USS Sulaco, *Aliens (1986)*

Antenna farm as seen on the USS Sulaco from Aliens (1986)

We often see menacing sharp communication spikes and clusters on spacecraft in movies, shows, games, and etc. It makes the ship look more utilitarian and imposing. Since I'm a big fan of accurately represented hard science fiction designs, I've always asked myself: why does it need so many antennas? Does it make sense logically and realistically to have giant antenna farms attached to spacecraft? Or is this just aesthetic? (including military, non-military, and station designs.)

EDIT From comments

'Currently designing a Trans-Lunar cargo ship which ships glass manufactured on the Moon to Mars (maybe Callisto). I was thinking it would be automated with the front portion occupied with the main control module were I think putting a small antenna farm would be suitable (would make it look a bit nicer too). The radiators need to be probably hidden within the shadow shield so they don't radiate the neutrons back onto the spacecraft.' (edit requested by Elmy)

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    To me it looks like they aren't antennas, but this is rather a really big spaceship and those are all corridors with rooms attached. The use of building it like this would then be to get heat out. Because yes, on a spaceship you'll more likely get problems with overheating than with freezing, since all the computers and humans produce heat, but only a little bit of radiation reduces it. More surface=more radiation output. – Fabian Röling Oct 19 at 12:08

Have you ever looked at a Navy ship? There are a ton of different antennas, each designed to serve a slightly different purpose. Multiple systems usually aren't designed together to work with the same antenna, so you will need a different one for every communication system you have. This image labels the radars specifically, but you will also have satellite uplink, GPS, traffic control, DirectTV, and so many more.

Navy ship covered in antennas

Your space ship will definitely require a number of different antennas as it will have a number of complex communication systems. Do they all have to be in the same place for a farm? Not necessarily, and especially in space, you may want some directional diversity. But unless you have a nice radome to cover everything and make it look pretty, you will definitely want a couple areas to place a bunch of antennas together.

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    Also I would guess there is also some need for redundancy. On a navy ship, some antennas might be destroyed by enemy fire. On a spaceship, even if it isn't a combat ship, antennas might be destroyed by micrometeorite impacts. – vsz Oct 20 at 15:22

We have real-life examples of jumbled antennas: antennas designed by Evolutionary Algorithms.

enter image description here

A whole ship antenna array would have a design that does not conform to any aesthetic considerations being literally function over form.

They would be complex to compensate for metal in the structure of the craft, adjust the internal phasing, having redundancy against some parts getting damaged, etc.

You might get some inspiration from real-world spacecraft, like the Ulysses and Gravity Probe B.

You'll notice that:

  • They have multiple antennas.
  • The antennas are arranged orthogonally -- pointing off in different directions.

Having a whole lot of antennas all pointed in the same direction might be a good idea if there's a need for lots of redundancy, although I can't think of any such reason off the top of my head.

Alternatively, it might make sense to arrange a set of radiators like this -- thermal or otherwise. But that might be outside the scope of your question.

  • Currently designing a Trans-Lunar cargo ship which ships glass manufactured on the Moon to Mars (maybe Callisto). I was thinking it would be automated with the front portion occupied with the main control module were I think putting a small antenna farm would be suitable (would make it look a bit nicer too). The radiators need to be probably hidden within the shadow shield so they don't radiate the neutrons back onto the spacecraft. – zertofi Oct 19 at 3:21
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    @zertofi This information is important for other people who want to answer your question, but not everyone reads all comments. Please edit your original question and add this information. Have a look at the tour to see how it's done. – Elmy Oct 19 at 6:16
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    Having a whole lot of antennas all pointed in the same direction How about beamforming? It's actually quite commonly used. For example here's an array used for communication using reflection from lunar surface. – AndrejaKo Oct 19 at 11:37

While they probably wouldn't look like menacing jumbles as in your example pic, antenna arrays definitely can have a functional purposes. Phased array antennas are used in many modern systems; check out the Aegis Combat System for a particularly sophisticated example.

Of course sci-fi spacecraft can have their own in-universe reasons (hyperspace communications needs weird looking arrays, etc.)

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    That's the thing I'm unsure about. I'm trying to go as hard SF as possible. How many antennas does it need? Will antennas be even in common use by then? In my universe there is no FTL and comms for military purposes for example is usually done trough laser means a lot of times. But I'm unsure if this will still be the case in 100 or so years. – zertofi Oct 18 at 23:10
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    @zertofi You will still need antennas because antennas broadcast in all directions while a laser is basically only going to be a single direction. So imagine trying to communicate with a fleet of ships, but you need to do it one by one with each ship. Same with emergency beacons and broadcasted communications. Remember that these are still electromagnetic waves which travel at the speed of light. – Shadowzee Oct 18 at 23:36
  • That's true. When I said laser comms I meant more in a way were a central command ship gets info/orders from a station/installation were it then uses an antenna probably to outsource it to the whole entire drone ship fleet. – zertofi Oct 18 at 23:42
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    @ Shadowzee: Antennas - at least those designed for current space probes - do not broadcast in all directions. They're designed to emit a tightly-focussed beam pointed at Earth. That's how e.g. the New Horizons probe can use a 12 watt transmitter to communicate with Earth when it's well beyond Pluto. The beam of the high-gain antenna is only 0.3 degrees wide: pluto.jhuapl.edu/Mission/Spacecraft/Systems-and-Components.php – jamesqf Oct 19 at 4:11
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    @zertofi The physical size and shape of an antenna will change both the radiation pattern (i.e. what directions is it sending/receiving in) and the frequencies that it will operate under efficiently (i.e. integer ratios of the wavelength, such as half or quarter are better than irrational ones) If a your spacecraft needs to use a lot of very different frequencies, radiation patterns, and purposes (e.g. some of them may be sensors like Radar instead of communications) then multiple antenna will use less energy – Chronocidal Oct 19 at 10:55

It not only makes sense, but there should likely be more antennas (although they may not be visible)

Let's take a quick look at what an antenna is. It serves one primary function: To best balance the impedance (think resistance if you're not an engineer) between the circuit producing/receiving the signal energy and free space.

(overly) Simplified explanation: If you are a photon of RF energy (yes, they are photons... and waves...) and are cruising around on a nice circuit board, zipping around at say 70% of the speed of light following nice gold or copper pathways, you're happy. There isn't much resistance. But suddenly someone gives you an energy drink x10000 (power amplifier) and throws you out in space at exactly the speed of light. You're going to hit lots of shock during this transition. The antenna is kind of like a smooth transition process for you so that you can acclimate to the change.

But back to the matter at hand, why would a space ship need so many?

The answer is quite simple. The ship needs to communicate. And being in space, there is no single direction relative to the body of the ship which it needs to communicate with. It is quite likely that the ship will need to communicate in many different directions at the same time, using different frequencies.

What this means is that any antenna built on a space ship will likely be used as part of an antenna array. Using fancy digital processing, the antenna 'beam' can be steered electrically while the antennas remain in fix orientation. While an overly-broad statement, the more antennas you have pointing in different directions, the more directions you can focus the RF energy towards without having to rotate an antenna. Also, the more antennas you have, the larger your overall gain is, which in distances of even light-minutes, could very well be important in space.

Also, some of the antennas could be used for directed energy weapons, which it stands to reason may require a massive increase in size due to the power densities involved. And ships need radars and other sensors, either passive or active, which will be looking in all directions around the ship, yet another reason to have more antennas.

Most of those aren't actually powered antenna - they are unpowered reflectors and parasitic elements to control the radiation pattern, and focus the transmission (like a Yagi-Uda antenna commonly used for receiving TV signals)

While there are multiple antenna in the "farm", they are either set up for different radiation patterns, or to send/receive efficiently on different frequencies, since fundamental resonance of a thin linear conductor occurs at a frequency whose free-space wavelength is twice the wire's length

Also - only some of them are for communications. Others are for various forms of scanning equipment, such as Radar

  • That is really interesting and I never knew that. – zertofi Oct 19 at 13:07

I appreciate that they are antenaes for something or lots of somethings, however as this is pure SciFi its not actually known what each one does, its just usually explained as the antenae array...

Possible explanation

I'm going to make some handwavium up to explain this which would accommodate for this sort of design. i'm not suggesting the below is the actual design of the Sulaco!

Perhaps the larger spike at the bottom is actually the barrel of a massive anti ship cannon or rail gun, the spikes surrounding it are massive radiators which also protected the gun barrel from being hit as easily.

Above that are some form of transmitter receiver with a few redundancies.

At the very edges could be spikes that actually house point defense systems and countermeasures but the size of the ship means we can't see the detail to explain this.

And then the furthest forward sections are detection systems for maneuvers. you'd want to be able to gauge exactly how far away the barrel of the big gun is away from debris.

I admit this is definitely just adding spiky bits to make it look cool and then adding in some fairly generic reasons for those spikes being there, but its a possible reasoning

It might be because the ships are upgraded in a progressive process rather than built in one piece.

The reason they are all aimed in one direction is because they are supposed to face backwards, otherwise they will be damaged by interstellar dust.

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    The first part sounds plausible, but i doubt that last part (all antennae in the back). Typically, the interesting things are mostly directly in front of the ship, which it's why it's headed there. If all your antennae were in the back, they would be blind towards the direction the ship is going (due to being shielded by the ship) – Burki Oct 19 at 10:08
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    Unlike aircraft or watercraft, a spacecraft (at least one using Newtonian propulsion) can travel in any attitude when operating outside an atmosphere. Said differently, the direction of travel is largely unrelated to the orientation of the spacecraft with respect to some arbitrarily selected reference. There will be some limitation to this in practice because the main engine as well as the thrusters are likely to be fixed in place, but once the spacecraft is in freefall, you can rotate it freely along all axis (roll, pitch, yaw) while keeping its direction of travel essentially constant. – a CVn Oct 19 at 11:22
  • @αCVn Only as long as your speed remains small relative to the speed of dust particles in the space that you fly through. If you are doing close-to-light speed travel, you want really substantial shields in front of you. Because you cannot hope to detect a particle the size of a grain of sand, yet each such particle can deliver more than a Gigajoule of destructive energy to your ship. The shields will clearly show in which direction the spaceship is supposed to be going. – cmaster Oct 20 at 16:46

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