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Comment by xiphias2 | Hacker News Reader

What is special/hard to make for Starhopper compared to Falcon 9?

Hm..I think I found it on the net: The Raptor engines are the same size but are about twice as powerful as the existing Merlin engines.

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The Raptor engine isn't just "more powerful" but uses an advanced "full-flow staged-combustion" cycle which has never flown before.

The Merlin is highly optimized but it uses a simpler "gas generator" cycle which is less efficient. The Falcon 9 and Merlin is famously optimized for "low-cost" instead of "high-tech" but with Raptor they are now advancing the state of the art in propulsion tech.

The Raptor engine is the first full-flow staged combustion cycle engine to every fly.

https://en.wikipedia.org/wiki/Staged_combustion_cycle#Full-f...

The word you have looked for is ever, not every.

It's clearly an unintentional typo, and also not possible to confuse for something else.

It's also worth mentioning that the Raptor engine is meant to use fuel made in ISRU systems on Mars. Most (nearly all?) components of Methane fuel for the Raptor can be extracted from the Martian soil, rocks, atmosphere, etc. A primary design consideration for Raptor was that it should enable Mars missions, and Mars missions are nearly impossible to do without manufacturing your fuel on location, so Raptor is ISRU-first with a Methane fuel.

Everything SpaceX does is moving towards a goal of enabling a colony of 1M+ people on Mars as soon as possible. A lot of people are confused by SpaceX decisions, but if you view it through the lens of Mars colonization, then it all usually makes more sense.

I think Raptor might be the first Methane-based rocket engine as well.

> I think Raptor might be the first Methane-based rocket engine as well.

If I remember correctly, John Carmack's Armadillo Aerospace tried burning methane in an engine. Though I don't think they were the only team - or even the first one.

Wikipedia lists a few methane/LOX engines that have been used in test flights. For example, NASA's experimental Morpheus lander had fifteen or so test flights -- all low altitude, but some higher and longer lasting than StarHopper's hop today. It's also being developed simultaneously with Blue Origin's BE-4 engine, which hasn't flown yet, but has been through an extensive ground test program, and will be used on both Blue's own New Glenn orbital rocket and on ULA's Vulcan. So depending on how quickly the relevant test programs go, Raptor may or may not wind up being the first to be part of an orbital vehicle. (But as neither Vulcan nor New Glenn is currently slated to use it for the second stage, Raptor will very likely be the first to go all the way to orbit.)

Yeah, Raptor is the first full-flow staged-combustion engine to fly, but not the first methalox.

I should point out that John Carmack's Armadillo Aerospace are the ones who actually built Morpheus.

How can methane be created on Mars? It is a gas right, and it isn't that cold there?

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

Methane is CH4. Carbon from Carbon Dioxide (CO2) and Hydrogen from Water (H2O).

Stoichiometrically, CO2 + (2)H2O -> CH4 + (2)O2

The process is performed via the Sabatier Reaction, which someone else linked to.

It's a gas at STP here on Earth. It's a liquid when it's being used as a rocket fuel.

https://everydayastronaut.com/raptor-engine/ is a great overview of why Raptor is such an interesting development.

The end game for Starhopper is the Super Heavy/Starship combo, which (if it all works out as planned) will be able to lift around 100 tons to low Earth orbit and be fully reusable with no refurbishment needed between flights.

A few things from a non-expert:

-Raptor is operating at previously unheard of pressure, and uses advanced new materials and heavily utilized GPU-powered flow simulations during design.

-it's super efficient. It's the first operational full flow staged combustion engine AFAIK. High thrust + High efficiency == a good time.

-it uses METHALOX fuel, which can be made on various celestial bodies somewhat easily (importantly: mars). Water + solar energy + CO2 == methane-oxygen fuel

-uses more difficult spark ignition w/unlimited restarts instead of more reliable but "cartridge" based TEA-TEB (sp?) igniters that rely on mixing volatile complex to manufacture toxic chemicals to start.

The test hopper has 1 engine. The orbital prototype will have 3. The production booster will have 31 of these bad boys and put out 2.0-2.7x the thrust of a saturn V

I’m slightly worried that at some point they will hit an integer overflow and crash the simulation.

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