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My idea is a corvette is dipped in radar reflecting paint that makes it look like a 50x50x70 foot asteroid. It shuts down its reactor and the crew all huddle in the ops deck with minimal heating and life support.

The ship sets itself drifting with a slow rotation to make it more asteroid like. Since it was launched in secret and almost no one knows about no one will be looking for it. Any ship that encounters it will just think it is an asteroid until it opens it torpedo tubes and its uber high tech jammers.

Will this stealth ship be able to escape detection and make it close enough to earth to destroy the shipyards?

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    $\begingroup$ "Captain, this is weird. There is an asteroid there but it doesn't show up on the radar." $\endgroup$
    – VLAZ
    Jan 6, 2021 at 13:38
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    $\begingroup$ It would show up on radar. The coating makes a scrambled return so it looks like an asteroid. \ $\endgroup$
    – 11Bravo
    Jan 6, 2021 at 13:46
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    $\begingroup$ An asteroid headed anywhere near a Collison course ship yard would be a pretty high priority target for removal. don't expect to fool them for long. $\endgroup$
    – John
    Jan 6, 2021 at 16:20
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    $\begingroup$ Link answers are bad, so I'll use comment then. projectrho.com/public_html/rocket/… Short version is that either your "asteroid" will be too unusually warm to pass as one, or your crew frozen to death long before reaching the target, since even zero degrees life support is about 70 Celcius warmer than your typical asteroid. $\endgroup$
    – Darth Biomech
    Jan 6, 2021 at 16:31
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    $\begingroup$ "Hey, Susan, that asteroid's orbit is going within torpedo range of the shipyard in a couple months. Put it on the to-be-nuked list for next week, will you? Can't be too careful." $\endgroup$
    – user535733
    Jan 6, 2021 at 17:35

11 Answers 11

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  • Don't use RAM paint. Use actual rock. Either outer hull plates made of rock cut to the right shape, or a ship tunneled into one genuine asteroid.
  • It is not just the crew that needs temperature. Power plants will produce waste heat, and without power the ship cannot sense, communicate, or shoot. Consider radiator panels on one side only, and hope that you are never outflanked.
  • Of course using the engines will probably produce a noticeable exhaust. A maneuvering ship can be detected and if it suddenly stops to maneuver the course will be quite predictable -- it is determined by the momentum and gravity wells. Once the ship is detected, breaking contact will be hard.
  • On the other hand, there are plenty of random rocks out there with different shape and albedo. Camouflaging as one of them should be relatively easy while the ship coasts.

So there are two conditions, and one potential problem:

  1. The ship must launch from a base which is not under observation, and never maneuver in view of a sensor.
  2. That means launching very far out, and coasting inward for a very long time.
  3. Earth might have defenses against natural asteroids.

The intruder must plot a fine line between being distant enough to be ignored, and close enough to shoot without lengthy (and detectable) maneuvers. It would help if they had the specs of the asteroid defense ...

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    $\begingroup$ There's also the main rule that people proposing stealthy ships in space often forget: assume the enemy has the same access to the same stealth tech, which means they can stealth their sensor platforms, and that will be a lot easier (they could, for instance, place them on actual asteroids in natural orbits, use passive sensors, and not require anywhere near the same amount of energy). So any stealth which relies on knowing where the enemy sensors are, such as directed radiators, runs into an immediate problem. $\endgroup$
    – Keith Morrison
    Jan 6, 2021 at 16:57
  • $\begingroup$ @KeithMorrison, two (or more) powers in the same system could then track the tugs emplacing sensors right from the factory if the factory is known and all departing drive signatures are watched. So stealth sensors need the tugs break contact. Maneuver out of sight of enemy stealth sensors? A nice chicken and egg. $\endgroup$
    – o.m.
    Jan 6, 2021 at 17:48
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    $\begingroup$ Not at all. You could send, for instance, research probes to visit a lot of asteroids, only some of which leave extra equipment behind. You could simply tell everyone where your sensors are, making sure that you'd force an enemy to have to use predictable trajectories in order to avoid them. You could put up a huge constellation, only some of which need be real. Or they may be cheap enough that they all are. $\endgroup$
    – Keith Morrison
    Jan 6, 2021 at 18:48
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    $\begingroup$ You'd basically be much better off just launching an actual asteroid at the planet, taking some erratic course that makes use of gravity boosts on its way. To make it more a sneak attack you could coat it with some special radar-absorbing paint from, say, Mars ahem $\endgroup$
    – Asteroids With Wings
    Jan 6, 2021 at 22:24
  • $\begingroup$ If you launch very far out that also means your trip takes a very very long time. long enough people may be able to try to harvest your asteroid since it will pass close by. $\endgroup$
    – John
    Jan 11, 2021 at 22:16
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What you describe is more camouflage than a stealthy set up, since your setup disguises the ship as an asteroid, it doesn't hide it.

I think it can be spotted by checking its orbital parameters: given its apparent size and its orbit it would be possible to estimate its mass once it passes close enough to another body or a probe is sent around it. That information would point that it is more empty than it looks, unless you disguise it the proper way. In other words, making it look like a icy asteroid will work better than making it look like an iron asteroid, because the apparent lower density can be more easily justified for the icy asteroid.

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    $\begingroup$ You would also probably have to ensure its not on a collison course with the earth otherwise we would probbaly try to destroy it. If you aimed it to be narrowly sailing straight past Earth we would probably leave it alone then just fire up the engines when your the closest. $\endgroup$
    – GamerGypps
    Jan 6, 2021 at 14:51
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    $\begingroup$ How are you estimating mass from size and orbit? $\endgroup$
    – fectin
    Jan 6, 2021 at 22:40
  • $\begingroup$ @fectin astronomy.stackexchange.com/a/6565 and quora.com/How-is-the-mass-of-a-celestial-body-measured $\endgroup$
    – L.Dutch ♦
    Jan 7, 2021 at 4:34
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    $\begingroup$ @L.Dutch-ReinstateMonica those links are both about estimating the mass of a very large object that exerts a measurable gravitational force on other objects. For a small object like an asteroid it can't be done. $\endgroup$
    – N. Virgo
    Jan 8, 2021 at 2:19
  • $\begingroup$ @Nathaniel citation needed. Rosetta has been able to estimate the mass of comet 67/P while orbiting it blogs.esa.int/rosetta/2014/08/21/… $\endgroup$
    – L.Dutch ♦
    Jan 8, 2021 at 3:37
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You can't hide in space.

Any space ship will produce waste heat, which has to be radiated into space, or else you'll cook the crew. This waste heat is very easy to pick out among the cold blackness of space. For perspective, we can pick up signals from the Voyager 1 probe, which is tens of millions of kilometers away, even though it has a paltry 20W power output, roughly the equivalent to a refrigerator light bulb. Running life support for the entire trip to earth at asteroid-like speeds without putting out any heat signature whatsoever likely is not feasible, unless your aliens can survive at extremely low temperatures.

See Is there any way to truly hide a spaceship? for lots more details on why it's impractical to carry a big heat sink and just not radiate anything, or to employ directional radiation methods.

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    $\begingroup$ But we've also tuned to the exact frequency of the Voyager 1 transmitter. If we didn't know the frequency, we probably couldn't detect the transmitter among the background noise. Could we detect its heat? No way. $\endgroup$
    – user253751
    Jan 7, 2021 at 0:08
  • $\begingroup$ I imagine it might also be possible to create a directional radiator, so you can still radiate heat but in a narrow beam which is far less likely to be detected. $\endgroup$
    – Turksarama
    Jan 7, 2021 at 2:09
  • $\begingroup$ Helium/hydrogen steamers are pretty much invisible in space, no? $\endgroup$
    – Jefferey Dawson
    Jan 7, 2021 at 8:53
  • $\begingroup$ @Turksarama It is, but a directional radiator needs to be increasingly large and complex as the angle of dispersion gets narrower, which eventually becomes so large that the apparatus needs its own radiator and the size/weight spirals out of control. Not totally impossible, but very impractical. $\endgroup$
    – Nuclear Hoagie
    Jan 7, 2021 at 14:19
  • $\begingroup$ @JeffereyDawson The exhaust might be invisible if its at ambient temperature, but the life support systems will necessarily produce waste heat. Unless you shut everything down and coast through space as an inert rock, any power usage at all will produce a heat signature. $\endgroup$
    – Nuclear Hoagie
    Jan 7, 2021 at 14:22
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The Hiding part of this can be made to work quite well.

Use a thin layer of actual rock. This will give it the correct radar and visual and thermal and spectroscopic appearance.
You might need to install some heat radiators to dispose of excess heat. Only operate them when facing away from all enemies, of course!

However, this will gain you almost nothing!

A 50x50x70 foot asteroid is a rare beast. A comparable meteor passes within 10 million km of Earth about once per year, only. (That's within 30 times the distance of the Moon!). You would have noticed the tabloid media going nuts about it every now and then.
One that happens to be headed on a near pass of any planet, base or shipyard will be scrutinized down to the last millimeter, even if only to ascertain it will not impact anything valuable. Such detail scrutiny will defeat the camouflage, rendering this approach useless.

But if you go smaller, yes. A 50x50x70 foot asteroid is a monster. But if you hide a bomb or a missile in a 5x5x7 foot asteroid, with similar grade stealth systems, then it is likely to pass inspection. Simply because there are more small asteroids than large ones. With occurrence roughly inversely related to mass. This tiny object, massing 1/1000th as much, will be roughly 1000 times more common (and 1/10th as easy to detect).
Earth routinely gets impacted by such smaller rocks 5-10 times per year, and hundreds of similar rocks pass within 1 million km of Earth each year.

What defeats your plan is the size (and thus rarity) of the fake asteroid needed to hide your ship.

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  • $\begingroup$ Essentially, the 100 duck-sized horses argument. :) It's not just that smaller asteroids are more difficult to detect, it's that there's so many of them that they essentially become background noise. I'd argue that as such, any sensor system would (could) only give such asteroids any more than a passing scan, and as such you wouldn't need to bother with any sort of stealth other than an outer rock sheath, which your missiles simply jettison when it's time for them to perform - essentially, swarm the enemy with an attack that pretty much can't be defended against. $\endgroup$
    – Ian Kemp
    Jan 8, 2021 at 14:00
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Apart from all of the other issues mentioned: any solar system developed enough for this to be a thing is likely a solar system that has mapped out all of its asteroids of this side, at which point your ship will be immediately obvious as "the asteroid that isn't in any of the records".

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  • $\begingroup$ +1 traking Near Earth Objects is already essential for operating the satelites currently in use. No civilization would develop spaceships and shipyards in orbit without mapping every single asteroid whose orbit comes anywhere near their solar system. Even a 1cm diameter rock smashing through the spaceship could have massive effects if it happens to strike the lifesupport systems (space debris goes at massive speeds and behaves much like a bullet). $\endgroup$
    – Poseidaan
    Jan 8, 2021 at 14:06
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The only way to achieve passive stealthiness is to have a ship that generates no heat, which is difficult under ideal circumstances and impossible with organic lifeforms aboard. So you need to have your "crew" be an AI, or the uploaded personalities of humans, that can be stored without energy usage.

Then you take an asteroid and build a ship into it. When the time comes to "launch" that ship, you use some kind of linear accelerator to fire it at Earth on the trajectory you desire. The ship starts off completely powered down so no heat output, but it has a timer in it set before the launch - when that timer triggers it opens a relay, and that brings your ship (and AI/personalities) online to fire whatever weapons they need. Off course, the defenders will light up your ship and crew pretty fast...

As such, this is likely going to be a one-way trip, so it's far simpler for your asteroid-ship to be controlled by a single, dumb computer program that wakes up, fires a bunch of torpedoes at a bunch of preselected targets, then overloads its reactor and self-destructs to prevent the enemy from figuring out precisely what just happened. You don't actually need a starship, just a stealthy weapons-delivery platform.

The alternative, much more reliable but much more difficult, approach is to compromise the sensor systems of your opponent (all of them, across all their ships too) so that any data read about your ship is ignored. A virus to achieve this would be incredibly difficult to detect (proving a negative) unless your enemy knows your ship is really there by some other means. This allows you to build a perfectly ordinary ship with perfectly ordinary parameters, but still remain wholly undetected - about the only stealth you'd need is black paint to prevent anyone using their can't-be-fooled organic eyes from picking your ship out.

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  • $\begingroup$ What’s really good about this is they will think that there was a stealth ship near right by earth. Bonus points for misdirection. $\endgroup$
    – 11Bravo
    Jan 7, 2021 at 13:40
  • $\begingroup$ "The only way to achieve passive stealthiness is to have a ship that generates no heat, which is difficult under ideal circumstances and impossible with organic lifeforms aboard." Technically, you could just use a massive heat sink that'd store the heat without radiating it out, or a laser to directionally emit the heat in a direction away from your enemy's sensors. $\endgroup$
    – nick012000
    Jan 8, 2021 at 1:42
  • $\begingroup$ Infecting all their sensor systems might be difficult if they have automatic missile defense systems, which need not even be connected to any internet. $\endgroup$
    – Poseidaan
    Jan 8, 2021 at 12:02
  • $\begingroup$ @nick012000 Problems with heatsinks is that unless the sink is most of the mass of the ship (which could be possible if the ship's built out of/into an asteroid - I did consider this), at some stage you're going to need to dissipate that heat, and that is definitely not going to be stealthy anymore. The laser idea is a good one but also not 100% stealthy. $\endgroup$
    – Ian Kemp
    Jan 8, 2021 at 13:41
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    $\begingroup$ @MartinvanIJcken The other thing is firmware updates... considering the distances involved in space and the number of weapons systems you'd require to adequately cover such distances, a firmware update requiring direct access to those systems would appear to be so resource- and time-intensive as to make it a non-possibility. Especially in cases where, for example, a critical issue is discovered and patched, you would definitely want that fix rolled out ASAP. Of course, if the fix also happens to contain some malicious code... $\endgroup$
    – Ian Kemp
    Jan 8, 2021 at 13:52
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Your ship will also be SLOW as well as hot

Firstly it could only target ballistic objects i.e. ships or more probably stations/structures that are not accelerating or capable of acceleration (basically in orbit around a planet or the local star. This is because the ship in this scenario absolutely cannot alter course or change velocity once its starts the mission. (Asteroids ducking and weaving look suspicious.)

Secondly and more importantly assuming your crew really wanted to make people think their ship was an asteroid it would have to commence its approach to the target from the orbital plane of the local asteroid belt. And that means your ship has to have aprox the same orbital velocity (relative to the target) as the asteroid belt it came from. So in the case of say Earth an asteroid heading towards us will have a velocity of somewhere around 40Kps. That may seem fast but the belt is what? 400 million kilometers or so away from Earth. And since all natural objects not accelerating follow curved paths around the solar system not straight lines you are looking at travel times measured in YEARS.

Now you could start the mission closer to the target by placing your ship on a trajectory that makes it look like it came from an asteroid belt but that means powered maneuvering to get to that point in the first place.

Solution; Don't use a crewed ship. Use one or more AI controlled missiles equipped with on-board liquid coolant supplies that they can use to reduce their hull temperature to that of local space. There's a description of what I'm talking about on the Matter Beams Tough SF blog.

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Radar is not the primary detection method for near earth objects.

This method of becoming stealthy will not work by itself. Optics (taking pictures) is still the most heavily relied upon method. The answers which indicate that you should actually disguise your ship to actually look like the asteroid are better because then the optics would match the radar, if they saw something that looked like a big asteroid on radar, but under optics it just looked black, or worse like a ship, that would set off all kinds of alarms and blow your operation.

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It depends on the scale of your fiction. In space everyone can see everywhere, you have to be a long way away to be outside of the range where you are obvious.

In the real world we have discovered about a third of all asteroids bigger than 140m that come within 50 million kilometers of Earth (roughly everything from Venus to Mars). More than 20,000 asteroids in total that come within that distance are tracked. Remember, this is using current day technology. In a world where we have space corvettes our tech will be so much better, every ship will have telescopes.

The answer to your question is: you can do it, so long as you are far enough away from everything else so you can't be seen when you begin your transit. For example, if humans in your world have colonized Mars and basically stick to the orbits between Mars and Earth, then Jupiter is outside the area of detection. You can hide out in a hidden base around Jupiter, launch your asteroid camouflaged ship (probably best to keep your ship inside an actual asteroid rather than using magic paint) and wait for the journey to Earth - just make sure to have enough supplies (including pre-cooled heat sinks) for the trip!

Other plausible ideas would be: Launch actual asteroids at extremely fast speeds at the shipyard from a very far distance. Launch tiny pre-programmed missiles that are too small to be detected and can run cold and fast. Disguise the ship as one with a legitimate purpose (combine with the asteroid idea to have an asteroid-hauler bringing a high value load of minerals into Earth orbit, only for it to actually be hollowed out and filled with ships!).

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Yes, but only from a single direction at a time

As others have said the heat of the ship will make it very visible compared to 4K of deep space. however it would be possible to use, essentially the same technology as a fridge to cool a shield/screen to ~4K which you can then hide the ship behind, the downside of this is that overall you generate even more heat and therefore are more visible from other directions so it would only work if you know where the enemy is

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Ship is actually an asteroid.

This would sidestep issues about being disguised as an asteroid. Use an unmodified asteroid and house your ship inside it. For storytelling purposes this could be cool. The little ship has got an engine capable of moving the asteroid when it needs to. If push comes to shove the ship can ditch out of the asteroid and the big engine then makes it very fast.

Your asteroid will be warmer than it should be in the infrared because your space people are inside and they insisted on having a hot tub, and not a small one. But that is ok. If an asteroid is hit energetically by another asteroid that will make it hot just like banging a nail with a hammer makes it hot. You have arranged that your asteroid was hit energetically (before you put the ship in it!). Someone noting excess heat will note big recently melted divot in the side of your asteroid and figure it is still warm.

In space you might actively scan with things besides radar. Visible light would work well and so you need to be shaped like an asteroid. Muons or other energetic particles would scatter very differently from a ship as opposed to an asteroid. But the scatter properties of a hollow asteroid and a nonhollow but less dense asteroid would be similar.

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  • $\begingroup$ Darn it, I was entering the nearly identical answer. I'd skip the crew, make the thing as close to an asteroid as possible. Stealth equipment would be under the surface to disguise the internal parts from deep scans. It would be closer to a missile launching space mine than a ship. Possibly even turned off and reactivated at the point the "ship" should be at attack range - it would be completely passive. If you need people, put them in some sort of deep-cryo with extremely low energy needs once crew are frozen. $\endgroup$
    – DWKraus
    Jan 6, 2021 at 23:03

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