantasy of cryosleep plus slow travel or FTL removes that in SF at least, but not so much in reality.
This thing on the other hand looks like a way to get a machine to another star using something that needs nothing more than some years of development (https://en.wikipedia.org/wiki/Solar_sail#Projects_operating_or_completed) instead of wishing so I do not get why you are calling it fantasy.
We've already "worked out" quantum entanglement enough to know that we can't "siwtch" an entangled particle's spin.
It's impossible to transmit information using entanglement.
systemd is Roko's Basilisk.
Given that you have to take all the fuel for deceleration with you
That's not how a solar sail works.
systemd is Roko's Basilisk.
Lolwut?
My first program:
Hell Segmentation fault
https://en.wikipedia.org/wiki/...
Not faster than light, which is what this was about.
Once we have the massive laser array for sending these things we can send one every week. It is not a one-off mission.
With current technology, that's all you'll be doing. Focus on Mars or Moon bases for now.
While the GP's complaint is fairly minor, a more serious error appears earlier in the summary when the author states that the brighter destination star allows for increased deceleration resulting in increased travel times. Spending some time proofreading can save a lot more time later explaining what you actually meant.
It's its, it isn't it's. Isn't it?
(and it's white dwarf companion)
its
Autocorrect really, really wants to make this mistake when you post from mobile.
It's impossible to transmit information using entanglement.
Just to clear this up, parent meant it's not possible to communicate faster-than-light using entanglement.
all of the peices of light sail have been demonstrated at some scale and the physics is extremely well understood (with the exception of some high power laser wierdness). EM drives seem to be magic, and the mechanism that creates the thrust isn't understood at all.
Oh, add in that the force from an EM drive is incredibly tiny.
We're doing it all backwards. In order to avoid navigational errors we have to get the star to draw us towards it or vicey versy. In other words, use attractive forces instead of repulsive ones.
“He’s not deformed, he’s just drunk!”
I assume you're joking. Or you haven't done high school physics yet. It's the difference between using your arms to push yourself against a wall, and holding both your hands together and claiming that pushing harder with the left arm your entire body will move right.
How about communicating over extremely long distances without using extra power or keeping a directional antenna perfectly aimed?
IIRC the one test we tried to do of a light sail didn't work very well. We seem to be pretty good about getting stuff into space at the moment, maybe we should try again. Kickstarter, anyone?
I'm trying to teach myself to set people on fire with my mind... Is it hot in here?
What if we were to send out a photon beam from a source half-way between Sirius and Earth. We can entangle photons of different frequencies such as X-rays and visible light. If the X-ray photon is absorbed somewhere, the visible light photon disappears. But if there is no intercept, the visible light photon remains. That would seem to suggest you could send two photons in opposite directions. If one is absorbed, then the other disappears. And since the source is halfway between the two destinations, information is transferred twice as fast as it normally would take.
https://phys.org/news/2014-08-...
Vintage computer adverts: http://www.vintageadbrowser.com/computers-and-software-ads
So when are we expecting Alpha Centauri to get there?
Confucius say, "Find worm in apple - bad. Find half a worm - worse."
Why is light sail considered entirely possible, while EM-propulsion remains in the domain of evolution-denying (and even Trump-voting)? Aren't they both using light (of some frequency or another) as, uhm, tangible? Something, against which it is possible to push, however slightly?
The difference is not that the momentum of light is different, it is in fact the same for both cases. The problem lies in the weight of the craft itself. With an onboard em source you would need to carry your own fuel and have a massive em emitter. You may perhaps use solar cells to supplement some of the fuel needs at the expense of lower efficiency per photon at the craft and even more mass is needed. With a light sail you can construct a massive array of base laser stations with huge power supplies, yet the craft can be ultra light. Further the brightness of the star(s) at your destination can serve as a light braking system, whereas this is much less effective with an onboard emitter/power source.
tldr - an onboard light drive accelerates like a super tanker propelled by a trolling motor while an ultra light solar sail accelerates like a French fry flung into a fire hose.
I find it hard to believe that something going that far is not going to collide with some other object. The idea is cool though, maybe we should use robots to see how well it goes?
I assume you're joking. Or you haven't done high school physics yet. It's the difference between using your arms to push yourself against a wall, and holding both your hands together and claiming that pushing harder with the left arm your entire body will move right.
Technically speaking, if you hold your hands together and yet push harder with the left arm then that would imply a net acceleration of your left arm to the right. Except in the case of massless arms, this would imply a net force acting to push on the body, moving it left in the absense of any other forces. Simply severing the arms near the end of their travel should suffice to keep the body in motion until it is altered by additional forces.
The solution is a two sail solution. The sail will break into two sails on approaching the destination star. The big primary sail will act as a mirror and beam light backward unto the smaller secondary sail slowing down the probe.
The method from the article uses interference "Bringing together both paths of the red photons (from the first and the second crystal) creates bright and dark patterns, which form the exact image of the object". That doesn't happen in your setup.
How about communicating over extremely long distances without using extra power or keeping a directional antenna perfectly aimed?
You need a classical signal to correlate the entangled pairs, meaning you'd have to send a beam of light/radio/neutrons/whatever to the other side so they can "decode" the entangled signal.
So you actually still need the same power and directional antenna. Plus some extra equipment to handle the entangled stuff.
Nope. You need a classical communication channel just the same. The quantum channel is only capable of communicating uncontrollable random garbage.
Quantum-encrypted communication is no more useful in space than on earth, in fact it gets more resource-intensive the longer the link distance. Because the entanglement state travels faster than light (somewhere between 10,000c and "instantaneously"), and the classical channel that actually carries information is at light speed, if you wanted a quantum-encrypted radio link in space, you'd have a store a loooong history of the stream of random noise from the entangled electron, so that when a bit arrives after travelling 40 light-years you can look up what your electron's spin state was 40 years ago to decrypt it.
"When information is power, privacy is freedom" - Jah-Wren Ryel
Seriously; if you're ignorant or an idiot - and you're clearly both - expect to be called out on it. Don't Iike it? There's an easy solution.
By not needing to bring the bulk of the fuel needed for interstellar transportation, and by efficiently utilizing em from nearby stars, it will be very hard to beat its speed for the foreseeable future. Even things like the em drive, if it's real (tldr extremely unlikely is being nice) require onboard fuel and would take far longer to make the same trip.
Ultimately the best setup possible to move through space in a normal fashion would be to create or mine a miniature black hole of roughly a billion metric tons, and utilize the Hawking radiation to convert mass to energy. The output would be a steady 350 Mw or so and the radius of the horizon would be roughly proton sized. One would need a confinement system similar to, but far more advanced than, particle accelerator beams used in research today. On paper you could even harvest mass along the way. Given the laws of physics, it is unlikely one could design a higher power thrust to weight of the drive system/craft over the long hauls of traditional interstellar travel.
Thought experiments are how you come up with an idea that nobody has thought of before.
Back in the late 1980sI was on an email discussion group for Traveller (a sci-fi RPG). Someone asked why hydrogen fuel (for fusion) was stored as water aboard ships. Someone answered that water stores hydrogen atoms more densely than hydrogen gas, and the energy needed to chemically break off the hydrogen atoms off of water was trivial compared to the energy you could get from fusing them into helium. That spawned a discussion about whether there were other molecules which stored hydrogen even more compactly. Methane (CH4) was an obvious choice - 4 hydrogen atoms per non-hydrogen base, compared to just 2 for water (H2O). But eventually we settled on ammonia (NH4) because it's liquid at room temperature and wouldn't require pressurization or cryogenic storage in a vehicle sharing space with a life support environment for humans.
It's totally useless info right now (and probably the next few decades). But it's something that will be important in the future.
That's not necessarily a problem — even a kilo of material contains enormous amounts of power (m*c*c), we just don't yet know, how to extract it...
It would seem, the first such craft — if any are built — will have both. The sail for long distance travel, and EM for shorter-distance maneuvering, when nearby stars may not be sufficiently "bright". Not at all unlike the first coal-powered ships, which still used sails too.
Heck, maybe, Alpha Centauri can be reached first, contrary to TFA, if the breaking is assisted by an EM-drive — with each kilo of its fuel burned, the breaking becoming easier and easier to achieve...
In Soviet Washington the swamp drains you.
The cover article in the March 2017 issue of Scientific American was about using multiple light sails and miniature sensors to visit Alpha Centauri, with a large array of lasers -- either earth-based or space-based -- as the primary accelerant. The use of light sails, however, can be problematical.
First of all, consider solar wind, the stream of gases and particles emitted by the sun. If solar wind is faster than the sails, it will accelerate them beyond the force of the proposed laser array. If the solar wind is slower than the sails, however, the sails will decelerate. In either case, the solar wind and the sun's gravity can alter the trajectory of the sails.
The Oort cloud also requires consideration. If the sails are not punctured by the particles in the Oort cloud, impacts of those particles on the sails will decelerate them. If the sails are punctured, they will become useless in decelerating the sensors when the target star is approached.
Then there is the fact that space is not a perfect vacuum. Without dark matter, space still contains gas and dust, which can decelerate the sails. If dark matter does indeed pervade space, the deceleration might be sufficient to prevent the sails and their sensors from ever reaching their target stars.
This does not make the concept of light sails impossible. Before such a project is launched, however, more knowledge is needed about the solar wind, the Oort cloud, and what exists in space between here and any target star.
If the X-ray photon is absorbed somewhere, the visible light photon disappears.
That's not what happens. It would violate conservation of momentum, for a start.
systemd is Roko's Basilisk.
Are you sure you're not missing a letter?
Well, not quite. You're constrained by the efficiency of your reflector, the maximum temperature your (electronics, mirror coatings, sail, shrouds, whatever is the most temperature-sensitive component of your actual vehicle design) can stand, and your launch laser. So you fire the laser until the probe has the velocity you can dispose of at the destination (which is what this paper is about), then leave it to fly. Re-point laser and launch again. You might not get one launched a week, but several a year is probably feasible. By the time they're flying past Eris, they're probably at cruising speed already.
Birds are not dinosaur descendants;birds are dinosaurs, for all useful meanings of "birds", "are" and "dinosaurs"
Well, at least you did RTFP. (I missed that. Or auto-corrected it below consciousness.)
Birds are not dinosaur descendants;birds are dinosaurs, for all useful meanings of "birds", "are" and "dinosaurs"
While I didn't work on this one, the Galileo mission was started at JPL in 1977 (there were lots of study work done before that) and was ended in 2003 with the planned plunge into the Jovian atmosphere. That's 26 years, which was at least for many of the engineers, scientists, technicians and managers on the project a good portion of their careers. 74 years or more (added 5 years for planning and implementation) isn't bad for an interstellar robot mission. The challenge is always the stability of the funding environment.
If we're going to use an EMDrive, why not just have a wizard make it go poof and reappear at the desired destination?
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The EmDrive is not EM propulsion, it's pseudoscientific nonsense, confirmation bias in action. As claimed to operate, the EmDrive is a closed system that does not emit anything, and so does not conserve momentum or energy. EM propulsion using on-board power would be a photon rocket, and while it might have some exotic applications in things like precision formation flying, it's not going to be good for any more than that without the ability to convert matter into EM radiation with high efficiency.
Also, even if you can make a compact power source that would be good enough for a photon rocket, it's still probably going to be massive enough that it's better used as a portable beam station pushing on a photon sail. Rather than point it forward and brake the whole thing, point it backwards, cut it loose, and use it to brake a much-lighter payload equipped with a photon sail.
how to manage a project that will last longer than a working lifetime
This is not a problem we cannot solve: Most engineers that witnessed Voyager 1 launch in 1977 are likely to be retired now. We still collect information from the probe, thank to younger engineers that joined after launch.
Assuming you could include on the spacecraft the necessary detection equipment to figure out where the relevant stars are, you could have it compute its own course corrections, right?
Is the point to just get to another solar system?
Or, get to a close one with the highest probability of life?
In any case, it seems that even unmanned probes are a waste of time until faster communication (Quantum Communication?) is developed.
A manned mission seems the best option if we must be going soonest.
Then, while that mission is in route, we will have (likely) developed faster technology and can pick them up on a subsequent mission.
(Yeah yeah yeah. I know. Greater challenges with generations in space travel, etc, etc, etc... Just sayin'...)
Self-importance and self-indulgence is the root of ALL evil.
How can you communicate information using entanglement at all? Entanglement is something like putting a red and a black card into separate envelopes. If you open your envelope and find a red card, you know the other guy has a black one, but that's not communication. It's a lot more complicated, actually, but what it will tell you is probabilities that the other guy will get certain results given certain experimental setups. The only way to make it communicate would be to be able to alter a property without breaking entanglement, and that doesn't work.
"When you have eliminated the unacceptable, whatever is left, however improbable, must be the truthiness" - Holmes
Are you referring to the EM drive using an asymmetric chamber to bounce microwaves around in that allegedly violates conservation laws without exotic technology? It is exceedingly unlikely that that works as described. It may wind up having interesting physics, but there is so much physics that works so well that's based on conservation of energy and momentum to make it extremely improbable that they're wrong. Moreover, by Noether's Theorem, this would imply that physical laws change over relatively short displacements of spacetime, which we don't observe. We've bounced microwaves around before, and found no anomalies. It's conceivable that we just haven't noticed these things before, but very very unlikely.
It's possible to use light as the equivalent of reaction mass, since it does have momentum. It just has very, very little momentum for energy input, so it's not so much impossible as ridiculously impractical.
A light sail relies on an external source of light, so it isn't limited by need to carry reaction mass or energy to power some sort of space drive. It would actually work.
"When you have eliminated the unacceptable, whatever is left, however improbable, must be the truthiness" - Holmes
https://en.wikipedia.org/wiki/...
That isn't communication by entanglement. That's making existing communication tamper-evident using entanglement. Information flows in the normal way, but uses quantum properties to ensure that nobody can resend a photon accurately once read. If Eve is trying to listen in on the key transmission from Alice to Bob, Bob will get a garbled key.
"When you have eliminated the unacceptable, whatever is left, however improbable, must be the truthiness" - Holmes