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Comment by phkahler | Hacker News Reader

I find the whole idea of carbon fiber inside a pressurized LOX contain a bit risky. Also, what about all those reports that we're running out of helium? Is that credible threat to ongoing space flight?

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The cost of the physical helium in rocketry is going to remain negligible for a long time. The total cost of materials in a modern rocket is something like 1/2 of a percent of the cost of a launch, and I'm confident saying Helium is a tiny fraction of that. It doesn't matter if it goes up in price by a few orders of magnitudes. We are also still producing it in large quantities (natural gas often contains a lot of helium, which we extract). Rocket's also use a tiny amount of helium percentage wise, simply because there are so few rocket launches.

However even if we did somehow run out of Helium entirely, once SpaceX switches to Methane fuel (as they plan to do for the ITS) they won't need it anymore. Currently it's used to pressurize the tanks, but Methane does that for itself. It would mean speeding up development of 'small' methane launch vehicles presumably, but that's it.

I imagine that there are other ways to accomplish the same goal, as well, such as using other noble gasses. Helium provides the best cost/benefit tradeoff but surely other approaches would be practical if helium becomes unavailable.

How would you pressurize the liquid oxygen needed for the methane to burn?

Per the other comment, no other noble gas has a low enough boiling point to remain a gas at LOX temperatures...

If you need to you can heat up the oxygen to increase it's volume until the pressure is correct. I forget the reason that it's easier to do with methane than oxygen but it's possible to do with oxygen too if you really need to. ULA's new ACES upper stage is planned to use autogenous pressurization for both it's oxygen and hydrogen tanks.

We're not really running out, it's just getting more expensive because the government doesn't regulate it's availability anymore since the strategic helium reserve was done away with. It won't be a big deal for (already expensive) rocketry. Buying helium balloons for your birthday will be pricey, though.

Um, no. We are in fact running out of helium. There's only a certain mount and nobody not even natural processes is making anymore in any significant quantity. And what we do have is rapidly being released into the atmosphere and escaping into space.

And given that the nearest natural source of helium is Jupiter, that is a little concerning.

New helium is generated by alpha decay, and it comes up in natural gas wells that happen to be located in areas with natural radioactivity.

Not much, though. A quick perusal of Wikipedia (buyer beware, etc.) indicates that about 3,000 tons of helium are generated per year through radioactive decay (that's all happening in assorted rocks throughout the Earth's crust, so much of it wouldn't be easy to recover, either) while current production rates are around 9,000 tons per year.

A natural gas well has 10s of millions of years of helium accumulation from its local area.

Right, which means that while it's renewable over geological timescales, it's more or less a fixed reserve in human timescales. Much like oil.

Avogadro's number is very big: 6e22.

It's even bigger than that: ~ 6e23.

https://en.wikipedia.org/wiki/Avogadro_constant

Thank you.

los grandes avogadro's :)

You can extract helium from natural gas.

An estimated 54 billion cubic feet (1.5×109 m3) of helium was detected in Tanzania in 2016

https://en.wikipedia.org/wiki/Helium#Modern_extraction_and_d...

Yes that is where all helium on earth comes from: trapped ground sources, often in natural gas and oil deposits. Alpha particles from the Earth's radioactive core propagate upwards and get trapped somewhere in the earths crust, where we find them. But it took hundreds of millions of years to create macroscopic amounts of helium, so once all the sources in the ground or tapped it's gone, on human timescales at least. And you can't recycle from the atmosphere because it escapes the Earth's gravity.

I'm pretty sure we could make more helium if we really needed it. Nuclear fusion produces helium as a waste, and I expect fusion to become widespread before we run out of natural sources of helium on Earth.

We already rely on nuclear reactors to get several elements that are used in radiotherapy. IIRC there was a major shortage of medical isotopes a few years ago when a Canadian reactor that used to supply most of them was shut down.

Of course, it will be expensive, so no more cheap helium balloons for our grandkids. For specialized applications, though, we can afford some artificial helium.

A big difference between radionuclides and helium is that radionuclides are only needed in a relatively "small" quantity (producable by fission). Nuclear fusion would create helium but in very small quantities. Having 1TWe of fusion reactors would only yield 5grams of helium/second. That is not much.

> And given that the nearest natural source of helium is Jupiter, that is a little concerning.

Sun is closer and produces helium all the time, but less practical to harvest it from.

The US government alone is in the process of disposing[1] 1 billion cubic meters of the stuff from it's strategic reserves dating to back when airships where a thing. That volume is equivalent to a cube 1km long on each side.

1. https://en.wikipedia.org/wiki/National_Helium_Reserve

And when it is gone?

I believe that it's very likely that SpaceX can recover the helium used during operation. The helium isn't expelled from the fuel tanks. Since the 1st stage returns, it could be recovered.

Its more of we are running out of cheap helium as the US has been selling off its massive stockpile and its nearly depleted.

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