I think the idea is very interesting, but please correct me if I’m wrong, isn’t the payload experiencing a sustained acceleration of hundreds of thousands of Gs, if not millions?

I am not sure that anything useful could survive that kind of sustained crushing acceleration. By comparison a rifle bullet being shot is around 100k Gs for millisecond , this would go on for weeks or months.

▲

ben_w 4 days ago | parent [-]

Given how short the proposal's tethers are, I'd suggest one can very easily reduce the peak G-force for any given linear speed by making the tethers longer. Once they get to the physical extremes (especially the bit at the end about enhancing tensile strength with an electric charge, which I suspect will involve surface voltages sufficient for pair production from any stray electrons accelerated from one to the other*), it stops being easy.

It's SpinLaunch from solar orbit rather than the surface of the Earth (in fact, they themselves say so at the end of 11.1). Even for the current tech demo of SpinLaunch, that was getting 10k G and the company found it wasn't too difficult to make payloads survive that: https://www.youtube.com/watch?v=g-DjBHroA1I

Yes, that's 10x-100x less than what you're asking (I've only skim-read the paper, your 100k-1M is certainly plausible given what they're focusing on is the "can it be done at all" and not a detailed launch proposal), but in practice if we were limited to 10k (we're probably not) that only means making the tether 10x-100x the length in this paper.

* My citation here is just "gut feeling" as I play around with ideas like this from time to time, and this particular thing, using electric forces for a non-gravitational orbit, was something I came up with and then rejected on this basis as part a hard-science tractor beam in the novel I've still not finished writing, and the accidental antimatter problem happened with relatively small accelerations for a plausible mass probe.

▲

EndsOfnversion 4 days ago | parent [-]

You can certainly make the tethers longer, but that re-introduces other problems with the tensile strength that the current proposed shape is intended to mitigate.

I’m very skeptical about Spinlaunch, but even if you can pour enough epoxy over something to allow it to survive 10k Gs for a few minutes, I am not sure you can scale it to 100k+ Gs for weeks, for a postage stamp sized payload that has to be almost perfectly flat - that just seems like a completely different problem domain.

I think the idea bears further investigation, but the omission from the paper feels a bit odd.

Good luck with the novel!

▲

ben_w 4 days ago | parent [-]

> I’m very skeptical about Spinlaunch, but even if you can pour enough epoxy over something to allow it to survive 10k Gs for a few minutes,

Please do watch the video I linked to — it was a surprise to the people whose cubesat design they lightly modified, that they didn't need to fill all voids with epoxy resin.

> I am not sure you can scale it to 100k+ Gs for weeks, for a postage stamp sized payload that has to be almost perfectly flat - that just seems like a completely different problem domain.

If anything, I expect "flat postage stamp" to be easier, even with a 100x increase in G-forces. Thin structure in compression -> total forces are still low. Balancing a fully laden lorry on a 10cm cube of steel (7.5kg vs 50 tons ~= 6,000x) seems borderline in the way that balancing a 10cm cube of steel on top of 1cm^2 of 80 gsm paper (=8mg vs 7.5kg ~= 937500) doesn't.

(Edit: forgot density of steel, thought it was 5 not 7.5)

> I think the idea bears further investigation, but the omission from the paper feels a bit odd.

100%. It does feel a bit like it's formalising my shower thoughts.

> Good luck with the novel!

Thanks, I'll need it! >_>

▲

EndsOfnversion 3 days ago | parent [-]

Ah, but that’s the thing it’s not compression it’s tension. Try hanging the same steel cube from the ceiling with a scrap of paper and things get decidedly more difficult.

And even if you can find some magic superglue left in the tube to hold it there, it has to hang there for weeks: A cubist sword of Damocles.

▲

ben_w 3 days ago | parent [-]

The tether is always in tension, in general the payload is allowed to be in either tension (if attached to the tether on the "top") or compression (if in a pouch of the same material as the tether, e.g. shepherd's sling configuration: https://en.wikipedia.org/wiki/Sling_(weapon)), at the preference of the system designer.

	▲	EndsOfnversion 3 days ago \| parent [-]
		It’s a good point: I’d assumed that the plan was to make the payload of basically the same material as the tether/structure, and have it destructively tear-off at the right moment (maybe by having a watching supervisor structure lasering a weak point) But I think pouching the payload (presumably forming the structure around the payload) just translates the problem into holding a 8kg steel block to the ceiling with 1cm square of paper formed into a harness, and expecting it to hold for weeks. Either way - hopefully it will be addressed in a follow-up