Rocket general questions 1

[rb1957]

From today's launch (nice launch, not so nice flight) of SpaceX ...
1) what gas are they venting ? can't think they've venting methane
2) how do they control pressure in the tanks ? do they have a bladder/balloon where they can add/remove gas/liquid (N2 ?)
3) they made a point of filling the header tanks (which would not be used) ... so they intended to dump a tank (small though it may be) full of methane into the Pacific ??
4) when they chill the plumbing and such before loading fuel, I assume they're only passing N2 through the system, and it doesn't hang around long (as it did when they did the cryo testing)

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[rb1957]

I'm talking about the clouds that surround the rocket on the pad, prior to launch. But I think I've "sussed" that ... O2 is vented overboard and fuel vapour is recovered.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[btrueblood]

I've not spent a lot of time looking at how the flight tanks are filled, but yes, you would probably dump LN2 into the tank and let it boil off through a regulator/pressure control valve. Eventually, when temperatures are low enough, you start pumping in LOX, and taper back on LN2. The lines and storage tanks for LOX likely have a shield layer through which more LN2 can be pumped to keep them cold, but I doubt flight tanks have cooling jackets like that. So...most of the vapor you see on the pad is LN2 boiling off, along with some oxygen as filling progresses. I think LN2 mixes with LOX, but the LN2 again evaporates/boils off at a lower temperature, leaving LOX behind.

When I was a rocket engineer, testing with H2/LOX - we chilled a jacketed tank with LN2 (through external jacket and also by trickling LN2 into the internal tank volume - this initially came through as gaseous N2, which kept the tank purged and dry. After several hours, monitoring tank wall temperature and internal tank temp - when temperature was low enough, we closed the LN2 purge trickling into the tank, and opened a valve and trickled in gaseous oxygen (LN2 jacket flow was maintained throughout) through a jacketed line, so it came into the tank fairly cold already. The tank being at LN2 boiling point would condense some/most of the incoming GOX. The residual LN2 in the tank would boil off pretty quickly. The oxygen would vent - and eventually this would start to spit blobs of LOX, which was how we knew we had a full tank. When ready to fire, we would dial up the pressure on the vent regulator (never cap a bottle of LOX, bad things can happen), and open a helium pressurization valve. Even with all that, it took a long run to finally get liquid oxygen down the pipe, through the injector dome, and into the combustion chamber - we were not running full SSME flow but just testing single injectors.

 

[WKTaylor]

Btrueblood... You are a true 'steely-eyed missileman'.

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[btrueblood]

Mmm...no, I was a lilly-livered missile man (LOL), then left for more civil pursuits after a decade or so. Lily livered: I preferred to be in a bunker somewhere well back from the business end of the motor doing calculations. Well, actually that's not really true, I just told the wife that so she wouldn't worry (but I doubt she bought that, she being a steely-eyed missile woman working in the stress analysis group). I do have a collection of...rapidly disassembled...test hardware from back in the day. The testing I mentioned before - on one occasion I had to walk back into the bunker to reset some optics that the mechanic had bumped. While doing that I noticed a jacketed LOX line was dripping from a Swagelock connector that joined the central (LOX) connection (a separate loop of tubing joined the outer LN2 jackets). I only discovered it because it was very quiet in there, and I could hear the "pop" as drops of LOX hit the concrete floor in the bunker. Concrete that had probably been there since WW1, and seen a lot of oil and fuel leaks over the decades. The pop sound was the LOX igniting and exploding some of that oil. I told the mechanic when I went back through the blast doors, and he went out and tightened the fitting with a pair of wrenches, and then we went ahead and ran our tests. Nobody died, but I did raise an eyebrow at him.

 

[WKTaylor]

BTW... did I not see any lightning strike/diverter towers around the Starship Launch pad?

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[rb1957]

thx Jennifer (you've been active today ... just joined up ?)

Thx, yes I figured they weren't venting fuel ... there'd be a "rapid disassembly" if they did !

Ok, so they chill the system with LN2 which boils away ?

How do they control the tank pressure ? I mean the propellants are liquid (yes?)but also boiling off vapour (no?) which would need to be vented ?
And how do they keep the propellent separated from any pressurising gas ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[WKTaylor]

OH, GREAT. SpaceX is cobbling together steel protective plate(s) to protect another launch-pad and concrete foundation. It does NOT seem to be an exhaust-blast-deflector/channel system common to professional launch pads.

I guess fake-it-till-you-make-it is Starship launch crew motto.

I wonder what unintended consequences are coming with the next Boca Chica launch, due to this pad modification...?

from what I can tell the pad sustains ~7+ seconds of rocket engine thrust-blast as engines come-on line... and the about +15 seconds more [diminishing] as the vehicle clears the tower.

I wonder what the pad static/dynamic pressures, thermal-flux and sonic-decibels are during this period. The numbers seem unimaginable.

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[rb1957]

I have to agree with you Will. It looks like bad solution ... to have the exhaust impact on a flat plate. "All" other pads deflect the exhaust to the horizontal. And I don't see know those water jets will survive against the rocket exhaust. I reckon we'll see just so much molten slag where the plates used to be.

But I don't see this as "fake it till you make it". He has a lot of smart guys (non gender specific) working with him. I'm sure they've done some numbers and convinced themselves it'll work. After the next test we'll know.

I mean, who thought landing rockets was either possible or a good idea ? And now he's shown it can be done nearly everyone ('cept for SLS) is doing it.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[WKTaylor]

rb...


EXCEPT... SpaceX did proof of concept testing with Falcon booster stages in the Texas desert... to get a grip on the physics and all the unknowns... and worked with the proven [then expended] Falcon9 boosters during real-world launches for learning how to land. However, each of these missions was FROM real LAUNCH PADS AND INSTRUMENTED RANGES... under strict NASA and FAA and DoD oversight.

ALSO, NOTE... NASA is now hedging it's bets by funding development of the Blue Origin Lunar lander designs for SLS.

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[btrueblood]

I am quite impressed with the Falcon landing and engine re-use (though the landing on rockets has been done before for the lunar and Mars landers). Cleaning up engines and turbopumps that have previously run on kerosene (or RP-1) is pretty messy - fuel used in the cooling passages can coke and form deposits; fuel burned in the turbine drives can soot up the turbine blades (generally the turbine drive is fuel-rich to moderate temperatures). Though, not sure if the Raptor engines are using LOX as coolant like the Russians did?

 

[rb1957]

"quite impressed" ... damn ! this is a tough crowd !

it was IMHO fricking awesome ! (particularly after a couple of failures)

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[WKTaylor]

Blue Origin Wins Contract For Second Lunar Lander

https://www.avweb.com/aviation-news/286327/

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[btrueblood]

I'm still not sure the SpaceX Starship is a viable lunar lander - though if they can throttle the engines to 1/7 of their rated thrust, then maybe they won't scour a pit large enough to bury the lander into? The longer landing legs and more dispersed (larger nozzles) thrust pattern makes it look more "fit for the mission". But I'm just armchair quarterbacking. Glad to know they got funding for more than just one design/contractor.

 

[rb1957]

don't forget they can bleed off a lot of their velocity somewhat above the moon's surface, and over the last 100ft or so may only have <10 fps to worry about.

and also final descent on only 1 engine ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[rb1957]

personally I still advocate for the Space 1999 Eagle lander.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[IRstuff]

But I don't see this as "fake it till you make it". He has a lot of smart guys (non gender specific) working with him. I'm sure they've done some numbers and convinced themselves it'll work. After the next test we'll know.

I'd worry that this is the same group that ostensibly gave the OK to use the launch pad that got thrashed by the last launch.

personally I still advocate for the Space 1999 Eagle lander.

I'd second that ;-)

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[WKTaylor]

IR... a thick steel plate 90-deg to the rocket blast could possibly reflect 'sonic pulses' back to the engines, even with water deluge... As opposed to [one or more] canted steel deflector plates, to blast exhaust and sonics sideways.

All-to-often I seen the law of unintended consequences disrupt the pathway to success.

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[btrueblood]

Ditto what Wil said, and I've said previously - 30 plus engines igniting and firing onto a 90-degree steel (or previously concrete) platform not very far away is going to create a very noisy environment directly below the engines, which are trying to get the flame lit (and the nozzles are still sub-sonic, so that reflected noise is getting to the combustion chamber). It's a recipe for not getting all the fires lit, and potentially starting fires and/or explosions in the aft structure, due to unburnt propellant gases travelling back up inside the heat shielding.

 

[thebard3]

I don't see how a significant reflected noise front can penetrate the flame front exiting the engines at several kilometers per second. Anything will be quickly forced sideward and out across the ground. I'm not espousing the design SpaceX has chosen, but I'm willing to wait and see what happens during the next launch. There is a lot of complex physics going on and SpaceX engineers seem determined that this design is sound.

Brad Waybright

The more you know, the more you know you don't know.

 

[btrueblood]

"I don't see how a significant reflected noise front can penetrate the flame front exiting the engines at several kilometers per second."

Watch some slow motion film of the shuttle main engine ignition sequence, and look at the swirling flow evident in the nozzle bells at the early moments of ignition. Basic physics: until the engine is ignited and running at a significant fraction of full rated thrust, the nozzle is NOT choked, and the flow exiting the nozzle is sub-sonic, and shock/blast waves can and do propagate upstream to the injector face. Those shocks can mess with the flow of the two propellants into the combustion chamber, and blow out the flame of the ignitors and/or cause mixture ratio excursions that can melt the chamber liner and/or push ignition flames back into the LOX dome where the metal of the injector can light off...basically lots of stuff happens during main engine ignition sequencing. NASA/Rocketdyne did dozens of ignition tests to get the sequence correct (timing of valve openings, etc.), with a lot of the first ones ending in molten/destroyed engines and hardware. These were tests done in proper flame-bucket and water deluge type thrust stands, in single engine and multi engine arrays.

"Anything will be quickly forced sideward and out across the ground."

So you did the plume analysis already? There's a lot of empty space between those 31 motors, and not much space between the motors and that big flat plate; there is no diverter bucket to turn the flow and you see on the last launch the result - a huge swirling cloud of dust and debris that completely obscures the engines for several seconds until the rocket lifts off, and several engines are "out", either not igniting or being shutdown automatically for having "excursions" like those early SSME test. I'm saying it's not an easy analysis, and it's obvious that they arm-waved it on the first go. I'm willing to bet we will see another launch with engines "out" at, or shortly after, liftoff.

"I'm willing to wait and see what happens during the next launch. There is a lot of complex physics going on and SpaceX engineers seem determined that this design is sound."

I'm wiling to wait and see too, 'cause it's not my circus nor my monkeys. I hope you are right, and they have fixed all the issues - but it doesn't look that way to me, and I used to do that job for a living. It smacks to me of hubris and a "damn the torpedos" mentality that can be dangerous. Luckily nobody has been hurt (yet) and it's just Elon's money not mine.