Poll

What will be the engine count at liftoff and throughout the achieved portions of flight?

33 engines at liftoff
18 (14.9%)
32 engines at liftoff
23 (19%)
31 engines at liftoff
20 (16.5%)
30 engines at liftoff
4 (3.3%)
6+ booster engine failures in flight
4 (3.3%)
<6 booster engine failures in flight, recoverable failure in 2nd stage
26 (21.5%)
<6 booster engine failures in flight, unrecoverable engine failure in 2nd stage (RVac)
3 (2.5%)
<6 booster engine failures in flight, unrecoverable engine failure in 2nd stage (non-vacuum Raptor)
3 (2.5%)
<6 booster engine failures in flight, LoM before 2nd stage flight for other causes
3 (2.5%)
No in-flight anomalies after liftoff
9 (7.4%)
<6 booster engine failures in flight, no 2nd stage engine failures
8 (6.6%)

Total Members Voted: 69

Voting closed: 10/07/2023 10:12 am


Author Topic: Propulsion performance in Starship's second launch  (Read 4371 times)

Offline eeergo

There's been a few conversations in the Starship section about the probable performance of Starship's Raptors when the time for the prototype's first flight eventually comes. I thought it would be interesting to gauge what people think might happen.

Assumption: limit of 4 non-functioning engines at liftoff remains unchanged from the first test flight, so there will be no liftoff with <30 functioning Raptors at T0.

Assumption: conditions for proper stage separation and subsequent 2nd stage operation cannot be met if more than 6 engines fail in the early stages of first stage flight.
Note: 2 votes can be cast, corresponding to liftoff conditions (options 1-4) and in-flight conditions (options 5-10). Engine failure count in-flight includes those selected as failed at liftoff (0-3).
-DaviD-

Online whitelancer64

Re: Propulsion performance in Starship's second launch
« Reply #1 on: 09/07/2023 02:54 pm »
I voted 31 engines at liftoff, with less than 6 total booster engine failures in flight, with possible SL Raptor failure in Starship. I think this is in line with what we've seen in past Raptor flights. Raptor Vac is a wildcard since we've never seen it perform in flight.

However, that's also about what I expected from the first flight test, which went poorly in that regard. For IFT-2, I fully expect to see stage separation, if this one does not get that far I would find that alarming.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
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Online eriblo

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Re: Propulsion performance in Starship's second launch
« Reply #2 on: 09/10/2023 01:48 am »
So S25 not having engine failures is unthinkable?

Offline SpeakertoAnimals

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Re: Propulsion performance in Starship's second launch
« Reply #3 on: 09/10/2023 02:00 am »
So S25 not having engine failures is unthinkable?
If booster engine shutdowns were related to input pressure fluctuations, I would think that would be less likely on SS, but other than that, it's a crap shoot.

Offline eeergo

Re: Propulsion performance in Starship's second launch
« Reply #4 on: 09/11/2023 01:01 pm »
So S25 not having engine failures is unthinkable?

It's covered in the poll: obviously "no in-flight anomalies" covers also upper stage operation. One could argue there could be <6 booster engine failures (allowing to proceed with the rest of the flight) and no upper stage failures, but I left it out in the interest of brevity.
-DaviD-

Online eriblo

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Re: Propulsion performance in Starship's second launch
« Reply #5 on: 09/12/2023 12:28 pm »
So S25 not having engine failures is unthinkable?

It's covered in the poll: obviously "no in-flight anomalies" covers also upper stage operation. One could argue there could be <6 booster engine failures (allowing to proceed with the rest of the flight) and no upper stage failures, but I left it out in the interest of brevity.
A shame, since I consider it to be just as valid an opinion as those available and had to choose a recoverable failure instead.

If there was just a single number for Raptor reliability then any <6 failures on booster option suggest <1 failure on ship.

Offline mandrewa

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Re: Propulsion performance in Starship's second launch
« Reply #6 on: 09/12/2023 01:30 pm »
So S25 not having engine failures is unthinkable?

It's covered in the poll: obviously "no in-flight anomalies" covers also upper stage operation. One could argue there could be <6 booster engine failures (allowing to proceed with the rest of the flight) and no upper stage failures, but I left it out in the interest of brevity.

I had the same reaction as Eriblo. There are some possibilities that are missing.

You are asking multiple questions in your poll:

a) How many engines will be shut down before lift-off?

b) Will it be more than six engines total or less than six engines total that fail over the course of the flight?

c) Will it be a vacuum version engine of the Raptor or the non-vacuum version that fails on the Starship stage?

d) Will the second stage engine failure be recoverable?

e) Will the test launch fail before the Starship stage separates?

f) Will there be no engine failures at all after the launch?

There seem to be a few possibilities missing here, including the one I would have voted for if it had been there.

Offline eeergo

Re: Propulsion performance in Starship's second launch
« Reply #7 on: 09/12/2023 02:48 pm »
Guys. It was an attempt to cut down on an already long list of poll options by leaving out what I thought would be an unlikely scenario of some failures on the most tested parts (booster and its engines) but none on the most untested parts (vacuum engines and high-altitude flight), consequently garnering few to no votes. However, since there appears to have been some feathers ruffled and interest in this eventuality, I have added the option in the interest of completeness. Apologies for those who have already cast a different vote for lack of this option.

On the other hand, point (e) above is actually wider than you portray: it covers not only events up to stage separation, but also the stage separation event itself. There are two possibilities: either the stage separation event is successful and allows for nominal 2nd stage flight (subsequently successful or not), or it isn't and causes LoM in spite of eventual upper stage engine operation. The edge case of a recoverable but off-nominal stage separation is covered in the "recoverable failure in 2nd stage" option. Not sure what other few possibilities related to the propulsion system's performance you miss.
-DaviD-

Offline mandrewa

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Re: Propulsion performance in Starship's second launch
« Reply #8 on: 09/12/2023 05:07 pm »
I voted optimistically for no engine failure on the second stage.  But really the situation isn't all that dramatically different than the first test flight.  To repeat what I said on the first flight: 

a bad day -- the stack explodes at the launch pad
a good day -- the starship stack makes it past Max-Q before breaking up
a very good day --  Booster 7 successfully separates from Ship 24 before there is some failure
an excellent day -- Ship 24 makes it to orbit or the closest thing to that
an awesome day -- Booster 7 does a simulated landing in the Gulf of Mexico and Ship 24 makes it to orbit
a really awesome day -- after a partial orbit Ship 24 makes it down to the troposphere before breaking up
a really, really awesome day -- after a partial orbit Ship 24 makes a belly flop simulated landing in the ocean as does Booster 7 while booster 7 makes a simulated landing in the ocean

It's four months later. There has been great progress, but this still applies to Booster 9 8 and Ship 25.

Edit: A correction from Dan Clemmensen.
« Last Edit: 09/13/2023 04:22 pm by mandrewa »

Offline Spindog

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Re: Propulsion performance in Starship's second launch
« Reply #9 on: 09/12/2023 05:18 pm »
So, for IFT2, I would expect the stack could easily reach nominal stage separation with 3 engines out if the others were throttled up to 100%. This is due to no payload. We don't know if the remaining raptors on IFT1 were ever at full throttle. I would then expect anything more than 3 out would lead to a sub-nominal stage separation which might still have SS reaching the planned suborbit if it performed perfectly due to no payload.

Online whitelancer64

Re: Propulsion performance in Starship's second launch
« Reply #10 on: 09/12/2023 05:31 pm »
I voted optimistically for no engine failure on the second stage.  But really the situation isn't all that dramatically different than the first test flight.  To repeat what I said on the first flight: 

a bad day -- the stack explodes at the launch pad
a good day -- the starship stack makes it past Max-Q before breaking up
a very good day --  Booster 7 successfully separates from Ship 24 before there is some failure
an excellent day -- Ship 24 makes it to orbit or the closest thing to that
an awesome day -- Booster 7 does a simulated landing in the Gulf of Mexico and Ship 24 makes it to orbit
a really awesome day -- after a partial orbit Ship 24 makes it down to the troposphere before breaking up
a really, really awesome day -- after a partial orbit Ship 24 makes a simulated landing in the ocean as does Booster 7

It's four months later. There has been great progress, but this is still applies to Booster 8 and Ship 25.

That's a really, really low bar.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
"There are lies, damned lies, and launch schedules." - Larry J

Offline ZachS09

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Re: Propulsion performance in Starship's second launch
« Reply #11 on: 09/12/2023 06:11 pm »
So, for IFT2, I would expect the stack could easily reach nominal stage separation with 3 engines out if the others were throttled up to 100%. This is due to no payload. We don't know if the remaining raptors on IFT1 were ever at full throttle. I would then expect anything more than 3 out would lead to a sub-nominal stage separation which might still have SS reaching the planned suborbit if it performed perfectly due to no payload.

I assumed that based on one of Elonís X posts before IFT-1, all Raptor engines would be at 90% throttle for the entire first stage burn regardless of how many engines flamed out.
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Online DanClemmensen

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Re: Propulsion performance in Starship's second launch
« Reply #12 on: 09/12/2023 06:14 pm »
a really, really awesome day -- after a partial orbit Ship 24 makes a simulated landing in the ocean as does Booster 7
That would not be awesome, at least not in a good way. A simulated SS landing is tail first at zero velocity at the ocean's surface. The IFT flight profile that SpaceX filed with the FAA calls for the SS to belly-flop horizontally into the ocean with enough force to break the downcomer, mixing the residual oxygen and methane and going BOOM to sink the wreckage.

Offline mandrewa

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Re: Propulsion performance in Starship's second launch
« Reply #13 on: 09/12/2023 06:30 pm »
I voted optimistically for no engine failure on the second stage.  But really the situation isn't all that dramatically different than the first test flight.  To repeat what I said on the first flight: 

a bad day -- the stack explodes at the launch pad
a good day -- the starship stack makes it past Max-Q before breaking up
a very good day --  Booster 7 successfully separates from Ship 24 before there is some failure
an excellent day -- Ship 24 makes it to orbit or the closest thing to that
an awesome day -- Booster 7 does a simulated landing in the Gulf of Mexico and Ship 24 makes it to orbit
a really awesome day -- after a partial orbit Ship 24 makes it down to the troposphere before breaking up
a really, really awesome day -- after a partial orbit Ship 24 makes a simulated landing in the ocean as does Booster 7

It's four months later. There has been great progress, but this is still applies to Booster 8 and Ship 25.

That's a really, really low bar.

SpaceX is set up to learn from its failures.  In these measures of success I'm assuming that if there is a failure, let's say past Max-Q but before separation, then it will be for some new reason.  I would feel a bit differently about this if the same thing happened on the second test flight as the first.

If I were talking about the SLS it would be a different scale.  The SLS program can't afford failure.  Their stacks take too long to build and they are very expensive.

We don't know what it costs SpaceX to build one of these stacks, but we know they have approximately eight ships that are either complete or almost complete right now.  And they have four boosters that are either complete or almost complete.

One of the bad things that could happen in this test flight is that SpaceX discovers that they have an issue with the booster design and have to scrap the other three boosters that are close to being ready for flight.

But the Starship program is set up to handle failures.  And I'm giving the Starship team the credit to assume that if there is a problem it will be probably be because of something that they didn't know about.  Or in other words something they can learn from.

Offline shm6666

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Re: Propulsion performance in Starship's second launch
« Reply #14 on: 10/02/2023 08:51 am »
Ohh, this pole was both hard and interesting. Letís divide this up in two parts. First the liftoff. After the failure of 7 / 24 they did learn a lot. But I have not found any conclusive statements regarding that Boster 7 did liftoff with three engines out. What caused that? Also, in regard to the two static fires that Boster 9 have done. We know that the first one did end early. Presumably there were to many engines that did shut down. The second one did go full duration. But two engines did shut down. I have not seen any reason for their shutdown. So, the first part is pure guesswork. I will go for that they will liftoff with two engines down. Basically, because we donít know why they did shutdown in this stage of the flight.

The next part is the flight to staging. Here from Boster 7 we do know a little more about the engines that did fail. They did have a fire in the engine room. Many of the 57 or so corrective measures regards is regards to plumbing and fire suppression. So here I do think they have a better understanding of the environment that the engines are operating in. However, I donít think they have full understanding of how the plumbing is going to hold up during assent. The shaking and the acoustic environment must be hard to model. There for I think it is good with all the cameras they have been added. But I do think they get to staging. But I do think they might lose some more engines. So ď<6 booster engine failures in flight, recoverable failure in 2nd stageĒ it is.

Offline eeergo

Re: Propulsion performance in Starship's second launch
« Reply #15 on: 11/15/2023 06:20 am »
Bumping this since it seems we're a few days out from the launch attempt. I will close it during the first countdown.
-DaviD-

Offline eeergo

Re: Propulsion performance in Starship's second launch
« Reply #16 on: 11/18/2023 12:35 pm »
Most impressive apparent performance of the Raptors. Unless there was something minor going on, I'd say the last two options are the winners (while we wait on why the upper stage failed late in the flight) - which TBH were not my voting choices at all.
« Last Edit: 11/18/2023 04:52 pm by eeergo »
-DaviD-

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