Hot Fire! NASA Tests Powerful Artemis Moon Rocket Engine [8:47]

YouTube ^ | October 21, 2026 | VideoFromSpace

[SunkenCiv]

NASA fired up an RS-25 rocket engine at Stennis Space Center in Mississippi on Oct. 21, 2026. It was a hot-fire test of developmental RS-25 engine No. 10001. 

The test was planned to last 500 seconds (8 minutes, 20 seconds), with the engine reaching up to 111% of its rated power level. The firing is part of ongoing testing to support NASA's Space Launch System (SLS) rocket, which will carry astronauts toward the moon on future Artemis missions. 

Four RS-25 engines power the core stage of each SLS rocket. 

Credit: NASA | edited by Space.com 

Hot Fire! NASA Tests Powerful Artemis Moon Rocket Engine | 8:47 
VideoFromSpace | 2.17M subscribers | 10,029 views | October 21, 2026

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TOPICS: Business/Economy
KEYWORDS: artemis; l3harris; nasa; rs25; sls

[SunkenCiv]

https://search.brave.com/search?q=RS-25+rocket+engine+comparison

RS-25 rocket engine comparison

The RS-25 engine is a high-efficiency, staged-combustion rocket engine originally developed for the Space Shuttle and currently powering NASA's Space Launch System (SLS) for Artemis missions. Manufactured by L3Harris (formerly Aerojet Rocketdyne), it uses liquid hydrogen and liquid oxygen to generate approximately 512,000 pounds of thrust at sea level, boasting a specific impulse of 366 seconds (sea level) and 452 seconds (vacuum).

While celebrated for its unmatched fuel efficiency and flight heritage, the RS-25 faces significant economic and operational disadvantages compared to modern engines like SpaceX’s Raptor 3. The RS-25 weighs ~7,000 pounds with a thrust-to-weight ratio of 73:1, whereas the Raptor 3 is lighter with a ratio of 200:1. Furthermore, the RS-25 costs approximately $60 million per engine and is now expendable on the SLS, while the Raptor 3 costs an estimated $1–2 million and is designed for full reusability and rapid production.

Key Technical Comparison: RS-25 vs. Raptor 3
Specification	NASA RS-25	SpaceX Raptor 3
Propellant	Liquid Hydrogen / LOX	Liquid Methane / LOX
Combustion Cycle	Staged Combustion	Full-Flow Staged Combustion
Sea Level Thrust	512,000 lbf (2.3 MN)	580,000 lbf (2.6 MN)
Vacuum Specific Impulse	452 seconds	350 seconds
Chamber Pressure	3,000 psi	5,000+ psi
Engine Cost	~$60 million	~$1–2 million
Reusability	Expendable (SLS)	Fully Reusable
Throttle Range	67–109%	40–100%+

The RS-25 remains the superior choice for single-use, high-energy missions where maximum payload efficiency is prioritized over cost, while the Raptor 3 is optimized for high-cadence, reusable commercial launches where lower engine cost and rapid refurbishment are critical.

AI-generated answer. Please verify critical facts.

[SunkenCiv]

🚀🛰️

[Jonty30]

Looks like an armadillo

[doorgunner69]

The F-1 still rules

[ClearCase_guy]

the engine reaching up to 111% of its rated power level

[Steely Tom]

I guess the higher Isp for the RS-25 has something to do with it’s burning fuel with a much lower density than Raptor. Chamber pressure is higher for Raptor, but it’s burning kerosene. Both are incredible engines. Raptor is incredible for a lot less money.

[rlmorel]

All that cost and statistics aside...I am wholly spoiled by the Raptor engines.

Spoiled. It isn't really a fair comparison, and these engines, by all accounts, did stellar and reliable work on the Space Shuttle. And I know they are from completely different eras.

But when I look at all that tubing, wiring, and complexity on the RS-25...it just makes me a bit queasy.

[NorthMountain]

Chamber pressure is higher for Raptor, but it’s burning kerosene.

Merlin (Falcon-9) burns kerosene (rp-1). Raptor burns liquid methane.

[fidelis]

The RS-25 engine is a high-efficiency, staged-combustion rocket engine originally developed for the Space Shuttle

I worked 13 years for the company that built the Space Shuttle Main Engines (SSME) in Southern California when it was simply called Rocketdyne, then a division of North American Rockwell. I was privileged to witness 2 or 3 test firings of these babies which were louder than 50 B-52's (which I served around before that) taking off and shook the ground like all those B-52's had released their payloads at once.

Glad to see after almost 50 years they are still doing the job--just like the B-52. We sure knew how to make stuff in those days.

[Paal Gulli]

Oh my, look at all the CARBONS that thing is spewing out!

Think of all the spotted Als and snail darters that thing is killing!

I think I’ll go out in my back yard and set a few styrofoam coolers alight to calm my frayed nerves.

I had family in central Florida back in the ‘60s. They said every time NASA launched a rocket from Cape Canaveral, it rained the next day, without fail.

[citizen]

The F-1 is like I heard in a movie: “A Timex watch in a digital world.”

Not that I dislike old tech, I’d rather drive a GTO than a Tesla.

[Steely Tom]

Thanks for straightening me out on that.

But methane still quite a bit higher molecular weight than hydrogen.

[Steely Tom]

Thanks for straightening me out on that.

But methane still quite a bit higher molecular weight than hydrogen.

[know.your.why]

NASA RS-25 cost to date for US taxpayers = $8 Billion
SpaceX Raptor 3 cost to date for US taxpayers = $0

Whats wrong with this picture?

[know.your.why]

Same for Blue Origin BE-3U and BE4. Elon Musk laughs at every single orbital space launch company in the world (esp Blue Origin and NASA and ULA). I sure hope that Elon has tons of personal protection to keep him safe.

[know.your.why]

But methane still quite a bit higher molecular weight than hydrogen.

It seems that Mr. Elon Musk has figured out how invalidate that particular reality.

[rlmorel]

LOL, it isn’t “fair” to compare other rocket companies to SpaceX, but...that’s the way it is!

[citizen]

I get your point but it’s not entirely true. According to AI, NASA has paid SpaceX approx. $15 billion in contracts awarded for specific deliverables (launches, Moon lander system development, and such.) Money is fungible and NASA payments easily helped pay for Raptor developments along the way, as a part of meeting the contracts’ goals.

[Islander7]

I once lived about 12 miles from Stennis Space Center where all shuttle engines were tested. On cool nights with little wind my windows rattled when the RS25 was fired up.

[citizen]

Windows rattling at 12 miles away! I was in and out of Florida thru the years but never near a launch.