Exactly What Went Wrong On Astra’s Most Recent Launch

The TROPICS-1 mission launched on June 12, 2022, on Astra’s Rocket 3.3, serial number LV0010. The rocket completed a nominal first stage flight, stage separation, and upper stage ignition. Shortly after the ignition of the upper stage engine, the upper stage’s fuel consumption rate increased and remained higher than normal for the remainder of the flight. Soon after we learned that the rocket had failed to reach orbit which led to the cancellation of the Rocket 3 line entirely.

Since this launch Astra, NASA, and the FAA have been working to figure out exactly what went wrong. Just a few days ago however the company finally released a full investigation report and the reason for the failed mission. It turns out a burn through in the upper stage engine caused thrust issues and eventually the payload falling back into Earth’s atmosphere.

The findings of this mission are very important as the company is currently in the process of creating Rocket 4, which utilizes a lot of technology and techniques from the previous rocket line. Here I will go more in-depth into exactly what went wrong on the last flight, Astra’s plan with this new information, its impact on Rocket 4, and more.

Credit:

Chapters:
0:00 - Intro
0:59 - Engine Problems
3:44 - Testing & Astra's Future

[WWeronko]

I listened to this video several times to see if it said what caused the partial blockage in the engine’s fuel injector that led to the engine failure. It didn't definitively explain. From what I understand the conclusion was gaseous fuel as the likely source. Apparently, the warm temperatures at Cape Canaveral on the day of launch, meant the fuel was slightly warmer than in prior flights and the engine was fine-tuned with “thin margins” for keeping the fuel from boiling during the regenerative cooling process. Moreover, the selection of a kerosene-like fuel with a higher vapor pressure than traditional rocket-grade kerosene (RP-1) had an adverse impact. As noted in the video, another contributing factor was an eroded thermal barrier coating in the combustion chamber. Not mentioned was the engine was never tested in a vacuum where engine exhaust jet expands to become “fully attached” to the inside of the nozzle. Therefore, the fuel passing through the engine during flight is heated to a higher temperature than during ground testing. Fuel boiled after going through the regenerative cooling channels resulting in gas rather than liquid fuel going through the injector that slowed the rate fuel flow through the injector and thereby through the regenerative cooling channels making them hotter. Resulting in a "runaway event" where fuel further boiled providing more gas to the nozzle that further reduced its ability to cool the chamber resulting in a burn through.

[saukhaven]

I know Astra's an underdog with multiple recent issues, but I'm still a big fan. I'm hoping their redirection to Rocket 4 will allow them to finally get traction and soar. Go Astra!

[martythemartian]

Thanks for the detail. It can be hard sometimes to find out what went wrong with a launch, and even though the cause is eventually found, we out here in Space Geek Land can be left out of the loop.

[just_rocket_science]

Around 06:46 - you mention that building rockets entirely out of metallic structures is "proven" and "cost-effective". Can you elaborate more here? Agreed that, initial investments are cheaper for metallic structures and tank but not proven to be the right choice for small sat launchers. IMO, the trade between metallic structures vs. composite structures becomes really murky as you reduce vehicle size. Penalties on payload capability is severe as you introduce more structural weight on the vehicle.

Rocket 3.0 had some of the lowest payload performance as compared to its' peers (Rocket Lab, Firefly, Virgin Orbit, etc.), so metallic structures (as a MFG benefit) may not have been the economically competitive choice overall. Rocket 4.0 is better in terms of capability (600 kg to LEO), so it remains to be seen if they can be competitive overall, with the choice to make structures out of metal vs. composite.

Fun video overall! Nice work.

[snakeification]

No, Rocket 4 isn't similar to Rocket 3 in any way. They don't even use similar engines