Kenneth_2003 said:

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Ok, let me put it this way... Lots of sloshing in the fuel tanks leads to poor fuel flow to the fuel pumps in the engines. The header tanks, separate fuel tanks for the landing sequence were supposed to alleviate this but it appears that they have not. Ullage is the process of accelerating the vehicle in a desired direction to intentionally slosh the fuel towards the fuel lines. Apollo would do it with their attitude control thrusters for burns during thier journey to and from the moon.

The draco or super draco thrusters burn gaseous fuels rather than liquid fuels so sloshing isn't a problem. These are the names of the systems SpaceX already uses for maneuvering their Dragon capsule in space and as the escape system should they need to get away from a booster.

These are hypergolic fuels, so as soon as they touch they go boom. No ignition system required. Think dropping metallic sodium in water or baking soda and vinegar vs needing a spark plug in your car.

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Part of the issue is they don't want to use draco/hypergolics on starship at all because the hope is the whole thing can some day be refueled/maintained from Mars (yes, this is a ways off). I think there was a scott Manley video last year discussing this; they work well but reliance on them if you're on Mars means basically you are really stuck if you run out of juice on an interplanetary trip but they think they can make methane and oxygen as needed some day on site.

Gotcha. So the cold gas thrusters are LOX bleedoff? I know Falcon used N2, but I guess no reason you can't use the LOX.

TriAg2010 said:

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Maximus_Meridius said:

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Unless I'm wrong (totally possible), they pretty much have to run journal bearings at those speeds and power ratings. Probably product lubricated, which makes life a lot more complicated.

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There are roller bearings suitable for those speeds and loads. The SSME turbo pumps used one cylindrical roller bearing plus one ball bearing on the LH2 side and one cylindrical and two ball bearings on the LOX side. I can't think of any flying turbo machinery that uses journal bearings. Journal bearings are typically used on industrial machinery only.

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Well, you learn something everyday. I knew there were high speed ball/roller bearings for mills/CNC and such, but did not think they would be used in such a high HP/speed operation.

Kenneth_2003 said:

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Gotcha. So the cold gas thrusters are LOX bleedoff? I know Falcon used N2, but I guess no reason you can't use the LOX.

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Well, basically, I think. I could be wrong, but it's also why they don't use TEA-TEB to ignite the raptors (unlike the merlins). They use a spark ignition (which, again, might have been an issue on relight). I wish I could find the video I watched over xmas about this but I couldn't within 5 minutes so I gave up/lunch is ending.

I don't know the ignition type for the methelox thrusters, but yes they run on methane and liquid oxygen.

https://forum.nasaspaceflight.com/index.php?topic=46574.0

That's another forum but I don't think it's really a competitive one so hope it's ok to post. We need more aerospace engineers on here to chime in probably...

https://m.washingtontimes.com/news/2021/feb/3/biden-cancels-elon-musks-adventures-in-space/

Quote:

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New president is making his space policy increasingly clear: America will remain grounded for the time being

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ETA sorry already posted. Just realized it was a couple days old.

I really think the Washington Times piece is poorly reasoned/lacks real insight. I am an enormous detractor of president asterisk, but the FAA issues with the Boca Chica launches I do think pertain to the parameters of the approvals and need to make sure chance of fatality is under .001 percent (something like that), plus accident investigation/documentation stuff.

I really doubt Biden can remember day to day who Musk or spacex are, and hasn't impacted the midlevel FAA bureaucracy yet. FAA pressure internally over safety is maximized now thanks to the Boeing stuff, not really Musk commenting on Gamestop etc.

My casual-watcher take is that the FAA knew that Trump was pushing for the moon and mars. The priority likely impacted the actions of individuals who knew that there could be ramifications for not playing nicely. Now that Trump is gone, the pressure has been released and risk-averse bureaucrats have returned to their natural state.

Get Off My Lawn said:

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My casual-watcher take is that the FAA knew that Trump was pushing for the moon and mars. The priority likely impacted the actions of individuals who knew that there could be ramifications for not playing nicely. Now that Trump is gone, the pressure has been released and risk-averse bureaucrats have returned to their natural state.

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You may be right about that, but it's not been documented/reported on anywhere about that being the case. Also, the Dem senators sending a letter about the importance of Artemis (moon program) probably means the Dems aren't going to gut the program/funding there, as well.

They'll just do what their natural propensity is on all goals; throw even more money/debt at 'climate research' funding via nasa.

Also, the shockwaves wouldn't be an issue but for the handful/3 or so houses where folks refuse to sell out to SpaceX in Boca Chica Village. Not sure what 'other weather conditions' might apply for the launch as we all know they won't fly it if it's raining etc. I don't understand why it was ok for Jerry Jones to get the state to condemn folks property for takings for Jerry world, but SpaceX can't seem to get any help at all on it, yet here we are.

I do doubt that the FAA folks are really 'here to help' so to speak.

Quote:

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First Tweet: It was foolish of us not to start 3 engines & immediately shut down 1, as 2 are needed to land
More Tweets:
Twitter: Will these changes be able to be implemented into the SN10 test flight?
Elon Musk: Yes.
Twitter: Wouldn't it be safer to light 3, and throttle 3 for landing just in case there's 1 engine failure?
Elon Musk: Yes, but engines have a min throttle point where there is flameout risk, so landing on 3 engines means high thrust/weight (further away from hover point), which is also risky
Twitter: So it will be determined which to cut off based on data available right after relight?
Elon Musk: Yeah. By default, engine with least lever arm would shut down if all 3 are good.
@Brendan2908: Here's what @elonmusk means by this tweet
Elon Musk: Yes
EDA: Someday the leverage arm won't matter as much when you go to hot gas thrusters though, right? Those will become a powerful source for the flip and the engines won't be as necessary, right? Or will the engines always light to aid in the flip even with hot gas thrusters?
Elon Musk: Intuitively, it would seem so, but turbopump-fed Raptors have much higher thrust & propellant mass fraction than pressure-fed gas thrusters & they're already there
Elon Musk: Higher Isp too
EDA: Oh right! That makes a lot of sense. I have kind of been snickering to myself thinking you're over there practicing this landing maneuver that will change and be obsolete the second you get hot gas thrusters Makes sense to continue the turn and burn! I love this stuff!
Elon Musk: That said, the ship landing burn has a clear solution. My greatest concern is achieving good payload to orbit with rapid & full reusability, without which we shall forever be confined to Earth.
Twitter: So does that mean for the time being you'll be sticking with cold gas rcs?
Elon Musk: Will still use hot gas maneuvering (RCS) thrusters, as ~5X more efficient than nitrogen (300 sec vs 60 sec Isp)

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Yeah, I assume the Dems would love to claim the title of "first female president puts the first female on the moon," so I doubt they're intentionally running things aground (to your point).

I have to assume that there's a significant cultural shift across the entire federal bureaucracy when you go from a "You're Fired!" president to an absentee-leadership-by-comittee "trust the experts" president*. The showing up of NASA may also have some less visible impacts as well.

More heat shield tiles on SN11

PJYoung said:

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What are the risks if the Starship does a big fiery splat in the sand?

TexAgs91 said:

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What are the risks if the Starship does a big fiery splat in the sand?

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It's for SpaceX to show there aren't any.

Musk said before the SN8 flight he expected a one-in-three chance at success. If the balance of expectations is that the test would result in a landing failure, then it was sort of ****ty to skip the homework to prove the failure would be benign, no?

nortex97 said:

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Also, the shockwaves wouldn't be an issue but for the handful/3 or so houses where folks refuse to sell out to SpaceX in Boca Chica Village. Not sure what 'other weather conditions' might apply for the launch as we all know they won't fly it if it's raining etc. I don't understand why it was ok for Jerry Jones to get the state to condemn folks property for takings for Jerry world, but SpaceX can't seem to get any help at all on it, yet here we are.

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Principally air temperature since that has a big impact on density and how effectively blast energy would propagate.

TriAg2010 said:

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TexAgs91 said:

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What are the risks if the Starship does a big fiery splat in the sand?

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It's for SpaceX to show there aren't any.

Musk said before the SN8 flight he expected a one-in-three chance at success. If the balance of expectations is that the test would result in a landing failure, then it was sort of ****ty to skip the homework to prove the failure would be benign, no?

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There is the same amount of risk with SN9 as with SN8. And did I mention it's in the middle of a bunch of sand? Plus they can blow it up if it veers off course.

"It didn't hurt anyone last time..." is not how we do things.

TriAg2010 said:

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"It didn't hurt anyone last time..." is not how we do things.

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You're being intentionally obtuse. The area had been evacuated.

Quote:

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Given the communication problem, FAA investigated not only the SN8 hard landing but also did "a comprehensive review of the company's safety culture, operational decision-making and process discipline." The investigation was done quickly and changes were incorporated for SN9.

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To some extent this is subjective opinion and dependent on an individuals temperament, but in brief chats with former SpaceX engineers, Id say they set a low bar for " safety culture, operational decision-making and process discipline."

I doubt it went far beyond making sure no one is nearby, and answering some questions from the government. Then fire it up in clear weather and see what happens.

At the opposite extreme is NASA which is so risk averse, they end up not accomplishing anything. I know a former NASA engineer who said the extremely low risk tolerance prevented them from accomplishing anything and took the fun out of working there. Too many meetings, reviews, etc. to do small things or make any changes.

TriAg2010 said:

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aTmAg said:

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Relighting engines is not that hard. Space X has been doing it for a long time, and the US in general has been doing it for decades.

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I think you're downplaying the challenges here. Most of the restartable engines in the world are simple pressure-fed hypergolic engines where start-up is just opening a valve. A restartable cryogenic engine is a mark of an advanced propulsion system and the U.S. was basically alone in with this capability for a long time. Europe didn't have this capability until 2005 and I don't think Russia or China have ever flown one. Even the cryogenic restartable engines the U.S. has flown - like RL10 and J-2 - are comparatively simple cycles compared to the staged combustion used by Raptor. This is a step change in complexity over anything SpaceX has done with the Merlin or what others have flown. It's closer to say, a restartable Space Shuttle Main Engine.

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Just gonna say you, and bthougigem05 were spot on a couple months ago about this being harder than some of us thought.

Some more analysis of Musk on the 3 engines relighting, and evolution of the landing plans;

https://www.teslarati.com/spacex-elon-musk-talks-starship-sn9-explosion/

bmks270 said:

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Quote:

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Given the communication problem, FAA investigated not only the SN8 hard landing but also did "a comprehensive review of the company's safety culture, operational decision-making and process discipline." The investigation was done quickly and changes were incorporated for SN9.

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To some extent this is subjective opinion and dependent on an individuals temperament, but in brief chats with former SpaceX engineers, Id say they set a low bar for " safety culture, operational decision-making and process discipline."

I doubt it went far beyond making sure no one is nearby, and answering some questions from the government. Then fire it up in clear weather and see what happens.

At the opposite extreme is NASA which is so risk averse, then end up not accomplishing anything. I know a former NASA engineer who said the extremely low risk tolerance prevented them from accomplishing anything and took the fun out of working there. Too many meetings, reviews, etc. to do small things or make any changes.

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Is that not safe? Rapid trials and iteration is the key to private industry efficiency in a field like this. Would take NASA years between tests and they do it in weeks. Get the FAA tf out of "culture" investigations

SpaceX's ability to put the crater on the landing pad with both SN8 and SN9 is simply remarkable, bears repeating.

JobSecurity said:

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bmks270 said:

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Quote:

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Given the communication problem, FAA investigated not only the SN8 hard landing but also did "a comprehensive review of the company's safety culture, operational decision-making and process discipline." The investigation was done quickly and changes were incorporated for SN9.

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To some extent this is subjective opinion and dependent on an individuals temperament, but in brief chats with former SpaceX engineers, Id say they set a low bar for " safety culture, operational decision-making and process discipline."

I doubt it went far beyond making sure no one is nearby, and answering some questions from the government. Then fire it up in clear weather and see what happens.

At the opposite extreme is NASA which is so risk averse, then end up not accomplishing anything. I know a former NASA engineer who said the extremely low risk tolerance prevented them from accomplishing anything and took the fun out of working there. Too many meetings, reviews, etc. to do small things or make any changes.

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Is that not safe? Rapid trials and iteration is the key to private industry efficiency in a field like this. Would take NASA years between tests and they do it in weeks. Get the FAA tf out of "culture" investigations

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Yes, as long as destruction of test article is properly budgeted and planned for, and the test plan developed around that as an acceptable outcome, then it's really not as bad as it seems.

I think this whole FAA aspect is because rocketry rarely blows up on the ground anymore - nearly all rocket accidents lately have been after launch and they're a ways away. I can think of maybe Proton (where they inverted an instrument and it came back down) and maybe a Chinese vehicle that exploded on the pad?

I think SpaceX is kinda the only organization actually blowing up rockets near landing pads anymore. Different acoustic modeling, also you're by definition as close to bystanders as you will ever be during the flight.

TexAgs91 said:

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TriAg2010 said:

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"It didn't hurt anyone last time..." is not how we do things.

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You're being intentionally obtuse. The area had been evacuated.

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No, I'm cognizant of normalizing deviance. SpaceX messed up, flew SN8 when they shouldn't have, and paid the price of a minor delay the next time they wanted to fly. Big deal. They will be hopefully be better for it in the future.

There's some serious Randy Marsh "I thought this was America" vibes going on. It's like a bunch of freshman who read Ayn Rand for the first time and can't believe the man is holding them down from blowing up rockets.

Decay said:

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I think this whole FAA aspect is because rocketry rarely blows up on the ground anymore - nearly all rocket accidents lately have been after launch and they're a ways away. I can think of maybe Proton (where they inverted an instrument and it came back down) and maybe a Chinese vehicle that exploded on the pad?

I think SpaceX is kinda the only organization actually blowing up rockets near landing pads anymore. Different acoustic modeling, also you're by definition as close to bystanders as you will ever be during the flight.

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SpaceX had a rocket blow on the pad carrying customer payload 2-3 years ago didn't they?

Musk just blows up rockets and isn't deterred. He blew up his first rocket attempt like 2 or 3 times. I really don't think he cares much about the bottom line as much as other organizations would, he has deep pockets.

They didn't blow up falcon 1 2-3 times.

The detonation on the pad of the falcon from a few years ago was tested, ironed out, and the results are currently launching US astronauts to the space Station

There's a difference between iterative testing in controlled conditions, and blowing things up because it's fun.

NASA spent how many decades launching humans on a shuttle system that was KNOWN to be damaging it's heathsield eveeytime it launched? But triag, you want to throw stones at a company who iterates on unmanned test articles.

They lost quite a few falcons early on. Similar goal I guess for Starship in some respects...iterative improvements.

NASA just had the privilege of blowing up all of their test vehicles at White Sands Missile Range. Don't think .gov is going to let Elon use that facility. NASA has also shattered a LOT of windows in Huntsville, AL.

Elon is blowing up rockets on the ground today because he's bringing them back in one piece. Everyone else with orbital capability is blowing up their spent stages in the upper atmosphere and dumping them in an ocean. (Well the Chinese drop a few in villages, but they don't count casualties in the single digits, and Russia might have flattened some bedouins over the years.)

nortex97 said:

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Kenneth_2003 said:

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Ok, let me put it this way... Lots of sloshing in the fuel tanks leads to poor fuel flow to the fuel pumps in the engines. The header tanks, separate fuel tanks for the landing sequence were supposed to alleviate this but it appears that they have not. Ullage is the process of accelerating the vehicle in a desired direction to intentionally slosh the fuel towards the fuel lines. Apollo would do it with their attitude control thrusters for burns during thier journey to and from the moon.

The draco or super draco thrusters burn gaseous fuels rather than liquid fuels so sloshing isn't a problem. These are the names of the systems SpaceX already uses for maneuvering their Dragon capsule in space and as the escape system should they need to get away from a booster.

These are hypergolic fuels, so as soon as they touch they go boom. No ignition system required. Think dropping metallic sodium in water or baking soda and vinegar vs needing a spark plug in your car.

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Part of the issue is they don't want to use draco/hypergolics on starship at all because the hope is the whole thing can some day be refueled/maintained from Mars (yes, this is a ways off). I think there was a scott Manley video last year discussing this; they work well but reliance on them if you're on Mars means basically you are really stuck if you run out of juice on an interplanetary trip but they think they can make methane and oxygen as needed some day on site.

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Totally unrelated, but kinda related... but a Scott Manley video a while back got me to thinking.... Someone was putting a satellite in orbit that was going to rendezvous with a satellite in Geostationary orbit, lock onto it's engine bell, and essentially become the tow truck that would enable the far more expensive unit to maintain orbit and continue its mission vs deorbit and a costly replacement.

That led me to think how cool it would be if you could build a "gas station" of sorts in orbit. Long life satellites going forward would be equipped with replaceable fuel pods, or canisters, where a maintenance satellite would move from low earth orbit to geostationary orbit and service units whose tech is still functional and viable, but is low/out of fuel to make orbital corrections. Empty fuel tanks/whatever could be returned to earth, collected, and refilled or the whole unit once empty could be simply sent to burn up. NASA probably wouldn't want it docked to the ISS because they don't want that much traffic in and out of their exclusion zone, but perhaps it could be in some other parking orbit. I realize that a single satellite servicing could take months of orbital maneuvering.

Coming back around to SpaceX and Starship, IF they were to use a hypergolic engine could you put those fuels in some form of removable tank and service the system, refuel it in orbit. It would be envelope pushing for sure, but it could also be revolutionary. Starship returns from Mars settles into LEO and gets a fresh set of Hypergolic fuel tanks to provide the ullage burn at landing.

The plan all along has been to refuel starship in orbit with other starships acting as tankers.

Moving stuff around in orbit, or refueling other satellites would be great, but would be most likely multiple generations of satellites away (to make their fuel accessible). The satellite manufacturers themselves aren't commercially motivated to make their systems serviceable in orbit to go for multiple decades. It's also not so simple to skirt around space and move stuff hundreds of miles worth higher etc., and methane/oxygen, while great, won't sit around for 10 years in a tank in orbit easily either.

I don't think using more hypergolics would make starship (with an expendable source as such) more easily refillable etc. Musk has stated directly/repeatedly a lot of his mars colonization objectives are built around a concept of producing fuel needed there. Flying a raptor up to 1,000 times, and using in situ resources on Mars etc. can't be done with hypergolic consumables as part of the process, period.

https://www.wired.co.uk/article/spacex-raptor-engine-starship

https://provscons.com/heres-why-spacex-uses-methane-in-starship/

This piece sort of details the radical plans for using a fleet of starships to colonize commercially mars itself;

https://www.nationalreview.com/2020/02/mars-elon-musk-plan-to-settle-red-planet/

Enjoyed that article. Thanks for posting!