The "Real Aerospace" Thread

[Mjolnir]

If things go well, Starship SN8 will make its first high-altitude flight attempt tomorrow:
https://www.youtube.com/watch?v=nf83yzzme2I

This will test (depending on how far it gets) flight with 3 engines to 12.5 km, control during descent using the body flaps, restarting engines from the header tanks, and the landing flip maneuver. Chances of it ending in a fireball are not small...and SN9 is almost ready if it does.

[GeoModder]

"Raptor" engines? Who comes up with such a name?

[Arioch]

"Raptor" engines? Who comes up with such a name?

A person who would name a baby "X Æ A-12."

[Mjolnir]

"Raptor" engines? Who comes up with such a name?

A person who would name a baby "X Æ A-12."

To be fair, I expect Grimes had input on that one. SpaceX's other launch vehicle engines are named Kestrel and Merlin, Raptor fits with the predatory birds theme.

Dragon was named after Puff the Magic Dragon (in response to critics who said his spaceflight projects were impossible), and the Draco/SuperDraco thrusters followed the Dragon theme.

[Arioch]

To be fair, I expect Grimes had input on that one. SpaceX's other launch vehicle engines are named Kestrel and Merlin, Raptor fits with the predatory birds theme.

Naturally, but SpaceX is known for its unorthodox naming protocols (ships named "Of course I still love you," "Just read the instructions," "GO Ms. Tree" and "GO Ms. Chief"; and the "Big F____ Rocket" (an early name for the Starship), as is Tesla (with car models S, 3, X, and Y). One cannot help but suspect that Elon had some influence here.

With this in mind, "Raptor" is about as normal a name as an Elon Musk-run company is capable.

[GeoModder]

If it were a military rocket, okay.
But a booster? Why not 'gazelle' or something?

[Mjolnir]

If it were a military rocket, okay.
But a booster? Why not 'gazelle' or something?

For a super-heavy launch vehicle's engine with 2.2 MN of thrust?

Just be glad Starship ended up with a relatively normal name, even with the bit of silliness about using the name "Starship" for both the upper stage and the complete stack.

[Mjolnir]

To be fair, I expect Grimes had input on that one. SpaceX's other launch vehicle engines are named Kestrel and Merlin, Raptor fits with the predatory birds theme.

Naturally, but SpaceX is known for its unorthodox naming protocols (ships named "Of course I still love you," "Just read the instructions," "GO Ms. Tree" and "GO Ms. Chief"; and the "Big F____ Rocket" (an early name for the Starship), as is Tesla (with car models S, 3, X, and Y). One cannot help but suspect that Elon had some influence here.

With this in mind, "Raptor" is about as normal a name as an Elon Musk-run company is capable. :D

Don't forget A Shortfall of Gravitas, a drone ship which is currently under construction.

I'm also pretty sure the Falcon 9 v1.2 Full Thrust is a reference to USB's insane marketing-driven version scheme...remember Full Speed/High Speed? (It's only gotten worse since: https://it.slashdot.org/story/19/02/26/ ... 2-branding)

[GeoModder]

Yeah, I suppose.

[Mjolnir]

Well, SN8 did a perfect skydive and flip maneuver, and hit the landing pad dead center...with what looked like one engine out (assuming it was intended to be a 2-engine landing burn) and the other burning itself out (exhaust should be blue, not green), and a bit too much vertical velocity.

https://youtu.be/ap-BkkrRg-o?t=6482

edit: the view from the pad: https://twitter.com/SpaceX/status/13368 ... 96992?s=20

[Arioch]

It was an exciting flight. Two engines cut out in succession on ascent, but this seems to have been planned. The craft performed its flop maneuver and descended using the aerodynamic fins, and this part seems to to have worked perfectly. It also did its controversial flip maneuver before landing with two engines lit (which, I believe, was also planned), but the fuel source switches from the main tanks to the header tanks for landing (the main tanks are supposed to be mostly empty by this point, and the flat attitude means the fuel is sloshing around and not feeding properly), and there seems to have been a pressure problem with the fuel feed from the header tanks, and though the ship performed its landing maneuver properly, in the last seconds the engines became starved for fuel and cut out, leading to a hard landing and a Rapid Unscheduled Disassembly. But it did land right on target, and the most controversial elements of the landing maneuver all worked very well.

Congratulations to SpaceX for a very successful test, and I'm looking forward to more testing with SN9, which appears ready to go.

(In before the mainstream media report a crash and "failed test" in the morning.)

[Mjolnir]

It was an exciting flight. Two engines cut out in succession on ascent, but this seems to have been planned. The craft performed its flop maneuver and descended using the aerodynamic fins, and this part seems to to have worked perfectly. It also did its controversial flip maneuver before landing with two engines lit (which, I believe, was also planned), but the fuel source switches from the main tanks to the header tanks for landing (the main tanks are supposed to be mostly empty by this point, and the flat attitude means the fuel is sloshing around and not feeding properly), and there seems to have been a pressure problem with the fuel feed from the header tanks, and though the ship performed its landing maneuver properly, in the last seconds the engines became starved for fuel and cut out, leading to a hard landing and a Rapid Unscheduled Disassembly. But it did land right on target, and the most controversial elements of the landing maneuver all worked very well.

Congratulations to SpaceX for a very successful test, and I'm looking forward to more testing with SN9, which appears ready to go.

I personally expected some control tweaking to be necessary to get it to the pad, but they seem to have had that dialed in perfectly. Musk gave it a 1 in 3 odds of landing intact, and it very nearly made it.

It's also worth noting that starving a rocket engine of fuel is about the worst possible thing you can do to it. The fuel's also the coolant, and if there's not enough of it the hot oxygen will happily use the engine as fuel. It looks like the last engine running was forced to continue running in conditions that would normally be far past triggering an emergency shutdown. It seemed to be losing thrust (either through damage or just insufficient fuel), but it didn't explode and kept going...

(In before the mainstream media report a crash and "failed test" in the morning.)

New York Times: "SpaceX Starship Explodes During Test Flight"

[Mjolnir]

The aftermath:
https://pbs.twimg.com/media/Eo6bPRYWEAAF32u.jpg:orig

And SN9 is getting moved to a test pad (they have 2 now) Monday.

[GeoModder]

The aftermath:
https://pbs.twimg.com/media/Eo6bPRYWEAAF32u.jpg:orig

Wow, that was a bigger craft then I thought. The people near the nose cone on that pic give a good idea of its real dimensions.

[Krulle]

Thanks for keeping me up to date, guys.


Impressive feat, SpaceX.

Now I'd love some data about why the third engine cut off on ascent, whether that was intentional, or even part of a test, or a technical failure/safety cutoff, as it seems to me as if the same engine did not reignite as well.

May have been a test how the autonomous systems take the loss of an engine.

But not enough fuel for a landing? Damn.... The third engine might have softened the landing, but would've needed even more fuel, and also increased the temperature surrounding the test vehicle even more.

[Mjolnir]

Thanks for keeping me up to date, guys.


Impressive feat, SpaceX.

Now I'd love some data about why the third engine cut off on ascent, whether that was intentional, or even part of a test, or a technical failure/safety cutoff, as it seems to me as if the same engine did not reignite as well.

May have been a test how the autonomous systems take the loss of an engine.

But not enough fuel for a landing? Damn.... The third engine might have softened the landing, but would've needed even more fuel, and also increased the temperature surrounding the test vehicle even more.

The first two engines shut down on the way up mainly to reduce acceleration, they can only throttle down to 40%. The third engine cut off to do an unpowered dive and test controlled flight with the flaps.

They were short of fuel pressure, not fuel. It should be able to land on any two engines and might intentionally drop to just one for the final moments of landing, just one engine can lift 220+ metric tons, but obviously that's assuming they're not starved of fuel. It's a self-pressurizing system that boils propellants using engine heat to provide pressure, something could have broken and leaked or maybe they just weren't generating as much methane gas as they expected.

[Arioch]

Scott Manley has a very good preliminary breakdown of the test:


TLDR: the engine cutoffs were intentional, but there was a fuel pressure problem with the landing tanks and green flame = engine eating itself.

Wow, that was a bigger craft then I thought. The people near the nose cone on that pic give a good idea of its real dimensions.

Yes, Starship is enormous. You can also see from the wreckage just how thin the steel hull is.

[tpkc_klick]

The first two engines shut down on the way up mainly to reduce acceleration, they can only throttle down to 40%. The third engine cut off to do an unpowered dive and test controlled flight with the flaps.

They were short of fuel pressure, not fuel. It should be able to land on any two engines and might intentionally drop to just one for the final moments of landing, just one engine can lift 220+ metric tons, but obviously that's assuming they're not starved of fuel. It's a self-pressurizing system that boils propellants using engine heat to provide pressure, something could have broken and leaked or maybe they just weren't generating as much methane gas as they expected.

It also doesn't help that all of the maneuvering to reorient the craft from the belly-flop attitude to the tail-first landing attitude is going to slosh the fuel around, which could lead to ullage and fuel and/or oxidizer flow problems. Basically, the propellant pumps are sucking in gas or foam rather than liquid, thus moving a smaller mass of propellant per second. The big green flame coming out of the engine right before the crash could be an indicator of copper-containing elements of the engine burning away in an oxidizer rich environment due to fuel starvation (as Scott Manley puts it, it was "engine-rich exhaust").

[Mjolnir]

Yes, Starship is enormous. You can also see from the wreckage just how thin the steel hull is.

Yeah. An advantage and disadvantage of steel: the Centaur tank walls are so thin they can't support themselves and the vehicle has to be kept pressurized. Aluminum of the same strength is thick enough to be rigid, but stainless steel's resistance to tearing makes it a very light way to construct a stage. At the same time, the SLS core required very expensive new welding equipment for handling the thick lithium-aluminum it's made of, while Starship's stainless steel plate and sheet metal is being put together with relatively mundane welding techniques, much of it initially done by hand and automated later.

Which happens to be handy for repairing damage from things like this: https://i.imgur.com/BBL3AeI.jpg
SN9's probably not making it to the pad by Monday.

[Mjolnir]

It also doesn't help that all off the maneuvering to reorient the craft from the belly-flop attitude to the tail-first landing attitude is going to slosh the fuel around, which could lead to ullage and fuel and/or oxidizer flow problems. Basically, the proellant pumps are sucking in gas or foam rather than liquid, thus moving a smaller mass of propellant per second. The big green flame coming out of the engine right before the crash could be an indicator of copper-containing elements of the engine burning away in an oxidizer rich environment (as Scott Manley puts it, it was "engine-rich exhaust").

Controlling slosh is a good part of why the "header" tanks exist. Also, the two engines started up and righted the vehicle, at which point it was under a couple gravities of settling acceleration. I doubt it was propellant slosh.