[HN Gopher] New solar sail may travel to Alpha Centauri
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New solar sail may travel to Alpha Centauri
Author : Brajeshwar
Score : 82 points
Date : 2022-03-13 15:37 UTC (7 hours ago)
(HTM) web link (earthsky.org)
(TXT) w3m dump (earthsky.org)
| mrfusion wrote:
| I'm really excited about this idea and if we prove it out we
| could gradually power larger and larger craft this way.
|
| Eventually we could build lasers in the Centauri system to let us
| also slow down as we approach.
| ck2 wrote:
| btw a fun read:
|
| [PDF]
| https://web.archive.org/web/20160318223348/http://ccrg.rit.e...
|
| https://en.wikipedia.org/wiki/Alcubierre_drive
|
| (ala Futurama "The engines don't move the ship at all. The ship
| stays where it is and the engines move the universe around it.")
| mmaunder wrote:
| Another fundamental challenge is how to receive telemetry and
| data from the probe once it gets there. The DSN can communicate
| receive from Voyager 2 - in fact it is right now.
| https://eyes.nasa.gov/dsn/dsn.html
|
| But our closest star is much further away and it's an interesting
| challenge to send a powerful enough transmitter that far - power
| being the main problem- and have an antenna on Earth or locally
| in space that can receive the data.
|
| There's also a question of bandwidth. Voyagers downlink is 160
| bits per second. Webb is about 25Mbps. What bandwidth is
| achievable at that range?
|
| It's doubtful the probe would be able to receive because you
| wouldn't want to send a massive antenna that far out.
|
| There's propagation delay which would be 4.2 years in one
| direction in the case of our closest star Proxima Centauri.
|
| If we take a long view - as in, the original team would be long
| dead when the mission completes - I suspect this is achievable.
|
| Check out the Lucy mission which is impressive in its orbital
| complexity and long time horizon if you're into this stuff.
|
| https://en.wikipedia.org/wiki/Lucy_(spacecraft)
| mrfusion wrote:
| So these are tiny and cheap so you stagger the launches so they
| can relay their data back to earth. Each one could be within a
| few 1000km of the next one.
| danparsonson wrote:
| That would require on the order of 10^10 probes...
| mrfusion wrote:
| Thanks for checking my math. Looks like we'd need to
| stagger them by about 100 million km to be somewhat
| reasonable.
|
| It's still 400,000 times less distance to transmit a signal
| so it would help.
| simonebrunozzi wrote:
| > power being the main problem
|
| nuclear power perhaps? Not now, but maybe in 15-20 years?
| badrabbit wrote:
| Nuclear fission isn't being used because it can't genenrate
| enough acceleration for a large spacecraft? I don't me to take
| off from earth but once in space, to reach relativistic speeds.
|
| https://en.m.wikipedia.org/wiki/Project_Longshot
| ericbarrett wrote:
| I think if we built a nuclear-propulsion probe it would use
| something like NERVA, which was a working prototype. Nuclear
| _pulse_ propulsion is far more speculative and too close to a
| weapon to be practical in the next few centuries.
| lmilcin wrote:
| I am more interested in how they are planning to fit in all the
| apparatus in a probe that small and especially how they plan to
| send a usable signal back to Earth.
| xwdv wrote:
| When I was younger I would look at technology like this and
| wonder in amazement at all the things humanity could do in space
| and expand our reach beyond the Earth.
|
| Nowadays, I think what's the point. Life in the universe may be
| extremely rare but we are going about the process of spreading it
| all wrong. Rather than sending humans to far off worlds we should
| focus on a simpler task of inseminating worlds with microbial
| multi-cellular organisms that can survive and evolve over the
| course of millions of years into full first class citizens that
| can thrive on these worlds and their environments. Humanity may
| die off soon but if we kick off a process on several worlds that
| triggers new forms of life to grow and reach sentience, then
| perhaps we will have done our part in the universe, and all of
| the human race could rest in peace knowing we have passed on the
| most precious resource the universe has to offer.
| thorum wrote:
| How big of a concern is collision with dust at these speeds? At
| .3 light speed would this material survive hitting a micrometeor?
| dmitrygr wrote:
| A similar idea to what was used for travel in the hard sci Fi
| novel series "Rocheworld" (highly recommended)
| mpreda wrote:
| Also in "The Mote in God's Eye" by Pournelle & Niven (1974).
| aurizon wrote:
| These goofs have zero comprehension of beam divergence at
| anything near that distance. Anything but a perfectly parallel
| beam can propagate to anything near that distance. The optical
| cavity is a box with reflective ends, one 100% and the other ~99%
| of a lasing medium that goes back and forth while pumped and 1%
| escapes one end - this is amplified - but the beam divergence is
| preserved. Takes an impractically large box = impossible du to
| time of flight. The other path to parallelism is a long self
| focussing amplifying tiny fiber that is pumped to the energy
| needed to make the most parallel beam and this is amplified. To
| get something that would project a 20 light year powerful beam
| without divergence is beyond doable or theoretical physics.
| ben_w wrote:
| They aren't aiming for a 20 light year focus, they're aiming
| for a 20 year flight duration after (a currently unachievable
| but much less difficult) ~ _10 light second_ acceleration path.
|
| They have a better grasp of how many unsolved problems they
| face than you or I have:
| https://breakthroughinitiatives.org/challenges/3
| aurizon wrote:
| That is partly true, there is no way a chip based laser can
| achieve the divergence even for a 1,860 million mile path.
| Chip geometry is intrinsically too divergent. A pumped self
| collimating fiber 1/1000 light second long = 186 miles,
| coiled in a large loop might not do it. I would have to look
| up the limits of self collimation? That said, we do not
| progress with leaps in thought and technique.
| ben_w wrote:
| Why do you even want self collimation? Can't it just focus
| the laser light with a (very) big mirror on the sending
| side?
|
| (Genuine question; my physics isn't at that level).
| aurizon wrote:
| This is commonly used in fibers, a gradual gradient in
| the refractive index from the center to the edge
| automatically steers the beam to the core path. Focus has
| limits, you can focus the sun to an image but not to a
| zero dimension point, although you can not focus stars to
| an image, they are so far away they are essentially
| parallel = many many light years so they appear to be a
| point and for most uses they are..
| jzer0cool wrote:
| 20 years?! -- A nearest star in a lifetime. I hope to see this
| project launch soon.
| account-5 wrote:
| I'm left wondering if that 20 years was from earth of the probe
| seeing as we're talking about relativistic times.
|
| If it's 20 years on earth how much time would have passed for
| the probe, and visa versa?
| lmilcin wrote:
| Lorentz factor at that speed is very small.
|
| https://en.wikipedia.org/wiki/Lorentz_factor
| pklausler wrote:
| This is nowhere near "relativistic" in velocity.
| prpl wrote:
| We generally regard things above .1c to be relativistically
| significant, but maybe not all that interesting for thought
| experiments
| Stevvo wrote:
| Actually it is, but not dramatically; for 20 years at 0.1c
| an extra 5 weeks will have passed for the probe.
| thaumasiotes wrote:
| > an extra 5 weeks will have passed for the probe.
|
| What does this mean? The only quantity I can see with an
| obvious meaning is that the probe will arrive somewhere
| after experiencing a certain amount of time since leaving
| Earth. But the time of the probe's arrival is not easily
| matched to _any_ time on Earth.
|
| Suppose the probe arrives and dispatches a message which
| travels back to Earth at the speed of light. For
| simplicity, the distance is exactly 4 light years.
|
| - How much time did the probe experience between leaving
| Earth and sending the "I made it" message?
|
| - How much time did Earth experience between the probe
| leaving and the "I made it" message arriving?
|
| It's kind of unsatisfying that these two questions don't
| share both their endpoints, but at least they both have
| well-defined answers.
| ben_w wrote:
| The Lorenz factor is 1.021, which sounds like it's just
| enough to make it engineering the mirror to not instantly
| vaporise _even harder_ without being enough to help with
| anything.
| jillesvangurp wrote:
| It would be another 20 years before we hear back from it. If at
| all.
| stewbrew wrote:
| No article about solar sails should miss out on mentioning that
| this idea like ... 100 years old? The laser is new, though.
| malfist wrote:
| Laser powered solar sails have been around a while, see:
| https://en.wikipedia.org/wiki/Laser_propulsion
|
| > Use of a laser-pushed lightsail was proposed initially by
| Marx in 1966, as a method of interstellar travel that would
| avoid extremely high mass ratios by not carrying fuel, and
| analyzed in detail by physicist Robert L. Forward in 1989
| DennisP wrote:
| The concept is old, but there's new engineering for a specific
| practical design.
| denton-scratch wrote:
| This article is rather thin on detail.
|
| It says the probe itself is the size of a microchip. Let's be
| generous and suppose it's the size of a modern Intel x86
| processor. How does it communicate with Earth? There has to be
| some kind of antenna dish; so OK, maybe the sail can serve dual
| functions. How does it do attitude adjustment?
|
| Presumably some of this chip-sized probe is a sensor of some
| kind; perhaps a camera. Without a sensor, it's hard to see how
| one could think of it as a "probe" at all. Does this camera have
| a lens? How big? A lens the size of an Intel processor won't
| capture much light, and I'm not sure the bandwidth from Alpha
| Centauri is going to be good enough for digital imagery.
|
| How is the probe's transmitter to be powered? A battery no larger
| than a microchip seems a little inadequate for communicating
| between Alpha Centauri and Earth.
|
| OK, so the probe doesn't start transmitting until it can harvest
| energy from Alpha Centauri itself. But now it needs a solar
| panel! A solar panel up to the job simply can't be made the size
| of a microchip.
|
| Maybe it's not supposed to send any data back at all; maybe it's
| just meant as a proof of concept. But even our best telescopes
| can't detect something 3m wide, in the region of Alpha Centauri.
| So the only concept this could ever prove is that you can
| accellerate something to c/5; there's no point in aiming it Alpha
| Centauri.
|
| The article doesn't say how long these lasers are supposed to
| keep running; it seems unlikely they'll stay focused on the sail
| much past the orbit of Jupiter. I haven't tried to do the maths,
| but to accellerate something the size of an x86 to c/5, I imagine
| the lasers will have to run continuously for over a year; how
| much is _that_ going to cost, for a probe that can 't send back
| data?
|
| Hmm - the article is bylined "Deborah Byrd". So I click on the
| byline, and get a photo and bio of astronomer Theresa Wiegert.
| Who is Deborah Byrd?
|
| I've never heard of earthsky.org before, but my confidence in
| this publication is immediately diminished on my very first
| visit.
| Helloyello wrote:
| stephenhuey wrote:
| This topic was discussed at length 6 years ago:
|
| https://news.ycombinator.com/item?id=11480840
| molticrystal wrote:
| Would a solution be to send them off like train cars, perhaps a
| few months apart or sooner for redundancy in case one of the
| "cars derail" and aligning their paths up as they leave earth
| so they can act as relays and improving their designs as time
| go on?
| JPLeRouzic wrote:
| > Who is Deborah Byrd?
|
| > I've never heard of earthsky.org before
|
| https://en.wikipedia.org/wiki/Earth_%26_Sky
| denton-scratch wrote:
| Ah, so Deborah Byrd runs the site; I still don' know who the
| article is attributable to.
| dylan604 wrote:
| >This article is rather thin on detail.
|
| You think? It's at the level of coming from someone's head
| written down on a napkin told at a cocktail party. Only, now,
| they've added a friggin' laser.
| [deleted]
| cesaref wrote:
| Doesn't sound like they're planning to stop when they get there.
| dylan604 wrote:
| Think Oumuamua. You're lucky to just arrive in the targeted
| solar system. There's no fuel for course correction let alone a
| deceleration burn to attempt orbit insertion around a rock.
| Would they even be able to supply enough fuel to insert into a
| solar orbit at a Neptune/Pluto like distance?
| BurningFrog wrote:
| If you're very lucky, a local planet will catch you in an
| orbit.
|
| Or the local "Space Coast Guard" will board the vessel.
| not2b wrote:
| A local planet will not catch an object going 0.2c, and there
| isn't a way to slow it down significantly.
| thaumasiotes wrote:
| > A local planet will not catch an object going 0.2c
|
| Maybe not gravitationally, but there's always the chance
| the planet will get in the way.
| throwawaybutwhy wrote:
| Ugh. Are we prepared for relativistic reprisals?
| jcims wrote:
| There's a bit of precedence for this with NASA missions:
|
| https://en.wikipedia.org/wiki/Interstellar_probe
| SideburnsOfDoom wrote:
| No. The craft is obviously disposable, on a one-way trip.
|
| I wonder if it will even slow down, is there any braking
| manoeuvre possible, or will it shoot through the target solar
| system at 0.2c ?
|
| What would be nice, would be if a signal - data, information
| about the target solar system could be sent back during the
| fly-by. But I see no sign of that.
|
| I've seen pictures of a barren desert landscape today, taken
| recently on Mars. It's marvellous, and I don't need the rover
| to come back for that.
|
| But without even information coming back, what's the point?
| nuccy wrote:
| From the original starshot project we know that information
| is exactly the aim. Though at the moment we are not yet on
| the level of technology to compactify enough the transmition
| equipment.
|
| There is no manuever which can help with 0.2c velocity drop.
| Individual gravitational assist manuever usian a planet of
| the solar system can add/remove hundreds of meters/second
| (depends on the planet mass and how close to its center we
| can pass). Plus the vehicle flyies-by the object used for
| such assist. Since Alpha Centauri is literally the closest
| star system, there is nothing on the way to be used for such
| an assist (preferably a star).
| Maursault wrote:
| The beautiful and famous (at least very popular) image in the
| article of Alpha Centauri and Beta Centauri is very confusing.
| It's an image of two separate star systems, with Proxima Centauri
| circled in red. It is easy to make the mistake (esp. if in
| passing) to think that this is an image of just the Alpha
| Centauri system, even with the caption explanation. What looks
| like a star on the left is Alpha Centauri, a binary system which
| Proxima Centauri orbits (thus a triple star system) all about
| 4.3-ish lightyears away. The apparent star on the right is the
| similarly constructed (binary with another orbiting star) Beta
| Centauri triple system and is about 400 lightyears away.
| akkartik wrote:
| Thanks for pointing this out.
|
| I see that https://en.wikipedia.org/wiki/Alpha_Centauri has a
| much better caption for the same image.
| perihelions wrote:
| Has anyone analyzed the nuclear pulse propulsion sail mentioned
| in the _Dark Forest_ trilogy? The 1950 's proposal was to carry
| nuclear explosives on a manned rocket and throw them out the back
| one by one. Cixin Liu's variation, for a lightweight, one-way
| probe, would preposition thousands of nukes throughout the solar
| system, and launch a thin radiation sail on a trajectory that
| flies through each detonation in sequence.
|
| I assume there's _some_ fatal flaw to this, but it takes more
| domain knowledge to identify it than I 'm familiar with.
| thorin1 wrote:
| Yes, there may be some fatal flaw in taking thousands of nukes
| to the orbit.
| KineticLensman wrote:
| > would preposition thousands of nukes throughout the solar
| system ...
|
| > I assume there's some fatal flaw to this
|
| It would take massive expenditure of energy to create and
| preposition all of those nukes.
|
| A direct contact blast (as in Project Orion) would obliterate a
| thin radiation sail. Radiation effects might impart a
| propulsive force to a more distant sail, but probably not
| enough to generate the sustained acceleration required. Pulsed
| acceleration blasts would dynamically disrupt the
| ultralightweight sail rigging (compared with a continuous
| gentle pressure from the sun or a launch laser). EMP effects
| might fry any electronics on an unshielded probe.
|
| [Edit] However, this idea is perhaps conceptually less
| completely barking than his strategy for recovering important
| hard drives from a defended ship passing through the Panama
| Canal in The Three-Body Problem. Spoiler ... ... you simply cut
| the ship (and crew) into tiny pieces using a nano-filament wire
| ambush, then recover the sliced hard drives from the sea bed
| and reassemble them. I basically stopped reading at that point.
| dylan604 wrote:
| So will the inhabitants of Alpha Centauri recognize this vessel
| as something other than Oumuamua?
|
| Given the shape of the solar sail, a new sci-fi story makes this
| the Veeger where our solar sail collects enough dust due to some
| unforseen negative ionic charge developing that pulls in galactic
| dust to make it look like generic rock floating from the
| Centurian Oort cloud and written off as actual contact from
| another planet.
| lmilcin wrote:
| Any civilisation that can detect an object of that size and
| categorise it as being unnatural in origin would have vastly
| more advanced technology that would allow them to detect humans
| on Earth in the first place.
| dylan604 wrote:
| We dtetected Oumuamua.
| lmilcin wrote:
| Oumuamua is a bit larger than a blanket on your couch.
|
| Also, a mirror flying through space is very hard to detect.
| It reflects very well but only in some directions meaning
| it is basically black when looking at it from any other
| direction.
| dylan604 wrote:
| It's also at about the altitude over your head the
| premise flew by you.
|
| It was a low brow sci-fi premise where the little probe
| that could collected all sorts of space dust on the 20
| year journey increasing its size.
| credit_guy wrote:
| Here's some numbers to make sense of this.
|
| The kinetic energy formula is mv^2/2. At the speed of 0.2c, the
| relativistic correction is only about 3%, so you can ignore it.
| Let's say you want a probe of only 2kg. At a speed of 60000km/s =
| 60 million m/s, the energy is 3600 x 10^12 joules or watt-
| seconds, which is the same as 1000 GWh. So, roughly the output of
| 1000 nuclear power plants for one hour. And this only if by some
| miracle we achieve 100% efficiency in converting electricity here
| on Earth in kinetic energy far out in space. We'll get back to
| this in a moment.
|
| How long does the acceleration phase take? At a gentle 1g
| acceleration, this would be 60 million m/s divided by 10 m/s2,
| which is 6 million seconds, or 69 days, so a bit more than 2
| months. At 1000g (mentioned in the article) it would only take
| 6000 seconds, or 100 minutes (1h40m). The average speed over this
| period is 0.1 c, so at the end of the acceleration phase, the
| spacecraft will be 10 min-light away from us, which is 180 mill
| km, or a bit more than 1 AU.
|
| Now, lasers don't produce a perfectly collimated beam (i.e.
| parallel rays). The best one can achieve is the optical
| diffraction limit, which means an angle of divergence of 2.44 x
| lambda/pupil diameter. Let's say our laser has a huge diameter of
| 1.22 meters and we use green light (500 nm wavelength). We end up
| with an angle of 1 microradian. For such small angles the tangent
| is equal to the angle, so it's going to be 1e-6. In other words,
| for each 1 million meters, the beam spreads out by 1m. At 100
| million kilometers, the beam spreads out by 100 kilometers. Since
| our spacecraft only has a diameter of 10m, it captures only
| 10^(-8) of the beam. Let's say you fiddle with the numbers (you
| use a bigger diameter laser, with a shorter wavelenght), and you
| reduce the divergence angle by a factor of 100. That means you
| still capture only 10^(-4) or less of the beam for most of the
| trip.
|
| So that 1000 nuclear power station just went to 10 million power
| stations. By the way, you better build them in space, otherwise
| the poor Earth atmosphere will not be so happy about this whole
| business.
|
| Ok, but let's now say you overcome all these issues.
| Congratulations, you just accelerated a spacecraft to 0.2c.
| What's out there in the vast empty space? Mostly molecules of
| hydrogen, and from time to time a speck of cosmic dust . Now that
| speck of dust is not so innocent. It can weigh as much as 100 mg
| [1]. 1 mg specs of dust are quite abundant. And such a tiny speck
| of dust is nasty, really nasty. Because it hits you at a speed of
| 0.2c, i.e. with an energy of mv^2/2 = 10^(-6) x (60 x 10^6)^2/2 =
| 0.5 x 3600 x 10^6 = 1800 MJ. For comparison, a modern American
| armor piercing tank shell has a weight of about 9 kg and a
| velocity of about 1600 m/s, so a total energy of 9 x 1.6 ^2 x
| 1e6/2 which is about 10 MJ. So one tiny speck of 1mg will hit you
| with the energy of 180 rounds of M1 Abrams.
|
| You only have to spend 20 years with these little fellows.
|
| [1] https://en.wikipedia.org/wiki/Cosmic_dust
| JPLeRouzic wrote:
| Many thanks for taking the time to calculate and share all of
| this.
| willcipriano wrote:
| If the people building this have any humor they will call
| themselves Morgan Industries.
| RaoulP wrote:
| There's no mention of instrumentation or relaying information
| back to earth. If there is none, what would be the point? I
| wonder what can be achieved in something "about the size of a
| microchip".
| zabzonk wrote:
| Yes, I've always wondered about this too - you would need a
| communication laser and a lot of power.
| taf2 wrote:
| And 4+ years added to find out what it finds. Also a very
| high speed camera that can maybe capture something
| interesting once you get to your destination because I don't
| think it can arrive and stop... it'll just buzz past at 20%
| speed of light
| spaetzleesser wrote:
| "it'll just buzz past at 20% speed of light"
|
| That's why I think it's not a worthy effort right now. You
| won't be able to aim correctly so you may speed by objects
| at large distance at an incredible speed with very small
| cameras. I wonder if the results ill wbe any better than
| what you can from earth (or will be able to do if you
| invest some money)
| dheera wrote:
| ()
| zabzonk wrote:
| Nice for the inhabitants! And have you heard of non-
| damaging spectroscopy?
| [deleted]
| pavlov wrote:
| What if you have a fleet of thousands of these acting as a
| cluster? All of them would have some limited radio capability
| to communicate with other nearby probes. Some would carry
| additional instruments to collect data near the star, and
| others would have higher-powered radios to send data back to
| Earth.
|
| It doesn't sound like you could fit this kind of system in the
| size of a microchip, but what do I know, I'm just a random
| Internet speculator.
| ck2 wrote:
| Why stop at thousands?
|
| If simple and small enough, railgun grains-of-rice sized
| probes at every "near" object in the visible galaxy and
| create a million node network to relay and repeat back to
| earth.
|
| Get the cost down to $100 each.
|
| Time the launching to say once a day so they travel behind
| each other as repeaters.
|
| Then they only need small transmitters/receivers with small
| power sources.
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