I was talking with a friend recently and he reasoned that a cold-blooded race would take longer to get to space, but survive more easily once the technology progressed enough. The rationale was that a lower metabolism meant less food to haul or produce, and endotherm space stations could fit more people since crowding wouldn't be affected by body heat as much.

While I don't 100% buy his theory (for instance, he didn't explain why getting to space would be harder), it brings up an interesting point. How would the advantages and disadvantages of being a cold-blooded species affect spacecraft design and operation? (Particularly long-term space colonization.)

For the purposes of this question, assume the hypothetical race is similar or identical to humans in all other regards, and their technology is current-day or near-future.

Some things that may be affected:

  • As stated above, food consumption and spacecraft population
  • EVA Spacesuits would probably be harder to regulate temperature
  • Space station heating/cooling would be affected
  • Probably a hundred other little things I can't think of
  • 2
    $\begingroup$ The first and foremost difference between a cold-blooded species and a warm-blooded species is that the warm-blooded species has very much greater endurance for any kind of effort. That's what warm-blooded means: the capacity to regulate body temperature both when sitting idle and when working hard. And, of course, the warm-blooded species can be active in a very much larger range of external temperatures... Your cold-blooded spacemen would need much stricter environmental controls, and would need to schedule 5 minutes breaks after each 1 minute of work. $\endgroup$
    – AlexP
    Commented Sep 8, 2023 at 1:21
  • $\begingroup$ heat lamps, basking chambers $\endgroup$
    – Anentropic
    Commented Sep 8, 2023 at 11:22
  • $\begingroup$ Also, lots and lots and LOTS of redundancy in the life support due do much smaller failure margins. $\endgroup$ Commented Sep 8, 2023 at 14:06
  • $\begingroup$ It's worth pointing out that "cold-blooded species" does not simply mean "can handle the cold." Cold blooded species still require heat - they simply must obtain most of it from external sources. It also means you need to explain the nature of your cold-blooded creatures. Do they have insulation? What minimum ambient heat do they require? You might want to look up what cold-blooded creatures on Earth are like and model your species after one or more of them - then ask this question. $\endgroup$
    – JBH
    Commented Sep 8, 2023 at 20:17
  • $\begingroup$ It's also worth pointing out that a cold blooded species could not be "similar or identical to humans in all other regards" by the simple nature that everything about a warm blooded species runs faster: thoughts, muscles, metabolism, and therefore; progress. Activity requires energy; spending energy has waste; ergo the most active organisms generate heat. Every science fiction makes their lizard-people fast and powerful, never really looking at actual activity levels of cold blooded creatures. Brain activity is the important distinction here since you're creating a space-faring species. $\endgroup$
    – Vogon Poet
    Commented Sep 9, 2023 at 5:37

2 Answers 2


Anabiosis would be easier to implement

Most cold-blooded creatures, likely including your species, are able to hibernate during cold seasons, with their body temperature going below zero Celsius. Although in order to perform interstellar travel such anabiosis would take more than several seasons, your species might survive the journey a lot better than hot-blooded species. This enables that civilization to build sleeper ships with less reliance on machinery, as cryo-sleep could well be a natural condition for the species.

Also this would lower the requirements to energy consumption mid-flight, as deep freezing would not damage the sleeping populace beyond repair. Say, 200K ambient temperature compared to at least 250K for hot-blooded species, this would allow retaining heat aboard with RTGs instead of running a reactor just to heat the ship mid-flight.

A generations ship would have the ability to cryo-conservate in case of major failure

If your species would build a generations ship instead of a sleeper ship, its inhabitants would have a chance at surviving in case of oxygen supply/replenishment failure by employing an emergency "winter", effectively turning the ship into a sleeper one, while a select few crewmembers could still remain heated and supplied with stuff in hopes of fixing the ship up, or at least get waked for deceleration supervision and probably be able to get the ship to orbit the destination star, increasing the expedition's chances of survival and actual colonization, as the populace would be largely available to drop to the surface upon arrival.

Such a ship might also include a "sleeper drone" or several, that would get separated should the main ship come close to an interesting system, that would host a small amount of species in hibernation, get detached from the ship and attempt a computer-powered deceleration towards a detected planet that could potentially be habitable by them. I expect a NIR/MIR telescope to be possibly mounted on the colonization ship to watch for nearby stars, and the initial route to be planned so that the ship would pass at least one extra star system on its way to destination. Building these would be easier for cold-blooded creatures due to the same issue that would allow easier sleeper ships.

I don't see the immediate major changes required for cold-blooded species regarding ship design, with probably one exception: their space stations and generation ships would need to have at least one area being colder than the rest, due to likely adaptation of their brain to be sleeping in colder environment than being active, leading to potential exhaustion should the sleep be not provided with required ambient temperature. Designing that area might include heat projectors to wake up crewmen as needed, an extra space suit layer might be needed that would help gain body heat required for action, and dressing in one would be required before going to sleep, some movable beds could be installed in such place, as cold-blooded creatures sleep immobile, thus the sleeping area could indeed be more densely packed, some planet-based traditions might exist to be transferred to space habitat, etc., but this all is not largely relevant to this question IMHO.

Getting to space would be indeed harder

"Getting to space" actually means the entire civilization development prior to having inhabited modules in space. This is harder for cold-blooded species because of having less time to think about space, as some time would be spent hibernating, also in low season those species would have hard time just moving, making them more vulnerable to external threats. Oases do exist, hydrothermal streams could be used to withstand winter, etc etc, but overall the civlization development would be gradually slower. Also their anatomy might pose an obstacle, as if they might not be able to see the stars to ever desire going up in the first place.


On Earth, the range of environmental conditions is quite narrow; most places where you’d find cold-blooded animals, the range of temperatures is perhaps 20 Kelvins. In that context, human thermoregulation is a big deal.

But in space that range is hundreds of Kelvins, and our built-in mechanisms for dealing with “extreme” temperatures are close to irrelevant. As far as space travel is concerned, we pretty much are cold-blooded.

So, while there is a debate to be had about how much warm-bloodedness is or isn’t required for civilization generally, I’m not convinced it weighs on space travel in particular.

The ability to hibernate/estivate could be handy, but that’s not exclusive to cold-blooded species anyway. The same is true of other details that might make space travel easier (like being physically small).

  • $\begingroup$ +1 for answering the letter of the question; the other answer was accepted for addressing the spirit of the question. $\endgroup$
    – hjk321
    Commented Sep 9, 2023 at 4:10
  • $\begingroup$ (1) Just to note that a range of temperatures of 20 K is very mild. There are very few places on Earth with such mild climate. For example, here in Romania we have many frogs and snakes and lizards, and the difference in temperature between a cold winter night and a hot summer day is more like 60 K. And the climate of Romania is not at all what one may call extreme... $\endgroup$
    – AlexP
    Commented Sep 9, 2023 at 7:03

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