Hacker News Reader

Comment by crispyambulance | Hacker News Reader

I reached my "article limit" for the month, but it makes me wonder, HOW MUCH better could optical fiber be if made in zero-gravity?

Presumably it's all about material purity and accurate/consistent geometry of the fiber itself and the doping profile for refractive index cross-section.

If it were "perfect" how much better would the fiber be? Double the reach? So you cut in half the cost of repeaters/re-generators on long-haul links. Those are definitely expensive, but I think space flight is quite "up there" in cost too.

View on HN

Use incognito to see it. The problem is that the glass needs to be cooled very quickly or it forms crystals, but drawing must be done slowly since molten glass can only flow so fast.

Microgravity has been shown to greatly improve the quality of the glass. The theory goes that convection (where hotter liquid rises past cooler liquid due to its lower density) causes small circular movements of glass that are really good at nucleating crystals.

> Those are definitely expensive, but I think space flight is quite "up there" in cost too.

The machinery is the expensive part. A million dollars of fiber, if it's 1 km, only weighs ~1 kg. On a Falcon 9 that's <$2000. Shipping and handling is usually a hell of a lot more than .2% of a product's cost!

> it makes me wonder, HOW MUCH better could optical fiber be if made in zero-gravity?

1-2 orders of magnitude less attenuation

>1-2 orders of magnitude less attenuation

Currently most of the cost of operating and deploying transatlantic fibre cables are the repeaters to boost the signal in between. If it is 1-2 orders of magnitude less attenuation, does that mean we could do away with the repeater?

I'd imagine yes, on some cables. If we can get 2 orders of magnitude, we go from needing repeaters every 90-120km to 9,000 to 12,000km.

They claim the kind of fiber (ZBLAN) fetches $1M/kg when manufactured on Earth. Looking elsewhere, I see that premium space made ZBLAN because it would be of higher quality could fetch as high as $21M/kg.

https://sites.google.com/site/cmapproject/case-studies/exoti...

Doing some back of the envelope calculations, a SpaceX cargo Dragon can return 3,000 kg to Earth. If they can achieve $1M kg advantage in value that would be $3B. Wow, that's enough to get anyone's attention.

> They claim the kind of fiber (ZBLAN) fetches $1M/kg when manufactured on Earth.

Because supply is so low perhaps?

> If they can achieve $1M kg advantage in value that would be $3B. Wow, that's enough to get anyone's attention.

I suspect the value would drop significantly as supply increases. Gold would be $1M/kg too if it were extremely rare and difficult to extract from the earth. As soon as it's less rare it's a lot less valuable.

I would guess the price is high because its really hard to make. And I doubt the cost of space made ZBLAN would be less than the cost of terrestrially made. The question is would there be enough demand for super high quality ZBLAN to cover the costs of doing it in space? If the value created by space made product was high enough it could kill off terrestrial production.

But I couldn't find any information about the size of the ZBLAN market, for all I know 3,000 kg could be many years worth of consumption. So, this is all guesswork but my back of the envelope calculation at least shows that the economics are not crazy.

> zero-gravity

There's a common misconception that LEO has zero gravity. You're barely off the ground so to speak and gravity is almost the same as on the surface. The difference is that you're constantly falling so you experience weightlessness.

So you are experiencing zero-g, not 0 gravity. You'd be hard pressed to go anywhere with an absence of gravity acting in that spot.

This being said the question is if the quality increase justifies the price (even for a hypothetical future mass implementation). Plenty of products get incremental upgrades, it doesn't have to be a massive jump. Again, if you can justify the cost.

> So you are experiencing zero-g, not 0 gravity.

You’re doing it, too. “g” is the acceleration due to gravity. Heck, scientists call drop tower experiments “microgravity” — it’s much less of a mouthful than “really quite a good approximation of free fall”. [0]

And if you believe in general relativity, LEO is a perfectly valid reference frame with no acceleration due to gravity (ignoring drag) but plenty of second order effects thrown in.

[0] I spent a summer at NASA’s Glenn Research Center doing microgravity combustion experiments studying how combustion is affected by the absence of gravity. I say that entirety unapologetically.

I was under the impression that zero-g is the accepted terminology for when you experience free fall (in orbit, in an elevator). Is that wrong?

Regardless of terminology, I tried to highlight the fact that floating in space is not due to the absence of gravity as many people assume. You're experiencing about 90% of the gravity at the planet's surface just that everything else around you is accelerating along with you.

As far as I know, people do call it zero-g. My point is that gravity is always around, so the more interesting thing to talk about is the acceleration due to gravity in one’s reference frame. For example, here on Earth, we usually neglect the Sun’s gravity unless we’re making accurate predictions of tides.

Yup. Creating a pedantic definition of zero-g to mean "no gravitational field" is pretty useless since you'll always be in the presence of a gravitational field no matter where you are in the universe. The accepted definition is just that your g-meter reads zero.

The term microgravity get used because things in orbit due to tidal forces, different orbital planes, air resistance, solar wind, and radiation pressure.

There's a lot of really strong feelings on the subject though. I'd like to think that GR would let people reach some common ground, but not so much.

https://en.wikipedia.org/wiki/Talk:Micro-g_environment

Hey, it's HN, it's the perfect place to clear up misconceptions. It's definitely not pedantry.

I would consider "misconceptions" which are irrelevant to the point being made to be the exact definition of pedantry. It detracts from the point being discussed, often is centered around some or other strict definition of a word, and is all-in-all about as constructive as being a grammar nazi. Yes, there is a gravitational field in LEO, but LEO is so negligibly close to an actual inertial frame of reference that for all intents and purposes we could (and do) call it one. The people and materials in LEO are in fact experiencing "zero gravity".

Calling it zero gravity is only technically wrong in Newtonian physics, but Newtonian physics are more than just technically wrong when it comes to the reality of general relativity.

Weird, your own explanation didn't stop you from discussing something that is not even tangentially relevant to the point.

My comment was meant to help and if it helped one person that's good enough for me. If you think calling me a grammar nazi (against your stated principles, might I add) helped anyone then by all means, trawl the web for opportunities to do it some more.

> You'd be hard pressed to go anywhere with an absence of gravity acting in that spot.

Okay I think I've found somewhere, but I'm not sure. What experiment should I perform to test that gravity is really absent?

Given the size of the universe and the fact that it's not entirely observable makes it... impractical to even consider measuring gravity. Where we can measure it it's done with accelerometers or doppler shift and measuring the orbital perturbation [0]. Objects close to home are studied more intensely.

You can't really conclude there is no gravity acting in some random point across the universe but you can use other methods to determine when it is acting even if you have no chance of putting an instrument there. Like gravitational lensing. [1]

There's definitely not enough space in a comment to discuss general relativity and measuring gravity of an object in free fall. But if you're curious for more and have time to read Wikipedia has one of the most accessible explanations that don't involve a pile of imperfect or misleading analogies. [2]

[0] https://www.youtube.com/watch?v=cMdjAKn_uXw

[1] https://en.wikipedia.org/wiki/Gravitational_lens

[2] https://en.wikipedia.org/wiki/General_relativity

You can't. You can only measure acceleration (with an accelerometer). If you get zero acceleration, you're in an inertial frame of reference and for all intents and purposes in zero gravity. Newtonian physics says you're technically wrong, but general relativity says Newton is wrong so you're okay.

It is better for making lasers, potentialy for laser weapons. Thats the new market that might make it profitable: small runs of expensive product where 1% improvements are monumental.

Reply on news.ycombinator.com