Astra Concludes Investigation into June 2022 Launch Mishap, Introduces Rocket 4 and ESA’s Sentinel-1C
Astra recently concluded the investigation into the June 2022 launch of its Rocket 3.3 vehicle from Cape Canaveral, Florida, and the launch failure of its two NASA TROPICS cubesats. The investigation found that the primary factor leading to the combustion chamber burn-through was a partial blockage of the injector. When the fuel injector is partially blocked, the rate of fuel passing through the cooling channels decreases, reducing the amount of heat the fuel can absorb and making the combustion chamber wall hotter. This can lead to a condition where the wall temperature can exceed the local boiling point of the fuel, causing some of the fuel to boil along the wall inside the channels. If too much of the fuel boils, its cooling capability is significantly and adversely impacted, and the wall temperature can go up and up until the wall fails and “burns through,” dumping a portion of the fuel flow directly into the combustion chamber – essentially wasting it.
The investigation also found that a secondary factor for the burn-through was thermal barrier coating erosion. A thermal barrier coating has been applied to sections of the engine's combustion chamber on the inner side, in order to insulate the chamber wall and reduce the amount of heat that the fuel needs to absorb for cooling. If any thermal barrier coating is absent, even in a tiny amount, that part of the wall can become hotter, thus increasing the possibility of a localized burn-through.
In response to the investigation, Astra has made the strategic decision to focus the majority of its resources on developing its next-generation launch vehicle: Rocket 4. This new, larger, and more reliable rocket incorporates key architectural choices (most notably, a different upper stage engine design and a different fuel) that completely eliminate the causes of the earlier mishap. The company is also introducing controls designed to eliminate a number of other potential failure modes, like FOD and helium ingestion, as well as overhauling its design review process and introducing a test-like-you-fly qualification process.
In addition to analyzing the causes of the TROPICS-1 mishap, the investigation also revealed the need for a significant gap in Europe's Earth observing capability. To address this, the European Space Agency is launching a Sentinel satellite – Sentinel-1C – to fill this gap.
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