Ryan Anderson

How do Zerg Fly in Space? Part 1: Mutalisks

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Ok folks, it’s time. We’ve all asked this question, but I’ve been putting off answering it because we all actually know the answer.

How do the Zerg fly in space?

Magic.

There’s a certain point in sci-fi or fantasy where you have to just suspend disbelief and go along for the ride, and I think that the Zerg ability to travel through space is a good example of this. That said, I’d like to take a look at one of the most common explanations that people give to justify the mutalisk’s ability to flap its wings and propel itself through space. As you’ll see, it’s completely implausible.

Now, we know that flapping doesn’t do anything in a vacuum: there’s nothing to provide any resistance, so you can flap all you want and it won’t move you forward. But what if mutalisks used their dragon-like wings as solar sails, catching the photons from a nearby star to cruise through interplanetary space? That might not explain the flapping, but it could explain how they can move, so let’s take a closer look.

The idea behind solar sails is the conservation of momentum. Even though photons of sunlight have no mass, they do have momentum. High school physics tells us that momentum is conserved, so if you have a bunch of photons with momentum being absorbed by a solar sail (or a mutalisk’s leathery wing) then their momentum must be transferred to the thing they’re hitting, exerting a force on it and causing it to move through space. So, how large would a mutalisk’s wings have to be to let it accelerate at a reasonable speed? To figure this out, we need to do a back of the envelope calculation, making some assumptions about how big mutalisks are.

In general, the sizes of units in the game are not reliable: I prefer to consider the cinematics as the authoritative source. So let’s take a look at this cinematic showing Jim Raynor’s battlecruiser being attacked by a swarm of mutalisks.

At about six seconds, one of the mutalisks flies over the right-hand side of the battlecruiser and crosses near a long row of windows. Based on its size compared to the set of windows, I would say that the creatures have a wingspan of around 100 meters and that their tube-like body is about the same length and maybe 5 meters across. If mutalisks are like most earth life, then they are mostly water. to get a rough idea of their weight we can calculate their volume and then multiply by the density of water. A cylinder 5 meters by 100 meters has a volume of about 2000 cubic meters. That would correspond to a whopping 2,000,000 kg or 2000 metric tons!

Now, obviously that’s too big for something to fly in at atmosphere, let alone in space by flapping its wings. But lets be generous and say that maybe mutalisks are made of some very low-density material, and maybe I overestimated their size. What if they were closer to 20 tons? How much oomph would their wings give them if they used them as solar sails. Again I’ll be generous and treat the wings as a square of material 100 meters on a side.

The momentum of a photon is given by: Momentum = Energy/Speed of Light, so near a sun-like star, where most photons are in the visible range, they have an energy of 2-3 electron volts, yielding a momentum of 1.6×10^-27 kg m/s per photon. That’s not much, but a star puts out a lot of photons, so let’s see if that balances it out and gives us a decent thrust.

Let’s say our theoretical mutalisk is orbiting the sun at the same distance as Earth, 150,000,000,000 m from the sun. The sun puts out 3.8×10^26 watts or roughly 8×10^44 photons per second, but that power is spread out in all directions. To figure out how much hits our solar-sailing mutalisk, we have to imagine spreading that power out over a sphere the size of our mutalisk’s orbit with a surface area of 4*pi*R^2 where R is the radius of the orbit. That gives 2.25×10^20 photons per square meter per second.

Solar sails don't make for the most maneuverable spacecraft, and they would be sitting ducks in any sort of space battle.

With a wing area of 100 m x 100 m (10,000 square meters), our mutalisk would intercept around 10^24 photons per second, corresponding to a whopping force of 0.0004 newtons! That’s enough force to accelerate a 20 ton mutalisk up to about 14 miles per hour in a year.

Edit: An astute reader points out that the size of mutalisks is described in the Starcraft novels as being much smaller than I described. They apparently have a wingspan of 20 feet and are only 7 feet long and about a meter across. to me that seems shockingly small, especially compared to the cinematics, and it also seems quite stubby compared to all of the art depicting mutalisks as having a body that is a long tube. Still, we can scale the above results to fit these new dimensions. Given a cylinder 7 feet long and 3.3 feet across, and again assuming a density like water, I get a mass of 1.7 metric tons. If we treat the wings generously as a 20 foot square, then their surface area is 37 square meters, so the thrust on wings of that size as compared to our 10,000 square meter example above would be .0004 newtons x .0037 = 1.5×10^-6 newtons. That’s enough to accelerate our 1700 kg mutalisk all the way up to 0.06 miles per hour in a year! Even assuming a much lower density, it would only accelerate a 170 kg mutalisk up to 0.6 miles per hour in a year.

You might not have followed every step of that (admittedly very crude) calculation, but that final value should give you some idea of how ridiculous it is to say that a Mutalisk’s wings could work as solar sails. Even assuming very large wings and a small body, the acceleration that you get is miniscule. Plus, solar sails are really only good for accelerating away from the star, and Mutalisks are like fighter jets: they need to be able to dodge and weave in all directions very quickly.

Bottom line, I can’t explain how the mutalisks fly in space. Heck, I can’t explain how something that big flies in air! Solar sailing certainly doesn’t cut it, so we’re left where we began. It’s magic. This is a part of the Starcraft Universe that just doesn’t fit with the laws of physics in our own universe, and that’s fine. Mutalisks are still cool, and it’s not like I’m going to stop playing Starcraft because I don’t know how they can fly in space.

Stay tuned: next I’ll take a look at all the non-winged Zerg fliers!

39 Comments

  1. I’d like to point out the fact that if you’ve read any of the novels, the Mutalisk body is closer in length to that of a Terran in a marine suit – about 7 feet (assuming that the average Terran is 6 feet tall), and their wingspan is around 20 feet – give or take 5. Please go reconfigure your calculations based on this new information.

    • Can’t edit my post, so I’d like to say that they’re also 1 meter in diameter – roughly.

      • Really? Wow! That’s much smaller than I would have thought based on the cinematics. In that case, flying in air seems much more plausible, but it makes it even less likely that their wings would work as solar sails since they would be so small.

        I’ve added a paragraph scaling the calculation to these new numbers and it makes the case for solar sail wings even more hopeless!

  2. I feel bad for derailing this topic with an immature idea…. They fart. REALLY hard. The gas would propel them.

    • Heh, as Joe says, that’s actually the most plausible explanation. I’ll take a look at it for Part II, where i consider all the zerg flyers who somehow don’t use wings to move.

      • Aw, it looks like you’ve abandoned this blog? I was looking forward to Part 2, especially on seeing all the shots of the Leviathan in space in HotS!

      • i read on the wiki, or something, that the space flapping is vestigal, and the release gas through vents, spircles, etc. to mpove in space. this is most likely how other zerg flyers move through spac

  3. One poooooooooossible handwaving explanation for “flapping” wings might be that the mutalisks have some charged or magnetized material in their wing that is interacting with a planetary or solar magnetic field, and the “flapping” is actually changing the direction of the Lorentz force vector on the mutalisk body. However, given how weak planetary magnetic fields tend to be, the same size-scaling arguments apply!

    Other group members in my lab have worked on maneuvering charged spacecraft in planetary magnetic fields, yielding “Lorentz augmented” orbits. The interaction scales with the charge-to-mass – or, for magnetized components, probably the magnetization-to-mass – ratio of the spacecraft. Most materials have some limit to how much they can be charged or magnetized before they fly apart, forcing us spacecraft engineers to try and spread them out over a very large volume or area. And, in the case of electrically charged spacecraft, natural space plasmas tend to discharge the spacecraft over time, forcing us to constantly feed power in.

    We can add as much cool physics to the mutalisk as we want – but I think the only plausible explanation for having wings is that they are solar collectors or thermal radiators, nothing to do with the propulsion system! Adalonus actually has the best idea!

  4. Very cool article. I like Joe’s idea of using a planet’s magnetic field.Another thing could be that they shoot out creep like an overlord or the glave fluid is shot out to propel itself in space

    I really think a more important problem is why an organic life-form mostly composed of water (or something) doesn’t freeze in space. One could argue that the flapping is to keep the mutalisk’s core temperature above freezing while the real propulsion is provided by some other mechanism. It could also be that the mutalisk is too stupid to know the difference between an atmosphere and a vacuum and merely flaps because it has to. SImilar to how birds tend to bob their heads forward and back while they walk.

    • Freezing in space is not as big a problem as most people think. Since there is no air to convect away the heat, the only way to lose heat is to radiate it, which is actually pretty inefficient. I think overheating would be the more likely problem when they’re close to a star, in which case the wings could help radiate heat.

  5. I’ll kinda agree with Adalonus. But I think their propulsion is in their wings rather than anywhere else in their bodies. This would allow them to be really fast and agile. On the other hand they don’t seem to move their wings like if this was the case.

  6. In the second scenario of the original Zerg campaign, the Overmind (or one of the Cerebrates) claim to have the means of “warp travel” through which Kerrigan’s chrysalis is transported, though I remain baffled as to how any entirely organic being is capable of such exertion.

  7. Lol, this is also a question that came up on my mind since SC1

  8. As we explore the cosmos, we will find all sorts of exotic life forms that baffle our current understanding of what is biologically possible.

  9. Considering that in SC1 several mutas could occupy the same four-dimensional set of coordinates without any difficulty, a simple thing like powered flight should be easy enough to achieve given their probabilistic nature.

  10. Actually, their bodies, if straightened out, could form a perfect ramscoop. Collecting hydrogen particles for a reaction, propelling them forward. The faster they go, the more hydrogen is scooped, the faster they go.
    Since they are a hive mind, they could use their entire mutalisk swarm as a processor to calculate a complicated organic wormhole. If its possible in science, it is possible an organic being could create an organic equivalent. So if they get enough numbers, they could spontaneously swarm and warp. It would make a natural way to expand and populate other words.

    • The catch here is that wormholes are not possible in the real world. To create a wormhole that would be traversable, you would need exotic matter with negative energy. And as for the ramscoop, they would have to have mouths kilometers across to collect hydrogen just to propel one mutalisk.

  11. Overlords flying through space is funny to picture.

  12. they were only from one planet. when outsiders land on the planet organisms of the overmind tag along to each of the planets that they land on and spread

  13. its not hard to hop onto someone elses ship

  14. where do zerg get all their energy

  15. Awesome speculation about how mutas fly in space. Not sure that solar sails would require mutas to flap their wings, and I’m also not sure they would be able to change direction so fast.

  16. all of you folks are trying to change the lore about the muta to make it fly which is wrong, but what we do know is that the muta flaps its wings in space. Why becuase there is a gas. i propse that there are glands under the airpits of the muta so to say that release gas under the wings and the mutas wings flap against it and gives thrust, maybe that why the muta cost vespin gas in the game

  17. internal propulsion, there could be an internal pendulum

  18. Space farts, the flapping of the wings is just to improve circulation for evaporative cooling.

  19. Zergs are the alien creatures which we are not familiar of…of course our current knowledge is just way too limited…
    and though i haven’t read any starcraft novels yet, but the Minotaur-class battlecruisers’ length is just 560m…width 82.4m…hyperion is a behemoth-class, the prior version of battlecruiser, both classes size are almost equal…and you are saying mutalisk’s wingspan is 100m….

    anyway, nice article

  20. Mutas almost certainly spend their entire existance on the wing, perhaps the flapping is a reflexive action? They do it even when they don’t need to.

    Perhaps while in space the flapping of their wings serves another function besides flight? It may be linked to their circulatory system, in which case they may NEED to flap in order to pump blood around their bodies.

    • Men need to pump blood to certain part of their bodies, too, so they, emh…automatically activate it, so it’s not far fetched to say that mutalisks flap their wings to pump blood in and out of them.

  21. Well, I’ve always notice them flap their wings even in space. Now, that’s kind of weird.

  22. I’ve found your blog very interesting to read. I have a theory about the “flapping wings in space”. In space, based on wikipedia research, there’s a lot of hydrogen, what if the Mutalisks’s wings flap the hydrogen, making it function like air.

  23. Ok, first of all, this page looks awesome. I myself have found myself thinking so much about how Starcraft stuff could work in a believable sci-fi model. And I have given a lot of thought to the flying Zerg part.

    First of all, I don’t believe that we should consider that space combat is very common. Combat in the high atmosphere or around some space platform? Sure. But most of the time, space travelers can’t alter their routes and inner space is ridiculously vast.

    In my head, the Zerg get out of a planet’s atmosphere and into space through Greater (super greater) Spires, which work like Space Elevators in the most developed of zerg hives, and simply reach the stratosphere in other planets. This is possible because they are made of an organic material similar to carbon nanotubes, which do have the density and strength necessary to reach such height without crumbling over their own weight. Once in a low atmosphere environment, mutalisk would move the same way fighter ships would: most of the time just being in orbit but saving a considerable amount of propulsion to change direction. In the case of mutalisks, this would be their glavies, which shooting them would allow them to propel in different directions, changing their course.
    In this enviroment, the wings would have a very important function: to allow the mutalisk to evade missiles and beams. While no flapping of wings would allow the muta to change the course of it’s center of mass, it could move it’s body relative to it. Here it’s tubular body also helps. Say a viking shoots a missile at the muta’s center of mass while in low or high vacuum. Then the muta can make a ring with its wings around it’s center of mass and dodge the missile without wasting glavies.

  24. Look what I’ve found
    http://us.battle.net/sc2/en/blog/7597722
    Last question.
    Basically, they do fart and they move their wings by instinct.

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