Comment by bumholio | Hacker News Reader

Comment by bumholio | Hacker News Reader

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This century, it will not. We are very far from a technology capable of achieving what Starshot proposes. Accelerating the spacecraft to a fraction of the speed of light using a laser would require power densities that would instantanously turn all known materials to plasma. The best mirrors and coatings are many orders of magnitude too dark. The required laser and energy bank would be, for all intents and purposes, a comics megaweapon capable of blowing spacecrafts from orbit, or, with proper space reflectors, incinerate enemy installations anywhere on the globe in seconds.

The craft would be completely unable to brake so it will pass past the target planets in a matter of minutes. It's unclear what kind of sensors could be employed to detect anything and we certainly lack the technology to beam and receive back signals sent by a postage stamp craft 5 light years away. Let me rephrase that: we haven't got even a theoretical model of a system that would allow communication at such vast distances with milliwatt power sources.

Needless to say, nobody is seriously working on this, nor will they for many decades at least.

If the craft is packed with instructions on how to get back to us, maybe we could get some sort of exchange going over multiple centuries.

On the other hand, if someone were to sent similar craft to us, would we even have a reasonable chance of detecting something that small without knowing exactly where, when and what to look for?

ʻOumuamua may have been a probe, yet even with our suspicions about it being something out of the ordinary, we more-or-less collectively yawned and went about our daily strife without making any effort to collect it.

[0] https://en.wikipedia.org/wiki/ʻOumuamua

On your other point - would we have a chance to detect something that small? No, absolutely no way, even considering that there would be a continuous 'stream' of these things spread out like beads on a string.

Say each one weighs a gram, and is 1m across - that's just impossibly small. The Hubble ST's resolving power means that it can resolve a 1m object (ie, make one pixel = 1m²) at something like 4000km away. In space terms, that is practically touching. In interstellar terms, that might as well be inside the planet!

Any transmitting that it might be doing would necessarily be very low power, which means it would need to be highly directional and pointed back the way it had come, behind what must be a reflector more reflective by far than anything we know how to build. Unless you managed to get its transmission pointed directly at you by being behind it, there'd be no way to see it.

After decades or more in the interstellar void, it would be about as equal to the ambient temperature as it's possible to be, and in any case, it's not made of very much 'stuff', so it would have no heat signature to detect.

Lastly, at 20% light speed, they would cover the average distance from Pluto to Earth in something like 36 hours. That's not a lot of time to search!

The only possible method I can think of would be to detect the results of these things crashing into dust within the solar system. How much of a 'puff' a gram of diffuse something travelling at 0.2c hitting a speck of rock makes I don't know. Still way too small to spot, I'm sure.

ʻOumuamua is fascinating, I agree - but the most remarkable thing about it is that it's the first object like it we've seen, followed closely by the fact that it's taken us so long to see one. Most models predict these are pretty common - it's just our lack of spotting capacity that's stopping us seeing more.

As far as collecting, I remember reading a back-of-the-envelope analysis that suggested that we might be able to catch it if we made a really concerted effort. We might then be able to hit it with an impactor (or just smack the probe into it) and do some spectroscopy on the resulting dust cloud, but it's going way too fast in an inconvenient direction for us to be able to collect anything, slow down and return it.

I have been obsessing over Oumuamua as well, but there's just not that much information, and we won't be getting more. Then there was the fact that it was tumbling and wasn't emitting anything - one would expect radar scans or radio transmissions, or at least something.

> Then there was the fact that it was tumbling and wasn't emitting anything

There is a range of the radio spectrum we can't really practically measure: the very, very low frequencies. Consider a nanohertz signal. Period of each sine wave: 31 years. You might also need an antenna the size of the solar system to grab anything.

passive sensors are safer if you are sending probes into unknown territory populated by potentially violent aliens.

violent aliens are much closer than you think ;-)

Project starshot does have a history, beyond this press release. And they have thought through the issues. There's a great youtube video here that goes into the details:

https://www.youtube.com/watch?v=bbi1hHPpTjY

They talk about using a 1km^2 earth based laser array to accelerate the craft. They also discuss using a 1W laser on the craft, and using that to transmit data back to earth (with a similar 1km^2 array to receive the signals).

They really seem to have thought through all the issues and come up with difficult, but plausible solutions.

I was wondering how much of that 100gW is lost in Earth's atmosphere - my naive assumption would be quite a bit, but maybe not so much that it would make sense to try and get the laser into orbit (also orbiting gigawatt laser would make everyone nervous, I imagine...)

They suggest using a frequency that minimises absorption by the atmosphere, and run the numbers. It's pretty interesting.

yup. its an awesome idea and the most credible possibility for an interstellar probe but im so sick of reading these pop science articles that make it sound like it's about to launch. we still need to do science on these problems, we aren't at the engineering phase. that said, people are working on it:

https://breakthroughinitiatives.org/research/3

Thank you - this article is interesting meat wrapped in lie-pastry.

The "will" in the title is just flat wrong. "Might possibly" is a stretch, even. People are sketching out the idea, enough that there are known but currently insurmountable problems in doing it. It's an interesting and promising approach in general though.

Some additional highlights:

> accelerate the nanocraft with a 60,000-G force

We're going to make a package of sensors, transmitters, power source and sail that weighs one gram and can also survive 60,000g's of acceleration for multiple minutes? For comparison, the US Navy's ship mounted railguns accelerate projectiles at something like 15,000-20,000g, and those are 10kg of high-precision tungsten, and need to do nothing except not disintegrate.

> The combined laser power needs to be something close to 100 gigawatts

If my maths are right, that's nearly the generation capacity of Japan (https://en.wikipedia.org/wiki/List_of_countries_by_electrici...). Granted, it wouldn't be required for long, but recruiting (or alternatively, storing) a whole-extra-Japan's worth of energy for even a few seconds is just completely ridiculous. We would need large-scale orbiting solar or commodity fusion power before we could even dream of anything like that.

A normal tank gun is 30,000 g and electronic fuzes work just fine for those.

Is that right? I assumed a railgun's acceleration would be about as high as we can go. Huh! In any case, anything that we accelerate like that is highly durable and rigid - you can imagine what happens if you accelerate one part of a 'soft projectile' at 60,000g and another part at 59995g.

Not much? Most things can easily withstand a 5g delta.

Most things like rigid metals or strong plastics, sure. Things like hair-thin strands of carbon fibre mesh and thin plastic films? Not so much.

For sure. Something like this might be useful to explore the Oort Cloud / Kuiper Belt, but I don’t expect to see anything like a star probe built in my lifetime.

Might be interesting to couple laser powered “solar” panels with an ion drive, though :-)

> a comics megaweapon capable of blowing spacecrafts from orbit

So it does have some use other than just launching probes..

I'm not sure that's an advantage. It adds a strong political component to something that's unlikely to be a cost effective weapon. So foreign powers will contest it and domestic powers will be unlikely to put their weight behind it. Kind of like nuclear rockets - in theory a workable technology, yet so controversial nobody will touch it.

That's no Moon!

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