zolotiyeruki
-
Posts
822 -
Joined
-
Last visited
Content Type
Profiles
Forums
Developer Articles
KSP2 Release Notes
Bug Reports
Posts posted by zolotiyeruki
-
-
29 minutes ago, Exoscientist said:
The problem is that is not standard usage in the industry. Commonly, you run an engine in static tests at full thrust and full fight duration to give confidence it can perform as expected during actual flights. This is also done as confirmation to potential customers that the rocket will actual deliver as expected.
C'mon, man. The whole "SpaceX isn't doing what's standard" concern has already been VERY thoroughly discussed and invalidated in this thread.
Many of the constraints of 60 years ago that resulted in "standard practices" no longer exist, and it would be foolish for SpaceX to slavishly follow them. We can see the results of such uncritical thinking in the performance of the SLS program: decades late, billions over budget, and still not 100% working, even though they started with their engines and boosters already designed. Why on earth would SpaceX want to follow such a path? "Standard practice" has morphed from a solution into the problem.
I'm reminded of a quote: "Contradictions do not exist. Whenever you think that you are facing a contradiction, check your premises. You will find that one of them is wrong." You have as a premise that "standard practice" is the only (or at the very least overwhelmingly most likely) way to achieve success in the space launch industry. SpaceX is not following standard practice, yet they are wildly successful, while their rivals, who are following standard practice and have decades more experience, are achieving mild success or are floundering. This appears to be a contradiction, and should prompt a reexamination of your premises.
In any case, I have a more sincere question: Starship's SL raptors are there to provide sufficient TWR after MECO stage separation, and for landing. At what point during the second-stage burn would the vacuum raptors provide enough TWR that the SL raptors could be shut down? How much efficiency could be gained by doing so?
-
Six weeks? Dang, they're not sitting around, are they?
-
1 hour ago, sevenperforce said:
See where this is going?
I'll bet we can pretty reliably predict Exoscientist's next dozen concern trolling posts. Can I try a few?
"SpaceX have got it to space, but they haven't demonstrated they can control SS enough to safely deploy satellites!"
"SpaceX is successfully deploying satellites, but they haven't demonstrated SS controllability through reentry!"
"SpaceX solved the controllability issue, but they shouldn't be launching until they can reliably demonstrate (with some sort of ground test) that the heat shield tiles won't fall off!"
"SpaceX have solved the landing burn relight problem, but they haven't demonstrated sufficient accuracy for the chopsticks!"
"SpaceX have captured the booster safely, but they haven't demonstrated reliable Raptor reuse!"
-
3 hours ago, Exoscientist said:
Actually, we do know definitely that the engines did not all relight during the landing burn for the booster. That proves something went wrong at this relight, and the damage could even have occurred during the first relight during boostback except that burn was not long enough to cause loss of vehicle.
If something goes wrong with the engines during flight, and it is a known problem to have occurred before during testing the first thing to suspect is that same issue is occurring again.
There's an assumption here that a longer boostback burn would/could have caused loss of vehicle. What's your rationale there? Keep in mind that these engines are designed to be reused, so the duration of the burn is pretty irrelevant.
The relights for boostback aren't a reasonable analog for relights for a landing burn. They just really aren't comparable.
You've typed a lot of words about how SpaceX need to be testing Raptor more before flying them. How do you propose they test the "light the engines while moving backwards at mach 3 at 35,000 feet and decelerating at 5g's" scenario?
-
I'm a bit skeptical about slosh causing the control issues on Booster during reentry and the landing burn. At that point, there's very little fuel left. Although....I suppose it's possible that even the small amount of sloshing force might be enough to mess up the PID control loops...
-
My impression is that the exhaust gases from SS don't cause SH to *decelerate*, since the core engines stayed lit during separation. Rather, they reduce SH's acceleration.
I also think they've got the flip maneuver itself figured out. But that's a really big tank doing a pretty radical maneuver with little acceleration to settle the fuel except for what the still-burning engines provide, so I imagine there's a lot of slosh going on. Maybe they just need to wait a few moments longer after the flip before relighting the engines for boostback?
-
12 minutes ago, JoeSchmuckatelli said:
So... from this, we can gather they liked the hot-staging.
But I doubt they've had time to address fluid hammer - if that was the thing.
Speculation: they're gonna try to get SS to the Pacific as the primary goal of the flight and just see what happens with a slower flip.
It'll be interesting to see how they've addressed the issue of the boostback burn on SH
-
Rats! I'm here with the family today, and we were hoping to watch it. Oh, well. KSC is a lot of fun anyway
-
11 hours ago, Nuke said:
i wonder if elon would let me borrow a raptor for snow removal.
It'd probably remove a few houses along with the snow!
-
42 minutes ago, Exoscientist said:
On the static stand you can gradually build up to full thrust and full flight duration. If you see out of nominal state for one or more engines, you can shut the test down, examine the engines not operating properly and compare to the ones that are. Then try again gradually building up to full flight conditions. In contrast if one or more engines fail in flight, even if it didn’t explode but had to be shutdown, usually you have to destroy it by FTS for fear it will stray too far out of the safety zone.
I'm glad you addressed the actual question, but it still sounds like you're grasping at (and missing) wildly speculative straws to support your "SpaceX is doing it wrong" thesis.
1) You might have missed it, but SpaceX are waaaay past the point of gradually ramping up Raptors to full thrust and full duration. See IFT-2. Clearly, their approach is working.
2) It sounds like you're suggesting that recovering the pieces of a failed engine would aid in identifying design issues. Do you have any evidence that SpaceX has collected any useful data from their static tests in McGregor?
3) The engines that have been flown to date have already been obsolete when they flew, so a full-duration test fire would be pointless anyway, as would collecting engine debris.
4) Gradually increasing the thrust and duration over multiple burns is silly, because A) the cumulative engine time isn't going to be representative of real-world use, and B) SpaceX is, as @Terwin said, "hardware rich." There's no need to be preserving engines.I'm still not seeing any comparative advantage to a full-duration static ground fire at this stage of the program.
-
14 minutes ago, Exoscientist said:
Consider, that is the standard industry practice. It is not just SpaceX and Nasa doing in that way in the past. Every company in the industry does it that way. Every company could just test single engines on test stands if they wanted to. That would be much cheaper. Instead they follow the accepted practice of doing full flight analog testing prior to test flights.
That the Soviet N-1 experienced not just engine shutdowns but engine explosions on every test flight and the SuperHeavy/Starship also experienced the same thing, including the engine explosions, suggests this is not a better approach to getting reliable engines.
Robert Clark
You still haven't answered the question: What benefit would static fires bring over test flights?
"Because that's how it has always been done" is not an argument. It's a logical fallacy called "Appeal to tradition." Tradition can result from rational thinking and sound logic, but is not proof of such.
"Suggests this is not a better approach" - Hang on. About the only similarities between the programs are that they both involve big rockets and have suffered some failures.* Literally nothing else is common between them. Different countries, gov't vs private, a half-century of technological advancement, different goals, different politics. You're trying to compare apples to oranges here.
-
On 1/5/2024 at 9:06 PM, Exoscientist said:
I have discussed this. It is standard industry procedure to do full thrust, full up(all engines), full flight duration(actual mission length) static fire tests before doing flight tests. Even SpaceX did this when qualifying the Merlins on the Falcon 9 for flight:
A few counterpoints:
1) You have written many, many words, but you still haven't answered the simple question: "what benefit would ground testing give you that modern flight testing doesn't?"
2) Sure, SpaceX and NASA have done integrated tests in the past. That doesn't mean they absolutely must adhere to that same practice for every engine and every vehicle. A wise young guy once told me "tradition has to claim on sanctity." Just because a full-up, full-thrust, full-duration static test was called for under a previous program a decade or a freaking half century ago doesn't mean that the same test is appropriate for this program at this stage with SpaceX's current development philosophy.
-
17 hours ago, sevenperforce said:
It continues to puzzle me why you insist that building a new facility for full-duration static test fires of Superheavy would somehow be categorically and qualitatively better than conducting full-duration test fires simultaneous with the test launches themselves.
This is the question that Exoscientist has been studiously avoiding. If, like SpaceX, you have the ability to flight test the hardware, why would you limit yourself to ground testing? I'm trying to think of what advantages a ground test fire would have over a flight test, and I'm coming up empty-handed.
If this were the Apollo era, and SpaceX were strapping astronauts into Starship for test flights, then a static fire might make sense. But this isn't the Apollo era, and these are unmanned test flights.
If this were the Apollo era, with severely limited telemetry, then a full-duration static test fire might make sense. But this isn't the Apollo era, and SpaceX can get all their telemetry from a test flight.
If they were launching over a populated area, then a full-duration static test fire might make sense. But they're not.
If "blowing up shortly after liftoff" is the concern, then a static test fire is arguably worse, because a flight test reduces the time the rocket is near the pad.
On 1/3/2024 at 2:17 PM, Exoscientist said:I suggest it is more than it should be for an engine at this stage in its development. Someone may want to count the percentage
Suggesting that the failure rate "is more than it should be" implies that either A) you know what Raptor's milestones and schedule should be, or B) Raptor should be following a similar R&D roadmap as other engines have. Since none of us are engineers or program managers at SpaceX, I think we can discard A and focus on B. It's clear that SpaceX *isn't* following a traditional engine development process, and therefore we cannot draw any conclusions about whether Raptor is meeting or falling short of expectations. Raptor's "stages of development" are not analogous to how other engines have developed, so the phrase "than it should be" means you're comparing apples to oranges.
During the space race, the concepts of rapid iteration and "fail fast" weren't even conceivable. Because each iteration took so much time and money to create, everything had to be as perfect and complete as possible before it could even be tested. That in turn made things even more expensive and slow. SpaceX have recognized that the ability to rapidly and cheaply iterate means that failure is an option. Unlike any space program before, it's ok if it doesn't work perfectly the first time, or the second, or the fifth.
There are many, many things to test, of which engine reliability is only one. Doing things the traditional way (waiting until everything is perfect before doing any flight testing) means that you end up with (likely imperfect) systems and concepts waiting around, ready to test, until other systems are ready. SpaceX knew at OFT-1 that Raptor had a ways to go--they were already building newer designs. They performed the launch with the old engines anyway, because it allowed them to test a bunch of other systems (like FTS and the flip-to-separate) without having to wait. Because the cost of the hardware is so much cheaper than it was 50-60 years ago, they can throw all sorts of spaghetti at the wall to find the best option, rather than being constrained to approaches that, while known and reliable, are suboptimal.
-
This is getting off topic, but water heaters have a TPS (temperature and pressure safety) valve specifically to relieve excess pressure if the water gets too hot or the pressure gets too high.
-
At stage separation, is there enough atmosphere left that the booster could flip and wait for drag to settle the propellants?
-
On 10/7/2023 at 9:50 AM, bigyihsuan said:
The forum doesn't support uploading images directly, you need to upload it to a site like Imgur and share the link to the photo.
You're right--it's been a while since I've posted images on the KSP forum, and I had forgotten the need for imgur. I've updated my post with the (potato-quality) photo.
-
I have something to contribute. The clouds last night broke just in time for my teenage daughter to catch this as they passed overhead:
-
18 hours ago, Deddly said:
Bing decided that Starship should be much bigger, and much more Kerbal
Holy cow, RIP GSE on liftoff...
-
11 hours ago, tater said:
Never gets old.
I've heard in the past that the first stage's trajectory initially just misses the ASDS, and that it corrects during the landing burn once everything is nominal, but it seems like in this clip, it was headed toward the ASDS from the get-go. Am I seeing something incorrectly? Maybe the correction happened before that clip started?
-
3 hours ago, RCgothic said:
I won't be posting any more content from Twitter (or X as it's about to become) - I'm now permanently logged out.
Relying on you guys now to get my SpaceX news!
Awww, that's too bad. I've really appreciated your (and everyone else's) efforts to post all the updates in this thread.
-
1 hour ago, tater said:
Functionally it would mean a multi-year pause would be my bet.
And THAT, I suspect, is the real goal, not some illusory risk.
-
What's the benefit of using the smaller nozzle on the second stage? A tiny bit of cost savings?
-
It seems like right after it started the gravity turn, it was already not pointed prograde. My guess is that losing 20% of the engines impacted TWR too much, and we all know how much more drag you get when you try to fly your rocket sideways! Maybe it didn't separate because it hadn't reached the appointed altitude?
-
A blunter nose also shifts the center of pressure slightly aft during the belly flop. May be a bit easier to fabricate as well.
SpaceX Discussion Thread
in Science & Spaceflight
Posted · Edited by zolotiyeruki
Just to be clear, what "mistake" is SpaceX repeating over and over again?
If it's "not doing a full duration burn," then you have to justify why that qualifies as a mistake.
If the qualification is "because raptors are unreliable," then you're wrong, because today's raptors are not the same as the ones that failed. Besides, failures are expected in SpaceX's development process, and therefore not doing the type of test burn you think they should do no longer qualifies as a mistake.
If by "mistake," you mean "not following industry standard procedure (whatever that is)," then we should all be overjoyed that they're making that "mistake," because it sure seems to be working pretty well for them.