27

In this answer to Why are there no robotic missions on Europa or Enceladus I wrote:

  1. Missions going through the ice and into the ocean are currently hypothetical and problematic. You need a lot of energy to get through 10 km of ice no matter how you do it, and unless your spacecraft is absolutely completely 100% certain sterile you may contaminate a lifeless ocean or disastrously infect it with Earth organisms. To my knowledge there is not yet documented capability that spacecraft can be absolutely sterilized and yet still functional.

Some life is easy to sterilize, but some isn't. We can say that Earth viruses and bacterial spores probably won't pose a threat to alien life and would be inert, but that's just wishful thinking and hand-waving.

There are even single protein molecules that can infect and kill animals and humans, something that was dismissed out of hand as impossible until enough people died.

So I'd like to ask:

Question: Is there any demonstrated or even proposed technology that can sterilize a spacecraft with 100% certainty and yet leave it electronically functional?

uhoh
  • 148,791
  • 53
  • 476
  • 1,473
  • 22
    100% certainty is a high bar. – Organic Marble Jul 25 '21 at 01:05
  • 1
    @OrganicMarble as it should be in this case. I mean, should 99% certainty we won't accidentally infect another world be "good enough for government work"? – uhoh Jul 25 '21 at 01:28
  • Some technology is easy to sterilize, and some isn't. The stricter your sterilization requirements, the more restrictive the set of technologies you can use. We could construct devices that you could just bring to red heat for an hour or so and be pretty damn certain they no longer contain any complex organic compounds, the question is if it can be given enough functionality to be useful. How much functionality do you require? (And getting said spacecraft to its destination without contaminating it is yet another issue.) – Christopher James Huff Jul 25 '21 at 01:53
  • @ChristopherJamesHuff the functionality would have to be sufficient to justify funding a mission to those bodies. In other words, a "standard deep space rover or ocean-swimmer." :-) – uhoh Jul 25 '21 at 02:58
  • 1
    You want 100% sterilization? Available today, use Tsar Bomba brand detergent. It really blows germs away! (for full 100% efficacy, repeated applications may be required)..... 100% is a very high bar to set indeed. – CuteKItty_pleaseStopBArking Jul 25 '21 at 07:11
  • 9
    What you wrote in that answer was incorrect. The only certainties in life are death and taxes. The goal for the planned Europa lander is a less than 1/10000 chance of infecting Europa with Earth life. Source: https://europa.nasa.gov/system/downloadable_items/50_Europa_Lander_SDT_Report_2016.pdf . – David Hammen Jul 25 '21 at 08:42
  • 4
    The premise that motivates the question incorrect; the goal is not 100%. The question remains valid, but the answer is a simple no. – David Hammen Jul 25 '21 at 09:52
  • 1
    @DavidHammen Thanks for the link but yikes! yikes that sounds way too high when it comes to (potentially) risking *somebody else's world. I'll read up on that now. – uhoh Jul 25 '21 at 11:29
  • 5
    @DavidHammen thanks for the link. Only a crazy engineering team would sign up for a 100% goal. To misquote Kirk: I don't believe in the no-lose scenario. – Organic Marble Jul 25 '21 at 18:53
  • 1
    The single proteins are non-viable and need not draw our consideration. We need only enumerate over the free-living forms that we have; any parasite will be too attuned to existing earth forms to find anything to infect. – Joshua Jul 25 '21 at 19:35
  • 4
    @Joshua NASA has similar (but reduced) forms of planetary protection rules for vehicles that land on Mars. The Perseverance rover probably has over 40000 spores spread across the body of the rover, and the entire lander system, less than 300000 spores. – David Hammen Jul 25 '21 at 21:25
  • 2
    @pcman Yeah, radiation from a fusion reaction is what I use to sterilize my masks in between uses. Turns out my car has a source of fusion radiation right on the dashboard, although that makes me feel really weird about driving my car now. I'm sure it's fine. – Harper - Reinstate Monica Jul 26 '21 at 01:30
  • 1
    The question is, if sterilization is enough when you can also transport simpler molecular contaminants like amino acids or lipids. – eckes Jul 26 '21 at 07:39
  • @eckes I'd mentioned "single protein molecules" as known infectious agents but that takes it to yet another level. – uhoh Jul 26 '21 at 08:02
  • @Harper-ReinstateMonica for best results, remember to remove any glass elements or gas atmospheres that might shield UV between your fusion reactor and the masks. – leftaroundabout Jul 26 '21 at 10:04
  • 1
    @DavidHammen I've just asked Who decided that a 1 in 10,000 probability of contaminating the europan ocean by a viable Earth microorganism was legally and ethical sufficient? – uhoh Jul 26 '21 at 16:02
  • Neutron bomb might do it. – it's a hire car baby Jul 26 '21 at 17:08
  • What level of electrical functionality do you want? No current non-silicon technologies will catch up to current integrated circuit tech for decades, if ever. If you only need a few transistors, well maybe... – Jon Custer Jul 26 '21 at 17:31
  • 1
    @samerivertwice - good thing that energetic neutrons don't impact electronic devices at all, right? Wait... – Jon Custer Jul 26 '21 at 17:32
  • @JonCuster check my previous answer to that question: "the functionality would have to be sufficient to justify funding a mission to those bodies. In other words, a 'standard deep space rover or ocean-swimmer.' :-)" Also, this answer describes silicon carbide ring oscillators already [published five years ago https://aip.scitation.org/doi/10.1063/1.4973429. – uhoh Jul 26 '21 at 22:41
  • 1
    The "no proteins, amino acids or lipids" standards seem a little excessive when you consider the fact that we can't guarantee that meteorite ejecta from Earth won't transport those things to Mars or Europa now. If interplanetary contamination from such weak sources was possible, surely it would have happened already at some point in the last billion years? – tbrookside Jul 26 '21 at 23:14
  • @tbrookside that's mentioned in a previous comment, but not in the question. I do mention infectious proteins, but only used as an example of something biological originally dismissed impossible turning out to be deadly serious. – uhoh Jul 26 '21 at 23:19
  • @uhoh - so a ring oscillator in SiC is about a quad nand gate, roughly 50 years behind silicon, and without the large commercial pressures to get to VLSI and beyond. As I said, decades to get to Galileo-equivalent ICs. – Jon Custer Jul 27 '21 at 00:09
  • @JonCuster I've spent ten years in the semiconductor industry. I was a process development engineer. I developed process, one after another, at breakneck speeds. Shrinking processes for a new material is far less challenging than it is for silicon because all the toolsets already exist. It's not necessary to develop the deposition, etch and lithography equipment for each generation this time, they all exist already. It's mostly just the materials-specific chemistries that are needed. I'm sorry but the idea that SiC will always be 50 years behind Si is simply wrong and uniformed. – uhoh Jul 27 '21 at 00:27
  • @JonCuster all of the process simulation software and device modeling and design software now exists as well and do not have to be developed from scratch. You just take a modern software package and swap the properties from Si to SiC and you can model start modeling your process immediately. The goal of the 2016 paper was to demonstrate the performance as a function of temperature, not to demonstrate the limits of the circuit complexity so the conclusions you draw from that are faulty. We use ring oscillators in scribe line test structures because they are optimized to reflect key parameters – uhoh Jul 27 '21 at 00:31
  • @uhoh - having developed rad-hard technologies myself, I think you are tremendously optimistic. It isn’t that easy. – Jon Custer Jul 27 '21 at 00:54
  • @JonCuster there's nothing that I wrote that suggest anything is easy. There's absolutely nothing easy about the semiconductor industry; never has been, never will be. I don't think you "50 years" is reasonable. The ring oscillators were the correct test structure to use for that experiment and do not reflect a limitation on complexity. I've just asked What is the current state of the art design rule for SiC VLSI? Technological impediments to making a microcontroller for a Venus lander at 460 °C? – uhoh Jul 27 '21 at 01:04
  • If you have $100B you could get to a multi-thousand transistor SiC chip in a decade. – Jon Custer Jul 27 '21 at 01:05
  • "But that's just wishful thinking and hand-waving." Considering how specialized microorganisms tend to be on Earth, and considering that we have no guarantee that alien organisms would even be made out of carbon, to say nothing of DNA, assuming that they existed, I think we can say that the probability of infection is low. Those prions that you mentioned? They tend to infect rather small classes of Earth organisms (e.g., only mammals). Fungal prions do not infect mammals and vice versa. – Obie 2.0 Jul 27 '21 at 12:38
  • As for the prions--a complete non-factor. A prion can only reproduce by finding a host that already makes exactly the same molecular chain. – Loren Pechtel Jul 27 '21 at 14:54
  • 2
    @OrganicMarble "100% certainty is a high bar." Indeed. I'm pretty sure planet Earth doesn't rise to that level in limiting the risk of spreading life: https://www.abc.net.au/news/2011-08-29/life-blasted-into-outer-space/2860438 – Don Branson Jul 27 '21 at 16:25
  • @LorenPechtel Yes, that's how known examples propagate but it doesn't necessarily mean that the chain reaction can't be started by a different molecule. That's actually a good basis for a Biology SE question but it will have to wait until this weekend. In this case I've just used it as an example of something that people didn't think possible turning out to be quite possible and catastrophic. – uhoh Jul 29 '21 at 14:52
  • 1
    To achieve anywhere near 100% sterilization & also avoid post sterilization contamination would require the launch vehicle to be sterilized post launch. – Fred Nov 14 '21 at 11:58
  • @Fred I think so too, so Are any space agencies working on a 100% reliable sterilization techniques for spacecraft bound for subsurface ocean worlds? suggests such a thing. – uhoh Nov 14 '21 at 13:09

2 Answers2

27

Absolute 100% sterilization is impossible. There's always a tiny chance that some microbe lands on a component during manufacturing, gets entombed inside the packaging, and therefore is unreachable by sterilization. Getting such a microbe out to the environment would require breaking the spacecraft in a very peculiar way, without incinerating or damaging the microbe itself. Most crash landings will either not break open the electronics, or will incinerate the electronics.

The gold standard for sterilizing electronics is ethylene oxide gas. It is used to sterilize implanted electronic medical devices, such as pacemakers, which also require strict sterilization to prevent putting microbes into the human body. (Autoclaving is also used for non-electronic implants, but the heat will destroy electronics.)

The NASA Contamination Control Handbook, pp. VI-21 to 23, describes the properties of ethylene oxide:

  • "Most versatile gas for sterilizing purposes"
  • Strong, rapid penetrating ability.
  • Easily penetrates a variety of materials which can be used as "sterile packaging", maintaining a device's sterility until it is used.
  • Moderately microbicidal. Effectiveness is increased by longer exposure times; 24 hours at high concentrations is as good as any other form of sterilization.
  • Absorbed into rubber and plastics; blisters rubber and attacks plasticizers; considerable aeration time required after sterilization for these materials.
  • Aeration after sterilization is effective at dispersing the gas. No residue.

Other sterilization methods listed in the Contamination Control Handbook (p. VI-17) are not suitable for electronics:

  • Wet heat (autoclaving) and dry heat will damage electronics by excessive heat.
  • Formaldehyde (steam or dunkbath) and beta propiolactone are in water solutions that can short out electronics. They are surface disinfectants with poor penetration, and do not penetrate sterile packaging. They will also outgas. Formaldehyde can also polymerize, leaving a residue.
  • Peracetic acid and sodium hypochlorite (bleach) corrode metals, are in water solutions, damage sterile packaging, and can outgas.
  • Ultraviolet radiation has low penetration.
DrSheldon
  • 47,946
  • 12
  • 162
  • 329
  • 2
    Instrumentation for UHV is routinely baked but doesn't have much electronics, but hight temperature semiconductors being developed for Venus missions will be able to handle quite high temperature. It's possible that baking will be the new gold standard for spacecraft that reach biologically viable environments. I suppose it would have to happen in the fairing in LEO to be edfective. – uhoh Jul 25 '21 at 07:35
  • 5
    You always trade something in and something out. High temperature semiconductors will always be limited in one way or another - how about reducing the transistor density 1000-fold? And, baking is not a panacea - some of our lifeforms are pretty hard to kill. – fraxinus Jul 25 '21 at 09:33
  • How about gamma/x-ray? Will that destroy electronics? – Peter - Reinstate Monica Jul 25 '21 at 18:32
  • 2
    @Peter-ReinstateMonica High energy radiation is why we can't have nice electronic things in space. The kind of radiation needed to kill various bacteria in spore form would fry the radiation hardened electronics we have to use in space. – David Hammen Jul 25 '21 at 20:01
  • @DavidHammen Well, maybe not hard gamma, and no charged particles ;-). But UV already sterilizes; X-ray certainly will also. And does X-ray that's just hard enough to penetrate the object indeed destroy robust electronics? – Peter - Reinstate Monica Jul 25 '21 at 20:06
  • @Peter-ReinstateMonica There are some bacteria in spore form that laugh at UV. The gamma ray dosage needed to kill some bacterial spores is huge. So I suspect they chuckle at X-rays as well. As fraxinus wrote, some of our lifeforms are pretty hard to kill. – David Hammen Jul 25 '21 at 20:45
  • @fraxinus but are those fundamental limitations, or just a result of high-temperature semiconductors not having the kind of commercial applications that brought about the shrinking of silicone electronics to what we have today? I would actually imagine that circuits with diamond-based transistors could be made smaller than silicone. And the manufacture of such transistors involves apparently “an immersion in a 200°C solution of (NH₄)₂S₂O₈ and H₂SO₄” and 450°C chemical vapour deposition... can't be many microbes that would survive those kind of conditions. https://doi.org/10.1109%2F5.90131 – leftaroundabout Jul 26 '21 at 09:53
  • @leftaroundabout both. The high temperature limits how much small features you can create because of the accelerated diffusion of everything. It also adds noise to any signal and you cannot do anything about this short of cooling down the circuits and the sensors. We cool the important things even with current technology, but the higher temperature, the less options for cooling we have available. A lot of our technology requires liquid substances (e.g. in electrolytic capacitors, in batteries, in a lot of sensors) that become less of an option as the temperature goes up. – fraxinus Jul 26 '21 at 10:21
  • Gamma, x-ray and other penetrating radiation (1) will kill electronics together with the lifeforms (high-energy radiation simply destroys any complex small-scale structures, that's why it is deadly in the first place) and (2) will still leave a lot of complex molecules (e.g. proteins, that are bad by themselves even if not a part of a working cell) more or less intact. – fraxinus Jul 26 '21 at 10:29
  • 1
    @fraxinus well, but all that is assuming standard silicone-transistor and electrolytic-capacitor technology. Diamond-based operates in a completely different domain, and I'm pretty sure you could also have capacitors whose electrolyte is liquid at 300°C or so (but probably would be solid at room temperature then). Cooling would actually work better at those temperatures as far as space applications are concerned, because radiation becomes an effective mechanism, no need for conductance and/or air convection. – leftaroundabout Jul 26 '21 at 10:40
  • 1
    ...Only problem I see, of course, that this kind of circuitry wouldn't be much use on Earth – there you'd need to spend a lot of energy just to keep it at high enough temperature. So no R/D help from the commercial sector. — Noise is of course also an issue, but because of the higher band gap you'd operate at higher voltages, so that would still work. (Just require more energy, but not like 1000-fold more.) – leftaroundabout Jul 26 '21 at 10:41
  • 4
    @leftaroundabout no high-value capacitors, no batteries and high thermal noise are not small factors. On the other hand, we use diamond electronics even right now (UV LEDs anyone) that don't require high temperatures in order to operate. The progress in the field undobtfully will affect our everyday life as well. – fraxinus Jul 26 '21 at 10:49
  • 1
    @leftaroundabout that's a good point. I was thinking that the silicon carbide ICs for Venus would be tolerant of baking. While the carrier concentrations in semiconductor ICs are defined by doping profiles they also require some finite temperature to ionize those dopants. I think I will ask a question in Electronics SE about this; I'll ping when I do. – uhoh Jul 26 '21 at 11:41
  • Naively, one expects that 600K operating temperatures require twice the energy as 300K because there is twice as much thermal noise (Landauer's principle). But there are decades of development done in 300K labs designing products for usage in 300K houses. So in practice we may expect 10 or 100x the energy and 1000x or more times the cost. That being said, 600K is thought to kill anything Earth-based, even extremophiles spores and prions, in under a second. – Kevin Kostlan Feb 17 '23 at 09:38
17

No, it is not possible to make it 100% sterile. Especially if you consider self-replication as only requirement to classify something as life (It's complicated. See obligatory xkcd reference)

Few issues to consider:

  • In addition to other answer, one would likely use chips and PCBs in your spacecraft. Those are usually manufactured outside Space agencies, and while they're certainly not manufactured at dirty premises, there is absolutely no guarantee that a virus or two won't have landed on chips and then being covered by epoxy, anti-corrosive paint or other sealant which would protect microbes inside during sterilization processeses (to be released into environment some thousand years later when sealant degrades).

  • also, even if one could make it completely sterile when manufactured, there is still an issue of launching your ship through atmosphere, which is full of microbes of various kinds, some of which have a non-zero chance of sticking to it and surviving. And even if you built your spaceship completely from scratch in orbit by mining asteroids and doing all manufacturing completely by robots, there is still non-zero chance that your space-factory was not 100% (but only for example 99.999999% clean). Or one of "infected" sub-millimeter pieces of space debris lands on it.

  • even then, there is no 100% guarantee that there isn't other (non-Earth originated) life in space that your spaceship might not collect in space, and then deposit in usually-more-protected destination (like boring or melting through 19km ice barriers)

So yes, chances of contamination are very low and space agencies (at least some of them) seem to try to make it as sterile as possible, but it is not going to be 100% free of life.

But then again, in colloquial speech, 100% almost never really means 100% (eg. taking a placebo pill is not 100% safe, as one could for example choke on it and die, or emotional response to it could put cardiovascular system at elevated - and thus more likely to fail - levels, etc.)

Matija Nalis
  • 320
  • 3
  • 8
  • The "obligatory xkcd reference" is neither obligatory nor scientifically factual. It sacrifices any value that it could potentially have in the context of being a reliable reference in favour of being "funny", and quite ironically does a bad job at being even remotely amusing, too, at least in my impression. I understand the "humour" is not to be taken literally, but in the case where actual and genuine humour is hardly even present, one might as well look at the scientific content instead to attempt finding at least some value, and that's where it begins to matter. – No Nonsense May 01 '22 at 00:15
  • 1
    @user47149 failure to understand why some people find something funny, is not a proof that something is not funny. You cannot invalidate someone's feelings by claims to the contrary. Also, that is how the jokes often work - by building from accepted, normal and probable to unexpected, unlikely and ridiculous. The linked xkcd (besides being funny to me and many others) is quite educational, as it highlights that there is currently no consensus regarding the definition of life itself, which is why it is relevant to thing being asked here. – Matija Nalis May 02 '22 at 09:44
  • "Failure"? That's quite accusative. Surprise, I actually understand the "jokes" and still regard them as poor quality humour. The only failure I could see is the author's failure to amuse me, I guess. SE network does not operate like a forum, but more like Wikipedia; you don't see random links to xkcd comics in Wikipedia articles, do you? And for a good reason. Lack of consensus regarding the definition of life is not equivalent to worldly entities existing on a spectrum where fungi are supposedly "more alive" than plants, or inanimate objects/phenomena, like fire and clouds, are {continues} – No Nonsense May 03 '22 at 00:28
  • supposedly "more" or "less" alive than one another. There is absolutely no value in linking to such comic, there is not even a punchline: only the author's neurotic turmoil presented as some sort of god-given truth. And especially given that you are, maybe unknowingly, subtly insulting your readers: the link in your answer does not even link to the original xkcd page, but to explainxkcd.com, which puts extremely condescending and pretentious phrase "Explain xkcd: It's 'cause you're dumb." at top before each article. Yikes. {continues} – No Nonsense May 03 '22 at 00:28
  • And also, voicing one's opinion is not an attempt of invalidating anyone's feelings -- please get away from me with such overreactively defensive woke nonsense. My original comment in this thread explicitly disclaims that the described observations are just my impression (implicitly: subjective impression). By the way, content on SE should be based on merit, not on validation of "feelings" -- the fact that, in your response, you brought said validation of "feelings" into the equation is yet another suggestion that this xkcd link has no business being there. – No Nonsense May 03 '22 at 00:33