SpaceX Starship - Integrated Flight Test #2 - Starbase TX - Including Post Launch Dissection

[Grendal]

Ellie showcases the post launch lack of damage to the launch area.

 

[ecarfan]

Re-watching the SpaceX webcast — AGAIN — I picked up on something; when the web hosts first discussed the new electric TVC system they said that it provided “regenerative charging”. What does that mean in this context? The batteries driving the TVC system are being charged during flight? Charged by what?

 

[bxr140]

SpaceX doesn't want to add in all the mechanisms (more mass) needed for "fin deployment." They probably did the math and figured the weight gain versus aero loss was not worth it.

Yep--those grid fins are friggin massive (and they look positively medieval up close). The mass required to not just deploy them airflow and but then also not break during use would be pretty ginormous.

Starship's grid fins are analogous to solid axles on leaf springs--they don't result in the most comfortable ride, but they're imperative to move a load that's a significant percentage of the vehicle's dry weight. You just can't move the same amount of load on linkage suspension with CV driveshafts.

 

[GWord]

Re-watching the SpaceX webcast — AGAIN — I picked up on something; when the web hosts first discussed the new electric TVC system they said that it provided “regenerative charging”. What does that mean in this context? The batteries driving the TVC system are being charged during flight? Charged by what?

Perhaps (some of?) the engines have something akin to a flux switching alternator installed.

 

[scaesare]

SpaceX doesn't want to add in all the mechanisms (more mass) needed for "fin deployment." They probably did the math and figured the weight gain versus aero loss was not worth it.

I wonder if that's likely to change now that(as previous posts have pointed out) they are subject to Starship's thrust during hot staging, and deceleration due to that thrust is speculated to be perhaps what contributed ullage collapse/fluid hammer and prevented complete Raptor re-lights on the booster, and they were designed before any of the hot staging....

 

[ecarfan]

flux switching alternator

Thank you. I had to look that up! Flux switching alternator

 

[scaesare]

They're out because they can't be stowed. They don't cause a lot of drag, but stowing them would add weight and complexity. It's doubly difficult because Starship's booster grid fins are made of steel, not titanium. So if they wanted to raise and lower them, they'd need a pretty hefty mechanism, or they could reduce the weight and make them of titanium, which would be more expensive.

It may be that in the future, when SpaceX is optimizing Starship, they'll figure out the perfect balance of factors and go back to stowable titanium grid fins. Given that they know they're going to be destroying vehicles during testing, they just want vehicles that they can fly as cheaply and as quickly as possible. That means stainless steel, heat tiles, and fixed steel grid fins.

"They don't cause a lot of drag..."

I've wondered about that... isn't part of their entire existence is exactly to cause drag? Or do they really just vector airflow with drag being a minimal component of their operation?

Down in the thick lower atmosphere it seems odd for them to be sticking out when they are adding features to optimize payload capability, and on F9 they obviously felt it was worthwhile...

 

[GWord]

Thank you. I had to look that up! Flux switching alternator

I used one in an electrical engineering design project in ye olden days, getting my degree. I had no idea what I was doing and chalked it up to “things best left to rocket engineers.“

 

[mongo]

"They don't cause a lot of drag..."

I've wondered about that... isn't part of their entire existence is exactly to cause drag? Or do they really just vector airflow with drag being a minimal component of their operation?

Down in the thick lower atmosphere it seems odd for them to be sticking out when they are adding features to optimize payload capability, and on F9 they obviously felt it was worthwhile...

It's both, they act like guide fins or an arrow's fletching to provide stability (though the engine heavy center of mass does a lot of that anyway). They also generate torque by diverting the airflow. At steep deflection they would turn into more of a speed brake, I think.

Superheavy has more thrust to deal with protruding fins than F9, it also has a stronger structure to handle the compressive load they exert on ascent. F9's folding fins allow for cross country shipping and Falcon Heavy stacking (moreso when center core was going to be recovered).

 

[scaesare]

It would be interesting to find out how much they contributed to the booster hot-staging deceleration event during IFT-2...

 

[mongo]

Re-watching the SpaceX webcast — AGAIN — I picked up on something; when the web hosts first discussed the new electric TVC system they said that it provided “regenerative charging”. What does that mean in this context? The batteries driving the TVC system are being charged during flight? Charged by what?

I'm guessing one of the two engine engine positions (centered or deflected) is lower energy (probably deflected). When transitioning to that orientation, they may use the actuator's motor as a generator to recoup some electrical energy. Basically, the motor would act like a brake against the thrust instead of being the thing pushing the engine around.

 

[bxr140]

Down in the thick lower atmosphere it seems odd for them to be sticking out when they are adding features to optimize payload capability, and on F9 they obviously felt it was worthwhile...

It is possible that SX will evolve to a deployed grid fin that’s mass/size/cost tenable at some point in the future. Elonco is nothing if not good for evolving/changing existing designs when better efficiency/performance/cost is more on the table.

Right now the system is optimized enough that (continuing the car analogy) the efficiency gain from stowed booster grid fins is probably similar to The Kids putting shouty exhaust on their cars to add HP. Yeah in some cases there is measurable gain…in most cases it’s at an inefficient cost.

 

[scaesare]

Counterintuitive to my mind... just seems so odd to have giant air-brakes hanging out there like that...

I wonder why they aren't oriented edge-on to minimize drag? (at least they aren't initially). Perhaps either their shape or degree to which they can rotate would put some unwanted forces on the craft...

 

[scaesare]

Feels like Berger is a bit fed up with the H8R's in his latest article:

SpaceX took the next step, to experiment with recovery, the loss of the first stage after completing its primary mission was somehow viewed as a failure by some observers. I'm sorry to say it, but that's just dumb.

 

[mongo]

Counterintuitive to my mind... just seems so odd to have giant air-brakes hanging out there like that...

I wonder why they aren't oriented edge-on to minimize drag? (at least they aren't initially). Perhaps either their shape or degree to which they can rotate would put some unwanted forces on the craft...

A full 90 degree deflection takes more mechanism that say +/- 45 which can use a crank arm.

The edge on crossection of the fins might not be less than the combined webbing thickness. A large flat object may also be higher drag that multiple smaller objects (but I'm not sure on that one). Definitely a lot of smaller shock cones.

 

[JB47394]

Another set of video from NASASpaceFlight. One new bit for me was the size of the gas cloud created by termination of the booster.

 

[Grendal]

The SpaceX website has additional information. It says FTS was initiated on Starship when it was going off course.

If I interpret this correctly, FTS was not used on the booster. It blew itself up. And did a good job of it too...

 

[ecarfan]

Thanks @Grendal but that graphic is a bit blurry to my eyes. Here’s the text of the bullet points:

• All 33 Raptor engines on the Super Heavy Booster started up successfully and, for the first time, completed a full-duration burn during ascent.
• Starship executed a successful hot-stage separation, powering down all but three of Super Heavy’s Raptor engines and successfully igniting the six second stage Raptor engines before separating the vehicles. This was the first time this technique has been done successfully with a vehicle of this size.
• Following separation, the Super Heavy booster successfully completed its flip maneuver and initiated the boostback burn before it experienced a rapid unscheduled disassembly. The vehicle breakup occurred more than three and a half minutes into the flight at an altitude of ~90 km over the Gulf of Mexico.
• Starship's six second stage Raptor engines all started successfully and powered the vehicle to an altitude of ~150 km and a velocity of ~24,000 km/h, becoming the first Starship to reach outer space and nearly completing its full-duration burn.
• The flight test’s conclusion came when telemetry was lost near the end of second stage burn prior to engine cutoff after more than eight minutes of flight. The team verified a safe command destruct was appropriately triggered based on available vehicle performance data.
• The water-cooled flame deflector and other pad upgrades performed as expected, requiring minimal post-launch work to be ready for upcoming vehicle tests and the next integrated flight test.

Interesting info. No FTS for the booster. Tank bulkhead failure? Engine plumbing failure?

But yes FTS for the ship. So many possible explanations. Hope we get more details on that.

 

[JB47394]

Tank bulkhead failure? Engine plumbing failure?

All engines were shut down, but there were explosions all over the back end, so I assume extensive plumbing damage and fires. The coup de grace was definitely the bulkhead letting go because you can see the booster burst right at that point. In color video, you can see a yellow tinge to the material coming out, so I'm assuming that there was some combustion involved. I don't know if the combustion (or detonation) was the reason for the bulkhead failure or if the bulkhead failure provided an ignition source for the mixing methane and oxygen. Either way, the yellow tinge vanishes pretty quickly because the gases weren't at the right density and mix to sustain combustion.

I also noticed that some burning stuff was ejected out the back prior to the final detonation, which again suggests internal explosions. The obvious candidate to me was a couple engines.

 

[Grendal]