totm nov 2023 SpaceX Discussion Thread

[sevenperforce]

15 hours ago, Exoscientist said:

He has an obvious error at item 4 -- "orbital" velocity. There is no indication whatsoever that Starship failed to reach its intended velocity or trajectory.

 That is a debatable point because Elon did say there was an 80% chance of the Starship reaching orbit on this flight:

There was a 0% chance of Starship reaching true orbit because that was not the design trajectory. If Starship had reached true orbit, then something had to go very, very wrong. So obviously Elon was not talking about true orbit; he was saying that there was an 80% chance of Starship making it successfully through staging and the full-duration second-stage burn to its intended SECO.

Otherwise you're saying that when Elon says "80% chance" he is actually saying that the mission only has a 20% chance of success.

15 hours ago, Exoscientist said:

But there still remains the question of why didn’t IFT-3 reach orbital velocity? In the case of IFT-2 they vented LOX reducing the velocity it was capable of, and Elon even said if they had a payload and had not vented LOX they would have reached orbit.

 But they didn’t vent LOX on IFT-3 and SpaceX said they had a full propellant load and from the view of the propellant gauges the propellant was virtually expended in both stages. So why were they not able to reach orbit even though carrying 0 payload?

I've already painstakingly explained this to you. The very sentence where SpaceX says they had a "full propellant load" they also state the total amount of propellant and it is significantly lower than the actual full capability of Starship, meaning that it was a "full propellant load for this mission" not a "full propellant load for the maximum design capacity".

Or would you argue that the BE-4 engines on the Vulcan Cert-1 mission must have been operating at above their stated thrust levels because Vulcan reached "full propellant load" and an actual full propellant load is too heavy for two BE-4s to lift? (Obviously not; Bruno specifically said that they underfilled the tanks, just like SpaceX specifically quoted a total propellant amount lower than the maximum design capacity).

And even if they HAD a "full propellant load" (which they did not), that doesn't mean they would have accidentally entered a true orbit. Burning for a high apogee achieves orbital velocity without fully circularizing. You've played KSP, right? Haven't you ever accidentally burned too early or burned at the wrong angle and ended up depleting your props with a high apogee before you finish circularizing? Plus, burning at lower throttle can achieve the same thing. They were targeting a specific re-entry zone for a reason.

8 hours ago, Exoscientist said:

I’ve suggested that SpaceX intentionally ran the Raptors on IFT-2 and IFT-3 at reduced power, i.e., thrust, to improve reliability. 

Even if there was evidence that the Raptors were run at reduced power during IFT-2 or IFT-3, this wouldn't necessarily imply a reliability issue; it can also be done to achieve a full-duration burn time with a decreased propellant load in order to avoid entering a true orbit.

You know, the thing that they explicitly said they were doing.

[Entropian]

Talk about beating a dead horse - at this point y'all are knocking on a skeleton

Last I checked, SpaceX was doing perfectly fine without needing to check arbitrary boxes set by not-SpaceX on SpaceX's own missions.

[Codraroll]

9 hours ago, Exoscientist said:

I’ve suggested that SpaceX intentionally ran the Raptors on IFT-2 and IFT-3 at reduced power, i.e., thrust, to improve reliability. 

Ah, yes, I was wondering whether this pathological fixation on concluding against all evidence that Starship doesn't have any lift capacity was separate from or a part of the already-demonstrated pathological fixation on concluding against all evidence that the Raptor engine is unreliable. Thanks for providing the missing link.

Edited April 1 by Codraroll

[tater]

 

[magnemoe]

10 hours ago, Exoscientist said:

 Thanks for that. Do you have a link where Beck said this? I’ve suggested that SpaceX intentionally ran the Raptors on IFT-2 and IFT-3 at reduced power, i.e., thrust, to improve reliability. 

This has broader implications than just the Raptor question:

Can running a rocket engine at reduced thrust extend lifetimes?

Can someone in rocket propulsion answer if this fact about jet engines also holds for rocket engines?

If so, increasing a turbopump rocket engine power just 10% to 15% cuts engine life in half. And conversely, decreasing it by 10% to 15% doubles engine life. And would this still work if we repeated the concept multiple times? If we reduced the thrust by .9^5 = .60, i.e., to 60%, which most turbopump engines can manage, then we could increase the lifetime by a factor of 2^5 = 32 times? Then a Merlin engine with a lifetime of, say, 30 reuses by running it only 60% power could have its lifetime extended to 1,000 reuses? 

 Is this a known fact about turbopump rocket engines their lifetimes increase radically by a relatively small decrease in their thrust levels?

  Bob Clark

Jet engines only run on full power during takeoff during normal runs. I also assume this is baked into maintenance requirements where an takeoff equals say 1 hour normal flying so an plane used only on an 1 hour flight will need maintenance more often than one who fly long distance. On the other hand 1-3 hour flights is usually so light they can just land again if they have an issue but long haul flight need to burn or dump fuel before landing. Was on one 2-3 hour flight who could not retract the nose wheel so they turned around and landed, got it fixed and took off again.  Obvious passenger questing is if the nose wheel will come out, its simpler to extend it than retract it. 
On a flight from US to Europe, plane had to turn around as they only had one working navigation system but needed two to cross the Atlantic.  They had to burn off fuel to land, pilot told that this was why the engines sounded different.  

[magnemoe]

1 hour ago, Codraroll said:

Ah, yes, I was wondering whether this pathological fixation on concluding against all evidence that Starship doesn't have any lift capacity was separate from or a part of the already-demonstrated pathological fixation on concluding against all evidence that the Raptor engine is unreliable. Thanks for providing the missing link.

This, launch was not strictly orbital and it was an good thing because it lost control. Unknown why the missile range next to Hawaii was not the splashdown site. I guess it was stuff in the Mexican gulf. 
But if they can can push the engine farther, you also have the old practice of using an oversize powder charge  in a gun to test fire it. 
Not done in a long time, gun barrels don't explode and if they do they are outside unlike on age off sail ships but made sense back then as making iron was still a bit hit and miss. 
But they might do something like this to stress test the engines, its not like you will reuse them anyway. 

[Exoscientist]

11 hours ago, sevenperforce said:

There was a 0% chance of Starship reaching true orbit because that was not the design trajectory. If Starship had reached true orbit, then something had to go very, very wrong. So obviously Elon was not talking about true orbit; he was saying that there was an 80% chance of Starship making it successfully through staging and the full-duration second-stage burn to its intended SECO.

Otherwise you're saying that when Elon says "80% chance" he is actually saying that the mission only has a 20% chance of success.

I've already painstakingly explained this to you. The very sentence where SpaceX says they had a "full propellant load" they also state the total amount of propellant and it is significantly lower than the actual full capability of Starship, meaning that it was a "full propellant load for this mission" not a "full propellant load for the maximum design capacity".

…

 

 Oddly, not just suggesting it could reach orbit before the mission, Elon said it did reach orbital velocity after the flight:

 What max propellant load are you saying SH/SS could carry?

  Bob Clark

[tater]

 

[tater]

 

[tater]

 

[Superluminal Gremlin]

I would like to interject with the fuel bars suggesting total fuel capacity for the mission (not the total design capabilities).

 

[Exoscientist]

3 hours ago, Superluminal Gremlin said:

I would like to interject with the fuel bars suggesting total fuel capacity for the mission (not the total design capabilities).

 

 Multiple sources give a 3,400 ton propellant load for the booster and 1,200 tons for the ship, for 4,600 ton max propellant load. The 4,500 ton total given in the SpaceX tweet is only 2% off this value. That could be just round off error or it could be you don’t want literally the tanks to be filled to the very top to allow for boiloff of the cryogenic propellant.

  Bob Clark

[NFUN]

Multiple sources give 235km for the apogee and -50km for the perigee, so 7677m/s at apogee for the ship. The 7763m/s total velocity given for a circular orbit is is only 1% off this value. That could be just round off error or it could be you don't literally want a test vehicle to achieve orbit to allow for a planned deorbit at a specific region

[tater]

 

[darthgently]

Static fire?  Booster? SS? 

 

 

[Meecrob]

23 hours ago, magnemoe said:

Jet engines only run on full power during takeoff during normal runs.

In fact, unless required for performance reasons, Transport Category aircraft will always use a de-rated takeoff.

The thrust provided by the engines operating normally is far in excess of what is required for a regular takeoff. The engine thrust requirements are set by engine-out takeoff calculations. The aircraft is certified to meet all regulatory requirements with one entire engine shut down/malfunctioning.

I hate to say it, but @Exoscientist nailed this one. Obviously a primary concern for Superheavy is engine-out scenarios, and to use engines that have the ability to go to (for example) 110-120% thrust if required is just good engineering.

I think we might be getting complacent around here. Its easy to read "Exoscientist" and think "here we go again..."

[magnemoe]

16 minutes ago, Meecrob said:

In fact, unless required for performance reasons, Transport Category aircraft will always use a de-rated takeoff.

The thrust provided by the engines operating normally is far in excess of what is required for a regular takeoff. The engine thrust requirements are set by engine-out takeoff calculations. The aircraft is certified to meet all regulatory requirements with one entire engine shut down/malfunctioning.

I hate to say it, but @Exoscientist nailed this one. Obviously a primary concern for Superheavy is engine-out scenarios, and to use engines that have the ability to go to (for example) 110-120% thrust if required is just good engineering.

I think we might be getting complacent around here. Its easy to read "Exoscientist" and think "here we go again..."

You are obvious correct, you should calculate for engine out and at full trust it would require much longer runways, two engine planes are hit harder than 4 engines. On an B-52 with 8 engines its just degraded performance. 

Now Starship makes B-52 redundancy look weak. Even if booster is write off but landing an Starship back at base or in Europe or Africa is significant not only for manned missions but also for expensive payloads. 
Pretty sure falcon 9 is set up as if an first stage engine fails it will it go disposable. 
Burn all fuel and get to and get into an orbit and wait for an tanker is also an option who was KSP only until this. 

Google released an paper on hard drive life expectancy, drive tend to fail the first 2 months or after 7 years. Looks like this is also true for cars. 

[PakledHostage]

The plane spotter YouTube channel LA Flights was able to track yesterday's Falcon 9 launch out of Vandenberg for about 4.5 minutes, from when it crested the terrain until well after staging.  See  timestamp 10:11:55 seconds in the video for the launch as it appeared from LAX:

https://www.youtube.com/live/gvEbKaEz2ss?

Edit: it won't let me embed the video for some reason. It gives me an error about my message containing an emoji, so the link above will have to suffice. 

Edited April 2 by PakledHostage
Attempted to fix video link

[RCgothic]

There's not a shred of evidence IFT-3 was anything other than a completely nominal flight until SECO or that raptors operated anything other than exactly as intended to achieve the final trajectory.

[darthgently]

3 hours ago, PakledHostage said:

it won't let me embed the video for some reason. It gives me an error about my message containing an emoji, so the link above will have to suffice.

Same happens to me.  Embedding has always been sketchy with this forum software, but it has gotten much better the last few months.  But the phantom emoji glitch remains

[mikegarrison]

8 hours ago, Meecrob said:

In fact, unless required for performance reasons, Transport Category aircraft will always use a de-rated takeoff.

That's not completely true. They often use derated takeoffs, because they are easier on the engines, but it's not true that they *always* do, even if they otherwise have enough runway length to do it.

Most operators will have policies to use derated takeoffs when possible, but it is always up to the flight crew what they do.

Edited April 3 by mikegarrison

[Exoscientist]

SpaceX Starship has a serious problem that no one is talking about!
https://www.youtube.com/watch?v=9SUbx3IkfRA

His argument is the pad damage after each flight might take a month or more to repair. That would extend the time for all the refueling flights for the Artemis missions to a year or more. But when you have cryogenic propellant stored in orbit that long it results in severe boiloff problems. That means additional refueling flights to replace the propellant lost to boiloff. But at a month or more between flights, that means even longer time in orbit for the propellant and additional boiloff, so even more refueling flights. The result is the number of refueling flights becomes impracticality large.

The answer might be you need a full flame diverter like used by Apollo to prevent pad damage. Gee, those Apollo guys really were smart.

 

  Bob Clark

[RCgothic]

Or these are just teething troubles as they discover what's vulnerable and better protect those bits; pad turnaround is getting faster between each flight; and they're going to have three or more pads to launch from.

[Deddly]

Agree, disagree - these are normal parts of a healthy debate and are encouraged on this forum. 

Criticising a person, however, is actively discouraged in this community. In fact, it's not even permitted at all. You might notice that some comments have been removed, and now you know why. 

That being said, moving from one negative thing to the next without acknowledging people's comments to the contrary can be perceived as trolling, so if someone makes a valid argument against you, it would be a good idea to address that before moving on.

[Superluminal Gremlin]

IFT-1 - Big Damage. Required a complete re-think of all involved systems

IF2-2 - Moderate Damage to the Test Stand, much reduced everywhere else

IFT-3 - There was damage? (Sarcasm ). Mostly dents and dings. Am surprised there are no moves to build some protection for the tank farm, for example.

 

At its rate, by IFT-5? the damage will be low enough, and SpaceX well enough versed in the way of the 3 R's. (Reduce Damage, Reuse parts and Recycle what they can).