HN Theater @HNTheaterMonth

Honorable mention: an aerospike engine has been flown by Arca space.

Well, kind off.. it's a spike, but they're using water steam as propellent, I'm guessing to "solve" the cooling problem. So not sure if it counts (and how successful their rocket will be).

But still.. https://www.youtube.com/watch?v=QsKE_SBY-kE

⬐ rbanffy

Well... If you have a hydrolox aerospike engine, what comes out of the exhaust is just very hot water... ;-)

⬐ BenjiWiebe

And MethaLox is just very hot soda water. :)

⬐ rbanffy

Sparkly!

⬐ pfdietz

LH2/LOX engines (and most others) typically are operated a bit fuel rich. At stoichiometric fuel/oxidizer ratio, the flame is so hot the mixture has significant dissociation, so it loses some of the chemical energy. It's advantageous to win back some of that by adding extra hydrogen, reducing the temperature slightly but also significantly reducing the average molecular weight of the gases.

⬐ panick21_

No it hasn't. Please stop ever linking to Arca space.

That is not a company, its a fraud. They defraud investors. They are not a real company.

I recommend ignoring them and warning people against them.

The most recent company who was seriously developing a areospike was Firefly. That was for a pressure fed rocket. They have since dropped that, and in the most recent interview between Everyday Astronaut and the CEO of Firefly he addresses why they did that.

⬐ bryanlarsen

I don't think ARCA's tea kettle is technically a rocket engine, since there's no combustion.

⬐ avmich

Hydrazine or hydrogen peroxide can be used as monopropellant, and it's still rocket engines, even without combustion.

⬐ bryanlarsen

True, but it's still a highly exothermic decomposition, the energy comes from a chemical reaction, unlike ARCA's silliness.

⬐ avmich

But it's not combustion. I guess you meant something else. Now you label they approach; do you think laying boundary line this way looks obviously correct? Say, nuclear rocket engines heat up gases - also without chemical reaction; resistor jets also have reasonable history in rocketry - why ARCA's approach is wrong?

⬐ SonicScrub

Because their vehicle ISP is ~90-100. Plug that number into the rocket equation and see how much delta-v you get.

⬐ p_l

There's no combustion requirement for a reaction drive ;-)

⬐ bernulli

I don't see that as a reasonable constraint - nuclear propulsion does not need combustion, thermo electric does not need combustion, and there's also things like cold gas thrusters, laser ablation etc. etc. etc.

⬐ bryanlarsen

Usually those are called thrusters rather than rocket engines.

⬐ bernulli

A bit big for a thruster, no? https://en.m.wikipedia.org/wiki/NERVA

⬐ CarVac

If that counts, then my flight of a demo Aerotech aerospike HPR reload counts.

⬐ SonicScrub

Ah yes, ARCA Space. That company founded by a guy who faced 13 counts of fraud, 5 counts of embezzlement, and one count of forgery. I'm not surprised that company has so many "buzzword" technologies that it's supposedly developing. What better way to scam... err I mean... provide opportunities for bold investors.

What's the ISP on a water rocket? 90?