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:

The ride back to earth after the abort has been widely glossed over by the international media thanks, in no small part, to the survival of the two-man crew. However, a ballistic descent of this type is no laughing matter. Hague and Ovchinin likely experienced something near to 8 Gs (or eight times the earth’s gravity) as they flew in a barely controlled and extremely steep descent back to earth. Unlike normal Soyuz “controlled reentry” landings, ballistic reentry involves using a steep descent to maximize the air resistance to (hopefully) create enough drag to make landing survivable.

American record-setting astronaut Peggy Whitson also survived a ballistic reentry in a Soyuz capsule — one of only four to ever occur.