totm nov 2023 SpaceX Discussion Thread

[Nuke]

i propose we split the space-x thread into two. one for routine launches, and another for blowing stuff up. 

[Exoscientist]

On 1/1/2024 at 11:21 AM, tater said:

We'll have another one to discuss soon enough I hope.

 Yes. As long as Raptors fail in flight tests, there will be questions about its reliability.

  Bob Clark

On 1/2/2024 at 3:12 AM, Hotel26 said:

Of course, what is crossing my mind right now, regarding this ongoing discussion, is that it may be time for full disclosure by all parties engaged, about stock holdings IRL.

Just, you know...  to know.  Yeah?

@Exoscientist?

 

 

 I don’t hold in stock with any companies, including any aerospace companies. I don’t like the Blue Origin lunar lander plan or the  third one either, whose name I can’t now remember.

 They all need multiple flights for a lander mission. My opinion a moon rocket should be A moon rocket(singular). We did this 50 years ago. There is no reason why we can’t do that now.

   Bob Clark

[NFUN]

can somebody please hit the jukebox it's acting up

[Exoscientist]

On 1/2/2024 at 2:43 AM, SunlitZelkova said:

But Starship isn't "certified for flight". It is in the testing phase. There is no issue with explosions right now because these are development flights.

What do you propose for correcting Starship? Ground tests? Cancellation?

 I have mentioned this before. I major irritation of mine is that SpaceX dismisses the lessons of Apollo. It dismissed the importance of a flame trench and dismissed the importance of having powered stage separation. But the most egregious of these is dismissing the importance of having full thrust, full up(all engines), full mission duration(actual minutes long flight length) static burns:

 Robert Clark

Edited January 3 by Exoscientist
Edit: corrected the video linked.

[tater]

34 minutes ago, Exoscientist said:

 They all need multiple flights for a lander mission. My opinion a moon rocket should be A moon rocket(singular). We did this 50 years ago. There is no reason why we can’t do that now.

Because this is not Apollo, and SLS can't do Apollo, and no amount of updates to it can do Apollo. It's an overpriced rocket to nowhere.

Single stack moon rockets for a small number of people to sortie to the surface for a day or two is not needed. We need a reusable transport infrastructure. You'd do better to pitch a return to the real STS concept:

This of course means cancelling everything in Artemis, and starting from a clean sheet.

27 minutes ago, Exoscientist said:

 I have mentioned this before. I major irritation of mine is that SpaceX dismisses the lessons of Apollo. It dismissed the importance of a flame trench and dismissed the importance of having powered stage separation. But the most egregious of these is dismissing the importance of having full thrust, full up(all engines), full mission duration(actual minutes long flight length) static burns:

They are not doing Apollo. They are building a reusable Mars ship.

They are doing full duration burns, it's called a flight. They have so much hardware the "next up" vehicles are all already deprecated, they need to be destroyed one way or another, so destroy them by testing them.

1 hour ago, Nuke said:

i propose we split the space-x thread into two. one for routine launches, and another for blowing stuff up. 

Or an old man shouting into the void about testing stuff on the ground instead of just flying thread.

(said as a probably similarly old man )

[Elthy]

1 hour ago, Nuke said:

i propose we split the space-x thread into two. one for routine launches, and another for blowing stuff up. 

I propose we split it up in another way: One for normal discussion about SpaceX, one where someone brings up the same stuff every page. The second one is propably better suited for "Forum Games"...

[magnemoe]

40 minutes ago, Exoscientist said:

 I have mentioned this before. I major irritation of mine is that SpaceX dismisses the lessons of Apollo. It dismissed the importance of a flame trench and dismissed the importance of having powered stage separation. But the most egregious of these is dismissing the importance of having full thrust, full up(all engines), full mission duration(actual minutes long flight length) static burns:

 

 Robert Clark

Starship stand works as an flame trench as in putting distance between the rocket and the ground. This works for superheavy and Starship as its simply lifted on to the stand. 
Saturn 5 was transported with the service tower and the launch platform with the crawler so they needed to build an artificial mound with an flame trench so the crawler could get onto. 
The problem with first test was no water spray on the bottom, this has been fixed. 

As for full duration static fire, as long as first stage engines fire up and burn stable and they are sure the thing clear the pad. An stand for an full duration SH burn will be significantly larger and more expensive than the current launch pad. And its not like SpaceX is not willing to expend an high number of SH during the testing caching various issues like likely the negative G during hot staging who an static fire would not catch nor issues returning. 

As for Saturn 5 https://en.wikipedia.org/wiki/Saturn_V
First 2 was used for integration and testing 3rd for static fire, then two test launches one an total success before manned flights as in Apollo 8. 
I rather launch 4-8 tests then start using if for cargo for +20 missions before even thinking of landing it on the moon, note that cargo missions does not need second stage to be recovered to work. None has reused an second stage outside the space shuttle who was not very economical. 
Only one company reuses first stages and KSP 1 was mature then they started doing it. 

 

[Exoscientist]

 

 

 This video attempts to argue the Raptor is reliable by looking at static fire tests.

A key question in the video is how many of the test fires fall short of the expected length, suggesting a test failure or for whatever reason the engine had to be shutdown. The video host suggests it is small number. 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
themselves where it is displayed graphically at about the 5:55 point in the video.

Also I don’t like the lengths of the engine tests. The video host says most are about 2 minutes, 120 seconds, suggesting that is where SpaceX thinks that is what the flight burning time should be. But judging from the test flights for the booster that should be in the 2 minutes 40+ seconds range, 160+ seconds, which means even for static fires of individual engines SpaceX is not doing realistic static fires:

Planned mission timeline[34]
….
00:00:55 Max q (moment of peak mechanical stress on the rocket — Later and lower Max q than planned[42]
00:02:49 Main engine cutoff (MECO) — Not attempted[43]
00:02:52 Stage separation
…
https://en.m.wikipedia.org/wiki/SpaceX_Starship_integrated_flight_test_1#Flight_profile.

 Additionally, SpaceX needs to be open about how many of these static fires are done at full power.

  Robert Clark

[Ultimate Steve]

As others have noted.

 

Flame trench: purpose is to put distance between the rocket and the nearest surface below it, and redirect exhaust outwards to prevent damage to both the rocket and the launch pad. An open on all sides flat deflector arguably performs this task better in most respects than a sloped open on one side deflector, all else held equal. Only real advantage a sloped deflector has is probably better Shockwave reflection characteristics.

Powered stage separation: jury is out on this one but SpaceX is trying as hard as they can to find a method that does not require maintainence, refurbishment, or replacing components between flights. While a traditional ullage system would work, it violates that above constraint. A pusher like falcon 9 might also work but it would be stupidly heavy. They will do this if they need to but they are going to try everything else first.

Full duration static fire is an economic problem. Is the cost of obtaining the land for, obtaining the permits for, constructing, building the transportation system for, and risking a catastrophic explosion of a full duration static fire stand that you are ideally only going to use one time if all goes well, or maybe once per booster, less than the cost of however many full stacks they blow up in flight due to issues that would have been uncovered during a full duration static fire plus the associated decrease in confidence due to in-flight failures?

So far that is maybe one full stack on the other side of the equation, so far at least. IFT 1 could have possibly been prevented or mitigated by a full duration static fire, at the cost of the booster itself which would have likely been toast either way if they didn't shut it down early. So the only thing you are saving is S24 (which would probably be scrapped anyway working towards the next flight) and if you are extremely optimistic, maybe B7.

Still, let's steel man this. Let's say 4/20, IFT 1 and IFT 2 were all destroyed explicitly by failures that would have been caught during a full duration static fire.

Now we don't know the cost of what a test stand would be. I am also having trouble finding the original construction cost for the B2 test stand. However, I did find an OIG document saying that the renovation of B2 to get it ready for the SLS core stage, which mind you, doesn't even have that much thrust and isn't even a flight condition static fire (boosters are by far the majority of the thrust and vibration), on a site which the land was already owned and developed, was to cost 250 to 350  million dollars.

Again, that is for modifying an already owned test stand for a far less powerful rocket than Starship.

Granted, SpaceX has a knack for doing things cheaply. Maybe they could manage to do a starship scale test stand from scratch under their already strained environmental permits for 250 million dollars and without causing schedule slip.

The question is now, are three starship stacks worth less than 250 million dollars?

No, of course not, that would be ridiculous for these early flight articles to cost under 100 million each, although it is on the edge of possibility. Maybe these things cost 200M a piece right now, maybe 300, maybe 100, we have no reliable estimates. They were literally building their GSE the same way a while back, so maybe the raw tanks are ridiculously cheap by themselves, maybe the whole thing is 50M.

But by most reasonable cost estimates for a full stack, SpaceX should probably have built a test stand.

But do you see just how many assumptions we had to give there? Assuming that all three stacks could have succeeded if one had test fired? Of which only 1 was partially explicitly destroyed by something first stage engine boost phase related? Discounting the massive environmental statement related stuff they would have to do in order for this to get built? Assuming the costs for renovation of a less powerful stand are comparable to the new construction of a more powerful stand? This is an analysis so thoroughly biased towards a test stand and even then the test stand just barely comes out on top, well within the margin of hindsight.

 

 

[Ultimate Steve]

Just a reminder of the long struggle SpaceX had to get the EIS through and the subsequent legal battles over their sound suppression system, which was dumping a small amount of freshwater, comparable to rainfall, into the ocean. The assumption that the full duration stand gets through with no resistance is doing a lot of heavy lifting.

[Shpaget]

19 minutes ago, Exoscientist said:

SpaceX needs to be open about how many of these static fires are done at full power.

No, they don't. Seriously. They don't owe us any info whatsoever. If there are third parties out there that do have a legitimate claim to this data, we don't see them complaining.

[tater]

1 hour ago, Ultimate Steve said:

This is an analysis so thoroughly biased towards a test stand and even then the test stand just barely comes out on top, well within the margin of hindsight.

The booster stand would need to cost less than ONE booster. IFT-1 failed in ways a static fire might have detected, IFT-2 was flawless until the flip, which no stand could test.

[Vanamonde]

If someone is really bugging you, just set that person to ignore status. Please don't make the discussions personal. 

[CatastrophicFailure]

Apollo used a significant percent of GDP at the time to put two dudes in a bedroom closet on the moon for a couple of days. I’d rather see all parties involved did not simply do that again, and actually expanded our scope and capabilities, for a fraction of the relative cost. 

Let’s not merely repeat the past, let’s actually build the future. I’m ok with a heavily-regulated player with massive oversight blowing up a few pre-prototype concept demonstration rockets to accomplish that. 

Edited January 4 by CatastrophicFailure

[Nuke]

if apollo was learning how to crawl, then the current program will be learning how to walk. it will be some time before we can run.  starship has legs if they can get it to work as advertised.

Edited January 4 by Nuke

[sevenperforce]

On 1/3/2024 at 12:06 PM, Exoscientist said:

As long as Raptors fail in flight tests, there will be questions about its reliability.

Why use "flight tests" here? Why not just say "as long as Raptors fail, there will be questions about its reliability" period? How is a flight test magically different from a static test?

On 1/3/2024 at 12:06 PM, Exoscientist said:

My opinion a moon rocket should be A moon rocket(singular). We did this 50 years ago. There is no reason why we can’t do that now.

No one wants a sortie lander. To achieve the goals of Artemis, we need substantial downmass -- something closer to the 46 tonne (launch) mass of the Altair lander. Add a reasonably-sized crew capsule, and doing this in a single launch means a vehicle capable of throwing upwards of 70 tonnes to TLI.

We also know you dislike solids generally, so let's look at an all-liquid architecture. Three stages are going to be required, obviously. Rule of thumb splits delta-v among stages, and you need 9.4 km/s to reach orbit and 3.2 km/s to reach TLI, so that's a total of 12.6 km/s, or 4.2 km/s on each stage. Notionally, let's imagine a kerolox first stage, a methalox second stage, and a hydrolox third stage.

The EUS packs 126 tonnes of hydrolox, so let's start there. With a 75-tonne payload, it develops just 3.5 km/s. If we swap out its four RL10C-3s for a pair of J-2Xs, it will get even less. But the EUS is the largest hydrolox upper stage in development, so let's stick with that. Now our first two stages need to somehow deliver 4.5 km/s each.

Now for our notional methalox second stage. We know you dislike Raptor, so let's imagine a BE-4U with improbably comparable specific impulse to RVac. Let's imagine a 45-tonne stripped-down Starship as our main tank, pushed by a quincux of BE-4Us. The BE-4 produces 2.4 MN at an estimated sea level specific impulse of 315 seconds, so if we bump that up to 380 seconds then five of them will produce a whopping 14.5 MN together. With the required nozzle extension they're going to weigh in around 4 tonnes each. The third stage and payload together come in at 232 tonnes so stage dry mass is 297 tonnes, which gets us a delightful 5.5 km/s from the 1000 tonnes of methalox onboard (reduced from 1200 tonnes because BE-4 can't take densified methalox). We've got a T/W ratio of 1.1:1, which is low but acceptable. ETwo stages deep, and we're ahead of schedule! Our first stage will only need to deliver 3.6 km/s (or roughly 4.1 km/s if you want to treat sea level specific impulse as pressure drag and just use vacuum specific impulse).

But here we have a problem. The most powerful kerolox engine in the world, the RD-171, gets 337.2 seconds of vacuum specific impulse. You need a wet:dry mass ratio of 3.5:1 to achieve 4.1 km/s, putting us at a liftoff mass of at least 4,500 tonnes, almost double the launch mass of the Saturn V. You'd need at least nine RD-171s or at least 17 RD-180s to get off the ground. Or you can use a cluster of 77 Merlin 1Ds.

Good luck with that.

On 1/3/2024 at 12:19 PM, Exoscientist said:

I major irritation of mine is that SpaceX dismisses the lessons of Apollo. It dismissed the importance of a flame trench and dismissed the importance of having powered stage separation.

How were these "lessons" from Apollo?

The Saturn V used a flame trench and powered stage separation, but these weren't lessons. NASA didn't attempt to go without powered stage separation and then fail and correct it; they just chose to use solid separation motors from the start. You seem to be confusing "lessons learned" (e.g., "we tried it one way and realized it didn't work and so we found a better way") with standard operating procedure ("this is the way we decided to do it and it worked").

Besides, Superheavy has always had a flame "trench". It's actually six very big trenches that go in every direction.

On 1/3/2024 at 12:19 PM, Exoscientist said:

But the most egregious of these is dismissing the importance of having full thrust, full up(all engines), full mission duration(actual minutes long flight length) static burns:

[snip]

The "T-Bird" S-IC-T was a Saturn V first stage designed specifically for static fire tests; it never flew and never could have flown. It completed its test firings prior to the construction of the actual flight articles.

AFAIK, neither the three S-IC stages launched in the Apollo 4-6 flight tests nor subsequent S-IC stages used for actual crewed missions ever received full-thrust, full-up, full-mission-duration static burns.

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.

On 1/3/2024 at 3:17 PM, Exoscientist said:

SpaceX needs to be open about how many of these static fires are done at full power.

We have no evidence that SpaceX fails to share thrust level and telemetry data with its government partners.

12 hours ago, CatastrophicFailure said:

Apollo used a significant percent of GDP at the time to put two dudes in a bedroom closet on the moon for a couple of days. I’d rather see all parties involved did not simply do that again, and actually expanded our scope and capabilities, for a fraction of the relative cost. 

Let’s not merely repeat the past, let’s actually build the future. I’m ok with a heavily-regulated player with massive oversight blowing up a few pre-prototype concept demonstration rockets to accomplish that. 

Agreed. As outlined above, building an actual single-launch architecture for meaningful moon landings would require a rocket almost double the liftoff mass of the Saturn V (and likely more).

[tater]

 

[RCgothic]

https://xkcd.com/2876/

The Range Mischief Officer has modified the trajectory to add a single random spin somewhere in the flight, but won't tell us where.

[Hotel26]

From the Structure of Scientific Revolutions, by Thomas S. Kuhn:

Quote

The paradigm shift does not merely involve the revision or transformation of an individual theory, it changes the way terminology is defined, how the scientists in that field view their subject, and, perhaps most significantly, what questions are regarded as valid, and what rules are used to determine the truth of a particular theory. The new theories were not, as the scientists had previously thought, just extensions of old theories, but were instead completely new world views. Such incommensurability exists not just before and after a paradigm shift, but in the periods in between conflicting paradigms. It is simply not possible, according to Kuhn, to construct an impartial language that can be used to perform a neutral comparison between conflicting paradigms, because the very terms used are integral to the respective paradigms, and therefore have different connotations in each paradigm. The advocates of mutually exclusive paradigms are in a difficult position: "Though each may hope to convert the other to his way of seeing science and its problems, neither may hope to prove his case. The competition between paradigms is not the sort of battle that can be resolved by proofs." Scientists subscribing to different paradigms end up talking past one another.

...

Edited January 7 by Hotel26

[tater]

January 7 Falcon 9 • Starlink 6-35

Launch time: Window opens at 4 p.m. EST (2100 UTC)
Launch site: SLC-40, Cape Canaveral Space Force Station, Florida

A SpaceX Falcon 9 rocket will launch another batch of second-generation Starlink V2 Mini internet satellites. The Falcon 9’s first stage booster will land on the drone ship ‘A Shortfall of Gravitas’ in the Atlantic Ocean.

 

January 7/8 Falcon 9 • Starlink 7-10

Launch time: Approx. 9 p.m. to 1:27 a.m. PST (12:00-4:27 a.m. EST, 0500-0927 UTC)
Launch site: SLC-4E, Vandenberg Space Force Base, California

A SpaceX Falcon 9 rocket will another batch of Starlink internet satellites from Space Launch Complex 4 East (SLC-4E). The Falcon 9’s first stage booster will land on the drone ship ‘Of Course I Still Love You’ in the Pacific Ocean.

[zolotiyeruki]

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.

[sevenperforce]

1 minute ago, zolotiyeruki said:

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. 

I'll even go one step further and point out that the development of the Saturn V actually deviated significantly from prior US launch vehicle development by doing an all-up test on the first actual launch. Prior to the Apollo program, virtually all rockets were tested one stage at a time. The first stage would be ground-tested, then test-launched with a dummy upper stage and payload. The second stage would then be ground-tested, and only after all of this would it be stacked onto the first stage with a dummy payload for an integrated flight test. For three-stage rockets, this would proceed even slower (first stage with two dummy stages, then first two stages with one dummy stage, then an all-up test with a dummy payload, then a true integrated test launch).

The Apollo program deviated dramatically from this approach by doing an integrated flight test of all three stages AND a functional CSM on Apollo 4. They focused on validating all of the systems independently (and in parallel) so that they would be able to put everything together on the first go. And of course the Apollo program was wildly successful.

So if there is a "lesson learned" from Apollo, perhaps it is the lesson that deviating from past practices can be a really good idea if you have a consistent vision and the resources to make it work.

[mikegarrison]

1 minute ago, sevenperforce said:

I'll even go one step further and point out that the development of the Saturn V actually deviated significantly from prior US launch vehicle development by doing an all-up test on the first actual launch. Prior to the Apollo program, virtually all rockets were tested one stage at a time. The first stage would be ground-tested, then test-launched with a dummy upper stage and payload. The second stage would then be ground-tested, and only after all of this would it be stacked onto the first stage with a dummy payload for an integrated flight test. For three-stage rockets, this would proceed even slower (first stage with two dummy stages, then first two stages with one dummy stage, then an all-up test with a dummy payload, then a true integrated test launch).

The Apollo program deviated dramatically from this approach by doing an integrated flight test of all three stages AND a functional CSM on Apollo 4. They focused on validating all of the systems independently (and in parallel) so that they would be able to put everything together on the first go. And of course the Apollo program was wildly successful.

So if there is a "lesson learned" from Apollo, perhaps it is the lesson that deviating from past practices can be a really good idea if you have a consistent vision and the resources to make it work.

But they had already flown the Saturn I, which used the third stage of the Saturn V as its second stage.

[sevenperforce]

8 minutes ago, mikegarrison said:

But they had already flown the Saturn I, which used the third stage of the Saturn V as its second stage.

Sort of, but not entirely. The Saturn I used an RL10-based second stage, while the Saturn IB used the same basic upper stage with a J-2 engine, which became the S-IVB-200. It flew a few times before Apollo 4. However, the third stage that flew on the Saturn V in the Apollo 4 test was a different configuration, the S-IVB-500, with a flared interstage, a different helium pressurization system, a new auxiliary propulsion system, and a different separation system. 

[Exoscientist]

On 1/3/2024 at 3:17 PM, Exoscientist said:

 

 

 This video attempts to argue the Raptor is reliable by looking at static fire tests.

A key question in the video is how many of the test fires fall short of the expected length, suggesting a test failure or for whatever reason the engine had to be shutdown. The video host suggests it is small number. 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
themselves where it is displayed graphically at about the 5:55 point in the video.

Also I don’t like the lengths of the engine tests. The video host says most are about 2 minutes, 120 seconds, suggesting that is where SpaceX thinks that is what the flight burning time should be. But judging from the test flights for the booster that should be in the 2 minutes 40+ seconds range, 160+ seconds, which means even for static fires of individual engines SpaceX is not doing realistic static fires:

Planned mission timeline[34]
….
00:00:55 Max q (moment of peak mechanical stress on the rocket — Later and lower Max q than planned[42]
00:02:49 Main engine cutoff (MECO) — Not attempted[43]
00:02:52 Stage separation
…
https://en.m.wikipedia.org/wiki/SpaceX_Starship_integrated_flight_test_1#Flight_profile.

 Additionally, SpaceX needs to be open about how many of these static fires are done at full power.

 

The video argues the Raptor has high reliability based on the tests on static stands at McGregor.

The author says the reliability is high because “most” tests were able to reach a planned length of 115 to 120 seconds. The problem is for a rocket engine to be used to power a crewed vehicle you want very high reliability. For instance the SLS has estimated reliability for its components of 99.9% and for the Merlins based on the number of successful flights we can estimate it as better than 99.9%. That is, less than 1 in a thousand would be expected to fail.

But going by counting the number of tests for the Raptor that fail to reach that 115 to 120 second mark, it may be 1 in 5 to 1 in 6 fail to reach it. Note as the author of the video observes some tests are planned to be shorter. For some for instance they were intended to be about 47 seconds long. But there are a block of tests I marked off in the attached image that appear to be aiming for that 115 to 120 second mark, and several of them don’t make it. I estimate 5 or 6 out of the 30 I marked off failed to reach that planned burn length.

Another questionable issue of these static tests is the planned lengths. The largest portion them were of a planned length of about 120 seconds, 2 minutes. But judging by the two test flights the actual burn time for the booster is in the range of 2 minutes 39 seconds to 2 minutes 49 seconds range. Only very few of the test stand burns went this long or longer.

The video gives a link where you can watch the test stand burns NSF.live/McGregor. Another useful aspect here is you may be able to judge the power level of the burns. There is a graphic that shows the sound level of the burns. From that you may be able to judge whether or not the engines were firing at or close to full thrust.

In the image below, the burns in white are those shorter burns of about 47 second lengths the author of the video made note of. They may be tests of the boost back or landing burns. The ones I’m commenting on are under the yellow bar, which I estimate to be at about the120 burn time. There 5 or 6 out of 30 don’t reach the planned burned time.

 Robert Clark