POGO: Is This 63-Year-Old Problem Threatening Starship's Success?

Ten minutes in, I still don't know what POGO is.

I'd suspect that the responsible engineers are aware of the problem, but at the current insane pressure it's just not possible to get a reliable ship. It will keep crashing and having mishaps, no question. Starship is the Cybertruck of SpeceX, unfortunately.

So no, it wasn't.

Looks like things slightly improved on the 3rd flight of block 2.

Pogo instability is an interaction between the whole vehicle structure oscillating lengthwise, affecting propellant flow to the engines which affects their thrust. It is a negative feedback instability where both engine thrust and structure oscillate together. But, they have on-vehicle sensors to measure thrust (at least via engine chamber pressure that is almost 1:1 with thrust), so they would surely know if pogo instability occurred. It was a problem in some early launch vehicles, but not since they understood it and found easy mitigation (check valves or pressure regulators in propellant lines).

SpaceX failures appear due to failure in propellant tanks and supply pipes, plus a few engine nozzle cracks. There are other possible engine instabilities (chug, combustion oscillations), but no word that Raptor engines have experienced those. Another concern is water hammer on propellant shut-off, which is suspected causal in some Soviet N1 launch failures (their Moon mission). But, in failure investigations every possibility must be considered so all ponderings are useful thoughts. At a higher level, SpaceX is experiencing similar problems as those of the 30-engine N1 vehicle, which it resembles in several ways. But, nobody here is part of the SpaceX team, with access to flight data.

First I heard that SLS was cancelled. It proved its part of the Moon Mission, by orbiting the Moon and returning the Orion capsule to a successful splashdown. The Artemis program has been waiting on Starship to prove its part as the Lunar Lander (I know, sounds absurd). So, NASA was pressured to drop the winning part of the team and put all money into the part that has shown continued failures?

Perfectly scripted and delivered narration. We have been waiting years for an efficient conveyance of information about complex things without it being dumbed down to 15 year old level (or lower). I tip my baseball cap to CSI Starbase.

We need a video on Flight 9 ASAP Zack

Can they not use something akin to a tuned mass damper withint eh chassis to tune out some of this. Same for the piping. Introduce a variable length pipe into the feed pipe to vary the natural harmonics of the system.

All i got from this video: "Starships are meant to fly"

I have been saying for a year+ that they are getting boiling of the fuel.

Hm. That is really surprising and suspicious that the starship team doesn't know all this stuff. If so, I hope someone from there watching this.

Aged like milk

Seeing this video after flight 9 is a blatant proof that Zack and his team are in their own league. Impressive…

What an DETAILED presentation !

BB's. Adding loose shot around the piping will absorb the excess vibratory energy and dampen the oscillations. Thoughts?

And now ship 35 lol 😆

Is it possible to see the renders in VR? 🙏
I think i would be amazing to see it all in real life size

Thanks!

The Saturn II center engine experienced POGO towards the end of the Stage burn. Resonant frequency of the trust structure center mount was 16Hz, The solution was to inject helium into an accumulator upstream of the center engine. This decoupled the fluid oscillation frequency from the structural resonant frequency. All booster stages I have worked on employed POGO suppression accumulators. 38 years of Propulsion experience here, now retired. The solution shown at the end will work and should have been designed into the Prelimin design. Saturn S-IC injected helium directly in the prevalves, since there was no room for accumulators. Cheers.

You cannot reproduce the inflight resonance frequencies during an engines test having the Starship firmly clamped to the pad. Having a vibrating pad inducing the same vibrations as the engines but moving the ship at the same time may be a better avenue.

Where can I buy one of your SuperHeavy Booster Stainless Steel Water Bottles? is it insulated?

Music too loud

It didn't

thanks for the x plane nation

ship 35 died the same way too

Now post flight 9, this episode seems prophetic.

One of the best channels if not the best!

Starship is absolutely ready to have musk go for a manned flight, personally. Send him to mars, or whatever. ANYTHING will be better than musk remaining on earh

Beyond the super heavy present Starship design which is at the bike stage in Design and manufacture and requires a certain percentage reduction in scalar resizing to perform supposedly without mishap... THERE IS ANOTHER TINY design using the X wings and twin water recycle engines.. in appearance similar to the Star Wars fighters.. Designed to fly between Earth and Moon. Using hydrogen plus water recycling in both engines so to speak. A StarWars lookalike. British invented JohnSearl engines or multiple lift Searl engines not required.

Zack!
A question for you that nobody else seems to address.
Ever since SpaceX started adding the hot staging ring to the super heavy boosters, I have been dumbfounded. I get the issue about propellant stability keeping the fuel at the back of the tanks, which can be a problem when the booster completely shut down until the second stage ignites. But they claimed the reason was something like, a 10% as I recall improvement in payload to orbit.
I failed to understand why there is any significant improvement in payload to orbit. At the altitude of stage separation, there is virtually no air resistance, so the only negative delta V would be due to gravity, which is there whether the engines are running or not. Would those few seconds of slightly negative delta V account for 10% payload to orbit? And if not, what would a more realistic figure be, especially when taking into account the extra mass of the booster required for the hot staging ring addition?

Excellent presentation of the issue, Subscribed (and liked).

Caskets are rectangular. Coffins are six sided (in plan).

I have a hard time believing that static fire tests aren't pushing us closer to the sun

I don't know, but I can't help but wonder if too many engines with too many moving components which are subject to vibration increases the odds that a mission critical malfunction will take place in flight,

very clear presentation, THANKs!

Finally, a description of these events from an engineering perspective! I can't thank you enough!

This POGO problem is fascinating. Since I am “on the spectrum” my thoughts about solutions are very likely to be very different while still solving the problem (I have, at least, several in mind already especially since I think in pictures similar to Temple Grandin). I would be interested in discussing my thoughts with SpaceX engineers about possible solutions to see if they have been considered and/or tested. During my education, I was forever being told by teachers and professors that they would never have thought of approaching a problem as I did. That’s why “head” hunters have purposefully looked for neurodiverse people for unique problem solving. Feel free to pass this on to any SpaceX engineers you may know. The ideal system is simple and constantly self correcting similar to dampening effects for ships and buildings. Marshall Dressel, BA, MS, MD, COL, USA (Retired)

excellent as always!

Tom Irvine has a great video on POGO

The Pintle Valve Engine with internal energized vortex is supposed to be resistant to pogo due to the cap if forms on the end of the resonating tube as well as the ability to vary flow as a throttle and or shut off non catastrophically. Pintle engine which came over to SpaceX via employee number one, Tom from Northrup etc companies. Said pintle engine was never chosen for large engines by NASA et al despite its superiority and this forms the core of SpaceX success over Soviet engines used on Atlas etc, and absurdly complex and expensive Rocketdyne engines used on the Space Shuttle and Senate Launch System. did I get this all right? could not active counter oscillations of the pintle suppress some or all of the feed pipe system oscillations? Is that being done to some extent?

The only solution is to strap on solid boosters as NASA with it's SLS

Great long-form video and I appreciate the effort that went into it. I do think there is a major issue that wasn’t addressed: Starship is simply too heavy. Period. The Raptor 2 engines do not have the thrust to get the ship into orbit with both Superheavy and Sharship being caught by chopsticks. And that's before attempting a flight with any meaningful payload. That’s why V2 got stretched for more propellant, and why everything rides on V3 engines being a major leap forward. The lack of fire suppression isn’t a “whoops, we forgot!” moment—it’s a deliberate trade-off to shave every possible kilogram in hopes of pulling off an early and stunning win. I'm not sure that Starship will EVER be viable platform unless someone admits they made a mistake and goes back to a composite design.

Increase the number of LOX and Methane feed tubes tubes plus reducing their diameters such that the resulting frequencies will be so impossibly high that POGO conditions can't ever reached. Yes, this will increase component weight in order to meet flow requirements, but the resulting self-damping will fix the problem ... might need some heating to prevent 'freeze' problems.

By the way you put it it truly seems like a previosuly believed secondary system for added stability is actually the game changer element necessary for the ship to work, and they clearly didn't design the ship for it, and that's a bit worrying.

elon owes you a billion bucks

Nothing can save starship. It’s a piece of shit

Is aerodinamicaly non symetrical and dynamically un-stable when flapses are actuated a-symetrically, not to mention the un-inspired cilindrical circular shape of bulk-head. There accumulate mechanical and thermic concentrators around actuators...