YazataMar 2, 2020 04:11 AM (This post was last modified: Mar 2, 2020 04:20 AM by Yazata.)
(Mar 2, 2020 01:19 AM)C C Wrote:
(Feb 29, 2020 06:14 PM)Yazata Wrote: [...] They already knew that their welds weren't right and had already decided not to try to fly SN1. But they apparently still wanted to see how the inferior welds did [...]
That makes it sound better. But just like with that junk-bucket Hoppy, at some point they actually need to luck out with the welds, or it starts looking like excusatory propaganda. "Oh, we're still not trying, couldn't care less. Next time we'll make a deliberate effort."
We could be watching NASA's SLS (Space Launch System), intended as NASA's new Moon rocket, begun in 2011, already costing something like $14 billion (as of 2018) and not anticipated to fly until 2021. It isn't reusable and will probably cost so much per-flight (many hundreds of millions) that it will hardly ever fly. (NASA has stopped providing estimates of per-flight cost.)
Compare that to Starship. We are only a little over a year since Hoppy was begun. Six months since its triumphant flight. SpaceX has rolled out and tested a brand new rocket engine (the most advanced in the world). And in the six months since Hoppy, both Mk.1 and SN1 (briefly) appeared. Both failed but lessons learned. Better than doing nothing. (It keeps us entertained at the very least.) A new rocket factory is taking shape and growing daily.
And far from SLS's inflated billions a year cost, each iteration (mk.1 and sn.1) reportedly only cost about $10 million each to build. If Starship can eventually fly repeatedly, divide the manufacturing cost by number of flights. (Elon wants thousands of flights per ship, like a commercial airliner.) That might be ambitious, but if he gets anywhere close, the biggest expense becomes fuel, which are methane and oxygen (cheap). The prospect of a ticket to orbit costing no more than an airline ticket today starts to become realistic.
Once they learned that the welds on SN.1 weren't satisfactory, they apparently consulted the welding technology company that hopefully helped them fix the problems. They also knew that welding a spaceship out in the wind was problematic at best. So they are busily building their tents and their 'highbay' vab building. But what to do in the meantime? So they decided to go ahead and see what they could come up with. And ultimately, they had all these pieces of SN.1 and the question what to do with them. They weren't good enough to fly. So junk them? (They just made them) Or use them as a static engine test stand? They needed to test the engine with the actual flight systems and controls and they needed to test the pressurization system that proposes to use gasses from the rocket engine to pressurize the tanks. (Other rockets already do this so it isn't unprecedented. But it's never been done with their particular engine.) Unfortunately, the LOX tank wouldn't hold the necessary pressure and blew up.
But nothing was lost that they wouldn't have lost if they hadn't even tried it. Except maybe $10 million, which is within Elon's budget. And Gwynne is peering over his shoulder. (I think that she plays 'Grownup in the room' when she has to. Elon listens to her.) Elon's said repeatedly that he doesn't mind failure all that much, if it was a good idea. What he hates most of all is not having any creative ideas and not even trying.
And while others have built rockets out of stainless steel (such as the old John Glenn era Atlas that lofted the Mercury capsules into space and today's Centaur upper stage) nobody has ever tried building a stainless steel rocket with a 9 meter diameter (almost 30 feet). So there are fabrication lessons to be learned as well. What can the Boca Chica builders (some of whom probably aren't terribly skilled) do easily and what do they struggle with? What kind of design changes can be made by the engineers back in Hawthorne that minimize the struggles?
We're stripping SN2 to a minimum to test the thrust puck to dome weld on pressure, first with water, then at cryo. Hopefully, ready to test in a few days.
So it sounds like they already know how the bottom dome failed, what part of it came loose, and which welds broke.
The "puck" seems to refer to what the engineers have been calling the "thrust structure". It's the solid thing to which the engines attach, designed to transmit the thrust to the entire vehicle. The mk.1 version had an elaborate thrust structure, separate from the LOX tank bulkhead, while the SN.1 version may have been trying to integrate it with the bottom LOX bulkhead to save weight. Speculation is that the "puck" is a circular solid metal disk (similar to a giant hockey puck) in the middle of the LOX dome. Problems can arise from different shapes and from welding materials of different thicknesses. One side might flex more than the other when under load, leading to fracturing.
They seem to have used pieces they had prepared for SN2 to make another Bopper 3.0. This one has the top dome (originally intended to be the top of the CH4 tank) on top and thrust dome (origionally intended to be the bottom of the LOX tank) on the bottom forming a single test tank with a few rings in between. Then it will be pressurized to test the integrity of the thrust dome.
Here's Elon's photo of it under construction in the not-yet-completed High Bay. The thrust dome with its engine mounting "puck" is visible (pointing upwards) and a nicely welded triple ring is being lowered over it. Then they flipped it upside down and the top dome and more rings was joined to it.
A smaller Roll Lift crawler has arrived to take Bopper (baby popper) 3.0 to the launch area.
They obviously realize that the dramatic engineering changes they made to Mk.1's thrust structure need further testing in light of the failure of SN.1's thrust structure upon tank pressurization. And the SN.2 thrust structure is designed for three engines, not just one, so it's a new never-tested item in its own right and an even bigger risk.
YazataMar 5, 2020 11:29 PM (This post was last modified: Mar 5, 2020 11:47 PM by Yazata.)
A really good article by Eric Berger in Ars Technica
Filled with stuff, straight from Elon, about his plans for Boca, photos of the site, descriptions of how fast its grown, and Elon's own account of the SN1 explosion and what led up to it.
For example this (the black text is Elon's words).
Quote:Basically, the SN1 failure boiled down to bad welds in a weak section of Starship near the engine. When exposed to pressure, the welds burst. Musk was not happy because he had not heard about this specific issue, in this section of starship, before the test failure. Do you think Musk addressed that with his team? Yeah, he addressed that.
“We sent out a note to the team that [SN1] was badly designed, badly built, and badly checked,” he said. “That’s just a statement of fact. I met with the whole quality team, and I said, ‘Did you think that that thing was good?’ They said, ‘No.’ I told them that, in the future, you treat that rocket like it’s your baby, and you do not send it to the test site unless you think your baby’s going to be OK. They said that they did raise the concern to one of the engineers. But that engineer didn’t do anything. ‘OK,’ I said, ‘then you need to email me directly.’ Now they understand. If you email me directly, and if I buy off on the risk, then it’s OK. What’s not OK is they think that the weld is not good, they don’t tell me, they take it to the pad and blow it up. Now I have been clear. There’s plenty of forgiveness if you pass me the buck. There is no forgiveness if you don’t.”
It sounds like some thankfully unnamed engineer is on Elon's shit-list.
More
Quote:Yet Musk has not been spending so much of his time in South Texas just to build a Starship. Rather, he's trying to build a production line for Starships. He wants to build a lot of them. And fast, always fast... Musk wants a linear flow through the tents, whereby rocket parts come into one end of the factory and move from station to station until large chunks of Starship end up in a high bay for stacking into a vehicle.
YazataMar 6, 2020 06:38 PM (This post was last modified: Mar 6, 2020 10:21 PM by Yazata.)
The new pressure-test Bopper 3.0 is on the move, on a Roll Lift trailer (smaller than the heavy duty crawlers) headed towards the launch area. There may be a pressure test tonight.
YazataMar 8, 2020 04:02 AM (This post was last modified: Mar 8, 2020 04:36 AM by Yazata.)
Roads are closed and LN2 (liquid nitrogen) pressurization test underway. This may or may not be an intentional test-to-destruction to see what the upper limit is on the new thrust dome on the bottom. The Cameron county sheriffs were nice and polite, but chased off SPadre from his customary streaming location. Given what happened to SN1, they might have tightened up their safety perimeter a bit.
Tie-downs for the top dome are easily visible. Dunno if they plan to intentionally pop Bopper 3.0 or whether they are just taking prudent precautions.
Edit: Now everyone is saying that today's testing is over. No frost was ever visible on the Bopper, so pretty clear it was never loaded with liquid nitrogen. Maybe another water pressure test like yesterday.
Mary has some excellent photos of a very large hydraulic ram placed underneath so as to push upwards on the Raptor engine mount. (There is no engine mounted.) The engineers think that this is to simulate the thrust of an engine. So Elon and the boys apparently want to know if the tank can hold the necessary pressures, and also whether it can do it while experiencing rocket engine thrust pushing up on its bottom thrust dome.
The engineers have been speculating about the design of the thrust dome, and it turns out to be a lot more complicated and elaborate than I'd imagined. A real engineering work of art it seems, so as to be able to take both tank pressure loading outward and thrust loading from the engines upward and distribute the loads the right way. Lots of structural elements and sophisticated geometry.
Apparently the way the different parts work together as a system is hard to computer model, hence the need for actual physical tests.
YazataMar 9, 2020 01:41 AM (This post was last modified: Mar 9, 2020 04:37 AM by Yazata.)
Edit: Sun is going down, light is golden, and the tank is venting furiously from both top and bottom. It looks beautiful... beautiful and explosive.
Edit 2: But the plucky little tank is still hanging in. (It's actually 9 meters/~30 feet wide, but little compared to the complete Superheavy/Starship stack.) Venting is less violent. Speculation that they may be cycling it up and down, raising then lowering the pressure repeatedly.
Edit 3: Mary says that the sheriffs are getting more zealous about enforcing the safety perimeter which was pretty loose earlier in the day. So they may have heard something about what SpaceX intends to do later in the evening. (Test-to-failure to see what the tank's upper limits are?) Nomadd reports they have just moved the west roadblock back a few hundred meters.
Edit 4: Venting seems to have ceased. Without pressure venting, internal pressure will rapidly rise. I bet Elon's got his eye on the pressure reading.
Edit 5: 20 minutes. The brave little tank is still in one piece. My guess is that it might not be in 20 mins more.
Edit 6: Modest venting. They appear to still be cycling pressure and release, at higher pressures.
Edit 7: Nomadd thinks that they are done. Not sure where he heard that, but he's right there at the western roadblock. (Mary is busy getting video.) Tank still has LN2 in it but they may be emptying it. Since it never blew, it apparently achieved all the test objectives. Way to go, brave little Bopper 3.0!
Mar 2, 2020 04:11 AM
(This post was last modified: Mar 2, 2020 04:20 AM by Yazata.)
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