A Russian rocket transporting American astronaut Nick Hague and Russian cosmonaut Alexey Ovchinin to the International Space Station suffered a malfunction shortly after launch on Thursday. The two-man crew separated their capsule from the malfunctioning rocket and initiated a “ballistic descent” back to the surface of the earth.

Ovchinin, the mission commander, made the decision to separate the Soyuz capsule a bit more than three minutes into the rocket’s flight, suggesting that the malfunction occurred after the Soyuz FG rocket separated from its first stage boosters and engaged the second stage. In footage captured inside the Soyuz capsule, the two men can clearly be seen shaking violently as a result of the malfunction. The Russian translator can be heard saying, “failure to booster” twice, before confirming that the capsule had separated. Thus far, what exactly went wrong remains a mystery.

NASA Astronaut and engineer Leroy Chiao posted this analysis to twitter: