Rocket engine anomaly during ISS cargo delivery investigated

The problem with the United Launch Alliance’s Atlas V rocket occurred on 22 March as the launcher shot off towards the low Earth orbit with Orbital ATK’s Cygnus space capsule aboard.

United Launch Alliance (ULA) said that according to preliminary investigation results, the rocket's first stage Russian-made motor for reasons unknown switched off six seconds early. However, the second stage engine made up for the failure and the cargo capsule successfully reached the orbital outpost on Saturday, 26 March. The investigation suggests the problem was in the first-stage fuel system and related components.

ULA, a joint venture between Lockheed Martin and Boeing, which has a monopoly for US military launches, has postponed further Atlas V launches for the duration of the investigation. The next launch scheduled for 5 April will take place with at least a week’s delay.

The US is reliant on Russian RD-180 engines for launches of its military and intelligence satellites but is looking for domestic replacement technology.

The US Air Force, which is ULA’s primary customer, is part of the investigation team.

Telemetry data during the launch revealed that the first stage engine shut down six seconds earlier than the planned  four minutes and 15.5 seconds. The Centaur upper stage kicked in only after the separation of the first stage, which went through as scheduled. The upper stage subsequently fired for over a minute longer than the scheduled 13 minutes and 38 seconds.

According to the NASAspaceflight website, Centaur spent all his propellant to make up for the first stage failure but delivered its payload to the correct 230km orbit needed for the mission to succeed. However, no fuel was left for the booster to perform its controlled re-entry and the rocket de-orbitted in an uncontrolled way.

The March 22 launch from Cape Canaveral Air Force Station in Florida was only the second for the Cygnus space capsule using Atlas V. The capsule was grounded for more than a year following an explosion of Orbital ATK’s own Antares rocket in October 2014.

Atlas V, in operation since 2002, has a flawless track-record. In 14 years it has suffered only one partial failure of the Centaur upper stage, which left two reconnaissance satellites in a lower than desired orbit. However, the satellites were able to manoeuvre into their correct position.