Hacker News Reader

Comment by semi-extrinsic | Hacker News Reader

Methalox can be a better choice if you are designing a reusable launch system and you are optimizing for low cost to orbit.

SLS is planned as an expendable launch system that will put spacecraft far beyond Earth orbit. They need the specific impulse that hydrogen offers.

And in related news, liquid hydrogen is going to become just as mainstream as LNG is today, within a decade from now. All the major LNG ship builders (KHI, GTT etc.) are building and testing LH2 transport ships as we speak. Suiso Frontier began operational sailing more than a year ago.

View on HN

Methalox ends up being preferable because Hydrogen ends up performing relatively similarly when accounting for the extra tank mass needed to effectively contain it (both in terms of thicker walls and larger tanks in general). Methalox can't achieve Hydrogen ISPs but in exchange it's much easier to contain, allowing for much lighter and simpler tanks, resulting in similar deltaV overall.

On top of that cryo methane and oxygen are at closer temperatures than hydrogen and oxygen, which simplifies storage further.

So effectively the difference is that Hydrogen embrittles everything and makes development more expensive even without reuse considerations, making Methane superior unless you're SLS and being wasteful is a feature.

It's been a while but it seemed to me that high ISP isn't very big win for the first stage anyways. Basically linear with everything being equal which as you mention it isn't. So slightly lower ISP means slightly heavy first stage.

Either way it's disappointing NASA is determined to keep the Space Shuttle's white tech elephant going.

Low cost to orbit is the whole ball game. If you have that, everything else is dramatically easier. Not optimizing for that is, as the grandparent comment put it, brain damage. (AKA politics)

The private space industry interprets brain damage as damage and routes around it.

> Methalox can be a better choice if you are designing a reusable launch system and you are optimizing for low cost to orbit.

The only reason to not design a reusable launch system in the past 7 years is because you lack foresight, or you have a design by committee where you're being forced into poor decisions for political gain.

> They need the specific impulse that hydrogen offers.

They wanted it, sure: there's more than one way to build a big rocket, and the choice that Congress/NASA made was to use hydrogen on a sustainer stage.

They could have made other choices.

Reply on news.ycombinator.com