Generation ship design project

[stevebowers]

...it appears that unless you use a generous amount of the very best shielding material humanity has to offer, you would have little luck surviving a short trip against the normal dust that exists everywhere.

That really depends on the speed of travel. At what speed does dust become a significant problem that a well-designed shield can't handle?

[AstroChara]

...it appears that unless you use a generous amount of the very best shielding material humanity has to offer, you would have little luck surviving a short trip against the normal dust that exists everywhere.

That really depends on the speed of travel. At what speed does dust become a significant problem that a well-designed shield can't handle?

Gotta admit we’ve only been assuming solid slabs of materials at the moment, but I was tinkering with a calculator my friend (with help from Luke Campbell) developed, and at 0.1c, a 1 metre thick slab of “graphite” (I assume this is a workable stand-in for carbon allotrophs and such that don’t shatter as easily) would survive for 16 light-years. Most materials last for a lot less. It seems the important property here is yield strength - more yield strength to reduce erosion rate. At 0.2 ly that drops to 3.9 ly. Also you presumably want the actual shield to have some redundancies for cases where your ship gets struck by larger than usual particles.

[stevebowers]

So by the late Federation era very good shields would be needed, because velocities were above 0.5c by then. Pandifico or corundumoid spring to mind. The very fastest ships would need metric shields, which are transapientech, probably.

[stevebowers]

A small magshield at the bow, filled with dusty plasma, could reduce the effects of dust impacts, too.

[Drashner1]

From past discussions, OA presumes (although not all that obviously) that inflight 'shielding' actually consists of multiple cooperating systems (mass, lasers, magnetic fields, plasma, perhaps other things). We should probably make that more explicit.

There is also this page - LINK - that was updated not that long ago and seems to be based on somewhat different conclusions re impacts on a mass shield. Maybe - perhaps the numbers actually line up with what is being mentioned here in the last few posts.

Another reason that we should probably spend some significant attention at some point on updating the shielding article and other pages dealing with interstellar travel.

Todd

[stevebowers]

Yeah; I suppose we need to organise the article into passive bulk shielding, on to more advanced self-repairing constructs, then move into active shielding, transapientech metric concepts and void bubbles.

[inkoalawetrust]

Realistically, the shielding for an interstellar spaceship would likely be multiple active and passive systems functioning in unison to protect the ship and cover each other's weaknesses like what Todd mentioned. Pulse lasers could be used to destroy and/or weaken interstellar cruft before it impacts, magshields repelling cruft away, plasma being fired out in advance to disintegrate them (What Steve suggested), smart particles or sacrificial interceptors being sent out (Particularly if the grains can be detected in advance), varying levels of self-repairability on the shield itself. Hell you could have even more esoteric defenses like a large self repairing gas bag that debris flies right into and gets burned up like atmospheric entry.

And then for the physical shield itself, well, from what I understand such high velocity impacts basically cause materials to splash like puddles regardless of what they are made of. So a physical shield could come in the form of a whipple shield of 100k+ layers instead of a solid block, each being able to withstand 1-3 impacts in the same spot (Assuming no self repair), or maybe they could even be shaped into some weird optimal (?) sponge-like consistency. Alternatively, if it's a solid block (Or even the whipple shields), it would be some composite made of metamaterials and materials like diamondroids etc, because few materials are just made of one actual material, ESPECIALLY armor.



That being said, this would likely still pose a major engineering problem early in the timeline. And just going slower would still be the simplest solution for a lot of cases, particularly since by then bionts are already ageless, so they can afford taking twice as long to arrive than needing super good engineering or carrying a 3000% higher risk of exploding just to get there a bit faster.

Also, I think this could be used to potentially justify the extent of ahuman factions and individuals even early on, fully grown bionts need a lot of heavy life support systems that take up precious shielding and/or passenger mass, even if they are tweaked to be more efficient. Meanwhile AIs and virtuals are just innately more efficient and compact by not having a full currently completely redundant body. Which would allow AI ships to travel more safely and/or faster than bionts would. So besides solsys era humanity having little urgency to go interstellar than the ahumans, the greater ease of doing so could also justify their early expansion and leg up.

Besides ahumans having another excuse for having more claims early on. The difficulty of economically shielding ships could also perhaps lead to more early interstellar trips being done by uploads, and/or being seedships carrying preserved embryos of their biont passengers (???), or just flat out being slower. It would also possibly provide a justification for developing the lightways early on.

[AstroChara]

From past discussions, OA presumes (although not all that obviously) that inflight 'shielding' actually consists of multiple cooperating systems (mass, lasers, magnetic fields, plasma, perhaps other things). We should probably make that more explicit.

There is also this page - LINK - that was updated not that long ago and seems to be based on somewhat different conclusions re impacts on a mass shield. Maybe - perhaps the numbers actually line up with what is being mentioned here in the last few posts.

Interstellar shielding generally being multiple systems sounds realistic to me. I do believe that even the very first missions would want to leverage every single technologies they have at disposal that could help and doesn’t cost too much to use.

Regarding the Interstellar Shielding article; indeed we did update it earlier, removing water ice as a viable shielding option due to its extremely high expected erosion rate, and probably also changing other entries. I haven't given it a proper read however so I am not sure what other parts may require update. I'd like to note that the author of the article, to my understanding, currently agrees with Luke Campbell’s method for calculating dust erosion of shield which finds very high erosion rate and such, so indeed this article should be updated.

EDIT: Regardless of what I mentioned here though, I don't really find fast interstellar travel to be unlikely at all — at worst ships might have to stop on a bunch of interstellar bodies to extract materials for repairs and such. But getting up to speed is one of the more well thought-out aspect of it, and I don't believe it'd be a big issue to get up to say 0.1c. An interplanetary society would also have plenty of opportunities to experiment with getting equipment to last decades or centuries, plus the repairing. And us not knowing the abundance of mission-ending big boulders is hardly a reason for ruling out fast interstellar. It's probably possible to constrain the number of at least some sizeable objects based on "extinction" of distant stars (that's not caused by dust), and for now I think the lack of concern about those affecting research into distant stars is probably good enough for us to say that there's no suffocating amount of interstellar pebbles out to end any interstellar mission.

[Drashner1]

Just to add a couple things to the mix:

a) Re lasers - optical phased arrays - particularly those based on PQDA technology might allow the entire front of the ship to act as a laser emitter firing a beam as wide as the whole front of the ship (this rather than specific individual emitters firing overlapping beams or the like). It might also make the system more resilient in that damaging part of the array would still leave the rest intact while repairs are made to the damaged bits.

Power requirements might be challenging - how much energy would a laser protection system need to emit anyway?

Related random thought that just came to me - perhaps the laser system (or other onboard lasers) could constantly energize a plasma cloud ahead of the ship to help vaporize potential impactors rather than try to shoot them down directly.

b) Although we don't make a big deal of it (and perhaps should make more of one) - we've long said that shielding is a major limiting factor for both the speed and maximum range of OA ships - even up into transapient levels. From the sound of things so far, that element is likely to be one we want to keep. Note that this is not arguing that OA ships have to be 'slow' in the later timeline - just that they don't (usually) do hyper-relativistic speeds where time dilation becomes significant. But with biostasis tech this isn't generally a big deal.

My 2c worth,

Todd

[AstroChara]

Just to add a couple things to the mix:

a) Re lasers - optical phased arrays - particularly those based on PQDA technology might allow the entire front of the ship to act as a laser emitter firing a beam as wide as the whole front of the ship (this rather than specific individual emitters firing overlapping beams or the like). It might also make the system more resilient in that damaging part of the array would still leave the rest intact while repairs are made to the damaged bits.

Power requirements might be challenging - how much energy would a laser protection system need to emit anyway?

Related random thought that just came to me - perhaps the laser system (or other onboard lasers) could constantly energize a plasma cloud ahead of the ship to help vaporize potential impactors rather than try to shoot them down directly.

b) Although we don't make a big deal of it (and perhaps should make more of one) - we've long said that shielding is a major limiting factor for both the speed and maximum range of OA ships - even up into transapient levels. From the sound of things so far, that element is likely to be one we want to keep. Note that this is not arguing that OA ships have to be 'slow' in the later timeline - just that they don't (usually) do hyper-relativistic speeds where time dilation becomes significant. But with biostasis tech this isn't generally a big deal.

My 2c worth,

Todd

a) Good point regarding PQDAs. I imagine you might also want it to light up any incoming projectiles as well. I'm not sure how much power would be required; not much luck checking research papers for heat capacities for the dust grain elements, and we don't even know how common the bigger sand grains/pebbles/boulders are, though in the latter cases lasers might not even help.

Regarding the plasma idea: I'm not sure how one could keep that plasma contained for extended periods in vacuum, while said plasma is receiving even more energy from the dust particles.

b) Shielding being a major limiting factor for speed and maximum range of interstellar vessels in Orion's Arm seems reasonable — alongside other factors (like cost and stuff breaking down) of course.

I'd mused about it on Discord before to check people's opinions, but I believe we might want to also look into the pre-Federation interstellar colonization (again), because we have missions flying at pretty fast speeds (0.2c, even 0.3c) as well as going for really, really distant locations (as far as Iota Horologii, at 57 ly) somehow. Back when I was working on this and chatting with Rynn, I was informed that the main limiting factor was cost of the mission — you need more fuel to go faster, and the likes.

I can make a thread for discussing about this topic, if people are interested.