Unforgiving Failures: The Challenges of Upper Stages in Orbital Launches
Introduction
Upper stages, the final propulsion systems of rockets, play a critical role in delivering satellites and spacecraft to their intended orbits. However, these stages face a unique set of challenges that can lead to mission failures, as evidenced by a string of setbacks in 2023.
Design Complexities
Upper stages are often more complex than booster stages, requiring multiple burns and precise maneuvers. “Each of those maneuvers needs to take place precisely or else the payloads may go into the wrong orbit,” said an industry source.
Forgiving Environments
Upper stages operate in unforgiving environments, with a much smaller margin for error than booster stages. “If your booster engine fails to ignite, you scrub and try again another day. If your upper stage engine doesn’t ignite, it’s game over,” the source added.
Electrical Anomalies
“Electrical arcs can form as a function of atmospheric conditions,” said Rocket Lab CEO Peter Beck, explaining the failure of their Electron stage. “This coincides with the region of the atmosphere where stage separation takes place.”
Engine Failures
Engine failures are another common issue with upper stages. The H3 and Terran 1 rockets suffered this fate in 2023 due to problems with propellant pressure and igniters, respectively. “The main valves for [the H3 engine] opened slower than expected, which affected the timing of propellant reaching the engine,” a Relativity Space statement explained.
Limited Testing Capabilities
Ground testing of upper stages can be challenging due to the unique environments they operate in. “All three Electron failures were caused by issues with the rocket itself involving the upper stage,” Beck noted. “A 2020 launch failed because of what we called a ‘really unusual thermal problem’ that affected an electrical connection.”
Mitigation Strategies
To address these challenges, companies are implementing various strategies, including increased inspections, testing, and quality control. “We took a big step back and had a look across the whole vehicle, and as a result, we’ve made a bunch of changes,” Beck said.
Conclusion
Upper stages are essential components of orbital launches, but their inherent complexity and unforgiving operating environments can lead to mission failures. While companies are working to improve design, testing, and mitigation strategies, understanding the challenges involved is crucial for the continued success of space exploration and satellite deployment.
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