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

Question

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

5. 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?

Answer 1

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.

Answer 2

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.)