Why is NASA Throwing Away Reusable Engines?

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The Artemis SLS is the latest and greatest rocket from NASA and more powerful than anything yet flown into space. And yet for all of its modernity for the upcoming moon missions and its competitors like SpaceX and Blue Origin concentrating on reusability, NASA will be throwing away four of possibly the best reusable engines yet made, the RS-25 with each launch just like they did in the 1960s & 70s with the Apollo mission and the one time use F-1 engines. So in this video, we look at how the RS-25 came about and why it's now a disposable item.
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Written, researched and presented by Paul Shillito
Images and footage : NASA, Pratt & Whitney, Rocketdyne, Aerojet General
And a big thanks go to all our Patreons :-)
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[@tmenzella]

Good to see you pushing out content regularly again buddy, hope you’re well on the way to a full recovery. Thanks for your channel. ✊🏻

[@ShainAndrews]

Why the emoji?

[@rolflandale2565]

Indeed, the althirthum of YT is horrendous, we haven't heard from Curious Droid, since eternity🙂. Yes there hasn't been much iconic launches since this year. Welcome back🖖.

[@bastadimasta]

Publishing. Pushing out means something else, something insulting.

[@dziban303]

Techno Varys will *not* be deterred

[@batman_2004]

Cringe emoji

[@sunspot42]

There’s reusability and then there’s reusability. I think each shuttle launch required about half a billion dollars in refurbishment expenses before the vehicle was ready to fly again, some insane amount like that. A big chunk of it was inspecting and refurbishing those awesome engines. If your launch volumes are sufficient, it isn’t at all clear if this is more efficient than simply using a cheaper disposable engine, one that could be produced for a fraction of the cost.

[@Jaxck77]

These do not cost a fraction though.

[@lordgarion514]

@@Jaxck77 I'm convinced that the amount they cost, and the amount of our money Congress is giving their friends for ot, are VASTLY different amounts.

[@sunspot42]

@@Jaxck77 True, but they were just going to sit around rusting and were already paid for out of the Shuttle budget. So they’re essentially free as far as the new rocket is concerned. If you think this program is delayed already, imagine how far behind schedule it would be if they’d tried to make more of the components reusable.

[@jimurrata6785]

Imagine how far ahead NASA would be if they just started from a fresh sheet instead of being shackled to Shelby and his cronies by congressional mandate. We're nearly a decade behind and tens of billions over budget with no end in sight if this continues. Over $4 billion per launch and $93 billion through 2025

[@colinjohnson5515]

Wasn’t the amortized of each shuttle mission like $1B? It’s amazing expensive LEO was before SpaceX. I wonder how much money NASA could save if they dropped success probability to 99%.

[@dion6481]

In a documentary I saw about the development of the SLS, is that, the RS-25 were not exactly powerful enough for the job. However, since they were now "disposable", they could be run way over their specifications, because, well, who cares if they are destroyed by the time their fuel is burned. So, from memory, I believe they are used to 115% of their designed thrust, which does give the necessary power needed.

[@dr4d1s]

I thought that it was 109%

[@michaelwalker6252]

They were run above their design rating on the shuttles for years. If you listen to one of the shuttle launches you'll hear the throttle up command to 104%, and I think later on it went up to 108%. This increased thrust was due to upgrades made to the engines over the years.

[@HighlanderNorth1]

@@dr4d1s 🤔 Well, it depends. I've managed to boost the power of R25 engines to 116.4%. You see, I bought 11 of them at a govt surplus auction to increase the altitude of my modified Estes model rockets from 800 feet to 800 miles. Unfortunately, I too have been unable to reuse my R25 engines, because the vastly increased altitude they provide has proven to be a double-edged sword. Now I can never seem to locate the rockets after launch. They no longer just float back down into my backyard! 😁

[@MattH-wg7ou]

What documentary was it? I wanna watch.

[@donraptor6156]

If you don't plan on reusing the hardware they can be uprated a Massive amount extra thrust since you can use it all up!

[@mtnbikeman85]

The flyback booster concept if it had continued would have essentially achieved what starship is trying today but almost 40 years prior.

[@TheEvilmooseofdoom]

@@MrWolfstar8 Nonsense.

[@johnmurphy5689]

@@MrWolfstar8 No your wrong, what actually happened instead is that the US Air Force pretty much forced NASA to develop the large Space Shuttle with the expendable External tank because they wanted a LARGE Space Plane that could launch and recover spy satellites over the North Pole, this prevented NASA from using a smaller cheaper Space Shuttle design that would have allowed the budget for a reusable flyback booster to be built. If NASA had not suffered from the budget cuts from Congress during the late 1960s and 1970s then they would never have been forced to rely on the USAF to provide funding for the Space Shuttle program.

[@dr4d1s]

@@MrWolfstar8 If cost is not a concern and large payloads are the measure, we did have the Shuttle Program that flew for 30+ years.

[@thesteelrodent1796]

@@MrWolfstar8 if it wasn't for the cost SpaceX wouldn't bother with making reusable boosters. It's not like they do it just as a gimmick

[@nutsackmania]

The original comment is correct. I'm sure if you're stupid you'll want to argue that it isn't, but--and I'm just being honest--that impulse is all the proof you need that you're a moron.

[@throwback19841]

The other thing which the rd-25 stood out for is the very large gimbal range it needed to keep the monstrosity that is the shuttle pointing skywards with flamey end down.

[@LambdaJack]

Yes! that was quite a fetish!!

[@SeanCMonahan]

​@@LambdaJack quite a _fetish_, you say? Different strokes for different folks, I guess 😂

[@loschwahn723]

most common problem by such kind of engines ? temperatures - even if they can be reused ...you should better not

[@rjm7168]

I worked at Rocketdyne for 12 years in Advanced Programs and am very familiar with the SSME, J2, J2 Aeorospike, and other rocket engines. They are all amazing pieces of machinery. To quote a friend of mine (another Rocketdyne Engineer) the SSME main fuel pump packaged 50,000 HP in the size of an office trash can. Anyway, there really is no such thing as a reusable rocket engine as most would think of. It isn't like parking a car and hopping in the next morning to drive it again. The SSME were removed from the Space Shuttle after every mission, partially disassembled, inspected, refurbished as needed, and reassembled before being used again. I believe the turbopumps were also partially disassembled during this inspection and refurbishment process. I suspect the Space X and other current reusable rocket engine systems are subject to a similar inspection and refurbishment process. So, throwing away reusable engines may not be that much more expensive than reusing them when you look at total cost, including recovery.

[@raymondzhao9557]

COOOOL

[@christianrogers5674]

Thanks for your perspective! I thought too was that if the engine is simplified and the cost per unit reduced, it may over time be cheaper to throw it away than to land it and refurbish it.

[@wrightmf]

>SSME main fuel pump packaged 50,000 HP in the size of an office trash can. for some reason my brain can't fathom a pump of the size of a trash can that has 50K horsepower.

[@JosephHarner]

That it needed such a high level of inspection and refurbishment seems like a failure of engineering, then. Either the project goals were set wrong to allow for a design that needed so much refurbishment between flights, or the product failed to deliver. I can cut the Space shuttle program some slack for the challenges they encountered that were previously unknown. Far less so the SLS, which responded to the challenges of reusability by throwing in the towel, going for a far less ambitious design, and yet still taking 20 years to deliver the world's most expensive way to put 100t into low earth orbit.

[@secondsein7749]

@@JosephHarner it's likely more for precaution's sake than anything else. Even if they managed to reduce the inspection and refurbishment to near zero, protoco/law would mandate high level inspection/refurbishment anyways. Like the OP says, space vehicles aren't like any other vehicles. Space vehicles that failed would garner public negative attention and space exploration PR tend to be on thin ice. You don't want your rocket to explode and later have to explain to the public that you put too much confidence in your engineering skills instead of life saving procedures. The same principle applies to jet fighters. They require extensive maintenance after each flight. Can the jets skip the maintenance after a flight? Sure but considering the cost of the plane and pilot, the military doesn't want to risk it. Better safe than sorry after all.

[@occhamite]

Actually, new RS-25 doesn't represent "coming full circle, as the F1 was a resueable engine which wasn't reused. Some F1's had accumulated as much as 8,000 seconds total run time, with only minor refurbishments between runs, like replacement of a few minor items like carbon nozzle throats.

[@battlesheep2552]

Damn, that's more than 2 hours. Just imagining an F1 running for that long is unimaginable

[@marvintpandroid2213]

You get the gold star for pedant of the day 🌟

[@jmwoods190]

And there were proposals for 4 outer F-1 engines to be reused, in the form of the S-1D which would've been a 1.5 stage version of the S-1C(and an upscaled version of the early 5-main engine proposal for the Atlas rocket, which was later reduced to 3 in the final design) in which 4 the outer engines were jettisoned and recovered to be re-used, leaving the center F-1 engine to complete and the rest of of the Single-and-a-Half-Stage-to-Orbit(SHSTO?!) flight!

[@Ingens_Scherz]

Could they land a first stage? Then no, they were not actually reusable even if they were potentially reusable. How do you feel about that?

[@lordgarion514]

@@Ingens_Scherz Sorry, but a machine being reusable or not, has nothing to do with whether or not the tech to keep it from crashing exists. They are two different things. English isn't hard.

[@SRFriso94]

This one mystefies me how they can justify it - they even developed a disposable variant of the RS-25 in the RS-68 for the Delta, precisely because the RS-25 was too expensive to be disposable. At least with the SRB's it makes a bit more sense, as the tally after the Shuttle Program ended showed that the recovery and refurbishment of those was pretty much just as expensive as if they had bought new ones every time.

[@sylvanelite]

AFIK, one of the main problems with the RS-68 is cooling. One of the reasons the RS-68 is cheaper than the SSME is the lack of regen cooling in the nozzle. If you packed them close together on one core, like in the SLS, they won’t be able to dissipate heat effectively. The RS-25 on the other hand has an actively cooled nozzle so they can be packed close together.

[@derrekvanee4567]

Jusify? Only need to justify how the 1% can get extra tax payer dollers, and be able to throw away the product at the end of its ffirst test, and 12 more after that.

[@maxkovalchick9529]

From what I've heard the main issue isn't proximity to each other, but that the RS-68's ablative nozzle being designed for the delta 4 series of rockets with shorter burn times actually doesn't have the durability for the longer burns of SLS, especially if one of the engines were to go out early. I still agree though, the RS-25 really is an engineering triumph, it's sad to see them be one and done on the pad.

[@sunspot42]

@@maxkovalchick9529 better than seeing them just rusting away in storage.

[@rocketman1104]

the RS-68 is not a variant of the RS-25, you are thinking of the constellation program, where they were trying to work out issues between using RS-25 and RS-68, they wanted the RS-68 because it provided more thrust, but required a new variant, the RS-68B, which had a regenerative cooled nozzle, it also needed to be man rated, this is incredibly expensive, and is fairly close to redesigning the entire engine since you need new plumbing and control on the engine to use a regeneratively cooled nozzle, versus ablative on the RS-68 and RS-68A. The RS-25 is already crew rated, and regeneratively cooled, so less development would bee required, however they would need more engines per core to provide the amount of thrust they wanted.

[@MrRioting]

Thank you for this very in-depth discussion. I enjoyed all of it. I have been following the space project since childhood and watched Neil Armstrong land on the moon, etc. Been keeping up with the technology and made the trip finally a few years ago to Canaveral. Got lucky in that it was between the Shuttle, which had been retired, and the new Artemis project, relatively unknown at that time amongst the masses, including us. We got to tour the VAB, which had not been possible in the past during the space race, and the shuttle lifetime due to it being used constantly, so that was real treat. Inside, there was a mockup of the Orion. We got to touch it! We learned then that they would be re-using Apollo and shuttle technology including the Apollo Command Module design, the solid boosters and the same engines and fuel tank designs of the shuttle system, and this was the common answer: "Why? Because it works!" We heard that a lot. They were also in the process of refurbishing the crawlers to carry the SLS out to 39 A and B, and of course, we got to tour 39A, which was quite a treat as well. Pictures do NOT do it justice! You have to stand where behemoth rockets blasted off from! I encourage everybody interested in our missions to space to make the trip. Do the tours! Go see the best use of tax dollars ever! The quest for universal knowledge. Put it in your bucket list and just do it! Go on their website and read the schedule of events and try to time it when you can actually tour the launch facilities. Maybe even take in a launch. Space Ex and others are doing it a LOT. Tickets are very affordable as is the whole Cape Canaveral experience. Over there in Orlando is the Fantasy theme parks, but over there at Cape Canaveral is REALITY! They even have a full sized Saturn 5 right there!

[@uuzd4s]

Good seeing you back into the New Commercial Space Race! I missed those Shirts . . . as well as your well researched space endeavour subject matter! I've worked on the larger P&W turboprop engines for decades and never knew of their Rocket Engine development until just recently. Their reverse flow turboprop's are robust and highly damage tolerant, I would expect the same out of their Rocket Engines. Good Show !

[@wizzardofpaws2420]

The Droid really does space the best!

[@firefly4f4]

I somewhat bristled when you called the core stage a modified shuttle main tank, because it's really not. The SLS carries its payload on top of the tank and thrust from the bottom, rather than both being to the side like with the shuttle. This means that although visually similar, the core tanks actually have very little in common with the shuttle tanks as the forces through them are so different. The diameter and basic shape is about all that's preserved, with even the insulation, despite the colour, being different. This tank redesign is reported to be one of the major reasons for the delays and cost overruns of the program. It would have been more appropriate to mention the boosters, as those actually do/did contain segments from actually shuttle launches. They too have been redesigned somewhat - being now 5 segments instead of 4, new insulation, and modified solid propellant mixture - but as stated actually do have former shuttle components that previously were recovered and now are being discarded.

[@robertfousch2703]

Exactly.

[@KirtFitzpatrick]

Nit picky nit picking. I'm sure Paul is aware of that given the depth of coverage in other areas. Probably oversimplified that section since this is a video on the engines and not the core stage itself.

[@dziban303]

I thought most of the stringers and frames were basically identical?

[@dr4d1s]

@@KirtFitzpatrick If he did then why didn't he say it then instead of what he did? People who are into rockets are pedantic because in rocketry being pedantic matters.

[@BTW...]

@@dr4d1s Like you work in the industry and it matters? Proud to be pedantic? It's not a great claim considering what it really means.

[@marvintpandroid2213]

There were some close calls on the shuttle main engines, including holes in the heat exchanger / rocket bell.

[@tangydiesel1886]

I can't remember if it was the cooling channels or the injectors, but they would plug the ones that didn't pass inspection between flights. The plug came dislocated during one of the flights and punched holes in different places on its way out.

[@laz7354]

This, 100%. This is why reuse is, when one blows up, way more expensive than new.

[@zandvoort8616]

It’s a great shame they didn’t used some kind of tech like what they plan for the Vulcan rocket to allow the engine section to return to Earth via an inflatable heat shield.

[@michaelwalker6252]

These engines were designed in the 70s. They have been reused over and over for years. SLS IS WHAT THEY ARE BEING USED FOR INSTEAD OF THROWING AWAY AFTER THE END OF THE SHUTTLE PROGRAM. Recovery systems are expensive so why spend the money to recover them?? This is them going out with a bang instead of being trashed. "Disposable" is not an accurate description.

[@CommyPlayz]

@@michaelwalker6252 This is true i mean, if you use the shuttle’s engines for SLS instead of it being placed in the Air & Space Museum it is the retiremnt flight of those engines. It did what it was meant to do for the past 30 years. I think it is fair to put these glorious pieces of the space race to an end (shuttle was from the 70’s post Apollo 17)

[@zandvoort8616]

Maybe somebody can recover them from the sea and bring these historic engines back to a museum. I thought SLS would be an ideal proving ground for the ULA/inflatable heat shield recovery system.

[@tma2001]

@pyropulse7932 yeah its not like SpaceX have launched more payload to orbit than the rest of the world combined this year ... hmm I wonder how they managed that.

[@CausticLemons7]

@pyropulse First reusable booster becomes operational and almost immediately takes over the market. But "reusability is niche" LOL

[@AspynDoesStuff]

This might sound a bit nitpicky, but the core sls stage is not at all a refurbished shuttle external tank. Shuttle external tanks were never recovered and the core is made out of a different metal all together. It just has the same foam insulation

[@tedmoss]

But we want to call it reusable!

[@josephpiskac2781]

I read one examination of the Shuttle that presented the difficulty and expense of reusable engines was tremendously underestimated. That the engines never achieved their life expectancy. Basically a regretted decision.

[@supernanga]

So good to see new content being pushed out! I hope you're doing well for a full recovery. All the best!

[@tomtierney792]

Thank you for this info. It seems that everyone is focused on the main engines. Of course, these give a great show at lift-off and NASA has to have something dramatic to show the public for all the money spent. I think that the Orbital Maneuvering Engine (AJ10-190) is another good engine being thrown away, ah, I mean disposed. It certainly isn't as sexy as the SSME but it was the one shuttle engine that met all the original specs. I find it difficult to find much info on this engine and would like you to do a video on it if you could.

[@barryhall7]

It is shocking that they just dump those RS engines

[@barryhall7]

@@sourandjaded2586 I would say that the bottom of the sea is definitely dumped.

[@atomicshadowman9143]

I guess gathering dust in a museum is better 🙄

[@RCAvhstape]

@@atomicshadowman9143 I prefer "reused dozens of times, then retired to gather dust in a museum", which is what they were built for.

[@nagualdesign]

@@RCAvhstape I prefer "reused dozens of times, then used to send astronauts to the Moon". They were not built to gather dust in a museum.

[@RCAvhstape]

@@nagualdesign Once they reach a number of flights you have to retire them. Nothing lasts forever.

[@AlexSchendel]

SLS is certainly an incredible vehicle to watch and will carry NASA into a new age of exploration, but man it really is incredible to see Boeing take Space Shuttle engines, Space Shuttle tanks, Space Shuttle SRBs, and an upper stage that is taken from the Delta IV Heavy... And then take 11 years and $20bn to find the right way to bolt them together... Great job there Boeing.

[@billymania11]

There were a number of strange decisions relating to the Senate Launch System (SLS) rocket.

[@tma2001]

oh and recover none of it - even the solid rocket casings had parachutes with the Space Shuttle.

[@AlexSchendel]

@@tma2001 probably because they learned that recovering and refurbishing spent SRBs from the ocean where they get heavily corroded with salt water is actually more expensive than building them new lol. Would've been cool if they did it Energia style and had deployable wings so they could just fly back to KSC haha. Not to mention it would've been such an awesome sight to behold.

[@ericmatthews8497]

The core stage is not a Space Shuttle tank..

[@AlexSchendel]

@@ericmatthews8497 I'm aware that it is stretched and heavily modified to have enough structural support too carry Orion and the upper stage as well as support the force of 4 RS-25s, but are we really saying that it is acceptable that it took 11 years to make this modification? Heck, even longer when you consider the development of Ares V. NASA gave Boeing a scathing report on Boeing's atrocious project management for a reason.

[@thomasackerman5399]

All right, right off the bat. The SLS core fuel tanks are NOT a modified Space Shuttle ET, they're almost a brand new design and use completely different tooling to build.

[@dogsbd]

True. But SLS was sold to congress, originally oh so many years ago, as using "modified" shuttle hardware as doing so would be economical. We have all seen how that turned out.

[@ManyTriangles]

I love the flashy title sequence. Really conveys that some epic learning is about to happen.

[@moonwalkhi]

It summarises the video well.

[@emirvmendoza]

I prefer the old title sequence, with a voiceover whispering "Curious Droid"

[@BlackEpyon]

Those RS-25's should have gone to museums. A team had redesigned the F-1 to be made using modern processes, but ultimately Congress had to keep their defence contractors in the black by having them take apart and redesign these re-usable RS-25's to be "disposable," and thereby saving... What, exactly? They could have built NEW engines for how much it cost them to redesign the RS-25's, not to mention that the F-1B's would have produced FAR more thrust! Just a colossal waste of money.

[@chestersnapdragonmcphistic579]

In the same way that a Falcon 9 Expendable or a Falcon Heavy core booster is discarded for maximum performance, the SLS must extract maximum performance from every launch or it just isn't worth the cost. A series of smaller reusable rockets could do the job cheaper than a much more expensive reusable SLS. It's really for high energy missions that can't be split up into multiple launches.

[@ericmatthews8497]

Bottom line.. It's cheaper to throw them away than to develop a way to recover them from near orbital velocities. And any reusability components added, would subtract from the performance of SLS to lunar orbit. Nothing is ever truly reusable without a trade-off. That is why Starship will need nearly twice the sea-level thrust and multiple launches with orbital refueling to reach a lunar orbit. Those are some FREAKING BIG trade-offs that might just fail completely.

[@steveaustin2686]

Exactly

[@FrankyPi]

Yep, the whole "holy grail of rocketry and reusability" thing is just another myth that Musk is propagating for his cult of personality and its followers. There is no such thing, there will always be drawbacks and a limited optimal use case. It remains to be seen whether Starship will even make it beyond LEO, and if it does it's guaranteed that it will come nowhere close to the grand goals and expectations.

[@jamese9283]

You stated everything very well. I am expecting NASA choosing Starship HLS to turn out to be a huge mistake.

[@bgebbq314]

Excellent video and historical perspective of the renowned SSME/RS25. Thanks for the mention of the Narloy Z !

[@brentboswell1294]

It's a shame that they don't even try to recover the SRB's, because the shuttle version was totally designed for that. The parachute package hardly added any weight to the boosters. The 5 segment version used for SLS was actually fully developed during the Shuttle era, but never flew due to the cancelation of the Space Shuttle program after the Columbia disaster .

[@IstasPumaNevada]

It's not really a shame; refurbishment of the Shuttle boosters cost just about as much as buying new ones, so the reusability was basically pointless. What's really a shame is that these major aerospace companies with decades of history could have had fully-reusable, controlled-landing first stages by now if they had incentive to develop them, but since they get paid massive government contracts whether or not they innovate, they just don't innovate.

[@steveaustin2686]

@@IstasPumaNevada The technology for reuse wasn't there until recently. Now, ULA, Blue Origin, Rocket Lab, Relativity Space, etc are all working on reuse.

[@nutsackmania]

Refurbishment of the SRBs was not as expensive as building new ones, sorry. It wasn't nearly as cost efficient as they hoped, but you're just extrapolating the cliche.

[@JB-kk4pv]

@@steveaustin2686 Technology was not there because they chose not to develop it. Moon lander landed vertically and then took off, not too hard to see them extrapolating to powered vertical landing on earth, could have had by late 70's if not early 80's. IstasPuma above has it right.

[@steveaustin2686]

@@JB-kk4pv There were many attempts at making reusable spacecraft since Apollo. The Shuttle as the most famous and it cost more and was harder than they thought it would be. The DC-X used vertical landing as well in the 1990s.

[@7891ph]

If I remember correctly, the biggest reason that the SSME's were so expensive is because of the amount of power the made vs what they weighed. At the time, pound for pound of weight, they were the most powerful engine's on the planet. Another article I read compared them to SpaceX's current Falcon 9 engine's, and they came out on top for power to weight by a good sized margin. It's the old drag racers dilemma; powerful, cheap, reliable. Three choices, you can only pick two. What's your decision???

[@eyeborg3148]

Not really - the thrust to weigh ratio on the RS-25 is not that high, Falcon 9’s Merlin engines have a much higher thrust to weight ratio. Part of the reason is just down to fuel - Falcon 9 uses kerosene as opposed to hydrogen, which on a volume basis produces a lot more energy per unit burned. The reason the RS-25 is expensive down to several factors - First it is very efficient, using a more fuel rich closed cycle design. Second, it is designed to be reused, so it is built with that in mind, and components are chosen for longer life than disposable engines. Also, it is regeneratively cooled as opposed to ablatively cooled, like cheaper disposable hydrogen engines like the RS-68. Third, it is designed to be efficient at a wide range of altitudes, from sea level to the vacuum of space. This means there are significant complexities in terms of nozzle design, in particular the engine bell of the RS-25 can change shape/expansion ratio depending on altitude.

[@simongeard4824]

I think the main reason they're so expensive is simply that they were complex engines made in very small production runs, so you'd never get anything resembling economies of scale, and you'd never pay down the R&D costs. Compare with Raptor 2 - it's near enough the same thrust as an RS-25 for half the mass, and even before one has ever flown, SpaceX have manufactured more of them than the total number of RS-25s ever built. And even if the unit costs for Raptor end up being ten times the aspirational figures they've claimed, that's still nearly one hundredth of the price of a single RS-25. And I'm pretty sure that the reason for that is almost entirely because SpaceX are designing it to be manufactured in vast numbers... building more in a year than Aerojet did in fifty years.

[@richardbaird1452]

@@eyeborg3148, Do you have a reference for that last point (changing shape/expansion ratio based on altitude)? My understanding is that the RS-25 engine bell is static is shape. It was designed to be slightly sub optimal in vacuum performance only to the degree necessary to prevent flow separation at sea-level, not that the shape/expansion ratio changes in any significant way due to altitude (excluding slight changes due to thermal expansion which happens to all nozzles). This was deemed acceptable as the majority of the run time was at higher altitudes where vacuum optimization would the primary goal.

[@eyeborg3148]

@@richardbaird1452 Actually you’re right, it doesn’t change shape, I misremembered things.

[@nutsackmania]

@@eyeborg3148 Do you know what specific impulse is? You should try figuring that out before you pop off.

[@marijnmolenaar2848]

Hope your well Paul! Again another insightful video

[@lostcarpark]

Not sure the shuttle could really need considered reusable. Refurbishable might be more accurate.

[@lightkeeper917]

Always, packed with interesting information. Thank you.

[@craigtanner6916]

I absolutely love your videos! Thanks for all the hard work bringing these videos to us!

[@dannyv.6358]

Happy to see uploads again!!! You're da best 👌

[@markiangooley]

It’s amazing what you can do with antique parts one would expect to be in museums…

[@tonyb3629]

To fly a fully disposable rocket in 2022 is utter madness, and even more crazy is that NASA take engines designed to be re-usable and dump them after one launch. No wonder SLS costs £3-4B per flight, and that's still using a large amount of SS tech!

[@steveaustin2686]

Booster reusability is great, but has drawbacks. First, if you don't have a fast enough launch cadence, you can spend more on recovery equipment and personnel than you save by reusing the booster. Second, you take a payload hit for the recovery system on the booster. The Falcon 9 B5 can lift up to 22.8 tons to LEO when expended (SX), but only up to 16.7 tons when landed on a drone ship (B1069.2). Doing a Return to Launch Site (RTLS) landing, costs even more payload as you have a boost back burn to cancel the lateral velocity and return back to the launch site. Third, the higher and faster you go, the harder reusability is to perform. The heavier the dry-mass of your booster, the harder reusability is to perform. So with SLS launching once a year, eventually, the cadence doesn't really justify recovering the booster. Not to mention that it gets higher and faster than a Falcon 9 as the SLS core stage almost reaches orbit, making recovery MUCH more difficult. The SLS core stage is travelling well over 3 times as fast as the Falcon 9 booster and is well over twice as high as the Falcon 9 booster at MECO. The dry mass of the F9 booster is 22-25 tons while the SLS core stage is 85 tons. The SLS Block 1 can get Orion to the Moon, but not with the kind of payload hit like F9 has. The SLS Block 1B will send along a Lunar Gateway module with Orion, so it really can't take the payload hit either. SLS started design work in 2011, 4 years before SpaceX landed the first booster and almost 6 years before they reused a booster.

[@bigratkiller1]

The Shuttle main tank wasn't reusable and was never recovered. The SLS tank is similar in colour only as it's a completely new tank but built at the shuttle tank factory

[@blackhatfreak]

No shit, it was clear he meant reusable in design. I knew that's what he meant.

[@bigratkiller1]

@@blackhatfreak No, he said is was modified showing real reusability. Go listen

[@steveaustin2686]

@@bigratkiller1 Yeah, it's not like they could just slap engines on the External Tank and call it a day. There were major changes for the core stage to have engines on the bottom and the second stage plus payload on top.

[@rileyk99]

People keep calling it a tank. It's a rocket.

[@top6ear]

They toss rocket engines like Frenchmen toss cigarette butts .

[@leadbomb5380]

Sacré bleu!

[@th3ranger]

It’s hard to care when you’re spending someone else’s money

[@derrekvanee4567]

Everyone loves mit when I do my french bit unfortuntately it doesnt work on the internet you need to make a finger moustacje and click your heels doing little dance jumps and bend your arms back and forth together in a push up motion and say with a thick french accent "Ho ho ho, oui oui oui. Cest la vyyyee! i am Ricardo Saison, and Im here to sayson these contracts make a lot of richardo dollers with contracts ho ho ho oui oui oui. bagette. perfume. cheese."

[@mjproebstle]

oui oui

[@robm.4512]

Do I detect a faint whiff of garlic about this thread? C’est assurement la possibilite, peut etre? I’ll get my beret. 😂

[@heartofdawn2341]

_Each_ of those four engines costs about as much as a Falcon Heavy in expendable mode, and throwing the entire vehicle away on every launch feels like an anachronism when ever major rocket company is using (or at least planning to build) reusable systems. The shuttle was dangerous, impracticable, and required major refurbishment after each flight, but the SLS is still a huge step backwards.

[@LukeBunyip]

In. A. Nutshell.

[@steveaustin2686]

The Falcon Heavy could barely lift the Orion, ESM, and ICPS when fully expended, but the aerodynamics of such a large stack on FH were an issue per former NASA Admin Bridenstine. Booster reusability is great, but has drawbacks. First, if you don't have a fast enough launch cadence, you can spend more on recovery equipment and personnel than you save by reusing the booster. Second, you take a payload hit for the recovery system on the booster. The Falcon 9 B5 can lift up to 22.8 tons to LEO when expended (SX), but only up to 16.7 tons when landed on a drone ship (B1069.2). Doing a Return to Launch Site (RTLS) landing, costs even more payload as you have a boost back burn to cancel the lateral velocity and return back to the launch site. Third, the higher and faster you go, the harder reusability is to perform. The heavier the dry-mass of your booster, the harder reusability is to perform. So with SLS launching once a year, eventually, the cadence doesn't really justify recovering the booster. Not to mention that it gets higher and faster than a Falcon 9 as the SLS core stage almost reaches orbit, making recovery MUCH more difficult. The SLS core stage is travelling well over 3 times as fast as the Falcon 9 booster and is well over twice as high as the Falcon 9 booster at MECO. The dry mass of the F9 booster is 22-25 tons while the SLS core stage is 85 tons. The SLS Block 1 can get Orion to the Moon, but not with the kind of payload hit like F9 has. The SLS Block 1B will send along a Lunar Gateway module with Orion, so it really can't take the payload hit either. SLS started design work in 2011, 4 years before SpaceX landed the first booster and almost 6 years before they reused a booster.

[@TheSwissGabber]

​@@steveaustin2686 Did you look at the numbers? the SLS (2 billion per launch) is 20x more expensive then FH, with 50% payload. You could launch 13 Falcon heavy for one SLS.

[@steveaustin2686]

@@TheSwissGabber Did you miss the point that the Falcon Heavy could not get Orion and the ESM to the Moon? The whole point of SLS. Rocket Lab's Electron is much cheaper than the Falcon Heavy, that does not mean that the Electron will replace the Falcon Heavy.

[@heartofdawn2341]

@@steveaustin2686 those projects were built specifically to give SLS something only it could do. A moon project with FH could have been viable if they did it differently, and in a much cheaper manner. But then they would not have SLS for what it _really_ is for; a pork barrel project to create jobs and keep members of congress' constituents happy so they can remain in power, and to shove a lot of cash in Boeing's direction

[@IvanQuaglia]

I guess there is a good reason behind it: maybe the fact of being very reliable even being reusable made it overengineered and quite expensive, so using the proven design can be made cheaper one use but reliable anyway, and is cheaper to make one than to recover and use it again

[@miguellopez3392]

SpaceX is testing out their Raptor 2 engine which is re usable and being produced at a rate of 7 per week.

[@morzee94]

It’s a good day whenever you upload :)

[@spencerthompson1049]

Love when Paul talks engines!

[@dvusGishzida]

There was actually another "failure" that seems to have been "scrubbed" from official history. There was a non-critical failure on STS-4 of a solid titanium High Pressure Fuel Pump first stage impeller. The impeller had three tight tolerance "lips" so that as the pump got up to operational speed the impellers would axially expand to seal against a teflon-like hi-temp resistant labyrinth seals in each stage of the pump. 13 seconds before MECO the first stage impeller "broke"" Two of the three labyrinth seal lips of the impeller about 3 to 5 inches long broke into pieces. The broken pieces were fed into the other two impellers of the HPFTP resulting in a sudden "white plume" in the engine exhaust as the pieces were turned to titanium powder then "burned" by the engine. Mission Control was aware that something had happened but the engines appeared "nominal" so they did nothing. How do I know this? I was part of the Quality Assurance team at Rocketdyne and inspected the damaged impeller once the pump was returned and disassembled at our Canoga Park manufacturing facility. The question NASA wanted answered was the failure unforeseeable or was it caused by something in the manufacturing process. The impellers were made from solid titanium castings and then machined into high precision impellers with labyrinth seal lips . Normally these were "refurbished" after each flight but STS-4 was considered a "test" flight and the engines had not flown before, After a review of all the evidence both Rocketdyne and NASA concluded that there was a undetectable flaw in the casting used to make this impeller and that the failure was unforeseeable. At one point in time there was a video of the event available on the Internet but I can't seem to find it. All of the STS-4 Launch videos I can find end before the failure occurred. Fun Fact: Each of the SSME engine controllers uses three MilSpec 80286 CPUs as the "brains." of its"Tell-Me-Three-Times" Engine Controller.

[@faroncobb6040]

Interesting, I was only aware of four near misses other than this. The first shuttle flight lost a bunch of tiles and had a number of other serious issues, one of the pre disaster Challenger flights almost shut down all engines before an emergency override stopped them and would have resulted in a very dicey cross Atlantic abort scenario if not for the quick thinking of the ground crew, the heat shield damage on the return to flight mission after the Challenger disaster that only didn't destroy the orbiter because a steel antenna plate protected the aluminum frame, and the gold pellet incident that almost ripped enough cooling channels open to destroy an engine while the solid boosters were still running. Am I correct in thinking that the seals held in place by the three seal lips you are talking about were what prevented hot, high pressure hydrogen from being squeezed down the shaft to the oxygen pump? Because if that was the case then any failure of the third seal would have resulted in the engine blowing up dramatically, which would have been bad at 15 seconds before MECO, but would have been catastrophic had it happened earlier in the flight while the boosters were still going.

[@josephpacchetti5997]

This is the question I had pondered before Artemis I launched, Why not reuse the engines, instead of letting them sleep with the fishes, well, your channel answered that question and many more, Thank You Curious Droid. 👍 subbed.

[@cyberdoom9666]

How

[@DarrylHart]

Video starts at 2:53

[@What2Have4Dinner]

Great video, glad to see you back at it man. Hope your doing better

[@okankyoto]

The cost of the rocket engines is miniscule compared to the cost of developing a system to return them from orbit. With a flight rate mandated at 2/year, the breakeven is just not there for reusability on SLS components. Even the SRBs barely broke even in the 80s with monthly launches, and at lower rates cost more to recover than was saved by reusing them. Same situation with SLS- as its primarily a heavy lift rocket designed around maximum mass through TLI. Compare to the Starship HLS plan which requires 14 refueling launches to send it through TLI. And if Starship isn't 100% as cheap as hoped, it suddenly becomes a massive cost to have all those launches compared to expendable. Reusability has its place but its not a panacea for lower costs!

[@Kowalski301]

Finally some common sense here. It's so depressing to see that many who firmly believe reuseable rockets comes with no downsides, especially at this launch rate.

[@imarchello]

the flight rate of 2 per year is because they have to make the rocket from scratch each time. With reusability they could fly more often.

[@shannonkohl68]

The caveat is that once you start manufacturing rocket fuel on the moon, it presumably will become much cheaper since cost to orbit should be much cheaper from there.

[@thesteelrodent1796]

currently Starship is just a giant money sink that is likely to end up costing so much to develop it will never pay for itself

[@anthonypelchat]

You can clearly see the issue, but yet somehow think it's a justification for expending rockets. SLS can only fly once or twice a year because that is all that can be made. They have already had to cancel any launches other than Artemis for SLS as they just cannot make enough. And if the costs could be brought down as well by making it reusable, there is a lot of launches that could use it. And being reusable doesn't mean that you cannot have the rocket expended at some point. Being built to be expended only is just a waste and removes any options. Take Falcon 9 as an example. It's reusability has allowed it to be the cheapest ride to space per kg and cheapest altogether during rideshare missions. Plus it has allowed SpaceX to pursue another path that wasn't previously feasible. And yet after over 10 successful missions each, 2 boosters were finally expended for heavy, long distance missions that finally required it. They had more than paid themselves off many times over prior to finally being expended. And with Starship HLS, you tried to justify the SLS again with talking about it sending it's max mass to TLI on a single expended launch while HLS needs 14 refueling missions for it's max mass payload. However, you completely miss that HLS is sending around 3-4x more payload and not just going to TLI, but completely landing on the Moon and having enough fuel to return to lunar orbit. And that is all while being reusable. It could easily carry more to TLI than SLS while being completely expended. And it could be expended after paying itself off with numerous missions like Falcon 9 has. Being reusable gives you options that just don't exist with an expended launch platforms. And it reduces costs so much that you don't have to worry about launch cadence.

[@greggesaman535]

The only justification for the SLS approach is -politics and retention of the shuttle worker force in home districts - no matter the cost. Mission accomplished.

[@TheEvilmooseofdoom]

@@MrWolfstar8 No, you dont' actually understand what's going on or how things work. Try again, this time, try informing yourself a little. Re-read Gregs post, he has a clue.. the one thing you lack.

[@bagofholding]

The simple answer that I'm not sure was even mentioned during this video was that these engines are now attached to the tank that was always thrown away every launch instead of attached to a space plane that can glide back.

[@nick4506]

did any rs25s make it to the 50 mission design? i know they got kinda sketchy after w while with the little brass plugs in the combuster falling out and leaks in the nose cooling.

[@100SteveB]

I would say that the main fuel tank on Artemis bares little in common with the tank used on the shuttle program, it is basically a complete redesign. The original tank was designed to take the thrust forces through mounts on the side of the tank onl;y, whilst the Artemis tank is designed to take thrust forces on both either side, and the bottom of the tank. The top of the tank is also totally redesigned, it now as to carry the load of the upper stages and capsule, whereas on the shuttle version it carried no load. But, like the shuttle version, the tank is not reusable. The other main part of the shuttle system that is being reused on Artemis are the side boosters, they have flown on previous shuttle missions. But for Artemis they have added an extra segment to increase the thrust output. But sadly, like the RS25 engines, they are not being recovered and reused, when of course on shuttle missions they parachuted back down to land in the Atlantic where they were recovered.

[@sunspot42]

The SRBs were never worth recovering in the first place, tho. Really on most rockets the only thing worth recovering are the engines themselves, assuming they’re built with reusability in mind. People forget just how insanely expensive the fuel is, and how valuable that last little bit of fuel is in an almost empty rocket. That can either be used to send considerably more cargo into orbit that launch, or consumed getting the rocket back to earth…where really the only component more valuable than that fuel are the engines.

[@blackhatfreak]

It's literally a longer tank with engines at the bottom. The side boosters have not flown on previous shuttle missions as these are new 5 segment boosters while the older ones are 4 segmented ones.

[@blackhatfreak]

@@sunspot42 Literally not true

[@100SteveB]

@@blackhatfreak You are correct about the boosters, with the exception of one segment which flew previously on Atlantis they are new segments. Though i believe they plan to use further used segments in the future. I know Nasa have said they have several segments from shuttle flights that can be reused. And yes, the main tank is longer, along with completely redesigned upper and lower ends. About the only thing that remained the same was the diameter.

[@sunspot42]

@@blackhatfreak What is “literally not true”? The last bit of fuel in a rocket delivers the greatest delta v to the payload, because the fraction of fuel mass vs payload mass becomes most favorable for the last of the fuel. If you try to return the booster you need to either reserve a bunch of the most-valuable fuel to do it with, or add some other thing to the booster that also increases its mass (wings, parachutes, etc.) in order to get it safely back down on the ground. It’s a big reason why reusability has always been of questionable value, given the expense and complexity involved.

[@billmcintyre3652]

Pretty amazing as huge and awesome the N-25 is the Saturn V still had a larger payload capacity. Everyone that worked on the Saturn V should be very proud of their almost unimaginable accomplishment. Only now are we edging close to what they pulled off in 1967. The Saturn V team were 55 years ahead of the technology curve.

[@CybershamanX]

Yeah, I'm a little sad seeing the shuttle boosters going up one last time. 😢

[@billyelliot4141]

Thankyou mr droid sir. No one does it better. 🇮🇪✌️

[@saxus]

There are some mistake in the video: first, the tanks aren't modified External Tanks, they're clean sheet design. It have different internal structure, different alloy, etc. The diameter is same and it both used SOFI, but that's all. Because it holds load on top instead of side had to change everything. Also it may Congress wrote in stone that NASA should use solids and RS-25 but when the SLS program have been started it started with two different teams: one who evaluated the LH2 based options and one who the Kerolox options. They even investigated Russian RD-180 based options too next to modernizes F-1B based options.

[@simongeard4824]

Yeah, the fuel tank was supposed to be ET derived, but by the time they'd "modified" the design to meet the new requirements, the only thing that was still common was the colour...

[@saxus]

@@simongeard4824 nope, the whole SLS was clean sheets from day 0, they just decided to use solids and RS-25 because that was who gives better TLI performance for this project. But the given engineering and economic restrictions lead in the same direction in some cases. But the tanks was clean sheet. SLS is eventually a merger of Ares V and DIRECT/Jupiter but not based on. There were a lot of different and really diverse concepts. Just check this: www.nasaspaceflight.com/wp-content/uploads/2018/04/2018-04-11-184524.jpg

[@Jakob_DK]

It is great that we are going back to the moon and beyond. Competition is a good thing.

[@Jakob_DK]

@@martinr1834 Yes our enemies may succeed in spreading devising, it seems they do

[@ADVBear]

Fantastic, as usual. Thanks, Paul.

[@srinitaaigaura]

I just wish they'd preserved some of these RS-25s in a museum.

[@waynep343]

Thinking about surplus engines. What did the air force and the cia do with the spare engines from the YF 12s and SR71s did they scrap them. I read an article by willis hawkins years ago that the engines were good for 3,400 miles an hour but the heating of the airframe was the limiting factor. Thank you for this. I wondered how nasa was going to handle the limited number of SSMEs.

[@wally7856]

The faster you go the narrower the mach cone, at about mach 3.65 the outer edges on the wings would make contact with the mach cone from the nose which would probably be disastrous so heating wasn't the only limiting factor.

[@kentaylor6563]

Good to see you back. Thanks for all the info.

[@nagualdesign]

They're not throwing them away, they're putting these retired/redundant engines to good use.

[@masterpython]

Like they do with ICBMs.

[@nagualdesign]

@@masterpython 😆

[@dannyarcher6370]

Once. And then they're throwing them away.

[@masterpython]

@@dannyarcher6370 so they should store and maintain them until a new shuttle is developed?

[@simongeard4824]

@@masterpython They literally took some of them out of museums to be refurbished, so that they could be used one more time and thrown away...

[@TomTimeTraveler]

The engineering that goes into the entire Artemis system is mind boggling. It is a tribute to the hard work and dedication of all the scientists and engineers. They stand on the shoulders of their Apollo-era counterparts. So too will the astronauts who will eventually return to the Moon.

[@fangugel3812]

To understand NASA, one must understand that its primary function is to transfer taxpayer money to private contractors that do nice things for the people who control NASA’s budget. We are lucky that they still manage to do fantastic science.

[@steven_baconbits]

Private Defense Contractors

[@Pyrolonn]

I never thought about them just being dumped in the ocean. I do see some complaints about non-reusability. The lesson of the Space Shuttle? Reusability can be more expensive than disposability.

[@steveaustin2686]

Exactly

[@brick6347]

Sls is a bit like a post war ocean liner: big, impressive, completely obsolete.

[@mrb.5610]

And what would you suggest instead ?

[@lordgarion514]

@@mrb.5610 How about anything that's not half reused parts and tech costing over $4 BILLION epr launch? Can't post links, so I'll paste this. "Appearing before a House Science Committee hearing on NASA's Artemis program, Martin revealed the operational costs of the big rocket and spacecraft for the first time. Moreover, he took aim at NASA and particularly its large aerospace contractors for their "very poor" performance in developing these vehicles. Martin said that the operational costs alone for a single Artemis launch-for just the rocket, Orion spacecraft, and ground systems-will total $4.1 billion. This is, he said, "a price tag that strikes us as unsustainable." "If one were to amortize development costs over 10 flights of the SLS rocket and Orion spacecraft, the $4.1 billion figure cited by Martin would easily double." Then, unprompted, Martin continued to criticize the programs set up by Congress to fund the rocket and spacecraft. House and Senate members told NASA to use "cost-plus" contracts, which ensure that companies involved in the development and operation of these systems receive all of their costs, plus a fee. This tends to disincentivize timely work completed within a set budget. (Remarkably, NASA was told to continue using cost-plus contracts even after the development program.) "We saw that the cost-plus contracts that NASA had been using to develop that combined SLS-Orion system worked to the contractors' rather than NASA's advantage," Martin said." "In fact, key members of Congress have been critical of NASA every time the agency has tried to break free of cost-plus contracting and use a more commercial approach through fixed-price contracts." How about anything that's not a direct ripoff of our money?

[@om617yota8]

@@mrb.5610 I would suggest government step out of the space launch biz and let private industry take over.

[@TheOwenMajor]

@@lordgarion514 So you're just complaining? Being a critic is easy. And as SpaceX is finding out, making a heavy launch vehicle is tough.

[@ancliuin2459]

The video is very interesting as usual. Just the question asked in the headline (why is NASA doing this?) is not answered. Some comments do, though. :)

[@voneschenbachmusic]

It doesn't make sense from an efficiency or cost perspective but makes lots of sense in terms of Congress requiring this stuff to direct federal funding to their states. It's a giant welfare project for the massive industrial complex built to support the shuttle system. Meanwhile new space will continue to make strides and all of this stuff will become increasingly irrelevant and expensive. It would be easily within the technical capabilities of old space to build a heavy lift reusable system but they are too busy sucking that sweet sweet cost-plus government teat to ever change.

[@masterpython]

So you propose these engines be stored and maintained until a new shuttle is developed? Put in museums or the on the lawns in front of them, cut into pieces and melted down for scrap? All kinds of old hardware gets repurposed.

[@dogsbd]

@@masterpython Old hardware gets repurposed if it is economical to do so. A 20+ billion dollar program to achieve a handful of SLS launches using a handful of SSME's doesn't qualify as economical no matter how you look at it. Yes, it would have made more sense to turn those SSME's into museum pieces.

[@EdgarKohl]

I'd take one as a souvenir.

[@abbeyhall4624]

It is such a massive shame about the forthcoming disposability by NASA. But I guess that is par for the course ATM until the other systems become common place.

[@SlartiMarvinbartfast]

NASA's rockets are a politically driven enormous waste of money. Say what you like about Musk, but at least SpaceX (and others) see the major benefits in major reusability.

[@mrb.5610]

It makes sense. You want as much payload capacity as possible - landing the first stage a la SpaceX reduces payload as it adds complexity and weight for the landing system plus fuel for the 'suicide' burn. And the engines probably weren't designed to be reignited - so this slso may be a factor.

[@derrekvanee4567]

People say "spacex shows how much out of tune and antique nasa is" and its true I must say, but spacex hasnt had a orbital starship at all let alone crew rated to the moon. But it is sucha waste I think its just because somr rich company ceo's lobby so they can build extra disposable engines. If we INVENTED and INNOVATED like the gemini mercury and apollo missions which gave us a HUGE amount of the things we take for gtanted in modern life ike mylar and computers today instead of using 50yo hardware thinkl of what we could accomplish!

[@SecretRaginMan]

@@mrb.5610 Starship is designed to be refueled so it can take tens of tons of payload to the lunar surface. It is able to put more payload on the surface than any other lander proposed. There is a reason why a certain Senator (Richard Shelby) threatened funding to ULA over the word "depot". Refueling in orbit, which was a concept and proposal long before SLS, reduces SLS to obsolescence quite thoroughly. Current heavy lift rockets like the retiring Delta IV Heavy, upcoming Vulcan Centaur and New Glenn, and current Falcon Heavy make monolithic launches like SLS unnecessary. FH is $150M for 64 tons to LEO. Could launch sixteen times for one SLS + Orion mission ($4B according to NASA's OIG). Even DIVH at $400M could launch ten times, or thirteen times at $300M. On-orbit assembly and fuel depots are the future, not SLS.

[@laz7354]

Single use is safer.

[@gregzarkodimos9711]

The headline 'Disposable heroes' is so... metal, if you catch my drift

[@markbeards4441]

They could be used to make rain machines for the most dry farming land.

[@robrod7120]

Thats not how this works. The amount of energy and - get this - WATER you need to make rocket fuel makes it entirely unrealistic and unreasonable. It would cost billions to make a single raincloud. Irrigation meanwhile actually makes sense.

[@Chef_PC]

It really blows me away that there weren’t any computer-aided design or physics simulations that we have now, and these are still some of the most technically advanced rocket engines we publicly have. All the engineering and mechanical designs were done with pencil on paper and the equivalent of a pocket calculator.

[@TheEvilmooseofdoom]

Nonsense. They had CAD and simulations in the 70's and 80's. Nothing like we have now, but it did exist.

[@Chef_PC]

@@TheEvilmooseofdoom You're right. I was thinking (not out loud, obvs) about the older engines built and designed in the 50s & 60s. I could have been clearer.

[@xliquidflames]

What a great video. I think most people don't realize SLS is made of Shuttle parts. They know it looks familiar. It has an orange tank and the two white solid boosters but they probably assume that's just what NASA rockets look like. Personally, I don't think they'll make it through developing the RS25F before Starship proves it's viability. I don't know if SLS will be completely canceled but it will at least be scaled way back. They might just use up what engines they have left and then let Starship take over all duties. If Starship can make orbital refueling a reality, there'll be no need for SLS.

[@robertmiller9735]

SLS is bound to be cancelled Starship or no Starship. We better hope Starship development has gone far enough by then.

[@HankScorpio64]

I mean I didn't know that but it doesn't surprise me especially since NASA is one the more cash strapped agencies of the US gov't and is normally the first to get budget cuts whenever anyone mentions cutting funding to something. (Though we are just as fine spending more money on the DoD and military even though the contractors are the same. Figure that one out) using space shuttle parts would make sense since there already infrastructure in place and the limited money that is there can go into more important components that do need some thought and design

[@newq]

Honestly, I kinda doubt this. Starship requires multiple refueling missions for TLI and deep space, which negates any cost benefits from being reusable. It'll be a hard sell for NASA. Starship probably has a better niche in heavy lift LEO launches. At the moment, SLS really is the most viable option for the moon and beyond.

[@nachobasket]

@@robertmiller9735 The government has no plans to cancel SLS. As long as they keep funding it, it will fly. Just because it is expensive doesn’t mean it will be cancelled. NASA can afford it and will keep construction going on it.

[@laz7354]

Personally, I wouldn't count on Moosk.

[@pratyushojha]

Nice to see you back.

[@bigmac85987]

The shuttle’s external tank was not reusable. The big orange tank was discarded after every launch to burn up during reentry. The SLS orange fuel tank is based on the shuttle’s external tank, but has a great deal of changes and improvements.

[@Josh1888USU]

Isn't it funny that the three competitors would later merge in a way. P&W would later acquire Rocketdyne and then later spin it off to Aerojet to form the current company Aerojet Rocketdyne.

[@steveaustin2686]

Booster reusability is great, but has drawbacks. First, if you don't have a fast enough launch cadence, you can spend more on recovery equipment and personnel than you save by reusing the booster. Second, you take a payload hit for the recovery system on the booster. The Falcon 9 B5 can lift up to 22.8 tons to LEO when expended (SX), but only up to 16.7 tons when landed on a drone ship (B1069.2). Doing a Return to Launch Site (RTLS) landing, costs even more payload as you have a boost back burn to cancel the lateral velocity and return back to the launch site. Third, the higher and faster you go, the harder reusability is to perform. The heavier the dry-mass of your booster, the harder reusability is to perform. So with SLS launching once a year, eventually, the cadence doesn't really justify recovering the booster. Not to mention that it gets higher and faster than a Falcon 9 as the SLS core stage almost reaches orbit, making recovery MUCH more difficult. The SLS core stage is travelling roughly 3 times as fast as the Falcon 9 booster and is well over twice as high as the Falcon 9 booster at MECO. The dry mass of the F9 booster is 22-25 tons while the SLS core stage is 85 tons. The SLS Block 1 can get Orion to the Moon, but not with the kind of payload hit like F9 has. The SLS Block 1B will send along a Lunar Gateway module with Orion, so it really can't take the payload hit either. SLS started design work in 2011, 4 years before SpaceX landed the first booster and almost 6 years before they reused a booster.

[@leftcoaster67]

Should have went ahead with Venturestar, and built a brand new heavy lift rocket. Or work with Space X on the Falcon Heavy or Starship.

[@mikecarr4178]

The shuttle never came close to meeting it's goals on launch frequency or affordability. Was insisting on reusable launch systems the way to go then? (I know there were a lot of compromises due to funding as well.)

[@michaelnash2138]

I've read (IIRC it was in a book called "Halfway to Anywhere" by Harry G. Stein. A good read. Clarke said it, too, though.) that the space shuttle was meant to be the DC-3 of space but after congress got ahold of it it turned into the DC-1 1/2. True reusability would have put the price to orbit via a TRUE shuttle at maybe $1000/lb. instead of the $10,000 it is now.

[@spudgun889]

Welcome back! I’ve missed you.

[@mrb.5610]

C'mon guys - let's show some love for Artemis - it's taking us back to the moon ffs - sure, a few setbacks for the launch but it's now travelled further our than sny other human rated rocket !

[@JustaKubrickFan]

How many crew members were on the flight?

[@JustaKubrickFan]

@@martinr1834 Does not count. Good try though.

[@thecrazyinsanity]

@@JustaKubrickFan its a test flight, instead would you like to see it not work and kill 4 people? edit: Its also gathering a lot of data, and launching some cubesats, apollo took a lot longer to do the same thing minus the cubesats

[@mrb.5610]

@@JustaKubrickFan About the same number that was on SpaceX first Crew Dragon 2 flight. But that's SpaceX and Elon's a God - and/or a right wing tosser - so that's alright then.

[@ceptimus]

Not true. The ascent stage of Apollo 10's lunar module, named Snoopy, was actually flown, in lunar orbit, by Thomas Stafford and Gene Cernan. After they returned to the command module, Snoopy's engine was fired again to put it in a heliocentric (sun-centred) orbit. It's been up to about 180 million miles from Earth, at times, so dwarfing the pathetic distance of the (wholly unmanned, so far) Artemis. Snoopy was tracked again in 2011, with 98% certainty, and is still orbiting the sun 52 years on from its original mission. It's now classed as a small, earth-crossing asteroid, and has been given the designation 2018 AV2.

[@Memeieli]

Absolutely love your channel Curious Droid.

[@T3H455F4C3]

Reuse-ability is great as long as it doesn't cost or weigh too much. At this point launching stuff into near-earth orbit favours reuse-ability. However when talking about escape velocity... Probably not.

[@TheEvilmooseofdoom]

What nonsense.

[@anthonypelchat]

That's just short sighted. Getting into Earth orbit requires more deltav than is required to get from Earth orbit to just about anywhere else in the solar system. Being reusable gives you options that expended does not. For example, instead of using the launch vehicle itself to send a payload to the moon or Mars, you could send a heavier payload to LEO that has it's own highly efficient engines that then goes out further.

[@T3H455F4C3]

​@@anthonypelchatIn the context of sending cargo to the moon I would agree with you. But no matter how you cut it, carrying extra fuel and whatnot is going to cut into your payload. Furthermore if your sending people to the moon you want all the delta v you can get. Making the trip longer than necessary is dangerous to the crew. Highly efficient engines are not your friend in this scenario.

[@T3H455F4C3]

@@TheEvilmooseofdoom A very concise critique. I'm afraid I have no rebuttal.

[@anthonypelchat]

@@T3H455F4C3 Highly efficient engines are always your friend in long distance missions. There are some that wouldn't be because they are too weak, but that doesn't mean ALL highly efficient engines are that way. Plus, if you are carrying dead weight, that slows you down and waste dv. When you are reusing launch vehicles, you gain options. It can be as simple as expending a booster that has already flown, or as complicated as making a better overall design in orbit instead of cramming everything into one vehicle. But if you don't have a reusable option, then you have no decent options available as you are now limited by both build times and costs for the launch vehicle.

[@mrsnow61]

I believe that reusability is for low earth orbit launches and throwaway is required for lunar insertion orbits. I I'm not mistaken even the Falcon-9 is mainlyt for low-earth orbit and ISS launches, with exo-earth orbit launches requiring use of Falcon Heavy, which in case of higher weight payloads (greather than a Tesla Roadster :D ) requires throwaway launches. I believe that as envisioned for lunar landing, even Starship HLS will require multiple refueling tankers; I believe that by Musk's own admition it will be 4 tankers, with other estimates being as high as 10+.. so even reusable is a nuanced concept.

[@TheEvilmooseofdoom]

F9 was designed specifically to service the satellite launcher market.

[@steverpcb]

There were very strict requirements for the new homes for the shuttles so that they could be brought back into service if needed, now the SLS is throwing 4 of their engines into the sea after each launch :(

[@steveaustin2686]

No they weren't. The Shuttle's were decommissioned.

[@allo-other]

Isinglass? What an amusing name .... ""Isinglass is a substance obtained from the dried swim bladders of fish. It is a form of collagen used mainly for the clarification or fining of some beer and wine. It can also be cooked into a paste for specialised gluing purposes."" Apt if the engines are to become non-swimming "bladders" at the bottom of the ocean.

[@brianbarrett2487]

Imagine being asked to give 110%, you can literally respond with "I can do 109% forever" and they drop you in the ocean. =/

[@laz7354]

115% ...and safely. One cheap corporate reusable failure and reusability will be synonymous with unnecessary risk.

[@richardshippful]

The legacy requirements of Artemis. Is like stepping into a bear trap to start a long journey.

[@DM-zs8go]

One word. Corruption!

[@laz7354]

Agree. Government funding private corporate greed monsters like SpaceX is corruption at its max.

[@kenjackson5685]

Your usual high standard Paul....1st class... thanks for sharing

[@MsZeeZed]

Its only “rocket science” because if you make an auto engine one minor misfire during its entire life doesn’t blow up the car in huge fireball. Rocket engines have to be pretty exact despite mostly just consisting of a fuel tank, burn chamber and a flow valve in between. The complexity just comes from trying to not waste an oz of fuel.

[@alonespirit9923]

That brings to mind a quote which has minor fame in certain circles, "There are a thousand things that can happen when you go light a rocket engine, and only one of them is good." Tom Mueller of SpaceX, in Air and Space, Jan. 2011

[@TheEvilmooseofdoom]

Wow, you have managed to oversimplify a rocket engine to the point of being ridiculous.

[@volentimeh]

Rocket engines really should be compared to top fuel dragsters rather than normal cars, both push engineering to their limits and occasionally explosively self dissemble, hell top fuel engines only need to last about 5-6s at full power..

[@WJV9]

There is a LOT of complexity as these engines have to be able to rotate in 2 axes while producing thrust to maintain the direction of rocket flight. They also have to be able to adjust their thrust to achieve proper speed. The valves and pumps that adjust the dual fuel flow have to work under high temp's, vibration and multiple G's of thrust. In order to verify that they will work correctly you would have to disassemble and test each valve/pump and also X-ray all components to look for cracks and temp/vibration damage. It might cost more than building a new one.

[@alonespirit9923]

@@volentimeh That brings to mind an acronym, RUD, Rapid Unscheduled Disassembly.

[@larryrich327]

Good to see you and your videos again

[@Haploanddogs]

Short Answer? The senate

[@twisterwiper]

Paul, how about video on the new B21 bomber? Maybe some perspective on future of bombers and stealth technology.

[@paulhaynes8045]

They cost a fortune to 'reuse', so it's probably better value for money to throw them away. I've often wondered if reusability is as good as we think it is. For instance, the effort required to recover and refurbish the F9 boosters is not insignificant. Given the state of rocket tech and experience now, could they not make a very simple, cheap, disposable booster instead? F9s are very clever, but a lot of that cleverness is unnecessary if you're going to throw it away. Why spend so much on all the tech, when all you really want is to blast things up to LEO?

[@RCAvhstape]

Unless you have SpaceX's balance sheet there's no way to answer your question.

[@jr2904]

Wasteful thinking

[@Apollorion]

To reuse is cleaner and, as for example the Falcon 9 shows, it can also be cheaper.

[@blueredbrick]

The end goal is still going to Mars and back, not LEO. Expendable doesn't lead to the proper path.

[@paulhaynes8045]

@@MrWolfstar8 considering who owns Space X, I don't entirely trust their figures! Plus there are lots of new rocket companies who aren't going for reusable. If the maths were that simple, wouldn't they all be going that route? Considering how simple a basic rocket is - two tanks, some electronics and an engine or two - I'm sure they could be made a lot cheaper than the cost of an F9, even with it being reusable. Especially if you strapped some cheap, simple SRBs (which are off-the-shelf these days) to them.

[@jefffiore7023]

Incredible video as usual - greetings to you Paul from Houston Tx!

[@RogerM88]

If NASA with an astronomical budget and a team of brilliant Engineers, the best they came up was the Space Shuttle and even so, it failed to be really an economical option due to operational costs as refurbishment...I'd take with some skepticism the over optimistic claims that Starship will decrease drastically in the long run the cost per Ton to LEO.

[@stardolphin2]

Actually, the Shuttle as we knew it was very much a budgetary *compromise*...

[@UncleKennysPlace]

The existing Falcon 9 is already vastly cheaper per unit of mass than the Shuttle system. SpaceX can build several engines per week for the StarShip. I'd not bet against it.

[@RogerM88]

@@UncleKennysPlace Merlin engines are based on the TRW - Lunar Descent Engines. They are around for decades. The Raptor engine is a complete new type of engine category.

[@RogerM88]

@@UncleKennysPlace if Falcon 9 rocket retrival made a huge difference in prices charged by SpaceX, then the cost per kg to LEO, should be drastically decreasing not increasing. And SpaceX wouldn't be rushing to decommissioning Falcon 9 for Starship.

[@SecretRaginMan]

@@RogerM88 Man, you really suck at both logic and economics. First of all, how the hell do you figure the cost per kg is increasing? Where is your source? Shuttle was over $10,000 per kg while SpaceX is just over $2,000. That's one fifth. Secondly, why would they keep Falcon 9 around if Starship is cheaper to operate? It won't need to recover fairings, saving cost; it won't need to land on a droneship but land more cheaply at the launch site, saving costs; it won't need to have a new second stage for every mission, saving costs; the engines won't get coked up from soot, saving costs. As for engines . . . really? Just gonna talk nonsense? The Merlin 1 is a kerolox (kerosene fuel, liquid oxygen oxidizer) gas generator engine that uses a pintle injector. The Apollo lunar descent module engine is a HYPERGOLIC engine that also uses a pintle injector. That injector type is the beginning and end of the similarities. The Raptor engine is not a "completely new type of engine" given that the Soviets also made a full flow staged combustion engine. It was fired successfully but never flew. SpaceX's FFSC Raptor engine is the first to have flown and entered mass production. What are you even on about? Talking shit is what.

[@MajSolo]

SRBs always come to rescue any project. But there is no throttle control. They were steerable and reusable and as all SRBs are they are heavy when loaded but very powerful. The RS25 could be made reusable if it could detach and use a parachute.

[@loosegoose41]

Throwing away hundreds of billions of dollars in hardware "all while others are pushing for maximum reusability"? Gotta keep those defense contractors funded somehow! 🙄

[@gresvig2507]

Sadly, that's likely the entire reason.

[@laz7354]

If you mean "maximum reliability" don't you? Those companies pushing reusable are one catastrophic failure away from losing their government contracts and funding.

[@tbranch227]

I'm happy we have Artemis. It's another platform doing moon missions and that's a good thing, but moving away from reusability is a mistake. I'm not sure it even saved time. Calling the old RS-25 is technically correct, but boy did they work hard to destroy themselves every flight. It's a platform that should be abandoned.

[@blurglide]

Because SLS is primarily a low risk jobs program designed to waste money

[@laz7354]

I prefer low risk. I'd hate to be the guy on a Moosk used rocket that blows up.

[@daveherbert6215]

Excellent video Paul