[HN Gopher] Starlight interstellar probe
___________________________________________________________________
Starlight interstellar probe
Author : Hooke
Score : 73 points
Date : 2022-10-09 20:20 UTC (3 days ago)
(HTM) web link (en.wikipedia.org)
(TXT) w3m dump (en.wikipedia.org)
| ck2 wrote:
| What's the effect on mass at 1/5th light speed?
|
| Ah okay, google says only +2%
|
| > A particle moving at one-fifth the speed of light (60,000
| km/sec or 37,000 mi/sec) has a mass only 2% greater than its rest
| mass. When a particle's speed approaches the speed of light,
| however, the mass increase (called the relativistic mass
| increase) is significant.
| gzer0 wrote:
| > _Currently, research models suggest that using this technology,
| a satellite massing 100 kilograms (220 lb) could reach Mars in 3
| days, a significantly shorter time than the current transit time_
| [1].
|
| Incredible. This is simply incredible. I hope humanity succeeds
| here.
|
| [1] https://en.wikipedia.org/wiki/DEEP-IN
| JPLeRouzic wrote:
| This means an acceleration of 85 g, what hardware can support
| this? What temperature the influx of energy will induce?
| varjag wrote:
| A GPS guided Excalibur shell acceleration peaks around
| 12000g.
| JPLeRouzic wrote:
| Thanks I learned something!
| JPLeRouzic wrote:
| Please, did you achieve to power on your MS1201.02 single-
| board PDP-11 ? Thanks!
| varjag wrote:
| Ha! Nope, some months after the post I re-capped it and
| installed modern DIP switches. Then I stumbled on another
| specimen in perfect condition and grabbed that one. Both
| are still collecting dust on my projects shelf: never got
| around to powering either on, even though I have the
| power circuit sequence and schematics. Something to be
| said about spreading yourself too thin! :)
| JPLeRouzic wrote:
| > Both are still collecting dust on my projects shelf:
|
| Ah, ah, it's something I know as well!
| euroderf wrote:
| Will the aliens that detect & intercept the probe wonder how
| something as simple as the nematode built & launched the probe.
| fallingfrog wrote:
| The prospect of aliens trying unsuccessfully to communicate
| with a nematode is pretty comical
| rrwo wrote:
| Nematodes manipulated evolution to produce organisms that would
| send them to other solar systems.
| dclowd9901 wrote:
| If they had our level of intelligence, probably.
| SideburnsOfDoom wrote:
| We couldn't intercept `Oumuamua and it wasn't travelling at a
| high fraction of light speed.
|
| Actually capturing an object with that much velocity would
| require a high level of sophistication, very fast reactions,
| and a big energy budget.
| usrusr wrote:
| Alpha Centauri aliens who'd be able to detect and intercept
| that probe would have their Twitter flooded with funny memes
| made from our hn discussions of the mission long before the
| actual probe arrives. Actual arrival wouldn't even make it into
| their news.
| adipginting wrote:
| That is a positive assesment. On the other hand, imagine if the
| aliens think that the senders of these probes were deliberately
| sending pathogens to the aliens' worlds. This is a statement of
| war.
| rapind wrote:
| They'll just assume that the idiot species sending out
| statements of war have already been taken care of (probably
| by themselves).
| spinlock wrote:
| The aliens could just send back blueprints for a black hole
| weapon and wait for us to do the wrong thing.
| Pxtl wrote:
| > They would fly at one-fifth of the speed of light
|
| what? I thought most materials would be obliterated by the damage
| caused by traveling through the interstellar medium at such
| speeds.
| sliken wrote:
| Would some be lost, likely. Would all have some holes in the
| large sails, sure.
|
| But some on board redundancy should let a decent fraction of
| them to survive. Keep in mind the lasers will boost the
| velocity for just minutes to hours, so you can launch many of
| them.
| jcfrei wrote:
| Is there any way for these probes to communicate with earth
| during their journey?
| dghughes wrote:
| These proposed devices use laser or solar on a giant multi
| kilometre area material. I wonder if the shape of the material
| could also be a dish used to transmit a signal back to earth.
| 0xf00ff00f wrote:
| From their report:
|
| > We have run link margin calculations including Zodi, CIB,
| galaxy and optical emission for such a wafer scale system run
| in a hibernate/burst mode using the DE-STAR array as both the
| transmitter of power to propel and communicate with the
| spacecraft as well as to receive the very weak signal from the
| spacecraft and conclude it is feasible to receive data (albeit
| at low rate) at light year distances.
|
| Source:
| https://www.nasa.gov/sites/default/files/atoms/files/roadmap...
| ncmncm wrote:
| There has been no hint of any answer to this question. Did they
| think no one would notice?
| sliken wrote:
| This isn't new, there's been many discussions. But generally
| you spend billions making lasers, on the ground, in orbit, and
| on the moon has been suggested. You make the space craft with a
| sail a few atom thick surface tuned for the frequency of the
| laser to minimize weight and maximize thrust.
|
| However even 1% of the speed of light means it's going to be
| too far to accelerate significantly on the order of 10 minutes
| to 10 hours. Sure we could put laser arrays on the outer
| planets, but that's not particularly feasible today.
|
| So what do you do with your $billions of lasers once post
| launch ... of course launch more. Especially since you are
| likely to lose some due to radiation and space dust.
|
| Launch once an hour and hopefully your communication system can
| handle hops of 4 or more ships, which would be 4 hours * 0.01C
| = 0.04 light hours or about 1/3rd the way to mars. With some
| fancy encoding that doesn't seem so hard. People get across the
| earth on a few watts with signals 20db below the noise floor,
| no line of site, and a message energy sapping atmosphere and
| bounces off not particularly reflective soil.
|
| For some idea on the difficulty, with 1970s tech (45 years
| ago), voyager 1 has a 22 watt transmitter and is still
| communicating from well past pluto.
| denton-scratch wrote:
| I'm not ssure it's ethical to deliberately send organisms to a
| distant planet. A novel organism can destroy all other life on a
| planet; it happened here.
|
| https://en.wikipedia.org/wiki/Cyanobacteria
| BurningFrog wrote:
| On the plus side, it could seed life on a lifeless planet.
|
| The probability that some earth bacteria would outcompete the
| local fauna on a planet it was not evolved for seems impossible
| to know.
|
| But my guess is very close to 0.
| Balero wrote:
| To be clear, you are not suggesting that Cyanobacteria
| originated from extraterrestrial origins. But when it evolved
| on earth, it then wiped out all non-Cyanobacteria?
| denton-scratch wrote:
| No, I'm not suggesting that!
|
| When cyanobacteria evolved, they filled the world with
| molecular oxygen, which was toxic to most of the other
| organisms on Earth. The cyanobacteria could cope with the O2;
| so effectively, they terraformed the Earth into a place they
| could live, at the expense of the organisms that were doing
| very nicely, thank you, until the cyanobacteria turned up.
|
| I don't believe that life travels between stars.
|
| It can't happen by accident; it has to be done by a
| sophisticated civilisation. The only evidence I have of such
| a civilisation is ours, and it's only been able to launch
| space rockets for a few decades. And our civilisation was
| living in caves just a few millennia ago. I have no reason to
| believe we are more than a flash in the pan. I feel sure that
| in a few more millennia, if we're still around, we won't be
| interested in interstellar probes we fired-off in antiquity.
| SideburnsOfDoom wrote:
| > But when it evolved on earth, it then wiped out all non-
| Cyanobacteria?
|
| Most, not all were either wiped out or survive only in small
| anaerobic niches. It was a mass extinction.
|
| https://en.wikipedia.org/wiki/Great_Oxidation_Event
| teeray wrote:
| Seriously... if a space probe filled with alien bacteria
| crashed into Earth and started wiping out life... well, we'd
| consider that an attack.
| dylan604 wrote:
| Or maybe someone had a rounding/least significant digit error
| and was aiming at Mars but hit Earth by a mistake? Obviously,
| they'd be calling the planets other names like Kepler-186f
| assuming they had a similar honorific naming convention.
| squarefoot wrote:
| What if one day we discover that bacteria sent from a distant
| star over here actually _started_ life on earth?
| denton-scratch wrote:
| > bacteria sent from a distant star
|
| I'm sort-of OK with the idea that life travels through
| space as fungus spores, or something like that. I'm not OK
| with the idea that they are "sent". So I can believe that
| life on Earth "fell from the sky". But I don't think that's
| really what happened.
| teeray wrote:
| The strawman would not change our reaction to a meteor
| filled with alien life that starts killing off the
| population.
| mannerheim wrote:
| Doesn't sound like the probe would be landing on a planet. At a
| fifth of the speed of light, there's no slowing down enough to
| do anything more than a flyby.
| denton-scratch wrote:
| If there's no plan to land, why the living cargo? But I
| agree, it isn't possible to land, except in a very high-
| energy crash. So again, why the living cargo?
| mannerheim wrote:
| I have no idea. Some sort of time capsule for aliens who
| catch it? Seems kind of pointless otherwise.
| elorant wrote:
| And what happens if the probe crashes on the planet with that
| much kinetic energy?
| kspacewalk2 wrote:
| Total annihilation of the tiny, light probe and its
| contents happens. It will either burn up in the atmosphere
| before impact, or if none is there this event be negligible
| compared to all other space objects impacting said planet.
| revolvingocelot wrote:
| At least the c. elegans don't survive to fuck up the
| biosphere, as per the root comment.
| BenjiWiebe wrote:
| If it's a few grams of mass and a few m2 of area, it will
| evaporate if it hits any atmosphere.
| fallingfrog wrote:
| It will be the size of a compact disc though. I'm not
| sure it will encounter enough atmosphere to absorb that
| much kinetic energy before it hits the ground. Meteors
| enter the atmosphere at 37 miles per second; this will be
| going a thousand times as fast. It will probably look
| like an instantaneous vertical spike of incredible
| brightness followed by a fairly large impact explosion. I
| imagine that at .2c the atoms of atmosphere would be
| essentially stationary, so the trail through the
| atmosphere would be a cylinder of total vacume surrounded
| by a rapidly expanding shell of exotic high energy
| particles. The air would be ionized and conduct a lot of
| electric current too, so this would be followed by a
| humongous lightning bolt. All that momentum is focused in
| a single direction, straight down- so I imagine the probe
| would penetrate pretty deep into the planet's crust,
| straight through to the mantle, maybe, which might cause
| a volcanic eruption. Would be quite a sight to see, I
| imagine. Like god's railgun.
| dylan604 wrote:
| This _NEEDS_ to be a scene in a disaster pr0n movie.
| Where 's JJ's Bad Robot when you need it?
| kristjansson wrote:
| This is the greatest thing I've read all week
| SideburnsOfDoom wrote:
| It's also way overestimating things. More like 10x the
| 2013 Chelyabinsk meteor
|
| https://news.ycombinator.com/item?id=33177030
|
| "Straight down" is odds against. Over a place that's not
| empty land or water is also odds against.
| JackFr wrote:
| > All that momentum is focused in a single direction,
| straight down
|
| Well, no. Straight down is possible, but not necessary or
| even necessarily likely.
|
| I think there's relatively little empirical evidence with
| respect to relativistic collisions at macroscopic scales,
| but isn't there a simpler conservation of energy argument
| to be made? Absent fancy orbital mechanics maneuvers,
| isn't the upper bound of the 'planet killing' energy of
| impact the total energy imparted by the accelerating
| lasers?
|
| Or am I missing something (could be physics was 30+ years
| ago.)
| SideburnsOfDoom wrote:
| > isn't the upper bound of the energy
|
| The energy of a 10g object at 0.2c is not just bounded,
| it is calculatable, and not really that large. The earth
| has had worse encounters, multiple times, in the last
| century. The above wildly overstates even a "best case
| straight down direct hit" scenario.
|
| https://news.ycombinator.com/item?id=33177030
| andrewmutz wrote:
| Space is massive and planets with life on them are (at
| best) extremely scarce.
|
| This probe crashing in to a planet that any life form cares
| about would be extremely unlikely.
| BenjiWiebe wrote:
| Also figuring 10g of mass, an online calculator suggests it
| would have about 4 megatons of tnt worth of kinetic energy,
| or 8% of the Tsar Bomba. Not negligible but not planet
| destroying either.
| [deleted]
| philipkglass wrote:
| I get 1.85 * 10^13 joules for 10 grams at 0.2 c from
| https://physicscalc.com/physics/relativistic-kinetic-
| energy-..., or about 4.4 kilotons of TNT equivalent. I
| think that you may have slipped a factor of 1000
| somewhere (calculating for a 10 kilogram probe, maybe?)
| Archelaos wrote:
| I also checked it, but you were faster to publish. My
| result was also 4.4 kilotons TNT equivalent, not
| megatons.
| SideburnsOfDoom wrote:
| for comparison, the 2013 Chelyabinsk meteor was
| "estimated ... to be equivalent to the blast yield of
| 400-500 kilotons of TNT"
|
| And it caused broken windows, other damage, over 1000
| injuries.
|
| This would be 10x larger?
|
| To be fair, if that meteor had hit over a big city, it
| would have caused much more damage. More probable if it
| had hit over open ocean, it would have done very little.
|
| https://en.wikipedia.org/wiki/Chelyabinsk_meteor
| LeifCarrotson wrote:
| That's almost suspiciously similar to the Tunguska event,
| [1] a 3-30 megaton event from 1908, which flattened a
| large area of Siberian forest. Airburst meteorites hit
| fairly frequently in our solar system.
|
| I don't even know if you could detect a difference
| between an extrasolar high-velocity (60,000 km/s) low-
| mass (10^-2 kg) airburst and an interplanetary
| 'low'-velocity (27 km/s) high-mass (10^+9 kg) airburst.
|
| Importantly, these events are purely thermal, not
| nuclear, so there would be no radioactive fallout.
|
| [1] https://en.wikipedia.org/wiki/Tunguska_event
| [deleted]
| rapind wrote:
| Slow version of the Death Star. 1) Send Cyanobacteria out. 2)
| Wait a few billion years for a competitive animal to evolve and
| nuke the planet to pieces. 3) Profit! (mine the asteroids).
| rnk wrote:
| This plan to spread organisms is criminal. It's insane,
| dangerous, should be blocked. We haven't even decided if we
| should do this in our own solar system, it's extremely
| controversial just going to Mars or other planets with only our
| earthly life known - we could impact life, including microbes
| on Mars, Europa or wherever it may be.
|
| Spreading living organisms far beyond our solar system is
| clearly a bad idea at this stage of development and knowledge.
| We could easily destroy other ecosystems. Imagine how we'd feel
| if the opposite happened. Of course anyone who pays attention
| knows that we have discovered all the precursors of life, the 4
| genetic bases (one of them is different between rna and dna so
| there are kind of 5 but they found that 5th one too) - we've
| already detected them in space, which is amazing in itself.
| It's extremely likely there will be other places in the
| universe, almost certain based on the number of galaxies and
| stars, that other planets have life on them. We can't just dump
| a bunch of developed microbes there that might have unknown
| effects.
| MockObject wrote:
| It's not obvious what ethics means outside the biosphere. By
| default, the biospheres exist in a _state of nature_ with
| respect to each other.
| alkonaut wrote:
| And I'm sure no one would ever do that without careful
| consideration. And this, obviously, isn't that. Not least
| because it's passing at 0.2c with no chance of stopping. If it
| hits a planet by an extremely unlikely accident it will be
| converted into a very brief firework.
| mcguire wrote:
| Why bother doing it at all?
|
| Do you have any reason to believe C. elegans or tardigrades
| will behave differently in the vicinity of Alpha Centauri?
| Wouldn't that mass be better used doing just about anything
| else?
| alkonaut wrote:
| Not sure tbh (might be clarified in the article). Could be
| just the combination of whether they survive the travel
| _and_ a reasonable milestone for the trip? I doubt there is
| any combination 1) between including living organisms and
| 2) passing a specific place in space. My hunch is that it's
| two separate goals done on the same trip.
| denton-scratch wrote:
| What is the mass of a few hundred tardigrades?
| swamp40 wrote:
| They should have included a way to kill it after the experiment
| was over.
| SideburnsOfDoom wrote:
| Impact at 0.2c will take care of that.
|
| Not impacting and sailing off into the dark for a few
| megayears is slower but also effective.
| spinlock wrote:
| I was thinking that I wouldn't appreciate aliens sending crazy
| microbes to earth just to see what happens.
|
| It's weird that NASA is funding the DEEP-IN part of the project
| but not the microbe part. IMO you cannot separate the two.
| spaetzleesser wrote:
| You can separate them. You want to send probes with sensors
| and get the data back. Just don't send microbes.
| dclowd9901 wrote:
| Since there's no objective morality, I'd say, for us, thank
| goodness it did.
| pokstad wrote:
| Reminds me of the Staircase program in the book Deaths End (third
| book of the Three Body Problem trilogy).
| idiocrat wrote:
| Perhaps it will quickly become mushy minced goo, a mix of protein
| parts -- after so many years of radiation.
| mofosyne wrote:
| Sounds like an important fact to figure out if true or not.
| That would inform if our exploration should be purely AI based
| or if we can transport humans across the stars.
| Pxtl wrote:
| Realistically our _existence_ will be purely AI based by the
| time we figure out how to transport things across the stars,
| if ever.
| DrBazza wrote:
| I thought there was another name for it, but it seems that the
| Wait Calculation, is applicable right now, i.e. if we send
| something now, we might as well wait for X years and send
| something that's faster and will over take whatever we send now.
|
| https://en.wikipedia.org/wiki/Interstellar_travel#Wait_calcu...
| tyho wrote:
| The wait calculation doesn't really apply to this project. The
| whole basis of it is that new technology can't speed up probes
| you have already launched. This isn't true for these probes as
| improvements in technology can be used to increase the speed of
| the probes that have already been launched. It also assumes
| that the bulk of the investment is in the hardware that's
| launched. With this project, the expensive stuff stays on the
| ground, the probes are cheap.
| cletus wrote:
| I love futurist content. Isaac Arthur's channel on Youtube is a
| fantastic resource for this. I'm convinced that a Dyson Swarm (ie
| orbitals around a star to near-fully capture the energy output of
| the Sun) is our inevitable future because it doesn't require any
| new physics or exotic tech. Specifically, solar power and
| stainless steel get you most of the way there. It just makes too
| much sense.
|
| This has all sorts of implications but an important one is how do
| you travel between stars. The rocket equation is bad news for
| interstellar travel. Getting to any significant percent of light
| speed (and decelerating at the other end) requires an insanely
| massive amount of energy that we really don't have any likely
| feasible method without exotic things like antimatter or black
| hole propulsion (yes, this is a thing). Even on vast timescales,
| you almost need viable nuclear fusion, which is far from a
| certainty.
|
| But these all assume you carry your fuel, which is the real
| tyranny of the rocket equation. Photos of course have momentum.
| Enough of them can be used as a form of propulsion, which is what
| the Starlight project is about.
|
| So one proposal for interstellar travel is so-called interstellar
| highways where energy from a star is concentrated to provide
| propulsion. You then only have to carry fuel to deceleate.
| Alternatively you can pre-build infrastructure to use the same
| technique to slow you down at the other end.
|
| Personally, i think this is likely the only viable method we've
| thus far conceived. I encourage you go watch this [1] if this
| interests you.
|
| [1]:https://www.youtube.com/watch?v=oDR4AHYRmlk
| JohnJamesRambo wrote:
| Re: Dyson Swarm not needing new tech
|
| 1. How do you keep the swarm from hitting each other and
| staying in the same place and not crashing into the sun as you
| capture the near-full output of the star?
|
| 2. How do you get the power transmitted to our planet?
| sbierwagen wrote:
| The outer layers will be heavily shadowed by the inner
| layers, of course. The builder will keep manufacturing nodes
| until it hits some equilibrium point between node
| manufacturing cost and how much power it captures over its
| lifetime.
|
| If nodes are cheap and lifetimes are centuries long you could
| be fine with outer nodes that only get 0.1% as much sunlight
| as the innermost nodes.
| sliken wrote:
| 1. Each one tracks it's nearest neighbors, which should have
| approximately zero differential velocity. A few gyroscopes or
| actuators to change the mirrors angles should give you plenty
| of thrust for controlling orbits. Inevitably probes will
| drift outward without counter thrust, after all they are
| basically solar sails. You could also use lasers, microwaves,
| or similar to cooperatively fly together without colliding.
| Of course you don't have to be perfect, just good enough that
| more expensive solutions aren't worth it.
|
| 2. Why bother? Make fuel, like antimatter for instance. Then
| launch them to where you need them. Maybe by a relay system
| and you could use the kinetic energy to help keep your ideal
| orbit.
|
| Keep in mind these don't have to last forever. Maybe have 3
| different designs for how close you are to the sun. Then you
| get installed in the inner most orbit of that band, then
| during your useful life you edge towards the outside edge of
| the band, launching anti matter payloads periodically and
| then get recycled at the outer edge. As long as you collect
| significantly more energy than your production cost it's a
| big win.
| ncmncm wrote:
| The planet does not need the power; it gets all it needs. It
| is used in space.
|
| They don't crash into each other for the same reason our
| satellites (mostly) don't: they are in selected orbits.
|
| But if we have not worked out aneutronic fusion by the time
| we would be able to build something like this, you might as
| well write off humanity.
|
| By then all the action will be out in the Kuiper Belt, where
| the truly valuable resource is: cold.
| vinaypai wrote:
| > They don't crash into each other for the same reason our
| satellites (mostly) don't: they are in selected orbits.
|
| Real world orbits != Kerbal space program orbits
|
| Things don't stay put in an orbit because the (a) earth
| isn't a perfect uniform sphere (b) gravitational influences
| from the rest of the solar system will perturb things.
| Satellites needs regular stationkeeping to keep them in
| specific orbits.
|
| And that is even though low earth orbit is mostly empty.
| There are only about 27,000 "objects larger than a
| softball" according to NASA's orbital debris and spacecraft
| tracking.
|
| To build a Dyson swarm you'd need to scale that up
| trillions of times to capture a significant portion of the
| Sun's output.
| skykooler wrote:
| Satellites in a Dyson swarm can use the Sun's light for
| stationkeeping, acting as a solar sail. It doesn't work
| that well at Earth's distance to the sun but the swarm
| would be much closer to maximise power production per
| satellite.
| ncmncm wrote:
| Presumably the energy would then be delivered to where it
| is needed via laser. With so many high-power laser beams
| going all the time, inner-system navigation might be
| hazardous.
|
| All the more reason to stay out in the Kuiper Belt.
| cletus wrote:
| The worst case is orbitals will require some active
| stationkeeping.
|
| If your civilization goes the route of interstellar
| highways well you already have the ability to focus a
| large amount of power on a sail of some sort to give
| propulsion. You could use exactly the same thing to
| correct orbits.
|
| It's also worth noting that orbitals around the Sun are a
| whole lot bigger volume than orbits around the Earth. LEO
| orbits have a radius of 6500-7000km. The Earth is
| 150,000,000km from the Sun so the radius of that is about
| 8 orders of magnitude more.
|
| If you assume orbits between Venus and Mars and include
| orbits off the Solar plane, the math for a full Dyson
| swarm the math (IIRC) works out to a mean distance
| between orbitals of around 100,000km, even with trillions
| of them.
| Ancalagon wrote:
| 1. ion engines and solar panels and plutonium
|
| 2. microwaves
|
| I think a bigger issue would be gathering the material and
| fuel to even consider this a probable future.
| exitb wrote:
| At 1/5th of speed of light the probes would cover 1AU in less
| than an hour, so the visit in the area would be extremely brief.
| Is there actually a way to get any meaningful data out of it? Or
| is it just so we can say that we've "been" there?
| SideburnsOfDoom wrote:
| Regardless of travel speed, it would take a lot of energy to
| get matter or even any identifiable bits of data back from
| Alpha Centauri to here.
|
| I don't see any discussion of how they propose to tackle that
| problem.
| ncmncm wrote:
| It is never even hinted how any information could ever be
| communicated back to Earth.
|
| It makes me think the whole project is not serious, like
| launching Voyager with no Deep Space Network to listen.
|
| Are they hoping that over the 40 years it takes to get there,
| a solar-system-sized radio telescope would be built to
| listen? Even with that it is implausible.
| simonh wrote:
| IIRC the idea is to send a chain of probes at regular
| intervals, and the probes would relay signals back along
| the chain.
| ncmncm wrote:
| So, even less plausible than a solar-system-sized radio
| telescope.
| skykooler wrote:
| According to https://en.wikipedia.org/wiki/Breakthrough_Sta
| rshot#Laser_da..., the probes should be able to talk to a
| 30-meter telescope on earth using lasers. The data rates
| are very low, of course, but that can be handled by making
| sure the probe has enough storage for its few-hour-long
| transit of the system and then transmitting that back over
| the following months.
| ncmncm wrote:
| How do they get the laser out there? What powers it?
| 0xf00ff00f wrote:
| From
| https://arxiv.org/ftp/arxiv/papers/2005/2005.08940.pdf
|
| > The sailcraft transmits 100 Watts, deriving its power
| from a 700-Watt hydrogen beam that is normally incident
| on the sailcraft when it faces Earth. This hydrogen beam
| is simply a manifestation of the interstellar medium,
| incident on the sailcraft at 0.2 c.
|
| From https://arxiv.org/pdf/1805.01306.pdf
|
| > One way to tap the sailcraft's kinetic energy could be
| via the interstellar medium: The Local Interstellar Cloud
| is primarily composed of 0.3 atoms/cm3 of partially
| ionized hydrogen. From the sailcraft's perspective
| traveling at cruise velocity, this manifests as a
| monochromatic hydrogen beam that is incident from the
| direction of travel, having a combined kinetic energy of
| 55W m-2, or 0.7 kW over the sail's area if it faces the
| direction of travel.
|
| The report for Starlight suggests a RTG:
|
| https://www.nasa.gov/sites/default/files/atoms/files/road
| map...
| UberFly wrote:
| I was thinking the same thing. That part seems like an
| afterthought. The real interesting part is the laser
| propulsion.
| Tepix wrote:
| The answer is to send not one probe, but many (thousands).
|
| If every probe manages to capture and transmit a couple dozen
| pictures while it is within the interesting range, it adds up.
|
| Also these probes could use each other as relays if we send a
| long string of them towards one destination.
| ianai wrote:
| Yeah. What I'd really like is proposals/discussion around
| intrastellar travel infrastructure like this. Park sources of
| light and coms at certain key locations around the solar
| system to enable faster traffic. Maybe hollow out some larger
| asteroids for habitats.
| cee_el123 wrote:
| as far as comms goes - nothing can speed it up - but yes
| the idea of using relays makes comms more
| reliable/repairable
| ianai wrote:
| Right, it's not about speed but the message reliably
| getting there.
| rthomas6 wrote:
| I wonder if it could unfurl a light sail when it got most of
| the way there to slow it down. Is that feasible?
| kadoban wrote:
| In short: no. It'd need to slow down enough to counter-act
| years worth of a laser specifically making it go faster.
| Without a laser on the other end, really no shot.
| KineticLensman wrote:
| >> Each spacecraft would be the size of a DVD disc
|
| Not much room for a light sail large enough to fully offset
| the power of the launch lasers.
| exitb wrote:
| Interesting idea, but I don't think the sail would be nearly
| enough to counteract the gravitational acceleration caused by
| getting near the target system, let alone losing enough speed
| to enter an orbit.
| fallingknife wrote:
| If you are able to determine orbital parameters of planets
| we'll enough, that would be more than enough time to get much
| better pictures of exoplanets than any telescope.
| spaetzleesser wrote:
| Why would you waste weight and send organisms? I can't see
| anything useful coming out of it. And it would be sad if these
| organism wiped out alien life.
|
| The probes need as many sensors as possible. It will already be
| super tricky to make any observations from a probe that goes at a
| tenth of the speed of light. And how do you get your data back
| from that distance without huge antennas?
| noduerme wrote:
| It's a great proposal, it's been around for some time. Who's
| going to implement it? I could see Musk throwing some spare
| change at it, but 20+ years is a long time to wait for a news
| cycle.
| sph wrote:
| Can we stop calling for notoriously fickle Elon Musk to lead
| space innovation?
|
| SpaceX is great, but it's starting to feel more and more like a
| cult of personality, and not that great of a personality
| either. Any time there's a post about space on social media (HN
| included), there's always some starry eyed commenters saying
| "Musk could maybe do it".
|
| It's not like he needs more publicity.
| fallingknife wrote:
| No one alive on Earth today has both the level of ability to
| execute and the available funds to match Elon Musk.
| skykooler wrote:
| I think it's mainly because there are basically only two
| individuals who own a space company and have the money to do
| a project like this. And Bezos has not been very successful
| at getting things done, space-wise.
| SturgeonsLaw wrote:
| The privatisation of spaceflight is opening up a new era, and
| will lead to an increasing pace of innovation in the space (get
| it), but this is why there should always be a place for
| publicly funded space projects, a la NASA.
|
| We all progress when there are entities out there who can take
| on the big, long term projects that don't have an ROI measured
| in quarters.
| onethought wrote:
| But NASA floundered about without even a launch capability
| for over a decade until private sector not measuring ROI in
| quarters with a long term vision to reach mars came along.
|
| Literally your example is the inverse of what has occurred.
| SpaceX sparked this current era, NASA in fact piggybacked on
| it, now that the cost of launch is lower NASAs fiddling
| around the edges is somewhat useful. But everyone is waiting
| around for SpaceX to solve the hard problems (cheap tonnage
| to orbit, and multi-planetary landing systems)... because
| NASA didn't.
|
| (Admittedly NASA funds are funding a lot of SpaceX)
| fallingknife wrote:
| The main reason for the rocket failure is because it wasn't
| a rocket program. It was a jobs program. NASA actually does
| extremely well with its science missions, because they are
| actually science missions, and not jobs programs.
| ceejayoz wrote:
| > But everyone is waiting around for SpaceX to solve the
| hard problems (cheap tonnage to orbit, and multi-planetary
| landing systems)... because NASA didn't. (Admittedly NASA
| funds are funding a lot of SpaceX)
|
| I don't think you're giving NASA enough credit here. The
| Commercial Crew and Cargo programs were innovative bets
| that paid off in spades. I hope they do more like it.
|
| I tend to blame the floundering period on Congress.
| onion2k wrote:
| If there's intelligent life at the other end they're going to be
| serious confused about how some microbes built a probe.
| barbegal wrote:
| The physics doesn't stack up for me. The spacecraft must be
| lightweight so it can be accelerated to high speeds but it must
| also have a very large area such that a large proportion of the
| laser photons hit it. This means a very thin disc shaped
| spacecraft (a few grams but with a few m2 of area). Whilst this
| may be able to be constructed it would be incredibly delicate for
| launch and I can't see how it would have the required strength to
| avoid it tearing apart under the force applied by the laser
| photons.
|
| A paper produced looking at the feasibility of such a system
| https://arxiv.org/pdf/1604.01356.pdf says
|
| >A critical issue will be the stability of the sail. There are a
| number of perturbative effects. These include laser instabilities
| and laser mode issues, differential forces on the sail and
| mechanical modes in the sail, heating of the sail and laser
| pointing instability. >This is a complex sets of issues that
| requires a significant amount of research and development. This
| will not be trivial.
|
| I believe these issues are show stopping rather than "not
| trivial" You can never fabricate a probe of small enough mass
| which has enough area for laser propulsion to work effectively
| whilst not tearing itself to pieces or overheating (at least not
| to anywhere near relativistic speeds).
| marcosdumay wrote:
| Well, you are referencing a paper that says they already got
| material good enough for 1% of c. The fact that the target of
| 25% of c is still not achieved isn't as large a showstopper as
| you are making it to be.
| fnordpiglet wrote:
| I have over 500 hours on kerbal space program and have been
| playing with the KSPIE mod that enables beamed power and sails.
| They definitely work.
| barbegal wrote:
| Oh yeah they work fine when you neglect certain critical
| parameters. How hot do your solar sails get in Kerbal? And
| what is the maximum torque between the sail and the
| spacecraft in Kerbal?
| simonh wrote:
| I suspect a close proximity of tongue and cheek in that
| comment.
| fnordpiglet wrote:
| They do actually. It's a really good game and mod. Highly
| recommend it. Especially if you need to use a solar sail
| that works
| LegitShady wrote:
| (in kerbal space program)
| fnordpiglet wrote:
| I mount my games.
| usrusr wrote:
| > "and the data they produce will be sent back to Earth"
|
| That's where my optimism limiters were triggered: sending
| something in the general direction of earth is all nice and
| well, but receiving that signal, sent from the confines of a
| "DVD sized" emitter, against the backdrop of a nearby star?
| They should try to find a way to harness optimism for
| propulsion...
| cee_el123 wrote:
| perhaps that can be overcome by a train/succession of such
| probes relaying the signals over shorter distances ?
| usrusr wrote:
| But how much shorter? Light years are a long distance to
| cover with relay stations if their peer to peer range is
| not unlimited. And when "DVD sized" should include both
| sender and receiver, p2p range most certainly won't be
| "astronomical" (which it would quite literally have to be).
| The relay approach implies symmetry and usually what we do
| with probes is the opposite, compensate a smaller device on
| one end with a bigger device on the other end.
| sliken wrote:
| Voyager 1 uses 22 watts and 1970s technology to
| communicate from 21 light hours away.
|
| Radio encoding has come a long way since then. In
| particular ft8/js8call uses an encoding that can
| communicate at over 20 db below the noise floor, allowing
| communications across the earth with a few watts which
| involves many 1000s of miles of atmosphere, bouncing
| (poorly) off the upper atmosphere and the ground many
| times.
|
| If we launched one an hour at 5% of C (better than today,
| but much worse than the goals of the project) they would
| only have to communicate across hops of 3 light minutes,
| er about half that since 5% of C is the final velocity
| not the average. Considering voyagers success at 21 light
| hours and the improvements in encoding that sounds quite
| feasible.
| usefulcat wrote:
| Let's say they make a sail that is large enough and light
| enough to allow the craft to accelerate to very high speeds
| (say, 0.1 - 0.2c?). It's quite a long way to Alpha Centauri,
| and even though interstellar space is very empty, it's not
| completely empty. As the sail hits the odd spec of dust here
| and there at those speeds it seems like it will be shredded.
| Maybe it's ok as long as it lasts long enough for it to be
| accelerated to a 'fast enough' speed?
| Ancalagon wrote:
| The original idea I recall for this was to send hundreds of
| these probes with the hope that a few might make it (because
| this launch method and the probes would be relatively cheap
| once you built out the laser system).
|
| But also, interstellar vacuum is very, very empty.
| Encountering a speck of dust even in that distance with that
| size of a probe is a pretty negligible risk if I recall
| correctly.
| fallingfrog wrote:
| I wonder- would an observer in the Alpha Centauri system be able
| to pick up the accelerating laser with a telescope? That would be
| a pretty powerful and tightly directed beam. If an observer did,
| they would have a few years advance warning and know the exact
| trajectory of the probe.
| sliken wrote:
| Exact?
|
| I've been hearing launch times in the minutes to hours before
| the probe is too far away to accelerate it enough to be worth
| while. The problem is lasers (on those scales) spread quickly
| so an ever smaller (even with perfect aiming) fraction of the
| laser energy will be delivered to the probe.
|
| I am curious if the red shift at 1% of the speed of light is
| enough to throw off the efficiency of the material that's
| designed for a specific laser frequency.
|
| For the same reason the cone of light will be larger than the
| orbit of any planets around Alpha Centauri. So the exact
| direction is tough, but that it's heading towards Alpha
| Centauri is easy.
|
| The formula for the angle (in radians) of dispersion: (The
| laser's wavelength)/(p x The laser's aperture)
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