If fast radio bursts really are revving up interstellar sailcraft, here's the maths Astrophysicists think that mysterious short millisecond-long blip of radiation may be distant aliens powering up their sailcraft. Over 20 such FRBs (fast radio bursts) have been detected since 2007. Avi Loeb of the Harvard-Smithsonian Center for Astrophysics speculates that the mysterious bursts could be powering interstellar …
How do you stop?
I mean, momentum can hurt quite a lot in space, and do you have to have another beam slow you down from the destination?
Or do you have to get a tiny craft with no propulsion down from millions of miles per hour to nothing with no on-board energy?
Niven and Pournelle describe this exact scenario in "The Mote In God's Eye" (1974). In their story a ship is accelerated to about 0.7c by lasers fired from their home planet. To decelerate the ship is aimed directly at the star in the destination system, tacking away at the very last moment using the light sail.
A fun enjoyable tale (As is the sequel). However the "lasers" are probably physically impossible (power and beam divergence) and it's just a nice story, not science.
Though a light sail does work, it's only any use for low acceleration outward from a star then coasting.
Forward's method puts a planet-width zone plate many AU's out, which converts that diverging beam into a converging beam, focused on the sail. Major engineering yes, but the physics is known.
Robert Forward has proposed having an outer ring on the sail that detaches and bounces the beam back to decelerate the craft.
https://en.wikipedia.org/wiki/Solar_sail#Interstellar_flight
You don't honestly think that a civilisation that can build interplanetary megastructures is going to be sending actual live examples of its self between stars, do you?
Much more likely, they long ago started going down the cybernetic route and are now more or less indistinguishable from computers, or are even just software ghosts running on a computing substrate of some sort. This transport system you see isn't shifting biological entities, but instead compacted, backed-up software and information.
@Tom 7
Rip the sail off?
Nah... you start with a *little* laser while the sail is close, and as it gets further away and faster, you build more lasers. Though I'd suggest an asteroid belt might be a better place to build the laser, if you don't want to toast the planet...
(er, provided the planet has the off-switch: reason left as an exercise for the student.)
>an area of a planet twice the size of the Earth
I assume this is with Earth level intensity of ~1 kW/m2 solar flux. But if you have that level of technology, couldn't you just move your solar capture array to an orbit much closer to the Sun? By definition, it's not going to be close to where it is delivering energy anyway, so you're free to move it where you want as long as you don't burn it up.
Mine's the Dyson sphere in my pocket.
"I assume this is with Earth level intensity of ~1 kW/m2 solar flux. But if you have that level of technology, couldn't you just move your solar capture array to an orbit much closer to the Sun? "
He's advanced an argument that water is used as a coolant. (You certainly need something plentiful for a planet-sized device.) If you move the array closer, then the water would become steam and you couldn't use it as a coolant. Also moving in closer would increase the tidal stresses. And finally, the vast majority of stars in the galaxy are a lot cooler than the sun and you'd have to be all touching their surface before you even got that irradiance.
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"If the concept involves visible light and mega-lasers, why is the term 'radio' used?... (Nothing to do with EM spectrum radio waves etc)."
First of all, far from having 'Nothing to do with EM spectrum radio waves etc.' visible light and radio waves are both examples of Electromagnetic Radiation; the only difference between them [visible vs. radio] is the frequency.
The current consensus is that sources of Fast Radio Bursts (FRBs) are extra-galactic in origin and typically several billions of light years away. This means that light emitted by these sources, especially at the lower end of the visible spectrum, will be red-shifted to the upper end of the radio spectrum by the time we receive it.
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> "FRB's remain static while we* sweep through the beam's path."
These putative transport beams are coming from quite far off, so the beam width would be ginormous, possibly hundreds or thousands of light years wide. But the pulses are "fast." It only makes sense if the source is changing the beam direction. Earth would need to be relativistic to cross such a wide, stationary beam in a short time. Somebody would notice!
Nevertheless, the paper suggests the sweep time is consistent with orbital motion of the beamer footprint. Indeed, the authors propose the silhouette of the lightsail could be detectable from interference patterns within the beam. The implication is clearly that we're catching glimpses of the beam 'at work' rather than shifting between targets.
"I can't see a reason for transport beams to be swept at all, unless it's hard to turn them off."
Yeah, along with the point made by Tom7, fast bursts of energy don't seem to make much sense as a solar-sail propulsion system at all.
The issue is that no material is perfectly reflective and this limits the amount of energy that can be beamed at the sail and its probe; beam too much energy at it and you'll simply vaporise it. At the same time though, a single burst of energy, at a level safe enough for the sail and probe, wouldn't be sufficient to effectively power it.
Another problem with the propulsion system idea is that if the source is a laser then you'd expect the bursts to have a very narrow bandwidth, which doesn't seem to be the case.
Although most of the FRBs recorded to date seem to be one-off events FRB121102 appears to have been the source of a total of 17 (non-periodic) FRBs since 2012 but even this source really doesn't seem like a plausible candidate for a propulsion system.
Great ! Now we just need a way to transport a person one atom at a time in said nano craft.
That should probably allow the pieces to survive the 28.41 years it should take to get there at that speed.
Oh, and we shouldn't forget to build another laser array on the other side before we get there, to slow the nanocraft down.
Then all we need to do is use a 3D printer to put all the atoms back together.
Childs' play, I tell you.
Well, I think its all silly, but you could always take the slow way to your destination with an automated ship that builds the laser array at the other end so you can start taking fast trips over there.
It would simply require a species with far far longer time horizons than humans. Either because they are effectively immortal, or their social structure is much more insect like than ours so they wouldn't consider resources to be wasted if their descendants won't benefit from them for a few hundred generations.
"or their social structure is much more insect like than ours so they wouldn't consider resources to be wasted if their descendants won't benefit from them for a few hundred generations."
I think you underestimate humans in this respect. It's the only way to explain investments in Twitter and Snapchat.
It would simply require a species with far far longer time horizons than humans
We could make a start ourselves by finding politicians with a longer time horizon than the next election, or, in Trump's case, longer than the next scandal (he's running at roughly one a week at present).
"so you can start taking fast trips over there"
Fast being a relative term here. You're still looking at years just to get to the closest stars.
(I've just noticed that to accelerate to the speed of light at 1G, would take almost exactly one year [353.8 days], weird coincidence no?)
Great ! Now we just need a way to transport a person one atom at a time in said nano craft.
That should probably allow the pieces to survive the 28.41 years it should take to get there at that speed.
Or just use the idea that Richard Morgan used in some of his sci-fi books - disposable clone bodies. Each with an in-head memory recorder (so that what you experience isn't lost). Interstellar travel consists of copying the data from the memory recorder (and the original is destroyed on a successful copy to avoid the multiple-clone problem) across interstellar distances. These are then downloaded into a new clone body at the destination.
It might take years to copy (and error correction would be fun) but you won't care since you are just a bunch of data and not experiencing any of it.
Of course, having the ability to write, store and read memories does leave you open to creative editing while in storage.
All hail our new orange overlord, Trump the First of His Name
More accurately, Niven got there in 1971. And of course over four decades earlier Konstantin Tsiolkovsky suggested the idea.
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You could have lasers pointing in both directions, from each src and dest, to slow down, just switch lanes.
If these things do reach near light speed, time would be slower for these interstellar commuters, so they wouldn't age so much, this band of renegades could meet up at "space diners" and discuss how much a planet had changed over the millenia (which might be a few months/years for the space truckers)...
There's a novel here if I wasn't too lazy to figure out how to shoehorn Pingu, General Krull and the Space Artifact in it...
Oh well
So far the only fast radio burst of which the source was identified is FRB 121102; a dwarf galaxy at a distance of 43 Mpc to 1.7 Gpc (Nature 5 januari 2017). The flux is 350 µJansky at 1.2 GHz (Brian D. Metzger et al. 2017). Because 1 Jansky is only 10-26 Wm-2Hz-1, this rules FRBs out as powersources for interstellar travel, even if the beam is more intense a couple of lightyears from the source.
See Kardashev scale
Someone reads too much SF. I even write the stuff and I've read it for 50 years. However while it might work as a plot device in a story, my money is on a natural explanation.
Motive: Why is someone going to build a massive generator and power a sail? Crazy Eddie is fictional.
Means: There is no evidence that such so called "Advanced" civilisations exist or that the Kardashev scale is any more than EE "Doc" Smith style "Skylark" extrapolation.
It's been suggested that the universe has been in a state where intelligent life can evolve for a relatively short time, perhaps less than one billion years. If so, we might easily be among the first intelligences in our galaxy. That would explain the Great Silence and the fact that we are not a colony world already.
As I recall, it mainly has to do with the increasing metallicity of galaxies over time, to the point where the necessary elements are present during a star's formation, which then allows carbon-based life to exist within that system. Then it's necessary to wait while the planets cool down a bit before multi-celled organisms can evolve. It took Earth several billion years to do that.
After that you may expect smart monkeys almost at once.
If you had a civilisation that wasn't too busy trying to kill each other or make money then you could easily build an array the size of two earths to collect the light in space and transfer it to the ground to then power the laser.
You could them send the materials onto the next planet or get them there to build another array for the return journey.
Which then makes you wonder, what happens when these potential aliens arrive and ask to be taken to your leader? I can't think of one countries current leader that wouldn't f*ck it up.
.. is what music they'll use for that radio transmission, Stairway to Heaven?
:)
Also thought to be some kind of alien comm system.
Since the sources are outside our galaxy the "fast" bit suggests it's us that are moving and the beam are just being glimpsed as we whizz across their path.
Of course it's bad news if this really is a drive system for a solar sail transport network.
That suggests that smarter minds than ours (working for a lot longer) have not come up with anything better than sub light travel.
No FTL liners plying their trade between the stars <sigh>
Way over my head (metaphorically and perhaps literally too) but this reminds me of using craft with large "sails" driven by solar wind which I remember reading about many years ago in Arthur C. Clarke's "The Promise of Space". At least I think that's where the memory is from. He reckoned it was a viable and relatively efficient means of propulsion for non-time-critical and even heavy cargo which could build up a reasonable speed over time because of what would be constant acceleration.
A lot of punters here will know he has form with such ground-breaking concepts. One of his essays was entitled "How I Lost A Billion Dollars In My Spare Time" ruing the fact that although he formulated the concept of communication satellites soon after WWII he never thought of taking out a patent.
Edit : Blimey. Just checked and the anniversary of his passing is days away - 19th March. Reminds me to raise a glass to a true original and selfless contributor to humanity.
IIRC the short story was called "The Wind from the Sun" but I've seen it re-titled as "Sunjammer," which I liked better.
Solar sailing both within a solar system and outside has been suggested. In principle it works best if you set up a "pipeline" of payloads going from A to B. It's slow but once you've mastered how to build large light sails (which IIRC was KE Drexlers Graduate thesis) it's relatively cheap in materials (10s of Kg of system pushes tonnes of payloads).
It's been suggested that sneaking up to a Sun behind an asteroid, then coming of it's shadow close in to the sun would give substantial (g's ) of acceleration which would bring it up to solar escape velocity.
Did anyone do the calculations for an FRB being responsible in some fashion for the Wow! signal?
My thinking here is that there could be some combination of natural events eg narrow beam of light hitting a cloud of hydrogen causing a brief spike at 1.42 GHz ?
This is an alternate hypothesis to the one suggested about natural maser action in molecular hydrogen from those two comets, and also could account (indirectly) for the relatively narrow band and lack of repeatability.
As it happens I might be able to test this with a fluorescent tube starter and small laser: any old DVD writer would work and the IR laser can be modified to focus on the empty area at the end of the tube.
-A
Call me an old cynic, but It's funny how many of these Bogus Science (BS) hare-brained ideas come out in March just as funding negotiations for the next financial year get under way.. The BBC usually repeat the Cumbre Vieja mega tsunami hoax around this time of year, too...
You're an old cynic.
Funding negotiations are not necessarily tied to the financial year - at least not in the UK, and I doubt in the USA either (where the financial year starts in October).
In any case, "Astrophysicists think ..." is pop-sci journalese for "At least one astrophysicist speculated ...". Which is fine, scientists are supposed to speculate (modulo Occam's Razor, which I suspect may kick in rapidly for this one).
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