This is not a very hard-science-fiction tale, but more about human relations and adaptability, but I still want it to sound plausible.

A space faring civilisation that descend from humans uses bio-ships, but instead of engineering them from birth they are natural born humans trained in astrophysics that voluntarily choose to go through a mutation process in a special "bacta" tank/shipyard that enlarges their brains, giving them incredible memory and processing power, and alters their bone structure and body shape until they form the chasis of a hundreds meters long ship. They are then implanted and reinforced with armor, computers, sensors, reactors and such until they look like normal ships in and out, so they are both mutants and cyborgs.

These Bio-ships have the capacity of self healing and decision-making that a living being does, they value human life and do not have the alien logic and/or bloodlust an AI or captured space faring animal might have.

The ship performs its own duties of navigation, detection and weapon handling, but they are fitted with a crew for command, tactics, special sensor or weaponry use, engineering for the technology and care taking for the biology. Means of propulsion, survival in the vacuum, nutrition and oxygenation will be covered in the narrative but are irrelevant for the question at hand.

In the story, also, one of this ships crash and can no longer function, but instead of leaving her behind the crew has an emergency procedure (probably some genetically engineered handwavium substance in a big syringe) that can reform the original human body from the bloated brain-mass, like a cocoon.

How long should, semi realistically, take a 70kg human, grow into a biomass equivalent to 2 elephants?

And, years later, for its one ton brain to become a cocoon that spews forth a human?

Extra question: If the body no longer has a significant muscular structure or limbs to move, what size do the internal organs and the nutrient intake need to be in relation to the brain mass?

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    $\begingroup$ Why transforming him into a ship? Seems way too troublesome and not really logical to me. If i can suggest something - maybe let the ship grow around the human, with the brain acting as central component or inhibitor that just spits him out in case of emergency. Saves you the pain of reconstructing the entire body. $\endgroup$
    – Daniel M.
    Jan 20, 2017 at 12:51
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    $\begingroup$ "Semi-realistically" doesn't really cut to the chase... Sounds like a lot of magic. And I can't find anything right know that would help in estimating how fast you could add mass to an organism like that. I think this depends a lot on the rest of your story and your convincing use of handwavium. If you want them to be rare it could be anything from 10 years to 100 years or more. For mass-production it could only take a few days. This sounds quite opinion-based. $\endgroup$
    – Secespitus
    Jan 20, 2017 at 12:52
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    $\begingroup$ Somehow reminds me of species 8472. Maybe Memory Alpha has some information about their bioships $\endgroup$ Jan 20, 2017 at 12:55
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    $\begingroup$ I'm always interested in why these questions are asked (not saying it is wrong) but at what point do you expect the reader will think: "Ah yes, body transforms into a space-ship, obviously,..... in an hour?! Hang about, something about this doesn't hold! I want to see the reasoning behind this." If they accept a human turning into a space-ship why would they need reasoning for how quickly it takes? $\endgroup$ Jan 20, 2017 at 13:30
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    $\begingroup$ Human to ship: Space travel is difficult, among other things, because of radiation. Having a big brain and a lot of tissue makes you susceptible to all kinds of cancer. Also, space is real big so a very smart creature would do a whole lot of nothing. Maybe down scaling your human is smarter. Ship to human: If your biological giant just has to produce 'a person' that is basically called a pregnancy in which the Gestation period for a human is 270 days. Animals that birth more functioning babies take a little longer. The same person might be more difficult. $\endgroup$ Jan 20, 2017 at 15:59

8 Answers 8


A blue whale has a gestation period of 11 months, weighs 3 tons at birth and gains 200 pounds a day for the first year, at the end of which time it weighs approximately 40 tons. (Source) Holy bouncing babies Batman!

If I were to assume your species had brilliant biological engineering I would assume they could mutate a human into a whale sized ship in about a year.

An elephant weighs anywhere from 2.5-7 tons. (source). Given the whale growth rate it would take 100 days to reach 10 tons (approximately 2 elephants).

But I think what we can learn from biology is that major reorganization takes more time than growing an existing structure. It takes almost a year for a fertilized egg (of most large mammals) to become a functioning organism. However as we see with the whale, it can then grow to enormous size in the same amount of time. Given that, I would be hesitant to set the human to ship conversion time at less than a year. Maybe it would make an interesting story point to make it several or many years.

To convert back to a human sized entity could be instantaneous. Just include an emergency ship container (body) as part of the complete ship. In case of emergency it ejects from the rest of the structure taking the memories, knowledge, and personality of the ship with it.

If you prefer not to have a built in emergency ship container then I think the 9 months (similar to pregnancy) estimate is appropriate.

Edit to answer the extra question about nutrition: A human brain weighs about 3lbs and uses somewhere in the neighborhood of 400 kcal in glucose a day. Scaling up to get a wild guess estimate for the 1 ton brain gives 270,000 kcal or about 667 liters of Coca Cola a day. This is just for brain activity not the energy for pumping fluids, heating, and etc.


Two elephants??? Bush Elephant (male) wt. = < 6,000 kg, 5000 is a good average. So, two would be 10,000 kg. This is less than the weight (mass) of a (loaded) truck. And this is going to house and transport people between stars? Riiiiiight. A blue whale's pregnancy lasts 1 year and the calf is 6 m long and weighs over 1000 kg. Here's the key point: a calf can put on 100 kg a day (when nursing). I agree completely with the other comments about the (lack of logic) behind needing increased brain size. Perhaps you should consider "neural nodes" distributed throughout the ship to do the routine stuff (air temperature, open doors, turn on lights, etc.). If the large brain is somehow magically necessary to enable FTL travel, then why not make that part out of silicon, and just connect it to the organic brain? One obvious problem is, if you change the structure of the human brain to accommodate the extra structures, then it won't be human anymore. Now, as to the question of how you'd change such a mind so that it actions would be indistinguishable from a human's, well there'd be an app for that.

  • $\begingroup$ The 10 tons are not the total mass of the ship, but the what conforms the central control system, with a basic bone structure for protection. All that will be covered for space faring, filled with computers and decks and living quarters. It would not be a good idea to have exposed nerves. The size is due to an expansion of the sensory and memory areas of the brain, among other things. the matter of propulsion and such will be covered but is not relevant for this topic. I like the idea of the neural nodes a lot and the obvious strains to the psychology of the character are part of the story. $\endgroup$
    – ThreeLifes
    Jan 20, 2017 at 18:57

Interesting ship. I think it could take 10 or 15 years to maturation.

Note that I shifted the focus away from biomass. Generating biomass is easy. Deep in the heart of every one of our genetic codes is the key to exponential growth. Yeast, for instance, know how to leverage this sort of exponential growth to take over an entire environment (such as a vat of soon-to-be-beer) and only stop that exponential growth with a quorum sensing system. Our eggs grow in the same way, doubling in size until chemicals tell them to stop growing that way.

In the case of real embryos and infants, there is a limit: the environment. At some point, the individual is going to be put out into the unfriendly real world and have to survive. Nature is unkind in that sense. It doesn't matter if you were almost done growing legs that would make Usain Bolt look slow, if they don't work when the predator arrives, they're useless. Nature has to slow down and take it carefully.

Your engineers don't need to take it carefully. They fully control the "bacta" tanks from start to finish. Accordingly, they can be more aggressive than normal. They can flood the tank with biomatter at exponential rates and then start coalescing the material into the right shapes afterwards.

The key is how long it takes to create all the complexity of a ship. That has nothing to do with biomass and everything to do with the particular structures needed to exist as a ship. Making large things is easy; making complex things is hard.

The most complex part, of course, is found in the nervous system. There we learn to control all of the hardware our genes have given us in the womb. We finish constructing the human body within 9 months, but we spend years learning the basics of how to control it, and spend a lifetime mastering it. No matter how quickly you grew the body in a vat, learning to control it will take the most time. It cannot be easy to control, or else there would be little to no advantage in having the biological control systems in the first place. The whole point of biological systems is to control systems that are too complicated to easily fit into a set of equations to optimized by a control systems engineer. Maturation time is what you need.

As for going back to being human, think of it this way. You just spent 15 years learning to control your arms and legs. You then spent many decades using them to do great things. Now, you're going to have those arms and legs hacked off. You're going to become a quadruple amputee. Sound like fun? I didn't think so. Losing all of that powerful control just to have to learn to control a human body all over again would be brutal. Ships would outright refuse to convert. Thus, you would need to have a biological system that forces them to.

We have prior art for this. We have real life examples of where a human, in complete control of their body, can create a cocoon within which a human brain forms. That human brain then learns to control arms and legs. The first part of the process takes 9 months, the second takes a few years. Eventually, it learns to master its arms and legs and walk this Earth.

Childbirth is a very violent process. It's beautiful, but truly violent. The mother's uterus contracts forcefully, against her will, insistently expelling the child. When this finally happens, against the will of both the child and all of the anatomy the mother has used to keep the child in its safe bubble for 9 months, the child is then disconnected from its source of oxygenated blood and literally left on its own until its blood O2 levels get so low (and CO2 levels get so high) that its brain forcefully shouts out along a nerve dedicated to a single muscle: the diaphragm. With this shuttering contraction, air rushes into the child's lungs and it acquires the potential to do the first action of its life: to cry. To cry with all the might it can possibly muster.

So, perhaps 15 years to mature a ship, and 9 months to return to human form.


This is only an indirect answer, but the basic process of growth can be exponential. That's a huge deal. Not many human-scale processes are exponential, so we tend to underestimate them. What this means is that things can get done much quicker than you'd think.

Consider biomass over time. In the first trimester a human fetus roughly doubles in size each week. In the second trimester a fetus slows down to doubling roughly every two to three weeks, and then slows further. The last ten weeks show another doubling.


Note that this chart only starts at week 8. I assume that the fetus doubles in weeks 1-7.

Here's my point: the fetus doubles in weight about 20 times in nine months. That implies the fetus is roughly one million times larger at the end of gestation than at the start.

Suppose your hand-wavy bio-process essentially reboots all the cells in a human body into a growth state, and you can re-start that process of exponential growth. What happens if a man who weighs 180 pounds suddenly starts re-growing at the same rate? The first time he doubles he weighs 360 pounds. The second time he weighs 720 pounds. And so on.

After doubling 20 times he weighs $180 \times 2^{20} = 188\,743\,680 \space\text{pounds}$. For comparison, that's roughly the size of the USS Gerald Ford aircraft carrier. With a crew of $4\,660$ you're already at the "floating town" scale of things. And it carries $75$ aircraft to boot.

Exponential growth man.


Answering your question directly:

About 6 months.

It takes a fertilized egg to grow a baby from the gestation to birth about nine months average, but we also have to take into account that the mother is also trying to survive herself so we can (Someone with medical knowledge correct me) shave off a few months if what we require is to make a pre-designed body, this body would be completely new and would require some weeks to months of adjustments, not counting the fact that it went from having the consciousness of a demi-god to a regular old joe so shell shock and possibly madness wouldn't be out of the question.

Spin 1

If you have the tech to make humans into ships, cloning is simple. Have a cloned body of the guy in a secured compartment and when shit hits the fan just dump the brain inside and eject him. (Or just detonate a charge in the brain of the ship to avoid the enemy from getting the info he has).

Spin 2

@Daniel M. had a great idea i would take it into consideration. My spin on that is this, lets assume that a human brain can't possibly manage that amount of information instead of spewing a human, make it so that the "brain" of the ship into a different entity much like a cockroach that the majority of his body is compromised by his brain, give him basic means of locomotion and cyber implants that allow him to connect to the ship and interface with it properly, this way one brain can connect with any ship and you don't have to suffer from inability to upgrade your ships. Also in the case of an emergency you pop the brain out and move it with your regular crew.

Nice to watch

Search for the series Far Scape, its oldie but good and it handles the theme of an organic ship.

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    $\begingroup$ You are right on the nose. For my narrative I need the character to BE the ship itself and not just a component that could be bypassed or substituted, so I will be making excuses of why is it not done in a simpler manner. Also the subject is not left gestating to its own devices, but rather cared an stimulated by specialists, that should make it faster. The madness of adjusting to suddenly be a regular human again is part of the story. I did like Far Scape. $\endgroup$
    – ThreeLifes
    Jan 20, 2017 at 18:37
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    $\begingroup$ Then your only limitation is the mind of the donor, so it should be as fast as the technology of that time can handle leashed by the "learning curve or adaptation curve" of the donor. So lets say that it should take a month for the mind to "slowly" adapt to the increased functionality and the psych understand the changes. Also lets say that the emergency body is pre-made on that period and ready for transfer, but the after being dumped on this new body the psych will need at least 6 months to re adjust (with therapy or a support group). The ship human form should be preconditioned for combat. $\endgroup$ Jan 20, 2017 at 21:30

I think you and most answers make a logical error here. Since this is not a natural process, you can not actually approximate its duration or nature from biology despite it being based on biotech. All that depends on how the process and the related equipment has been designed. Which is limited by the limitations of the available technology:

Unfortunately the technology here is in the handwavium territory so it does not have any real limitations. You could perfectly reasonably say it is a process of "push button and wait five seconds for the bell to ring" as far as hard limits go.

However there are some reasonable assumptions we can make.

First detaching from the ship must work as an emergency procedure.

If something goes catastrophically wrong and the ship must be abandoned, the pilot must have a realistic chance to walk (or run) away. This means detachment can not rely on the ship being intact enough to grow a cocoon and a body and then transfer memories to the brain in the body after the crew triggers the process.

THis means that both the protective cocoon and the backup body must exist from the beginning, be constantly maintained at working condition by the cocoon and at all times contain a warm backup of the mind.

If the detachment is triggered either by the crew or by the ship systems collapsing the backup is simply cutoff from the cocoon which makes the cocoon and some sort of an emergency exit to pop open.

This is fast and simple and should take somewhere between five seconds and five minutes. Probably closer to the seconds as the body would probably be pumped full of drugs that instantly snap it fully awake and suppress inevitable confusion and disorientation.

Waiting while you grow up sucks, ask any teen ager

It makes no real sense (as noted in comments) to wait while you grow up to be a ship, if you need a human body anyway for emergency detachment and the growing up is handled by huge engineering marvel with handwavium technology.

Why would people actually do that?

Instead you should model the process on modern pilot training. The pilots are trained and the ship are built in parallel. This instantly makes the process twice as efficient. It also means that pilot training or ship construction failures do not instantly freeze the other part of the process.

How do you make the pilot?

Astrogation training is fine but modern airlines do not give some lectures on aviation and then put you responsible to flying hundreds of people safely. Instead simulators are used.

This would go doubly here since the pilots would need to directly and persistently connect to their ships. As such the necessary neural links would be created during the training process, the pilots would be trained using simulator cocoons that allow them get used to "being a ship instead of a human" in bite size steps.

This would also allow them to find out if they have issues not being a human anymore before being transformed into ridiculously expensive spaceship. And make the necessary adjustments over years of simulator training with constantly available counseling and even therapy. People funding all this would also appreciate only needing to built ships for people who are actually good at it in simulations.

Same would go in reverse. While being a ship the pilot would periodically, possibly subconsciously. run simulations of running and acting as a human. It would be embarrassing if you woke up as a monkey in an emergency that killed your real body and it turned out that you have forgotten how to run away.

These simulation might allow the ship to interact as a human with the crew in virtual reality but I am not sure if someone mentally adjusted to being a huge ship would want to interact with monkeys that mostly think of having sex and eating bananas. Simulated emergency training would make sense at this level of technology though.

Building the ship

After the pilot has finished the training and gotten good enough scores to merit a ship and has adjusted to being in the simulator cocoon all the time, the ships body will be assembled around the cocoon and the ship systems will replace their simulated replacements one by one.

The ship components would be built in parallel with the final step being fairly fast assembly from pre-fabbed components. The actual speed would depend on the maturity of technology.

Faster is better for business (the cradle for ship assembly must be very expensive and limited resource) but failing the assembly would probably be even more expensive so if the technology is new their will be an iterative process of testing and adjustment needed for every component and components will be added one by one.

With more mature technology increasing portion of testing and adjustment can be done before assembly and component can added in parallel allowing very fast construction.

I'd go from few days to few weeks. This seems very fast but most of the work would be done in parallel with the years of pilot training. You can even instead see the assembly around the pilot as a process of inserting the cocoon and the pilot inside it into the ship and get the time down to hours but nothing in the question suggests a need for such rush jobs and it would not fit the flavor of the setting.

But this destroys the biological flavor!

Not really. We associate such things with mechanical or hardware solutions but they are actually technology neutral results of the economics. We just do not have enough control of the biological processes to do large scale construction with biotech. The people described in the question do.

With premises in the question a biological growing of a ship would not be a slow and awkward process, instead it would be faster, more efficient, and more convenient than our processes for constructing aircraft or buildings from prefabbed components.


One problem that I see immediately is that the modifications to the brain will make the resulting spaceship non-human in the way it thinks.

If I were doing this, I would have the human bonded (in a cocoon) inside a highly modified animal that would be the ship. This animal could have a lot more modifications to make it a ship, so that it needs many fewer mechanical modifications like shielding. You'd still need to add computers and some life support, though the central part of the life-support would be part of the animal.

The pilot would be bonded to the ship with some sort of direct brain connection so that he feels like he is the ship.

There are many advantages to this way of doing things.

First, creating a modified human might be a difficult problem, especially increasing the brain function without driving them totally insane. With the animals, you'd have less ethical problems with experimenting with them to get the process right.

Second, it might be easier to make several different classes of ships from animals.

Third, an animal could be allowed to grow so that it becomes a larger ship over the centuries.

And I think it's way cooler to do it that way.

One interesting story "Mayflies" by Kevin O'Donnel. A human brain is put in charge of a mechanical generation ship. The people in charge thought the brain was brain-dead, so they used it as a computer. Then he woke up.

I've read a few short stories where humans were their own starships, but either they had evolved into something without a traditional body, or in one case the mechanics to do this (FTL engine, shield generator, life support) were implanted within a normal human. These are old stories, I ready them in college (40 years ago) and they were old then.


I like the premise of human -> ship, but the rationale behind it ('ship is human') and the possibility of reforming a humanoid are both deeoply flawed. To have a once-human perform as a spaceship, she needs spaceship 'reflexes' (downshift on the handwavium if the phlebotium generator exeeds gargle) and she does not need human 'reflexes' (kick, if your knee-tendon is hit, is a reflex, those are hardwired and will be fine; i'm talking about human 'reflexes' like catching a ball) - so because the human 'reflexes' are unused, they will atrophy and vanish. Walking with legs, talking with a mouth, smiling if smiled at, those will all fade, over time. At the same time, the spaceship 'reflexes will get sharper with every passing hour as a spaceship. They will be learned, and as such they will have a physical representation in the neural matrix, altering the brain in ways that make it less and less comparable to that of a human. Sense of self will be vastly altered, with other people walking around in oneself. The sensorium will change massively - even attention, that elusive spotlight, will need to be completely retooled - you can't have a spaceship that loses track of the navigation while admiring a cool nebula. Autonomous functions must abound, but they will still need some kind of possible willful intervention (you breathe without thought, but you can hold your breath) creating even more interfaces that need to be mapped onto the neural substrate. you'll have a fledgeling ship that can't hold its antimatter, so to speak, and that will learn and literally 'grow into' it's new role - but the human that was will be essentially dead - memories triggered by familiar smells will now map onto brain structures that are part of the life-support, and backed up sewer pipes in sector C will evoke memory of aunt Petunias brownies cooling on the windowsill - no rhyme or reason to any of it. 'locked in' patients of today have a very hard time coping with the cessation of any muscular activity, but the ship people will have that plus the complete rewiring of their sensorium. Refer to the anectotal evidence of gangbangers becoming moral and well-adjusted humans after a very small stroke (and the reverse, 'good people' becoming thugs after a medium size brain injury) - and the justification of 'ships need to be people, because people aren't evil/alien/unknown goes completely out the window.

Reforming a humanoid from a ship: Same process in reverse, just more abrupt, if it is to be a last ditch rescue move. So do not expect the reformed human to be sane, and especially do not expect the reformed human to be anything like the human that transformed into the ship.

As per your question: A growth rate of 1% per day is absolutely possible (this would amount to an approximate doubling of weight every 8 weeks, as is usual for, i.e. pigs) even 5% (as the blue whale calf, meaning doubling of weight every two weeks) would not seem overly ambitiuous, so your 70kg human would need between 100 and 500 days to 10 ton mass. I don't know what your humship needs exactly in terms of organs and structures (your wish for bones is a mystery to me - do you want them for their marrow? But why not just the marrow?), but if the brain is the largest organ, you'll need a steady and absolutely unimpeachable supply of glucose so i'd invest in some fat, too. The circulatory system is probably machine augmented, and i'd not deal with a digestive tract, and rather go for intravenous feeding and blood filtering to get rid of metabolites. The filtering will make kidneys obsolete, but i'd keep the liver, possibly even in more than one copy, if you are not 100% sure that your blood filtering is impeccable. Oxygenation of the blood is better done via machine, especially if the circulatory system is mainly machine anyways - a lung will only complicate matters in 0g and no-exercise conditions. Muscles are just meat, get rid of them, without excretion, breathing and circulatory functions, they are superfluous. Lymphatic organs - again, it depends on how good you deem your filtration system. Skin? possibly not, because with all the machine interference, you'll need a ton of i/o-ports anyways, so why not go completely synthetic?

Timebase for the reforming: completely dependent on what exactly happens - shedding of everything but a core brain? Minutes. - Resorption of ship-stuff and reforming of human stuff (with shedding of superfluous ship-stuff) Days, with the metabolising might of a ten-ton organism behind it, but, again, the result will just be a delirious humanoid, not the one that went in.


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