On its fourth flight since debut, the GSST Rhea rocket lifted off under 240,000kg of thrust on the 23rd of May, 2025, at 5:45 PM EDT from Launch Complex 1 at Rodriguez Key, Florida. The mission carried the second GAS&T satellite for GTRAD. The payload was confirmed deployed at 5:59:57 PM EDT, 14 minutes and 17 seconds after launch.

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Owned by Chris_HadfieldCA, GTRAD’s GAS&T constellation is designed to provide real time aircraft tracking across the globe. This marks the second satellite, with the first having launched on the 13th April aboard Rhea’s third flight.

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The mission, while successful, was not without incident.

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At T+2 minutes and 24 seconds, just moments before main engine cutoff, Rhea’s first stage suffered a failure of Engine #2, one of its BS-4B engines. Despite the failure, the vehicle’s onboard guidance systems compensated, allowing Stage 2 to complete the mission and deliver the payload to its intended orbit.

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“Successful mission from Rhea once again,” said Allan, head of management at GSST. “We had an on time liftoff of Rhea with no issues during the countdown. During ascent, we did have an anomaly late in the burn, which GTRAD recently closed the investigation on. Either way, Stage 2 compensated for the engine loss with it reaching its desired orbit for the payload.”

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"Another GTRAD L :C" said its CEO, Chris_HadfieldCA.

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Shortly after the launch, GTRAD published a preliminary incident report detailing the sequence of events that led to the failure:

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T+00:02.16 – Exhaust valve prematurely closed

T+00:02.17 – Turbopump downstream overheating

T+00:02.18 – Turbopump upstream overheating

T+00:02.25 – Catastrophic pump failure and engine cutout

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According to the report, a cascading pump overheating event triggered the shutdown of BS-4B #2. The anomaly has prompted an immediate fleet-wide grounding of all BS-4B engines.

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A formal notice issued by GTRAD stated:

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"GRN 5.V2 MANDATES THE IMMEDIATE STANDDOWN FROM ALL FLIGHTS, TESTING, AND OTHER USE OF THE BS-4B. ALL ARTICLES MUST BE RETURNED TO GTRAD FOR SERVICE AND UPGRADES. FAILURE TO DO SO MEANS ACCEPTING ALL LIABILITY AND RISK INVOLVED WITH CONTINUED OPERATION."

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Despite the in-flight anomaly, the mission marked another milestone for GSST’s reusability research. The Rhea booster successfully executed a hard ocean splashdown at 5:50:54 PM EDT, 5 minutes and 33 seconds after liftoff.

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The booster’s descent employed an upgraded experimental guidance software system, activated after reaching apogee. GSST reported that the system performed nominally, collecting high value telemetry for future recovery developments.

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“We also had assets deployed out in the Atlantic, capturing splashdown of the Rhea booster, which should be uploaded on YouTube soon once we finish reviewing that footage,” Allan said. “The booster guidance systems did perform well on descent, and our results will help for future return profiles for the Theia booster.”

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The Theia booster, a larger and more powerful cousin to Rhea, is currently in testing and is expected to benefit directly from the lessons learned on this flight.

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With the BS-4B engine anomaly now under investigation and recovery data in hand, the path forward for Rhea appears cautiously optimistic. Unfortunately, future flights may face schedule delays pending the return and recertification of engine hardware from GTRAD.

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Still, the success of GAS&T II's deployment and booster recovery underscores Rhea’s growing reliability even under off nominal conditions.

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