Interstellar Probes
This episode is sponsored by Raycon. “Only those who will risk going too far can possibly find out how far one can go.” – T.S.
Eliot. In last month’s episode, Surveying for Habitable Interstellar Star Systems, I mentioned that as soon as I started the topic, I knew it was going to require more than one episode; so we briefly discussed interstellar probes and manned scouting missions down to a planet in that episode, but we focused on distant astronomical techniques. Today, we’ll be taking a deeper dive into interstellar probes, both flyby-missions and long-term orbiters. However, we’ll follow up the next two weeks with a look at slow-boat colonization of the galaxy at less than 1% light speed, what we call “Crawlonizing”, and the week after that we’ll be asking what life as a Planetary Explorer will be like. Today our focus is on those probes though so don’t forget to subscribe and hit the notifications bell if you want alerts when those and other episodes come out. In our Surveying episode, we pointed out that the nature of telescopes and probes at the interstellar scale meant that you could always get a probe to park itself around a world a little bit quicker than the time it would take for a colonization fleet to arrive, but that a flyby probe, since it can use all of its fuel for accelerating and doesn’t need to save any for decelerating, can get there in half the time, and, of course, a telescope can actually get there backward in time, seeing the world not when your probe arrives, but as it was when light from it left and got to us back here.
Let’s create an example to give this some context, with a system about 100 light years away, where we’ll imagine that we detect an anomaly right before the start of the 22nd century. After short discussion and the New Year’s celebration, its decided to investigate. A flyby probe launched in the year 2100 AD, sent out to achieve 10% of light speed to a system about 100 light years away, Epsilon Fornacis, one of the dimmest stars visible to the Naked Eye, an ancient binary system composed of both a star that’s a bit less massive than our own, and its medium-distant binary neighbor, about half our Sun’s Mass, estimated to be in excess of 12 billion years old. This is not a great place to be hunting for rocky planets, being so old that it predates most supernovae, but we got a ping, not much, just a brief bit of signal that might have been natural or might not have been, in that hazy “Wow! Signal” range of uncertainty, and when we examined it with an available telescope, some of the spectrography and infrared didn’t really match what we expected. So, right away, 6 things happen: First, a signal is sent out to that system, initially, several loud attention-getting signals, then a lexicon, and a general greeting, along with informing them that probes are en route and their ETA and trajectory are given, along with a self-destruct code.
They are then told that manned missions will follow and that if either a specified signal is sent or the self-destruct alert signal from the probes is received, that mission will abort. In this way, not only have we said hello and established a method of communication if anyone is there, we’ve made every reasonable attempt to avoid giving the impression of being reckless, neglectful or threatening, but without including unnecessary delays. Of course, if we don’t get a response, we may wait until hearing back from the probe before deciding to send a manned probe, but in this case we won’t those two centuries.
Second, Epsilon Fornacis gets a telescope dedicated to staring at it, with a variety of instruments, which is nicknamed Nicolas, in honor of Nicolas-Louis de Lacaille, the astronomer who first documented the Constellation Fornax, during his time at the Cape of Good Hope in the 1750s, though he originally named it the Chemical Furnace. The telescope Nicolas sees the system as it was in the year 2000, a century back, when the light left. They will be monitoring this system for the next few thousand years. Third, the flyby probe, Louis, is launched to reach 10% of light speed, and will arrive in 1000 years, the year 3100 AD.
This would actually be a little over 1100 years after the initial anomaly was detected. Some additional probes are sent out towards plausible colonization candidates in that same general trajectory. Fourth, the probe carrier Lacaille is launched, carrying squadrons of various planetary and solar probes at 5% light speed, and able to accelerate and decelerate at 100 gees, they need about 9 hours total to speed up and slow down, and they will arrive January 1, 4100 AD. Fifth, the Firefly, a vanguard manned vessel is launched that will move at 5% light speed as well, but will only accelerate at 5 gees, and thus they will arrive on January 3, 4100 AD. The crew will exist in suspended animation, having received prototype augmentation and nanotechnology.
The volunteers have been informed that this is high-risk. Sixth, Musketeer, an armed colony fleet of three Super-Orion-Drive vessels, the Athos, Porthos, and Aramis, will be launched and will also travel at 5% light speed, but it will use a classic ark ship approach, a big rotating habitat drum, and will not exceed a tenth of a gee of acceleration, thus will arrive July 1st of 4100 AD. No significant construction times are needed as everything has been re-tasked from other colonial ventures and there is heavy automation in 22nd century manufacturing. The colony ship will be able to send information and directives to the probes and receive information from them, and thus will be able to redirect the second wave of probes off the flyby data. Similarly, the Vanguard team will gain consciousness a bit later, by January 4th and review the first 4 days of second-wave probe data, while having just under 6 months before the colony fleet arrives.
Complicating factors are numerous, hence Louis, the flyby probe and the second-wave probe on board Lacaille, if they determine the system is unexpectedly hostile, natural or by alien artifice, can send an abort code to the Firefly or Musketeer to divert to another of the potentially habitable worlds further out that would require minimum delta-v to redirect to, that we sent those other flyby probes to. But the efforts of the Firefly and Musketeer will depend entirely on what the Louis and Lacaille probes will achieve, and it’s the efforts of these two probes that we will consider today. Firefly and Musketeer will have to wait a couple weeks for their episode. Now, Louis is no simple camera on a power supply with a transmitter, he is a 50-ton probe, shaped like a needle, now wrapped in his cloak, the remnants of the vast solar sail he powered out of the Sol System with that now serves as radiation shielding, where before, it was a kilometer-wide sheet of slowly self-healing reflective foil, designed to be targeted by lasers to push him up to speed, then retracted to minimize interstellar collisions and reduce wear and tear. Louis can spin this back out to serve as a massive parabolic dish, both for communication back home and for serving as a mirror for its own telescopes.
This may also be used as it approaches a star to slow or redirect it, and to funnel light to a solar panel for recharging its graphene batteries. Louis is not a complex AI, he knows his job and very little else. He has a number of smaller probes he can detach and give a tiny shove to the side, and he plans to do this as he approaches Epsilon Fornacis and can combine information from Telescope Nicolas back home, and his own sensor, to get locations for planets or any other objects of interest. Louis is aware he has a small thermonuclear device on board, that can be triggered by himself or others with the right code, and this does not bother him.
Given that he is a 50-ton object moving at 10% of light speed, and thus has a kinetic energy equal to over 5000 megatons of atomic weapons, more than existed during the Cold War, Louis would not assume this nuclear bomb was intended as a weapon of aggression. Louis’s protocols include a number of self-destruct failsafes, for scenarios like him finding himself on an intercept course with a planet or clearly artificial structure, or if he loses the ability to determine this, such as instrument failure. It is designed to shred him down to the molecules, where his fragments, moving at 10% of light speed, wouldn’t be big enough to harm anything they collide with eons later. Fragments need to be small though, even a tiny sliver of metal, no bigger than a pencil, weighing maybe 10 grams, would carry about a kiloton of explosive power. For this reason, like most of the probes in his class, Louis also includes a number of small spikes he can send out to hit objects, causing a nuclear-level explosion, whose dust and debris clouds could be analyzed by his instruments to tell him more about that object’s makeup, however, these have been explicitly disabled for this mission. Mission control does not expect to find anything alien, but it considers this much more likely than normal and is intent on making sure it doesn’t accidentally blow up any aliens or start a war.
With that in mind, no AI will have any capacity for doing damage and even the manned missions have strong controls in place. This is an important thing with any interstellar probe, you need to contemplate any reasonably plausible way the thing might inflict damage, particularly if it suffers damage itself. So if Louis can no longer see his surroundings clearly, he can no longer be sure he’s not on a collision trajectory and will need to self-destruct once a reasonable effort is made to repair or restore those, if unsuccesful. Same for if his beacons go out, because he’s cruising along at 10% light speed and that means, without a beacon, he’s not really very easy to see in time to react if you just happen to be some small outpost or vessel.
His actual odds of running into anything are virtually nil, even if his trip was across the whole galaxy, but sending a probe into a system where there is a suspicion there’s a civilization means raising those odds immensely, as does sending it on a straight-line path between any two star systems, where, if there are ships traveling between them, would be where those ships are most likely to be traveling. Space is huge but those straight corridors between stars are much smaller and thus you have better odds of encountering someone traveling between two planets, especially two with bio or technosignatures. Sending it into where there might be a lot of spaceships and space habitats makes that even worse, and while our telescopes will have picked up every planet and maybe even every dwarf planet or larger moon by then, space habitats or ships might be harder to pinpoint. And an unknown alien beacon is likely to be something that people, or aliens, would want to rendezvous with and dissect. With that in mind, you need to make sure the self-destruct goes off only when the probe is disabled but before a lack of sensory data could cause it to unknowingly detonate within range of someone who would be damaged by the blast.
Which is to say, if it goes blind from sensor damage, it needs to detonate itself before someone could plausibly have gotten into range of it or its own path unknowingly wandered of course into something. After that, it can't know if someone has rendezvoused with it or its veered toward a colonized system. And its giant detonation also tells anyone watching it that it has detonated and need no longer be worried about. There’s a second aspect of this too, because we need to contemplate any reasonably plausible way that the thing might inflict damage, and that includes psychological and diplomatic damage, like them worrying the message and detonation was a ruse and the probe is still coming toward them on course to hit their world. Any probe is a two-way street when it comes to information, at least if those the probe goes to look at are aware of its existence. If they’re a technological civilization, they likely will have the ability to spot anything moving into their system at dangerous kinetic energies.
Stealth is very difficult in space, especially when trying to stealth something threatening, because that’s exactly what folks are going to build their detection gear to find and its not likely to be hard to get a budget through your alien congress or parliament for detecting 5000 Megaton bombs headed into your colonized system. If your aims are peaceful and you want to build a relationship with aliens, it helps to make it clear that you were thoughtful when you built your probes, and that means assuming they will either dissect your probe or do a public records request to get the schematics and mission planning one day. First impressions are probably as important to aliens as to us, and while science fiction likes to show us horribly misunderstanding a peaceful alien who merely ‘seemed hostile’, so that we needlessly attacked them, we don’t want to stick aliens in a similar situation where they thought our intent was hostile when it wasn’t. We want to build trust from day 1, as well as an incentive to work with us, and that means making it clear we not only have good intentions, but are also competent and thoughtful. Thus good potential partners and allies and dangerous enemies. That means that even though we’re anthropomorphizing Louis the Probe here, we didn’t send an advanced AI on our probe that was smart enough to even vaguely qualify as human, for four reasons: First, we don’t need that much brains on a camera.
Second, we don’t want to be throwing artificial intelligence out into the galaxy, far from where humans can check up on them and see that they’re not mutating horribly, which means not sending probes out to where we’ll never follow or will be centuries following up, that have high intelligence and any sort of capacity of self-replication, which a self-repair system might be jury-rigged to work as. That’s how you get von Neumann Berserker Probes, or grey goo, in the galaxy. Third, we don’t want aliens thinking we’d casually do that either. And fourth, we don’t want our first interaction with another intelligent species very unlike us to involve them seeing us using an AI – an intelligent entity very unlike us - as a disposable slave with orders to commit suicide. It might give them the wrong impression about us.
Or, it might give them a bad impression anyway, and hopefully a wrong one. The critical concept is that, before we ever send an interstellar probe out, we need to have a good idea how it might be viewed by others, especially if we have any plausible expectations that there are going to be other sentient lifeforms at its destination. This is just as important as all instruments we’ll be using to view those star systems, to help make sure what we see isn’t an alien armada packing up and heading our way to discuss the 5000 megaton bomb we slammed into one of their worlds or artificial habitats. So, Louis is very much built along the lines of being a harmless probe, but without forgetting that he also looks like a giant doomsday device.
Of course he still has a real mission, which is providing us with intel on what’s assumed to be an uninhabited solar system, just maybe less guaranteed to be one than normal. While he’s been traveling towards this system, Louis has been continuing to get updates from home, and realistically, that will include every planet in that solar system’s approximate orbital path and timing. In this particular case, it’s actually got three different solar systems to be looking for, as the primary and secondary are far enough apart to possibly have stable orbits in their habitable zones while also potentially having habitable worlds orbiting around both stars, circumbinary, at least in terms of what is habitable to technological civilizations. This is complicated because the primary star, while less massive than our own Sun, is much older, and is now a subgiant that’s grown brighter as it has aged, and is four and half times brighter than our Sun is today, with a habitable zone that’s 212% the width of our sun’s, but would have been only 60% as bright as our sun during its main sequence, and its habitable zone only 77% as wide as ours.
Meaning, if anyone evolved on a world here, billions of years before, they either had to migrate or do some serious planetary engineering to keep their homeworld livable. The secondary star is only a few percent as bright as our Sun, and even a world that’s a fifth of an AU away might be too cold to live on. But, of course, that’s not what we’re really looking for, because we’re looking for either a place that humans of the 42nd century will be able to colonize, or a place that emitted a technosignature in the year 2000 and either has survived for another 1100 years when Louis arrives, or has died off. None of those scenarios really care about naturally habitable worlds.
So, Louis can redivert a little bit, but essentially has to pick a straight-line path through this system that gives it a chance to photograph one planet decently up close, and the rest at distances of billions of kilometers. Those other planets will get a smaller probe detached from Louis, but they’ll basically be 20 kilogram cameras with a little guidance and solar panels and a charged up battery. They are going to detach if, and only if, Louis’ pre-programmed criteria, when he’s about a light year out, are satisfied that sending those probes on flybys isn’t going to cause a Kessler Syndrome event or any other kind of would-be catastrophe. Louis himself has a number of more detailed missions that will begin with that detaching and with spreading out his sails as he enters the system, at about 60 AU, for his window of roughly one week for useful observations.
He’s been repairing or re-melting his sail during his voyage so that it’s nice and smooth, and now configured as telescope mirrors, making it part of one giant telescope that Louis is transforming into, with a host of sensors that exceed his smaller, older cousins, Hubble and Webb. Louis will be passing by a world that’s half again as massive as Earth, that was almost an AU out from the primary, and is now quite hot and nearly airless but which may have been habitable millions of years ago. He will be taking pictures of many other things as he passes through though, being far more powerful than the smaller drones he dispatched to flyby each planet. These probes are going to tell us far more about each world than the Voyager probes could, but moving at 10% of light speed, they will have less than a minute where they will be as close to their planet as the moon is to us.
After that, their only remaining job will be to leave the sensors on for any other useful readings they might offer and to try to rendezvous with Louis, who will seek to either reabsorb them or send them their own detonation code once they’re back out to deep space, and their components would have lightyears to drift and fragment before encountering anything else. Louis will be attempting to use his sail to swing toward his follow-up star. Those lesser drone probes will not be as powerful as Hubble was and not have long to image, and Hubble could not see the Moon Landing Site in any detail from orbit of Earth, so we are not expecting zoomed in photos of alien lifeforms. But they will see every continent and mountain and larger lake and island, and they would see a city. Louis will do even better, though fundamentally his focus is really the whole system, and collecting and transmitting that data homeward. Nonetheless, he detects some interesting anomalies on that world as he passes closely, which we will now designate as Louis Epsilon Fornacis, or the planet Lef.
In a millenia, armed with Louis’s data, which it will receive in 3150 AD, the Lacaille Probe carrier will arrive, then slow, and will begin sending probes to orbit those worlds of interest. It will go and park itself in orbit around Lef, and begin taking detailed readings as good as our entire modern orbital surveillance grid can produce in terms of spysats, weather, infrared, and more. They will even be able to begin setting up ground-penetrating radar and microwave detectors to help look for signs of underground caves, tunnels, buried ruins, or bunkers. Though it will have only a few days to gather data before the Firefly arrives with its Planetary Explorers, but we’ll save that discussion, of Lef, its anomalies, and its intrepid human and robot explorers, for another day.
Now, how realistic was our tale? Ignoring my shoehorning-in a probable alien civilization? Well, it has a couple breaks with reality, though it’s hard to say where. For instance, I’ve made a big point of saying how a flyby probe can get away with traveling twice as fast as practically identical probes and ships meant to stop there, but that specifically has to do with propulsion systems that operate on the rocket equation, whether that’s chemical fuel, fission, fusion, or antimatter. In our case, its real speed would be about whatever speed we could achieve during the window back home where we can keep a laser focused on that probe, and the amount of energy we are willing and able to spend. Project Starshot thinks it can get probes up to a third of light speed with a ground-based laser, using essentially modern tech. Having gotten to meet its director, Peter Worden, and chat about it in person, I believe this will be possible, and in this century.
Truth be told, and for folks who remember our prior videos on laser propulsion, I already believed this, but Peter Worden is a compelling and expert speaker, and he burned out any lingering doubts I had. In such a setup, your flyby probe like Louis has only maneuvering fuel, and its speed has no relation to the other vessels that need to slow down using some sort of rocket, even if they were also laser propelled, and probably to a lower speed since the faster a laser can accelerate you, the more gees, the higher your speed when it loses contact at its maximum distance. In this case, I think flyby interstellar probes will be moving at a minimum of a third of light speed and maybe much higher, even 99% light speed, it will depend on how well we can absorb or evade interstellar dust collisions. Those other ships may be able to leave at the same speeds, though often would require a longer launch period and distance to avoid super-high acceleration routes, and unlike a flyby, they have to be able to slow from whatever speed they reach, which means they can’t go much faster than they could have without that light sail initial boost, though we discussed some tricks for that in our Exodus Fleet Episode.
I also assumed everyone launched at the same time, to emphasize the time difference that acceleration rate makes, which you wouldn’t expect to be the case with that colony ship at least. You might scramble a dozen explorers off for a hibernation ship on a few days notice, to prep the ship and give them time to say goodbye, as they’ll awake 2 millenia later, but that colony ark ship is not just going to be sitting, waiting with prepared colonists, and I can’t imagine rediverting a colony ship set to launch elsewhere without at least giving folks a chance to think on it and opt to wait for another ship. Though diverting a colony ship already part way toward another system and on a close enough path to be able to divert is also an option. There’s also that big question if you should be launching probes and scouts, let alone colony missions, before you have even given your signal time to reach them let alone receive a reply. In practice though, I think you would because two centuries is a long time to wait when if the answer is ‘abort mission’ it means you either redivert to another empty system or have on hand ambassadors ready to go. Keep in mind, we probably would not be offended by having an alien colony fleet show up, if they had pre-messaged us their friendly intent and offered to either redirect or settle some asteroid and serve as an embassy, to trade cultural knowledge and technology.
And as we discussed in Hidden Civilizations, there’s an expectation that you post clear no trespassing signs if you’re capable of doing so. I suspect you’d wait but not two centuries, just in the context of giving yourself more prep time for the colony and scout missions. Also if there are alien ruins, you don’t need a scout team of a dozen explorers, you need many thousands of archeologists and an infrastructure to supply them, there’s no villagers to buy food from on this planet and there’s an entire planet, or even solar system, that needs digging up. Still, the key concepts are there. Once you park things in orbit, the difference between a simple probe taking photos can begin blurring as we contemplate artificial intelligence and manned missions. How much AI you’re willing to give a probe matters a lot, and whether or not you want to give it self-repair and replication, and the ability to land on a planet.
If you do, then you’d probably first send it to an asteroid to eat the thing up and gain the resources needed for a major deployment system-wide, to orbit and down to the ground and potentially even acting as not just explorers, but colonizers, as we looked at in our seed ships and self-replicating robots episodes. Now, AI on interstellar probe missions is often regarded as a necessity, but I don’t think so. Reckless deployment of high-intelligence or self-replicators is dangerous, and if you trust the AI and it’s human smart, then I think that, practically and ethically, we’re talking about a kind of ‘manned mission’ the term just lacks some accuracy, but then it already does, which is why the term ‘crewed mission’ is often preferred. Today we were only contemplating sub-human intellect or none at all, I don’t really think the term ‘probe’ is really appropriate if it does have a real mind onboard it, natural, artificial or some blend of both. To me that’s a scout. What else is missing? Well, we’re not just surveying that whole system because we suspect it might have techno signatures and thus might have a presence off a habitable planet.
The normal job of these probes in any case where it’s not about some anomaly of scientific interest, like a tech or bio signature, is scoping for all those minor worlds and asteroids and nailing down their orbital paths during the week or so of flybys of the whole system, because to colonists, those low-gravity objects are the first point of interest in their chronology of colonizing a system. They’re not planning to go and orbit one planet and dump everything down on its surface, they want to get their orbital and interplanetary infrastructure started before descending down into a gravity well, and so they need a map of the best candidates for exploitation. We’ll examine both of these topics more in the next couple weeks though, as we look at slow colonization of the galaxy, crawlonizing, and find out what the anomaly was as Lacaille and Firefly arrive at Lef.
So a fairly critical concept to interstellar probes is that they let us get up close to an object, and that circumvents all the noise and signal loss. This same thing applies to listening to music or audiobooks and podcasts, and is why you want a nice pair of noise reducing or isolating earbuds, and I’ve been using my Raycon earbuds now for over 2 years to listen audiobooks while mowing my lawn or taking a nap and the other thing I love about them is that don’t fall out of my ear, whether I go over a bump or sleep on my side. Raycon’s Everyday Earbuds have optimized gel tips for the perfect in-ear fit, so they are comfortable and they will not budge or fall out, and they give you high quality audio at half the price of other premium audio brands. That’s probably while Raycon Everyday Earbuds have tens of thousands of 5-star reviews, including mine. The individual earbuds have a 8 hour playtime battery life and they recharge in their compact carrying case, for 32 hours of listening time without needing to plug into a wall, and they have a wireless charging feature for the case too you can try out.
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So if you’re looking for a great and affordable listening experience and want to help support our show while you’re at it, just click the link in the description box or go to buyraycon.com/isaacarthur to get 15% off your Raycon purchase! All right, that wraps us up for today but we’ll be back next Thursday to look at the concept of Crawl-onizing the Galaxy, how humanity can still settle the stars even if we are limited to spaceships moving at less than 1% of light speed, and what that will look like. Then we’ll have part 3 of today’s episode, as we join the scout missions down to Lef and see what Life as an Interplanetary Explorer might be like.
We’ll also have our livestream Q&A coming up Sunday, June 26th. Then it is on to July for a look at Deep Space Habitats, then Extragalactic Sanctuaries. If you want alerts when those and other episodes come out, don’t forget to subscribe to the channel and hit the notifications bell. And if you enjoyed today’s episode, and would like help support future episodes, you can got to our website, IsaacArthur.net, which we’ve recently relaunched new and improved, and check out our donate tab for ways to help, and all those other options are linked in the episode description, along with our social media forums like facebook, reddit, and discord, where you can chat with others about today’s episode and many other futuristic ideas. Until next time, thanks for watching, and have a great week!
2022-06-18 01:15
