totm nov 2023 SpaceX Discussion Thread

[tater]

Real launch coming up, as well:

 

 

[Geonovast]

I've got 8 hours of driving on Sunday, I hope we're to the hotel by then!

[RealKerbal3x]

Right in the middle of the day for me, and on a Sunday too. I’ll be able to watch that.

Scratch that, I did my timezone conversion wrong  It’s in the middle of the night. I guess I’ll watch the replay in the morning.

Edited July 15, 2019 by RealKerbal3x
D’oh!

[MinimumSky5]

Half past midnight for me, but I'm unemployed ATM, so it's not a major issue! 

[CatastrophicFailure]

26 minutes ago, RealKerbal3x said:

Right in the middle of the day for me, and on a Sunday too. I’ll be able to watch that.

Scratch that, I did my timezone conversion wrong  It’s in the middle of the night. I guess I’ll watch the replay in the morning.

Some things are worth losing sleep over. ಠ_ಠ

You can just sleep in class, or at work, wherever. 

Also, caffeine.

[tater]

 

[NSEP]

Because the first hop attempt should be tomorrow, and Starhopper is still tethered, im geussing we will see a static fire today. The road is also closed from 14:00-20:00 CDT, so the within the next 6 hours we might see raptor come back to life. They did pre-burner tests yesterday.

[tater]

 

[tater]

Posted at NSF by Chris Bergen:

Quote

SpaceX release:


On Saturday, April 20, 2019 at 18:13 UTC, SpaceX conducted a series of static fire engine tests of the Crew Dragon In-Flight Abort test vehicle on a test stand at SpaceX’s Landing Zone 1, Cape Canaveral Air Force Station in Florida.

Crew Dragon’s design includes two distinct propulsion systems – a low-pressure bi-propellant propulsion system with sixteen Draco thrusters for on-orbit maneuvering, and a high-pressure bi-propellant propulsion system with eight SuperDraco thrusters for use only in the event of a launch escape. After the vehicle’s successful demonstration mission to and from the International Space Station in March 2019, SpaceX performed additional tests of the vehicle’s propulsion systems to ensure functionality and detect any system-level issues prior to a planned In-Flight Abort test.

The initial tests of twelve Draco thrusters on the vehicle completed successfully, but the initiation of the final test of eight SuperDraco thrusters resulted in destruction of the vehicle. In accordance with pre-established safety protocols, the test area was clear and the team monitored winds and other factors to ensure public health and safety.

Following the anomaly, SpaceX convened an Accident Investigation Team that included officials from the National Aeronautics and Space Administration (NASA), and observers from the Federal Aviation Administration (FAA) and the National Transportation Safety Board (NTSB), and began the systematic work on a comprehensive fault tree to determine probable cause. SpaceX also worked closely with the U.S. Air Force (USAF) to secure the test site, and collect and clean debris as part of the investigation. The site was operational prior to SpaceX’s Falcon Heavy launch of STP-2 and landing of two first stage side boosters at Landing Zones 1 and 2 on June 25, 2019.

Initial data reviews indicated that the anomaly occurred approximately 100 milliseconds prior to ignition of Crew Dragon’s eight SuperDraco thrusters and during pressurization of the vehicle’s propulsion systems. Evidence shows that a leaking component allowed liquid oxidizer – nitrogen tetroxide (NTO) – to enter high-pressure helium tubes during ground processing. A slug of this NTO was driven through a helium check valve at high speed during rapid initialization of the launch escape system, resulting in structural failure within the check valve. The failure of the titanium component in a high-pressure NTO environment was sufficient to cause ignition of the check valve and led to an explosion.
 
In order to understand the exact scenario, and characterize the flammability of the check valve’s titanium internal components and NTO, as well as other material used within the system, the accident investigation team performed a series of tests at SpaceX’s rocket development facility in McGregor, Texas. Debris collected from the test site in Florida, which identified burning within the check valve, informed the tests in Texas. Additionally, the SuperDraco thrusters recovered from the test site remained intact, underscoring their reliability.

It is worth noting that the reaction between titanium and NTO at high pressure was not expected. Titanium has been used safely over many decades and on many spacecraft from all around the world. Even so, the static fire test and anomaly provided a wealth of data. Lessons learned from the test – and others in our comprehensive test campaign – will lead to further improvements in the safety and reliability of SpaceX’s flight vehicles.

SpaceX has already initiated several actions, such as eliminating any flow path within the launch escape system for liquid propellant to enter the gaseous pressurization system. Instead of check valves, which typically allow liquid to flow in only one direction, burst disks, which seal completely until opened by high pressure, will mitigate the risk entirely. Thorough testing and analysis of these mitigations has already begun in close coordination with NASA, and will be completed well in advance of future flights.

With multiple Crew Dragon vehicles in various stages of production and testing, SpaceX has shifted the spacecraft assignments forward to stay on track for Commercial Crew Program flights. The Crew Dragon spacecraft originally assigned to SpaceX’s second demonstration mission to the International Space Station (Demo-2) will carry out the company’s In-Flight Abort test, and the spacecraft originally assigned to the first operational mission (Crew-1) will launch as part of Demo-2.
 

 

[Barzon]

https://www.spacex.com/news/2019/07/15/update-flight-abort-static-fire-anomaly-investigation

[tater]

 

 

 

[RealKerbal3x]

Good to know that it wasn’t the engines. If it was, the abort test and DM-2 could have been delayed for a lot longer.

[MinimumSky5]

That is an expensive and embarrassing way to further the study of high pressure chemistry. 

[kerbiloid]

Happily, this was just a leakage of highly toxic, flammable, explosive hypergolic fuel right inside the very safe crew capsule hull once they've tried to ignite a LES engine,
not a dangerous, toxic, inappropriate hypergolic rocket in 20 m below the capsule equipped with a solid motor LES tower.

Spoiler

U C, it was not in a spoiler, cuz I was not joking, lol.

 

Edited July 15, 2019 by kerbiloid

[tater]

 

6 minutes ago, MinimumSky5 said:

That is an expensive and embarrassing way to further the study of high pressure chemistry. 

Not really either.

It was expensive to the extent that they can't reuse an otherwise 100% paid for capsule to test, but then again, the one they use for the abort test can be reused as a cargo Dragon (previously flow Crew Dragons will be used for CRS missions).

I don't see it as embarrassing, They discovered a new failure mode for existing hardware apparently (check valves used on many other craft apart from Dragon vs burst disks that they will replace them with).

 

[mikegarrison]

There is a long and sordid history of check valves either failing to "check" or failing to open. Those things are a PITA.

[tater]

32 minutes ago, mikegarrison said:

There is a long and sordid history of check valves either failing to "check" or failing to open. Those things are a PITA.

You think their move to a burst disk is a good one?

[mikegarrison]

5 minutes ago, tater said:

You think their move to a burst disk is a good one?

Not my area of expertise. I've mostly dealt with identifying the consequences of failed check valves when they cause noise problems, not how to fix the root cause.

Obviously, a burst disk is only an option for a "use once" application. I guess that applies to the LES functionality of this system. Fused designs like that can tend to also be a problem, though, because it's hard to non-destructively test that they are going to work when you need them to.

[CatastrophicFailure]

52 minutes ago, mikegarrison said:

Fused designs like that can tend to also be a problem, though, because it's hard to non-destructively test that they are going to work when you need them to.

IIRC, SpaceX has really shied away from such things in the past, for exactly that reason. Speaks to the potential magnitude of the problem. 

Also: stuff’s on fire, yo. 

Er, the good kind. 

Edited July 16, 2019 by CatastrophicFailure

[tater]

6 minutes ago, CatastrophicFailure said:

IIRC, SpaceX has really shied away from such things in the past, for exactly that reason. Speaks to the potential magnitude of the problem. 

Yeah, and with Starship moving along, I think they simply don't care about propulsive landing. Of course, once initiated, multiple on/off cycles are presumably not a problem in the space of several minutes (which is all EDL would take).

[mikegarrison]

7 minutes ago, CatastrophicFailure said:

Also: stuff’s on fire, yo.

Er, the good kind. 

Yeah. Better to burn methane than just let it loose. The CO₂ from burning it is much less of a greenhouse gas than the CH₄ itself is.

[tater]

 

[magnemoe]

5 hours ago, tater said:

Posted at NSF by Chris Bergen:

 

Nice, now they know how to make an simple range safty abort system for dragon 2

 

26 minutes ago, mikegarrison said:

Yeah. Better to burn methane than just let it loose. The CO₂ from burning it is much less of a greenhouse gas than the CH₄ itself is.

And more important venting methane is an obvious fire and explosion hazard, far more so if you also leak oxygen.  

Not sure if the flame is boil off or just an pilot flame to make sure they dump a lot it will burn, might be an combination. 
Oil industry has mostly moved away from pilot flames but hopper jump testing is not an 24/7 operation
 

[zolotiyeruki]

That flare is a whole lot bigger than you'd need as a pilot.

[CatastrophicFailure]

Some good, in-depth info about Raptor testing I don’t think has made the rounds here, yet:

Longest test firing to date: 86 seconds. 

Edited July 16, 2019 by CatastrophicFailure