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Comment by samarama | Hacker News Reader

For those wondering about interstellar travel in sleeping pods, at room temperature humans could only be “frozen” for 10 years (1% bonds broken) before too much DNA damage would have occurred.

However, in temperature below zero at -5 degrees Celsius for example, half life of DNA is actually 10,000 years or more. https://en.m.wikipedia.org/wiki/Ancient_DNA

Still, this would also only allow 200 years of freezing before more than 1% of bonds would have been broken.

The third and probably most viable option is to wake up the crew every 200 years to repair accumulated DNA damage.

Also, a small percentage of the crew would probably be awake at all times for repairs etc., so the crew could rotate every 200 years.

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>> crew would probably be awake at all times for repairs etc

If the ship requires human crews to conduct regular repairs, then the ship probably won't last long enough to get where it is going. A ship that is going to last for 10,000 years will need to be built like an Egyptian pyramid, solid enough to last forever and be functional despite millennia of erosion. Putting someone on that pyramid to conduct repairs might sound good, but after 10,000 years those repairs would become just another source of erosion. The activities of that one person would wear down any system with which they interact.

Erosion in space is much different than on earth. Even the rovers left on the moon 50 years ago should in theory still work.

Except the batteries on that rover are long dead. Many, if not all, of the plastic and paper insulators exposed to vacuum are now brittle and broken. All labels or painted surfaces are likely bleached white. Differential expansion during lunar daylight cycles has likely snapped a few things here and there too. Fifty years of exposure to static electric charges on the moon has put lunar dust in all sorts of places it doesn't belong. Powering up the electrical systems would be interesting/scary. Any metal parts that have been touching each other, again in vacuum, are now contact/cold-welded together. The wheels might still turn, but the bearings are likely shot. And that is all before any talk of micrometeors.

The above poster is talking about physical erosion by human interaction. There are ruts worn into solid rock in many parts of the world with old roads that are only 1000 or 2000 years old. Over 10,000 years anything that is touched by humans will be worn away to no material at all.

Those areas received a lot of traffic, and the rocks in question are not particularly durable as durable rocks such as quartzite are much harder to use in large scale construction projects.

Depending on the speed of an interstellar craft, even trace amounts of dust between stars could be a source of significant erosion over a long enough period of time.

And it’s silly to think about. Who cares. 300 years from now people will be taking trash out in mars and people will be picking it up. We will spread our disease at least within out universe.

There's no biosphere on Mars, nothing alive there, our Terran notion of pollution makes no sense on Mars.

Our Terran notion of pollution makes no sense anywhere without Terran compatible atmospheres.

In a ship with 20 million parts, 19.9 million can probably be automated, but there’s simply 100k parts that can’t always be fixed 100% in advance.

If you go fast enough, accelerating and decelerating at 1 g, you can travel a million light years in a perceived time of about 27 years.

Yes, but you also need nearly infinite fuel.

An efficient engine could use antimatter as its battery/fuel source and move itself forward by using antimatter to eject propellant close to the speed of light in the opposite direction right? That probably wouldn’t require a large mass of antimatter/propellant. Especially since you can collect propellant from the interstellar medium wherever you’re going

Even antimatter has limits, and those limits deny reaching a relativistic gamma of 1e6/27:

http://www.projectrho.com/public_html/rocket/enginelist3.php

But even if you ignore that limit, at that kind of speed you also need to account for your outer hull undergoing significant damage as each stray intergalactic hydrogen you hit has a kinetic energy of 34.75 TeV in your frame of reference, and while this will create a large supply of antimatter, it will do so in a way significantly less helpful to your goal than the fact we can transmute lead into gold by using the former as a radiation shield in a nuclear reactor is useful to someone who wants to get rich quick.

Bonus fact: this energy level is higher than the LHC, so you may have some extra weird mass-modification effects besides relativity as the front of your spaceship is now a Higgs Boson torch.

Nah, just 3e18 kg ;)

That's a more difficult problem compared to DNA repair, crew rotation, or material erosion.

Don’t we have highly durable generational spaceships already? They’re called asteroids. If we find an asteroid that’s large enough to have internal geothermal activity, you could put a bunch of people in an underground system and nudge it into a trajectory towards another star system.

As long as it can support crops, oxygen generation, etc the passengers just proceed to live a “normal” life for the next couple generations until they arrive in orbit around a brand new star.

The hardest part would be maintaining culture to still identify with the purpose of the mission after there’s no one of the original passengers left over

Don’t we have highly durable generational spaceships already? They’re called asteroids.

A planet. You're describing a planet. And we're doing a pretty terrible job keeping this planet we're traveling on sustainable for human habitation.

Well the one we’re on has made it 4 billion years. Getting one to last 10,000 years should be a lot easier

It has only been about 5000 years since humans became sedentary and formed civilisations and we're already seriously disrupting the ecosystem. That's the timeline you'd have to look at.

If we get to a point where we can acquire a planet and hurl it in a specific direction with meaningful speed, then we must’ve developed enough to also keep the planet livable long enough.

Well if you’re gonna do that, you might as well have it accompany a star to give it energy for that journey.

Add a gas giant or two (or 4) to protect it against incoming space debris and help stabilize orbits.

Add some neighboring rocks to also help with that + give them extra material to use once they arrive.

Implant ideas of leaving the rock and coming from a place of great power into the colony’s generational memory.

Include some infrastructure to aid them.

This scenario looks oddly familiar.

Less than a flash in the physical history of this world. Crazy!

> sustainable for human habitation

Even the worst outcomes predicted by climate change models leave some inhabitable regions right? Definitely not sustainable for current population levels though...

At least on a barren rock, we don't have to worry about disrupting existing natural systems and throwing them into chaos? Starting from scratch as it were, presuming we are responsible enough to maintain it...

I don't think most asteroids are large or dense enough to have adequate geothermal heat to sustain a human population?

Anyone got a back-of-the-envelope calculation for what size asteroid we'd need for this?

https://arc.aiaa.org/doi/10.2514/6.2014-4373

How structurally solid are asteroids, comets? I thought they were mostly balls of 'snow'.

What about water?

I do concede a certain amount of hand waving in this proposed solution

I like your thinking! A couple of points:

(1) we don't really know the threshold yet to be beyond repair I think. It may be 1% but may be 20%.

(2) as others noted, it's 15 years for 0.1% damage using your math.

(3) your timeline directly contradicts the article doesn't it, which suggests keeping people in ideal conditions would have a DNA half life of millions of years.

(4) it's not a given that you need to wake people up to repair DNA. Maybe you just need to bring them to 1 degree Celsius or something. Or maybe nanobots can work on you while completely frozen. I think we are quite far from knowing right now.

So yes, for long term travel DNA repair will be important but how it actually works I think we know little about.

Good points, but why is it 15 years for 0.1%?

How about frozen embryos and artificial wombs for gestating those embryos X years before arrival?

Then you only need a crew of X people at any given time to keep the ship operational. Some generations would be born and die during the trip (kinda depressing, but I like to think I would be happy in that scenario)

If you don't like the idea of having a machine as your mother, you could also do IVF with the women that are alive and well and constitute ~50% of the crew keeping the ship operational

A half-life of 10,000 years means the fraction (0 to 1) of healthy bonds at year t can be modeled by (1/2)^(t/10000). To have 1% bonds broken, it would take an expected 145 years. EDIT: Fixed the numbers, my bad!

  >>> log(0.99, (1/2)**(1/10000))
  144.99569695122509

I don't understand this. Does half-life even say anything else about the probability distribution? aren't you assuming specific distribution here?

It's not a terrible assumption to make. We just need to assume[1] that the decay events are independent, that is, every bond flips a coin every 500 years and if it comes up heads, it breaks, independent of what the other bonds do. That is, the process is inherently "local", individual bonds having no way of knowing what the other bonds are doing.

[1] It may be a bit worse in the long run, since if many bonds break, the higher order DNA structure gets damaged and that may change the rate of decay experienced by individual bonds (?).

half lives (specifically, the "decay" of any individual thing is stochastic but the aggregate of many molecules models exponential decay (in radioactivity. I have no idea what happens in a complex mash of DNA)

This shows the importance of mental gut checks.

If indeed 1% break after 15 years, then 10% (ignoring compounding) break after 150 years, and 50% after 750 years. That doesn’t square with a half life of 10,000.

I always forget Bernoulli's inequality. Your gut isn't as clever as mine :)

Your 15 years number is for 0.1%

I'm sure there are ways in which we are still learning and right out of the plot of a film that needs no mention: https://newatlas.com/science/extract-insect-dna-amber/

Even in a -80C freezer with dehydrated and frozen cells they don't recommend over 5 years.

https://www.researchgate.net/post/How-long-can-fresh-frozen-...

At the speed of travel you would want to traverse space, wouldn't the time dilation make the half life of passengers less of a problem?

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