# What does the physiology and biochemistry of a vacuum adapted post-human look like? Part 3: Metabolism

I am a post-human adapted for permanent life in vacuum and micro-gravity. How might my physiology and biochemistry overcome the following challenges?

Please note I have a strong cultural aversion to augmenting my body in order to help me survive: i.e. enclosing myself in artificially-constructed protective shells, etc.

## Current status

See Part 1 on radiation resistance

See Part 2 on temperature control

At this stage, I look similar to an enormous shining pangolin with interlocking plates of keratin-analogue that are alloyed with steel to protect against ionizing radiation. My radically engineered DNA and its unparalleled checksum and repair functions keep the doctor away. I can move these plates to help dissipate heat and - just like a Terran pangolin - curl up in a protective ball to shield my more sensitive parts. I have a reactive outercoating that allows me to alter my pigmentation (which I typically set to polished silver in order to minimise heat loss).

## Part 3: Metabolism

I've reviewed some previous discussion around convergent solutions but pretty much the only thing I know about my metabolism right now is that I am a liquid breather (e.g. perfluorocarbons). I may be post-human, but I'm guessing water or an equivalent solvent is still essential to my metabolism. My large surface area helps cool me and prevent water loss, but I think I need a highly efficient recycling mechanism to survive without regular access to it.

The molecules fuelling your baseline metabolic pathways - carbohydrates, lipids and proteins - won't do unless I can crack them out of raw materials I have access to in the interplanetary medium, from asteroids, comets etc. Eating, drinking, in fact orifices in general, are also a no-no. You think it's difficult to grow rice in space, but have you ever tried eating a sandwich out here?

Although I live in complex societies with other vacuum adapts and homo sap, and therefore have access to abundant fuel/sustenance, I would like to be able to function independent of industrial civilisation. To live off my 'natural habitat' so to speak - even if this comes at the cost of winding-down to a lower metabolic gear, kind of like hibernating, or stockpiling rawmat when the going is good for consumption over extended periods.

Essentially there's not much food/fuel to be had out here in the void, and I'm not always hanging around easy sources of volatiles like a Kuiper belt object. At the same time, I need to maintain a relatively active lifestyle - overseeing asteroid mining operations, undertaking deep space repairs - rather than floating in circumsolar orbit gazing at the pretty lights of the Milky Way and the CMB all waking.

If necessary, I can dedicate significant amounts of time to activities to generating or harvesting metabolic inputs.

So, how do I convert fuel or food into energy to power my cellular processes out here in the big dark? What are said sources of fuel/food, and how does my body obtain and store them?

See part 4 on locomotion

See part 5 on senses

• "So, how do I convert fuel or food into energy to fuel my cellular processes out here in the big dark?" - basically the same way humans do, right? If you want to be active, you need to take into account metabolic needs pf brain (rather easy to find) plus energy needs of the activities you need (you tell us) and that is about it. We convert food to energy all the time, and we are radn efficient about it already. – Mołot Nov 6 '18 at 14:07
• @Mołot edited for clarity – Chairman Yang Nov 6 '18 at 14:27
• "my large mass helps cool me", I presume you mean "my large surface area", as the more mass you have the more heat you'll generate and due to the square cube law the less comparative surface area to lose said heat. – Demigan Nov 6 '18 at 16:12

1. Many comets have naturally-occurring deposits or constituents which are quite complex organic chemistry see here so perhaps you are a comet capturer and devourer. This could involve an externaslised machination and initial dissolution apparatus (think like an arthropod here) or could involve a complex mouth which is in effect like an in-body airlock.
2. Obvious, I know, but as already stated, light harvesting across a wide range of wavelengths can help a lot - you already stipulated your plating was engineered to resist ionising radiation - why not engineer it to capture and convert it instead? Especially as your DNA has extra error checking, so a little breakthrough isn't the end of the world. Bear in mind that in open space, far from planetary magnetospheres or from our solar system's heliosphere, there are a fairly high number of UV photons and x-ray photons per cubic meter just... bopping about... so if you can effectively harvest and metabolise the energy they represent, you will be sitting pretty.
3. Depending upon where you are, if you are orbiting amongst planets, planetoids or transiting through their spheres of influence, you may be able with your metal enhanced carapace to gather energy via induction as you pass through magnetic lines of force - this can create a fair amount of energy and has in the past cooked some satellite electronics, so don't assume it's all microwattage - if you develop this one in concert with harvesting ionising radiation, you could for example transition near the lagrange point between Io and Jupiter and gain enormous energy - the interaction between Io and Jupiter's magnetosphere is ludicrously energetic, and there are high energy ionising radiation belts there too.
4. There is significant interstellar gas and potentially a fair amount of "dark matter" dust, dirt etc in the interstellar medium (estimates of ratios of gas to dust vary, but at a minimum 1% is assumed to be dust of some form) and most of that gas is neutral hydrogen (average density of about one molecule per cubic cm) but there are concentrations of this in the spiral arms of galaxies which are far higher - if you add hydrogen catalysis to your metabolic tricks, you'll have an unending, omnipresent food source, but one which will never be prolific enough for a surfeit. 4a. If you can detect microwave radiation, and can move yourself in space, you could hunt interstellar molecules, which tend to occur in the midst of gas and dust clouds - where they are cooled enough relative to overall higher radiation exposure to not be instantly broken down by UV or X-ray photons, which as we discussed earlier, abound in space.

I would posit that due to your being an engineered specie, your metabolism would in fact be highly multi-faceted and optimised, able to be actively managed, and could encompass multiple pathways, modes and approaches - heck, perhaps like a tardigrade, you can manufacture glasslike DNA and cell wall protective materials inside each cell as you dehydrate and enter a TUN hibernation state, with your metabolic rates dropping to 0.01% of typical, and survive a crossing between solar systems, only to resuscitate when you encounter adequate incident energies.

Hope some of this helps.

Well, if you are floating into space you know that your body will be showered by a lot of photons with all energy flavors.. from radiowave to gamma ray... why not thriving on them, especially the most energetic ones (UV, X-ray, gamma ray)?

You just need some molecules which can absorb the above said radiation, turn into an excited state and then relax back to the original state by releasing the absorbed energy into useful chunks, which you can use for your needs. Considering the energy per photon we are talking here, this might include also molecules which can break and reform.

By accumulating the excited molecules you can cope with times of photonic scarcity, at the price of a slower rate of action. But anyway, if you are floating into the Boötes void there is really not much to be active about, isn't it?

Let's give some figures for the needed surface: assuming an absorption efficiency of 100% at any wavelength, and assuming the only photons come from the Sun, to generate 10 W of power you would need a surface in $$m^2$$ of about:

• 0.007 at 1 AU from the Sun
• 0.73 at 10 AU (1/3 of the distance to Kuiper belt) from the Sun
• 73 at 100 AU
• How much energy can one get from a square meter out in the Belts? How many square meters of skin would he need to power human brain (around 12 watts)? – Mołot Nov 6 '18 at 14:30
• @Molot he could increase the capture surface by using very long hair instead of skin – Subbies Nov 6 '18 at 15:14
• @Subbies maybe. But I can't figure out capture surface needs, and without that, I find this answer incomplete - we can't calculate how long hair / how big skin is needed, can we? And thus, we can't paint this homo vacuum ;) – Mołot Nov 6 '18 at 15:19
• @Mołot, added some estimates – L.Dutch Nov 6 '18 at 15:53
• I've read that a homo sap adult male uses about 97 joules per second, so average power of about 97 watts. Seems like I'd need some kind of solar sail to generate that? – Chairman Yang Nov 7 '18 at 9:03