Stealth Spaceships

Stealth Spaceships

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This episode is brought to you by Morning Brew. Possibly the biggest difference between detecting  a ship in space as opposed to on Earth is that   there is no horizon to hide behind… except  perhaps for a black hole’s event horizon. Probably one of the most popular tropes in  science fiction is the idea of the stealth   or cloaked enemy vessel, station,  or even planet. For today’s Scifi   Sunday I thought we would explain why stealth  in space is considered so difficult to achieve   and discuss a few of the possible  workarounds to each hurdle to hiding things.   As always this will be a detailed discussion  of the topic, so if you can slip past your   housemates unnoticed, go discreetly grab a drink  and a snack and settle in for a while with us.  I want to emphasize though that under known  science the burden is high for achieving stealth   and a lot of our workarounds will qualify as what  we call Clarketech, technologies so advanced they   are Indistinguishable from Magic, and probably  technologies that will be fictional for a very   long time and maybe forever. With that in mind,  it is a good choice for a Scifi Sunday since we  

tend to relax how stringently we stick to known  physics compared to our regular Thursday episodes.  We probably need to start by asking what we  mean by stealth. We are talking about hiding a   spaceship from physical detection from an opponent  with roughly equal resources and technology.   I feel this is a fair point to emphasize on  the grounds that your biggest motivation for   stealth in science fiction is usually trying to  sneak to seize tactical or strategic advantages,   and you do not need those if you are some advanced  civilization going up against one much younger,   smaller, and less technologically advanced.  You can just go in and kick their butts,  

and sneaking up on your enemy can be reserved  for when you don’t already have armadas orders   of magnitude bigger, each composed of ships  able to destroy their armadas single-handedly.  So we are talking about stealth as hiding  physically from a technologically equal watcher,   but we’ll exclude trickery like getting an inside  man in to shut off their detection grid or feed   it shovelfuls of garbage data. Note that these  are two exceptions to our no stealth in space   rule already, and neither should be ignored.  Anthropological surveying of primitive alien  

worlds might require hiding from the natives  and certainly implies no parity of technology   on their part. So too, an awful lot of sneaking  and stealth in modern and historical contexts   is achieved by trickery or bribery or so on. Another option for sneaking in undetected is   to be trying for a level of stealth deemed to have  a prohibitive cost to benefit ratio for detection.  

In other words, your adversary could detect any  vessel you send at them, if they’re willing to   dedicate unlimited resources, technology,  and manpower to watching for it. But there   is always going to be a point at which the  expense of bigger detectors, more detectors,   better processing of data, and vast manpower  exceeds their desire for it or their resources.  As an example if the defense agency deems the  most stealthy threat to your solar system to   be a Relativistic Kill Missile, or RKM, and  deems themselves able to safely destroy one   a light day out without endangering those in the  inner system, and the current grid already allows   detection of them fully a light month out, it is  hard to justify the need to expand that grid out   to a light year. You might do it anyway, but  if the junior Senator from Pluto rises to ask   for quadrupling the defense budget to build a grid  able to detect them a light year out--and maintain   that extended network for decades or centuries--  some might argue that it is pointlessly expensive.  The counter argument might be that the detection  level necessary to see a RKM that far out was also   what was needed to see some unknown but plausible  new threat under development. Or perhaps even an  

indirect threat like a small probe that might  latch onto an Oort Cloud object, where it could   quietly hide and spy on the system, so a bigger  grid was necessary for those, the unknown threat   and the spy. However, that might be deemed the  sort of thing that just wasn’t worth preventing,   trying to stop unknown unknowns or keep them from  spying on you. Especially given that enemy’s with   little intel or bad intel on their neighbors  often act dangerously erratically, as many   argue often happened in the Cold War. Sometimes  you want the enemy to know what you are doing,   and not for the purpose of intimidation  or misdirection, since having them think   you are building a giant fleet when you are not  might make them act desperately to counter that.  There is also something to be said about openness  as a policy as an alternative to stealth.  

In the Star Trek setting, at least in the Mid-90s  TNG and DS9 eras, we see the Romulans and Klingons   both possessing stealth technology, cloaking  fields, but the Federation not having them.   There are some contradictory reasons offered  for this but the main presented reason   is a treaty between the Federation and Romulans  that the Federation won’t use cloaking technology.  On the surface this sounds like the sort  of negotiated deal that only happens when   you just unconditionally surrendered after  losing or your negotiators turn out to be   taking bribes from the other team. However  it is worth noting that we don’t know what  

the Federation might have gotten in exchange  for that, and one also has to acknowledge that   while cloaking technology very much fits the  sneaky conniving Romulan civilization we see,   with lots of intrigue and misdirection  throughout their culture and government,   it is the polar opposite to the way the  Federation normally acts and idealizes.  For long-time Trek fans, it's fair to say that  a cloaking field doesn’t really benefit the   Federation much, they already have holograms  for hiding from low-tech civilizations they   are studying, for obeying the Prime Directive,  and that’s their only real desire for stealth.   Examples like Section 31 aside, the presumption  on the Federation is that it's pretty open   about what Starfleet does and genuinely respects  concepts like “the People have a right to know”.  The Federation’s whole Modus Operandi is  non-stealth, and they probably assumed with   good reason that they could nullify the stealth  edge when needed. Indeed, depending on the episode  

they seem to have a detection grid in place that  at least alerts them when cloaked vessels enter   the Neutral Zone. Alternatively their society  isn’t well-configured for keeping secrets   so stealthy bases on the enemy’s border, or  those of prospective new members and allies,   would probably be detected through espionage.  Or even just reading the newspaper.  The cloaking device tends to be pivotal to a lot  of debates on how the Federation does things and   acts as a proxy for how we ought to do things.  Personally I’m opposed to the Prime Directive, and   I don’t approve of spying on the natives because  I wouldn’t approve of my neighbor spying on me,   but the Federation at least offers a  reasonably ethical reason for hiding   themselves from primitive cultures. I emphasize that because I mentioned   how a civilization is bound to draw some sort  of risk vs cost line on how big and omnipresent   their detection grid needs to be, but they  also might not like the idea of their own   government being quite that omniscient since  it might turn its eye on its own citizens too,   and thus they might build internal blindspots in. Indeed that same sort of acceptable or even  

intentional weakness is what enemy saboteurs can  take advantage of. Such being the case you might   even limit your external capabilities somewhat  in acknowledgement that the new extended detector   offers minimal advantage but the enemy could  easily hire a mercenary strike force from   your own population to go blow it up for a  thousandth the price you pay to maintain it.  Now those are some ways you can sneak  around without needing to be stealthed,   but we’re really interested in physically  hiding right now, and that’s very difficult.   To explain why, let’s start by pointing out that  the light coming from the dimmest stars visible   to the naked eye hits Earth with a brightness per  unit area of about 20 nanowatts per square meter.  

In relative terms, we can see the star Vega  very clearly even though it's 25 light years,   or 240 trillion kilometers, away. It  is the second brightest star in the sky   and the one whose apparent magnitude  is set at exactly 0 for that scale.   It gives off roughly 16 x 10^27 Watts of power,  40 times what our Sun emits. It would drop off  

the edge of naked-eye visible if moved about 20  times farther away, where it would be 20-squared   or 400 times dimmer. In other words, something  400 times dimmer than Vega appears in our sky   would be just barely visible to the naked eye. Needless to say we can do a lot better than the   naked eye, but as an example of the visibility of  spacecraft, the old Shuttles on takeoff emitted   around 12 gigawatts of heat and light as they  launched. Vega is more than a billion, billion   times brighter than that, but because light falls  off with the inverse square of distance, the   shuttle would be roughly as bright as Vega when it  was about billionth as far away or about 277,000   kilometers away, nearly as far as the Moon is. The  shuttle should still be naked-eye visible over 5  

million kilometers away with main engines on. Keep  that in mind when next reading a scifi story about   a daring smuggler landing their ship undetected on  a planet. Our best modern optical telescopes could   see that shuttle-bright object about 10,000 times  further away incidentally, out at distances we   only discuss in terms of AU or light days, 360 AU  or 2 light days, about ten times the distance to   Pluto. We might assume more advanced civilizations  have better telescopes than our current ones.  Obviously you would have to be looking  right at the object to see it, which is   a distinct limitation with a telescope as it  necessarily has a very limited range of view,   but it illustrates a point that is probably as  relevant as the claim that there is no stealth   in space, and that is that any stealth you had is  gone the moment the searcher has good reason to   point their gear in your general direction. It is also important to understand that the  

Shuttle’s drive is far too weak to do anything  like the maneuvering the way we see on your   typical stealthy scifi spaceship. They need  more power than that, and a powerful engine   emits either EM radiation or very hot gas that  gives off EM radiation. But their only methods   for stealth are either to find some way not to  emit it at all, to direct most of it in a way that   will miss the enemy’s detectors, or to have that  power come out as something they cannot detect.   Your eye for instance can’t see infrared light  or radio waves, and while we can make instruments   that can see those, we have a hard time seeing  neutrinos and still can’t see dark matter.  So if your thrust is coming out as neutrinos or  dark matter, you would be quite stealthy to us,   but it also implies you have a material  for deflecting, reflecting, or absorbing   neutrinos or dark matter and those are capable of  interacting with those particles by definition,   so you can also use them to build detectors for  those particles. Which triggers our earlier caveat  

about how we aren’t discussing your ability to  be stealthy to a searcher whose technology is   way inferior to your own. In other words, if you  can build a drive based on some exotic technology,   assume your adversaries can build detectors  based on it too. This is usually much easier.  The thing is, even these seemingly invisible  things as propellants, invisible to us anyway,   still would not result in a ship we could  not detect. Everything in known physics emits  

light – and truth be told even black holes are not  really an exception to this, not in a practical   sense. The frequency of that light can vary, ultra  hot things can emit frequencies far higher than   our eye can see, like ultraviolet or even X-rays  or Gamma rays. Colder objects can emit frequencies   far lower than we can see, like infrared and  microwaves, but nothing can really stay as cold   or colder than the ambient local temperature,  and that is 2.7 Kelvin everywhere from the Cosmic   Microwave Background Radiation, and in fact higher  inside galaxies and higher yet in a solar system.  We can detect microwaves and we could detect  something that was somehow even cooler and gave   off radio waves as its blackbody radiation. This  is the light emitted simply by an object having a   surface that is not at absolute zero. As a quick  note though, this is not totally undetectable but  

it is pretty dark. An object at a mere 5 or 6  Kelvin, double the CMB but probably as cold as   you could plausibly get the hull of a spaceship  to be for an extended period even with everything   shut off including life support, would emit  less than 100 microwatts per square meter,   several million times less than the infrared  emitted by a room temperature object per square   meter of surface area. Very weak, but remember  what we calculated with seeing a star or space   shuttles. A cellphone or walkie talkie or  wifi router is only broadcasting 10-10,000   times stronger than a single square meter of that  ship’s hull is emitting. That ship is probably   a lot bigger than a square meter. Remember that  we could hear the voyager space probe even after   it went past Pluto and its radio transmitter  was only a bit stronger than your cellphone. 

So everything emits light, in some frequency  or another and the frequencies and spectrum it   emits tells us a lot, indeed you can calculate  speed off the redshift or blue shift of the   light off from what you would anticipate from  other characteristics of the ship or object.  Not only does everything emit light, everything  also has specific amounts it reflects, absorbs,   or transmits light through itself, and for  any given frequency of incoming light too.   This means it's very hard to be stealthy against  someone engaging in an active scan, which is where   you emit light at an object and see what bounces  back rather than just what hits it naturally.  A couple things folks forget when  discussing this topic a lot. First,  

they are not limited to detecting return signals  from the emitter, which is how we can outfox a   lot of terrestrial radar systems with clever  bouncing of radar signals hitting an aircraft.   Especially if it's their home system, they  probably have millions of satellites scattered all   over the place that can pick up scattered signals. You have to remember the plausible scale of such   civilizations, they really ought not be  tiny little villages on a single planet   in an otherwise empty solar system, they  probably have billions of space habitats on, in,   or around every hunk of rock in that system home  to quadrillions of people all living on an economy   powered by cheap energy and smart automation.  They don’t have a starship or two out patrolling   deep space and a few defense satellites,  they’ve got scouts, vanguards, and picket   ship squadrons that probably would dwarf the  typical high-budget scifi films displayed armadas.  And you have to remember that scale, when they  send out an active signal, if they want to,   they can be ‘pinging’ a pocket of space with  thermonuclear warheads, not flashlights,   and probably have directional detection beams  that can turn gigawatts of power on some tiny   volume of suspect space whole light years away. But suppose your ship has a magic ultra-black   hull that can absorb any frequency  of light it encounters. That’s great,  

now it gets warmed up by that light and emits  blackbody radiation. Your ship was already   emitting blackbody radiation, so the increase and  frequency tells your enemy even more about you.  Okay, instead your ship can scatter light,  perfectly reflect it and away. That is also great,   your enemy probably has probes and detectors  all over the place, especially in their home   turf. They probably also know about the trick of  using a signal as their active detection emission.   So you’re not just bouncing some random light off,  you’re bouncing a specific frequency with some   pattern in it too, like the time the signal  was sent at and the ID code of the sender.  

Now two other detectors at different angles  pick that up and between the two of them   they know exactly where you were  when that signal bounced off you.  That does still leave being transparent to  the light, but we will come back to that.  You also have to worry about blocking ambient  light, all those stars behind you, and while   you can simulate those by having lights on your  hull of the right wavelengths, mimicking the   spectrum of the star you would be blocking, that  obviously only works on one single line of sight.   Folks off to the side wouldn’t expect you to  block that star and would think it weird to   pickup that frequency. That said, that is a good  way to sneak toward a star system. You come in   from the direction of a very distant and bright  star, or a galaxy or Nebula that’s a bit of blob,   and because solar systems are huge but still tiny  compared to interstellar distances, this means you   have to be pretty close – in interstellar terms –  before the folks on Mars or Ganymede will notice   that there’s a dot in front or just to the edge of  that distant Hypergiant or galaxy that isn’t quite   reading what it should or is not reading what  the folks over at Venus or Neptune are getting. 

Indeed this is one reason we suggested colonizing  the Oort Cloud, in the episode of that name.   You would put detectors way out at light  months of distance from each other,   and vastly extend your parallax or how far out you  could be seeing reflected and scattered emissions.   Using absorbed emissions, would allow you to  detect a ship passing through a beam of light   between two places, and you could also detect a  break in that light beam if you had a signal in it   and were spinning it around and reading  its scatter or lack thereof from drops   when something absorbed it for a brief instant. Though as a caveat and speaking of light beams,   a ship mounting several beam or laser arrays each  capable of emitting a picked spectrum could aim   one at Earth, one at Mars, one at Venus and  so on so that each got a tailored spectrum.  

In this way each can be fed a different beam  mimicking a different direction tailored to   what you want them to see. This trick would only  work if you knew where their detectors were all   at and would be hard to pull off, but  same as you can't hide from them normally,   their detectors are likely to be known to you too. So everything emits light and everything reflects,   scatters, and absorbs light. Everything moving through space  

also has to move through everything in space  too. By and large a spaceship while coasting is   pretty stealthy, especially compared to when it  does anything to change its speed or direction.   Any use of thrust is going to be a big  signal flare and will be hard to hide   by imposing something between you and the other  folks, like an asteroid, for three big reasons. 

First, Let’s say you’re using an asteroid for  cover. Light from your exhaust may not be visible,   but you still have a big stream of hot gas blowing  backwards. Hot gas gives off light, and gas   scatters and absorbs light in a characteristic  fashion. So your rocket plume is still very   visible and this would probably apply to most  other drives we might imagine in some way too.   Second, you’re only invisible to folks  on the opposite side of that asteroid,   so same as with trying to ride a star in as cover  like we just discussed, by mimicking its signal,   anybody at a different angle is going to see you. And third, the faster you are going relative to  

that object, the less time you  have for pulling any maneuvers.   A rapid course change at interplanetary  speeds will kill everyone in that ship,   and if you’re going much faster than the tens of  kilometers per second we consider interplanetary,   less than a thousandth of light speed,  you would even manage to kill cyborgs,   posthumans, androids, or AI with such a tight  turn. If you don’t complete the turn that fast,   they still see you. Turning behind something  big and distant like a star helps, so fleets   might alter course when they thought they  had a star between them and their enemy,   but their enemy probably would be aware that  blind spot was coming up and pay close attention. 

Don’t rely on trying to turn behind a black  hole either, they are actually smaller than such   asteroids and they won’t hide your turn unless you  make it inside the event horizon, in which case   you are successfully stealthed but you would never  get a chance to brag about the accomplishment.  Conversations about stealth in space tend to often  bring in black holes and I would warn folks off   assuming they offer any advantages for that. Black  holes are not invisible, you would never have a   shot of getting a normal black hole undetected  anywhere near a star system. And beyond being   very visible in terms of their gravitational pull,  in the electromagnetic sense they are just much   darker than stars, except for when there’s lots of  gas and dust nearby them, in which case they can   be much brighter than stars. And that brings  up interstellar gas because it is everywhere  

and denser in some spots and it reacts to being  hit by fast moving objects. Space may be pretty   empty but when you are moving at a decent fraction  of light speed you are hitting a lot of gas and   dust particles and each is going off with energies  comparable to atomic bombs, or even antimatter,   in terms of energy released per unit of mass. This is not something that is terribly stealthy,   and the faster you want to go, the  bigger this signature is going to be,   rising loosely with the cube of speed even before  factoring in relativistic effects. If you go ten   times faster each collision carries ten-squared  more energy, and collisions with gas and dust   are happening ten times as often since you plow  through ten times as much space every moment.  

10 times the speed, 10-cubed means 1000 times  the power signature of plowing through space.   On the alternate side of this, the slower you go,  the more time the enemy has to detect you and the   more time they have to act once you are detected. This does bring up one other example of effective   stealth though, because same as you often have to  uncloak in fiction to fire your weapons, there is   a point at which you are going to get detected  and there is a point at which that no longer   matters, especially if you don’t have a crew on  board that needs to survive. It is hard to throw  

a black hole at a star system without someone  noticing, not just the gravity but the accretion   disc it will pick up as it travels and all the  light and gas it will bend or accelerate and   all the signals passing by it that it will warp. Still it’s a lot stealthier than a star of equal   mass and it has an advantage going for it:  It is really hard to do anything to stop a   black hole rolling into your solar system  even with light years of advanced notice.  See our episode Weaponizing Black Holes for  a lot of the uses as well as the counters   and counter-counters of various natural  and artificial black holes as weapons. 

So that’s the basic of why we  say there is no stealth in space,   in one sense it is hyperbole, we  gave plenty of ways you can hide,   but in another it’s one of those really  ironclad statements approaching a law,   like thermodynamics, entropy, and no free lunches,  or faster than light travel. You need a perpetual   motion machine or warp drive or time machine,  various bits of Clarketech, to violate those.  To close for the day, those also offer  some possible modes of stealth but often   the technology offers a means of detection too,  which is why I put that caveat near the beginning   about stealth only counting for opponents of  similar technological prowess. A time machine can  

obviously let you avoid detection, you just jump  back before their detector grid existed and blowup   the folks who designed it, or the amoeba they  evolved from. Same some material that lets you   turn into a phantom or ghost who doesn’t interact  with outside particles, be it interstellar gas or   photons, might permit stealth but makes navigation  difficult for you too. The tech that might permit   you to navigate while in phantom mode probably  can be used to detect ships in phantom mode too.  A FTL drive, or Faster than Light drive, lets you  arrive before the light you are emitting arrives,   or the light they bounced  off you as you approached.   Some sort of perpetual motion  machine, violating entropy as it does,   might offer true cooling, even down to near  absolute zero temperatures of nanokelvin,   rather than our normal method of just moving heat  around. A ship propelled by selected matter to  

energy conversion might be able to convert matter  into beams of neutrinos to shoot out the back,   and further aim them off in directions so  no one directly behind them and pursuing   them could detect. Or directly in front  of them as they slowed to attack a planet.  But beware assuming these offer no counter. If  your ship runs by shooting some faster than light   particle out the back, or communicates to home  with such particles, then the enemy sensors can   detect those particles. If you’ve got perpetual  motion machines for keeping your ship eternally  

supercool, then the enemy has them for generating  constant and powerful active detectors and more   importantly maybe, for running their economy and  factories to churn out endless armies of probes.   We also need to keep that in mind for  quasi-stealth options like slipping your   ship in as a mundane natural object or as one  tiny ship with a fake transponder code around   a busy planet’s orbital space. This might  work but do need to be kept in context,   that such civilizations probably  do have those swarms of probes   and detectors and countless humans or AI checking  for anomalies in the data, but such pathways   probably do offer a better chance for success. We never know what new science and technology  

might emerge to shatter this apparent rule about  stealth in space, but hopefully by now it's   clearer why this is so hard. Feel free to suggest  and debate some scenarios for stealth in space   with hypothetical technologies in the comments  below, or for ways to do stealth under known   science too of course, if you can think of one. I’ve heard a lot of them suggested over the years,   but if there’s a way to be unseen under  known science, I have yet to see it.  So we were talking about stealth spaceships  today sneaking up on us and I suspect I’m   not the only one who often checks my social  media only to find out some new crisis or   talking point has snuck up on me that  everyone seems to be talking about. On   the other hand it’s just plain unhealthy  to tune into the 24/7 doom-and-gloom news   cycle. You need to keep up with the news  though and that’s why I read Morning Brew. 

It’s a daily Free Newsletter that gets you update  on tech, business, and finance news in just five   minutes, replacing dry, dense, and boring news  with witty, relevant, and informative content   and in a fast fashion that lets me get up to date  on the world in five minutes over a cup of coffee.   So I can get updates on the current space race  or how Bitcoin and cryptocurrency are doing,   and again all the content is free, it  only takes about 15 seconds to subscribe.  To envision the future we need to  stay up to date on the present,   and if you’re interested in business, finance,  or tech, there’s no reason not to subscribe,   just click the link in the episode description and  start waking up with Morning Brew every morning. So we looked at hiding spaceships today  and on September 23rd we’ll continue   that discussion by looking at not just at  hiding spaceships but entire civilizations,   as we return to the Fermi  Paradox for Hidden Civilizations.   Before that though, next week we will celebrate  the 7th anniversary of our first episode,   Megastructures in Science and Science Fiction, by  looking at Megastructure Death, on September 16th.  

Then we’ll have our Monthly Livestream Q&A  on Sunday, September 26th at 4pm Eastern   Time before closing the month out by asking  if it’s possible for future civilizations   to exist without money, on Sept 30th. Now if you want to make sure you get notified   when those episodes come out, make sure subscribe  to the channel, and if you enjoyed the episode,   don’t forget to hit the like button and share it  with others. If you’d like to help support future   episodes, you can donate to us on Patreon, or our  website,, which are linked in the   episode description below, along with all of our  various social media forums where you can get   updates and chat with others about the concepts  in the episodes and many other futuristic ideas.  Until next time thanks for  watching, and have a great week!

2021-09-13 21:57

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