Starlight interstellar probe
en.wikipedia.org
en.wikipedia.org
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.
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.
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.)
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.
I did misspeak I said "straight down", that's not necessarily true. Could be along a diagonal at any angle.
With respect, I think that _is exactly_ how a meteor works.
So the extreme velocity times smaller mass gives us a middling kinetic energy. The difference, the extreme velocity, means that the energy is burned up as the object disintegrates into atoms over milliseconds not seconds as a regular meteor with the same energy would. Atoms and small fragments won't sustain their velocity.
There's a fast bright flash of superheated air, a clap of thunder as the trail collapses, done.
Respect to you as well!
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.
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.
This probe crashing in to a planet that any life form cares about would be extremely unlikely.
Most, not all were either wiped out or survive only in small anaerobic niches. It was a mass extinction.
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.
Not impacting and sailing off into the dark for a few megayears is slower but also effective.
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.
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.
I think in a few years we'll find some kinds of microbes on mars or other bodies. If nothing else they came from earth, floating around, but more probably they are created everywhere naturally by dna molecules just randomly combining. Anyway, when we find life on mars, or Europe or where-ever, should we not allow people to send earth based microbes to do things. We could send lichen to mars to start growing, maybe it would survive and it might kill native microbes. Is that okay? I think it's not but it's pretty complicated and maybe inevitable. Also I think with meteors hitting mars they are probably knocking bits of dust into the air and eventually they hit here. Same for earth to mars but our atmosphere blocks them.
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?
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.
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).
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...
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.
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.
Actually capturing an object with that much velocity would require a high level of sophistication, very fast reactions, and a big energy budget.
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. 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?
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.
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.
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.
Stray light from all those x-ray lasers blasting in all directions 24/7 ought to make anything like this easy to spot.
All the more reason to stay out in the Kuiper Belt.
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.
2. microwaves
I think a bigger issue would be gathering the material and fuel to even consider this a probable future.
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.
Not much room for a light sail large enough to fully offset the power of the launch lasers.
I don't see any discussion of how they propose to tackle that problem.
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.
> 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/roadmap...
Actually it would vaporize any part of the system needed to control or communicate.
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.
https://en.wikipedia.org/wiki/Interstellar_travel#Wait_calcu...
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.
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)
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.
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.
what? I thought most materials would be obliterated by the damage caused by traveling through the interstellar medium at such speeds.
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.
Incredible. This is simply incredible. I hope humanity succeeds here.
Ah, ah, it's something I know as well!
> 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...
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.
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?
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.
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)/(π × The laser's aperture)