The launch failure of Russia’s Progress MS-04 cargo spacecraft was due to an emergency shutdown of the third stage engine, which occurred at the same time as premature separation between the third stage and the spacecraft according to Russia’s Mission Control Center. Further details were not officially released, but Anatoly Zak, editor of RussianSpaceWeb.com, has gleaned more insight from industry sources.

Progress MS-04, the fourth of this latest version of Russia’s venerable robotic space station resupply spacecraft, was lost 382 seconds after launch on December 1, 2016. Launched by a Soyuz-U rocket, it was carrying 2.6 metric tons of fuel, water, oxygen and other supplies to the International Space Station (ISS). NASA refers to this as Progress 65 or 65P because it is the 65th Progress mission to the ISS, but Progress has been in use since 1978 when it debuted as a resupply vehicle for the Soviet Union’s Salyut 6 space station. It continued in use for the Soviet Salyut 7 and Mir space stations and now in the ISS era.

Russia’s news agency TASS reported on December 7 that the Mission Control Center issued a statement that Progress MS-04 did not reach orbit “due to the emergency shutdown” of the third stage engine. Russia’s space state corporation Roscosmos has not issued any statements about the failure since December 6 when it said search teams had arrived in the Tuva Republic in Siberia to look for debris.

Zak reports that postings on the Russian online forum Novosti Kosmonavtiki (Space News) by Russian space industry sources reveal more about what they know of the last moments of flight. Briefly, the third stage and the spacecraft separated, for unknown reasons, 140 seconds prematurely. The spacecraft interpreted the separation as the normal event that would occur once it was in orbit and began deploying its antennas and preparing its attitude control thrusters. The third stage was still firing and bumped into the spacecraft, sending it tumbling and leading to catastrophic failure of both. Zak provides many more details and some of the speculation as to possible causes.

The bottom line, however, is that they still do not know why the third stage and the spacecraft separated early.

Russia launches four or five Progress spacecraft to the ISS each year. The U.S. SpaceX Dragon and Orbital ATK Cygnus spacecraft, as well as Japan’s HTV, also resupply the station. The most recent HTV, HTV6 (or Kounotori 6), was launched on Friday morning and will dock with ISS on Tuesday, so the six-person ISS crew is well supplied. One of the main functions of Progress MS-04, however, was to refuel the space station’s engines that are used to periodically raise its orbit. Only Progress can perform that task.